Modern Dictionary of Electronics [7 ed.] 0750698667, 9780750698665

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MODERN DICTIONARY of

ELECTRONICS SEVENTH EDITION REVISED AND UPDATED

Rudolf F. Graf is an author whose name is well-known to engineers, technicians, and hobbyists around the world. He graduated as an electronics engineer from Brooklyn Polytechnic Institute and did his graduate work New York University. Mr. Graf has been active in the electronics industry for more than fifty years in capacities ranging from design and consulting engineer, chief engineer, chief instructor at electronics and television schools, and consulting editor. He also held various sales and marketing positions. h4r. Graf is the author or co-author of more than 150 technical articles published by major magazines. He has written about 50 books on electricity and electronics, with more than 2 million copies in print, including the best-selling Kdeo Scrambling & Descrambling for Satellite & Cable TV,Second Edition and the Circuits series of books, both published by Newnes. A number of his books have been translated into several European languages as well as Chinese, Japanese, and Russian.

MODERN DICTIONARY of

ELECTRONICS SEVENTH EDITION REVISED AND UPDATED

Rudolf F. Graf

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Newnes is an imprint of Butterworth-Heinemann. Copyright 0 1999 by Rudolf F. Graf

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Library of Congress Cataloging-in-Publication Data Graf, Rudolf F. Modem dictionary of electronics / Rudolf F. Graf.-7th ed., revised and updated. p. cm. ISBN 0-7506-9866-7 (alk. paper) 1. Electronics -Dictionaries. I. Title TK7804.G67 1999 99-17889 621.381'03 -dc21 CIP British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Butterworth-Heinemann 225 Wildwood Avenue Wobm, MA 01801-2041 Tel: 781-904-2500 Fax: 78 1-904-2620 For information on all Butterworth-Heinemann publications available, contact our World Wide Web home page at: http://www.bh.com 109 8 7 6 5 4 3 2 1 Typeset by Laser Words, Madras, India Printed in the United States of America

It gives me great pleasure to dedicate this edition to Allison, Sheryl, Daniel, David, Russell and Scott, the loveliest children this side of heaven.

When the first edition of this dictionary was published in 1961, today's everyday items like color TVs, VCRs, CD players, computers, FAX machines, ATMs, cordless and cell phones, pagers, tape recordeirs, digital watches, pocket calculators, lasers, and many others too numerous to mention, were non-existent or mere laboratory curiosities. Since then, electronics has undergone significant changes based primarily on the meteoric expansion of integrated circuits and their apparently limitless applications. Vacuum tubes were replaced by semiconductors, and numerous technologies like ferrite core or bubble memories were relegated to the electronics graveyard. No other industry has ever grown so much and matured so fast, paced by technological advances that occur at a feverish pace. The first edition of this dictionary contained about 10,000 definitions of then current terms. And now, a scant 38 years later, this seventh edition contains approximately 25,000 terms-a clear indication of the phenomenal growth of our industry. As technologies evolve and fresh products and concepts are introduced, suitable terminology must be developed to be able to communicate. The originators of the new words give them their initial meaning, but their exact definitions change with technological advances and through actual use by others. The contents of this dictionary is thus an analysis of words and their meanings as determined by common usage, written in a modern and popular style to provide clear and concise explanations of each entry. Continual updating of a work such as this is vital, so that those involved in the world of electronics have the power to communicate with those about them and to grasp new concepts as they emerge. All entries are allowed as much space as is necessary for complete and meaningful definitions. 'Terms are explained clearly and precisely without excessive technical jargon. Original entries from the previous edition have been reviewed and many were revised to keep pace with current usage. Where more than one definition exists for a term, they are arranged numerically. This method, however. does not necessarily imply a preferred order of meanings. Important words from formative technologies that are no longer in use are retained in this edition for their historical interest. My thanks go out to Ms. Tara Troxler Thomas and to Charles Thomas whose dedication to this project iind skill at the word processor made it possible to deliver the manuscript for this work to the ]publisher in a timely fashion. Industry and technical sources-notably the IEEE and the ASA-generously aided in defining many terms during the preparation of earlier editions of this work. While this volume is as up-to-date as possible at the time of writing, the field of electronics is expandiing so rapidly that new terms are constantly being developed and older terms take on broader or more specialized meanings. It is the intention of the publisher to periodically issue revised editions of this dictionary; thus suggestions for new terms and definitions are always welcome. Rudolf F. Graf February 1999

A

A- 1 , Abbreviation for angstrom unit, used in expressing wavelength of light. Its length is centimeter. 2. Chemical symbol for argon, an inert gas used in some electron tubes. 3. Letter symbol for area of a plane surface. 4. Letter symbol for ampere. a-Letter symbol for atto- (lo-''). A0 -'The Federal Communications Commission (FCC) designation for radio emission consisting solely of an unmodulated carrier. A1 -The FCC designation for radio emission consisting of a continuous-wave carrier keyed by telegraphy. A-1 or A.1-The atomic time scale maintained by the 1J.S. Naval Observatory; presently it is based 'on weighted averages of frequencies from cesium-beam 'devices operated at a number of laboratories. A2 -'The FCC designation for radio emission consisting of a tone-modulated continuous wave. A3-The FCC designation for radio emission consist.ing of amplitude-modulated speech transmission. A4--The FCC designation for radio emission consist-ing of amplitude-modulated facsimile signals. A5-The FCC designation for radio emission consist:ing of amplitude-modulated television video signals. A- (A-minus or A-negative) -Sometimes called F-. Negative terminal of an A battery or negative polarity of other sources of filament voltage. Denotes the terminal to which the negative side of the filament-voltage source should be connected. A+ (A,-plus or A-positive)-Sometimes called F+. Positive terminal of an A battery or positive polarity of other sources of filament voltage. The terminal to which the positive side of the filament voltage source should be connected. ab- -The prefix attached to names of practical electric units to indicate the corresponding unit in the cgs (centimetler-gram-second) electromagnetic system, e.g., abampere, abvolt, abcoulomb. abac -- See alignment chart. abampere -Centimeter-gram-second electromagneIic unit of current. The current that, when flowing through a wire 1 centimeter long bent into an arc with a radius of 1 centimeter, produces a magnetic field intensity of 1 oersted. One abampere is equal to 10 amperes. A battery- Source of energy that heats the filaments of vacuum tubes in batteryoperated equipment. abbreviated dialing- 1. A system using specialgrade circuits that require fewer than the usual number of dial pulses to connect two or more subscribers. 2. Ability of a phone system to require only two to four digits, while the network dials the balance of the seven to fourteen digits required. abc ---Also ABC. See automatic bass compensation. abcoulomb -Centimeter-gram-second electromagnetic unit of electrical quantity. The quantity of electricity

passing any point in an electrical circuit in 1 second when the current is 1 abampere. One abcoulomb is equal to 10 coulombs. aberration -1. In lenses, a defect that produces inexact focusing. Aberration may also occur in electron optical systems, causing a halo around the light spot. 2. In a cathode-ray tube, a defect in which the electron "lens" does not bring the electron beam to the same point of sharp focus at all points on the screen. 5. Failure of an optical lens to produce exact point-to-point correspondence between an object and its image. 4. Blurred focusing of light rays due to the difference in bending (refraction) imparted on different light frequencies (colors) as they pass through a lens. a b f a r a d -Centimeter-gram-second electromagnetic unit of capacitance. The capacitance of a capacitor when a charge of 1 abcoulomb produces a difference of potential of 1 abvolt between its plates. One abfarad is equal to lo9 farads. a b h e n r y -centimeter-gram-second electromagnetic unit of inductance. The inductance in a circuit in which an electromotive force of 1 abvolt is induced by a current changing at the rate of 1 abampere per second. One abhenry is equal to henry. a b m h o -Centimeter-gram-second electromagnetic unit of conductance. A conductor or circuit has a conductance of 1 abmho when a difference of potential of 1 abvolt between its terminals will cause a current of 1 abampere to flow through the conductor. One abmho is equal to lo9 mho. Preferred term: absiemens. abnormal glow-In a glow tube, a current discharge of such magnitude that the cathode area is entirely surrounded by a glow. A further increase in current results in a rise in its density and a drop in voltage. abnormal propagation -The phenomenon of unstable or changing atmospheric andlor ionospheric conditions acting on transmitted radio waves. Such waves are prevented from following their normal path through space, causing difficulties and disruptions of communications. a b n o r m a l reflections-See sporsldic reflections. abnormal termination -The shutdown of a computer program run or other process by the detection of an error by the associated hardware, indicating that some ongoing series of actions cannot be executed correctly. a b o h m -Centimeter-gram-second electromagnetic unit of resistance. The resistance of a conductor when, with an unvarying current of 1 abampere flowing through it, the potential difference between the ends of the conductor is 1 abvolt. One abohm is equal to ohm. abort-1. To cut short or break off (an action, operation, or procedure) with an aircraft, guided missile, or the like, especially because of equipment failure. An abort may occur at any point from start of countdown

AB power p a c k

- absolute tolerance

or takeoff to the destination. An abort can be caused by human technical or meteorological errors, miscalculation, or malfunctions. 2. The process of halting a computer program in an orderly fashion and returning control to the operator or operating system. 3. Abnormal termination of a computer program, caused by hardware or software malfunction or operator cancellation. AB power pack-Assembly in a single unit of the A and B batteries of a battery-operated circuit. Also, a unit that supplies the necessary A and B voltages from an ac source of power. abrasion m a c h i n e -A laboratory device for determining the abrasive resistance of wire or cable. The two standard types of machines are the squirrel cage with square steel bars and the abrasive grit types. abrasion resistance-A measure of the ability of a wire or wire covering to resist damage due to mechanical causes. Usually expressed as inches of abrasive tape travel. abrasion soldering -Soldering difficult metals by abrading the surface oxide film beneath a pool of molten solder. abrasive trimming -Trimming a ceramic capacitor or a film resistor to its nominal value by notching the surface with a finely adjusted stream of abrasive material such as aluminum oxide. abscissa-Horizontal, or x, axis on a chart or graph. absence-of-ground s e a r c h i n g selector-In dial telephone systems, an automatic switch that rotates, or rises vertically and rotates, in search of an ungrounded contact. absolute accuracy-1. The tolerance of the fullscale set point referred to as the absolute voltage standard. 2. Parameter for a d/a converter. It is the overall accuracy of the converter, in which all levels are compared with an absolute standard. Absolute accuracy includes the combination of all nonlinearity and end-point errors. absolute address-1. An address used to specify the location in storage of a word in a computer program, not its position in the program. 2. A binary number assigned permanently as the address of a storage location in a computer. 3. A fixed location in the memory of the CPU, as opposed to a relative address, which is specified according to its distance from another location. absolute altimeter- 1. Electronic instrument that furnishes altitude data with regard to the surface of the earth or any other surface immediately below the instrument, as distinguished from an aneroid altimeter, the readings of which depend on air pressure. 2. An altimeter that employs transmitted and reflected radio waves for its operation and thus does not depend on barometric pressure for its altitude indication. absolute code-A code using absolute addresses and absolute operation codes; that is, a code that indicates the exact location where the reference operand is to be found or stored. absolute coding-Coding written in machine language. It can be understood by the computer without processing. absolute delay-The time interval between the transmission of two synchronized radio, loran, or radar signals from the same or different stations. absolute digital position transducer-A digital position transducer, the output signal of which is indicative of absolute position. Also called encoder. absolute efficiency-Ratio of the actual output of a transducer to that of a corresponding ideal transducer under similar conditions. absolute error- 1. The amounts of error expressed in the same units as the quantity containing the error.

2 2. Loosely, the absolute value of the error, that is, the magnitude of the error without regard to its algebraic sign. absolute gain of an antenna-The gain in a given direction when the reference antenna is an isotropic antenna isolated in space. absolute instruction -A computer instruction that explicitly states, and causes the execution of, a specific operation. absolute language-The language in which instructions must be given to the computer. The absolute language is determined when the computer is designed. Synonyms: machine language, machine code. absolute loader--Program to load a computer program at specified numerical addresses. absolute maximum rating -Limiting values of operating and environmental conditions, applicable to any electron device of a specified type as defined by its published data and not to be exceeded under the worst probable conditions. Those ratings beyond which the life and reliability of a device can be expected to decline. absolute maximum supply voltage-The maximum supply voltage that may be applied without the danger of causing a permanent change in the characteristics of a circuit. absolute minimum resistance-The resistance between the wiper and the termination of a potentiometer, when the wiper is adjusted to minimize that resistance. absolute Peltier coefficient-The product of the absolute temperature and the absolute Seebeck coefficient of a material. absolute power -Power level expressed in absolute units (e.g., watts or dBm). absolute pressure transducer- 1. A pressure transducer that accepts two independent pressure sources simultaneously, and the output of which is proportional to the pressure difference between the sources. 2. A transducer that senses a range of pressures, which are referenced to a fixed pressure. The fixed pressure is normally total vacuum. absolute scale-See Kelvin scale. absolute S e e b e c k coefficient-The integral from absolute zero to the given temperature of the quotient of the Thomson coefficient of a material divided by its absolute temperature. absolute spectral response -Output or response of a device, in terms of absolute power levels, as a function of wavelength. absolute s y s t e m of units- Also called coherent system of units. A system of units in which a small number of units is chosen as fundamental, e.g., units of mass, length, time, and charge. Such units are termed absolute units. All other units are derived from them by taking a definite proportional factor in each of those laws chosen as the basic laws for expressing the relationships between the physical quantities. The proportional factor is generally taken as unity. absolute temperature-Temperature measured from absolute zero, a theoretical temperature level variously defined as -273.2”C, -459.7”F, or 0 K. absolute temperature scale-Thermodynamic temperature scale, named for Lord Kelvin (1848), in which temperatures are given in kelvins (K). (In the SI system the degree sign and the word degree are not used for Kelvin temperatures.) The absolute zero of temperature is 0 K, -273.2”C, or -459.7”F. The kelvin is the same size as the Celsius degree. a b s o l u t e tolerance- Also called accuracy. The maximum deviation from the nominal resistance (or capacitance) value, usually given as a percentage of the nominal value.

3

absolute units-A system of units based on physical principles, in which a small number of units are chosen as fundamental and all other units are derived from them; e.g., abohm, abcoulomb, abhenry, etc. absolute value-The numerical value of a number or symbol without reference to its algebraic sign. Thus, 3 is the ablsolute value of 131 or 1-31. An absolute value is signified by placing vertical lines around the number or symbol. absolute value device-A computing element that produces an output equal to the magnitude of the input signal, but always of one polarity. absolute zero-Lowest possible point on the scale of absolute temperature; the point at which all molecular activity ceases. Absolute zero is variously defined as -273.2”C, -459.7”F, or 0 K. absorbed wave-A radio wave that becomes lost in the ionosphere due to molecular agitation and the accompanying energy loss it undergoes there. Absorption is most pronounced at low frequencies. a b s o r b e r - I. In a nuclear reactor, a substance that absorbs neutrons without reproducing them. Such a substance may be useful in control of a reactor or, if unavoidably present, may impair the neutron economy. 2. Any material or device that absorbs and dissipates radiated energy. 3. In microwave terminology, a material or device thiat takes up and dissipates radiated energy. It may be used For shielding, to prevent reflection, or to transmit one or more radiation components selectively. absoirption -1. Dissipation of the energy of a radio or sound wave into other forms as a result of its interaction with matter. 2. The process by which the number of particles or photons entering a body of matter is reduced by interaction of the particle or radiation with matter. Similarly, the reduction of the energy of a particle while traversing a body of matter. This term is sometimes erroneously used for capture. 3. Penetration of a substance into the body of another. 4. Conversion of radiant energy into other forms by passage through, or reflection from, matter. 5. The adhesion of a fluid in extremely thin layers to the surfaces of a solid. 6. Reduction in strength of an electromagnetic wave propagating through a medium, determined by dielectric properties of the material. ttenuation-Loss in an optical fiber impurities, including metals, such as and iron, as well as OH ions. ircuit -A tuned circuit that dissipates energy taken from another circuit or from a signal source. This effect is especially evident in a resonant circuit such as a wavemeter or wave trap.

absorption coefficient- 1. Measure of soundabsorbing characteristics of a unit area of a given material compared with the sound-absorbing characteristics of an open space (total absorption) having the same area. 2. Ratio of loss of intensity caused by absorption to the total original intensity of radiation. absorption current-The current flowing into a capacitor following its initial charge, due to a gradual

absolute units - abvolt penetration of the electric stress into the dielectric. Also, the current that flows out of a capacitor following its initial discharge. absorption dynamometer-An instrument for measuring power, in which the energy of a revolving wheel or shaft is absorbed by the friction of a brake. absorption fading-A slow type of fading, primarily caused by variations in the absorption rate along the radio path. absorption f r e q u e n c y meter-See absorption wavemeter. absorption loss- 1. That part of transmission loss due to dissipation or conversion of electrical energy into other forms ( e g , heat), either within the medium or attendant upon a reflection. 2. The loss of optical flux or energy caused by impurities in the transmission medium as well as intrinsic material absorption. Expressed in decibels per kilometer. absorption m a r k e r -1. A sharp dip on a frequencyresponse curve due to the absorption of energy by a circuit sharply tuned to the frequency at which the dip occurs. 2. A small pip or blank introduced on an oscilloscope trace to indicate a frequency point. It is so called because it is produced by a frequency-calibrated tuned trap similar to an absorption wavemeter. absorption modulation -Also called loss modulation. A system for amplitude-modulating the output of a radio transmitter by means of a variable-impedarxe device (such as a microphone semiconductor or vacuum-tube circuit) inserted into or coupled to the output circuit. absorption trap- A parallel-tuned circuit coupled either magnetically or capacitively to absorb and attenuate interfering signals. absorption wavemeter- Also called absorption frequency meter. An instrument for measuring frequency. Its operation depends on the use of a tuned electrical circuit or cavity loosely coupled inductively to the source. Maximum energy will be absorbed at the resonant frequency, as indicated by a meter or other device. Frequency can then be determined by reference to a calibrated dial or chart. absorptivity-A measure of the portion of incident radiation or sound energy absorbed by a material. abstraction -A simplified description or specification of a system that emphasizes some of the system’s details or properties while suppressing others. A high level of abstraction or a highly abstract machine is one in which very few machine details are apparent to a programmer, who sees only a broad set of machine concepts. Abstract machines are created by surrounding a primitive machine with layers of operating systems. To converse with higher levels of abstract machines, the user needs higher levels of languages. A/B s w i t c h -A switch that selects one of two inputs (A or €3) for routing to a common output while providing adequate isolating between the two signals. A-B test- 1. Direct comparison of two sounds by playing first one and then the other. May be done with two tape recorders playing identical kpes (or the same tape), two speakers playing alternately from the same tape recorder, or two amplifiers playing alternately through one speaker, etc. 2. An audio comparison test for evaluating the relative performance of two or more components or systems by quickly changing from one to the other. The left- and right-hand channels or the record and replay sound signals are often designated A and B. A and B test facilities are installed at most high-fidelity dealers. abvolt -Centimeter-gram-second electromagnetic unit of potential difference. The potential difference between two points when 1 erg of work is required to

ac - acceptor transfer 1 abcoulomb of positive electricity from a lower to a higher potential. An abvolt is equal to lo-* volt. ac -Abbreviation for alternating current. ac bias-The alternating current, usually of a frequency several times higher than the highest signal frequency, that is fed to a record head in addition to the signal current. The ac bias serves to linearize the recording process. accelerated aging -A test in which certain parameters, such as voltage and temperature, are increased above normal operating values to obtain observable deterioration in a relatively short period. The plotted results give expected service life under normal conditions. Also called accelerated life test. accelerated g r a p h i c s port -Abbreviated AGP. A slot inside PCs for high speed video to be used instead of the standard slot type, called PCI. accelerated life test -Test conditions used to bring about, in a short time, the deteriorating effect obtained under normal service conditions. accelerated service test-A service or bench test in which some service condition, such as speed, temperature, or continuity of operation, is exaggerated to obtain a result in a shorter time than that which elapses in normal service. accelerating conductor or relay-A conductor or relay that causes the operation of a succeeding device to begin in the starting sequence after the proper conditions have been established. acceleratingelectrode-An electrode in a cathoderay or other electronic tube to which a positive potential is applied to increase the velocity of electrons or ions toward the anode. A klystron tube does not have an anode but does have accelerating electrodes. accelerating time -The time required for a motor to reach full speed from a standstill (zero speed) position. accelerating voltage-A high positive voltage applied to the accelerating electrode of a cathode-ray tube to increase the velocity of electrons in the beam. acceleration-1. The rate of change in velocity. Often expressed as a multiple of the acceleration of gravity (g = 32.2 ft/s2). 2. The rate of change in velocity of a stepping motor measured in rads; it is the result of rotor torque divided by rotor and load inertia. 3. A vector quantity that specifies rate of change of velocity. acceleration at stall -The value of servomotor angular acceleration calculated from the stall torque of the motor and the moment of inertia of the rotor. Also called torque-to-inertia ratio. acceleration time -In a computer, the elapsed time between the interpretation of instructions to read or write on tape and the possibility of information transfer from the tape to the internal storage, or vice versa. acceleration torque-Numerical difference between motor torque produced and load torque demanded at any given speed during the acceleration period. It is this net torque that is available to change the speed of the driven load. acceleration voltage -Potential between a cathode and anode or other accelerating element in a vacuum tube. Its value determines the average velocity of the electrons. accelerator-A device for imparting a very high velocity to charged particles such as electrons or protons. Fast-moving particles of this type are used in research or in studying the structure of the atom itself. 2. A circuit that speeds up a computer or monitor. Typically a circuit card with an extra processing chip and/or additional RAM. accelerator board -An adapter with a microprocessor that makes a computer run faster.

accelerator d y n a m i c test -A test performed on an accelerometer by means of which information is gathered pertaining to the overall behavior frequency response and/or natural frequency of the device. accelerometer- 1. An instrument or device, often mounted in an aircraft, guided missile, or the like, used to sense accelerative forces and convert them into corresponding electrical quantities, usually for measuring, indicating, or recording purposes. It does not measure velocity or distance, only changes in velocity. 2. A transducer that measures acceleration and/or gravitational forces capable of imparting acceleration. 3. A sensor whose electrical output is proportional to acceleration. TO INTEGRATORS

MASS

Accelerometer.

accentuation-Also called preemphasis. The emphasizing of any certain band of frequencies, to the exclusion of all others, in an amplifier or electronic device. Applied particularly to the higher audio frequencies in frequency-modulated (FM)transmitters. accentuator- 1. Network or circuit used for preemphasis, that is, an increase in amplitude of a given band of usually audible frequencies. 2. A circuit or device, such as a filter, tone control, or equalizer, used to emphasize a band of frequencies, usually in the audio-frequency spectrum. acceptable-environmental-range test-A test to determine the range of environmental conditions for which an apparatus maintains at least the minimum required reliability. acceptable quality level -Abbreviated AQL. The maximum percentage of defective components considered to be acceptable as an average for a process or the lowest quality a supplier is permitted to present continually for acceptance. Also see AQL. acceptance angle-1. The solid angle within which all incident light rays will enter the core of an optical fiber. Expressed in degrees. 2. In fiber optics, a measure of the maximum angle within which light may be coupled from a source or emitter. It is measured relative to the fiber’s axis. 3. The critical angle, measured from the core centerline, above which light will not enter an optical fiber. It is equal to the half-angle of the acceptance cone. 4. The maximum angle within which light will be accepted by an element, such as a detector. acceptance cone- 1. A parameter that defines acceptable light-launching angles. Only light launched at angles within this cone will be waveguided (fiber optics). 2. A cone with an included angle twice that of the acceptance angle. acceptance pattern-In fiber optics, a curve of total transmitted power plotted against the launch angle. acceptance sampling plan-A plan for the inspection of samples as a basis for acceptance or rejection of a lot. acceptor- Also called acceptor impurity. An impurity lacking sufficient valence electrons to complete the

5 bonding arrangement in the crystal structure. When added to a semiconductor crystal, it accepts an electron from a neighboring atom and thus creates a hole in the lattice structure of the crystal, making a p-type semiconductor. 2. An impurity from column I11 of the periodic table, which adds a mobile hole to silicon, thereby making it more p-type and accepting of electrons. Boron is the primary acceptor used to dope silicon (compare with donor). acceptor circuit- 1. A circuit that offers minimum oppositioln to a given signal. 2. A circuit tuned to respond to a single frequency. acceptor impurity-See acceptor. acceptor-type semiconductor -A p-type semiconductor. access- 1. To gain access to a computer’s memory location in which binary information is already stored or can be stored. 2. To open up a set of connections to allow reading from or writing into this location. access arm-In a computer storage unit, a mechanical device that positions the reading and writing mechanism. access code- 1. The preliminary digit or digits that a telephone user must dial to be connected to a particular outgoing trunk group. 2. A group of characters or numbers that identifies a user to a computer or any other secure system. 3. One or more numbers and/or symbols that are keyed into the repeater with a telephone tone pad to activate a repeater function, such as an autopatch. access control-1. The control of pedestrian and vehicular traffic through entrances and exits of a protected area or premises. 2. The process of limiting access to resources of a system to only authorized users, programs, processes, or other systems. access grant -Multiprocessor system response that satisfies a previous service request. access hole-A hole drilled through successive layers of a multilayer board to gain access to a land or pad location on one of the inside layers. access method- 1. A data-management technique available for use in transferring data between the main storage and an input/output device. 2. A software component of a computer operating system that controls the flow #ofdata bletween application programs and either local or remote peripheral devices. access mode- 1. A technique used in COBOL to obtain a specific logic record from, or to place it into, a file ,assignedto a mass storage device. 2. The operation of an #alarmsystem such that no alarm signal is given when the protected area is entered; however, a signal may be given .if the sensor, annunciator, or control unit is tampered with lor opened. acce6sory card -An additional circuit card that can Ibe mounted inside a personal computer and connected to ihe system bus. access protocol-A defined set of procedures that -Function as an interface between a computer user and a network, enabling the user to employ the services of that network. access provider -Telecommunications company !hat links businesses and individuals to the Internet using imodem devices, high-speed ISDN lines, or dedicated links. ac6ess time-Also called waiting time. 1. The itime interval (called read time) between the instant of calling for data from a storage device and the instant fief completion of delivery. 2. In a memory system, the itime delay, at specified thresholds, from the presentation of an enable or address input pulse until the arrival of the memory data output. 3. The time required for a (computerto move data between its memory section and its

acceptor circuit

- accuracy

CPU. 4. A time interval that is characteristic of a storage device. Essentially, it is a measure of the time required to communicate with that device, or, more specifically, it is the time between the application of a specified input pulse (assuming that other necessary inputs are also present) and the availability of valid data signals at an output. The access time can be defined only with reference to an output signal. 5. The time required by a computer to begin delivering information after the memory or storage has been interrogated. 6. The time it takes a computer to retrieve a piece of information. With hard disks or compact discs, maximum access time is measured as the time it takes to move from one end of the disk to the other, find a piece of information, and transfer that information to RAM. accidental jamming -Jamming caused by transmission from friendly equipment. ac circuit breaker-A device that is used to close and interrupt an ac power circuit under normal conditions or to interrupt this circuit under faulty or emergency conditions. accompanying audio (sound) channel -Also known as co-channel sound frequency. The rf canier frequency that supplies the sound to accompany a television picture. ac component-In a complex wave (i.e., one containing both ac and dc), the alternating, fluctuating, or pulsating member of the combination. accordion-A type of contact used in some printedcircuit connectors. The contact spring is given a z shape to permit high deflection without excessive stress. ac-coupled flip-flop-A flip-flop that changes state when triggered by the rise or fall of a clock pulse. There is a maximum allowable rise or fall time for proper triggering. ac coupling-Coupling of one circuit to another circuit through a capacitor or other device that passes the varying portion but not the static (dc) characteristics of an electrical signal. accumulationkey-In a calculator, it automatically accumulates products and totals of successive calculations. accumulator- 1. In an electronic computer, a device which stores a number and which, on receipt of another number, adds the two and stores the sum. An accumulator may have properties such as shifting, sensing signals, clearing, complementing, etc. 2. A chemical cell able to store electrical energy (British). Also called secondary cell. 3. The “scratch pad” section of the computer, in which arithmetic operations are carried out. 4. A register and related circuitry that hold an operand for aithmetic and logic operations. 5. A register or latch internal to the MPU where data is stored temporarily before being sent to another location internal or external to the MPU chip. accuracy- 1. The maximum error in the measurement of a physical quantity in terms of the output of an instrument when referred to the individual instrument calibration. Usually given as a percentage of full scale. 2. The quality of freedom from mistake or error in an electronic computer, that is, of conformity to truth or to a rule. 3. The closeness with which a measured quantity approaches the true value of that quantity. (See true value.) 4. The degree to which a measured or calculated value conforms to the accepted standard or rule. 5. The measure of a meter’s ability to indicate a value corresponding to the absolute value of electrical energy applied. Accuracy is expressed as a percentage of the meter’s rated full-scale value. To be meaningful, accuracy specifications must always consider the effects of time, temperature, and humidity. 6. Confidence in the correlation between measurements in one location and another,

accuracy rating of an instrument - acorn tube or between a measurement and a recognized standard. 7. The correctness or certainty of position when the rotor of a stepping motor comes to rest. It is usually expressed as a percentage of the step angle, but can also be specified in degrees or minutes of arc. In steppers, the error is not cumulative, but occurs only at the completion of the last step. 8. The degree of freedom from error, that is, the degree of conformity to some standard. Accuracy is contrasted with precision. For example, four-place numbers are less precise than six-place numbers; however, a properly computed four-place number might be more accurate than an improperly computed six-place number. 9. As applied to an adc, the term describes the difference between the actual input voltage and the full-scale weighted equivalent of the binary code. a c c u r a c y rating of an instrument-The limit, usually expressed as a percentage of full-scale value, not exceeded by errors when the instrument is used under reference conditions. ACD -Abbreviation for automatic call distributor. A switching system that automatically distributes incoming calls to a centralized group of receivers in the sequence in which the calls are received. It holds calls until a receiver is available. ac/dc -Electronic equipment capable of operation from either an ac or dc primary power source. Abbreviation for alternating currenVdirect current. ac/dc receiver-A radio receiver designed to operate directly from either an ac or a dc source. ac/dc ringing-A method of telephone ringing in which alternating current is used to operate a ringing device, and direct current is used to aid the action of a relay that stops the ringing when the called party answers. ac directional overcurrent relay-A device that functions on a desired value of ac overcurrent flowing in a predetermined direction. ac dump -The intentional, accidental, or conditional removal of all alternating-current power from a system or component. An ac dump usually results in the removal of all power, since direct current is usually supplied through a rectifier or converter. ac erasing h e a d -In magnetic recording, a device using alternating current to produce the magnetic field necessary for removal of previously recorded information. acetate-A basic chemical compound in the mixture used to coat recording discs. acetate base -The transparent plastic film that forms the tough backing for acetate magnetic recording tape. acetate disc- A mechanical recording disc, either solid or laminated, made mostly from cellulose nitrate lacquer plus a lubricant. acetate tape -A sound-recording tape with a smooth, transparent acetate backing. One side is coated with an oxide capable of being magnetized. ac generator- 1. A rotating electrical machine that converts mechanical power into alternating current. Also known as an alternator. 2. A device, usually an oscillator, designed for the purpose of producing alternating current. A channel-One of two stereo channels, usually the left. achieved reliabili@-Reliability determined on the basis of actual performance of nominally identical items under equivalent environmental conditions. Also called operational reliability. a c h r o m a t i c - 1. In color television, a term meaning a shade of gray from black to white, or the absence of color (without color). 2. Black-and-white television, as distinguished from color television. 3. Literally, color free. In an optical system, the term is used when chromatic aberration is corrected for at least two wavelengths. A

6 color that is defined as being achromatic is often referred to as gray. 4. Having no color; being a neutral such as black, white, or gray. a c h r o m a t i c lens-A lens that has been corrected for chromatic aberration. Such a lens is capable of bringing all colors of light rays to approximately the same point of focus by combining a concave lens of flint glass with a convex lens of crown glass. A lens that transmits light without separating it into its constituent colors. a c h r o m a t i c locus- Also called achromatic region. On a chromaticity diagram, an area that contains all points representing acceptable reference white standards. a c h r o m a t i c region-See achromatic locus. acicular-Needle-shaped; descriptive of the shape of the magnetizable particles composing the coating of a recording tape. Modern tapes are premagnetized during the coating process to line the “needles” up with the direction of the tape, thus providing maximum sensitivity from the oxide. acid -A chemical compound that dissociates and forms hydrogen ions when in aqueous solution. acid depolarizer-An acid, such as nitric acid, sometimes introduced into a primary cell to prevent polarization. acid fluxes-Fluxes consisting of inorganic acids and salts, which are used when a surface to be soldered is below the ideal for rapid wetting. Also called corrosive fluxes. acknowledge-A control signal used to complete a handshaking sequence in telecommunications. The acknowledge signal indicates that the information has been accepted by the receiving computer. ac line -A power line delivering alternating current only. ac line filter-A filter designed to dissipate or bypass to ground any extraneous signals or electrical noise on an ac power line, while causing virtually no reduction of the power-line voltage or power. Used to keep unwanted signals and noise out of sensitive equipment. aclinic line-Also called isoclinic line. On a magnetic map, an imaginary line that connects points of equal magnetic inclination or dip. ac magnetic biasing -In magnetic recording, the method used to remove random noise and/or previously recorded material from the wire or tape. This is done by introducing an alternating magnetic field at a substantially higher frequency than the highest frequency to be recorded. ac noise-Noise that displays a rate of change that is fast relative to the response capability of the device. ac noise immunity-A measure of a logic circuit’s ability to maintain the prescribed logic state in the presence of such noise. It is defined in terms of the amplitude and pulse width of an input noise signal to which the element will not respond. acorn tube -A button- or acorn-shaped vacuum tube with no base, designed for UHF applications. Electrodes are brought out through the glass envelope on the side, top, and bottom.

Acorn tube.

7 acoustic- Also acoustical. Pertaining to sound or the science of sound. acoustic absorption loss-The energy lost by conversion into heat or other forms when sound passes through or is reflected by a medium. acoustic absorptivity -The ratio of sound energy absorbed by a surface to the sound energy arriving at the surface. Equal to 1 minus the reflectivity of the surface. acoustical-See acoustic. acoustical attenuation constant-The real part of the arcoustical propagation constant. The commonly used unit is the neper per section or per unit distance. acoustical coupler-A device for connecting a telephone handset to a computer input port. acoustical-electrical transducer-A device designed to transform sound energy into electrical energy and vice versa. acoustical material-Any material considered in terms of its acoustical properties; especially, a material designedl to absorb sound. acoustical mode -A mode of crystal-lattice vibration that does not produce an oscillating dipole. acoustical ohm -A measure of acoustic resistance, reactance, or impedance. One acoustical ohm is equal to a volume velocity of 1 cubic centimeter per second when produced by a sound pressure of 1 microbar. acoustical phase constant-The imaginary part of the acoustical propagation constant. The commonly used unit is the radian per section or per unit distance. coustical reflectivity-See sound-reflection coefficient. acousticaltransmittivity-See sound-transmission coefficient. acoustic burglar alarm -Also called acoustic intrusion detector. A burglar alarm that is responsive to sounds produced by an intruder. Concealed microphones connected to an audio amplifier trip an alarm when sounds within a predetermined range of frequencies exceed a predetermined normal level. acoustic capacitance-In a sound medium, a measure of volume displacement per dyne per square centimetler. The unit is centimeter to the fifth power per dyne. acoustic clarifier-A system of cones loosely attached to the baffle of a speaker and designed to vibrate and absorb energy during sudden loud sounds, thereby suppressing them. acou~sticcompliance- 1. The measure of volume displacement of a sound medium when subjected to sound waves. 2. That type of acoustic reactance which corresponds to capacitive reactance in an electrical circuit. acoustic coupler- 1. A device that converts digital signals into audio signals, enabling data to be transmitted over the telephone lines via a conventional telephone. 2. A modem device that connects a terminal or computer to the handset of a telephone. acoustic coupling --Coupling resonator elements by mechanical means through the use of wires, rods, or nonelecboded sections of quartz or ceramic. The terms acoustic and mechanical can be used interchangeably. acoustic delay line--A device that retards one or more signal vibrations by causing them to pass through a solid or liquid. acoustic dispersion -The change of the speed of sound with frequency. acoustic elasticity- 1. The compressibility of the air in a speaker enclosure as the cone moves backward. 2. The compressibility of any material through which sound is passed.

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Acoustic coupler.

acousticfeedback- 1. Also called acoustic regeneration. The mechanical coupling of a portion of the sound waves from the output of an audio-amplifying system to a preceding part or input circuit (such as the microphone) of the system. When excessive, acoustic feedback will produce a howling sound in the speaker. 2. The pickup, by a turntable, of vibrations from the speaker. If these vibrations reach the cartridge, they will be reamplified, causing noise (usually a rumble, but in extreme cases a howl) and/or distortion. Also, feedback resulting from such sound waves setting some part of an amplifier circuit into vibration and thus modulating the currents in the circuit. Acoustic feedback usually causes howling or whistling. acoustic filter- 1. A sound-absorbing device that selectively suppresses certain audio frequencies while allowing others to pass. 2. Any sound-absorbing or soundtransmitting arrangement, or combination of the two, that passes sound waves of desired frequency while attenuating or eliminating others. acoustic frequency response-The voltageattenuation frequency measured into a resistive load, producing a bandwidth approaching sufficiently close to the maximum. acoustic generator-A transducer, such as a speaker, headphones, or a bell, that converts electrical, mechanical, or other forms of energy into sound. acoustic homing system-1. A system that uses a sound signal for guidance purposes. 2. A guidance method in which a missile homes in on noise generated by a target. acoustic horn-Also called horn. 1. A tube of varying cross section having different terminal areas that change the acoustic impedance to control the directivity of the sound pattern. 2. A tapered tube (round or rectangular, but generally funnel shaped) that directs sound and, to some extent, amplifies it. acoustic impedance- 1. Total opposition of a medium to sound waves. Equal to the force per uait area on the surface of the medium divided by the flux (volume velocity or linear velocity multiplied by area) through that surface. Expressed in ohms and equal to the mechanical impedance divided by the square of the surface area. One unit of acoustic impedance is equal io a volume velocity of 1 cubic centimeter per second produced by a pressure of 1 microbar. Acoustic impedance contains both acoustic resistance and acoustic reactance. 2. The degree of resistance to transmitting sound imparted by the characteristic elasticity of a given substance. acoustic inertance-A type of acoustic reactance that corresponds to inductive reactance in an electrical circuit. (The resistance to movement or reactance offered by

acoustic intensity - acoustic transmission the sound medium because of the inertia of the effective mass of the medium.) Measured in acoustic ohms. acoustic intensity-The limit approached by the quotient of acoustical power being transmitted at a given time through a given area divided by the area as the area approaches zero. acoustic interferometer- An instrument for measuring the velocity or frequency of sound waves in a liquid or gas. This is done by observing the variations of sound pressure in a standing wave, established in the medium between a sound source and a reflector, as the reflector is moved or the frequency is varied. acoustic intrusion detector-See acoustic burglar alarm. acoustic labyrinth -A loudspeaker enclosure in which the rear of the loudspeaker is coupled to a tube which, at the resonant frequency of the loudspeaker, is one quarter of a wavelength long. The tube, folded upon itself in order to save space, gives the appearance of a labyrinth. acoustic lens- 1. An array of obstacles that refract sound waves in the same way that an optical lens refracts light waves. The dimensions of these obstacles are small compared with the wavelengths of the sounds being focused. 2. A device that produces convergence or divergence of moving sound waves. When used with a loudspeaker, the acoustic lens widens the beam of the higher-frequency sound waves. acoustic line-Mechanical equivalent of an electrical transmission line. Baffles, labyrinths, or resonators are placed at the rear of a speaker to help reproduce the very low audio frequencies. acoustic memory-A computer memory using an acoustic delay line. The line employs a train of pulses in a medium such as mercury or quartz. acoustic mine-Also called sonic mine. An underwater mine that is detonated by sound waves, such as those from a ship’s propeller or engines. acoustic mirage-The distortion of a sound wavefront by a large temperature gradient in air or water. This creates the illusion of two sound sources. acoustic ohm-The unit of acoustic resistance, reactance, or impedance. One acoustic ohm is present when a sound pressure of 1 dyne per square centimeter produces a volume velocity of 1 cubic centimeter per second. acoustic p h a s e constant-The imaginary part of the acoustic propagation constant. The commonly used unit is the radian per section or per unit distance. acoustic phonograph-A mechanical record player (now obsolete) in which the needle sets a thin diaphragm into vibration. The diaphragm in turn causes the air in a horn to vibrate, thus reproducing the recorded sound. acoustic pickup -1. In nonelectrical phonographs, the method of reproducing the material on a record by linking the needle directly to a flexible diaphragm. 2. In an acoustic phonograph, a pickup consisting of a needle, needle holder, and vibrating diaphragm. acoustic radiator-In an electroacoustic transducer, the part that initiates the radiation of sound vibration. A speaker cone or headphone diaphragm is an example. acoustic radiometer -An instrument for measuring sound intensity by determining the unidirectional steady-state pressure caused by the reflection or absorption of a sound wave at a boundary. acoustic reactance-That part of acoustic impedance due to the effective mass of the medium, that is, to the inertia and elasticity of the medium through which

8 the sound travels. The imaginary component of acoustic impedance; expressed in acoustic ohms. acoustic reflectivity-The ratio of the rate of flow of sound energy reflected from the surface on the side of incidence to the incident rate of flow. acoustic refraction-A bending of sound waves when passing obliquely from one medium to another in which the velocity of sound is different. acoustic regeneration -See acoustic feedback. acoustic resistance-That component of acoustic impedance responsible for the dissipation of energy due to friction between molecules of the air or other medium through which sound travels. Measured in acoustic ohms and analogous to electrical resistance. acoustic resonance -An increase in sound intensity as reflected waves and direct waves that are in phase combine. May also be due to the natural vibration of air columns or solid bodies at a particular sound frequency. acoustic resonator -An enclosure that intensifies those audio frequencies at which the enclosed air is set into natural vibration. acoustics-1. Science of production, transmission, reception, and effects of sound. 2. In a room or other location, those characteristics that control reflections of sound waves and thus the sound reception in it. acoustic scattering -The irregular reflection, refraction, or diffraction of a sound wave in many directions. acoustic shock-Physical pain, dizziness, and sometimes nausea brought on by hearing a loud, sudden sound. (The threshold of pain is about 120 dBm.) acoustic surface-wave component -A passive electroacoustic device that has metallized interdigital transducer elements deposited on the surface of a piezoelectric substrate. The device allows acoustic energy to be generated, manipulated, and detected on the substrate surface. Most of the acoustic energy is confined to a region within one wavelength of the surface of the substrate. When the metallization is subjected to an alternating voltage, a strain develops between the interdigital fingers and also at the frequency of excitation. This alternating strain on the crystal surface launches a Rayleigh surface-wave front that travels in both directions and that originates from the center of the transducer. The wave exists as an electroacoustic vibration. acoustic suspension- 1. A loudspeaker system in which the moving cone is held by an overcompliant suspension, the stiffness required for proper operation being supplied by air that is trapped behind the cone in a sealed enclosure. While relatively inefficient, such a system permits good bass reproduction in a unit of moderate size. 2. A speaker enclosure design in which the speaker cone is suspended in an airtight box. This enables the acoustic pressure of the air enclosed therein to provide the principal restoring force for the diaphragm of the speaker. It needs somewhat more power from the amplifier than a free speaker but has better low-frequency performance. acoustic system -Arrangement of components in devices designed to reproduce audio frequencies in a specified manner. acoustic telemetry-The utilization of sound energy for the transmission of information. It differs from other telemetry methods in that information derived from the received signal is encoded by the transmitting source. acoustic transformer-A device that transmits power along a glass or ceramic rod and isolates the power supply from the signal input. acoustic transmission -Direct transmission of sound energy without the intermediary of electric currents.

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acoustic transmission system -An assembly of elements adapted for the transmission of sound. acoustic treatment -Use of certain soundabsorbing materials to control the amount of reverberation in a room, hall, or other enclosure; that is, to make the room 1es;slive. acoustic wave -A traveling vibration by which sound energy is transmitted in air, water, or the earth. The characteristics of these waves may be described in terms of change of pressure, particle displacement, or density. acoustic wave fitter-A device designed to separate sound waves of different frequencies. (Through electroacoustic transducers, such a filter may be associated with electric circuits.) acoustoelectric effect-Generation of an electric current in a crystal by a traveling longitudinal sound wave. acousto-optic Bragg cell -A modulation device that impiresses analog information on light beams. This transducer is composed of two sets of interleaved electrodes off alternating polarities deposited on an optical waveguide. An electrical signal applied to each pair of adjacent electrodes buckles the film between them. This distortion changes the refractive index of the waveguide and creates physical waves in the film, commonly called surface waves. These waves are generated at a rate equal to that of the applied electrical signal. acousto-optics -The study of the interactions between sound waves and light in a solid medium. Sound waves can be made to modulate, deflect, and focus light waves - an important characteristic in laser and holographic applications. ac plate resistance- Also called dynamic plate resistanae. Internal resistance of a vacuum tube to the flow of alternating current. Expressed in ohms, the ratio of a small change in plate voltage to the resultant change in plate current, other voltages being held constant. ac power supply-A power supply that provides one or more ac output voltages, e.g., ac generator, dynamotsor, inverter, or transformer. acquiisitiosl- 1. The process of pointing an antenna or telescope so that it is properly oriented to allow gathering of tracking or telemetry data from a satellite or space probe. 2. In radar, the process between the initial location of a target and the final alignment of the tracking equipment on the target. 3. The gathering of data from transducers or a computer. cquisition and tracking radar-A radar set that locks onto a strong signal and tracks the object emitting or reflecting the signal. May be airborne or on the ground. ‘Tracking radars use a dish-type antenna reflector to produce a searchlight-type beam. acquiisition radar-A radar set that detects an approaching target and feeds approximate position data to a fire-control or missile-guidance radar, which then takes over the function of tracking the target. a c q u i ~ ~ trangei~n Also called capture range. The range of input hequency about f under which a phaselocked loop, which is initially unlocked, will become locked. This range is narrower than the normal tracking range and is a function of the loop-filter characteristics and the input amplitude. ~ c ~ u itimes ~ t1. ~ Time ~ delay ~ between request for data conversion and the holding of the analog value by a saniple-and-hold amplifier. 2. In a sample-and-hold circuit, how long it takes after the sample command is given f o r the hold capacitor to be charged to a full-scale voltage change and to remain within a specified error band around its final value. 3. The time it takes for the output of a sample-and-hold circuit to change from its previous value to a new value when the circuit is switched from the hold mode to the sample mode. It includes the slew

acoustic transmission s y s t e m - activation time and settling time to within a certain error band of the final value and is usually specified for a full-scale change. ac receiver -A radio receiver designed to operate from an ac source only. ac reclosing relay-A device that Controls the automatic reclosing and locking out of an ac circuit interrupter. ac relay-A relay designed to operate from an alternating-current source. ac resistance-Total resistance of a device in an ac circuit. See also high-frequency resistance. a c r o n y m -A word formed from the first letrer or letters of the words describing some item, e.g., FORTRAN from formula translation. across-the-line starting -Connection of a motor directly to the supply line for starting. Also called fullvoltage starting. ac signaling-Using ac signals or tones to transmit data and/or control signals. ACTCRBS -Abbreviation for air traffic control radar beacon system. A control system in use worldwide. Air separation infomation exchanged between plane and air traffic controller must be sent by radio. ac time overcurrent relay-A device that has either a definite or an inverse time characteristic and functions when the current in an ac circuit exceeds a predetermined value. actinic--In radiation, the property of producing a chemical change, such as the photographic action of light. actinium -A radioactive element discovered in pitchblende by the French chemist Debierne in 1889.Its atomic number is 89, its atomic weight 227, and its symbol Ac. actinodielectric-A photoconductive dielectric. actinoelectric-Exhibiting a temporary rise in electrical conductivity during exposure to light. actinoelectric effect- 1. The property of some special materials whereby when an electric current is impressed on them, their resistance changes with light. 2. The property of certain materials (such as selenium, cadmium sulfide, germanium, and silicon) that causes them to change their electrical resistance or generate a voltage on exposure to light. actinoelectricity-Electricity produced by the action of radiant energy on crystals. actinometer -An instrument that measures the intensity of radiation by detemining the amount of fluorescence produced by that radiation. action area-In the rectifying junction of a metallic rectifier, that portion which carries the forward current. action current-A brief and very small electric current that flows in a nerve during a nervous impulse. action potential -1. The instantaneous value of the voltage between excited and resting portions of an excitable living structure. 2. The voltage variations in a nerve or muscle cell when it is excited or fired by an appropriate stimulus. After a short tim-e, the cell recovers its normal resting potential, typically about 80 millivolts. The interior of the cell is negative relative to the outside. activate-To start an operation, usually by application of an appropriate enabling signal. activating-1. Chemically treating a basic metal to remove oxides and other passive films to make it more receptive to electroplating. 2. A treatment that renders nonconductive material receptive to electroless deposition. (Nonpreferred synonyms: seeding, catalyzing, and sensitizing.) activation - 1. Making a substance artificially radioactive by placing it in an accelerator such as a cyclotron or by bombarding it with neutrons. 2. To treat the cathode or target of an electron tube in order to create or increase its

activation time - a c t i v e matrix emission. 3. The process of adding electrolytes to a cell to make it ready for operation. 4. Causing the acceleration of a chemical reaction. activation time-In a cell or battery, the time interval from the moment activation is initiated to the moment the desired operating voltage is obtained. activator- An additive that improves the action of an accelerator. active- 1. Controlling power from a separate supply. 2. Requiring a power supply separate from the controls. 3. Containing, or connected to and using, a source of energy. active area-The portion of the rectifying junction of a metallic rectifier that carries forward current. active b a l a n c e -In operation of a telephone repeater, the summation of all return currents at a terminal network balanced against the local circuit or drop impedance. active circuit-A circuit that contains active elements such as transistors, diodes, or integrated circuits. active communications satellite-A communications satellite in which on-board receivers and transmitters receive signals beamed at them from a ground terminal, amplify them greatly, and retransmit them to another ground terminal. Less sensitive receivers and less powerful transmitters can be used on the ground than are needed for passive satellites. Also called active comsat. active component- 1. Those components in a circuit that have gain, or direct current flow, such as SCRs, transistors, thyristors, or tunnel diodes. They change the basic character of an applied electrical signal by rectification, amplification, switching, and so forth. (Passive elements like inductors, capacitors, and resistors have no gain characteristics.) 2. A device, the output of which is dependent on a source of power other than the main input signal. 3. A device capable of some dynamic function (such as amplification, oscillation, signal control) and which usually requires an external power supply for its operation. 4. Broadly, any device (including electromechanical relays) that can switch (or amplify) by application of low-level signals. active computer-The one of two or more computers in an installation that is online and processing data. active comsat -See active communications satellite. active current-In an alternating current, a component in phase with the voltage. The working component as distinguished from the idle or wattless component. active decoder-A device that is associated with a ground station and automatically indicates the radar beacon reply code that is received in terms of its number or letter designation. active delay line-A digital delay module that incorporates a passive delay line and a series of logical gate circuits. These modules are used specifically with digital or logic signals. Also called digital delay line, digital delay unit, digital delay module, and digital programmable delay line. active d e v i c e -See active component. active display-A display, such as a cathode-ray tube, electroluminescent display, or plasma panel, that presents information by emitting light. active ECM-See jamming. active electric network- An electric network containing one or more sources of energy. active element-1. The driven or self-excited element in a multielement antenna or antenna array. 2. Also known as the responsive element. That part of a detector on which the infrared energy is projected and which, when radiation falls on it, undergoes a physical change that results in an electrical signal. See active component.

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active equalizer- An equalizer designed to correct deficiencies in a speaker system’s response. Such equalizers, which are designed to precisely match specific speaker systems, usually connect between the amplifier and preamplifier, or in one of the amplifier’s tape-monitor circuits. active filter- 1. A device employing passive network elements and amplifiers. It is used for transmitting or rejecting signals in certain frequency ranges or for controlling the relative output of signals as a function of frequency. 2. A high-pass, low-pass, bandpass, or bandelimination filter that uses an active element, such as an operational amplifier, and relatively small capacitors, rather than the larger inductors and capacitors that would be required in a conventional passive filter. 3. A circuit whose gain depends on the frequency of the input signal. 4. A filter, consisting of an amplifier and suitable tuning elements, usually inserted in a feedback path. 5 . A filter that uses active devices such as operational amplifiers to synthesize the filter response function. This technique has an advantage at high speeds because the need for inductors (with their poor high-frequency characteristics) is eliminated. active guidance -See active homing. active homing -A system whereby a missile homes in on a target by means of a radar aboard the missile. Also called active guidance. active infrared detection -An infrared detection system in which a beam of infrared rays is transmitted toward one or more possible targets, and the rays reflected from the target are detected. active infrared system-A system in which the object is irradiated by a source of infrared energy, which, in turn, is reflected by the object onto a detector. A snooperscope is an active infrared system. active intrusion sensor- An active sensor that detects the presence of an intruder within the range of the sensor. Examples are an ultrasonic motion detector, a radio-frequency motion detector, and a photoelectric alarm system. See also passive intrusion sensor. active jamming- 1. Intentional radiation or reradiation of electromagnetic waves to impair the use of a specific portion of the electromagnetic-wave spectrum. 2. Transmission or retransmission of signals for the express purpose of disrupting communications. active junction-In a semiconductor, a change in ntype to p-type doping, or vice versa, by a diffusion step. On discrete transistors there are two active junctions, the collector-base junction and the emitter-base junction. a c t i v e leg -Within a transducer, an electrical element that changes its electrical characteristics as a function of the applied stimulus. active line-In a US. television picture, one of the lines (approximately 488) that make up the picture. The remaining 37 of the 525 available lines are blanked; they are called inactive lines. active maintenance downtime -The time during which work is actually being done on an item, from the recognition of an occurrence of failure to the time of restoration to normal operation. This includes both preventive and corrective maintenance. active material-1. In the plates of a storage battery, lead oxide or some other active substance that reacts chemically to produce electrical energy. 2. The fluorescent material, such as calcium tungstate, used on the screen of a cathode-ray tube. active matrix-A display matrix with a transistor at each pixel location to individually store its state (on or off). Pixels in active matrix panels only need to be addressed when they are being turned on or off.

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active mixer and modulator-A device requiring a source of electrical power and using nonlinear network elements to heterodyne or combine two or more electrical signals. active network- 1. A network containing passive and active (gain) elements. 2. An electrical network that includes a source of energy. active pressure-In an ac circuit, the pressure that produces a current, as distinguished from the voltage impressed on the circuit. active p r o b e -A test probe, generally used with an oscilloscope, that is so named because of the active components used within probe circuitry. These components consist of one or all of the following: transistors, diodes, integrated circuits, or FETs. If FETs are used, these probes are often referred to as FET probes. active pull-up-An arrangement in which a transistor is used to replace the pull-up resistor in an integrated circuit in order to provide low output impedance without high povver consumption. active RC network-A network formed by resistors, capacitors, and active elements. active redundancy-That redundancy wherein all redundant items are operating simultaneously rather than being switched on when needed. active repair time-That portion of corrective maintenance downtime during which repair work is being done on the item, including preparation, fault location, part replacement, adjustment and recalibration, and final test time. It may also include part procurement time under shipboard or field conditions. activle satellite-A satellite that receives, regenerates, and retransmits signals between stations. See also communications satellite. activlesensor -A sensor that detects the disturbance of a radiation field that is generated by the sensor. See also passive sensor. ctive sonar-See sonar. ctive splitter-See line splitter. active substrate-1. A substrate in which active elements, axe formed to provide discrete or integrated devices. Examples of active substrates are single crystals of semiconductor materials within which are transistors, resistors, and diodes, or combinations of these elements. Another example is ferrite substrates within which electromagnetic fields are used to perform logical, gating, or memory functions. 2. A substrate for an integrated component in which parts display transistance. 3. A working part of the electronic circuit, which it supports physically. 4. In an integrated circuit, a substrate consisting of singlecrystal semiconductor material into which the various IC components are formed; it acts as some or all of the components. This is in contrast to a substrate consisting of a dielectric, on whose surface the various components are deposited. active swept-frequency interferometer radar--A dual radar system for air surveillance. It provides angle and range information of high precision for ting target locations by trigonometric techniques. ive systems-In radio and radar, systems that require transmitting equipment, such as a beacon or transponder, to be carried in the vehicle. active tracking system-Usually, a system that requires the addition of a transponder or responder on board the vehicle to repeat or retransmit information to the tracking equipment; e.g., dovap, secor, azusa. active transducer-1. A type of transducer in which its output waves depend on one or more sources of power, apart from the actuating waves. 2. A transducer that requires energy from local sources in addition to that which is received.

active mixer and modulator - adaptive control active trim-Trimming of a circuit element (usually resistors) in a circuit that is electrically activated and operating to obtain a specified functional output for the circuit. See functional trimming. active wire-The wire of an armature winding that produces useful voltage. That portion of the winding in which induction takes place. activity- 1. In a piezoelectric crystal, the magnitude of oscillation relative to the exciting voltage. 2. The intensity of a radioactive source. 3. Operations that result in the use or modification of the information in a computer file. activity curve-A graph showing how the activity of a radioactive source varies with time. activity ratio-The ratio of the number of records in a computer file that have activity to the total number of records in the file. ac transducer-A transducer that, for proper operation, must be excited with alternating currents only. Also a device, the output of which appears in the form of an alternating current. actual height-The highest altitude at which refraction of radio waves actually occurs. actual power-The average of values of instantaneous power taken over one cycle. actuating device-A mechanical or electrical device, either manual or automatic, that operates electrical contacts to bring about signal transmission. actuating system- I. In a device or vehicle, a system that supplies and transmits energy for the operation of a mechanism or other device. 2. A manually or automatically operated mechanical or electrical device that operates electrical contacts to effect signal transmission. actuating time-The time at which a specified contact functions. actuator- 1. In a servo system, the device that moves the load. 2. The part of a relay that converts electrical energy into mechanical motion. 3. Switch part to which an external force is applied to operate the switch. 4. A manual or automatic switch or sensor, such as a holdup button, magnetic switch, or thermostat, that causes a system to transmit an alarm signal when manually activated or when the device automatically senses an intruder or other unwanted condition. 5 . A motorized arm that moves a satellite dish into position under the control of a receiver. ACU -Abbreviation for automatic calling unit. ac voltage -See alternating voltage. acyclic m a c h i n e -A direct-current machine in which the voltage generated in the active conductors maintains the same direction with respect to those conductors at all times. ald -Abbreviation for analog-to-digital. Also a-d, A-D, or AD. adapter-1. A fitting designed to change the terminal arrangement of a jack, plug, socket, or other receptacle, so that other than the original electrical connections are possible. 2. An intermediate device that permits attachment of special accessories or provides special means for mounting. 3. A device for connecting two parts of an apparatus that would not be directly connectable because of incompatible dimensions, terminations, currents, voltages, frequencies, etc. adaptive communication-A method in which automatic changes in the communications system allow for changing inputs or changing characteristics of the device or process being controlled. Also called selfadjusting communication or self-optiwizing comunication. adaptive control-1. A control method that uses sensors for real-time measurement of process variables

adaptive control system - address constant with calculation and adjustment of control parameters as a method of achieving near-optimum process performance. 2. A method of control in which actions are continuously adjusted in response to feedback. adaptive control s y s t e m -A device whose parameters are automatically adjusted to compensate for changes in the dynamics of the process to be controlled. An AFC circuit utilizing temperature-compensating capacitors to correct for temperature changes is an example. a d a p t i v e telemetry -Telemetry having the ability to select certain vital information or any change in a given signal. adaptor-A device that locates and supports products to be tested. Generally, it is made of an insulating material with locator pins mounted to precisely position the product to a spring contact probe test pattern. Also, an adaptor serves as an intermediate between the circuit verifier and the interchangeable test head that contains the test pattern. adc -Abbreviation for analog-to-digital converter. Also ADC. A d c o c k antenna-A pair of vertical antennas separated by one-half wavelength or less and connected in phase opposition to produce a figure-8 directional pattern. A d c o c k direction finder -A radio direction finder using one or more pairs of Adcock antennas for directional reception of vertically polarized radio waves. type of radio range A d c o c k radio range-A utilizing four vertical antennas (Adcock antennas) placed at the comers of a square, with a fifth antenna in the center. a/d converter-Abbreviation for analog-to-digital converter. Also a-d, A-D, or A/D converter. 1. A unit or device that converts an analog signal, that is, a signal in the form of a continuously variable voltage or current, to a digital signal. 2. A circuit that accepts information in a continuously varying ac or dc current or voltage and whose output is the same information in digital form. 3. A circuit or device for producing a set of digital output signals representing the magnitude of a voltage applied to its input. add-and-subtract relay-A stepping relay capable of being operated so as to rotate the movable contact arm in either direction. addend-A quantity that, when added to another quantity (called the augend), produces a result called the sum. adder - 1. A device that forms the sum of two or more numbers or quantities impressed on it. 2. In a color TV receiver, a circuit that amplifies the receiver primary signal coming from the matrix. Usually there is one adder circuit for each receiver primary channel. 3. An arrangement of logic gates that adds two binary digits and produces sum and carry outputs. add-in -Components (expansion boards, cartridges, or chips) that can increase a computer’s capabilities, such as memory, graphics, and communications. Add-ins usually refer to an entire circuit board. See also add-on. add-in memory- Additional computer memory that is added to a computer system within the computer’s physical housing. Typically the add-in memory is inserted, in board form, into an available card slot on the assembly, the connections for which have already been placed on the existing computer. Additional memory may be in the form of semiconductor RAM, CCD, bubble memory, disk, or tape. additional station -Any amateur radio station licensed to an amateur radio operator, normally for a specific land location other than the primary station. addition record-A new record created during the processing of a file in a computer.

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additive -Sometimes referred to as the key. A number, series of numbers, or alphabetical intervals added to a code to put it in a cipher. additive color-A system that combines two colored lights to form a third. additive primaries-Primary colors that can be mixed to form other colors, but which cannot themselves be produced by mixing other primaries. Red, green, and blue are the primaries in television because, when added in various proportions, they produce a wide range of other colors. additive process -A printed-circuit manufacturing process in which a conductive pattern is formed on an insulating base by electrolytic chemical deposition. additive synthesis- A technique for creating musical notes whereby sine waves are added together to create new waveforms. Frequently used in electric organs rather than in synthesizers. additron -An electrostatically focused, beamswitching tube used as a binary adder in high-speed digital computers. (No longer used.) add mode -Allows entry of numbers in a calculator to two decimal places without the need to enter the decimal point. add-on -Circuitry or system that can be attached to a computer to increase memory or performance. See also add-in. add-on component or add-on device-A discrete or integrated prepackaged or chip component that is attached to a film circuit to complete the circuit functions. add-on memory -Additional computer memory that is added externally and is plug compatible with the computer system. The add-on memory is connected with an external connector cable to the computer, where provision has been made for memory expansion. Such a memory device is also available in its own housing, in which case it is physically placed beside the computer’s main cabinet. Additional memory may be in the form of semiconductor RAM, CCD, bubble memory, disk, or tape. address - 1. An expression, usually numerical, that designates a specific location in a storage or memory device or other source or destination of information in a computer. 2. An identification, as represented by a name, label, or number, for a register, location in storage, or any other data source or destination, such as the location of a station in a communications network. 3. Loosely, any part of an instruction that specifies the location of an operand for the instruction. 4. To select the location of a stored information set for access. 5. In computer technology, a number used by the central processing unit (CPU) to specify a location in memory. 6. Element(s) of a packet frame that identifies the source and/or destination stations by means of an agreed bit pattern. 7. A unique sequence of letters or numbers for the location of data or the identity of an intelligent device. address bus-1. A unidirectional bus over which digital information appears to identify either a particular memory location or a particular device. 2. The set of output pins from a microprocessor chip and the associated circuitry linking them to other devices for the purpose of addressing those chips or parts of them. See a h bus system. address c h a r a c t e r s -Blocks of alphanumeric characters that identify users or stations uniquely. address comparator-In a computer, a device that ensures that an address being read is the right one. address c o m p u t a t i o n -The process by which the address part of an instruction in a digital computer is produced or modified. address constant -See base address.

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addressed memory-In a computer, memory secitions containing each individual register. address field-The portion of an instruction that specifies the Location of a particular piece of information -in a Computer memory. addressing mode- An addressing method. One of several different addressing methods possible in micro]processors. address modification-In a computer, a change -in the address portion of an instruction or command :such that, if the routine which contains that instruction or command is repeated, the computer will go to a new address or location for data or instructions. address part- In an electronic computer instrucition, a portion of an expression designating location. See also instruction code. address-routing indicator-Group of characters tcontained in a message heading that designates the tdestinatiom of the message. add-subtract time-The time required by a digital computer to perform addition or subtraction. It does not -include tlhe time required to obtain the quantities from storage and put the result back into storage. add time-The time required in a digital computer it0 perform addition. It does not include the time required ito obtain the quantities from storage and put the result back into storage. aid encoder -Analog-to-digital encoder. A device ithat changes an analog quantity into an equivalent digital representation. Also referred to as an a-d, A-D, or (encoder. adf-See automatic direction finder. Also referred to as ADF. adiabatic damping -A reduction in the size of an accelerator beam as the energy of the beam is increased. adiabatic demagnetization -A technique used to obtain temperatures within thousandths of a degree of absolute :zero. It consists of applying a magnetic field to a substance at a low temperature and in good thermal (contact with its surroundings, insulating the substance ithermally, and then removing the magnetic field. A-display -Also called A-scan. A radarscope presentation in which time (distance or range) is one coordinate (usu.ally horizontal) and the target appears displaced ]perpendicularto the time base. a d j a o e n c y -In character recognition, a condition -in which the character-spacing reference lines of two (charactersprinted consecutively on the same line are less ithan a specified distance apart. adjaoent- and alternate-channel selectivity.A measure of the ability of a receiver to differentiate lbetween a desired signal and signals that differ in fretquency from the desired signal by the width of one chaninel or twlo channels, respectively. adjaclent audio (sound) c h a n n e l -The rf carrier :frequency that contains the sound modulation associated with the next-lower-frequency television channel. a d j a c e n t channe! -That frequency band immediately above or below the one being considered. adjaclent-channel attenuation -See selectance. adjaoent-channel interference-Undesired sig!rials received on one communication channel from a ibansmitter operating on a channel immediately above or Ibelow. adjacent-channel selectivity-The ability of a ireceiver to reject signals on channels adjacent to the (channelof the desired station. a d j a c ' e n t conductor -Any conductor next to another conductor, either in the same multiconductor cable layer or in adjacent layers.

addressed memory - advanced license a d j a c e n t sound channel -In television, the rf channel containing the sound signal modulation of the next lower channel. a d j a c e n t video carrier-The rf carrier that carries the picture modulation for the television channel immediately above the channel to which the viewer is tuned. a d j u s t a b l e component -Any circuit component whose electrical value may be varied at will, e.g., adjustable capacitor, inductor, resistor, or load. a d j u s t a b l e resistor- 1. A resistor that has the resistance wire partly exposed to enable the amount of resistance in use to be adjusted occasionally by the user. Adjustment requires the loosening of a screw, the subsequent moving of the lug, and retightening of the screw. 2. A fixed resistor with a movable contact (or tap) that can be positioned along the length of the resistive path.

Adjustable resistor. a d j u s t a b l e voltage divider --A wirewound resistor with one or more movable terminals that can be slid along the length of the exposed resistance wire until the desired voltage values are obtained. a d j u s t e d circuit -Also called bolted-fault level. In a circuit, the current measured under short-circuit conditions with the leads that are normally connected to the circuit breaker bolted together. a d j u s t e d decibels-An expression of the ratio of the noise level to a reference noise at any point in a transmission system, when the noise meter has been adjusted to allow for the interfering effect under specified conditions. admittance-1. The ease with which an alternating current flows in a circuit. The reciprocal of impedance; usually expressed in siemens. Symbol is Y or y . 2. The (sinusoidal) current in a circuit divided by the terminal voltage. 3. The vector sum of a resistive component of conductance and a reactive component of susceptance. ADP -Abbreviation for automatic data processing. ADSL -Abbreviation for Asymmetric Digital Subscriber Line. A video display terminal distribution video system delivering video over existing (i.e., copper) telephone lines. adsorption-The deposition of a thin layer of gas or vapor particles onto the surface of a solid. The process is known as chemisorption if the deposited material is bound to the surface by a simple chemical bond. ADU -Abbreviation for automatic dialing unit. advance ball -In mechanical recording, a rounded support (often sapphire) that is attached to a cutter and rides on the surface of the recording medium. Its purpose is to maintain a uniform mean depth of cut and to correct for small irregularities on the surface of the disc. advance calling -A telecommunications feature in which voice messages can be spoken into the telephone for automatic delivery at a prearranged time to my other telephone or telephones. a d v a n c e d license-A license issued by the FCC to amateur radio operators who are capable of sending

advance wire - agonic line and receiving Morse code at the rate of 13 words per minute and are familiar with general and intermediate radio theory and practice. Its privileges include exclusive use of certain frequencies. advance wire- An alloy of copper and nickel, used in the manufacture of electric heating units and some wirewound resistors. aeolight-A glow lamp that uses a cold cathode and a mixture of inert gases. Its illumination can be regulated with an applied signal voltage and it is often used as a modulation indicator for motion picture sound recording. aerial-See antenna. aerial cable-A cable installed on a pole line or similar overhead structure. aerodiscone antenna- An aircraft antenna that is aerodynamically shaped and is physically small compared with other antennas having similar electrical characteristics. Its radiation pattern is omnidirectional and linearly polarized. aerodrome control radio station -A radio station providing communications between an airport control tower and aircraft or mobile aeronautical radio stations. aerodynamics-The science of the motion of air and other gases. Also, the forces acting on bodies such as aircraft when they move through such gases, or when such gases move against or around the bodies. aeromagnetic-Pertaining to the magnetic field of the earth as surveyed from the air. aeronautical advisory station-A station used for civil defense and advisory communications with private aircraft stations. aeronautical broadcasting service-The broadcasting service intended for the transmission of information related to air navigation. aeronautical broadcast station -A station that broadcasts information regarding air navigation and mete orological data pertinent to aircraft operation. aeronautical fixed service-A fixed service intended for the transmission of information relating to air navigation and preparation for and safety of flight. aeronautical fixed station-A station operating in the aeronautical fixed service. aeronautical ground station -A radio station operated for the purpose of providing air-to-ground communications in connection with the operation of aircraft. aeronautical marker-beacon station-A land station operating in the aeronautical radionavigation service and providing a signal to designate a small area above the station. aeronautical mobile service- A radio service between aircraft and land stations or between aircraft stations. aeronautical radio-beacon station -An aeronautical radionavigation land station transmitting signals that are used by aircraft and other vehicles to determine their position bearing or position in relation to the aeronautical radio beacon station. aeronautical radionavigation sewice-A radionavigation service intended for use in the operation of aircraft. aeronautical radio service- 1. Service carried on between aircraft stations andor land stations. 2. Special radio for air navigation. 3. Service that includes aircraft-to-aircraft, aircraft-to-ground, and ground-toaircraft communications important to the operation of aircraft. aeronautical station-A land station (or in certain instances a shipboard station) in the aeronautical mobile service that carries on communications with aircraft stations.

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aeronautical telecommunication-Electronic and nonelectronic communications used in the aeronautical service. aeronautical telecommunication agency -An agency to which is assigned the responsibility for operating a station or stations in the aeronautical telecommunication service. aeronauticaltelecommunication log -A record of the activities of an aeronautical telecommunication station. aeronautical telecommunications-Any telegraph or telephone communications of signals, writing, images, and sounds of any nature by wire, radio, or other system or process of signaling, used in the aeronautical service. aeronautical telecommunication service-

Telecommunication service provided for aeronautical purposes. aeronautical telecommunication station-A station in the aeronautical telecommunication service. aeronautical utility land station -A land station located at an airport control tower and used for communications connected with the control of ground vehicles and aircraft on the ground. aeronautical utiiity mobile station -A mobile station used at an airport for communications with aeronautical utility land stations, ground vehicles, and aircraft on the ground. aerophare-See radio beacon. AES- Abbreviation for Audio Engineering Society. A professional group; the official association of technical personnel, scientists, engineers, and executives in the audio field. AF -See audio frequency. AFC -See automatic frequency control. afocal-An optical system with one set of object and image points at infinity. Literally, “without a focal length.” An afocal system receives its input image from infinity and projects its output image to infinity. AFSK- Abbreviation for audio-frequency shift keying. With this method of modulation, two tones (mark = 2125 Hz, space = 2295 Hz) are fed directly into the microphone jack of the transmitter. afterglow -Also called phosphorescence. 1. The light that remains in a gas-discharge tube after the voltage has been removed, or on the phosphorescent screen of a cathode-ray tube after the exciting electron beam has been removed. 2. The luminosity that remains in a rarefied gas after an electrodeless discharge has traversed the gas. afterpulse -In a photomultiplier, a spurious pulse induced by a preceding pulse. AGC-See automatic gain control. age-To maintain an electrical component in a specified environment, as with respect to pressure, temperature, applied voltage, etc., until its characteristics stabilize. aggregate function-A command that perfoms calculations based on a set of values rather than on a single value. agile receiver- A satellite receiver that can be tuned to any desired channel. aging- 1. Storing a permanent magnet, capacitor, semiconductor, meter, or other device, sometimes with voltage applied, until its desired characteristics become essentially constant. 2. The change of a component or a material with time under defined environmental conditions, leading to improvement or deterioration of properties. agonic line-An imaginary line on the earth‘s surface, all points of which have zero magnetic declination.

15 AGP -- Abbreviation for accelerated graphics port. AGREE- Advisory Group on Reliability of Electronics Equipment. I -See artificial intelligence. aided tracking-A system of tracking a target signal in bearing, elevation, or range (or any combination of these variables) in which manual correction of the tracking error automatically corrects the rate at which the tracking mechanism moves. AlEE -Abbreviation for American Institute of Electrical Engineers. Now merged with IRE to form IEEE. air bearing-A means of supporting magnetic tape on an ai^ film rather than by means of a sliding or rolling contact. Usually, an air bearing is a perforated cylinder; pressurized air flows through the perforations and forms a film that prevents the tape from contacting the cylinder. airboirne intercept radar- Short-range airborne radar employed by fighter and interceptor planes to track down their targets. airboirrae long-range input -Airborne equipment designed to extend air-surveillance coverage seaward so that long-range interceptors may be used. airborne moving-target indicator-A type of airborne-radar display that does not present essentially stationary objects. airboirne noise-Undesired sound in the form of fluctuatioas of air pressure about the atmospheric pressure as a mean. airborne radar platform -Airborne surveillance and height-finding radar for early warning and control. air capacitor-A capacitor in which air is the only dielectric material between its plates. aircarrier aircraft station -A radio station aboard an aircraft that is engaged in or essential to the transportation of passengers or cargo for hire. air cell-A primary cell in which depolarization at the positive electrode is accomplished chemically by reduction of the oxygen in the air. air column-The air space within a horn of an acoustic (chamber. air colndenser-See air capacitor. air-cooled tube- An electron tube in which the generated heat is dissipated to the surrounding air directly, through metal heat-radiating fins, or with the aid of channels or chimneys that increase the air flow. air-core cable-A telephone cable in which the interstices in the cable core are not filled with a moisture barrier. air-core coil-A number of turns of spiral wire in which no1 metal is used in the center. air-core transformer-A transformer (usually rf) having two or more coils wound around a nonmetallic core. Tr,msformers wound around a solid insulating substance or on an insulating coil form are included in this category. aircraft bonding -Electrically connecting together all the metal structure of the aircraft, including the engine and metal covering of the wiring. aircraft flutter-Flickering (repetitive fading and intensifying) in a TV picture as the signal is reflected from flying aircraft. The reflected signal arrives in or out of phase with the normal signal and thus strengthens or weakens the latter. aircraft station -A radio station installed on aircraft and continuously subject to human control. air d e f e n s e control center -Principal information, communications, and operations center from which all aircraft, antiaircraft operations, air-defense artillery, guided missiles, and air-raid warning functions of a

AGP - air-position indicator specific area of air defense responsibility are supervised and coordinated. air defense identification zone-Airspace of defined dimensions within which the ready identification, location, and control of aircraft is required. air dielectric capacitor-A capacitor with a dielectric consisting of air. airdrome control station-A station used for communication between an airport control tower and aircraft. air environment -In communications electronics, all airborne equipment that is part of the communicationselectronics system, as distinguished from the equipment on the ground, which belongs to the ground environment. air gap-1. A nonmagnetic discontinuity in a ferromagnetic circuit. For example, the space between the poles caf a magnet-although filled with brass, wood, or any other nonmagnetic material -is nevertheless called an air gap. This gap increases magnetic reluctance and prevents saturation of the core. 2. The air space between two magnetically or electrically related objects. air/ground control radio station -An aeronautical telecommunication station with the primary responsibility of handling communications related to the operation and control of aircraft in a given area. air/ground liaison code-Set of symbols for a limited number of words, phrases, and sentences used for communications between air and ground forces. air-motion transformer-A type of speaker in which the air is not pushed into vibration by a piston, but rather squeezed by the contractions of a folded diaphragm. air navigation radio aids -Aeronautical ground stations, radio beacons, direction finders, and similar facilities. airplane flutter rejection-The measure of a receiver’s immunity to the effects of wavering signals produced by aircraft in the reception path. airport beacon-A beacon (light or radio) to indicate the location of an airport. airport control station -A station that furnishes communications between an airport control tower and aircraft in the immediate vicinity; messages are Limited to those related to actual aviation needs. airport radar control-The surveillance-radar portion of radar approach control. airport runway beacon -A radio-range beacon that defines one or more approaches to an airport. airport s u r f a c e detection equipment -Abbreviated ASDE. 1. Radar that shows the movement of aircraft and other vehicles on the ground at an airport. Valuable tool at night and during low visibility. 2. A digital radar system used to track planes and vehicles on airport runways and up to 200 feet in altitude. Unlike previous surface radar systems, ASDE provides clear images in bad weather. airport surveillance r a d a r -1. Abbreviated ASR. A short-range radar system that maintains constant surveillance over aircraft at the lower levels of flight. Distinct from air route surveillance radar (ARSR), which is long-range radar- 150-mile (241-km) radius- to control traffic between terminals. 2. An air-traffic-control radar that scans the airspace 30 to 60 miles (48 to 98 km) around an airport and displays the location of a11 aircraft below a certain altitude and all obstructions near the control tower. air-position indicator -Airborne computing system that presents a continuous indication of aircraft position on the basis of aircraft heading, air speed, and elapsed time.

air-spaced coax

- aliasing

air-spaced coax-A coaxial cable in which air is basically the dielectric material. The conductor may be centered by means of a spirally wound synthetic filament, by beads, or by braided filaments. This construction is also referred to as an air dielectric. air surveillance-Systematic observation of airspace by electronic, visual, or other means, primarily to identify and determine the movements of aircraft and missiles, friendly and enemy, in the airspace under observation. airtime-Time spent on a cellular phone, which is usually billed to the subscriber on a per-minute basis. air-to-ground communication -Transmission of radio signals from an aircraft to stations or other locations on the earth’s surface, as differentiated from ground-toair, air-to-air, or ground-to-ground communications. air-to-ground radio frequency-The frequency or band of frequencies agreed upon for transmission from an aircraft to an aeronautical ground station. air-to-surface missile -A missile designed to be dropped from an aircraft. An internal homing device or the aircraft’s radio guides it to a surface target. airwaves-Slang expression for radio waves used in radio and television broadcasting. alacritized switch- 1. A mercury switch treated to yield a low adhesional force between the rolling surface and mercury pool, resulting in a decreased differential angle. 2. A mercury switch in which the tendency of the mercury to stick to the mating parts has been reduced. alarm-A device that signals the existence of an abnormal condition by means of an audible or visible discrete change, or both, intended to attract attention. An alarm circuit produces or transmits an alarm signal. alarm condition-A threatening condition, such as an intrusion, fire, or holdup, sensed by a detector. alarm device-A device that signals a warning in response to an alarm condition, such as a bell, siren, or annunciator. alarm discrimination-The ability of an alarm system to distinguish between those stimuli caused by an intrusion and those which are a part of the environment. alarm hold-A means of holding an alarm once sensed. The typical magnetic trap does not hold or latch, and thus the reclosing of a trapped door resets the typical magnetic trap. A hold circuit applied to such a device indicates that the door has been opened and continues to so indicate until reset. alarm line-A wired electrical circuit used for the transmission of alarm signals from the protected premises to a monitoring station. alarm relay-A relay, other than an annunciator, used to operate, or to operate in connection with, a visual or audible alarm. alarm state-The condition of a detector that causes a control unit in the secure mode to transmit an alarm signal. alarm system-An assembly of equipment and devices designated and arranged to signal the presence of an alarm condition requiring urgent attention, such as unauthorized entry, fire, temperature rise, etc. The system may sound a local warning or alert the police, a central station, or a proprietary service. albedo-The reflecting ability of an object. It is the ratio of the amount of light reflected compared with the amount received. ALC -Abbreviation for automatic level (volume) control. 1. A special compressor circuit included in some tape recorders for automatically maintaining the recording volume within the required limits regardless of changes in the volume of the sound. 2. A circuit that automatically maintains recording levels within permissible limits, so that, no matter how loud or soft the sound being recorded,

16 the signal on the tape will not get strong enough to overmodulate and distort or soft enough to be lost in noise. Also known as automatic volume control (AVC). Alexanderson alternator- An early mechanical generator used as a source of low-frequency power for transmission or induction heating. It is capable of generating frequencies as high as 200,000 hertz. Alexanderson antenna-A vlf antenna consisting of a horizontal wire connected to ground at equally spaced points by vertical wires with base-loading coils; the transmitter is coupled to an end coil. Alford antenna-A square loop antenna comprising four linear sides with their ends bent inward so that capacitive loading is provided to equalize the current around the loop. algebraic adder-In a computer, an adder that provides the algebraic rather than arithmetic sum of the entered quantities. algebraic logic-A calculator mode that permits all calculations to be done in the order in which they are written. algebraic sum-The sum of two or more quantities combined according to their signs. (Compare with arithmetic sum.) ALGOL - 1. An international problem language designed for the concise, efficient expression of arithmetic and logical processes and the control (iterative, etc.) of these processes. From algorithmic language. 2. A highlevel language that has a context-free structure. algorithm- 1. A set of rules or processes for solving a problem in a finite number of steps (for example, a full statement of an arithmetic procedure for finding the value of sin x with a stated precision). See also procedure. 2. A series of equations, some of which may state inequalities, that cause decisions to be made and the computational process to be altered based on these decisions. 3. A set of rules or directions for getting a specific output from a specific input. The distinguishing feature of an algorithm is that all vagueness must be eliminated; the rules must describe operations that are so simple and well defined they can be executed by a machine. Furthermore, an algorithm must always terminate after a finite number of steps. 4. An ordered sequence of mathematical steps that always produces the correct answer to a problem, though the solution may be more lengthy than necessary. 5. A set of well-defined procedures for the solution of a problem in a limited number of steps. Algorithms are implemented in a computer by a programmed sequence of instructions. algorithmically generated pattern -An array of digital data automatically generated by a predetennined software routine or program. algorithmic language -An arithmetic language by which a numerical procedure may be presented to a computer precisely and in a standard form. algorithmic pattern generation -Real-time generation of input test patterns during test execution according to specified procedures, formulas, or algorithms. Also refers to procedures or algorithms used in automatic-testgeneration software for specific fault sets. alias-An alternate label. For instance, a label and one or more aliases may be used to identify the same data element or point in a computer program. aliasing-1. The introduction of error into the Fourier analysis of a discrete sampling of continuous data when components with frequencies too great to be analyzed with the sampling interval being used contribute to the amplitudes of lower-frequency components. 2. A phenomenon arising as a result of the sampling process in which high-frequency components of the original analog signal (whether information or noise) appear as lower frequencies in the sampled signal. Aliasing occurs when the

aliasing noise - alkaline cell

17 sampling rate is less than twice the highest frequency existing in the original analog signal. 3. Undesirable distortion component that can arise in digital audio equipment when the input signal’s frequency exceeds onehalf of the digital circuitry’s sampling rate. 4. The m i s taking of some object or situation for another, especially because of the way data is examined. Examples: movies of propellers and wagon wheels that seem to turn backward, muisical notes that are wrongly analyzed by sequential measurement (for instance, thought to be an octave too low), and, especially, “jaggies.” 5. Undesirable stairstep distortions in computer-generated images caused by inproper sampling techniques. The most common effect is a jagged edge along object boundaries. aliasiing noise -A distortion component that will be created if a sampled signal bandwidth is effectively greater than one-half the sampling rate. align .- 1. To adjust the tuned circuits of a receiver or transmitter for maximum signal response. 2. To put into proper relative position, agreement, or coordination when placing parts of a photomask together or placing a photornask over an etched pattern in the oxide on a semiconductor wafer. 3. To adjust the tuning of a multistage device so that all stages are adjusted to the same frequency or so that they work together properly. aligned bundle-See coherent bundle. aligned-grid tube- A multigrid vacuum tube in which at leash two of the grids are aligned one behind the other to give such effects as beam formation and noise suppression. alignment -1. The process of adjusting components of a system for proper interrelationship. The term is applied especially to (a) the adjustment of tuned circuits in a receiver to obtain the desired frequency response and (b) the synchronization of components in a system. 2. In a tape recorder, the physical positioning of a tape head relative to the tape itself. Alignment in all respects must conform to rigid requirements in order for a recorder to function properly. 3. The accuracy or proper relative position ‘of an image on a photomask with respect to an existing image on a substrate, as in a photoresist coating, or etched1 in the oxide of an oxidized silicon wafer. 4. A technique in the fabrication process of semiconductors by which a series of six to eight masks are successively registered to build up the various layers of a monolithic device. Each mask pattern must be accurately referenced to or aligned to all preceding mask patterns. 5. The accuracy of coordination or relative position of images on a semiconductor oxide coating and on the photomask, or any other images placed in relation to those. alignment chart- Also called nomograph, nomogram, or abac. Chart or diagam consisting of two or more lines on ,which equations can be solved graphically. This is done by laying a straightedge on the two known values and reading the answer at the point where the straightedge intersects the scale for the value sought. alignment pin- 1. A pin in the center of the base of a tube. A, projecting rib on the pin ensures that the tube is correcfly insefied into its socket. 2. Any pin or device that will ensure the correct mating of two components designed to be connected. alignment protractor-An instrument that indicates error in a pickup’s lateral alignment. It fits on the center spindle of the turntable, and the pickup stylus fits into a small hole on the device. The correct indication is shown when the angle of lateral movement of the pickup head is at 90” to the tangent of the groove at any point, although minimal tracking error is expected with most pickup arms. alignment tool -A special screwdriver or socket wrench used for adjusting trimmer or padder capacitors

A

C

B

9

10

Alignment chart. or cores in tuning inductances. It is usually constructed partly or entirely of nonmagnetic material. See also neutralizing tool.

! x HEXAGONAL SMALL TIP

Alignment tools.

alive- 1. Electrically connected to a sonrce of potential difference, or electrically charged to have a potential different from that of the earth. 2. Energized. 3. Reverberant, as a room in which sound reflects and echoes. alive circuit-A circuit that is energized. alkali-A compound that forms hydroxyl ions when in aqueous solution. Also called a base. alkaline cell- 1. A primary cell, similar to the zinccarbon cell, in which the negative electrode is granular zinc mixed with a potassium hydroxide (alkaline) electrolyte; the positive electrode is a polarizer in electrical contact with the outer metal can of the cell. A porous separator divides the electrodes. This type of cell delivers a terminal potential of 1.5 volts and has a 50 percent to 100 percent higher capacity than does a 1.5-volt zinc-carbon cell. Also called an alkaline-manganese cell. 2. A primary dry cell that has a very low internal resistance and high CATHODE

MIX

COL LECTOR

Alkaline cell.

CAP

all-channel tuning

- alphabetic string

service capacity. It is characterized by a relatively flat discharge curve under load. all-channel tuning -Ability of a television set to receive all assigned channels, VHF and UHF, channels 2 through 83, as well as cable channels. all-diffused monolithic integrated circuit Also called compatible monolithic integrated circuit. A microcircuit consisting of a silicon substrate into which all the circuit parts (both active and passive elements) are fabricated by diffusion and related processes. Allen screw-A screw having a hexagonal hole or socket in its head. Often used as a setscrew. Allen w r e n c h -A straight or bent hexagonal rod used to turn an Allen screw. alligator clip-A spring-loaded metal clip with long, narrow meshing jaws similar to the jaws of an alligator; it is used for making temporary electrical connections, generally at the end of a test lead on interconnection wire.

SCAEW

Alligator clip.

allocate-In a computer, to assign storage locations to main routines and subroutines, thus fixing the absolute values of symbolic addresses. allocated channel-A channel assigned to a specific user. allocated f r e q u e n c y band-A segment of the radio-frequency spectrum established by a competent authority that designates the use that may be made of the frequencies contained therein. allocated-use circuit-1. A circuit in which one or more channels have been allocated for the exclusive use of one or more services by a proprietary service; may be a unilateral or joint circuit. 2. Communication link specifically assigned to user@) warranting such facilities. allocation technique-The method of providing a process access to a shared resource. allochromatic-Exhibiting photoelectric effects due to the inclusion of microscopic impurities or as a result of exposure to various types of radiation. allophone-A variation in the pronunciation of a phoneme. An allophone can be regarded as the sound that results when a phoneme is placed in its environment. allotter -In a telephone system, a distributor, associated with the finder control group relay assembly, that allots an idle linefinder in preparation for an additional Call. allotter relay-In a telephone system, a relay of the linefinder circuit, the functions of which are to preallot an idle linefinder to the next incoming call from the line and to guard relays. allowable deviation -The permissible difference between any range of conditions and a reference condition. alloy- 1. A composition of two or more elements, of which at least one is a metal. It may be a solid solution, a heterogeneous mixture, or a combination of both. 2. Method of making pn junctions by melting a metallic dopant so that it dissolves some of the semiconductor material and then hardens to produce a doped alloy. alloy deposition -The process of depositing an alloy on a substrate during manufacturing. alloy-diffused transistor -A transistor in which the base is diffused and the emitter is alloyed. The

18 collector is the semiconductor substrate into which alloying and diffusion are effected. alloyed contact-An ohmic contact formed by an alloy process. alloy junction-Also called fused junction. A junction produced by alloying one or more impurity metals to a semiconductor. A small button of impurity metal is placed at each desired location on the semiconductor wafer, heated to its melting point, and cooled rapidly. The impurity metal alloys with the semiconductor material to form a p or n region, depending on the impurity used. alloy-junction photocell -A photodiode in which an alloy junction is produced by alloying (mixing) an indium disc with a thin wafer of n-type germanium. alloy-junction transistor -Also called fusedjunction transistor. A semiconductor wafer of p- or n-type impurities fused, or alloyed, into opposite sides of the wafer to provide emitter and base junctions. The base region comprises the original semiconductor wafer. alloy process -A fabrication technique in which a small part of the semiconductor material is melted together with the desired metal and allowed to recrystallize. The alloy developed is usually intended to form a pn junction or an ohmic contact. alloy transistor-A transistor in which the emitter and collector junctions are both alloy junctions. all-pass filter-A network designed to produce a delay (phase shift) and an attenuation that is the same at all frequencies; a lumped-parameter delay line. Also called all-pass network. all-pass network-A network designed to introduce phase shift or delay but not appreciable attenuation at any frequency. all-relay central off ice- An automatic centraloffice dial switchboard in which relay circuits are used to make the line interconnections. all-wave antenna -A receiving antenna suitable for use over a wide range of frequencies. all-wave receiver -A receiver capable of receiving stations on all the commonly used wavelengths in shortwave bands as well as in the broadcast band. alnico-An alloy consisting mainly of aluminum, nickel, and cobalt plus iron. Various subscripts and combinations of letters are available. Material can be found both in cast and sintered form, including isotropic and anisotropic alloys. Capable of very high flux density and magnetic retentivity, the alloy is used in permanent magnets for speakers, magnetrons, etc. alpha- 1. Emitter-to-collector current gain of a transistor connected as a common-base amplifier. For a junction transistor, alpha is less than unity, or 1. Alpha is usually defined as the ratio of a small change in collector current to the corresponding change in emitter current, when the collector-base voltage is kept constant. 2. Brain wave signals whose frequency is approximately 8 to 12 Hz. The associated mental state is relaxation, heightened awareness, elation, and in some cases, dreamlike. alphabet-An ordered set of all the letters and associated marks used in a language, for example, the Morse code alphabet, the 128 characters of the U.S. ASCII alphabet. a l p h a b e t i c coding -A system of abbreviation used in preparing information for input into a computer. Information may then be reported in the form of letters and words as well as in numbers. alphabetic-numeric-Having to do with the alphabetic letters, numerical digits, and special characters used in electronic data processing work. a l p h a b e t i c string -A character string containing only letters and special characters.

alpha cutoff frequency

I. 9

alpha cutoff frequency -The frequency at which the current gain of a common-base transistor stage has decreased to 0.707 of its low-frequency value. Gives a rough indication of the useful frequency range of the device. alphameric (alphanumeric) -Generic term for alphabetic letters, numerical digits, and special characters that are machine processable. alphameric characters-1. A character set that rnixes alphabetic characters, numeric characters, and usually punctuation characters. The alphabetic characters may be uppercase and/or lowercase or even in Japanese or Arabic script. 2. Consisting of letters and numbers. Also called alphameric or alphanumeric. alphai?umeric- 1. A generic term for alphabetic letters, numerical digits, and special ASCII characters that can be processed by a computer. A character set containing any combination of the above, 2. Consisting of letters and numbers. 3. All letters in the alphabet, the numbers 0 through 9, and special characters -such as -, I', *, $, (), and #-that are machine processable. alphailaumeric code-In computer practice or in communications, a code in which the letters of the alphabet are represented by numbers. alphainumeric display -Device consisting of a 1.ypewriter-stylekeyboard and a display (CRT) screen on which text is viewed. alphainumeric keys-Keys on a data entry device that resemble those on a standard keyboard. Usually they are used to manually input or edit text for the display system, although they can also be used in a function key mode. a ~ ~ h a i ~ u m ereader r ~ c -An instrument that reads ;alphabetic, numeric, and special characters by means of ;a photosensor that measures the varying intensity of the characters reaected from a light source. alphanumeric readout--A type of digital readout that displays both letters and numerals. alpha particle-A small, electrically charged partiicle thrown off at very high velocity by many radioactive materials.,including uranium and radium. Identical to the .nucleus of a helium atom, it is made up of two neutrons and two protons. Its electrical charge is positive and is lequal in magnitude to twice that of an electron. alpha ray-A stream of fast-moving alpha particles that produce intense ionization in gases through which they pass, are easily absorbed by matter, and produce a glow on a fluorescent screen. The lowest-frequency radioactive emissions. system -A signaling system in which the code to be used is designated by alphabetic characters. a ~ ~ ~ a detectoir-A - ~ a ~ e device that detects and displays alpha-wave segments of brain wave output. Used ter or sensor.

+,

edium that may be

alteration switch --A manual switch on a computer console or a program-simulated switch that can be set on or of1 to control coded machine instructions. alternate channel -A channel located two chanabove or below the reference channel. l ~ e r ~ ~ a t e - c h a n ~interference el -Interference caused in one communication channel by a transmitter operating; in the channel after an adjacent channel. See also second-channel interference.

- alternating-currenttransmission

alternate facility-A communications-electronics facility that is established for the purpose of replacing or supplementing another facility or facilities under real or simulated emergency conditions. alternate frequency -The frequency assigned for use at a certain time, or for a certain purpose, to replace or supplement the frequency normally used. alternate mode-A means of displaying on an oscilloscope the output signals of two or more channels by switching the channels, in sequence, after each sweep. alternate route or routing-A secondary or backup communications path to be used if the normal (primary) routing is not possible. alternate voiceidata Operation -Modem operations coordinated by voice over the same line that accommodates transmission. The modem is patched out of the circuit to allow this. A special switch, called an exclusion key, converts the line from voice to data. alternating-charge characteristic-The function relating, under steady-state conditions, the instantaneous values of the alternating component of transferred charge to the corresponding instantaneous values of a specified periodic voltage applied to a nonlinear capacitor. alternating current-Abbreviated ac. 1. -A flow of electricity that reaches maximum in one direction, decreases to zero, then reverses itself and reaches maximum in the opposite direction. The cycle is repeated continuously. The number of such cycles per second is the frequency. The average value of voltage during any cycle is zero. 2. Any signal that varies with time. It usually means that the current actually changes polarity with time. The plot of current versus time usually is a sine wave that comprises a succession of instantaneous values, the greatest of which is the amplitude or peak value. The time taken by one complete cyclic repetition is the period, and the number of periods in one second is the frequency.

Alternating current.

alternating currenVdirect current--A term applied to electronic equipment indicating it is capable of operation from either an alternating-current or directcurrent primary power source. alternating-current erasing head-An erasing head used in magnetic recording, in which alternating current produces the magnetic field necessary for erasing. Alternating-current erasing is achieved by subjecting the medium to a number of cycles of a magnetic field of a decreasing magnitude. The medium is, therefore, essentially magnetically neutralized. alternating-currentgenerator-A rotary machine that generates alternating current when its rotor, which may be either the armature or the field, is rotated by an engine or a motor. Also called an alternator. alternating-currentpulse -An alternating-current wave of brief duration. alternating-currenttransmission -In television, that form of transmission in which a fixed setting of the controls makes any instantaneous value of signal correspond to the same value of brightness only for a short time.

alternating f l a s h e r

- ambience

alternating flasher -A control that provides voltage first to one load and then to another load. This cycle repeats normally at a fixed rate per minute. alternating quantity-A periodic quantity that has alternately positive and negative values, the average value of which is zero over a complete cycle. alternating voltage-Also called ac voltage. Voltage that is continually varying in value and reverses its direction at regular intervals, such as that generated by an alternator or developed across a resistance or impedance through which alternating current is flowing. alternation -One-half of a cycle-either when an alternating current goes positive and retums to zero, or when it goes negative and returns to zero. Two alternations make one cycle. The complete rise and fall of a current traveling in one direction, or one-half of an alternating-current cycle. alternator -A device for converting mechanical energy into electrical energy in the form of an alternating current. alternator transmitter -A radio transmitter that generates power by means of a radio-frequency alternator. altimeter- An instrument that indicates the altitude of an aircraft above a specific reference level, usually sea level or the ground below the aircraft. It may be similar to an aneroid barometer, which utilizes the change of atmospheric pressure with altitude, or it may be electronic. altimeter station -An airborne transmitter, the emissions from which are used to determine the altitude of an aircraft above the surface of the earth. altitude delay-The synchronization delay introduced between the time of transmission of the radar pulse and the start of the trace on the indicator. This is done to eliminate the altitude circle on the plan-position-indicator display. ALU-Abbreviation for arithmetic and logic unit. 1. A device that performs the basic mathematical operations such as addition, subtraction, multiplication, and division of numbers (usually binary) presented to its inputs and provides an output that is an appropriate function of the inputs. 2. The arithmetic and logic unit internal to the microprocessor chip. This register handles all arithmetic and logical operations carried out as part of a microprocessor instruction. 3. The part of a CPU that executes adds, subtracts, shifts, AND logic operations, OR logic operations, etc. 4. A complex array of gates that can be used to perform binary arithmetic, logic operations, shifts and rotates, and complementing. 5 . One of the three essential components of a microprocessor, the other two being data registers and control. The ALU performs addition and subtraction, logic operations, masking, and shifting (multiplication and division). alumina -1. A ceramic used for insulators in electron tubes or substrates in thin-film circuits. It can withstand continuously high temperatures and has a low dielectric loss over a wide frequency range. Aluminum oxide (ALzOs). 2. The substrate material on which are deposited thin conductive and resistive layers for thin-film microwave integrated circuits. aluminized-screen picture tube -A cathode-ray picture tube that has a thin layer of aluminum deposited on the back of its fluorescent surface to improve the brilliance of the image and also prevent ion-spot formation. aluminizing-The process of applying a film of aluminum to a surface, usually by evaporation in a vacuum. aluminum-electrolytic capacitor-A capacitor with two aluminum electrodes (the anode has the oxide film) separated by layers of absorbent paper saturated with the operating electrolyte. The aluminum-oxide film

20 or dielectric is repairable in the presence of an operating electrolyte. aluminum-steel conductor-A composite conductor made up of a combination of aluminum and steel wires. In the usual construction, the aluminum wires surround the steel. alumoweld-A thin coating of aluminum fused to a steel core. Used in line wire and cable messengers. AM -See amplitude modulation. amateur -Also called a ham. 1. A person licensed to operate radio transmitters as a hobby. Any amateur radio operator. 2. A nonprofessional, usually noncommercial, devotee of any technology (as a hobby). amateur band -Any one of several radio frequency bands assigned for noncommercial use by licensed radio amateurs. In the United States, there are twelve such bands between 1.80 MHz and 1.3 GHz. Assignments are made by the Federal Communications Commission. amateur c a l l letters-Call letters and numbers assigned to amateur stations by the licensing authority. Call-letter combinations consist of a letter prefix denoting the country in which the station is situated, plus a number designating the location within the country, and two or more letters identifying the particular station. Example: K2ABC (K or W = United States, 2 = New York, and ABC = identification of individual licensee issued alphabetically except for special circumstances). amateur extra license-A license issued by the FCC to amateur radio operators who are able to send and receive Morse code at the rate of 20 words per minute and who are familiar with general, intermediate, and advanced radio theory and practice. Its privileges include all authorized amateur rights and the exclusive rights to operate on certain frequencies. amateur radio -The practice of operating electronic communications equipment as a hobby in the amateur service. Also refers to the equipment used for this purpose. amateur radiocommunication -Noncommercial radiocommunication by or among radio stations solely with a personal aim and without pecuniary or business interest. amateur radio license-The instrument of authorization issued by the Federal Communications Commission, comprised of a station license and, in the case of the primary station, incorporating an operator license. amateur radio operation -Radiocommunication conducted by an amateur radio operator from an amateur radio station. amateur radio operator- 1. A person interested in radio technique solely with a personal aim and without pecuniary interest, and holding a valid Federal Communications Commission license to operate amateur radio stations. 2. A private citizen who operates electronic communications equipment as a hobby. amateur radio service-A radiocommunication service of self-training, intercommunication, and technical investigation carried on by amateur radio operators. amateur service- A radiocommunication service that licensed operators with no pecuniary interest use for self-training, communication, and technical investigations. amateur station -A radio transmitting station operated by one or more licensed amateur operators. amateur-station call letters-See amateur call letters. ambience -1. Reverberant or reflected sound that reaches a listener’s ear from all directions as sound waves “bounce” successively off the various surfaces of a listening area-the walls, ceiling, etc. The term is usually reserved for large areas such as auditoriums and

21 concert halls, though home listening-rooms have their own ambience effects. 2. The indirect sounds heard in a concert hall or other large listening area that contribute to the overall auditory effect obtained when listening to live per€ormances. ambient -Surrounding. The surrounding environment calming into contact with the system or component in question. See also ambient noise; ambient temperature. ambient level -The level of interference emanating from sources other than the test sample, such as inherent noise of the measuring device and extraneous radiated fields. ambient light-Normal room light. Light existing in a room or other location that is characteristic of the environment. a ~ b ~ e n t - l i gfilter-A ~t filter used in front of a television picture-tube screen to reduce the amount of ambient light reaching the screen and to minimize the reflections of light from the glass face of the tube. ambiient lighting -Lighting designed to provide a substantially uniform level of illumination throughout an area, exclusive of any provision for special local requirements. arnbiient noise-1. Acoustic noise in a room or other location. Usually measured with a soundlevel meter. The term room noise commonly designates ambient noise at a telephone station. 2. Unwanted background noise picked up by a microphone, that is, any extraneous clatter in a room. Also any acoustic coloration that influences sounds. brought about by the acoustic properties of a room in which a recording is being made or replayed. 3. Interference present (in a communication line) at ;dl times. 4.Background electrical noise in electrical measurements and operation. perating temperature -The temperature of the air surrounding an object, neglecting small localized variations. ambient pressure -The general surrounding atmospheric pressure. ambient temperature- 1. Temperature of air or liquid surrounding any electrical part or device. Usually refers to the effect of such temperature in aiding or retarding removal of heat by radiation and convection from the part or device in question. 2. The prevailing temperature in the immediate vicinity of an object; the temperature of its environment. 3. A temperature within a given volume, e.g., a room or building. ambient temperature range-The range of environmental temperatures in the vicinity of a component or device over which it may be operated safely and within specifications, For forced-air cooled operation, the ambient temperature is measured at the air intake. ~ ~ b i '1. ~ An undesirable ~ i ~ -tendency of a synchro or servo system to seek a false null position in addition to the propler nuU position. 2. Inherent error resulting from multiple-.bit changes in a polystropic code. (Proper logic design prevents such errors.) ~ ~ ~ i count~ u Q A count u ~ on an electronic scaler that is obviously impossible. a r n b i reproduction ~ ~ ~ ~ ~ -The recreation of the ambience of an original recording situation with associated directionality. Sound from every direction is picked up by a tetrahedral microphone m a y and is then encoded onto two channels, which, upon decoding, produce sound through several speakers in a continuous range of directions around the listener, thus approximating the original. It can be subdivided into periphonic and pantophonic systems, the former concerning a complete sphere of information, the latter relating to a horizontal circle. Pantophonic reproduction does not distinguish vertical directionality, but still achieves remarkable realism.

AM broadcast channel -Any of the 1O-kHz wide bands of radio frequencies, which extend from 530 to 1710 kHz and are used for standard amplitude-modulated radio broadcasts. American Institute of Electrical Engineers (AIEE) -Now merged with IRE to iorm the IEEE. American Morse code-A system of dot-anddash signals originated by Samuel F. B. Morse and stili used to a limited extent for wire telegraphy in North America. It differs from the international Morse code used in radiotelegraph transmission. American National Standards Institute, inc. Abbreviated ANSI. An independent, industry-wide association that establishes standards €or the purpose of promoting consistency and interchangeability among the products of different manufacturers. Fonnerly United States of America Standards Institute (USASI) and American Standards Association (ASA). American Radio Relay League (ARRL organization of amateur radio operators. American Standards Association -Abbreviated ASA. See American National Standards Institute, Pnc. American wire gage (AWG) -The standard system used for designating wire diameter. Gage sizes range from No. 40, the smallest diameter wire, to No. 4/0, the largest. AWG sizes are used for specifying both solid and stranded wire. Gage numbers have an inverse relationship to size, i.e., larger numbers have smaller diameter.

American wire gage (AWG)

AWG

Diameter (mm)

AWG

(mm)

1 2 3 4 5 6 7 8 9 i0 11 12 13 14 15 16 17 18 19 20

7.35 6.54 5.83 5.19 4.62 4.12 3.67 3.26 2.91 2.59 2.31 2.05 1.83 1.63 1.45 1.29 1.15 1.02 0.912 0.812

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

0.723 0.644 0.573 0.511 0.455 0.405 0.361 0.321 0.286 0.255 0.227 0.202 0.180 0.160 0.143 0.127 0.113 0.101 0.090 0.C80

Diameter

AMIFM receiver-A device capable of converting either amplitude- or frequency-modulated signals into audio frequencies. AMIFM tuner-A device capable of converting either amplitude- or frequency-modulated signals into low-level audio frequencies. AML -Abbreviation for automatic modulation limiting. A circuit that uses an agc (automatic gain control) effect to prevent overmodulation. As a stronger voice signal is applied, this stage reduces the gain of the

ammeter - amplifier

22

audio amplifier(s), keeping the modulation level below 100 percent. ammeter -An instrument for measuring either direct or alternating electric current. Its scale is usually graduated in amperes, milliamperes, microamperes, or kiloamperes. ammeter s h u n t -A low-resistance conductor placed in parallel with the meter movement so that most of the current flows through this conductor and only a small part passes through the movement itself. This arrangement extends the usable range of the meter.

Iv/ SHUNT

Ammeter shunt.

ampere-hour meter- An electrical meter that measures and registers the amount or the integral, with respect to time, of the current that passes through it and is consumed in the circuit. Ampere’s rule-Current in a certain direction is equivalent to the motion of positive charges in that direction. The magnetic flux generated by a current in a wire encircles the current in the counterclockwise direction when the current is approaching the observer. ampere-turn -A measure of magnetomotive force, especially as developed by an electric current, defined as the magnetomotive force developed by a coil of one turn through which a current of 1 ampere flows; that is, 1.26 gilberts. a m p - h r -Abbreviation for ampere-hour or amperehours. amplidyne -A special direct-current generator used extensively in servo systems as a power amplifier. The response of its output voltage to changes in field excitation is very rapid, and its amplification factor is high. COMPENSATING FIELD

amorphous-A characteristic, particularly of a crystal,determining that it has no regular structure.

amorphous silicon-A noncrystalline form of silicon used to fabricate transistors on large-area flat displays. Although it is not as good a semiconductor as crystalline silicon, amorphous silicon is much easier to lay down. a m o r p h o u s silicon cell -A photovoltaic cell made of silicon and hydrogen atoms deposited in an irregular atomic structure on substrate. amortisseur winding -See damper winding. amp -Abbreviation for ampere. ampacity-The maximum current an insulated wire or cable can safely carry without exceeding either the insulation or jacket material limitations. Expressed in amperes. See nlso current-carrying capacity. amperage-The number of amperes flowing in an electrical conductor or circuit. ampere-Letter symbol: A. 1. A unit of electrical current or rate of flow of electrons. One volt across 1 ohm of resistance causes a current flow of 1 ampere. A flow of 1 coulomb per second equals 1 ampere. An unvarying current is passed through a solution of silver nitrate of standard concentration at a fixed temperature. A current that deposits silver at the rate of 0.001118 gram per second is equal to 1 ampere, or 6.25 x loJ8 electrons per second passing a given point in a circuit. 2. The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular sections, and placed 1 meter apart in a vacuum will produce between these conductors a force equal to 2 x newtons per meter of length. ampere-hour-A current of 1 ampere flowing for 1 hour. Multiplying the current in amperes by the time of flow in hours gives the total number of amperehours. Used mostly to indicate the amount of energy a storage battery can deliver before it needs recharging, or the energy a primary battery can deliver before it needs replacing. One ampere-hour equals 3600 coulombs. a m p e r e - h o u r capacity-The amount of current a battery can deliver in a specified length of time under specified conditions. For example, a 100-ampere-hour battery can supply 20 amperes for 5 hours. ampere-hour efficiency -The number of amperehours obtained from a storage battery divided by the number of ampere-hours required to recharge the storage battery to its original condition.

CONTROL OUTPUT

Amplidyne.

amplification -1. Increase in size of a medium in its transmission from one point to another. May be expressed as a ratio or, by extension of the term, in decibels. 2. An increase in the magnitude of a signal brought about by passing through an amplifier. amplification f a c t o r (A) - 1. In a vacuum tube, the ratio of a small change in plate voltage to a small change in grid voltage required to produce the same change in plate current (all other electrode voltages and currents being held constant). 2. In any device, the ratio of output magnitude to input magnitude. amplified AGC -An automatic gain-control (AGC) circuit in which the control voltage is amplified before being applied to the tube or transistor, the gain of which is to be controlled in accordance with the strength of the incoming signal. amplified b a c k bias -Degenerative voltage developed across a fast time-constant circuit within a stage of an amplifier and fed back into a preceding stage. amplifier-1. A device that draws power from a source other than the input signal and that produces as an output an enlarged reproduction of the essential features of its input. The amplifying element may be an electron tube, transistor, magnetic circuit, or any of various devices. 2. A device for increasing the magnitude of a signal by means of a varying control voltage, maintaining the signal’s characteristic form as closely as possible to the original. 3. An electronic device for magnifying (and usually controlling) electrical signals. High-fidelity amplifiers consist of a preamplifier equalizer section, plus a power or basic amplifier section. In an integrated amplifier, both sections are built on one chassis and made available as a single unit. Alternately, the two sections are available as separate units. 4.Device for increasing power associated with a signal (voltage or

23 current). Basic types include dc, ac, audio, linear, radio, video, differential, pulse, logarithmic. amplifier noise -All spurious or unwanted signals, random or otherwise, that can be observed in a completely isolated amplifier in the absence of a genuine input signal. amplifier nonlinearity- 1. The inability of an amplifier to produce an output at all times proportionate to its input. 2. Gain deviation from a straight l i e on a plot of amplifier output versus input (the transfer curve). amplify -To increase in magnitude or strength, usually said of a current or voltage. amplifying delay Fine-A delay line used in pulse-compression systems to amplify delayed superhighfrequency signals. amplistat-A self-saturating type of magnetic amplifier. Amplitron -(Raytheon) A broadband crossed-field amplifier with a reentrant electron stream. The electron stream interacts with the backward wave of a nonreentrant rf structure. amplitude- 1. The magnitude of variation in a changing quantity from its zero value. The word must be modified with an adjective such as peak, rms, maximum, etc., which designates the specific amplitude in question. 2. The level of an audio or other signal in voltage or current terms. 3. The extent to which an alternating or pulsating current or voltage swings from zero or from a mean value. ampliitude-controlled rectifier -A rectifier circuit in which a thyratron is the rectifying element. amplitude density distribution-A function that gives the fraction of time that a voltage is within a narrow range. ~ ~ ~ l distortion ~ ~ u --Distortion d e that is present in an amplifier when the amplitude of the output signal fails to follow exactly any increase or decrease in the amplitudie of the input signal. It results from nonlinearity of the transfer function and gives rise to harmonic and intermodulation distortion. No amplifier is completely free from the effect because its transfer function is slightly curved. The nature of tlie curvature determines the order of the distortion produced, but negative feedback and other circuit configurations help minimize the curvature within the dynamic range and hence keep the distortion at a very low level. amplitude distribution function -A function that gives the fraction of time that a time-varying voltage is below a given level, amplitude fading -Fading in which the amplitudes of all frequency components of a modulated carrier wave are uniformly attenuated. ~ ~ p l i t ~ d ~ - f r e distortion ~ u e n c -The ~ distortion that occurs when the various frequency components ,of a cornplex wave are not amplified, attenuated, or transmitted equally well. amplitude-frequency response -The variation of gain, loss, amplification, or attenuation of a device or :system as a function of frequency. Usually measured in ithe region where the transfer characteristic is essentially linear. amplitude gate -See slicer. amplitude-level selection-The choice of the voltage level at which an oscilloscope sweep is triggered. amplitude limiter-A circuit or stage that automatiically recEuces the amplification to prevent signal peaks from exceeding a predetermined level. ~ ~ ~ l ~ ~ u d e - m o d utransmitter lated -A transmitter in which the amplitude of its radio-frequency wave i.s varied at a low frequency rate-usually in the audio or video range. This low frequency is the intelligence r:infomation) to be conveyed.

amplifier noise

- a ~ ~ l i t u dofenoise

ASSIGNED RF CARRIER RADIO FREOUENCY WITH AF OF STATION SUPERIMPOSED

AUDIO FRMUENCY

Ltb

Amplitude-modulated transmitter.

amplitude-modulated wave -A constant-frequency waveform in which the amplitude varies in step with the frequency of an impressed signal. amplitude modulation -Abbreviated AM. 1. Modulation in which the amplitude of a wave is the characteristic subject to variation. Those systems of modulation in which each component frequency ( f ) of the transmitted intelligence produces a pair of sideband frequencies at carrier frequency plus f and carrier frequency minus f.In special cases, the carrier may be suppressed; either the lower or upper sets of sideband frequencies may be suppressed; the lower set of sideband frequencies may be produced by one or more channels of information. The carrier may be transmitted without intelligence-canying sideband frequencies. The resulting emission bandwidth is proportional to the highest frequency component of the intelligence transmitted. 2. A process in which the program information is imposed on a carrier signal of constant frequency by varying its amplitude in proportion to program level. Used on the standard broadcast band (530 to 1710 kHz) and on long-wave and shortwave bands.

AUDIO MODULATING SIGNAL

E. = E.12 FOR 50% MODULATION

~

-

CARRIER

MODULATED WAVE

Amplitude modulation.

amplitude-modulation noise level -Undesired amplitude variations of a constant radio-frequency signal, especially in the absence of any intended modulation. amplitude noise-The effect on radar accuracy of the fluctuations in amplitude of the signal returned by the target. These fluctuations are caused by any change in aspect if the target is not a point source. amplitude of noise-When impulse-type noise is of random occurrence and so closely spaced that the individual waveshapes are not separated by the receiving equipment, then the noise has the waveshape and characteristics of random noise. Random-noise amplitude is proportional to the square root of the bandwidth. If the impulses are separated, the noise no longer has the

amplitude permeability

- analog network

waveshape of random noise and its amplitude is directly proportional to the bandwidth of the transmission system. amplitude permeability -The relative permeability at a stated value of field strength and understated conditions, the field strength varying periodically with time and no direct magnetic-field component being present. amplitude range -The ratio, usually expressed in decibels, between the upper and lower limits of program amplitudes that contain all significant energy contributions. amplitude resonance -The condition that exists when any change in the period or frequency of the periodic agency (but not its amplitude) decreases the amplitude of the oscillation or vibration of the system. amplitude response-The maximum output amplitude that can be obtained at various points over the frequency range of an instrument operated under rated conditions. amplitude selection -The process of selecting that portion of a waveform which lies above or below a given value or between two given values. amplitude separator -A television-receiver circuit that separates the control impulses from the video signal. amplitude-shift keying -Abbreviated ask. The modulation of digital information on a carrier by changing the amplitude of the carrier. amplitude-suppression ratio -In frequency modulation, the ratio of the magnitude of the undesired output to the magnitude of the desired output of an FM receiver when the applied signal is simultaneously amplitude and frequency modulated. Generally measured with an applied signal that is amplitude modulated 30 percent at a 400hertz rate and is frequency modulated 30 percent of the maximum system deviation at a 1000-hertz rate. amplitude versus f r e q u e n c y distortion-Distortion caused by the nonuniform attenuation or gain of the system, with respect to frequency under specified terminal conditions. AM rejection ratio-The ratio of the recovered audio output produced by a desired FM signal with specified modulation, amplitude, and frequency to that produced by an AM signal, on the same carrier, with specified modulation index. AM suppression-The ability of an FM tuner to reject AM signals. Expressed in decibels, it is the ratio between the tuner output with a 100-percent modulation FM signal to its output with a 30-percent modulated AM signal. AM tuner- A device capable of converting amplitudemodulated signals into low-level audio frequencies. amu -Abbreviation for atomic mass unit. analog -1. In electronic computers, a physical system in which the performance of measurements yields information concerning a class of mathematical problems. 2. Of or pertaining to the general class of devices or circuits in which the output varies as a continuous function of the input. 3. The representation of numerical quantities by means of physical variables, e.g., translation, rotation, voltage, resistance; contrasted with digital. 4. A continuous representation of phenomena in terms of points along a scale, each point merging imperceptibly into the next. An analog voltage, for example, may take any value. Realworld phenomena, such as heat and pressure, are analog (compare with digital). analog adder-An analog circuit or device that receives two or more inputs and delivers an output that is equal to their sum. analog amplifier-A device whose output is continuously proportional to the input stimulus.

24

analog channel-A computer channel in which the transmitted information can have any value between the defined limits of the channel. analog circuit-A circuit in which the output varies as a continuous function of the input, as contrasted with digital circuits. analog communications -A system of telecommunications employing a nominally continuous electrical signal that varies in frequency, amplitude, etc., in some direct correlation to nonelectrical information (sound, light, etc.) impressed on a transducer. analog computer- 1. A computer operating on the principle of creating a physical (often electrical) analogy of the mathematical problem to be solved. Variables such as temperature, light, pressure, distance, angle, shaft speed, or flow are represented by the magnitude of a physical phenomenon such as voltage or current. The computer manipulates these variables in accordance with the mathematical formulas “analogued” on it. 2. A computer system in which both the input and output are continuously varying signals. 3. A computing machine that works on the principle of measuring, as distinguished from counting. 4. A computer that solves problems by setting up equivalent electric circuits and making measurements as the variables are changed in accordance with the corresponding physical phenomena. An analog computer gives approximate solutions, whereas a digital computer gives exact solutions. 5. A nondigital computer that manipulates linear (continuous) data to measure the effect of a change in one variable on all other variables in a particular problem. (Compare: digital computer.) analog computing -Computing system in which continuous signals represent mechanical (or other) parameters. analog data -1. A physical representation of information such that the representation bears an exact relationship to the original information. The electrical signals on a telephone channel are an analog data representation of the original voice. 2. Data represented in a continuous form, as contrasted with digital data represented in a discrete (discontinuous) form. Analog data is usually represented by physical variables, such as voltage, resistance, rotation, etc. analog input module-An UO rack module that converts an analog signal from a user device to a digital signal that may be processed by the processor. analog meter -An indicating instrument that employs a movable coil and pointer arrangement (or equivalent) to display values along a graduated scale. analog multiplexer-1. Circuit used for timesharing of analog-to-digital converters between a number of different analog information channels. Consists of a group of analog switches arranged with inputs connected to the individual analog channels and outputs connected in common. 2. Two or more analog switches with separate inputs and a common output, with each gate separately controllable. Multiplexing is performed by sequentially turning on each switch one at a time, switching each individual input to a common output. 3. A device that selects one of several analog signals according to a digital code. Analog multiplexers (amux) are available in many forms; their chief application is as a front end in data-acquisition systems, enabling a single analog-to-digital converter to monitor more than one information channel. analog network -A circuit or circuits that represent physical variables in such a manner as to permit the expression and solution of mathematical relationships between the variables, or to permit the solution directly by electric or electronic means.

analog output - AN

25

analog output-1. A signal (voltage) whose amplitude is continuously proportionate to the stimulus, the proportionality being limited by the resolution of the device. 2. An output quantity that varies smoothly over a continuous range of values rather than in discrete steps. analog panel meter-See APM. analog recording-A method of recording in which same characteristic of the record current, such as amplitud'e or frequency, is continuously varied in a manner analolgous to the time variations of the original signal. analolg representation -A representation that does not have discrete values, but is continuously variable. analog signal - 1. An electrical signal that varies continuously in both time and amplitude, as obtained from temperature or pressure, or speed transducers. A voltage level that changes in proportion to the change in a physical variable. 2. A signal representing a variable that may be continuously observed and continuously represented. analog s w i t c h -1. A device that either transmits an analog signal without distortion or completely blocks it. 2. An:y solid-state device, with or without a driver, capable of bilaterally switching voltages or current. It has an input terminal, output terminal, and, ideally, no offset voltage, low on resistance, and extreme isolation between the signal being gated and control signals. 3. A means to interconnect two or more circuits whose information is represented in analog form using a network that may or .may not be time divided and may or may not consist of linear elements. analog-to-digital conversion -1. The process of (converting a continuously variable (analog) signal to a (digital signal (binary code) that is a close approximation of the original signal. 2. The process of quantizing a rcontinuous function. analog-to-digital converter-Abbreviated a-d converter, adc, or ADC. 1. A circuit that changes a continuously varying voltage or current (analog) into a digital output. The input may be ac or dc, and the output may be seriai or parallel, binary or decimal. 2. Device that translates analog signals (voltages, pressures, etc.) from sensors in.to numerical digital form (binary, decimal, etc.).

I'N

Analytical Engine-An early form of generalpurpose digital computer invented in 2833 by Charles Babbage. analyzer- 1. An instrument or other device designed to examine the functions of components, circuits, or systems and their relations to each other, as contrasted with an instrument designed to measure some specific parameter of such a system or circuit. 2. Of computers, a routine the purpose of which is to analyze a program written for the same or a different computer. This analysis may consist of summarizing instruction references to storage and tracing sequences of jumps. 3. An instrument that evaluates and/or measures one or more specific parameters (e.g.9 voltage, current, frequency, logic level, bit time, distortion). 4. A test assembly that checks the performance of, or locates trouble in, electronic equipment. Also called test set and tester. anastigmat-A lens system designed so as to be free from the aberration called astigmatism. anchor-An object, such as a metal rod, set into the ground to hold the end of a guy wire. ancillary equipment -Equipment not directly employed in the operation of a system but necessary for logistic support, preparation for flight, or assessment of target damage; e.g., test equipment, vehicle transport. AND circuit-Synonym for AND gate. AND device-A device that has its output in the logic 1 state if and only if all the control signals are in the logic 1 state. Anderson bridge -A bridge normally used for the comparison of self-inductance with capacitance. It is a six-branch network in which an outer loop of four arms is formed by four nonreactive resistors and the unknown inductor. An inner loop of three arms is formed by a capacitor and a fifth resistor in series with each other and in parallel with the arm opposite the unknown inductor. The detector is connected between the junction of the capacitor and the fifth resistor and at that end of the unknown inductor separated from a tePmind of the capacitor by only one resistor. The source is connected to the other end of the unknown inductor and to the junction of the capacitor with two resistors of the outer loop. The balance is independent of frequency.

0

D/A CONVERTER

Anderson bridge.

Analog-to-digital converter.

analog transmission -Transmission of a continuously variable signal as opposed to a discretely variable one. analog value -A continuously variable value, such a s a current or voltage.

AND gate- 1. In an electronic computer. a gate circuit with more than one control (input) terminal. No output signal will be produced unless a pulse is applied to all inputs simultaneously. 2. A binary circuit, with two or more inputs and a single output, in which the output is logic 1 only when all inputs are logic I, and the output is logic 0 if any one of the inputs is logic 0. AND/NOR gate-A single logic element that performs the operation of two AND gates with outputs feeding a NOR gate. No access to the internal logic elements is provided (ie., no connection is available at the outputs of the AND gates).

AND/OR circuit

- angle of incidence

26

L I

I

,

AND GATE (SCHEMATIC)

D*:C

AND GATE (LOGIC DIAGRAM)

AND gate with three inputs.

AND/OR circuit-A gating circuit that produces a prescribed output condition when several possible combinations of input signals are applied. It exhibits the characteristics of the AND gate and the OR gate. android - 1. A mobile mechanism possessing the ability to manipulate objects external to itself under the constant control of its own resident intelligence, operating within guidelines initially established and occasionally updated by a human being, a computer, or some other external intelligence. 2. Automaton of manlike form. a n e c h o i c -Nonreflective, producing no echoes. anechoic chamber-1. A room or chamber specially designed to absorb all sound within, thus preventing sound reflections or reverberation. Such rooms are used for evaluation of microphones and speakers. 2. A room lined with material that traps sound waves so the sound is perfectly absorbed and the room is acoustically dead. Such a chamber is used for testing microphones and speakers. 3. A derived term for a room or enclosure that is designed to be echo free over a specified frequency range. Any sound reflections within this frequency range must be less than 10 percent of the source sound pressure. a n e c h o i c enclosure -A special echo-free enclosure used for testing audio transducers, in which all wall surfaces have been covered with acoustically absorbent materials so that reflections of the sound waves are eliminated. Also known as a dead room or an anechoic room. a n e c h o i c room-A room whose walls have been treated so as to make them absorb a particular kind of radiation almost completely; used for testing components of sound systems, radar systems, etc., in an environment free of reflections. anelectronic-See anelectrotonus. anelectrotonus -The reduced sensitivity produced in a nerve or muscle in the region of contact with the anode when an electric current is passed through it. anemometer -An instrument used for measuring the force or speed of wind. angels -Short-duration radar reflections in the lower atmosphere. Most often caused by birds, insects, organic particles, tropospheric layers, or water vapor. angle- 1. A fundamental mathematical concept formed when two straight lines meet at a point. The lines are the sides of the angle, and the point of intersection

0"

90"

-F

180"

270"

360"

Angle.

is the vertex. 2. A measure of the distance along a wave or part of a cycle, measured in degrees. 3. The distance through which a rotating vector has progressed. angle jamming -An electronic countermeasures technique in which azimuth and elevation information present in the modulation components of the returning echo pulse of a scanning fire-control radar is jammed by transmitting a pulse similar to the radar pulse but with angle information of erroneous phase. angle modulation-Modulation in which the angle of a sine-wave carrier is the characteristic varied from its normal value by modulation. Phase and frequency modulation are particular forms of angle modulation. angle noise-Tracking error introduced into radar by variations in the apparent angle of arrival of the echo from a target due to finite target size. (This effect is caused by variations in the phase front of the radiation from a multiple-point target as the target changes its aspect with respect to the observer.) angle of arrival-Angle made between the line of propagation of a radio wave and the earth's surface at the receiving antenna. angle of azimuth -The angle measured clockwise in a horizontal plane, usually from the north. The north used may be true north, Y-north, or magnetic north. angle of beam-The angle that encloses most of the transmitted energy from a directional-antenna system. angle of convergence -Angle formed by the lines of sight of both eyes when focusing on an object. angle of deflection-The angle formed between the new position of the electron beam in a cathode-ray tube and the normal position before deflection. angle of departure-The angle of the line of propagation of a radio wave with respect to a horizontal plane at the transmitting antenna. angle of divergence-In cathode-ray tubes, a measure of its spread as the electron beam travels from the cathode to the screen. The angle formed by an imaginary center line and the border line of the electron beam. In good tubes, this angle is less than 2". angle of elevation-The angle between the horizontal plane and the line ascending to the object. angle of incidence-The angle between a wave or beam striking a surface and a line perpendicular to that surface.

21

angle of lag -The angular phase difference between one sinusoidal function and a second having the same frequency. Expressed in degrees, the amount the second function must be retarded to coincide with the first.

Angle of lag.

angle! of lead- 1. The time or angle by which one alternating electrical quantity leads another of the same cyclic period. 2. The angle through which the commutator brushes of a generator or motor must be moved from the normal position to prevent sparking.

B A LEADS 8 BY 90"

Angle of lead, 1.

angle sf radiation -The angle between the surface of the earth and the center of the beam of energy radiated upward into the sky from a transmitting antenna. angle of reflection-The angle between a wave or beam reflected from a surface and a line perpendicular to that surface. This angle lies in a common plane with the angle of incidence and is equal to it. angle of refraction-The angle between a wave lor beam as it passes through a medium and a line perpendicular to the surface of that medium. This angle lies in a common plane with the angle of incidence. angle tracking noise-Any deviation of the tracking axis from the center of reflectivity of a target. The resultant of servo noise, receiver noise, angle noise, and amplitude noise. angstrom unit-A unit of measurement of wavellength of light and other radiation. Equal to one ten-thousof a micrometer or one hundred-millionth andth ( of a centimeter cm). The visible spectrum extends from about 4000 to 8000 angstrom units. Blue light has a wavelength in the region of 4700 angstroms; yellow, 5800; and red!, 6500. A measure of wavelength equal to meter, or 0.1 nanometer, the preferred term. a n g u l a r acceleration -The rate at which angular velocity changes with respect to time, generally expressed in radians per second. angular accelerometer-A device capable of measuring the magnitude of, and/or variations in, angular acceleration. a n g u l a r aperture-The largest angular extent of wave surface that an objective can transmit. angular deviation loss-The ratio of the response of a microphone or speaker on its principal axis to the response at a specified angle from the principal axis (expressed in decibels). angular distance -The angle subtended by two bodies at the point of observation. It is equal to the

distance of wavelengths multiplied by 2n radians or by 360". angular frequency-Frequency expressed in radians per second. It is equal to the number of hertz (cycles per second) multiplied by 2n. angular length -Length expressed in radians or equivalent angular measure equal to 2 n radians, or 360", multiplied by the length in wavelengths. angular momentum-The momentum that a body has by virtue of its rotational movement. angular p h a s e difference-Phase difference between two sinusoidal functions expressed as an angle. angular rate -The rate of change of bearing. angular resolution-The ability of a radar to distinguish between two targets solely on the basis of angular separation. angular velocity-The rate at which an angle changes. Expressed in radians per second, the angular velocity of a periodic quantity is the frequency multiplied by 2n. If the periodic quantity results from uniform rotation of a vector, the angular velocity is the number of radians per second passed over by the rotating vector. Generally designated by the Greek letter omega (w). a n h a r m o n i c oscillator- An oscillating system in which the restoi-ing force is a nonlinear function of the displacement from equilibrium. anhysteresis-The process whereby a material is magnetized by applying a unidirectional field upon which is superimposed an alternating field of gradually decreasing amplitude. ANIK-The Canadian domestic satellite system used to transmit the network television feeds of the Canadian Broadcasting Corporation. All ANIK satellites are operated by TeleSat Canada of Ottawa. A N K satellites have both 4-GHz C-band and 12-GHz Ku-band transponders. ANIK means brother in Innit (Eskimo). animation -A moving on-screen representation of the activities taking place in a simulation. anion - 1. A negatively charged ion which, during electrolysis, is attracted toward the anode. A corresponding positive ion is called a cation. 2. A negative ion that moves toward the anode in a discharge tube, electrolytic cell, or similar device. anisotropic- 1. Describing a substance that exhibits different magnetic, electrical, optical, and other physical properties when measured along axes in different directions. 2. A material that has characteristics such as wave propagation constant, magnetic permeability, conductivity, etc., that vary with direction; that is, not isotropic. anisotropic body-A body in which the value of any given property depends on the direction of measurement, as opposed to a body that is isotropic. anisotropic magnet -A magnetic material having a better magnetic characteristic along the preferred axis than along any other. anisotropic material -A material having preferred orientation so that the magnetic characteristics are superior along a particular axis. This may be as a result of rolling, heat treatment in a magnetic field, or, in the case of some of the sintered magnets, the direction of press. anisotropy- Directional dependence of magnetic properties, leading to the existence of easy or preferred directions of magnetization. Anisotropy of a particle may be related to its shape, to its crystalline structure, or to the existence of strains within it. anneal -1. To heat a metal to a predetermined temperature and then let it cool slowly. This process prevents brittleness and often stabilizes electrical characteristics.

annealed laminations

- anodic protection

2. To heat and then gradually cool in order to relieve mechanical stresses. Annealing copper makes it softer and less brittle. annealed laminations -Laminations that have been annealed for transformers or choke coils. annealed wire-Wire that has been softened by heating and gradual cooling to remove mechanical stresses. annotation -An added descriptive comment or explanatory note. annular -Ringed; ring-shaped. annular conductor -A conductor consisting of a number of wires stranded in three reversed concentric layers surrounding a saturated hemp core. The core is usually made wholly or mostly of nonconducting material. This construction has the advantage of lower total ac resistance for a given cross-sectional area of conducting material by eliminating the greater skin effect at the center. annular transistor-A mesa transistor in which the semiconductor regions are arranged in concentric circles about the emitter. annulling network- An arrangement of impedance elements connected in parallel with filters to annul or cancel capacitive or inductive impedance at the extremes of the passband of a filter. annunciation relay- 1. An electromagnetically operated signaling apparatus that indicates whether a current is flowing or has flowed in one or more circuits. 2. A nonautomatic reset device that gives a number of separate visual indications upon the functioning of protective devices, and which may also be arranged to perform a lockout function. annunciator-1. A visual device consisting of a number of pilot lights or drops. Each light or drop indicates the condition that exists or has existed in an associated circuit and is labeled accordingly. 2. A device for sounding an alarm or attracting attention. The indication is usually aural, but occasionally may be visual or both aural and visual. 3. An alarm-monitoring device that consists of a number of visible signals, such as flags or lamps indicating the status of the detectors in an alarm system or systems. Each circuit in the device is usually labeled to identify the location and condition being monitored. In addition to the visible signal, an audible signal is usually associated with the device. When an alarm condition is reported, a signal is indicated -visible, audible, or both. The visible signal is generally maintained until reset either manually or automatically. anode- 1. The positive electrode, such as the plate of a vacuum tube; the element to which the principal stream of electrons flows. 2. In a cathode-ray tube, the electrodes connected to a source of positive potential. These anodes are used to concentrate and accelerate the electron beam for focusing. 3. The less noble and/or higher-potential electrode of an electrolytic cell, at which corrosion occurs. This may be an area on the surface of a metal or alloy, the more active metal in a cell composed of two dissimilar metals, or the positive electrode of an impressed-current system.

+NoDY TRIODE

Anode.

DIODE

28

anode-balancing coil -A set of mutually coupled windings used to maintain approximately equal currents in anodes operating in parallel from the same transformer terminal. anode b r e a k d o w n voltage -The potential required to cause conduction across the main gap of a gas tube when the starter gap is not conducting and all other tube elements are held at cathode potential. a n o d e - b y p a s s capacitor- Also called platebypass capacitor. A capacitor connected between the anode and ground in an electron-tube circuit. Its purpose is to bypass high-frequency currents and keep them out of the load. anode characteristic curve-A graph that shows how the anode current of an electron tube is affected by changes in the anode voltage. anode circuit breaker-A device used in the anode circuits of a power rectifier for the primary purpose of interrupting the rectifier circuit if an arcback should occur. anode current-The electron flow in the element designated as the anode. Usually signifies plate current. anode d a r k space-In a gas tube, a narrow, dark zone next to the surface of the anode. anode dissipation -The power dissipated as heat in the anode of an electron tube because of the bombardment by electrons and ions. anode efficiency-See plate efficiency. anode-load impedance -See plate-load impedance. anode modulation -See plate modulation. anode neutralization -Also called plate neutralization. A method of neutralization in which a portion of the anode-cathode ac voltage is shifted 180" and applied to the grid-cathode circuit through a neutralizing capacitor. anode power input-See plate power input. anode power supply-The means for supplying power to the plate of an electron tube at a more positive voltage than that of the cathode. Also called plate power supply. anode pulse modulation-See plate pulse modulation. anode rays-Positive ions coming from the anode of an electron tube; these ions are generally due to impurities in the metal of the anode. anode saturation-See plate saturation. anode s h e a t h -A layer of electrons surrounding the anode in mercury-pool arc tubes. anode strap -A metallic connector between selected anode segments of a multicavity magnetron, used principally for mode separation. anode supply-Also called plate supply. The dc voltage source used in an electron-tube circuit to place the anode at a high positive potential with respect to the cathode. anode terminal -1. In a diode (semiconductor or tube), that terminal to which a positive dc voltage must be applied to forward-bias the diode. Compare with cathode terminal. 2. In a diode (semiconductor or tube), that terminal at which a negative dc voltage appears when the diode is employed as an ac rectifier (blocking). 3. That terminal which is internally connected to the anodic element of any device. anode voltage -The potential difference existing between the anode and cathode. anode voltage drop (of a glow-discharge, cold c a t h o d e tube) -Difference in potential between cathode and anode during conduction, caused by the electron flow through the tube resistance (ZR drop) anodic protection -Corrosion inhibition based on the electrolytic formation of a protective passive film on

anodic silver

29 metals by applying to them a positive (anodic) potential; e.g., alurninum is anodized (oxidized) by a positive charge in a sulfuric acid solution. anodic silver-A precious metal used in plating; fine silver in different configurations, such as shot, cones, bars, etc., is sacrificed during the silver-plating process. anodization-The formation of an insulating oxide over certain elements, usually metals, by electrolytic action. The most commonly anodized materials are tantalum, aluminum, titanium, and niobium. Anodization is particularly useful where protection of a conductor is required. The base metal can form the conductor and the anodized surface layer can form the insulator. anodke- To deposit a protective coating of oxide on a metal by means of an electrolytic process in which it is used as the anode. anodiizing-An electrochemical oxidation process used to improve the corrosion resistance or to enhance the appearance of a metal surface. Aluminum and magnesium parts are frequently anodized. anomalous displacement current -Also called dielectric absorption. The current in addition to the normal leakage current in a circuit containing a capacitor with an imperfect dielectric after the normal charging or discharging current has become negligibly small. anomalous photoconductivity-A spectral phenomenon in which the degree of the photoresponse of an illumilaated semiconductor is determined by the wavelength colmposition of the incident light. anomalous propagation - 1. Propagation that is Enusual or abnoimal. 2. The conduction of UHF signals through atmospheric ducts or layers in a manner similar to that of a waveguide. These atmospheric ducts carry the signals with less than normal attenuation over distances far beyond the optical path taken by UHF signals. Also 'called sulperrefraction. 3. In sonar, pronounced and rapid variations in the strength of the echo due to large, rapid focal fluctuations in propagation conditions. ~ n o n ~ f FTP ~ o (File ~ s Transfer Protocol) -The .procedure of connecting to a remote computer as an ,anonymous or guest user in order to transfer public files lback to a local computer. See also FTP; protocol. ri3db range-A navigational aid that provides uiisignal zones for aircraft guidance. Deviation from the assigned course is indicated aurally by the Morse code letters A (--) or N (-.). On-course position is jmdicated by an audible merging of the A and N code !si nuous tone. an National Standards Institute. The 1u rganization with responsibility for the development and promulgation of (among others) data

signal --A

- antenna bandwidth

tripped by a unique access code, a short predetermined message is broadcast. answerback unit -An electromechanical device used with a teletypewriter set to transmit a predetermined message of not more than 21 characters in response to a request signal. It can transmit either a five-level 7.42 unit code or an eight-level 11.0 unit code at speeds of up to 100 words per minute. answering cord-The cord nearest the face of a telephone switchboard. It is used for answering subscriber's calls and calls on incoming trunks. answering service- A business that contracts with subscribers to answer incoming telephone calls after a specified delay or when scheduled to do so. It may also provide other services, such as relaying fire or intrusion alarm signals to proper authorities. answer lamp-In a telephone switchboard, a lamp that lights when an answer cord is plugged into a line jack; it extinguishes when the telephone answers and lights when the call is complete. answer tone -Tone signal, with a frequency between 2025 and 2225 Hz and a duration of at least 1.5 s, used by an answering modem to indicate its ready condition to an originating modem. antenna- Also called aerial. 1. That portion, usually wires or rods, of a radio transmitter or receiver station used for radiating waves into or receiving them from space. It changes electrical currents into electrornagnetic radio waves, and vice versa. 2. A section of wire or a metallic device designed to intercept radio waves in the air and convert them to an electrical signal for feeding to a receiver. Under relatively difficult reception conditions, such as created by location, terrain, obstructions, etc., an antenna becomes fairly critical and should be one especially designed for its intended purposes. 3. A device for transmitting and receiving radio waves. Depending on their use and operating frequency, antennas can take the form of a single piece of wire, a dipole, a grid such as a yagi array, a horn, a helix, a sophisticated parabolic-shaped dish, or a phase array of active electronic elements of virtually any flat or convoluted surface. 4. A device that collects and focuses electromagnetic energy, Le., contributes an energy gain. Gain is proportional to surface area for a microwave dish. antenna array- 1. A combination of antennas assembled to obtain a desired pickup or rejection pattern. 2. An arrangement of two or more directional antennas, spaced and connected so that they are in phase and their effects are electrically additive.

radio-range, quadrant-designation ilot whether he or she is on

keyboard -Abbreviation for American National Standards Institute keyboard. A typewriter standard unit that offers a choice of uppercase characters only or uppercase and lowercase combined. series of standards recomANSI s t a n d a r d s - A mended by the American National Standards Institute. a n s w e r b a c k - 1. The response of a terminal to remote-control signals. 2. A signal sent by a data receiver to a data transmitter indicating that it is ready to receive data or is acknowledging the receipt of data. See also handshaking. 3. -A reply message from a terminal, manually or automatically initiated, to verify that the right terminal has been accessed and is in operation. a n s w e r b a c k (W-R-U) s y s t e m -A system capable of being remotely controlled by another station. When

Antenna array.

antenna bandwidth- 1 . The range of frequencies over which the impedance characteristics of the antenna are sufficiently uniform that the quality of the radiated signal is not significantly impaired. 2. The frequency range

antenna beam width - antenna impedance over which a certain antenna characteristic falls within acceptable limits. For instance, an antenna may have a bandwidth of 1 MHz over which the standing-wave ratio is 2 : 1 or less. 3. The frequency range throughout which an antenna will operate at a specified efficiency without the need for alteration or adjustment. antenna beam width-The angle, in degrees, between two opposite half-power points of an antenna beam. antenna coil -In a radio receiver or transmitter, the inductance through which antenna current flows. antenna coincidence-That instance when two rotating, highly directional antennas are pointed toward each other. antenna-conducted interference-Any signal that is generated within a transmitter or receiver and appears as an undesired signal at the antenna terminals of the device, e.g., harmonics of a transmitter signal, or the local-oscillator signal of the receiver. antenna cores-Ferrite cores of various cross sections for use in radio antennas.

POWERED-IRON CORE

WINDING

Antenna core.

antenna coupler -1. A radio-frequency transformer used to connect an antenna to a transmission line or to connect a transmission line to a radio receiver. 2. A radiofrequency transformer, link circuit, or tuned line used to transfer radio-frequency energy from the final plate-tank circuit of a transmitter to the transmission line feeding the antenna. antenna crosstalk-A measure of undesired power transfer through space from one antenna to another. Usually expressed in decibels, the ratio of power received by one antenna to the power transmitted by the other. antenna current -The radio-frequency current that flows in an antenna. antenna detector-A device consisting of an antenna and electronic equipment to warn aircraft crew members of their being observed by radar sets. The device is usually located in the nose or tail of the aircraft and illuminates a light on one or more panels when radar signals are detected. antenna diplexer-A coupling device that permits several transmitters to share one antenna without troublesome interaction. antenna-directivity d i a g r a m -A curve rcprcscnting, in polar or Cartesian coordinates, a quantity proportional to the gain of an antenna in the various directions in a particular plane or cone. antenna disconnect s w i t c h -A safety switch or interlock plug used to remove driving power from the antenna to prevent rotation while work is being performed. antenna duplexer-A circuit or device that permits one antenna to be shared by two transmitters without undesirable interaction. antenna effect -1. Cause of error in a loop antenna due to the capacitance to ground. 2. In a navigational system, any undesirable output signal that results when a directional antenna acts as a nondirectional antenna. 3. The tendency of wires or metallic bodies to act as antennas, i.e., to radiate or pick up radio signals.

30

antenna effective area-In any specified direction, the square of the wavelength multiplied by the power gain (or directional gain) in that direction, and divided by 4n. (When power gain is used, the effective area is that for power reception; when directive gain is used, the effective area is that for directivity.) antenna efficiency-The relative ability of an antenna to convert rf energy from a transmitter into electromagnetic waves. If the gain rating of a directional antenna is 10 dB, for example, it is often assumed that the effective radiated power will be 10 times greater than the rf power fed to it. However, if the antenna efficiency is, say, 50 percent, a loss of 3 dB,the true gain will be only 7 dB (10 - 3 = 7 dB). antenna elevation-The physical height of an antenna above the earth. antenna factor-The value of decibel that must be added to a two-terminal voltmeter reading to obtain the actual induced antenna open-circuit voltage or the electric-field strength. antenna farm-A large plot of ground (5 to 2000 acres) surrounding a radio transmitting or receiving station that provides space and adequate clearance for the installation of several large antennas, such as rhombic antennas. antenna field-1. The region defined by a group of antennas. 2. A group of antennas placed in a geometric configuration that is specific for a particular trajectory measuring system. 3. The effective free-space energy distribution produced by an antenna or group of antennas. antennafier -An integrated low-profile antenna and amplifier for use with compact, portable communications systems. antenna front-to-back ratio-The ratio of field strength in front of a directional antenna (i.e., directly forward in the line of maximum directivity) to the field strength in back of the antenna (i.e,, 180” from the front). Measured at a fixed distance from the radiator. antenna gain- 1. The effectiveness of a directional antenna in a particular direction, compared against a standard (usually an isotropic antenna). The ratio of standard antenna power to the directional antenna power that will produce the same field strength in the desired direction. 2. The increase in signal level at the antenna terminals with reference to the level at the terminals of a half-wave dipole antenna, expressed in decibels. 3. For a given antenna, the ratio of signal strength (received or transmitted) to that obtained with a simple dipole antenna. antenna ground system-That portion of an antenna closely associated with the earth and including an extensive conducting surface, which may be the earth itself. a n t e n n a height -The average height above the terrain from 2 to 10 miles (3.2 to 16 km) from the antenna. In general, the antenna height will be different in each direction from the antenna. The average of these various heights is considered the antenna height above average terrain. antenna height above average terrain-The height of the center of radiation of an antenna above an averaged value of the elevation above sea level for the surrounding terrain. antenna illumination -Describes how a feedhorn “sees” the surface of a dish as well as the surrounding terrain. antenna impedance-The impedance an antenna presents to a transmitter or receiver at the attachment point of the transmission line or feeder. It varies from about 50 to 600 ohms, depending on antenna type and installation.

antenna induced microvolts - anticoincidence circuit

31

antenna induced microvolts-The voltage that exists across the open-circuited antenna terminals, as calculated from a measurement. antenna Iens-An arrangement of metal vanes or dielectric material used to focus a microwave beam in a manner similar to an optical lens. antenna lobe-See lobe. antenna matching -Selection of components to make the impedance of an antenna equal to the characteristic impedance of its transmission line. antennamitter- An integrated low-profile antenna and oscillator for use with compact, portable communications systems. antenna pair-Tko antennas located on a base line of accurately surveyed length. The signals received by these antennas are used to determine quantities related to a target position. antenna pattern -Also called antenna polar diagram. A plot of angle versus free-space field intensity at a fixed distance in the horizontal plane passing through the center of the antenna.

Antenna pattern.

antenna-pattern measuring equipment Devices used to measure the relative field strength or intensity existing at any point or points in the space immediately surrounding an antenna. antenna pedestal -A structure that supports an antenna assembly (motors, gears, synchros, rotating joints, etc.). antenna polar diagram-See antenna pattern. antenna polarization -The position of an antenna, with respect to the surface of the earth, that determines the wave polarization for which the antenna is most efficient. A vertical antenna radiates and receives vertically polarized waves; a horizontal antenna radiates and receives horizontally polarized waves broadside bo itself and vertically polarized waves at high angles off its ends. antenna power-The square of the antenna current of a transmitter, multiplied by the antenna resistance at the point where the current is measured. antenna power gain-The power gain of an antenna in a given direction is four times the ratio of the radiation intensity in that direction to the total power delivered to the antenna. (The term is also applied to receiving antennas.) antenna preamplifier-A low-noise rf amplifier, usually mast-mounted near the terminals of the receiving antennas, used to compensate for transmission-line loss and thereby improve the overall noise figure. antenna reflector-In a directional-antenna array, an element that modifies the field pattern in order to reduce the field intensity behind the array and increase

it in front. In a receiving antenna, the reflector reduces interference from stations behind the antenna. antenna relay-A relay used in radio stations to automatically switch the antenna to the receiver or transmitter and thus protect the receiver circuits from the rf power of the transmitter. antenna resistance-The total resistance of a transmitting antenna system at the operating frequency. The power supplied to the entire antenna circuit, dwided by the square of the effective antenna current referred to the feed point. Antenna resistance is made up of such components as radiation resistance, ground resistance, radio-frequency resistance of conductors in the antenna circuit, and equivalent resistance due to corona, eddy currents, insulator leakage, and dielectric power loss. antenna resonant frequency-The frequency (or frequencies) at which an antenna appears to be a pure resistance. antenna stabilization-A system for holding a radar beam steady despite the roll and pitch of a ship or airplane. antenna structure-A structure that includes the radiating system, its supporting structures, and appurtenances mounted thereon. antenna switch-Switch used for connecting an antenna to or disconnecting it from a circuit. antenna s y s t e m - An assembly consisting of the antenna and the necessary electrical and mechanical devices for insulating, supporting, and/or rotating it. antenna terminals -On an antenna, the points to which the lead-in (transmission line) is attached. antenna tilt error- The angular difference between the antenna tilt angle shown on the mechanical indicator and the electrical center of the radar beam. antennaverter -A receiving antenna and converter combined in a single unit that feeds directly into the receiver IF amplifier. antenna wire-A wire, usually of high tensile strength, such as coppenveld, bronze, etc., with or without insulation, used as an antenna for radio and electronic equipment. antiaircraft missile -A guided missile launched from the surface against an airborne target. anti-aliasing-The smoothing or removal of diagonal lines in digitized images at low resolutions that appear as stair-steps in order to recreate smoother diagonal lines. anti-aliasing filter-A filter (normally low pass) that band-limits the input signal before sampling to less than half the sampling rate to prevent aliasing noise. anticapacitance switch-A switch with widely separated legs, designed to keep capacitance at a minimum in the circuits being switched. anticathode-Also called target. The target of an X-ray tube on which the stream of electrons from the cathode is focused and from which the X-rays are radiated. anticlutter circuit-In a radar receiver, an auxiliary circuit that reduces undesired reflection in order to pennit the detection of targets that otherwise would be obscured by such reflections. anticlutter gain Control -A device that automatically and gradually increases the gain of a radar receiver from low to maximum within a specified period after each transmitter pulse. In this way, short-range echoes producing clutter are amplified less than long-range echoes. anticoincidence-A nonsimultaneous occurrence of two or more events (usually, ionizing events). anticoincidence circuit -1. A counter circuit that produces an output pulse when either of two input circuits receives a pulse, but not when the two inputs receive

anticollision radar

- antistatic sprays

pulses simultaneously. 2. A circuit that provides an output only when all inputs are absent; a NAND circuit. radar system used in an anticollision radar-A aircraft or ship to warn of possible collision. antiferroelectricity-The property of a class of crystals that also undergo phase transitions from a higher to a lower symmetry. They differ from the ferroelectrics in having no electric dipole moment. antiferroelectric materials- Those materials in which spontaneous electric polarization occurs in lines of ions; adjacent lines are polarized in an antiparallel arrangement. antiferromagnetic materials-Those materials in which spontaneous magnetic polarization occurs in equivalent sublattices; the polarization in one sublattice is aligned antiparallel to the other. antiferromagnetic resonance-The absorption of energy from an oscillating electromagnetic field by a system of processing spins located on two sublattices, with the spins on one sublattice going in one direction and the spins on the other sublattice in the opposite direction. antiferromagnetism -A phenomenon of magnetism characterized by the elimination of magnetic moments and decrease in magnetic susceptibility with a decrease in temperature due to the q u a l power of atomic magnets. antihunt-A stabilizing signal or equalizing circuit used in a closed-loop feedback system of a servomechanism to prevent the system from hunting, or oscillating. Special types of antihunt circuits are the anticipator, derivative, velocity feedback, and damper. antihunt circuit- A circuit used to prevent excessive correction in a control system. antihunt device-A device used in positioning systems to prevent hunting, or oscillation, of the load around an ordered position. The device may be mechanical or electrical. It usually involves some from of feedback. antijamming- 1. Minimizing the effect of enemy electronic countermeasures to permit echoes from targets detected by radar to be visible on the indicator. 2. Controls or circuit features incorporated to minimize jamming. antijamming radar data processing -Use of data from one or more radar sources to determine target range in the presence of jamming. antilogarithm-The number from which a given logarithm is derived. For example, the logarithm of 4261 is 3.6295. Therefore the antilogarithm of 3.6295 is 4261. antimagnetic-Made of alloys that will not remain in a magnetized state. antimicrophonic -Specifically designed to prevent microphonics. Possessing the characteristic of not introducing undesirable noise or howling into a system. antimissile missile-A missile that is launched to intercept and destroy another missile in flight. antinode-The point on a transmission line at which the current is maximum and the voltage is minimum. antinodes-Also called loops. The points of maximum displacement in a series of standing waves. Two similar and equal wave trains traveling at the same velocity in opposite directions along a straight line result in alternate antinodes and nodes along the line. Antinodes are separated from their adjacent nodes by half the wavelength of the wave motion. antinoise carrier-operated device -A device commonly used to mute the audio output of a receiver during standby or no-carrier periods. Usually the automatic volume control voltage is used to control a squelch tube which, in turn, controls the bias applied to the first audio tube so that it is permitted to operate only when a

32 carrier is present at the receiver input. Thus, the receiver output is heard when a signal is received, and is muted when no signal is present. antinoise microphone-A microphone that discriminates against acoustic noise. A lip or throat microphone is an example. antiphase-Two identical signals disposed in 180" phase opposition. When superimposed, they tend to cancel each other because their waveform patterns are of equal magnitude but opposite polarity. antiproton-An elementary atomic particle that has the same mass as a proton but is negatively charged. antirad-A material that inhibits damage caused by radiation. antiresonance-A type of resonance in which a system offers maximum impedance at its resonant frequency. a n t i r e s o n a n t circuit -A parallel resonant circuit offering maximum impedance to the series passage of the resonant frequency. antiresonant frequency- 1. The frequency at which the impedance of a system is very high. 2. Of a crystal unit, the frequency for a particular mode of vibration at which, neglecting dissipation, the effective impedance of the crystal unit is infinite. antisidetone- 1. In a telephone circuit, special circuits and equipment that are so arranged that only a negligible amount of the power generated in the transmitter reaches the associated receiver. 2. Pertaining to the reduction or elimination of interference in telephone circuits between the microphone and earphone of the same telephone. antisidetone circuit-A telephone circuit that prevents sound, introduced in the local transmitter, from being reproduced in the local receiver. (Reduces sidetones.) antisidetone induction coil -An induction coil designed for use in an antisidetone telephone set. antisidetone telephone set-A telephone set with an antisidetone circuit. antiskating bias-A bias force applied to a pivoted pickup arm to counteract the inward force (toward the center of the record) resulting from the drag of the stylus in the groove and the offset angle of the head. antiskating device-A mechanism found on modern phonograph pickups that provides a small outward force on a pickup arm. This counteracts the arm's tendency to move toward the turntable center (inward) due to offset geometry, and reduces stylus/gmve friction. antistatic agents -Methods employed to minimize static electricity in plastic materials. Such agents are of two basic types. Metallic devices that come into contact with the plastics and conduct the static to earth give complete neutralization initially, but because it is not modified, the surface of the material can become prone to further static accumulation during subsequent handling. Chemical additives, which are mixed with the compound during processing, give a reasonable degree of protection to the finished products. antistatic cleaner -Substance used on phonograph records that helps to prevent the buildup of a static charge that attracts dust. antistatic coating -1. An electrically conductive layer for carrying off static charges that could accumulate on a surface. 2. A conductive coating applied to a TV or monitor screen (or on a glass panel immediately in front of the screen) that conducts away any static charge and prevents dust from adhering to the surface of the television. antistatic s p r a y s -Chemical agents which, when applied to circuits and plastic surfaces, leave a conductive

antistickoff voltage

33 coating that acts to repel dust and dirt and changes surface characteristics. Good antistatic sprays will leave a resistivity reading of 20 to 100 megohms per square inch (3-15 MsZ/cm2) on plastics and 100 megohms or more per square inch on glass surfaces. See static eliminators. antistickoff voltage-A small voltage, usually applied to the rotor winding of the coarse synchro control transformer in a two-speed system. The antistickoff voltage acts to eliminate the possibility of ambiguous behavior in the system. antitransmit-receive box- A second transmitreceive switch used in a radar antenna system to minimize absorption of the echo signal in the transmitter circuit during the interval between transmitted pulses. antitransmit-receive s w i t c h -Abbreviated atr switch. An automatic device employed in a radar system to prevent received energy from being absorbed in the transmitter. antitiransmit-receive tube -See atr tube. antivoice-operated transmission-A method of radiocommunication in which a voice-activated circuit prevents the operation Of the transmitter during reception of messages on an associated receiver. aperiodic- 1. Having no fixed resonant frequency or repetitive characteristics or no tendency to vibrate. A circuit that will not resonate within its tuning range is often called aperiodic. 2. Not characterized by predictable periods or steps. aperiodic antenfla -An antenna designed to have a constant impedance over a wide frequency range (for example, a terminated rhombic antenna) due to the suppression of reflections within the antenna system. aperiodic damping -Also called overdamping. The condition of a system when the amount of damping is so large that when the system is subjected to a single disturbance, either constant or instantaneous, the system comes to a position of rest without passing through that position. Although an aperiodically damped system is not strictly an oscillating system, it has such properties that it would become an oscillating system if the damping were sufficiently reduced. aperiodic function-A function having no repetitive characteristics and not repeatable within a specified period. apericadic waveform -A nonrepeating, random, one-shot waveform. aperture -1. In a unidirectional antenna, that portion of tlhe plane surface which is perpendicular to the direction of maximum radiation and through which the major part of the radiation passes. 2. In an opaque disc, the hole or window placed on either side of a lens to control the amount of light passing through. 3. Also called aperture time. The amount of certainty about the exact time when the encoder input was at the value represented by a given output code. In general, the aperture is equal to the conversion time: it may be reduced by the use of sample-and-hold circuits. 4. In an electron gun, the open.mg that determines the size of, and has an effect on, the shape of the electron beam. In television optics, it is the effective diameter of the lens that controls the amount of light reaching the photoconductive or photoemitting image pickup tube. 5. An opening that will pass light, electrons, or other forms of radiation. aperture antenna-A type of antenna whose beam width is determined by the dimensions of a horn, lens, or reflector. aperture compensation -Reduction of aperture distortion by boosting the high-frequency response of a f elevision-camera video amplifier.

- apogee

aperture correction-Compensation for the loss in sharpness of detail because of the finite dimensions of a scanning beam in the horizontal dimension. aperture delay time-The time elapsed from the application of the hold (or encode) command until the sampling switch in a sample-and-hold circuit opens fully and the device actually takes the sample. Aperture delay time is a fixed delay time and is normally not an error source since the hold clock edge can be advanced to compensate for it. aperture distortion-In a television signal, the distortion due to the finite dimension of the camera-tube scanning beam. The beam covers several mosaic globules simultaneously, resulting in a loss of picture detail. aperture illumination -The field distribution in amplitude and phase through the aperture. aperture jitter- Also called aperture uncertainty time. 1. In a sample-and-hold circuit, the time variation or uncertainty with which the switch opens, or the time variation in aperture delay. 2. A source of error in a sampling system, which determines the maximum slew rate limitation of the sampled analog input signal for a given system resolution. aperture mask-Also called shadow mask. A thin sheet of perforated material placed directly behind the viewing screen in a three-gun color picture tube to prevent the excitation of any one color phosphor by either of the two electron beams not associated with that color.

APERTURE MASK

R

G

BLUE GUN

Aperture mask.

aperture plate-A femte memory plate containing a large number of uniformly spaced holes arranged in parallel rows and interconnected by plated conductors to provide a magnetic memory plate. aperture time- 1. In a sample-and-hold circuit, the averaging time of a sample-hold during the sample-tohold transition. 2. The time required by a sample-and-hold device to go from the sample mode into the hold mode, once the hold command has been received. The aperture time is generally a few nanoseconds, measured from the 50-percent point of the mode-control transition to the time when the output stops tracking the input. See aperture, 3. aperture-time uncertainty -The possible variation in aperture time from one sample-to-hold transition to the next. APL -Abbreviation for average picture level. The average luminance level of the part of a television Line between blanking pulses. APM -Abbreviation for analog panel meter. A scaleand-pointer meter capable of indicating a continuous, rather than incremental, range of values from zero to the rated full-scale value. apogee-The point in an elliptical satellite orbit that is farthest from the surface of the earth. Geosynchronous satellites that maintain circular orbits around the earth are

A positive (A+ or A plus)

-AQL

first launched into highly elliptical orbits with apogees of 22,237 miles. When the communication satellite reaches the appropriate apogee, a rocket motor is fired to place the satellite into its permanent circular orbit of 22,237 miles. Also see perigee. A positive (A+ or A plus)-1. Positive terminal of a battery or positive polarity of any other sources of voltage. 2. The terminal to which the positive side of the filament-voltage source of a vacuum tube should be connected. A power supply-A power supply used as a source of heating current for the cathode or filament of a vacuum tube. apparatus- 1. Any complex device. 2. Equipment or instruments used for a specific purpose. apparatus wire and cable-Insulated wire and cable used in connecting electrical apparatus to a power source, also including wire and cable used in the apparatus itself. apparent bearing-The direction from which the signal arrives with respect to some reference direction. apparent power-In an ac circuit, the power value obtained by simple multiplication of current by voltage with no consideration of the effect of phase angle. (Compare with true power.) apparent power loss -For voltage-measuring instruments, the product of nominal end-scale voltage and the resulting current. For cwrent-measuring instruments, the product of the nominal end-scale current and the resulting voltage. For other types of instruments (for example, wattmeters), the apparent power loss is expressed for a stated value of current or voltage. Also called volt-ampere loss. apparent source-See effective acoustic center. Applegate diagram -A graphical representation of electron bunching in a velocity-modulated tube, showing their positions along the drift space. This bunching is plotted on the vertical coordinate, against time along the horizontal axis. applet-A small computer program that performs a simple task. AppleTal k- A networking protocol developed by Apple Computer for communication between Apple Computer products and other computers. This protocol is independent of what network it is layered on. Appleton layer-In the ionosphere, a region of highly ionized air capable of reflecting or refracting radio waves back to earth. It is made up of the F1 and Fz layers. apple tube-A color-television picture tube in which the three colors of phosphors are laid in fine vertical strips along the screen. The intensity of the electron beam is modulated as its sweeps over them so that each color is produced with appropriate brightness. appliance-Any electrical equipment used in the home and capable of being operated by a nontechnical person. Included are units that perform some task that could be accomplished by other, more difficult means, but usually not those used for entertainment (radios, TVs, hi-fi sets, etc.). appliance wire and cable-A classification of Underwriters’ Laboratories, Inc., covering insulated wire and cable intended for internal wiring of appliances and equipment. Each construction satisfies the requirements for use in particular applications. application- 1. The use of a computer for a specific purpose, e.g., designing a brochure or writing a letter. 2. System or problem to which a computer is applied. An application may be of the computational type, in which arithmetic computations predominate, or of the data-processing type, in which data-handling operations predominate. See also application program.

34 application factor-A modifier of the failure rate. It is based on deviations from rated operating stress (usually temperature and one electrical parameter). application-oriented language -1. A programming language that is primarily useful in some specialized area. 2. A problem-oriented programming language whose statements resemble or contain the terminology of the computer user. application program -1. A computer program intended to solve a problem or do a job, as distinct from systems programs, which control the operations of the computer system. 2. A computer program that performs a data-processing function rather than a control operation. 3. A program used to perform some logical or computational task that is important to the user rather than some internal computer function. 4. Software designed for a specific purpose, such as accounts payable, inventory, payroll, and word processing. 5. A computer program that accomplishes specific tasks, such as word processing. application s c h e m a t i c diagram -Pictorial representation using symbols and lines to illustrate the interrelation of a number of circuits. application-specific integrated circuit -See ASIC. applicationssoftware- 1. Aprogramthatdepends on the specific end application and is used to do the real work or apparent work that is visible to the user. Generally this is the software that is used for dedicated computer-based systems (systems designed to perform a single or specific set of functions). Typical applications include food and chemical processing, production control, automotive electronics, computer-controlled sewing machines, photographic equipment (both for computercontrolled cameras and for darkroom computerized processing), energy distribution systems, word processing, mailing lists, payrolls, and inventory. 2. Computer programs that perform specific tasks, such as word processing or database management. applicators (applicator electrodes) -1. In dielectric heating, the electrodes between which the dielectric item is placed and the electrostatic field developed. 2. Appropriately shaped conducting surfaces between which an alternating electric field is established for the purpose of producing dielectric heating. 3. In medical electronics, the electrodes applied to a patient undergoing diathermy or ultrasonic therapy. applied voltage -1. The potential between a terminal and a reference point in any circuit or device. 2. The voltage obtained when measuring between two given points in a circuit with voltage applied to the complete circuit. 3. The voltage presented to a circuit point or system input, as opposed to the voltage drop resulting from current through an element that results from the applied voltage. applique circuit-A special circuit provided to modify existing equipment in order to allow for some special usage. approach-control radar- Any radar set or system used in a ground-controlled approach system, e.g., an airport-surveillance radar, precision approach radar, etc. a p p r o a c h path-In radio aircraft navigation, that portion of the flight path in the immediate vicinity of a landing area where such a flight path terminates at the touchdown point. approved circuit-See protected wireline distribution system. APT -Abbreviation for automatically programmed tool. A high-level or simplified programming language. AQL- Abbreviation for acceptable quality level. A statistically defined quality level, in terms of percent defective accepted on an average of 95 percent of the

aquadag layer

35 time. In other words, a sampling plan with 1 percent AQL passes (accepts) lots 1 percent defective 95 percent of the time. aquadag layer -Trademark of Acheson Industries, Inc. A conductive graphite coating on the inner side walls of some cathode-ray tubes. It serves as an electrostatic shield or as a postdeflection and an accelerating anode. Also applied to outer walls and grounded here it serves, with the inner coating, as a capacitor to filter the applied high vol.tage.

Aquadag coating.

arbiter- The section of a multiprocessor network’s operating system that resolves simultaneous systemresource requests. arbitrary function fitter-A circuit having an output voltage or current that is a presettable, adjustable, usually nonlinear function of the input voltage(s) or current@) fed to it. arbitrary waveform generator-See waveform generator. arbor-See mandrel. arc- 1. A luminous discharge of electricity through a gas. Characterized by a change in space potential in the immediate vicinity of the cathode; this change is approximately equal to the ionization potential of the gas. 2. A prolonged electrical discharge, or series of prolonged discharges, between two electrodes. (Both produce a bright-colored flame, as contrasted with a dim coronaglow discharge). 3. To form an arc. 4. The electric current in a flamelike stream of incandescent gas particles. 5. An electric current through air or across the surface of an insulator associated with high voltage; usually occurs when a contact is opened, or when deenergizing an inductive load. arcback-Also called backfue. Failure of the rectifying action in a tube, resulting from the flow of a principal electron stream in the reverse direction due to the formation of a cathode spot on the anode. This action limits the peak inverse voltage that may be applied to a particular rectifier tube. arc converter-A form of oscillator utilizing an electric arc to generate an alternating or pulsating current. arc discharge- 1. A discharge between electrodes in gas or vapor. Characterized by a relatively low voltage drop and a high current density. 2. The sustained, luminous thermionic discharge between anode and cathode in a gas-filled tube. arc-discharge tube -A gas-filled or mercuryvapor tube that utilizes ionic phenomena for switching, voltage regulation, or rectification. arc drop -The voltage drop between the anode and cathode of a gas rectifier tube during conduction. aredrop loss-In a gas tube, the product of the instantaneous values of arc-drop voltage and current averaged over a complete cycle of operation. arc-drop voltage -The voltage drop between the anode and cathode of a gas rectifier tube during conduction.

- arc-through

arc failure -1. A flashover in the air near an insulation surface. 2. An electrical failure in the surface heated by a flashover arc. 3. An electrical failure in the surface damaged by the flashover arc. arc function -An inverse trigonometric function. arc furnace-An electric furnace heated by arcs between two or more electrodes. architecture- 1. Organizational structure of a computing system, mainly referring to the CPU or microprocessor. 2. The manner in which the basic computer functions are organized and partitioned on the silicon chips. 3. The manner in which a system (such as a network or a computer) or program is structured. archival -Pertaining to long-term storage of data. archival backup-Backing up only files that have been changed since the last backup. archive -1. A procedure for transfemng information from an online storage diskette or memory area to an offline storage medium. 2. To copy computer programs and data onto an auxiliary storage medium, such as a disk or tape, for long-term retention. arcing -The production of an arc, e.g., at the brushes of a motor or ai the contact of a switch. arcing contacts-Special contacts on which the arc is drawn after the main contacts of a switch or circuit breaker have opened. arcing time- 1. The interval between the parting, in a switch or circuit breaker, of the arcing contacts and the extension of the arc. 2. The time elapsing, in a fuse, from the severance of the fuse link to the final intemption of the circuit under the specified condition. arc lamp -Source of brilliant artificial light obtained by an electric arc passing between two carbon rods. The arc is struck by bringing the two rods together and then rapidly separating them. As the arc bums, the carbon rods are vaporized away. A mechanism is employed to keep the space between the two rods constant. This type of lamp is used extensively in motion picture projectors and spotlights. The illuminaticm of the arc lamp is derived from the incandescence of the positive electrode and from the heated, luminous, ionized gases or vapor that surround the arc. arc oscillator-A negative-resistanceoscillator comprising a sustained dc arc and a resonant circuit. arcover-The (usually abrupt) creation of an arc between electrodes, contacts, or plates of a capacitor. arcover resistance-The resistance of a material to the effects of a high-voltage, low-current arc (under prescribed conditions) passing across the surface of the material. The resistance is stated as a measure of total elapsed time required to form a conductive path on the surface (material carbonized by the arc). arcover voltage -Under specified conditions, the minimum voltage required to create. an arc between electrodes separated by a gas or liquid insulation. arc percussive welding-A type of welding in which the materials to be welded are separated by a gap, across which an arc is struck the arc melts the sm-aces of the materials, and the materials are simultaneously brought together. See also pulse arc welding. arc resistance-The length of time that a material can resist the formation of a conductive path by an arc adjacent to the surface of the materid. Also called tracking resistance. arc suppressor-A device, or combination of devices, used for arc suppression. See spark suppressor. arc-through-In a gas tube, a loss of control with the result that a principal electron stream flows in the normal direction during what should be a nonconducting period.

area code - armor area code-A three-digit number code identifying one of the geographic areas of the United States, Canada, and Mexico to permit direct distance dialing on the telephone system. The area code precedes the central office code in the complete 10-digit telephone number, and must be used when the called telephone is in a numbering plan area different from that of the calling telephone. The first digit of the area code is never a 1 or 0. See also direct distance dialing. area protection-Protection of the inner space or volume of a secured area by means of a volumetric sensor. area redistribution-A method of measuring the duration of irregularly shaped pulses. A rectangle is drawn having the same peak amplitude and the same area as the original pulse under consideration. Because the same time units are used in measuring the original and the new pulse, the width of the rectangle is considered the duration of the pulse. area s e n s o r - A sensor with a detection zone that approximates an area, such as a wall surface or the exterior of a safe. A register-The accumulator for all arithmetical operations in a computer. Also called A accumulator. argon-An inert gas used in discharge tubes and some electric lamps. It gives off a purple glow when ionized; its symbol is Ar. argon glow lamp-A glow lamp containing argon gas that produces a pale blue violet light. argument-1. A variable upon which the value of a function depends. The arguments of a function are listed in parentheses after the function name. The computations specified by the function definition are made with the variables specified as arguments. 2. The number that a function works on to produce its results. 3. The independent variable of a function. Arguments can be passed as part of a subroutine call where they would be used in that subroutine. arithmetic and logic unit -Computer element that can perform the basic data manipulations in the central processor. Usually it can add, subtract, complement, negate, rotate, AND, and OR. Abbreviated ALU. arithmetic capability-The ability to do addition, subtraction, and in some cases multiplication and division. arithmetic check-A check of a computation making use of the arithmetical properties of the computation. arithmetic element -Synonym for arithmetic unit. arithmetic mean -1. Usually, the same as average. It is obtained by first adding quantities together and then dividing by the number of quantities involved. 2. A figure midway between two extremes and is found by adding the minimum and maximum together and dividing by two. arithmetic operation-1. In an electronic computer, the operations in which numerical quantities form the elements of the calculation, including the fundamental operations of arithmetic (addition, subtraction, multiplication, comparison, and division). 2. Adding, subtracting, incrementing, or decrementing data in registers or memOrY.

arithmetic organ -See arithmetic unit. arithmetic shift-In a digital computer, the multiplication or division of a quantity by a power of the base used in the notation. arithmetic statement - 1. An expression and a variable separated by an equals sign. The expression is evaluated and the resulting value is assigned to the variable. 2. Instruction specifying an arithmetic operation. arithmetic s u m -The sum of two or more quantities regardless of their signs. Compare with algebraic sum. arithmetic s y m m e t r y -Filter response showing mirror-image symmetry about the center frequency when frequency is displayed on an arithmetic scale. Constant

36 envelope delay in bandpass filters usually is accompanied by arithmetic symmetry in the phase and amplitude responses and generally requires a computer design. See also geometric symmetry. arithmetic unit- Also called arithmetic element or arithmetic organ. In an automatic digital computer, that portion in which arithmetical and logical operations are performed on elements of information. armature-The moving element in an electromechanical device, such as the rotating part of a generator or motor, the movable part of a relay, or the spring-mounted, iron portion of a bell or buzzer. armature contacts- 1. Contacts mounted directly on the armature. 2. Sometimes used for movable contacts. armature control of speed-The varying of voltage applied to the armature of a shunt-wound motor to control the motor’s speed over the basic speed range. armature core -An assembly of laminations forming the magnetic circuit of an armature. armature gap-The space between the armature and pole face. armature hesitation-A delay or momentary reversal of the motion of the armature. armature-hesitation contact chatter-Chatter caused by delay or momentary reversal in direction of the armature motion of a relay during either the operate or the release stroke. armature-impact contact chatter-Chatter caused by impact of the armature of a relay on the pole piece in operation, or on the backstop in release. armature overtravel -That portion of the available stroke occurring after the contacts of a relay have touched. armature reaction-In an armature, the reaction of the magnetic field produced by the current on the magnetic lines of force produced by the field coil of an electric motor or generator. armature rebound-Return motion of a relay armature after striking the backstop. armature-rebound contact chatter-Chatter caused by the partial return of the armature of a relay to its operated position as a result of rebound from the backstop in release. armature relay-A relay operated by an electromagnet that, when energized, causes an armature to be attracted to a fixed pole or poles. armature slot-In the core of an armature, a slot or groove into which the coils or windings are placed. armature stud-In a relay, an insulating member that transmits the motion of the armature to an adjacent contact member. armature travel -The distance traveled during operation by a specified point on the armature of a relay. a r m a t u r e voltage control-A means of controlling the speed of a motor by changing the voltage applied to its armature windings. armature wire -Stranded annealed copper wire, straight lay, soft loose white cotton braid. It is used for low-voltage, high-current rotor winding motors and generators. Straight lay permits forming in armature slots, and compressibility. a r m c h a i r copy- Amateur term for clear, static-free signals. armed sweep -See single sweep. arming t h e oscilloscope sweep -Closing a switch that enables the oscilloscope to trigger on the next pulse. armor -A braid or wrapping of metal, usually steel, placed over the insulation of wire or cable to protect it from abrasion or crushing.

armor clamp - artificial intelligence

37

armor clamp-A fitting for gripping the armor of a cable at the point where the armor terminates or where the cable enters a junction box. armored cable-Two or more insulated wires collectively provided with a metallic covering, primarily to protect the insulated wires from damage. Armstrong frequency-modulation s y s t e m -A phase-shift modulation system originally proposed by E. H. Armstrong. Armstrong oscillator- An inductive feedback oscillator that consists of a tuned gate circuit and an untuned tickler coil in the drain circuit. Feedback is controlled by varying the coupling between the tickler and the gate circuit.

TICKLER

5-25V

Amstrong oscillator.

arr-- See automatic repeat request. array- 1. In an antenna, a group of elements arranged to provide the desired directional characteristics. These elements may be antennas, reflectors, directors, etc. 2. A series of items, not necessarily arranged in a meaningful pattern. 3. The group of patterns on a wafer or in the artwork or photomask for semiconductor processing. See random-access memory. a r r a y antenna -An antenna comprising a number of radiating elements, generally similar, arranged and excited to obtain directional effects. a r r a y device -A group of many similar, basic, complex, or integrated devices without separate enclosures. Each has at least one of its electrodes connected to a common conductor, or all are connected in series. array noise -Unwanted disturbance in a memory integrated circuit generated by the normal movement of data within the array. a r r a y processor-1. A computer optimized in architecture and instruction set to handle programs involving computations on large batches of data, such as fast Fourier transforms and large matrix computations. An array processor takes blocks of data and instructions from a host mini or large computer and performs the computations at speeds many times as high as those that are possible through the host computer alone. The host may be considered the data-organizing front end; the array processor is the processing unit. 2. A computer dedicated by its design to performing repetitive arithmetical calculations on large arrays of data with high precision, wide dynamic range, and high throughput. Usually most input/output operations and file management chores are left to the host computer in order to free the peripheral array processor to concentrate on its calculations. 3. A single computer that operates on one piece of data at a time. 4. A processor in a computer that performs matrix arithmetic much faster than is clone in a standard computer. Capable of performing operations on ail the elements in large matrices at one time. Also called a vector processor.

arrester-Also called a lightning arrester. I. A protective device used to provide a bypass path directly to ground for lightning discharges that strike an antenna or other conductor. 2. A power-line device capable of reducing the voltage of a surge applied to its termnals, interrupting current, if present, and restoring itself to original operating conditions. 3. Device that diverts high voltages to ground and away from the equipment it protects. ARRL -Abbreviation for American Radio Relay League. a r r o w h e a d -A linearly polarized, frequency-independent, log-periodic antenna. ARSR -Abbreviation for air route surveillance radar. ARTCC -Abbreviation for air route traffic control center. A complex data-handling facility designed by Burroughs, IBM, and Raytheon to computerize as much in-route air traffic control as possible. articulation-Sometimes called intelligibility. 1. In a communications system, the percentage of speech units understood by a listener. The word articulation is customarily used when the contextual relationships among the units of speech material are thought to play an unimportant role; the word intelligibility is used when the context is thought to play an important role in determining the listener’s perception. 2. A quantitative measurement of the intelligibility of human speech. where 100 percent is completely understandable. For the typical sound reinforcement or other communications system, no more than a 15-percent articulation loss is acceptable. 3. The ability of a mechanism to pivot, grasp, or extend. articulation equivalent-The articulation of speech reproduced over a complete telephone connection, expressed numerically in terms of the trunk loss of a working reference system that is adjusted to give equal articulation. artificial antenna-Also called dummy antenna. A device that simulates a real antenna in its essential stics and has the necessary power, but which does not radiate or receive radio waves. Used mainly for testing and adjusting transmitters. artificial ear -A microphone-equipped device for measuring the sound pressures developed by an earphone. To the earphone it presents an acoustic impedance equivalent to the impedance presented by the human ear. artificial echo- 1. Received reflections of a transmitted pulse from an artificial target, such as an echo box, comer reflector, or other metallic reflecting surface. 2. A delayed signal from a pulsed radio-frequency signal generator. artificial horizon - A gyroscopically operated instrument that shows, within limited degrees, the pitching and banking of an aircraft with respect to the horizon. Lines or marks on the face of the instrument represent the aircraft and the horizon. The relative positions of the two are then easily discernible. artificial intelligence- Abbreviated AI 1. The design of computer and other data-processing machinery to perform increasingly higher-level cybernetic functions. 2. The capability of a device to perform functions that are normally associated with human intelligence, such as reasoning, learning, and self-improvement. Related to machine learning. 3. The imitation by artificial systems of characteristics described as intelligent when observed in humans. Artificial intelligence embraces concepts and theories from many different disciplines, including mathematics, cybernetics, computer science, psychology, biology, and others. 4. Overlapping subsets called expert systems, knowledge representations, inference schemes, program synthesis, scene analysis, and robotics. 5. The ability of a machine to perform certain complex functions

artificial ionization

- aspect ratio

normally associated with human intelligence, such as judgment, pattern recognition, understanding, learning, planning, and problem solving. 6. Computer programs developed to mimic human intelligence, such as reasoning, learning, problem solving, and making decisions. Artificial intelligence programs enable computers to perform tasks such as playing chess, proving mathematical theorems, etc. 7. An area of computer science dedicated to the development of machines that can learn, understand, interpret, and arrive at conclusions in a manner that would be considered intelligent if a person were doing it. artificial ionization -Introduction of an artificial reflecting or scattering layer into the atmosphere to permit beyond-the-horizon communications. artificial language-In computer terminology, a language designed for ease of communication in a particular area of activity, but one that is not yet natural to that area (as contrasted with a natural language evolved through long usage). artificial line-A lumped-constant network designed to simulate some or all the characteristics of a transmission line over a desired frequency range. artificial line duct- A balancing network simulating the impedance of the real line and distant terminal apparatus. It is employed in a duplex circuit to make the receiving device unresponsive to outgoing signal currents. artificial load-Also called dummy load. A dissipative but essentially nonradiating device having the impedance characteristics of an antenna, transmission line, or other practical utilization circuit. Energy is dissipated in the form of heat. Used to test radio transmitters, engine generators, etc. Permits testing under load conditions without the creation of any standing waves or radiating a signal. artificial radioactivity-Radioactivity induced in stable elements under controlled conditions by bombarding them with neutrons or high-energy, charged particles. Artificially radioactive elements emit beta and/or gamma rays. artificial voice-A small speaker mounted in a specially shaped baffle that is proportioned to simulate the acoustical constants of the human head. It is used for calibrating and testing close-talking microphones. Artos stripper-A machine that, when properly adjusted, will automatically measure to a predetermined length, cut, strip, count, and tie wire in bundles. ARTS -Abbreviation for Automated Radar Terminal System. A multiprocessor computing system used at terminal radar approach controls (tracons) and airport towers, based on Speny Univac 1140 computers. Various configurations, differing in size of memory and number of processors, exist at different facilities; the largest, ARTS IIIE, is installed at the New York tracon. artwork- 1. A topological pattern of an integrated circuit, made with accurate dimensions so that it can be used in mask making. Generally, it is a large multiple of the final mask size, and final reduction is accomplished through the use of a step-and-repeat camera. 2. Detailed, original drawing (often developed with the aid of a computer) showing layout of an integrated circuit. 3. The images formed by drawing, scribing, or by cutting and stripping on a film or glass support, which are reduced, contact-printed, or stepped and repeated to make a photomask or intermediate. 4. Layouts and photographic films created to produce thick-film screens and thin-film masks. ASA- Abbreviation for American Standards Association. See American National Standards Institute. ASA code-A code that was recommended by the American Standards Association for industry-wide use in the transmission of information. Now ANSI code.

38

asbestos -A nonflammable material generally used for heat insulation, such as in a line-cord resistor. No longer used on new equipment. A-scan -Also called A-display. On a cathode-ray indicator, a presentation in which time (range or distance) is one coordinate (horizontal) and signals appear as perpendicular deflections to the time scale (vertical).

PULSE Y

a P

-

RECEIVER NOISE (GRASS)

RANGE

A-scan on a CRT.

ASCII-Acronym for American Standard Code for Information Interchange (pronounced “ask-ee”). 1. A standard code used extensively in data transmission, in which 128 numerals, letters, symbols, and special control codes are each represented by a seven-bit binary number 0000000 through 1111111. For example, numeral 5 is represented by 011 0101, letter K by 100 1011, percent symbol (%)by 010 0101, and start of text (STX) control code by 000 0010.2. A standard code used by many computers, video-display terminals, teleprinters, and computer peripherals. A full eight-bit ASCII word may be transmitted in parallel or serial form, with the eighth bit often providing parity information. Keyboard encoders convert a single switch closure into an ASCII data word; character generators convert stored ASCII data words (and some timing commands) into groups of dots suitable for raster-scan display. A-scope-An oscilloscope that uses an A-scan to present the range of a target as the distance along a horizontal line from the transmitted pulse pip to the target, or echo pip. Signals appear as vertical excursions of the horizontal line, or trace. ASDE-See airport surface detection equipment. as-fired -Values of thick-film resistors or smoothness of ceramic substrates as they come out of the firing furnace prior to trimming and polishing, respectively (if required). AS1 -An abbreviation for standards published by the American Standards Institute. Now American National Standards Institute. ASIC -Abbreviation for application-specific integrated circuit. l. Semiconductor circuits specifically designed to suit a customer’s particular requirement, as opposed to general-purpose parts that can be used in many different systems or applications. 2. An integrated circuit designed to fill the specific requirement of a unique application. ask-See amplitude-shift keying. aspect ratio -1. Ratio of frame width to frame height. 2. The ratio of an object’s height to its width. In graphics this ratio usually pertains to the face of a rectangular CRT or to the characters or symbols drawn by the character generator. 3. The ratio between the length of a film resistor and its width: equal to the number of squares of the resistor. 4. The ratio of the width of a

39 television picture tube to its height. In the United States, the television standard is 4 :3. asplerities-Local microscopic points on an electrode surface at which there is considerable field enhancement. They lead to a dependence of electric strength on electrode area (area effect). aspheric- 1. Not spherical; an optical element having onle or more surfaces that are not spherical. 2. A mirror or lens surface that varies slightly from a true spherical surface. This is done to reduce lens aberrations. ASFl -Abbreviation for automatic send and receive and airport surveillance radar. 1. A terminal equipped with recording devices, usually a paper-tape reader and punch, which is capable of answering a call, recording a message, or sending data loaded in its tape reader without the need for an operator in attendance at the time of the call. Also used to specify terminals that have paper-type equipment used by the operator. 2. A teletypewriter that contains a keyboard, page printer. paper-tape transmitter, and paper-tape punch. Paper tape can be prepared offline, which can take place while hard copy is being received from the line or while other paper tape is being transmitted. -Abbreviation for automatic stereophonic recordiing amplifier. An instrument developed by Columbia Broadcasting System for stereo recording. Compression of the vertical component of the stereo recording signal is automatically decreased or increased as required by the recording conditions. assemble -1. To collect, interpret, and coordinate the data required for a computer program, translate the data into computer language, and project it into the master routine for the computer to follow. 2. To translate from a symbolic program to a binary program by substituting bmary. loperation codes for symbolic operation codes and replacing symbolic addresses with absolute or relocatable addresses. assembler- 1. A program that prepares a program in machine language from a program in symbolic language by substituting absolute operation codes for symbolic operation codes and absolute or relocatable addresses for symbolic addresses. 2. A unit that converts the assembly language of a computer program into the machin(:: language of the computer, accepting mnemonics and symbolic addresses instead of actual binary values for addresses, instructions, and data. 3. A program that accepts instructions, addresses, and data in symbolic form (character stsings that represent machine instructions, addresses, data, among others). Then it automatically translates symbols into their corresponding numerical values. It permits symbolic addressing by assigning values to labels used to indicate program-jump locations. 4. A simple programming language that allows the programmer to define labels and fixed values and to then use these labels with a mnemonic instruction set to produce a machine code program. 5. Program that converts sourcecode (mnemonic) input into op-code (binary) machine language instructions. If such a program were not available, the programmer would have to enter all instructions in ones and zeros, a much more tedious and error-prone procedure. 6. A computer program that converts a higherlevel (Englishlike) programming language into machinereadable instructions. assembler program -Software, usually supplied by the computer manufacturer, to convert an assembly language application program into machine language. assembly- 1. A complete operating unit, such as a radio receiver, made up of subassemblies, such as an amplifier and various components. 2. Process in which instruchons written in symbolic form by the programmer are changed to machine language by (he computer.

assembly language- 1. A computer language that has one-to-one correspondence with an assembly program. The assembly program directs a computer to operate on a program in symbolic language to produce a program in machine language. See also high-order language; machine language, 3; and source language. 2. Grouped alphabet characters, called mnemonics, that replace the numeric instructions of machine language. These mnemonics are easier to remember than machine instructions and hence easier to develop into a working program. 3. A machine-oriented language based primarily on a one-to-one relationship between machine instructions and user-supplied source code. 4. Microprocessor commands written in mnemonic form. Typically, threeletter abbreviations, called mnemonics, are used to represent each instruction, and each mnemonic can usually be equated to one machine-code instruction. 5 . A humanoriented symbolic-mnemonic source language that is used by the programmer to encode programs and associated databases. Assembly language programs are read by the assembler and converted to executable machine language programs during the assembly process. Assembly language is easier to remember and manipulate than machine language. 6. Human-oriented varieties of machine languages. Precisely the same final program code can be produced from an assembler as by hand-coding machine language. However, assembly languages prove more convenient for people than the numeric-only machine languages. assembly-language p r o ~ r a ~ m ~ n bolic-language programming. assembly-output language-An optionai symbolic assembly language listing of the object-code output from a high-level language compiler. Can be quite helpful as a debugging tool because it shows exact machine code in a readable format. assembly program-A program that enables a computer to assemble mnemonic language into machine language; for example, a FORTRAN assembly program. Also called assembly routine. a s s e m b l y robot -A computerized robot, probably a sensory model, designed specifically for assemblyline jobs. For light, batch-manufacturing applications, the arm’s design may be fairly anthropomorphic. assembly routine -See assembly program. assertion checking -Evaluating a program by embedding statements that should always hold true. assignable cause -A definitely identified factor contributing to a quality variation. assigned frequency-The center of the frequency band assigned to a station. assigned f r e q u e n c y band -The frequency band, the center of which coincides with the frequency assigned to the station, and the width of which equals the necessary bandwidth plus twice the absolute value of the frequency tolerance. associative memory-A computer memory in which the data are stored and indexed by content, as in a dictionary, in contrast with the storage of a random-access memory. 2. A memory in which the storage locations are identified by their contents rather than by their addresses. Enables faster interrogation to retrieve a particular data element. associative storage -Computer storage in which locations may be identified by specification of part or all of their contents. Also called parallel-search storage or content-addressed storage. astable- 1. Pertaining to a device that has two temporary states: the device alternates between these states with a period and duty cycle determined by circuit time constants. See also bistable. 2. Refers to a device that

astable circuit

- a s y n c h r o n o u s communication

has two temporary states. The device oscillates between the two states with a period and duty cycle predetermined by time constants. astable circuit -A circuit that continuously alternates between its two unstable states at a frequency determined by the circuit constants. It can be readily synchronized by applying a repetitive input signal of slightly higher frequency. A blocking oscillator is an example of an astable circuit. astable multivibrator (free-running) -A circuit having two momentarily stable states, between which it continuously alternates, remaining in each for a period controlled by the circuit parameters and switching rapidly from one to the other.

A I IN SECONOS.A

IN OHMS c IN FARADS&

Circuit

output.

Astable multivibrator.

astatic- 1. Having no particular orientation or directional characteristics; such as a vertical antenna. 2. Being in neutral equilibrium; having no tendency toward any change of position. astatic galvanometer -A sensitive galvanometer used for detecting small currents. Consists of two small magnetized needles of equal size and strength arranged in parallel and with their north and south poles adjacent, suspended inside the galvanometer coil. Since the resultant magnetic moment is zero, the earth’s magnetic field does not affect the system. A station-One of a pair of transmitting stations in a loran system. The A-station signal always occurs less than half a repetition period after the immediately preceding signal of the other station of the pair and more than half a repetition period before the next succeeding signal of the other station. astigmatism-A type of spherical aberration in which the rays from a single point of an object do not converge on the image, thereby causing a blurred image. Astigmatism in an electron-beam tube is a focus defect in which electrons in different axial planes come to focus at different points. astrionics -Electronics as involved with astronautics.

40

astrocompass -An instrument for determining direction relative to the stars. It is unaffected by the errors to which magnetic or gyrocompasses are subject. astrodome -A rigid hemispherical structure used to cover large tracking instruments to protect them from the elements. It is usually constructed so that the dome rotates with the instrument. astronautics-The science and art of operating space vehicles. astrotracker-A device for tracking stars. A-supply -The A battery, transformer filament winding, or other voltage source that supplies power for heating the filaments of vacuum tubes. a s y c h r o n o u s motor- An ac motor whose speed is not proportional to the frequency of the supply voltage. asymmetrical cell-A cell, such as a photoelectric cell, in which the impedance to the flow of current is greater in one direction than in the other direction. asymmetrical distortion -Distortion affecting a two-condition or binary modulation or restitution, in which all the significant intervals corresponding to one of the two significant conditions have longer or shorter durations than the corresponding theoretical dnrations of the excitation. If this particular requirement is not met, distortion is present. asymmetrical SCR -A fast silicon-controlled rectifier (SCR) with low reverse blocking, which is voltage that causes conduction without an input trigger at the gate input of the SCR. a s y m m e t r i c sideband transmission -See vestigial sideband transmission. a s y m m e t r y control -In pH meters, an adjustment sometimes provided to compensate for differences in the electrodes. asymptote -A line that comes nearer and nearer to a given curve but never touches it. asymptotic breakdown voltage-A voltage that will break down insulation if applied over a long period. a s y n c h r o n o u s - 1. A communication method in which data is sent when it is ready without being referenced to a timing clock, rather than waiting until the receiver signals that it is ready to receive. 2. Transmission in which each data byte is preceded by a start bit and followed by one or more stop bits. Data transmission is intermittent, with an irregular time interval between data bytes. 3. Lacking a regular time relationship; not related through repeating time patterns. Hence, as applied to computer program execution, unexpected or unpredictable with respect to the instruction sequence. 4. Modems, terminals, and transmissions in which each character of information is individually framed (synchronized), usually by start and stop elements. The interval between characters is not fixed. 5. An external interface that can be started and stopped by a microprocessor or other equipment. The opposite is synchronous, which means that the data is randomly available. 6. Having no set pattern, cycle, or speed of transmission. 7. Not synchronized by a clocking signal; in code sets, character codes containing start and stop bits. 8. A mode of data transmission in which time intervals between transmitted characters may be of unequal length. Transmission is independently controlled by start and stop elements at the beginning and end of each character. 9. Pertaining to a mode of data communications that provides a variable time interval between characters during transmission. a s y n c h r o n o u s communication -1. A method of transferring data in which the timing of character placement on connecting communication lines is not critical. Each transferred character is preceded by a start bit and followed by a stop bit, permitting the interval between characters to vary. 2. A relatively simple and

41 cheap system for moving data between machines at speeds up to 1200 or 2400 baud. 3. Data communication of the s t d s t o p type. Each character is sent individually without regular or predictable time relationships with other characters. 4. Method of communications in which data is sent as soon as it is ready. asynchronous computer - 1. An automatic digital computer in which an operation is started by a signal denoting that the previous operation has been completed. 2. A computer in which each operation starts as a result of a signal generated by the completion of the previous operation or by the availability of the equipment required for the next operation. asynchronous device-A device in which the speed of operation is not related to any frequency in the system to which it is connected. asynchronous input/output -The ability to accept input data while simultaneously delivering output data. asynchronous inputs-The terminals that affect the output state of a flip-flop independently of the clock terminads. Called set, preset, reset, or clear; sometimes referred to as dc inputs. asynchronous logic-Logic networks whose operational speed depends only on the signal propagation through the network, rather than on clock pulses as in synchronous logic. asyiichronousmachine- 1. Any machineinwhich its speed of operation is not proportionate to the frequency of the system to which the machine is connected. 2. A multiprocessor system whose processes occur as needed by, and whose operations follow, input data instead of an autonomous clock. asynchronous operation-1. Generally, an operation that is started by a signal at the completion of a previous operation. It proceeds at the maximum speed of the (circuits until it is finished and then generates its own completion signal. 2. A mode in which entry of data into a flip-flop does not require a gating or clock pulse. 3. Operation of a switching network by a free-running signal that triggers successive instructions. The completion of one instruction triggers the next. 4. A computer operation that does not proceed in step with some external timing. ~ s y r ~ ~ h r o n shift o u s register-A shift register that does not require a clock. Register segments are loaded and shifted only at data entry. asyrichronous transmission -Transmission in which each character of the information is synchronized individually (usually by the use of start and stop elements). ATARS -Acronym for Automated Traffic Advisory and Resolution Service. A ground-based automatic collision-avoidance system being developed for use at air terminals. TC - I. Abbreviation for automatic temperature control (General Motors). A means of automatically maintaining desired passenger compartment temperature in a vehicle. Temperature is sensed by a thermistor. Control valves are actuated by a vacuum motor to adjust the proportion of heated or cooled air. 2. Also abbreviation for automated technical control. A computer system used to n control of a data-communication network. - which has an opposite charge. electrostatic component -The portion of radiation due to electrostatic fields. electrostatic-convergenceprinciple -The principle of electron-beam convergence through use of an electrostatic field. electrostatic copier -A type of copier that employs the principles of photoconductivity and electrostatic attraction. electrostatic coupling -Method of coupling by which charges on one surface influence those on another through capacitive action.

BASE

HEATER

CATHODE

GRID

FOCUSING

ACCELERATING

ANODE

PLATES

- electrostatic latent image

electrostatic deflection- 1. In a cathode-ray tube, the deflection of the electron beam by means of pairs of charged electrodes on opposite sides of the beam. The electron beam is bent toward a positive electrode and bent away from a negative electrode. 2. The deflection of an electron beam by the action of an electrostatic field that has a component perpendicular to the direction of the beam. elecrostatic discharge -See ESD. electrostatic electrography-That branch of electrostatography which produces a visible record by employing an insulating medium to form latent electrostatic images with the aid of electromagnetic radiation. electrostatic electrophotography- That branch of electrostatography which produces a visible record by employing a photoresponsive medium to form latent electrostatic images with the aid of electromagnetic radiation. electrostatic energy -The energy contained in electricity at rest, such as in the charge of a capacitor. electrostatic field-The vector force field set up in the vicinity of nonmoving electrical charges. The strength of this static field at a point is defined as the force per unit charge on a stationary positive test charge. provided the test charge is so small that it does not disturb the original charge distribution. electrostatic flux- The electrostatic lines of force existing between bodies at different potentials. electrostatic focusing- 1. The focusing of an electron beam by the action of an electric field. 2. A method of focusing the cathode-ray beam to a fine spot by application of electrostatic potentials to one or more elements of an electron lens system. electrostatic galvanometer -Galvanometer operated by the effects of two electric charges on each other. electrostatic generator-A device for the production of electric charges by electrostatic action. electrostatic headphones- A device held against the ear that reproduces incoming electrical signals as sound. It relies on changes in electrical charge across a diaphragm stretched between two perforated, polarized plates. All parts of the diaphragm experience equal force, and the sound is inherently more linear. electrostatic induction - 1. The process of inducing stationary electric charges on an object by bringing it near another object that has an excess of electric charges. A positive charge will induce a negative charge, and vice versa. 2. Capacitive induction of interfering signals over an air gap separating an instrument (e.g., from its wiring or housing). electrostatic instrument --An instrument that depends for its operation on the attraction and repulsion between electrically charged bodies. electrostatic latent image-In an electrostatic copier, the invisible image formed on the zinc-oxidecoated paper by the action of light.

HORIZONTAL

BEAM

Electrostatic deflection.

AOUADAG

ENVELOPE

SCREEN

electrostatic lens - e l e c t r o s t a t o g r a p h y electrostatic lens -A lens producing a potential field capable of deflecting electron rays to form an image of an object. electrostatic loudspeaker-Loudspeaker in which the mechanical forces are produced by the action of electrostatic fields. electrostatic memory- Also called electrostatic storage. A memory device in which information is retained by an electrostatic charge. A special type of cathode-ray tube is usually employed, together with associated circuitry. electrostatic m e m o r y tube- Also called storage tube. An electron tube in which information is retained by electric charges. electrostatic meter-A meter with a movement consisting of fixed and movable metal plates interleaved to form a capacitor. Rotation of the movable plates is proportional to the dc or ac voltage applied across the capacitor. electrostatic m i c r o p h o n e -Also called capacitor microphone or condenser microphone. 1. A microphone that contains a metal plate and a thin metal diaphragm set close together. The capacitance of the microphone is thus affected by movement of the diaphragm from air pressure waves. A polarizing voltage is applied to the plates. 2. A microphone whose transduction principle is based on the varying electrical charge across a sound-modulated capacitor. 3. A microphone whose capacitance varies with sound pressure; electronic circuits within the microphone convert this change in capacitance to a varying voltage signal. Electrostatic microphones, unlike other types, require a battery or other voltage source. 4. A type of microphone characterized by its wide frequency range and low distortion. Used for precision measurements and highquality recording. Can be omnidirectional or cardioid. electrostatic potential-The voltage that can be measured between any two objects that have different static charges. electrostatic precipitation -The process of removing smoke, dust, and other particles from the air by charging them so that they can be attracted to and collected by a properly polarized electrode. electrostatic printer- 1. A nonimpact printing technique that forms a copy by attracting toner particles to a static charge on the surface of a photoconductor, then transferring the toner image to the surface of a sheet of copy paper. The image is formed by a laser that develops an electrostatic image charge on the photoconductor according to information being supplied through the input data stream. Each bit of data can be related to a character shape in the memory of the printing system; in most cases, characters are formed by a dot-matrix method similar in concept to that of the matrix printer. Paper is sheet or roll fed. 2. A nonimpact printer that prints dot-matrix characters one at a time by means of wires or pins that supply an electrical charge in the desired patterns onto an aluminum-coated paper; particles of dry ink adhere to the magnetized areas and are then fixed by heat. electrostatic process- 1. A reproduction method in which image formation depends on electrical rather than chemical changes induced by light. 2. A nonchemical, nonimpact imaging process in which a light source, corresponding to the image to be formed, discharges a charged dielectric photoconductive surface to form a latent image. This surface (a photoconductor) containing the latent image is then dusted with dielectric toner powder, which adheres to the charged areas, rendering the image visible. electrostatic recording -Recording by means of a signal-controlled electrostatic field.

254

electrostatic relay-A relay in which two or more conductors that are separated by insulating material move because of the mutual attraction or repulsion produced by electric charges applied to the conductors. electrostatics-The branch of physics concerned with electricity at rest. electrostaticseparator- An apparatus in which a finely pulverized mixture of the materials to be separated is passed through the powerful electrostatic field between two electrodes. electrostatic series-See triboelectric series. electrostatic shield - 1. A shield that prevents electrostatic coupling between circuits, but permits electromagnetic coupling. 2. A metallic enclosure or screen placed around a device so it will not be affected by external electric fields. electrostatic s p e a k e r -Also called capacitor or condenser speaker. A speaker in which the mechanical forces are produced by the action of electrostatic fields.

STATIONARY PL& VIBRATING PLATE,

+I HIGH 1VOLTAGE Electrostatic speaker.

electrostatic spraying -A technique of spraying wherein the material being sprayed is given a high electrical charge, while the test piece is grounded. electrostatic storage- 1. The storage of changeable information in the form of charged or uncharged areas, usually on the screen of a cathode-ray tube. 2. Information storage on a dielectric medium that represents the data as those spots on the medium having electrostatic charges, forming an observable record of the data. electrostatic transducer -A transducer that consists of a capacitor. at least one plate of which can be set into vibration. Its operation depends on the interaction between its electric field and a change in its electrostatic capacity. electrostatic tweeter-A speaker with a movable flat metal diaphragm and a nonmovable metal electrode capable of reproducing high audio frequencies. The diaphragm is driven by the varying high voltages applied across it and the electrode. electrostatic unit- An electric unit based primarily on the dynamic interaction of electric charges. Defined as a charge that, if concentrated on a small sphere, would repel with a force of 1 dyne a similar charge 1 centimeter away in a vacuum. electrostatic voltmeter-A voltmeter depending for its action on electrostatic forces. Its scale is usually graduated in volts or kilovolts. electrostatography-The process of recording and reproducing visible patterns by the formation and utilization of latent electrostatic charge patterns.

electrostriction - elongation

255

electrostriction-1. A mechanical deformation caused by the application of an electric field to any dielectric material. The deformation is proportional to the square of the applied field. This phenomenon results from the induced dipole movement caused by the applied field, resulting in the mechanical distortion. 2. Elastic deformation of a dielectric caused by volume force when the dielectric is placed in an inhomogeneous electric field. electrostrictive effect -The elastic deformation of a dielectric by an electrostatic field. electrostrictive relay-A relay whose operation is produced by an electrostrictive dielectric actuator. electrosurgery -The surgical use of electricity in such applications as dissection, coagulation, laser heating, laser welding, diathermy, desiccation of tumors, and .hemostasis. electrosurgical unit -An rf generator whose out'put is applied to a blade or wire loop used instead of a conventional scalpel for surgical incision or excision. electrotape -An electronic distance-measuring (device. e l e c t r o t h e r a p e u t i c s -See electrotherapy. electrotherapy- Also known as electrotherapeuitics. 1. The medical science or use of electricity to treat a disease or ailment. 2. Applying electric current to the lbody for massage or heat treatment. electrotherapy apparatus -Equipment for apply:ing electric current to the body for massage or heat treatment. electrothermal-The heating effect of electric current, or the electric current produced by heat. electrothermal expansion element -An actuating element consisting of a wire strip or other shape and having a high coefficient of thermal expansion. electrothermal recorder- A recorder in which Ineat produces the image on the recording medium in response to the received signals. electrothermal recording -See electrothermal secorder. electrothermic instrument- An instrument that depends for its operation on the heating effect of a current. ]Examples are the thermocouple and bolometric, hot-wire, and hot-strip instruments. electrothermics-The branch of science concerned with the direct transformation of electric energy into heat. electrotinning -Electroplating tin on an object. electrotyping -The production of printing plates by electroforming. electrowinning -The process by which metals are recovered from a solution by electrolysis. element-1. One of the 104 known chemical substances that cannot be divided into simpler substances by chemical means. A substance whose atoms all have the same atomic number (e.g., hydrogen, lead, uranium). 2. In a computer, the portion or subassembly that constitutes the means of accomplishing one particular function, such as the arithmetic element. 3. Any electrical device (such as an inductor, resistor, capacitor generator, line, or electron tube) with terminals at which it may be connected directly to other electrical devices. 4. The dot or dash of an International Morse character. 5. A radiator, either active or parasitic, .thatis part of an antenna. 6. The smallest portion of a televised picture that still retains the characteristics of the picturle. 7. A portion of a part that cannot be renewed without destruction of the part. 8. A part of an integrated circuit that contributes directly to its electrical characteristics. An a'ctive element exhibits gain, such as a transistor; a passive element does not have gain, such as a resistor or capacitor. 9. Lowest level design entity having an identifiable logical, electrical, or mechanical function.

elemental area -See picture element. elemental semiconductor -A semiconductor containing only one element in the undoped state. elementary charge-A natural unit or quantum into which both positive and negative charges appear to be subdivided. It is the charge on a single electron and has a value of about 4.8037 x lo-'' electrostatic units. element error rate-The ratio of the number of elements incorrectly received to the total number of elements sent. elevation -The angular position perpendicular to the earth's surface. elevation-position indicator-A radar display that simultaneously shows angular elevation and slant range of detected objects. elevator leveling control -A positioning control used to align the platform of an elevator with the floor level of the building. Metal vanes are mounted in the elevator shaft at each floor level, and an oscillator is mounted on the elevator car. When the elevator is properly leveled, the metal vane is between the plate and the grid coils of the oscillator. A relay connected in the oscillator circuit now energizes. The contacts of this relay are connected in the motor-control circuit of the elevator so that the elevator stops in alignment with the floor level. ELF -Abbreviation for extremely low frequency. eliminator- Also called a battery eliminator. A device operated from an ac or dc power line and used for supplying direct current and voltage to a battery-operated circuit. €-lines -Contour lines of constant electrostatic field strength with respect to some reference base. elliptically polarized wave -An electromagnetic wave whose electric intensity vector describes an ellipse at one point. elliptical polarization -Polarization in which the wave vector rotates in an elliptical orbit about a point. elliptical stylus-A stylus whose cross section, as seen from above, is an ellipse placed across the record groove. Elliptical styli can more readily trace the finer high-frequency modulations of the groove than can spherical styli. Such styli have two radii (e.g., 0.4 x 0.7 mil). See biradial stylus. elliptic function -A mathematical function employed in obtaining the squarest possible amplitude response, or the sharpest passband magnitude rolloff, of a filter with a given number of circuit elements. The elliptic function has a Tchebychev response in both the passband and the stopband. The phase response and transient response of an elliptic-function filter are poorer than for any of the classical transfer functions.

- I

PASSBAND RIPPLE

OUTPUT INPUT

0

\

RESONANCES IN STOP BAND

FREQUENCY

>

Elliptiefunction filter passband

elongation-Extension of the envelope of a signal as a result of the delayed arrival of certain of the multipatb components.

elm - emissivity e/m-The ratio of the electric charge to the mass for particles such as electrons and positive rays. For slow-moving electrons, the value of elm is 1.7588 x lo4 coulombs per gram. The value decreases with increasing velocity, however, because of an increase in effective mass. e-mail- Abbreviation for electronic mail. 1. Messages, usually text, sent from one person to another via computer. E-mail can also be sent automatically to a large number of addresses (mailing list). 2. A system for transmitting messages from one computer terminal to another, where it can be displayed at the receiver’s convenience. embedded code -Machine instructions for checking copy protection that are interspersed with code for other purposes. e m b e d d e d software-Computer code that is not visible to the end user. embedded system-A system into which one or more computing devices (which may be microprocessors or microcontrollers) are incorporated in such a way that the embedded device or devices are not directly accessible to the user of the system. embedding-A general term for all methods of surrounding or enclosing components and assemblies with a substantial thickness of electrically insulating solid or foam material that substantially fills the voids or interstices between parts. embedment -The complete encasement of a part or assembly to some uniform external shape. A relatively large volume of a complete package consists of the embedment material. embossed-foil printed circuits-A printed circuit formed by indenting the desired pattern of metal foil into an insulating base and then mechanically removing the remaining unwanted raised portion. embossed-groove recording -A method of recording sounds on discs or film strips by embossing sound grooves with a blunt stylus rather than by cutting into them with a sharp stylus. Embossing throws the material up in furrows on each side of the sound groove without actually removing any of the material in the disc or strip.

Embossed-groove recording.

embossing stylus-A recording stylus with a rounded tip that forms a groove in the recording medium by merely displacing the material instead of removing it completely. EMC-Abbreviation for electromagnetic compatibility. e m e r g e n c y communication -The transmission or reception of distress, alarm, urgent, or safety signals or messages relating to the safety of life or property, or the occasional operation of equipment to determine whether it is in working condition. e m e r g e n c y radio c h a n n e l -Any radio frequency reserved for emergency use, particularly for distress signals.

256 e m e r g e n c y receiver -Receiver immediately available in a station for emergency communication and capable of being energized solely by a self-contained or emergency power supply. emergency service-The radiocommunication service carrier used for emergency purposes. emf -Abbreviation for electromotive force. EMG-Abbreviation for electromyography. EM1-Abbreviation for electromagnetic interference. emission-1. The waves radiated into space by a transmitter. 2. The ejection of electrons from the surface of a material (under the influence of heat, for example). emission characteristic-The relationship between the emission and the factor controlling it, such as temperature, voltage, or current of the filament or heater. This relationship is usually shown on a graph. emission current-The current produced in the plate circuit of a tube when all the electrons emitted by the cathode pass to the plate. emission efficiency-The rating of a hot cathode. Expressed in milliamperes per watt. emission power-The time rate at which radiant energy is given off in all directions per unit surface area of a radiating body at a given temperature. emission spectrum- 1. The spectrum showing the radiation emitted by a substance, such as the light emitted by a metal when placed in an electric arc, or the light emitted by an incandescent filament. 2. The spectrum formed by radiation from an emitting source, in contrast to absorption spectra. emission types -The classification of modes of radio transmission adopted by international agreement. The AM designations are as follows: Type AO: Unmodulated continuous-wave transmission Type Al: Telegraphy or pure continuous waves Type A2: Modulated telegraphy Type A3: Telephony Type A4: Facsimile Type A5: Television emission-type tube tester- Also called an English-reading tube tester. A tube tester for checking the electron emission from the filament or cathode. The indicating meter is generally calibrated to read “good” or “bad.” The tester connects all elements, such as the plate and screen, suppressor, and control grids, together and uses them as an anode. emission velocity-The initial velocity at which electrons emerge from the surface of a cathode, ranging from zero up to a few volts (attained by very few electrons). This effect accounts for the existence of virtual cathodes and also for the shape of the cutoff region of plate current. emissive power-The emissivity of a body times the emissive power of a blackbody at the same temperature. For a blackbody, it is the total radiation per unit area of radiating surface. emissivity- 1. The ratio of the radiant energy emitted by a radiation source to the radiant energy of a perfect (blackbody) radiator having the same area and at the same temperature and conditions. 2. The percentage of infrared energy emitted from a surface for a given temperature compared with the total energy it should emit for that temperature. Instead of percentage, emissivity ( E ) is expressed in terms of unity. A perfect blackbody has an E = 1.0. When the surface has less than 100-percent radiating efficiency, the difference between the E of the surface and 1.0 represents the approximate reflectivity of the surface. Reflectance varies inversely with emissivity. This allows surrounding ambient surfaces to add to or subtract from the temperature.

:257 emitron-A cathode-ray tube developed in England ;by J. H. Hixenweaver in 1955. emitron camera -A British television camera tube resembling an iconoscope. emittance-The power per unit area radiated by a source of energy. emitter-Also called source. 1. One of the three !regions that form a bipolar transistor. Under forward bias of the emitter-base pn junction, the emitter injects minority {carriers(electrons or holes) into the base region, ,where they either recombine or diffuse into the collecitor. The flow of minority carriers from the emitter to the icollector is controlled by the base-emitter pn junction, ithereby giving rise to signal amplification. 2. An electrode within a transistor from which carriers are usually minor:ity carrie.rs; when they are majority carriers, the emitter :is referred to as a majority emitter. 3. In fiber optics, the :source of optical power. See coherent emitter; incoherent emitter. emitter-base and collector-base junction-In a semiconductor, the region where the base and collector ;and the emitter and base meet. These junctions are defined on the surface of the chip as an oxide step. emitter bias-The bias voltage applied to the emitter of a transistor. emitter-coupled logic-See ECL. emitter current-The direct current flowing in the emitter circuit of a transistor. emitter cutoff frequency -That frequency at which the of a transistor is down 3 dB from the lowfrequency value. emitter depletion-layer capacitance -The part of the capacitance across an emitter-base junction of a semiconductor that is associated with its depletion layer. The emitter depletion-layer capacitance is a function of Ibe total potential drop across the depletion layer. emitter follower-A transistor amplifier circuit configuration analogous to a vacuum-tube follower. The circuit is characterized by relatively high input impedance, low output impedance, and a voltage gain of less than unity. emitter junction- 1. A semiconductorjunction norinally biased in the low-resistance direction so that minority carriers are injected into the interelectrode region. 2. A junction between the base and emitter regions of a semiconductor normally biased in the forward direction, and though which the charge carriers flow from a region in which they are majority carriers to one in which they are minority carriers. emitter region-That part of a transistor lying between the emitter junction and the emitter electrode f ~ o mwhich carriers flow across the emitter junction. emitter resistance-The resistance in series with the emitter lead in the common-T equivalent circuit of a transistor. emitter semiconductor- A junction normally biased in the low-resistance direction to inject minority carriers into an interelectrode region. emitter series resistance-The resistance between the emitter terminal of a semiconductor and the internal inaccessible emitter point in an equivalent circuit. emitter terminal-The specified externally available point. of connection to the emitter region. emitter voltage -The voltage between the emitter terminal and a reference point. EMP -Abbreviation for electromagnetic pulse. emphasizer-A circuit or device that provides an intentional increase in signal strength at certain audio frequencies.

emitron - encapsulant empire Cloth-A cotton or linen cloth coated with varnish and used a5 insulation on coils and other parts of electrical equipment. empirical- 1. Based on actual measurement, observation, or experience, as opposed to theoretical detennination. 2. Based solely on experiment or observation, rather than on scientific theory. 3. Pertaining to a statement or formula based on experience or observation rather than on deduction or theory. EMR -Abbreviation for electromagnetic radiation. emu -Abbreviation for electromagnetic unit. emulate-1. To imitate one system with another, such that the imitating system accepts the same data, executes the same programs, and achieves the same results as the imitated system. 2. To imitate a computer system by a combination of hardware and software that allows programs written for one computer to be run on another. See simulate. emulation-1. The imitation of all or part of one device, terminal, or computer by another, so that the emulating device accepts the same data, performs the same functions, and appears to other network devices as if it were the emulated device. 2. The imitation of a computer system, performed by a combination of hardware and software, that allows programs to run between incompatible systems. 3. For PCs, the process of imitating the behavior of one operating system using a completely different operating system. 4. The generation of one system’s code set by another so that the two may communicate. For example, a system with TTY emulation appears like a Teletype system when communicating with another Teletype. 5. The use of hardware or software to generate in real time the expected correct output responses for comparison to the device under test. 6. A hardware model of the target microprocessor used to check out the target system. This can be either the same microprocessor model as used in a target system, or bit-slice architecture that mimics the target microprocessor’s function. Using the target microprocessor is called substitutional emulation or in-circuit emulation. See also in-circuit emulation. emulator- 1. A device that is capable of operating in such a manner that it appears to have all of the characteristics of another device. For example, a hardware and software combination that enables one computer to execute programs written for another computer, or a device that produces the same set of outputs for a given set of inputs as does another device. 2. The combination of programming techniques and special machine features that permit a given computing system to execute programs written for another system. 3. A program or a hardware device that duplicates the instruction set of one computer on a different computer, allowing program development for the emulated computer without that computer being available. emulsion --A suspension of finely divided photosensitive chemicals in a viscous medium, used in semiconductor processing for coating glass masks. enable-To pexmit a circuit to be activated by the removal of a suppression signal. enabling gate--A circuit that determines the start and length of a generated pulse. enabling pulse- 1. A pulse that opens a normally closed electric gate, or otherwise pennits occmence of an operation for which it is a necessary but not sufficient condition. 2. A pulse that prepares a circuit for some subsequent action. enameled wire -Wire coated with a layer of bakedenamel insulation. encapsulant -A material, usually epoxy, used to encase and seal all components in an electronic circuit.

encapsulate - end effect

encapsulate -To embed electronic components or other entities in a protective coating, usually done when the plastic encapsulant is in fluid state so that it will set in solid form as an envelope around the work. encapsulated relay-A relay embedded in a suitable potting compound. encapsulating -1. Coating by dipping, brushing, spreading, or spraying an electronic component or assembly. An encapsulated unit usually retains its original geometry. 2. Enclosing an article in an envelope of plastic by immersing the object in a casting resin and allowing the resin to polymerize or, if hot, cool. encapsulating material -A composition primarily adapted for use on or around an electrical device to provide protection from the surrounding environment. encapsulation -1. A protective coating of cured plastic placed around delicate electronic components and assemblies. It is similar to potting, except the cured plastic is removed from the mold. The plastic therefore determines the color and surface hardness of the finished part. The molds may be made of any suitable material. 2. An embedding process using removable molds or other techniques in which the insulating material forms the outer surfaces of the finished unit. 3. The process of either (a) applying a conformal coating by dipping an object in a high viscosity or thixotropic material, or (b) using containment and a low viscosity material to provide a relatively thin protective encasement (50 to 100 mils or 1.27 to 2.54 mm) to a part or assembly. encased control -A self-contained motor speed/ torque control completely housed in an enclosure. Switching, indicating, and adjusting devices are provided on the outside of the enclosure. Unit portability, safety, and component protection are leading assets of this design. encipher-To convert a message from ordinary language into a secret form. See also encode e n c i p h e r e d facsimile communications -Communications in which security is provided by mixing pulses from a key generator with the output of a facsimile converter. Plain text is recovered at the receiving terminal by subtracting identical key pulses. Unauthorized persons are unable to reconstruct the plain text unless they have an identical key generator and they know the daily key setting. enclosed relay-A relay in which both the coil and the contacts are protected from the environment. enclosed s w i t c h -Switch having internal parts protected by a housing. The enclosed switch can be dust proof, moisture proof, oil or contamination proof, or hermetically sealed. enclosure- 1. An acoustically designed housing or structure for a loudspeaker; also any cabinet for a component, electrical, or electronic device. 2. A surrounding case designed to provide a degree of protection for equipment against a specified environment and to protect personnel against accidental contact with the enclosed equipment. encode -Also called encipher. 1. To use a code, frequently one composed of binary numbers, to represent individual characters or groups of characters in a message. 2. To change from one digital code to another. If the codes are greatly different, the process usually is called conversion. 3. To substitute letters, numbers, or characters, usually with the intention of hiding the meaning of the message except from persons who know the encoding scheme. 4. The process of converting an event such as a switch closure into a form suitable for transmission over a communication channel. encoder -1. A device used to electronically alter a signal so that it can only be viewed on a receiver

258 equipped with a special decoder. 2. Any device that modifies information into the desired pattern or form for a specific method of transmission. 3. An electromechanical device that can be attached to a shaft to produce a series of pulses to indicate shaft position; when the output is differentiated, the device is an accurate tachometer. (It is fundamentally oriented to digital rather than analog techniques.) An encoder contains a disc with a printed pattern; as the disc rotates, it makes and breaks a circuit. The more make-and-break cycles per revolution, the better the resolution. 4. A digital-to analog converter. 5 . Circuitry in a quadriphonic sound system that, by matrixing in the recording process, turns four signals into two for inscribing, stereo style, on each wall of the record groove. 6. Electromechanical device that transforms analog motion into digital electrical signals. The outputs are incrementally constant for uniform motion characterized by a staircase function, where the output remains constant for a small range of input values. 7. A digital device for converting an input digital signal into its equivalent binary code. See also code converter. encoder accuracy -The maximum positional difference between the input to an encoder and the position indicated by its output; includes both deviation from theoretical code transition positions and quantizing uncertainty caused by converting from a scale having an infinite number of points to a digital representation containing a finite number of points. encoding -1. Translation of information from an analog or other easily recognized form to a coded form without a significant loss of information. 2. The process of converting an event such as a switch closure into a form suitable for transmission over a communication channel. 3. The scrambling of a signal to prevent viewing of a program by nonsubscribers. encryption-I. A change made to data, code, or a file such that it can no longer be read or accessed without processing (or unencrypting). 2. The technique of modifying a known bit stream on a transmission line to make it appear like a random sequence of bits to an unauthorized observer. end-around carry- A computer operation in which the carried information from the left-most bit is added to the results of the right-most addition. It is used for ones complement and nines complement arithmetic. end-around shift-In a computer, the movement of characters from one end of the register to the other end of the same register. end bell-An accessory that is similar to a cable clamp and attaches to the back of a plug or receptacle. It serves as an adapter for the rear of connectors. Some angular end bells have built-in cable clamps. Angular end bells up to 90" are available. See also end shield. e n d bracket-See end shield. end-cell rectifier- A small trickle-charge rectifier for maintaining the voltage of storage-battery end cells. end cells- Cells that can be switched in series with a storage battery to maintain the output voltage of the battery when it is not being charged. end central off ice -The local central telephone office that interconnects customer lines and trunks. It is designated a Class 5 office in the DDD or intertoll network. end distortion-A shifting of the ends of all marking pulses of start-stop teletypewriter signals from their proper positions relative to the beginning of the start pulse. end effect-The capacitive effect at the ends of a half-wave antenna. To compensate for this effect, a dipole is cut slightly shorter than a half wave.

:259

end effector-Teiminal on a robot arm that carries a hand, welding gunl painting nozzle, or other tool. end finish-Surface condition at the optical conducitor face. end-fire array-A linear or cylindrical antenna lhaving its direction of maximum radiation parallel to the long axis of the array. end instrument-A device connected to one terminal of a loop and capable of converting usable intelligence .into electrical signals or vice versa. Includes all generat:ing, signal-converting, and loop-terminating devices at the itransmitting and/or receiving location. endless loop recorder -A dictation system in ,which a nonremovable magnetic tape is sealed in a tank ;and the tape runs in a continuous loop. end mark--]in a computer, a code or signal used to indicate the termination of a unit of information. endocardiac electrodes-See implantable pacemaker. endodyne reception -A British term applying to reception of unmodulated code signals. A vacuumcube circuit having a local oscillator whose frequency is slightly different from that of the carrier signal. Thus, a beat signal in the audio range is produced. end-of-block signal -A symbol or indicator that defines the end of a block of data. end of file-Abbreviated EOF. A code placed by a program after the last byte of a file to teIP the computer's operating system that no additional data follows. end-of-file mark-In a computer, a code instruction indicating that the last record of a file has been read. end of message -The end of data to be transmitted. It can be indicated by a special control code, as in the ASCII code set; by an absence of data for a specified time interval; or by a particular sequence of block gaps and data. as is done on magnetic tape. end of tape -The point on a computer tape at which The system or operator is given a warning that the physical end of the tape i s approaching. It is approximately 25 feet (7.62 m) from the actual end of the tape on lh-inch (12.7mm) computer tape and approximately 50 feet (15.24 m) from the halt marker on 1/4-inch (6.35-mn) tape. end-of-tape marker-A marker placed on a magnetic tape to indicate the end of the permissible recording area. It may be a photoreflective strip, a transparent section of tape, or a particular bit pattern. end-of-transmission card -Last card of each message; used to signal the end of a transmission. Contains the same information as the header card, plus additional.data for traffic analysis. endogeneous variable -A variable whose value is determined by relationships included within the model. See also exogenous variable. end-on armature-Of a relay, an armature that moves in the direction of the core axis, with the pole face at the end of the core and perpendicular to this axis. e n d - o n directional antenna-A directional antenna that radiates chiefly toward the line on which the antenna elements are arranged. e n d o r a d i o g r a p h -Equipment for X-ray examination of internal organs and cavities by means of radiopaque materials. endoradiosonde -Also called radio pill. A device for detecting and transmitting physiological data from the gastrointestinal tract or other inaccessible body cavities. endothermic-A term describing a chemical reaction in which heat is absorbed. e n d o t h e r m i c reaction -A reaction that is accompanied by the absorption of heat.

end effector - e n e r g y conversion devices end point -The shaft positions imnediately before the first and after the last measurable change(s) in output ratio after wiper continuity has been established, as the shaft of a precision potentiometer moves in a specified direction. end-point control-Quality control by means of continuous automatic analysis. In highly automatic processes, the final product is analyzed, and if any undesirable variations are detected, the control system automatically brings about the necessary changes. end-point sensitivity-The algebraic difference in electrical output between the maximum and minimum value of the measurand over which an instrument is calibrated. end-point voltage-The terminal voltage of a cell below which equipment connected to it will not operate or should not be operated. end resistance -The resistance of a precision potentiometer measured between the wiper terminal and an end terminal, with the shaft positioned at the corresponding end point. end-resistance offset -In potentiometers, the residual resistance between a terminal and the moving contact, at a position corresponding to full rotation against that terminal. end-scale value -The value of the actuating electrical quantity that corresponds to end-scale indication of an instrument. When zero is not at the end OK at the electrical center of the scale, the higher value is tzken. Certain instruments such as power-factor meters, ohmmeters, etc., are necessarily excepted from this definition. end setting -In a potentiometer, the minimum resistance that is measured between one end of a potentiometer and the wiper, with the wiper mechanically positioned at that end. end shield- 1. Frequently called end bracket or end bell. In a motor housing, the part that supports the bearing and also guards the electrical and rotating parts inside the motor. 2. In a magnetron, the shield that confines the space charge to the interaction space. end spaces -In a multicavity magnetron, the two cavities at either end of the anode block that terminate all the anode-block cavity resonators. end-to-end check-Tests conducted on a completed wire and/or cable run to ensure elecsrical continuity. end use-The way the ultimate consumer uses a device. energize-To apply the rated voltage to a circuit or device, such as to the coil of a relay, in order to activate it. energized -Also called alive, hot, and live. Electrically connected to a voltage source. Turned on, alive. energized part-A part at some potential with respect to another part, or the earth. energy-I. The capacity for performing work. A particle or piece of matter may have energy because it is moving or because of its position in relation to other particles or pieces of matter. A rolling ball is an example of the first; a bell at rest at the top of an incline is an example of the second. 2. The capacity for doing work and overcoming resistance. e n e r g y conversion -The change of energy from one form to another, e.g., from chemical energy to electrical energy. e n e r g y conversion devices-Devices including primary and secondary cells; fuel cells; photovoltaic systems; electrochemical energy converters; radiation conversion devices; thermionic converters; converters using solar, ionic, or nuclear energy sources; devices for cresting a plasma in an interaction space between an emitter and a collector; electrostatic generators for creating an

energy density - entropy electrical output; organic and inorganic ion exchange and membrane devices; electron volt energy devices; devices for direct conversion of fuel to electricity; and electricalenergy storage-unit devices capable of delivering a power output. energy density -1. The energy output of a battery, expressed in watt-hours, per unit weight or volume of the battery. 2. The energy per unit volume of a medium. e n e r g y dispersal waveform -A triangular-shaped signal at 30 Hz synchronized with the vertical blanking interval in the TV signal from the satellite, which ensures that the signal will average its power out over the whole channel, even when just the carrier is present. This waveform is removed by the receiver after FM demodulation. e n e r g y efficiency ratio-Term used to gauge the relative electrical efficiency of appliances; found by dividing btu-per-hour output by the number of electrical watts used. e n e r g y gap-The energy range between the bottom of the conduction band and the top of the valence band of a semiconductor. e n e r g y level-A particular value of energy of a physical system, such as a nucleus, that the system can maintain for a reasonably long length of time. Systems on an atomic scale have only certain discrete energy levels and cannot occupy values between these levels. energy-level diagram -A line drawing that shows the increase or decrease in electrical power as current intensities rise and fall along a channel of signal communications. energy-measuring equipment -Equipment used to measure energy in electrical, electronic, acoustical, or mechanical systems. e n e r g y of a charge-Represented by E = 1/2QV, given in ergs, when the charge Q and the potential V are in electrostatic units. energy product-The product of the magnetic flux density B in gauss times the magnetic field strength H in oersteds. Used as an index of magnet quality. The larger the maximum energy product, the smaller the required magnet for a given job. energy-product curve-A curve obtained by plotting the product of the value of magnetic induction B and demagnetizing force H for each point of the demagnetization curve of a permanent magnetic material. Usually shown together with the demagnetization curve. e n e r g y redistribution-A method of finding the duration of an irregularly shaped pulse by considering it as a power curve. The area under the curve can be represented by an equivalent rectangle of the same area and peak amplitude. The original-pulse duration is equal to the rectangle width. e n e r g y state-The position and speed of an electron relative to the position and speed of other electrons in the same atom or adjoining atoms. e n e r g y storage capacitor-Specifically designed capacitor for use in applications wherein the capacitor can be charged over a relatively long period and discharged in a short period, thus increasing the instantaneous power in energy storage systems. Provisions are made to permit the very high currents that accompany the high rate of energy discharge. When the number of discharges is very large, the actual total time during which the capacitor may be subjected to the maximum operating voltage is relatively short. energy-variant sequential detection -A technique for sequential detection in which a fixed number of transmitted pulses of varying energy are received with a single (upper) threshold device. ENG -See electronic news-gathering.

260 e n g i n e e r e d military circuit - 1. Leased long lines of which only the station equipment, local loops, and reserved positions of interexchange channels are paid for continuously. The unresevered portions of leased long lines or interexchange channels are on a steady status and are placed in an operational status and paid for only when required by the command concerned. 2. A standby or on-call circuit that is engineered specifically to meet military criteria. engineering -A profession in which a knowledge of the natural sciences is applied with judgment to develop ways of utiIizing the materials and forces of nature. English-reading tube tester-See emission-type tube tester. enhanced carrier demodulation -An amplitudedemodulation system in which a synchronized local carrier of the proper phase is added to the demodulator. This has the effect of materially reducing the distortion produced in the demodulation process. e n h a n c e m e n t -Modification of the subjective features of an image to increase its impact on the observer. e n h a n c e m e n t mode- 1. An MOS transistor that is normally off with zero gate voltage applied. A gate voltage of the correct polarity attracts majority carriers to the gate area, thus “enhancing” it and forming a currentconducting channel. 2. A device type that is normally off with zero gate voltage. A threshold voltage is then required to turn the device on. enhancement-mode field-effect transistor -A field-effect transistor in which no device current flows (leakage only) when VGSis zero volts. Conduction does not begin until Vcs reaches the threshold voltage. enhancement mode operation -The operation of a field-effect transistor such that changing the gate-tosource voltage from zero to a finite value increases the magnitude of the drain current. e n h a n c e m e n t MOS transistor-A type of MOS transistor in which no current flows in the absence of an input control signal on the control terminal (called the gate) of the transistor; Le., a control signal input is required to turn on the device. This reduces power dissipation (power dissipation occurs only when an input signal is present) and results in excellent logic state recognition (full off being one state and on the other). ensemble-A collection of sample functions of a random process, all of which start from the same zero time. enterprise number -Also called toll-free number. Unique telephone exchange number that permits the called party to be automatically billed for incoming calls. entrance box- A metal box that houses overcurrentprotection devices and serves as the point of distribution for the various electrical circuits in a structure. entrance cable-A cable by means of which electrical power is brought from an outside power line into a building. entrance delay-The time between actuating a sensor on an entrance door or gate and the sounding of a local alarm or transmission of an alarm signal by the control unit. This delay is used if the authorized access switch is located within the protected area, and permits a person with the control key to enter without causing an alarm. The delay is provided by a timer or timing circuit within the control unit. entrapped material-Gas or particles bound up in an electrical package so that they cannot escape the package. entropy- 1. A measure of the unavailable energy in a thermodynamic system. 2. The unavailable information in a set of documents. 3. An inactive or static condition (total entropy). 4. A measure of the amount of information

entry

26 1 in a communication signal, equal to the average number of bits per symbol. entry --Each statement in a computer programming system. entry point-In a computer, the programmer-defined jnstructioin at which a task is to begin execution. enunciation-The act of pronouncing words clearly and distinlctly. Articulation. envelope-I. Also referred to as a bulb. The glass or metal housing of a vacuum tube. The glass housing that encloses an incandescent source. 2. The curve passing through the peaks of a graph and showing the waveform of a modulated radio-frequency carrier signal.

ENVELOPE

Envelope, 2.

envelope delay- 1. The time that elapses as a transmitted wave passes any two points of a transmission circuit. Such delay is determined primarily by the constants of the circuit and is measurable in milliseconds or microseconds. 2. Sometimes called time delay or group delay. The propagation time delay undergone by the envelope of an amplitude-modulated signal as it passes through a filter. Envelope delay is proportional to the slope of the curve of phase shift as a function of frequency. Envelopedelay distortion is introduced when the delay is not the same at all frequencies in the passband. 3. The time difference between the longest. delay and the shortest delay for a given band of frequencies. 4. A type of distortion CIB~ an analog line in which the signal delay varies with signal frequency. 5. Characteristics of a circuit that result in some frequencies arriving ahead of others, even though they were transmitted together. envelope-delay distortion -The distortion that occurs during transmission when the phase shift of a circuit or :systemis not constant over the frequency range. envelope generator-A circuit in a synthesizer that produces a single, carefully defined waveform. Useful in creating attacks and decays to define notes or for special effects. environment -The aggregate of all conditions that externally influence a device’s performance. environmental chambers-Test chambers designed to expose the subject being tested to external conditions:, such as heat, shock, pressure, and moisture, for the study of their effects of the subject. environmental conditions -External conditions of heat, shock, vibration, pressure, moisture, etc. environmentally sealed-Provided with gaskets, seals, potting, or other means to keep out contamination that might reduce perfomance. environmental testing -The testing of a system or component under controlled environmental conditions, each of which tends to affect its operation or life. environmentproof switch -A switch that is completely sealed to ensme constant operating characteristics. Sealing normally includes an O-ring on the actuator shaft and fused glass-to-metal terminal seals or complete potting and an elastomer plunger-case seal.

- epitaxial material

EOG-Abbreviation for electro-oculography. episcotister-A device consisting of alternate opaque and transparent discs that rotate at a speed that interrupts light beams at an audio-frequency rate. It modulates the light beam used to excite a photoelectric element. epitaxial-Pertaining to a single crystal layer on a crystalline substrate, oriented the same as the substrate. In certain semiconductor processes, an expitaxial layer is grown on a silicon substrate during the fabrication of transistors and integrated circuits. epitaxial deposition -1. The growth of additional material, usually in a thin film, on a substrate. Often the added material has a crystal struchue and orientation controlled by matching that of the substrate. 2. Epitaxy. The technique of growing a semiconductor layer on an existing crystal by depositing it directly from reactant vapors, so that the structure of the new layer is isomorphic with, or simply an extension of, that of the original crystal. epitaxial device-A device constructed in such a manner that the crystalline structure of successive layers is oriented in the same direction as that of the original base material. epitaxial film- I. A film of single-crystal semiconductor material that has been deposited onto a singlecrystal substrate. 2. Any deposited film, provided the orientation of its crystal is the same as that of the substrate material. epitaxial growth-1. A semiconductor fabrication process in which single-crystal p or n material is deposited and grows on the surface of a substrate. Usually, this material has a different conductivity than the substrate. 2. Crystal growth obtained by depositing a film of monocrystalline semiconductor material on a monocrystalline substrate. 3. The process of producing an additional crystal layer of semiconductor material on a semiconductor substrate. The crystalline structure of the substrate is continued into the epitaxial layer; however. the impurity concentration can be made to differ greatly. 4. The deposition of a single-crystal film on the surface of a single-crystal substrate so that the crystal orientations of the two layers are alike. 5. A process of growing layers of material on a selected substrate. Usually silicon is grown in a silicon substrate. Silicon and other semiconductor materials may be grown on a substrate with compatible crystallography, such as sapphire (silicon-on-sapphire). epitaxial-growth mesa transistor- A transistor made by overlaying a thin mesa crystal over another mesa crystal. epitaxial growth process-The process of growing a semiconductor material by depositing it in vaporized form on a semiconductor seed crystal. The deposited layer continues the single-crystal structure of the seed. epitaxial layer-I. A grown or deposited crystal layer with the same crystal orientation as the parent material and, in the case of semiconductor circuits, of the same basic material as the original substrate. 2. A single-crystal p-type or n-type material deposited on the surface of a substrate. 3. A thin, precisely doped monocrystalline silicon layer grown on a heavily doped thick wafer, into which are difised semiconductor junctions. In conventional processing of an integrated circuit, the thick wafer is p doped and the epitaxial layer is n doped. 4. A single crystal layer that has been deposited or grown on a crystalline substrate having the same structural arrangement. 5. A layer of silicon grown atop single-crystal silicon that reproduces the same crystallographic orientation as the single-crystal material. epitaxial material-A material whose atoms are arranged in single-crystal fashion upon a crystalline

epitaxial planar transistor

- equalizing pulses

substrate so that its lattice structure duplicates that of the substrate. epitaxial planar transistor -A transistor in which a thin collector region is epitaxially deposited on a lowresistivity substrate, and the base and emitter regions are produced by gaseous diffusion with the edges of the junction under a protective oxide mask. epitaxial process- The process of growing from the vapor phase a single-crystal semiconductor material with controlled resistivity and thickness. epitaxial transistor-A transistor with one or more epitaxial layers.

BASE CONTACT

\

EMITTER CONTACT

\

EMITTER

EASE

/

/

\ COLLECTOR REGION

Epitaxial transistor (triple diffused).

epitaxy- 1. The controlled growth on a crystalline substrate of a crystalline layer, called an epilayer. In homoepitaxy (e.g., silicon layers on a silicon substrate), the epilayer exactly duplicates the properties and crystal structure of the substrate. In heteroepitaxy (e.g., silicon on sapphire), the deposited epilayer is a different material with a different crystalline structure than that of the substrate. 2. The growth of a crystal on the surface of a crystal of another substance in such a way that the orientation of the atoms in the original crystal controls the orientation of the atoms in the grown crystal. E-plane-The plane of an antenna containing the electric field. The principal E-plane also contains the direction of maximum radiation. E-plane bend -Also called E-bend. The smooth change in direction of the axis of a waveguide. The axis remains parallel to the direction of polarization throughout the change. E-plane T-junction -Also called series T-junction. A waveguide T-junction in which the structure changes in the plane of the electric field. epoxy- 1. Pertaining to a family of thermosetting materials that are widely used for casting and potting and as adhesives. 2. A family of thermosetting resins used in the packaging of semiconductor devices. Epoxies form a chemical bond to many metal surfaces. EPROM-Abbreviation for erasable programmable read-only memory. A type of nonvolatile memory device whose contents can be erased by exposure to ultraviolet light. See also EEPROM; PROM. epsilon -The Greek letter E, or E , frequently used to represent 2.71828, which is the base of the natural system of logarithms. equal-energy source -A source of electromagnetic or sound energy that emits the same amount of energy at each frequency in the spectrum. equal-energy white-The light produced by a source that radiates equal energy at all visible wavelengths. equalization-1. The process of reducing the frequency and/or phase distortion of a circuit by the introduction of networks to compensate for the difference in attenuation and/or time delay at the various frequencies in

262 the transmission band. 2. A process of compensating for increases in attenuation (signal loss) with frequency. Different signal frequencies are attenuated differently over a given distance. 3. An intentional departure from response flatness to compensate for complementary characteristics introduced elsewhere in the system (as with discs, tape, and FM broadcasting). Also used to correct for response deficiencies in speakers and other components. 4. Different equalization characteristics are used in the recording and playback amplifiers of a tape recorder, to compensate for the magnetic characteristics of the tape and the heads. Playback equalization is standardized to give flat frequency response with any properly recorded tape, while recording equalization is a property of a particular machine, depending on its head design and the tape for which it was meant. 5. Reshaping the playback characteristics of a recording during playback mode. The simplest way is to adjust the treble and bass controls, but true equalization requires continuous adjustment of the playback frequency response curve at several points. A graphic equalizer is often used for this. 6. The selective amplification or attenuation of certain frequencies. Also refers to recognized industry standards for recording and reproducing characteristics, such as the NAB Standard. 7. The intentional increase in level of certain portions of the audio-frequency spectrum. The term is sometimes misapplied when actually referring to the attenuation of portions of the audio-frequency spectrum. 8. A technique used to compensate for distortions present on a communication channel. Equalizers add loss or delay to signals in inverse proportion to the channel characteristics. The signal response curve is then relatively flat and can be amplified to regain its original form. equalize-To apply to a circuit an electrical network whose transmission characteristics are complementary to those of the line, so that when the loss (or delay) in the line and that in the equalizer are combined, the overall loss (or delay) is almost the same at all frequencies. equalizer- 1. A passive device designed to compensate for an undesired amplitude-frequency andlor phasefrequency characteristic of a system or component. 2. A series of connections made in paralleled, cumulatively compound direct-current generators to give the system stability. 3. A network, usually adjustable, that corrects the transmission-frequency characteristics of a circuit to permit it to transmit ail the frequencies that it passes in a uniform manner. 4. An electronic circuit that introduces compensation for frequency-discriminative effects of elements within a television system. 5. An electronic device that amplifies (boosts) andlor attenuates certain portions of the audio-frequency spectrum. There are many different types of equalizers. 6. A device to allow the frequency response of an audio-signal path to be adjusted in some way. equalizer circuit breaker- A breaker that serves to control or to make and break the equalizer or the current-balancing connections for a machine field, or for regulating equipment, in a multiple-unit installation. equalize voltage-A voltage applied to a battery for charging at installation and as a periodic boost charge, common in lead-antimony lead-acid battery systems. equalizing current -A current circulated between two parallel-connected compound generators to equalize their output. equalizing network-A network connected to a line to correct or control its transmission frequency characteristics. equalizing pulses-1. A series of pulses (usually six) occurring at twice the line frequency before and after the serrated vertical TV synchronizing pulse. Their purpose is to cause vertical retrace to occur at the correct

263

equal-loudness contours

instant for proper interlace. 2. In the standard television signal, pulses that minimize the effect of linefrequency pulses on the interlace. equal-loudness contours- See Fletcher-Munson curves. equation function -As applied to microelectronic circuitry, a combination of electronic elements or circuits capable of solving the electronic-counter portion of a mathematical or Boolean equation. In obtaining the solution, it perfoms the necessary function within an electronic or electromechanical system. equation solver-A computer, usually of the analog type, designed to solve systems of linear simultaneous (nondifferential) equations or to find the roots of polynomials. equilibrium-In a semiconductor context, that state of a semiconductor crystal when there is no net current through the crystal. A crystal is normally in this state when no external voltages or current are impressed on it. equilibrium brightness-The brightness of the viewing screen when a display storage tube is in a fully written condition. equilibrium electrode potential-A static electrode potential when the electrode and the electrolyte are in equilibrium with respect to a specified electrochemical reaction. equiphase surface-In a wave, any surface over which the field vectors at the same instant are either in phase or 1180" out of phase. equiphase zone -in radionavigation, the region in space within which the difference in phase between two radio signals is indistinguishable. equipment- 1. An item having a complete function apart from being a substructure of a system. Sometimes called a set. 2. A general term referring to p t i c a l l y every part of an electrical system, including the parts consuming electrical energy. (Devices are also included in this category.) equipment augmentation-1. Procuring additional automatic data-processing equipment capability tlo accommodate increased workload within an established data system. 2. Obtaining additional automatic data-processing equipment capability to extend an established data system to additional sites or locations. equipment bonding jumper -The connection between two or more portions of the equipment grounding conductor. equipment chain-A group of units of equipment that are functionally in series. The failure of one or more individual units results in loss of the function. equipment characteristic distortion-A repetitive display or disruption peculiar to spec& portiom of a teletypewriter signal. Normally, it is caused by improperly adjusted or dirty contacts in the sending or receiving equipmenit. equipment ground-A connection from earth ground to a non-cunrent-canying metal part of a wiring installation of electric equipment. It reduces shock hazard and provides electrostatic shielding. equipment life-The arithmetic mean of the cumulative operating times of identical pieces of equipment beginning with the time of acceptance by the ultimate consumer and ending when the equipment is no longer serviceable. equipotential-A conductor having all parts at a single potential. The cathode of a heater-type tube is equipotential, whereas the filament is not because its voltage varies from one end to the other. equipotential cathode -See indirectly heated cathode.

- equivalent differential input impedance

equipotential line- An imaginafy line in space having the same potential at all points. equipotential surface-A surface or plane passing through all points having the same potential in a field of flow. equisignal localizer-Also called tone localizer. A type of localizer in which lateral guidance is obtained by comparing the amplitudes of two modulation frequencies. equisignal radio-range beacon-A radio-range beacon used for aircraft guidance. It transmits two distinctive signals, which are received with equal intensity only in certain directions called equisignal sectors. equisignal surface -The surface formed around an antenna by all points that have a constant field strength (usually measured in volts per meter) during transmission. equisignal zone-In radionavigation, the region in space within which the difference in amplitude between two radio signals is indistinguishable. equivalence-A logic operator having the property that if P is a statement, Q is a statement, R is a statement, etc., then the equivalence of P, Q, R... is tme if and only if all statements are true or all statements are false. equivalent absorption-The rate at which a surface will absorb sound energy, expressed in sabins. Defined as the area of a perfect absorption surface that will absorb the same sound energy as the given object under the same conditions. equivalent absorption area -Area of perfectly absorbing surface that will absorb sound energy at the same rate as the given object under the same conditions. The acoustic unit of equivalent absorption is the sabin. equivalent binary digits- 1. The number of binary digits equivalent to a given number of decimal digits or other characters. 2. The number of binary places required to count the elements of a given set. equivalent circuit- 1. An arrangement of common circuit elements that has characteristics over a range of interest electrically equivalent to those of a different or more complicated circuit or device. 2. A simplified circuit that has the same response to changing voltage and frequency as a more complex circuit. Used to facilitate mathematical analysis. equivalent circuit of a piezoelectric crystal unit -The electric circuit that has the same impedance as the unit in the frequency region of resonance. It is usually represented by an inductance, capacitame, and resistance in series, shunted by the direct capacitaxe between the terminals of the crystal unit. equivalent component density-h circuits in which discrete components are not readily identifiable, the volume of the circuit divided by the number of discrete components necessary to perform the same function. equivalent conductance-The normal conductance of an atr tube in its mount, measured at its resonance frequency. equivalent dark-current input-The incident luminous flux required to give an output current equal to the dark current. equivalent differential input capacitance-The equivalent capacitance looking into the inverting or noninverting inputs of a differential amplifier with the opposite input grounded. See also equivalent differential input impedance. equivalent differential input impedance-The equivalent impedance looking into the inverting or noninverting input, with the opposite input grounded and the operational amplifier operated in the linear amplification region.

equivalent differential input resistance - erasing speed equivalent differential input resistance-The equivalent resistance looking into the inverting or noninverting input of a differential amplifier with the opposite input grounded. See also equivalent differential input impedance. equivalent diode- An imaginary diode consisting of the cathode of a triode or multigrid tube and a virtual anode to which is applied a composite controlling voltage of such a value that the cathode current would be the same as the current in the triode or multigrid tube. equivalent faults -Two or more faults that cause the same output responses and that cannot be isolated from the board output pins and internal nodes being monitored by the tester. equivalent four-wire system-A transmission system using frequency division to obtain full-duplex operation over only one pair of wires. equivalent grid voltage -The grid voltage plus plate voltage divided by the mu of the tube. equivalent height-The virtual height of an ionized layer of the ionosphere. equivalent input noise current-The equivalent input noise current that would reproduce the noise seen at the output of an operational amplifier if all amplifier noise sources were set to zero and the source impedances were large compared with the optimum source impedance. equivalent input noise voltage -The equivalent input noise voltage that would reproduce the noise seen at the output of an operational amplifier if all amplifier noise sources and the source resistances were set at zero. equivalent input offset current-The difference between the two currents flowing into the inverting and noninverting inputs of a differential amplifier when the output voltage is zero. equivalent input offset voltage-The amount of voltage required at the input to bring the output to zero. Usually this voltage is adjustable to zero by using either a built-in or an external variable resistor (balance control). equivalent input wideband noise voltage-The output noise voltage of a differential amplifier with the input shorted, divided by the dc voltage gain of the amplifier. This voltage is measured with a true rms voltmeter and is limited to the combined bandwidth of the amplifier and meter. equivalent loudness-The intensity level of a sound relative to some arbitrary reference intensity, such as a 1000-hertz pure tone, that is judged by the listeners to be equivalent in loudness. equivalent network-One network that replaces another in a system without altering in any way the electrical operation of the system external to the network. equivalent noise conductance-The spectral density of a noise-current generator expressed in conductance units at a specified frequency. equivalent noise input-In a photosensitive device, the value of incident luminous flux that produces an rms output current equal to the rms noise curent within a specified bandwidth when the flux is modulated in a stated manner. equivalent noise pressure -See transducer equivalent noise pressure. equivalent noise resistance- A measure of the residual noise output of a potentiometer while the slider is being actuated. (The residual noise consists of active components in the form of self-generated voltages arising in the slider contact interface, and passive components in the form of ohmic contact resistance at the point of slider contact.) equivalent noise temperature- The absolute temperature at which a perfect resistor with the same

264

resistance as the component would generate the same noise as the component at room temperature. equivalent open-circuit rms noise currentThat noise which occurs at the input of the noiseless amplifier due only to noise currents. It is expressed in picoamperes per hertz at a specified frequency or in nanoamperes in a given frequency band. equivalent periodic line-A periodic line that, when measured at its terminals or at corresponding section junctions, has the same electrical behavior at a given frequency as the uniform line with which it is compared. equivalent permeability- The relative permeability that a component would have under specified conditions if it had the same reluctance as a component of the same shape and size but different materials. equivalent plate voltage -The plate voltage plus mu times the grid voltage. equivalent resistance-The concentrated or lumped resistance that would cause the same power loss as the actual small resistances distributed throughout a circuit. equivalent series resistance-Abbreviated ESR or R. 1. In a circuit or component, the square root of the difference between the impedance squared and the reactance squared. All internal series resistance of the circuit or component treated as being concentrated in a single resistance at one point. 2. All internal ac series resistance of a capacitor treated as a single resistor. 3. An effective resistance that, if connected in series with an ideal capacitor of a capacitance value equal to that of the capacitor in question, would result in a power loss equal to the active power dissipated in that capacitor at a given frequency. equivalent time -In random-sampling oscilloscope operation, the time scale associated with the display of signal events. equivalent time sampling -A method of allowing the storage of repetitive events that occur faster than the maximum digital oscilloscope sampling frequency. The scope acquires the waveform during multiple sweeps by taking samples at various times until scope memory is filled. equivocation -In a computer, the conditional information contained in an input symbol given an output symbol, averaged over all input-output pairs. erasable programmable read-only memory Abbreviated EPROM. A field-programmable read-only memory that can have the data content of each memory cell altered more than once. An EPROM is bulk-erased by exposure to high-intensity ultraviolet light. Sometimes referred to as a reprogrammable read-only memory. erasable storage-Storage media in a computer that hold information that can be changed. erase-1. To replace all the binary digits in a storage device by binary zeros. In a binary computer, erasing is equivalent to clearing; in a coded decimal computer, in which the pulse code for decimal zero may contain binary ones, clearing leaves decimal zero, whereas erasing leaves all-zero pulse codes in all storage locations. 2. To remove all information from a register or a memory. Sometimes this consists of writing a zero into all memory positions. erase head-1. A head on a tape recorder that applies a strong high-frequency alternating magnetic field to the tape so that earlier recordings may be erased as the tape runs past the head. 2. A magnetic tape head that removes previously recorded signals from a tape, usually by applying inaudible high-level, high-frequency bias signals. erasing speed-In charge-storage tubes, the rate of erasing successive storage elements.

265

erasure -1. A process by which a signal recorded on a tape is removed and the tape made ready for rerecording. 'This may be accomplished by ac erasure, in which the tape is demagnetized by an alternating field that is reduced in .mplitude from an initially high value, or by dc erasure, in which the tape is saturated by applying a primarily unidirectional field. 2. The neutralization of the magnetic pattern stored on tape. E regton -The region of the ionosphere about 50 to 100 mile!; (80 to 160 km) above the earth's surface. E register-The extension of the computer A:register €or use in double-precision arithmetic or logicshift operations. E, - E,-The resultant color television signal when .E, is subtracted from the original full red signal. erg - 1. The absolute centimeter-gram-second unit of energy and work. The work done when a force of 1 dyne 11sapplied1 through a distance of 1 centimeter. 2. Measure $ofenergy. 1 erg = lo7 joules = 6.25 x 10" eV. ergonomics -The science of designing office systems to meet the needs of the human body. ERP-,Abbreviation for effective radiated power. The amount of power radiated by an antenna, which may be more or less than the power absorbed by it from the ixansmitter. error - I. In mathematics, the difference between the true value and a calculated or observed value. A quantity (equal in absolute magnitude to the error) added I O a calculated or observed value to obtain the true value is called a correction. 2. Any discrepancy between a computed, observed, recorded, or measured quantity LINE END OF FIELD

262-% LINES PER FIELD

-

HORIZ0NTP.L-

Scanning lines.

scanning linearity -:h television, the uniformity of the scanning speed during the trace interval. scanfling-line f r e q u e n c y -The number of scanning lines per second. See also stroke speed. scanning loss-In a radar system employing a scanning antenna, the reduced sensitivity that occurs in

scatter read - S c h o t t k y

668 MOST OF ENERGY

?

Qy

SEVERAL HUNDRED

\ C,R2 = C,R, C,R,=C,R,

Schering bridge. Scatter propagation.

scatter read -The ability of a computer to distribute data into several memory areas as it is being entered into the system from magnetic tape. SCC -Abbreviation for spark control computer. An analog electronic system (Chrysler Corp.) that accurately controls spark timing in response to various inputs, including engine temperature, manifold pressure, air temperature, and air pressure. Used with EGR, it provides for cleaner exhaust and better fuel economy. scc wire -Abbreviation for single-cotton-covered wire. SCEPTRON -Acronym for spectral comparative pattern recognizer. A device that automatically classifies complex signals derived from any type of information that can be changed into an electrical signal. s c h e d u l e d maintenance-Maintenance performed according to an established plan. scheduling -Determining the order in which job programs will use the available computer facilities. schematic-1. A diagram that shows, by means of graphic symbols, the electrical connections and functions of a specific circuit arrangement. 2. A representation of the components of an electrical circuit and their interconnections by symbols and lines. s c h e m a t i c circuit diagram -See schematic diagram. s c h e m a t i c diagram- Also called a schematic circuit diagram, diagram, or schematic. 1. A diagram of the electrical scheme of a circuit, with components represented by graphical symbols. 2. A drawing that shows by means of graphic symbols the electrical connections, components, and functions of a specific circuit arrangement. 3. A functional diagram of an electrical circuit in which the components arc represented by conventional symbols, and wires interconnecting them by lines. S c h e r i n g bridge- A four-arm alternating-current bridge used for measuring capacitance and dissipation factor. The unknown capacitor and a standard loss-free capacitor form two adjacent arms, the arm adjacent to the standard capacitor consists of a resistor and capacitor in parallel, and the fourth arm is a nonreactive resistor. schlieren -An optical system that produces images in which the illumination or hue at a given point is related to the angular deflection a light ray undergoes in passing through the corresponding point in the object. The object is back-illuminated, and a straightedge, circular aperture, or graded density or multicolored filter is employed in the system to discriminate between deflected and undeflected rays. S c h m i d t antenna-A microwave scanning antenna similar in principle to the optical Schmidt camera. The

spherical reflector has a spheric microwave lens at the center of curvature and a scanner is located approximately halfway between these elements. S c h m i d t optical system- An optical system for magnifying and projecting a small, brilliant image from a projection-type cathode-ray tube onto a screen. S c h m i t t limiter-See Schmitt trigger. S c h m i t t trigger-Also called Schmitt limiter. 1. A bistable pulse generator in which an output pulse of constant amplitude exists only as long as the input voltage exceeds a certain dc value. The circuit can convert a slowly changing input waveform to an output waveform with sharp transitions. Normally, there is hysteresis between an upper and a lower triggering level. 2. A regenerative circuit that changes state abruptly when the input signal crosses specified dc triggering levels. 3. A bistable device that utilizes the effect of hysteresis. In the Schmitt trigger, hysteresis is a form of nonlinear operation that forces the output to be dependent not only on the absolute value of the input, but also on the most recent prior value of the input. This hysteresis is characterized by two different switching theshold levels: one for positivegoing input transitions and the other for negative-going input transitions.

+ "cc

6 -VEE

Schmitt trigger.

schmoo plot-An x , y plot giving the padfail region for a specific test while varying the parameters in x and y coordinates. s c h o o p i n g -Spraying metal onto the ends of the roll of a metallized capacitor. This provides a metal surface on the ends of the roll to which the leads arc then soldered. Schottky-A bipolar technology that is faster than standard TTL but often uses more power.

Schottky barrier - scintillation

669 Schottky barrier-- 1. A simple metal-to-semiconductor interface that exhibits a nonlinear impedance. 2. A metal and a semiconductor. A metal-insulatorsemiconductor (MIS) barrier contains a very thin film of oxide between lhe metal and semiconductor Iayers; in a semiconductor-insulator-semiconductor (SIS) barrier, a high-conductivity, transparent, large-bandgap semiconductor layer replaces the metal of the MIS cell. 3. A junction diode with the junction formed between the semiconductor and a metal contact rather than between dissimila semiconductor materials, as in the case of an ordinary pn diode. Schottky-barrier detector-A detector based on a Schotf.ky barrier-a current-rectifying contact at a junction between a semiconductor and a metal. Schottky barrier diode- Also called Schottky diode and hot carrier diode. 1. A junction diode with the junction formed between the semiconductor and a metal contact rather than between dissimilar semiconductor materials, as in the case of an ordinary pn diode. 2. A special diode characterized by nanosecond switching speed, but relatively low voltage (45 V max) and limited temperature range (125T to 150'C). Schottky diode-See Shottky barrier diode. Schottky rectifier- A high-speed rectifier that makes M S of ~ the rectification effect of a metal-to-silicon barrier. Low forward-voltage characteristics provide high rectification efficiency, while majority carrier forward conduction enhances switching speed. Schottky transistor logic -Abbreviated STL. An improved version of integrated injection logic that has a power-delay product that is three times lower than that for 1%. Schottky TTL-1. A TTL circuit that incorporates Schottky diodes to greatly speed up TTL circuit operation. 2. A very high speed TTL circuit using metdsemiconductor diodes (Schottky diodes) to prevent transistors from saturating. 3. Integrated circuits modified by having a special diode built into each transistor. These diodes enable the transistor to be turned off much faster than would otherwise be possible. scierntCfic notation-In a calculator, the number entered or a result displayed in terms of a power of 10.

Schematic. ISOLATION

02

D3

P

EMITTER

BASE

Schottky barrier diode.

For example, the number 1234 is entered as 1.234 x lo3, and the number 0.001234 would appear as 1.234 x scintillate-To emit flashes of light. scintillation- 1. In radio propagation, a random and usually relatively small fluctuation of the received field about its mean value. 2. Also called target glint or wander. On a radar display, a rapid apparent displacement of the target from its mean position. 3. The flash of light produced by an ionic action. 4. A momentary breakdown of a tantalum oxide film in a capacitor, accompanied by rapid heating of the dielectric. Such events are caused by capacitor overvoltages or improper techniques of capacitor manufacture. 5. The flash of light produced by certain crystalline materials when a charged particle is passed through them. 6. Rapid fluctuation in parameters such as the amplitude or the phase of a wave passing though a medium with small-scale irregularities that cause irregular changes in the transmission path with time; akin to twinkling.

'

P

02

Y N - P

OXIDE

7,-P

COLLECTOR

Cross section.

01

01

90,

EN

N + Y

Schottky transistor logic.

03

C

E,

P

Y

P

scintillation conversion efficiency

- scrambled speech

scintillation conversion efficiency-In a scintillator, the ratio of the optical photon energy emitted to the energy of the incident particle or photon of ionizing radiation. scintillation counter -A device that indirectly detects charged particles and gamma rays and neutrons by using a photomultiplier tube to convert the short flashes of light produced as the particle passes through a transparent scintillating material into electric signals that can be recorded. One advantage of scintillation counters is that they are very fast; by this is meant that they have a very small resolving time. scintillation-counter cesium resolution-The scintillation-counter energy resolution for the gamma ray or conversion electron emitted from cesium-137. scintillation-counter energy resolution -In a scintillation counter, a measure of the smallest discernible difference in energy between two particles or photons of ionizing radiation. scintillation-counter energy-resolution constant-The product of the square of the scintillationcounter energy resolution times the specified energy. scintillation-counter h e a d -The combination of scintillators and photosensitive devices that produces electrical signals in response to ionizing radiation. scintillation-counter time discrimination-In a scintillation counter, a measure of the smallest time interval between two successive individually discernible events. Quantitatively, the standard deviation of the timeinterval curve. scintillation crystals- Special crystals that emit flashes of light when struck by alpha particles. scintillation d e c a y time-The time required for the decrease of the rate of emission of optical photons in a scintillation from 90 percent to 10 percent of the maximum value. scintillation duration -The interval from the time of emission of the first optical photon of a scintillation to the time when 90 percent of the optical photons of the scintillation have been emitted. scintillation rise time-The time interval occupied by the increase of the rate of emission of optical photons of a scintillation from 10 percent to 90 percent of the maximum value. scintillator-The combination of the body of scintillator material and its container. scintillator material -A material that exhibits the property of emitting optical photons in response to ionizing radiation. scintillator-material total-conversion

670

scoring s y s t e m -In motion-picture production, a system for recording music in time with the action on the film. Scott connection -A method of connecting transformers to convert two-phase power to three-phase or vice versa. Scott’s b r e a k d o w n theory-Breakdown is due to the attainment of a critical avalanche size that leads to a conducting path. SCR -Abbreviation for silicon controlled rectifier. The formal name is reverse-blocking triode thyristor. 1. A thyristor that can be triggered into conduction in only one direction. Terminals are called anode, cathode, and gate. 2. A semiconductor device that functions as an electrically controlled switch for dc loads. The SCR is one type of thyristor. 3. A power switching device in which a pulse at the gate (input) initiates a switching action in the output circuit. It conducts only during the positive half-cycle of ac. 4. A type of thyristor that is designed for forward bias, unidirectional power switching, and control. See also thyristor.

MOLDED PLASTIC

GATE

WIRES

SILICON CHIP

In molded plastic case.

CURRENT

HEAVY. CONDUCTION REGION

effi-

ciency-In a scintillator material, the ratio of the produced optical photon energy to the energy of a particle or photon of ionizing radiation that is entirely absorbed in the scintillator material. scissor-To apportion a drawing into segments that can be viewed on a CRT screen. scissoring -The ability of the vector generator to blank the beam whenever it is moved outside of the screen (where the image becomes distorted). scope -Slang for a cathode-ray oscilloscope. s c o p h o n y television s y s t e m -A mechanical television projection system developed in England. In it, ingenious optical and mechanical methods provide large, bright images suitable for theater installation as well as home television receivers. The apparent screen brightness is multiplied several hundred times because several hundred picture elements are projected simultaneously. s c o r e d substrate-A substrate that has been scribed with a thin cut at the break lines. See snap-strate.

/

REVERSE BREAKDOWN

Characteristic curve.

SCR. scramble- 1. To transpose andlor invert bands of frequencies, or otherwise modify the form of the intelligence at the transmitting end, according to a prearranged scheme in order to obtain secrecy. 2. To mix, in cryptography, in a random or quasi-random fashion. scrambled s p e e c h -Also called inverted speech. Speech that has been made unintelligible (e.g., for secret transmission) by inverting its frequency. At the receiving end, it can then be converted back into intelligible speech by reinverting the frequency.

67 1 scrambler-1. A device used to electronically alter a signal so that it can only be viewed or heard on a receiver equipped with a special decoder. 2. An electrical device that uses one or more methods to convert speech or video into a secret, unintelligible form. 3. A device that changes data so it appears to be in a random pattern. A descrambling device can change (unscramble) this data back to its original pattern. scrambler circuit-Also called a speech scrambler. A circuit in which essential speech frequencies are divided into several ranges by filters and then inverted to produce scrambled speech. See also speech inverter. scrambling-A method of altering the identity of a video or audio signal in order to prevent its reception by persons not having authorized decoders. scratch filter--A low-pass filter, often an integral part of an amplifier circuit, that attenuates the higher frequency noise derived from disk recordings. The scratch filter is also suitable for the suppression of background noise produced by tape background hiss. scratch pad -1. hiformation that the processing unit of a computer stores or holds temporarily. It is a memory containing subtotals for various unknowns that are needed for final results. 2. An area of RAM used for short-term storage of data during a process. 3. Group of general-purpose registers without specific function, providing a high-speed workspace. Usually, an internal RAM in a computer. scratch-pad memory- 1. A high-speed, limitedcapacity computer information store that interfaces directly with the central processor. It is used to supply the central processor with the data for the immediate computation, thus avoiding the delays that would be encountered by interfacing with the main memory. (The function of the scratch-pad memory is analogous to that of a pad of paper used for jotting down notes.) 2. A highspeed memory used to temporarily store small amounts of data that may be needed often and without delay. 3. Any memory space used for the temporary storage of data. Typically, scratch-pad memories are high-speed integrated circuits that are addressed as internal registers. Screen- 1. The sudace on which the visible pattern is produced in a cathode-ray tube. 2. A metal partition that isolates a device from external electric or magnetic fields. 3. See screen grid. 4. Surface on which the master artwork of the circuit pattern is projected. Screen fabrics include polyester, stainless steel, nylon, and silk. 5 . The surface of a medium on which a visible image, pattern, or picture is produced, generally within a camera or cathoderay tube. screen angle-A vertical angle bounded by a straight line from the radar antenna to the horizon and the horizontal at the antenna, assuming a 413 earth's radius. Screen deposition-The laydown of a circuit pattern on a substrate using the silk screening technique. Screen dissipation-The power that the screen grid dissipates as heat after bombardment by the electron Strealtl.

screen grid-Also called a screen. A grid placed between a control grid and an anode in a vacuum tube and usually maintained at a fixed positive potential. By reducing the electrostatic influence of the anode, it prevents the electrons from bunching in the space between the screen grid and the cathode. screen-grid modulation -Modulation produced by introducing the signal into the screen-grid circuit of any multigrid tube where the carrier is present. screen-grid tube-A vacuum tube in which a grid is placed between the control grid and the anode to prevent the latter from reacting with the control grid.

scrambler

- scrolling

screen-grid voltage -The direct-voltage value applied between the screen grid and the cathode of a vacuum tube. screening- 1. The process whereby the desired film circuit patterns and configurations are transferred to the surface of a substrate during manufacture by forcing a material through the open areas of the screen, using the wiping action of a soft squeegee. 2. 'The display of raw or processed data for operator verification. 3. The process of performing 100-percent inspection on product lots and removing defective units. screening test-A test or combination of tests intended to remove unsatisfactory items or those likely to exhibit early failure. screen printing (thickfilm)-- 3. The art of depositing conductive, resistive, and insulating materials on a dielectric base. This deposition is made through selected open areas in screens with inks or pastes forced through the open areas of the screen by squeegee motion onto the substrate base. In some cases, masks instead of conventional mesh screens may be used. 2. The basic thickfilm deposition process in which the paste is squeegeed through a fine-mesh stencil screen to produce a prescribed pattern on a substrate. screen savers -Software that automatically blanks a monitor screen or displays a moving pattern if there has been no user interaction with the computer for a specified time. Screen savers are used to preventing a fixed pattern from being burned into the screen phosphor. As soon as the operator touches any key or moves the mouse, the screen saver disappears and the original display returns to the screen. scribe and break-ne procedure used to separate a processed semiconductor wafer into individual ICs. Nmow channels between individual ICs are mechanically weakened by scratching with a diamond tip (scribe), sawing with a diamond blade, or burning with a laser. The wafer is mechanically stressed and broken apart along the channels (called scribe lines), thereby separating the individual ICs (dice). scribe projection--A method of automatic information presentation in which information is placed on a small metallic-coated glass slide by using a movable, servocontrolled, fine-pointed scribe to remove the coating. Light passed through the scribed area is projected onto a screen. scribing- 1. A process, similar to glass cutting, in which a slice of semiconductor devices is scored in rows and columns so that it may be separated easily into individual devices. The process is performed in a machine called a scriber by repeated movement of a weighted diamond stylus across the slice to form the scored pattern. 2. Scratching a tooled line or laser path on a brittle substrate to allow a wafer to be cleft or broken along the line, producing IC, transistor, or diode chips when all breaks are completed. scribing machines and tods-Equipment used to separate wafers into individual devices, chips, or dice. This has been done by crude techniques similar to glass cutting, but is now accomplished by more efficient methods using truncated pyramid diamond scribers, automated machines, conical tools, or lasers. script-Much like a macro, a set of program commands used to automate routine computing tasks. scroll -1. To move a video display up or down, line by line, or side to side, character by character. 2. To move all or part of the screen material up or down, or left or right, to allow new information to appear. scrolling -1. Moving the contents of the screen of a CRT up or down by one line at a time. 2. A multiplerung display function that allows all displayed rungs to be

s c r u b b i n g action

- secondary cell

moved up or down, adding the next or preceding rung at the bottom (or top) of the display. (As determined by the user, the display may be changed either one rung at a time or continuously.) 3. The vertical movement of information on a CRT screen, caused by the dropping of one line of displayed information for each new line added; the movement appears as an upward rolling if the new line is added at the bottom of the screen, and vice versa. scrubbing action-Rubbing of a chip device around on a bonding operation to break up the oxide layer and improve wetability of the eutectic alloy used in forming the bond. SCS-Abbreviation for silicon-controlled switch. SCU-Abbrevitaion for subscriber channel unit. A telephone interface circuit. S-curve-An S-shaped frequency-response curve showing how the output of a frequency-modulation detector or circuit varies with frequency. SDLC-Abbreviation for Synchronous Data Link Control. 1. A communications line discipline that initiates, controls, checks, and terminates information exchanges or communications lines. SDLC is designed for full-duplex operation (simultaneously sending and receiving data). 2. A protocol specifying a layered approach to serial data communications. sea clutter-See sea return. seal-Any device used to prevent gases or liquids from passing through. sealed contacts-A contact assembly enclosed in a sealed compartment separate from the other parts of the relay. s e a l e d - g a g e pressure transducer -A pressure transducer that has the sensing element sealed in its case at room ambient pressure. The sealing method holds the original internal pressure for long periods of time. s e a l e d meter-A meter constructed so that moisture or vapor cannot enter the meter under specified test conditions. sealed relay- A relay that has both coil and contacts enclosed in a relatively airtight cover. sealed tube-A hermetically sealed electron tube used chiefly for pool-cathode tubes. sealing compound-A type of wax or pitch compound used in dry batteries, capacitor blocks, transformers, or circuit units to keep out air and moisture. sealing off-The final closing of the bulb of a vacuum tube or lamp after evacuation. seam welding -A resistance welding process in which overlapping spot welds are made progressively along a joint by means of circular electrodes. The circular seam-welding wheels roll along the overlapping edges to be welded, and the control circuit is arranged to pass current at sufficiently close intervals to produce the desired degree of overlapping of the spot welds. The primary purpose of a seam-welding joint is to produce liquid or airtight containers from comparatively thin sheet metal. search-1. In a radar operation, the directing of the lobe (beam of radiated energy) in order to cover a large area. A broad-beam antenna may be used, or a rotating or scanning antenna. 2. A systematic examination of the available information in a specific field of interest. 3. To scan available stored information. 4.The process of applying a sweeping tuning signal to the free-running oscillator portion of a phase-locked oscillator, causing the oscillator output frequency to pass within the capture bandwidth of the feedback network and ensuring a locked condition in response to a new reference frequency. 5. The process of finding a particular item in a file. Search

672 techniques include the sequential or linear search, the binary or logarithmic search, and direct lookup. s e a r c h coil -See magnetic test coil. search engine- 1. A computer program that helps users find information in most databases. 2. A database or index that can be queried to help find information on the World Wide Web. s e a r c h gate-A gate pulse that is made to search back and forth over a certain range. searchlighting -In radar, the opposite of scanning. Instead, the beam is projected continuously at an object. searchlight-type sonar- An echo-ranging system employing the same narrow beam pattern for both transmission and reception. search radar-A radar intended primarily for displaying targets as soon as possible after their entrance into the coverage area. s e a r c h receiver -See intercept receiver. s e a r c h time-The time required for location of a particular data field in a computer storage device. The process involves comparison of each field with a predetermined standard until an identity is obtained. Contrasted with access time. sea return-Also called sea clutter. In radar, the aggregate received echoes reflected from the sea. seasonal factors-Factors that are used to adjust sky-wave absorption data for seasonal variations. Those variations are due primarily to seasonal fluctuations in the heights of the ionospheric layers. seasoning -Overcoming a temporary unsteadiness of a component that may appear when the component is first installed. seating time-The elapsed time after the coil of a relay has been energized until the armature of the relay is seated. sec- Abbreviation for secondary winding of a transformer. SEC-Abbreviation for secondary-electron conduction. The transport of charge by secondary electrons moving through the interparticle spaces of a porous material under the influence of an externally applied electric field. SECAM-Abbreviation for Sequential Color and Memory System (Sdquential Couleur avec it46mire). A color TV system with 625 lines per frame and 50 fields per second, used primarily in France, Russia, parts of Africa, and the former states of the Soviet Union. SECAM uses alternating lines of U, V chroma information to modulate the frequency. It is quite different from NTSC and PAL standards. s e c o n d a r y - 1. The transformer output winding in which the current is due to inductive coupling with another coil called the primary. 2. Low-voltage conductors of a power-distributing system. s e c o n d a r y area -See secondary service area. secondary breakdown -A condition that occurs in bipolar transistors brought on by hot spots occurring within the device structure. This is a type of thermal runaway and in most cases causes permanent device damage. s e c o n d a r y calibration -Also called sense step. Calibration of accessory equipment in which a transducer is deliberately unbalanced electrically to change the output, voltage, current, or impedance. Generally performed by means of a calibration resistor that is placed across one leg of the bridge. s e c o n d a r y cell-A voltaic cell that, after being discharged, may be restored to a charged position by an electric current sent through the cell in a direction opposite that of the discharge current. See also storage cell, 1.

s e c o n d a r y circuit

673 s e c o n d a r y circuit-The high-voltage part of an ignition system. s e c o n d a r y coior--A color produced by combing any two primary colors in equal propodons. In the lightadditive process, the three secondary colors are cyan, magenta, and yellow. S e c o n d a r y C o m m u n i c a t i o n s Authorization See SCA. s e c o n d a r y electron-An electron emitted from a material as a result of bombardment by electrons or of the collision of a charged particle with a surface. secondary-electron conduction tube -A sensitive TV tube that uses a two-step process to convert the invisible image to a charge image. In the image intensifier stage, fight ejects electrons from a photoemitter. After imaging and amplification in the middle or imaging section, the primary photoelectrons fall on the thin-film face of the secondary target. This charge image modulates the scanning beam current from the reading section. The electric field applied across the film causes a majority of the secondary electrons to be transported through a potassium chloride low-density fih layer to produce a secondary conduction current. secondary-electron multiplier -An amplifier tube in which the electron stream is focused onto a succession of targets, each of which adds its secondary electrons to the stream. In this way, considerable amplification is provided. secondary emission -The liberation of electrons from an element other than the cathode as a result of being struck by other high-velocity electrons. In a vacuum tube there are usually more secondary than primary electrons -a desirable phenomenon in electronmultiplier or dynatron-oscillator tubes. However, pentodes have a suppressor grid to nullify the undesirable effect of secondary emission. secondary-emission ratio-The average number of secondary electrons emitted from a surface per incident primary electron. secondary-emission tube-A tube that makes use of secondary emission to achieve a useful end. The photomultiplier is an example. s e c o n d a r y failure-1. A failure occurring as a direct result of the abnormal stress on a component brought about by the failure of another part or parts. 2. Any falure that is the direct or indirect result of a primary failure. secondary grid omission -Emission from the grid OF a tube as a result of high-velocity electrons being driven against it and knocking off additional electrons. The effect is the same as for primary grid emission. secondary insulation -A nonconductive material whose prime functions are to protect the conductor against abrasion and provide a second electrical barrier. Placed over the primary insulation. secondary line-The conductors connected between the secondaries of distribution transformers and the consumer service entrances. s e c o n d a r y radar--See radar. s e c o n d a r y radiation -Random reradiation of electromagnetic waves. secondary service area-Also called the secondary area. The service area of a radio or television broadcast station within which satisfactory reception can be obtained only under favorable conditions. s e c o n d a r y standard -A unit (e.g., length, capacitance, weight) used as a standard of comparison in individual countries or localities, but checked against the one primary standard in existence somewhere in the world. secondary station-Station licensed for a land location other than &e primary station location, i.e., for

- section

use at a subordinate location such as an office, vacation home, etc. secondary storage- Also called auxiliary storage. 1. Storage that is not an integral part of a computer, but which is directly linked to and controlled by it. 2. Devices that are used to store large quantities of data and programs. To be processed, these data and programs must first be loaded into primary storage. secondary voltage -The voltage across the secondary winding of a transformer.

..

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L -

SECONDARY WINDING

t

SECONDARY VOLTAGE

Secondary voltage.

secondarywinding -Abbreviatedsec. 1. The winding on the output side of a transformer. 2. A transformer winding that receives its energy by electromagnetic induction from a primary winding. secondary X-rays -X-rays given off by an object irradiated with X-rays. Their frequency depends on the material in the object. second breakdown- 1. A condition in which the output impedance of a transistor changes almost instantaneously from a large value to a small limiting value. It may be distinguished from normal transistor operation by the fact that once it occurs, the base no longer controls normal collector characteristics. Second breakdown is associated with imperfections in the device stnxture, usually being more severe in multiple-diffused, highspeed devices. 2. Lateral current instability through a transistor when operating at relatively high voltages and current. It has its greatest effect under dc conditions, but falls off with increasing temperature and frequencies; the breakdown caused is usually permanent. 3. A potentially destructive phenomenon that occurs in all bipolar transistors. This phenomenon may occur when the transistor operates in the active region with a forward-biased emitter-to-basejunction, or with the application of reverse bias during the cutoff mode of transistor operation. second-channel attenuation -Alternate-channel attenuation. See also selectance, 2. s e c o n d - c h a n n e l interference -Also called alternate-channel interference. Interference in which the extraneous power originates from an assigned (authorized) signal two channels away from the desired channel. second detector- Also called a demodulator. In a superheterodyne receiver, the portion that separates the audio component from the modulated intermediate frequency. second generation --In reference to computers, the period during which transistors took the place of vacuum tubes; the period began in the mid-1950s. second-generation computer-A computer in which solid-state components are used. second source- 1. The manufacturer of a device, other than the original manufacturer. 2. A reference to the manufacture by a competitive company of a part that is electrically and mechanically identical to the original part. second-time-around e c h o -An echo received after a time interval greater than the pulse interval. section -1. A four-terminal network that cannot be divided into a cascade of two simpler four-terminal networks. 2. One individual span of a radio relay system;

sectional center - s e i s m o g r a p h the number of sections in a system is one more than the number of repeaters. sectional center-A toll switching point to which are connected a number of primary outlets. sectionalized vertical antenna -A vertical antenna separated into parts by insulators at one or more points along its length. When suitable reactances or driving voltages are placed across the insulated points, the current distribution is modified to give a more desirable radiation pattern in the vertical plane. sectionalizing-Breaking up of a distribution feeder into smaller sections to minimize the extent of power interruption to customers. sector- 1. The smallest recordable unit on a CD. A disc can contain [(75 sectors per second) x (60 seconds per minute) x (number of minutes on disc)] sectors. The amount of data contained in the sector depends on the physical format and mode in which it is recorded; for regular CD-ROM (Mode 1) data, 2048 bytes (2 kilobytes) of data can fit. 2. A segment of a magnetic disk's track, typically occupied by one block of data. 3. The smallest contiguous storage area on a magnetic secondary storage medium. In microprocessor systems with flexible diskette drives as the secondary storage medium, sector size is typically 128 bytes. sectoral horn-A horn with two parallel and two diverging sides.

Sectoral horn.

sector cable-A multiconductor cable in which the cross section of each conductor is essentially a sector of a circle, an ellipse, or some figure intermediate between them. Sector cables are used in order to make possible the use of larger conductors in a cable of given diameter. sector conductor-A stranded conductor whose cross section is approximately the shape of a sector of a circle. A multiconductor insulated cable with sector conductors has a smaller diameter than the corresponding cable with round conductors. sector display- A range-amplitude display used with a radar set. The antenna system rotates continuously, and the screen (of the long-persistence type) is excited only while the beam is within a narrow sector centered on the object. sector scan -A scan in which the antenna oscillates through a selected angle. sector scanning-Modified circular scanning in which only a portion of the plane or flat cone is generated. secular variation-A slow variation in the strength of the earth's magnetic field.

674

secure mode -The condition of an alarm system in which all sensors and control units are ready to respond to an intrusion. secure voice-Voice message that is scrambled or coded, therefore not transmitted in the clear. SED -Abbreviation for spectral energy distribution. S e e b e c k coefficient-The ratio of the open-circuit voltage to the temperature difference between the hot and cold junctions of a circuit exhibiting the Seebeck effect. S e e b e c k coefficient of a couple-For homogeneous conductors, the limit, as the difference in temperature approaches zero, of the quotient of the Seebeck emf divided by the temperature difference between the junctions. By convention, the Seebeck coefficient of a couple is considered positive if, at the cold junction, the first named conductor has a positive potential with respect to the second. It is the algebraic difference between either the relative or absolute Seebeck coefficients of the two conductors. S e e b e c k effect- 1. The production of an electromotive force (emf) in a circuit composed of two dissimilar metals when their two junctions are at different temperatures. The emf is considered to be the resultant of the Peltier and Thomson emfs around the circuit. 2. Characteristic of dissimilar metals in thermoelectric solar cells whereby separate junctions exhibiting distinct temperatures transform incident voltage into a current. Seebeck e m f -Also called thermal emf. The emf produced by the Seebeck effect. seed-A special single crystal from which large single crystals are grown by the Czochralski technique. seed crystal -A crystal used to start the growing of a large semiconductor ingot. s e e k - 1. With reference to a computer, to look for data according to information given with respect to that data. 2. Moving a set of readwrite heads so that one of them is over the desired track. s e e k time-The time needed to position the head of a disk drive over the specified track. segment-1. In a routine, the part short enough to be stored entirely in the internal storage of a computer, yet containing all the coding necessary to call in and jump automatically to other segments. 2. To divide a program into an integral number of parts, each of which performs a part of the total program and is short enough to be completely stored in internal memory. segmental conductor-A round, stranded conductor composed of three or four sectors slightly insulated from one another. This construction has the advantage of lower ac resistance (less skin effect). segmentation-A technique for managing variablesliced areas of memory, termed segments, that contain logical program parts. segmented thermoelectric arm -A thermoelectric arm made up of two or more materials that have different compositions. segmenting -See partitioning. segment table-A table that describes all segments of a task and is used by the operating system for memory allocation, relocation, and paging. seismic mass- The force-summing member for applying acceleration andor gravitational force in an accelerometer. seismic sensor -A sensor, generally buried under the surface of the ground for perimeter protection, that responds to minute vibrations of the earth generated as an intruder walks or drives within its detection range. s e i s m o g r a p h -An instrument for recording the time, direction, and intensity of earthquakes or of earth shocks produced by explosions.

475 seize-To access or connect to a communications circuit while at the same time making it busy to prevent intrusion. selcal- Acronym for selective calling system. This system allows a teleprinter to be remotely controlled by a unique code. selectance- 1. A measure of the drop in response as a resonant device loses its resonance. It is the ratio of the amplitude of response at the resonant frequency to the response at some other specified frequency. 2. Often expressed as adjacent-channel attenuation (ACA) or secondchannel attenuation (SCA). The reciprocal of the ratio of the sensitivity of a receiver tuned to a specified channel to its sensitivity at another channel a specified number of channels away. selected mode--A mode of operation for an encoder selector circuit in which one set of brushes is selected to be read and another inhibited from being read; also a mode of operation for a system controlling several encoder outputs in which the encoder is selected to be read and all others inhibited from being read. selection check-A verification of a computer instrwtion, usually automatic, to ensure that the correct register or device has been chosen. selection ratio-The ratio of the least magnetomotive force used to select a cell or core to the maximum magnetomotive force used that is not intended to select a cell or core. selection sort-A simple sorting algorithm for putting aU the elements in a file in order. selective-The characteristic of responding to a desired frequency to a greater degree than to other frequencies. selective absorption-Absorption of rays of a certain group of frequencnes only. selective calling -I. A means of calling in which code signals are transmitted for the purpose of activating the automatic attention device at the station being called. 2. A type of operation in which the transmitting station can specify which of several stations on a line is to receive a message. selective diffusion -The process in which specified isolated regions in a semiconductor material are doped. The components in a silicon integrated circuit are formed in this way. selective dump-A dump of a selected area of internal computer storage. selective fading-Fading in which the received signal does not have the same variation in strength for all frequencies in the band. Selective fading usually occurs during multipath transmission. selective interference -Interference whose energy is concentrated within narrow frequency hands. selective ringing-An arrangement used on telephone party lines so that only the bell of the called subscriber rings. selective s q u e l c h ---See squelch circuit. selectivity- 1. The characteristic that determines the extent to which the desired signal can be differentiated from disturbances of other frequencies. 2. A tuner’s abirity to discriminate between a wanted signal and an interfering signal on adjacent frequency settings of the tuning dial. It is the ratio (in decibels) of the signal strength that produces a standard output on the desired channel to the strength of a signal on a nearby channel needed to produce an output 30 dB below the standard level. Selectivity measurements usually refer to signals on the alternate channel (400 kHz from the desired channels in FM and 20 kHz in AM); selectivity measured on the adjacent channel (200 kHz for FM, 10 kHz for AM)

seize - self-balancing recorder is usually lower. The higher the selectivity, the less interference there will be from signals on nearby channels, which is most important in crowded metropolitan areas. 3. The characteristic that determines the extent to which the desired frequency can be differentiated from other frequencies. selectivity control-The control for making a receiver more selective. select lines-In a core memory array, the wires that pass through magnetic cores and carry the selecting coincident currents. selector pulse-A pulse used to identify one event of a series. selector relay-A relay capable of automatically selecting one or more circuits. selector s w i t c h --A multiposition switch that permits one or more conductors to be connected to any of several other conductors. selectron-A computer-memory tube capable of storing 256 binary digits and permitting very rapid selection and access. selenium-A chemical element with marked photosensitive properties and a resistance that varies inversely with illumination. It is used as a rectifier layer in metallic rectifiers. selenium cell -A photoconductive cell consisting of a layer of selenium on a substrate whose electrical resistance varies with the illumination falling on the cell. (Selenium cells have been largely replaced by photocells of one kind or another.) selenium rectifier-A metallic rectifier in which a thin layer of selenium is deposited on one side of an aluminum plate and a highly conductive metal is coated over it. Electrons flow more freely from the coating to the selenium than in the opposite direction, thereby providing rectification.

Selenium rectijier.

self-adapting --Pertaining to the ability of a system to change its performance characteristics in response to its environment. self-adaptive system-A system that can exhibit the qualities of reorganization andlor learning. self-adjusting communication-See adaptive communication. self-aligned t h i c k oxide-A term used to describe a proprietary low-voltage, self-aligned gate process. self-aligning-gate MOS-Abbreviated SAG MOS. 1. An MOS device in which a polycrystalline silicon layer is substituted for the usual aluminum metal gate. The key feature is a different processing technology in which the gate is automatically aligned. 2. A process in which materials like polycrystalline silicon or refractory metals are used in place of aluminum at the gate. These materials act as a mask and result in the gate being automatically aligned between source and drain regions. self-balancing recorder-A recording device operating on the servomechanism principle.

self-bias - self-quenching oscillator self-bias- Also called automatic bias. The voltage developed by the flow of vacuum-tube current through a resistor in a grid or cathode lead. self-capacitance -See distributed capacitance. self-checking code-In computers, a code in which errors produce forbidden combinations. A single self-checking code produces a forbidden combination if a digit gains or loses a single bit. A double self-checking code produces a forbidden combination if a digit gains or loses either one or two bits, and so forth. self-cleaning contact-See wiping contact. self-complementing code-A machine language in which the code of the complement of a digit is the complement of the code of the digit. self-contained instrument -An instrument that has all the necessary equipment built into the case or made a corporate part thereof. self-demagnetization -The process by which a magnetized sample of magnetic material tends to demagnetize itself by virtue of the opposing fields created within it by its own magnetization. Self-demagnetization inhibits the successful recording of signal components having short wavelengths or sharp transitions. self-diagnostic -The hardware and firmware within a controller that allows it to continuously monitor its own status and indicate any fault that could occur within it. self-discharge-The loss of useful capacity of a cell or battery in storage due to internal chemical reactions; for example, chemicals evaporating, or electrolyte slowly reacting with the anode even on open circuit. self-energizing -A type of electrostatic phone that uses the stepped-up signal voltage to supply the dc polarizing voltage required for operation. self-erasure -The tendency for strongly magnetized areas of the tape coating to erase adjacent areas of opposite-polarity magnetization. This is a major cause of loss of high frequencies at reduced tape speeds. self-excitation -The supplying of required exciting voltages by a device itself rather than from an external source. self-excited -A type of generator that provides the current for its own field coils. self-excited oscillator-An oscillator that operates without external excitation and solely by the direct voltages applied to the electrodes. It depends on its resonant circuits for frequency determination (i.e., not crystal controlled). self-extinguishing -Material that ignites and bums when exposed to flame or elevated temperature, but which stops burning when the flame or high temperature is removed. self-focused picture tube- A television picture tube with an automatic electrostatic focus designed into the electron gun. self-generating transducer -A transducer that requires no external electrical excitation to provide an output. self-healing - 1. The characteristic of metallized capacitors by which faults or shorts occurring during operation are removed, or healed, by an internal clearing action, and the part continues to function. See also clearing, 1. 2. The process by which the electrical properties of the capacitor, after local breakdown of the dielectric, are instantaneously and essentially restored to the values before the breakdown. self-healing capacitor-A capacitor that restores itself to operation after a breakdown caused by excessive voltage. The electrode layer is so thin that a small part of the energy released in a breakdown condition is quite sufficient to evaporate the metal layer around the

676 breakdown point and, thus, to terminate the breakdown in the shortest possible time. Only a small healed area is produced in the dielectric, and the capacitor voltage only drops to a minimal extent during the breakdown. self-heated thermistor -A thermistor whose body temperature is significantly higher than the temperature of its ambient medium as a result of the power being dissipated in it. self-heating coefficient of resistivity-The maximum change in resistance due to temperature change caused by power dissipation, at constant ambient temperature. Usually expressed in percent or per-unit (ppm) change in nominal resistance per watt of dissipation. This parameter is actually the product of the power coefficient and the resistor temperature coefficient. self-impedance-At any pair of terminals of a network, the ratio of an applied potential difference to the resultant current at these terminals (all other terminals open). self-inductance- 1. The property that determines the amount of electromotive force induced in a circuit whenever the current changes in the circuit. 2. At any pair of terminals of a network, the ratio of an applied potential difference to the resultant current at these terminals, all other terminals being open. self-induction -The property that causes a counterelectromotive force to be produced in a conductor when the magnetic field produced by the conductor collapses or expands with a change in current. self-inductor- An inductor used for changing the self-inductance of a circuit. self-instructed carry- A system of executing the carry process in a computer by allowing information to propagate to succeeding places as soon as it is generated, without receipt of a specific signal. self-latching relay-A relay in which the armature remains mechanically locked in the energized position until deliberately reset. self-optimizing communication -See adaptive communication. self-organizing -Having to do with the ability of a system to arrange its own internal structure. self-organizing machines-Machines that can recognize, or learn to recognize, such stimuli as patterns, characters, and sound, and which can then adapt to a changing environment. self-passivating glaze-The glassy material in a thick-film resistor that comes to the surface and seals the surface against moisture. self-powered -Equipment containing its own power supply. It may be either a combination of wet and dry cells, or dry cells in conjunction with a spring-driven motor. self -pulse modulation -Modulation accomplished by using an internally generated pulse. See also blocking oscillator, 1. self-pulsing -A special type of grid-pulsing circuit that automatically stops and starts the oscillations at the pulsing rate. self-quenched counter tube-A radiationcounter tube in which reignition of the discharge is inhibited. s e l f - q u e n c h e d detector-A superregenerative detector in which the grid-leak grid-capacitor time constant is sufficiently large to cause intermittent oscillation above audio frequencies. As a result, normal regeneration is stopped just before it spills over into a squealing condition. self-quenching oscillator- An intermittent selfoscillator producing a series of short trains of rf oscillations separated by intervals of quiescence. The quiescence

677 is caused by rectified oscillatory currents, which build up to the point at which they cut off the oscillations. self-rectifying X-ray tube- An X-ray tube operating with an alternating anode potential. self-refresh -In a dynamic RAM, a method of asynchronously refreshing during a battery backup mode of operation with only one control pin held active. self-regulation -The tendency of a component or system io resist change in its condition or state of operation. self-repeating timer-A form of he-delay circuit in which relay contacts are used to restart the tirne delay. self-reset- Automatically r e w i n g to fie original position when normal conditions are resumed (applied chiefly to relays and circuit breakers). self-saturating rectifier-A half-wave rectifyingcircuit element connected in series with the output reactor in a self-smmting windings of a magnetic-amplifier circuit. self-saturation-The saturation obtained in a magnetic amplifier by rectifying the output current of a saturable reactor. self-screening range-The range at which a target can be detected by a radar in the midst of its jamming mask, with a certain specified probability. method of self-selecting v Scan-The vpScan redng a po~ystrop~c cde (primarily the binary code), in which diode logic circuits are used internally in the encoder to perform &e necessary bit-to-bit selection to prevent ambiguity in the encoder output data. syns y n c h r o n o u s m0tor-A chronous motor provided with the equivalent of a squirrelcage winding so it can be started like an induction motor. counter self-stopping modulo-n counter-A having IZ distinct states that stops when it reaches a predetermined maximum number; it then does not accept count pulses until it is reset to a number less than the maximum number. self-,sustained oscillations-OscilIations maintained by the energy fed back frorn the output the input circuit. Self-testing-The ability of a piece of equipment to automaticd'y verify the Propr OFration Of its components or subsystems. se''-threading ree'-A device for and storing tape; in Particular, one that does not require aid affix Or start the first turn Of tape On its winding surface or hub. Flanges on such reels can be continuous and free O f windows; winding Surfaces are continuous and free of distortion-producing threading Slots. self-wiping contacU-See wiping contact. s e l s y n -Electrical remote-indicating instrument operating on direct current in which the angular position of the transmitter shaft carrying a contact arm moving on a resistance strip controls the pointer on the indicator dial. SEN! - 1. Abbreviation for standard electronic module. A subassembly configuration format that meets a particular US.Navy set of specifications. 2. Abbreviation for scanning electron microscope. semantics -The relationships between symbols and their meanings. semaphore-See lock byte. semiacthe homing guidance-A system of homing guidance in which radiations used by the receiver in the nnissile are reflected from a target being illuminated by an outside source. semiactive repeater -A communications satellite that uses a minimum of onboard electronics to take a modulated signal beamed at it from a ground station and

self-rectifying X-ray tube - semiconductor device transfer its information (modulation) into an unmodulated beam (on a different frequency) set up by the receiving station. For this transfer it uses Van Atta or other directive arrays and nonlinear elements. Semiautomatic Ground Environment -Abbreviated SAGE. An air-defense system in which data from air surveillance is processed for transmission to computers at direction centers. semiautomatic keying circuits-Mechanization that provides torn-tape switching systems in teleprinter links. Incoming and outgoing messages are placed on tapes that are inserted m m d Y into a distrhtor that provides automatic mechanical keying of the circuit. f%?miautomatic message switching CentW-A center at which messages axe routed by an operator on the basis Of information contained in them. s e m i a u b l l l a t i cph0nograph-A PhonoWPhhaving automatic arm return and motor shutoff at the end of a record, but no automatic start and tonearm setdown at the beginning Of play. semiautomatic starter-A starter in which some of the operations are not automatic, but selected portions are s e m i a u t o m a t i c tape relay-A method of communication whereby messages are received and retransmitted in teletypewriter tape form involving manual intervention in the transfer of the tape from the receiving reperforator transmitter. to the semiautomatictelephone '#em-' system in which operators receive orders from the calling parties verbally, but use automatic apparatus in making connections' semiconducting material-A solid or liquid having a resistivity midway between that of an insulator and a metal, semiconductor-^, A class of materials, such as silicon and whose electrical properties lie between those of conductors (such as copper and aluminum) and insulators (such as glass and rubber), in which the charge carrierconcentration increases with increasing temperature over some temperature range. Over most of the practical temperature range, the resistance has a negative coefficient. negative semicondncto~possess two types of electrons and positive holes. The charge carriers are usually electrons, but there may be also some ionic conductivity, 2. An electronic device whose main functioning parts are made from semiconductor materials. Examples include lead lead teuwride. selenium, silicon, silicon carbide. Used in &odes, photocells, thermistors. and transistors. 3, A device (or with an electrical conductivity that lies between metal conductors and insulator devices. 4. A material whose resistivity is between that of insulators and conductors. The resistivity is often changed by light, heat, and electric field, or a magnetic field. Current is often achieved by transfer of positive holes as well as by movement of electrons. 5. A material that exhibits relatively high resistance in a pure state and much lower resistance when it contains small amounts of certain impurities. The term is also used to denote electronic devices made from semiconductor materials. semiconductor carrier -A permanent protective structure that provides for mounting and for electrical continuity in application of a semiconductor chip to a major substrate. semiconductor c h i p -A single piece of semiconductor material of any dimension. semiconductor device- 1. A device in which the characteristic distinguishing electron conduction takes place within a semiconductor material, ranging from the

semiconductor diode

- sender

single-unit transistor to multiple-unit devices such as the semiconductor rectifier. Other devices are diodes, photocells, thermistors, and thyristors. 2. A device in which n-type and p-type materials are used in combination to obtain specific characteristics for controlling the flow of current. 3. A device, including its encapsulation and terminals, whose essential characteristics are governed by the flow of charge carriers within a semiconductor material. semiconductor diode-1. A device consisting of n-type and p-type semiconductor material joined together to form a pn junction, which passes current in the forward direction (from anode to cathode) and blocks current in the reverse direction. High reverse voltages, such as transients greater than a specified limit, can destroy the junction due to excessive reverse leakage currents. See also crystal diode. 2. A light-emitting diode that emits coherent light by suitably arranged geometry. Gallium arsenide is used for lasers of this type. 3. A two-electrode semiconductor device that conducts current more easily in one direction. semiconductor-diode parametric amplifier A parametric amplifier using one or more varactors. semiconductor ignition system-An ignition system for internal combustion engines that employs solid-state semiconductors for switching purposes. semiconductor integrated circuit -Abbreviated SIC. 1. Complex circuits fabricated by suitable and selectively modifying areas on and within a wafer of semiconductor material to yield patterns of interconnected passive as well as active elements. The circuit may be assembled h m several chips and use thin-film elements or even discrete components to achieve a specified performance when the necessary device parameters cannot be achieved by materials modification. 2. The physical realization of a number of electric elements inseparably associated on or within a continuous body of semiconductor material to perform the function of a circuit. semiconductor intrinsic properties-Properties of a semiconductor that are characteristic of the ideal crystal. semiconductorjunction -The region of transition between semiconducting regions of different electrical properties, usually between p-type and n-type materials. semiconductor laser- 1. A device in which laser action takes place through stimulated recombination of free electrons in the conduction band with holes in the valence band of a direct-gap semiconductor such as gallium arsenide. 2. A light-emitting diode that uses stimulated emission to produce a coherent-light output. See also diode laser. semiconductor lead wire-Fine wire used to connect semiconductor chips to substrate patterns, packages, other chips, etc. Usually made from an aluminum alloy or gold. semiconductor material-1. A material in which the conductivity ranges between that of a conductor and an insulator. The electrical characteristics of semiconductor materials such as silicon are dependent on the small amounts of added impurities, or dopants. 2. A chemical element, such as silicon or germanium, that has a crystal lattice whose atomic bonds are such that the crystal can be made to conduct an electric current by means of free electrons or holes. semiconductor memory- 1. A memory whose storage medium is a semiconductor circuit. Often used for high-speed buffer memories and for read-only memories. 2. A memory in which semiconductors are used as the storage elements; characterized by low-to-moderate cost storage and a wide range of memory operating speed,

678 from very fast to relatively slow. Almost all semiconductor memories are volatile. 3. A memory with storage elements formed by integrated semiconductor devices, as opposed to a memory composed of ferrite cores. Semiconductor readwrite memories are characterized by low cost, wide speed ranges, and data volatility. Semiconductor read-only memories are nonvolatile. 4. A computer memory that uses silicon integrated-circuit chips. semiconductor photodiode-A semiconductor diode utilizing the photoelectric effect. semiconductor rectifier diode-A semiconductor diode designed for rectification and including its associated mounting and cooling attachments if integral with it. semicustom IC-An LSI circuit that incorporates either linear or digital components. Semicustom ICs are designed to serve as replacements for small- to mediumscale ICs and are based on the concept of integrating extremely complex functions onto a single IC to fulfill a particular custom function. One semicustom IC may replace anywhere from several to more than 100 individual ICs. The semicustom IC, initially processed up to, but not including, the interconnect level, is adapted to specific requirements with relative ease through patterning of the metal interconnect layer. By connecting the transistors (which may number in the thousands) on a single IC in different ways, various functions, such as flip-flops, gates, adders, and parity control, are created. These blocks are then interconnected to form an entire system function on the chip. semicustom large-scale integrated circuitSee gate array, 3. semicustom logic-Chips whose logic functions can be determined in the final stages of manufacturing, such as PLAs and gate arrays. semidirectional microphone-A microphone whose field response is determined by the angle of incidence in part of the frequency range but is substantially independent of the angle of incidence in the remaining part. semiduplex-In a communications circuit, a method of operation in which one end is duplex and one end simplex. This type of operation is sometimes used in mobile systems, with the base station duplex and the mobile station or stations simplex. A semiduplex system requires two operating frequencies. semimagnetic controller-An electrical controller whose basic functions are not all performed by electromagnets. semimetals -Materials, such as bismuth, antimony, and arsenic, having characteristics that class them between semiconductors and metals. semiremote control-Radio-transmitter control performed near the transmitter by devices connected to but not an integral part of the transmitter. semiselective ringing-An arrangement in which the bells of two stations on a telephone party line are rung simultaneously; differentiation is made by the number of rings. semitone-Also called half step. The interval between two sounds. Its basic frequency ratio is equal to approximately the twelfth root of 2. semitransparent photocathode-A photocathode in which radiant flux incident on one side produces photoelectric emission from the opposite side. sender-That part of an automatic-switching telephone system that receives pulses originated by a dial or other source and, in accordance with the pulses received, controls the further operations necessary to establish the connection.

679

sending-end impedance -Also calledthe drivingpoint impedance. The ratio of an applied potential difference of a transmission line to the resultant current at the point where the potential ,differenceis applied. sending filter-A filter used at the transmitting terminal to restrict the transmitted frequency band. sensation level -See level above threshold. sense- 1. In navigation, the relationship between the change in indication of a radionavigational facility and the change in the navigational parameter being indicated. 2. In some navigational equipment, the property of permitting the resolution of 180" ambiguities. 3. To examine or determine the status of some system components. 4. To read holes in punched tape or cards. sense amplifier-1. A circuit used to sense lowlevel voltages such as those produced by magnetic or plated-wire memories and to amplify these signals to the logic voltage levels of the system. 2. A circuit used in communications-electronics equipment to determine a change of phase or voltage and to provide an automatic control function. sense finder-In a direction finder, that portion which permits determination of direction without 180" ambiguity. sense-reversing reflectivity-The characteristic of a reflector that reverses the sense of an incident ray. (For example, a perfect comer reflector is invisible to a circularly polarized radar because it reverses the sense.) sense step-See secondary calibration. sense switch-Qne of a series of switches on the console of the digital computer that permits the operator to control some parts of a program externally. sense wire-A wire threaded through the core of a magnetic memory to detect whether a logical 1 or 0 is stored in the core when the core is interrogated by a read pulse. This technology is no longer in use. nsing -1. The process of determining the sense of an indication. 2. A technique used in a power supply regulator for monitoring the output voltage or current. In local sensing, the monitor points are the output terminals. In remote sensing, the monitor points are located at appropriate locations in the circuit being powered, connected by wire to sensing input terminals on the supply. sensing element-See primary detector. sensing field-The zone in which an object can be sensed by a proximity switch. sensistor -A silicon resistor whose resistance varies with temperature, power, and time. sensitive relay- 1. A relay requiring only a small current. It is used extensively in photoelectric circuits. 2. Any of a number of diEerent types of relays requiring very IOW pickup power. Generally considered to be one requiring less than 100 milliwatts of pickup power. sensitive volume -In a radiation-counter tube, the portion responding to a specific radiation. sensitivity -1. The minimum input signal required in a radio receiver or similar device to produce a specified output signal having a specified signal-to-noise ratio. This signal input may be expressed as power or voltage at a stipulated input network impedance. 2. Ratio of the response of a measuring device to the magnitude of the measured quantity. It may be expressed directly in divisions per volt, milliradians per microampere, etc., or indirectly by stating a property from which sensitivity can be computed (e.g., ohms per volt for a stated deflection). 3. The signal current developed in a camera tube per unit incident radiation density (Le., per watt per unit area). Unless otherwise specified, the radiation is understood to be that of unfiltered incandescent source of 2854 K, and its density, which is generally measured in watts per unit

sending-end impedance

- sensor

area, may then be expressed in lumens per foot. 4. The degree of response of an instrument or control unit to a change in the incoming signal. 5. In tape recording, the relative intensity of the magnetic signal recorded by a magnetizing field of a given intensity. 6. A measurement of the electrical output of a microphone for a given sound pressure level at its diaphragm. 7. The smallest input change that a DMM is able to display. It is equal to the least significant digit on the lowest measurement range. For example, a three-digit DMM with a 100mV range has 100 pV sensitivity. 8. Generally expressed in dBm at a specified impedance (usually 600 ohms), sensitivity is a measure of the lowest DTMF signal level that a receiver can detect. It represents an absolute threshold below which detection of a single frequency is not generated. 9. Measure of the ability of a device or circuit to react to a change in some input. 10. In television, a factor expressing the incident illumination on a specified scene required to produce a specified picture signal at the output terminals of a television camera. 11. A measure of relative output for a given input of a tape, microphone, etc. 12. Characteristic of a receiver that determines the minimum input signal strength required for a given signal output. Sensitivity is usually measured in microvolts (pV). sensitivity a d j u s t m e n t -Also called span adjustment. The control of the ratio of output signal to excitation voltage per unit measurand. Generally accomplished in a system by changing the gain of one or more amplifiers. The practice of placing excitation control components (such as potentiometers or rheostats) in series with the excitation to a transducer is a sensitivity adjustment for the system. However, in the latter case no significant change is introduced in the output-to-input ratio of the transducer. sensitivity control -The control that adjusts the amplification of the radio-frequency amplifier stages and thereby makes the receiver more sensitive. sensitivity-time control-Also called gain-time control or time gain. The portion of a system that varies the amplification of a radio receiver in a predetermined manner. sensitizing (electrostatography) -The establishing of an electrostatic surface charge of uniform density on an insulating medium. sensitometer- An instrument used to measure the sensitivity of light-sensitive materials. sensitometrl(--easurement of the light-response characteristics of photographic film. sensor- 1. In a navigational system, the portion that perceives deviations from a reference and converts them into signals. 2. A component that converts mechanical energy into an electrical signal, either by generating the signal or by controlling an external electrical source. 3. See primary detector. 4. An information-pickup device. 5. A transducer designed to produce an electrical output proportional to some time-varying quantity, as temperature, illumination, pressure, etc. 6. The component of an instrument that converts an input signal into a quantity that is measured by another part of the instrument. 7. Any device that can detect the presence of, or a change in the level of, light, sound, capacitance, magnetic field, etc. 8. A device or component that reacts to a change; the reaction is then used to cause a control or instnunent to function. For example, a thermistor changes resistance as temperature changes, and the resistance changes can be used in an electric circuit to vary current. 9. A transducer that converts a parameter at a test point to a form suitable for measurement by the test equipment. 10. A sensing element. The basic element of a transducer that usually changes some physical parameter to an electrical

sensory robot - sequential interlace signal. 11. A device that is designed to produce a signal or offer indication in response to an event or stimulus within its detection zone. 12. A component that provides an electrical signal in response to a specific physical or chemical stimulus such as heat, pressure, magnetic field, or a particular chemical vapor. Microsensors are fabricated using processes similar to those for manufacturing ICs, or extensions of such processes. Integrated microsensors incorporate an integrated circuit on the same die as that used for the sensor element. sensory robot-A computerized robot with one or more artificial senses, usually sight or touch. sentinel-1. A symbol marking the beginning or end of some piece of information in digital-computer programming. 2. See tag. separate excitation-Excitation in which generator field current is provided by an independent source, or motor field current is provided from a source other than the one connected across the armature. separately instructedcarry--Executing the carry process in a computer by allowing carry information to propagate to succeeding places only when a specific signal is received. separation-The degree to which two stereo signals are kept apart. Stereo realism is dependent on the successful prevention of their mixture before reaching the output terminals of the power amplifier. Tape systems have a separation capability inherently far superior to that of the disc systems. separation circuit-A circuit that separates signals according to their amplitude, frequency, or some other selected characteristic. separation filter-A combination of filters used to separate one band of frequencies from another-often, to separate carrier and voice frequencies for transmission over individual paths. separation loss-The loss that occurs in output when the surface coating of a tape fails to make perfect contact with the surfaces of either the record or reproduce head. separator- 1. An insulating sheet or other device employed in a storage battery to prevent metallic contact between plates of opposite polarity within a cell. 2. An insulator used in the construction of convolutely wound capacitors. 3. See delimiter. septate coaxial cavity-A coaxial cavity with a vane or septum added between the inner and outer conductors. The result is a cavity that acts as if it had a rectangular cross section bent transversely. septate waveguide-A waveguide with one or more septa placed across it to control microwave power transmission. septum-A thin metal vane that has been perforated with an appropriate wave pattern. It is inserted into a waveguide to reflect the wave. Plural: septa. Sequem- 1. The order in which objects or items are arranged. 2. To place in order. 3. A succession of terms so related that each may be derived from one or more of the preceding terms in accordance with some fixed law. sequence checking routine -A checking routine that examines every instruction executed and prints certain data concerning this check. Sequence control-Automatic control of a series of operations in a predetermined order. sequencer- 1. The component of a processor that controls the program flow by implementing branches for subroutine processing and handling interrupts. 2. A device or computer program that records, edits, and plays back MIDI data much like a word processor for music, such that you can fix wrong notes or lengthen or shorten notes.

680 3. A mechanical or electronic device that may be set to initiate a series of events and to make the events follow in sequence. 4. A circuit that pulls information from the control store memory, based on external conditions. 5 . In a bit-slice system, the module in charge of providing the next microprogram address to the microprogram memory. Essentially a complex multiplexer, but may include stack facilities and a loop counter. sequence relay-A relay that controls two or more sets of contacts in a predeteimined sequence. sequencer register-In a computer, a counter that is pulsed or reset following the execution of an instruction to form the new memory address that locates the next instruction. sequence timer - A succession of time-delay circuits arranged so that completion of the delay in one circuit initiates the delay in the following circuit. sequencing equipment -A special selecting device by means of which messages received from several teletypewriter circuits may be subsequently selected and retransmitted over a smaller number of trunks or circuit. sequency of operation-A detailed written description of the order in which electrical devices and other parts of the equipment should function. sequential access-1. An access mode in which records are retrieved in the same order in which they were written. Each successive access to a file refers to the next record in the file. 2. A term used to describe files such as magnetic tape that must be searched sequentially to find any desired record. 3. Computer access method in which a word is accessed by scanning sequential blocks or records. For example: a tape. 4. Data on storage, such as magnetic tape, that much be searched serially from the beginning to find any desired record. sequential-accessfile-A type of file structure in which data may only be accessed sequentially, one record at a time. Data stored on magnetic tape is an example of a sequential file. sequential-access memory -Abbreviated SAM. 1. A serial-type memory in which words are selected in a fixed order. The addressing circuit steps from word to word in a predetermined order, with the result that the access time for the stored information (words) is variable. 2. A method of information retrieval in which the complete memory is scanned and each word is, in its turn,read out, worked on, then rewritten. sequential circuit-A digital circuit that changes state according to an input signal (normally under clock control); it must be tested with a sequence of signals. sequential color television -A color television system in which the three primary colors are transmitted in succession and reproduced on the receiver screen in the same manner. sequential color transmission --The transmission of television signals that originate from variously colored parts of an image in a particular sequential order. sequential computer-A computer in which events occur in time sequence with little or no simultaneous occurrence or overlap of events. sequential control-Digital-computer operation in which the instructions are set up in sequence and fed to the computer consecutively during the solution of a problem. sequentiaf element-A device having at least one output channel and one or more input channels, all characterized by discrete states, such that the state of each output channel is determined by the previous states of the input channels. sequential interlace-A method of interlacing in which the lines of one field are placed directly under the corresponding lines of the preceding field.

68 1 sequential lobing -.A direction-determining technique utilizing the signals, of overlapping lobes existing at the same time. sequential logic-4. A circuit arrangement in a computer in which the output state is determined by the previous state of the input. See also combinatorial logic. 2. Part of a circuit iin which the output values are a function of the inputs and data stored within the circuit. sequential logic element-A device that has one or more output channels and one or more input channels, all of which have discrete states, such that the state of each output channel depends on the previous states of the input channel. sequential operating connector-A form of connector that has two or more groups of contacts that open and close in a predetermined sequence. For example, a connector that is designated for use with ground connections, power distribution, and signal circuits. Operates in such a way that when the connector is closed, the ground contacts close first, power contacts second, and signal contacts last. This sequence is reversed when the connector is opened. sequential operation-The carrying out of operations one after the other. sequential relay- A. relay that controls two or more sets of contacts in a predetermined sequence. sequential sampling -Sampling inspection in which the decision to accept, reject, or inspect another unit is made following the inspection of each unit. sequential scan--A system of TV scanning in which each line of the raster is scanned sequentially. sequential scanning -In television, rectilinear scanning in which the distance from center to center of successively scanned lines is equal to the nominal h e width. sequential switcher- A device that automatically permits the viewing of pictures from a number of CCTV cameras on one CCTV mionitor in a selected sequence. sequential timer--A timer in which each interval is initiated by the completion of the preceding interval. All intervals may be independently adjusted. sequential with memory-See SECAM. serial! - 1. Pertaining to time-sequential transmission of. storage of, or logical operations on the parts of a word in a computer-the same facilities being used for successive parts. 2. The technique for handling a binary data word that has more than one bit. The bits are acted upon one at a time, analogous to a parade passing a review point. 3. Typically refers to a port on a computer for transmitting one bit at a time. Modems and mice typically connect to a serial port. serial access- 1. Pertaining to transmission of data to or from storage in a sequential or consecutive manner. 2. Pertaining to the process in which information is obtained from or placed into storage with the time required for such operations dependent on the location of the information most recently obtained or placed in storage. See also random access. seriaii adder-A device in which additions are performed in a series of steps: the least significant addition is performed first, and progressively more significant additions are performed in order until the sum of the two numbers is obtained. serial arithmetic unit-In a computer, a unit in which the digits are opeirated on sequentially. See also parallel arithmetic unit. serial bit-Pertaining to computer storage in which the individual bits making up a word appear in time sequence. serial computer- A computer having a single arithmetic and logic unit.

sequential lobing - serial programming serial counter -Also called ripple-though counter. A counter in which each flip-flop cannot change state until after the preceding flip-flop has changed state; relatively long delays after an input pulse is applied to the counter can occur before all flip-flops reach their find states. serial data -Data transmitted sequentially, one bit at a time. serial digital computer-A computer in which the digits are handled serially. Mixed serial and parallel machines are frequently called serial or parallel, according to the way the arithmetic processes are performed. An example of a serial digital computer is one that handles decimal digits serially, although the bits that comprise a digit might be handled either serially or in parallel. See also parallel digital computer. serial interface- 1. A data channel that transfers digital data (1s and Os) in a serial fashion, one bit after another. Serial interfaces save space by requiring fewer lines compared with parallel interfaces, bnt at the sacrifice of data transfer speeds. 2. A port that sends or receives the eight bits in each byte one by one, much like beads on a string. Printers located far from a computer usually require a serial interface. serial 110-A method of data transfer between a computer and a peripheral device in which data is transmitted for input to the computer (or output to the device) bit by bit over a single circuit. serialize -To convert from parallel-by-bit to serialby-bit. serially reusable routine-A computer routine in main storage that can be used by another task following conclusion of the current use. serial memory- 1. A memory in which information is stored in series and reading or writing of information is done in time sequence, as with a shift register. Compared with a RAM, a serial memory has slow to medium speed and lower cost. See sequential-access memory. 2. A memory whose contained data is accessible only in a fixed order, beginning at some prescribed reference point. Data in any particular location is not available until all data ahead of that location has been read. Such a memory is inherently slow compared with a random-access memory. serial mode-A type of computer operation that is performed bit by bit, generally with the least significant bit handled first. Read-in and readout are accomplished bit after bit by shifting the binary data through the register. serial operation-1. In a digital computer, infonnation transfer such that the bits are handled sequentially, rather than simultaneously as they are in parallel operation. Serial operation is slower than parallel operation, but it is accomplished with less complex circuitry. 2. Type of information transfer within a programmable controller whereby the bits are handled sequentially rather than simultaneously, as they are in parallel operation. Serial operation is slower than parallel operation for equivalent clock rate. However, only one channel is required for serial operation. serial-parallel--Having the property of being partially serial and partially parallel. serial port-A method of data communication in which bits of information are sent consecutively through one wire. serial printer-A device that can print characters one at a time across a page. serial processing-The sequential or consecutive execution of more than one process into a single device such as a channel or processing unit. Opposed to pardel processing. serial programming -Programming of a digital computer in such a manner that only one arithmetical or logical operation can be executed at one time.

serial storage - serrated rotor plate serial storage -1. In a computer, storage in which time is one of the coordinates used in the location of any given bit, character, or word. 2. A storage media organization in which data or text is serially recorded one character or text block after another. Text access points are retrieved by serially searching through the medium (usually a magnetic-tape cassette or cartridge). serial transfer-Data transfer in which the characters of an element of information are transferred in sequence over a single path. serial transmission -1. Information transmission in which the characters of a word are transmitted in sequence over a single line. 2. The transmission of a character’s bits one at a time (implies a single transmission pathway). 3. A method of transferring information in which the code elements or pulses are sent sequentially, one after another. 4.Moving data in sequence one at a time, as opposed to parallel transmission. s e r i e s -1. The connecting of components end to end in a circuit, to provide a single path for the current. 2. An indicated sum of a set of terms in a mathematical expression (e.g., in an alternating or arithmetic series). series circuit- 1. A circuit in which resistances or other components are connected end to end so that the same current flows throughout the circuit. 2. A circuit in which the current has only one path to follow. 3. An electric circuit in which all the receptive devices are arranged in succession, as distinguished from a parallel circuit. The same current flows through each part of the circuit.

Series circuit.

series connection -A way of making connections

so as to form a series circuit.

series excitation-The field excitation obtained in

a motor or generator by allowing the armature current to flow through the field winding. series-fed vertical antenna -A vertical antenna that is insulated from ground and energized at the base. series f e e d -The method by which the dc voltage to the plate or grid of a vacuum tube is applied b u g h the same impedance in which the alternating current flows. series field-In a machine, the part of the total magnetic flux due to the series winding. series-gate noise limiter -See noise limiter. series loading-hading in which reactances are inserted in series with the conductors of a transmission circuit. series modulation -Modulation in which the plate circuits of a modulating tube and a modulated amplifier tube are in series with the same plate-voltage supply. series motor -Also called series-wound motor. A motor in which the field and armature circuits are connected in series. In small motors with laminated field frames, the performance will be similar when operated on direct current or alternating current. For this reason, the series motor is kquently called a universal motor. A series motor has a high starting torque, but its speed varies with the load. series operation-The connection of two or more power supplies together to obtain an output voltage of the combination equal to the sum of the individual supplies. A common current passes through all the supplies.

682

series-parallel network-Any network that contains only resistors, inductors, and capacitors and in which successive branches are connected in series and/or in parallel. series-parallels w i t c h -A switch that changes the connections of lamps or other devices from series to parallel or vice versa. series peaking network-See peaking network. series regulator-A device that is placed in series with a source of power and is able to automatically vary its series resistance, thereby controlling the voltage or current output.

LOAD

Series-regulated power supply.

s e r i e s resistance -Any sum of resistances installed in sequential order within one circuit. series resistor-A resistor generally used for adapting an instrument so that it will operate on some designated voltage or voltages. It forms an essential part of the voltage circuit and may be either internal or external to the instrument. series resonance-The condition existing in a circuit when the source of electromotive force is in series with an inductance and capacitance whose reactances cancel each other at the applied frequency, thereby reducing the impedance to minimum. series-resonant circuit -A circuit in which an inductor and capacitor are connected in series and have values such that the inductive reactance of the inductor will be equal to the capacitive reactance of the capacitor at the desired resonant frequency. At resonance, the current through a series-resonant circuit is at maximum. series-shunt network-See ladder network. series T-junction -See E-plane T-junction. series winding-In a motor or generator, a field winding that carries the same current as the armature; i.e., this winding is in series with the armature rather than in parallel with it. Series-wound motors are used in fractional-horsepower ac-dc applications, such as fans and electric mixers. Their other chief use is in heavy-duty dc traction equipment, such as electric locomotives, because of their extremely high starting torque. series wound-Characteristic of a generator or motor whose armature and field windings are connected in series. series-wound motor-A commutator motor with field and armature circuits in series. See also Series motor. serpentine cut-A trim cut in a film resistor that follows a serpentine or wiggly pattern to effectively increase the resistor length and increase resistance. serrated pulse-A vertical synchronizing pulse divided into a number of small pulses, each acting for the duration of half a line in a television system. serrated rotor plate -Also called a slotted or split rotor plate. A rotor plate with radial slots that permit different sections of the plate to be bent inward or outward

683 so that the total capacitance of a variable-capacitor section can be adjusted during alignment. serration- 1. The sawtooth appearance of vertical and new-vertical Lines in a television picture. This is caused by their starting at different points during the horizontal scan. 2. A designed irregular surface used as a reservoir to retain excess infiltrating material and/or multiple points to obtain high-current-density resistance welding or resistance brazing. serrodyne -A frequency translator or frequency converter based on linear sawtooth modulation of phase shift or time delay. One convenient modulable device for serrodyne use is a traveling-wave tube, which provides gain as well as frequency translation. serve -1. With reference to cable construction, a type of separator applied directly over the conductor or conductors. The serve may consist of one or more materials such as paper, cotton, silk, nylon, or rayon. These materials may be applied spirally or laterally. 2. A filament or group of filaments, such as fibers or wires, wound around a central core. server- 1. A computer on a network that serves as a central repository for data and programs and which can be accessed over the network by other computers, called clients. 2. A computer or processor that holds applications, files, or memory shared by users on a network. 3. A computer, or a software package, that provides a specific kind of service to allow client software to run on other computers. The term can refer to a particular piece of software, such as a WWW server, or to the machine on which the software is running. A single server could have several different server software packages running on it, thus providing many different servers to clients on the network. server PG-Microcomputer used by a network as a source of disk drives and information. sewice-1, A function offered by some part of an open system to communicating application processes. 2. The conductors and equipment for delivering energy fr0.m the elecwicity supply system to the wiring system of the premises served. serviceability- Those properties of an equipment design that facilitate service and repair in operation. service area -1. The area within which a navigational aid is of use. 2. The area surrounding a broadcasting station where the signal is strong enough for satisfactory reception at all times (i.e., not subject to objectionable interference or fading). service band-The band of frequencies allocated to a class of radio service. service channel - A band of frequencies, usually including a voice channel, utilized for maintenance and fault indication on a communication system. service circuit- An interconnecting circuit in a switching network that may be connected to lines or trunks as required to perform various functions, such as dial pulse detection and audible ringing. service conductors;-The supply conductors that extend from the street main or from the transformers to the service equipment of the premises served. sewice drop -The overhead service conductors from the last pole or otheir aerial support to and including the splices or taps, if any, connecting to the serviceentrance conductors at the premises served. service entrance -The conductors and equipment used for delivering energy from the utility pole to the premises. seavice life- 1. The period of t h e during which a device is expected to perform in a satisfactory manner. 2. The length of time a primary cell or battery needs to

serration - servomotor reach a specified final electrical condition on a service test that duplicates normal usage. service oscillator -See rf signal generator. service provider- A company that provides Internet access. For end users, this service can be as simple as providing Internet e-mail accounts, access to Usenet news groups, ftp, and web browser access via the service provider’s servers. A service provider can also provide a way for connecting an enterprise’s LAN to the Internet, allowing an enterprise to place their own servers on the Internet. service rating-The maximum voltage or current that a component is designed to carry continuously. service request- 1. The appeal by a process or task for access to a system resource. 2. A notification to a system that one element wants to access a resource. service routine-1. In digital computer programming, a routine designed to assist in the actual operation of the computer. 2. A set of instructions to perform a programmed operation, typically in response to an intempt. service switch-A switch, usually in a box, for disconnecting the line voltage from the circuits it services. service unit --In a microwave system, the equipment or facilities used for maintenance communications and transmission of fault indications. serving -1. Of a cable, wrapping applied around the core before a cable is leaded, or over the lead if the cable is armored. Some common materials are jute, cotton, or duct tape. 2. A wrapping of thread or yarn over a relay coil to protect it from damage. servo -Short for servomotor. A device that contains and delivers power to move a control or controls. servoamplifier-A servo unit in which information from a synchro is amplified to control the speed and direction of the servomotor output. servo control- A technique by which the speed or position of a moving device is forced into conformity with a desired or standard speed or position. For example, the speed of a servo-controlled turntable is established by a precision voltage or frequency standard to which it is compared and automatically adjusted to reduce the difference to a minimum. In a servo-controlled tonearm, a small departure of the cartridge from tangency to the groove is sensed and used to activate a motor drive that moves the tonearm to minimize the error. servo IooP-I~a servoamplifier, the entire closed loop formed by feedback from ~ u t p u tto input. In a position servo, the output position is compared to a command signal at the input. servomechanism-1. An automatic feedback-control system in which one or more of its signals represent mechanical motion. 2. A system in which output is compared to input to control error according to desired relationship, or feedback. 3. A self-contained system (except for inputs) in which the feedback signal is subtracted from a desired value so that the difference is reduced to zero. 4.A control system that provides the following: a command instrument t~ control or program the final process; amplification to strengthen and modify the command signal; work instrumentation to maripulate the controlled process; and feedback provision to initiate corrective action when needed. Since feedback signals go from the controlled process back to the original command station, a servo system is said to operate closed-loop. 5. A device in a closed-cycle system that controls a process based on direct feedback from the process. servomotor-A motor used in a servo system. Its rotation or speed (or both) are controlled by a corrective electric signal that has been amplified and fed into the motor circuit.

servo noise

- setup

servo noise-The hunting of the tracking servomechanism of a radar as a result of backlash and compliance in the gears, shafts, and structures of the mount. servo oscillation-An unstable condition in which the load tends to hunt back and forth about the ordered position. servo system-An automatic control system for maintaining a condition at or near a predetermined value by activation of an element such as a control rod. It compares the required condition (desired value) with the actual condition and adjusts the control element in accordance with the difference (and sometimes the rate of change of the difference). servo techniques-Methods of studying the performance of servomechanisms or other control systems. servovalve-Electrohydraulic flow control. An electrical-input, fluid-control valve capable of continuous control. sesquisideband transmission -A system in which the carrier, one full sideband, and half of the other sideband are transmitted. set- 1. To place a storage device in a prescribed state that is opposite to the reset state. 2. To place a binary cell in the 1 state. 3. A permanent change, attributable to any cause, in a given parameter. 4. See equipment. 5. Pertaining to a flip-flop input used to affect the Q output. Through this input, signals can be entered to change the Q output from 0 to 1. It cannot be used to change Q to 0. Opposite of clear. 6. An input to a binary counter or register that forces all binaries to assume the maximum binary state. 7. To place a binary device into a given logic state, usually the 1 state. set analyzer-A test instrument designed to permit convenient measurement of voltages and currents. set breakpoint-A user debug command that causes the setting of a breakpoint in a specified memory location. At program execution, encountering this breakpoint causes temporary program suspension and a transfer of control to the system debug routine. See breakpoint. set composite-A signaling circuit in which two signaling or telegraph legs may be superimposed on a two-wire interoffice trunk by means of one of the balanced pairs of high-impedance coils connected to each side of the line with an associated capacitor network. set input-An asynchronous input to a flip-flop used to force the Q output to its high state. set noise-Inherent random noise caused in a receiver by thermal currents in resistors and by variations in the emission currents of vacuum tubes. set point-In a feedback control loop, the point that determines the desired value of the quantity being controlled. set pulse-A drive pulse that tends to set a magnetic cell. set-reset flip-flop -A standard flip-flop except that if both the set and reset inputs are a 1 at the same time, the flip-flop will assume a prescribed state. set terminal -The flip-flop input terminal that triggers the circuit from its first state to its second state. setting accuracy-The ability to set a knob, switch, or other adjustment to the desired time delay, speed, light, sound, or other parameter. Normally specified in percent of maximum or at set point. settling time- 1. The time interval, following the initiation of a specified stimulus to a system, required for a specified variable to enter and remain within a specified narrow band centered on the final value of the variable. 2. In an operational amplifier, the interval between the time of application of an ideal step input and the time at which the closed-loop amplifier output enters and remains within a specified band of error, usually symmetrical

684 about the final value. Settling time includes a propagation delay and the time needed for the output to slew to the vicinity of the final value, recover from the overload condition associated with slewing, and settle within the specified error range. 3. In a feedback control system, the time required for an error to be reduced to a specified fraction, usually 2 percent or 5 percent, of its original magnitude. 4.The time required for the output frequency of a voltage- or current-tuned oscillator to change from the initial value to within a specified window around the final value in response to a voltage or current stop on the tuning input port. 5. The period required for a digital multimeter’s input circuits to reach a steady-state condition before analog-to-digital conversion is started. There are actually three settling times to evaluate. They are the settling time required with an input step change when operating in a fixed range, the settling time required with a range change, and the settling time required with a function change, such as a switch in measurement from ac to dc volts. 6. Time necessary for a multiplexer’s output to be within a certain error percentage of the input signal once the channel is selected, or turned on. It may be specified as either the semiconductor switch’s switching time plus analog output settling time, or an analog output settling time alone. 7. The time delay between a change of input-signal value and the resultant change in the output signal. Usually expressed in terms of how long it takes the output to arrive at, and remain within, a certain error band around the final value. Often given for several different magnitudes of input-step change. 8. The time required for an amplifier to approach within a percentage of its final steady state value after the application of a step input. It can be specified as 1 percent, 0.1 percent, or 0.01 percent. 9. The elapsed time after a code transition for DAC output to reach a final value within specified limits, usually f 1/z lsb. 10. The time elapsing between the start of a measurement and the instant that the indicator reaches, and remains within, a certain percentage of the final measured value (typically f l percent).

=

SETTLING TIME TO AEJ OR k A E / E , X 100%

Settling time.

set-top unit -Abbreviated STU. Typically refers to the unit/device that sits on top of a television for current cable TV reception. Also refers to digital set-top units, which accept digital media and sometimes support interactivity. setup- 1. The ratio of the difference between black level and blanking level to the difference between reference white level and blanking level, usually expressed in

setup diagram - 8

685 percent. 2. An arrangement of data or devices for the solution of a particular problem. 3. The difference between the reference black level and the blanking level of a composite video signal. setup diagram-A diagram that specifies a given computer setup. setup time-l. The time, measured from the point of 10-percent input change, required for a capacitor-diode gate to open or close after the occurrence of a change of input level. 2. The length of time that data must be present and unchanging before a1 flip-flop is clocked. 3. Time required before a signal can be changed from its prior state. seven-segment display-A display format consisting of seven bars so arranged that each digit from 0 to 9 can be displayed by energizing two or more bars. LED, LCD, and gas-discharge displays all use seven-segment display formats.

CATH~DE LEADS

u"

'CoMMoN ANODE

Seven-segmlent LED display.

severn-unit teleprinter code -Frequently called Teletype code. A code that represents the letters of the alphabet, the numerals, the punctuation marks, and the various control functions necessary on a teleprinter (such as line feed, carriage return, upshift, and downshift) by five-unit combinations of mark and space conditions. In addition to the five units that indicate the letter or other data, the code contains a start unit, which is always a space, and a stop unit, which is always a mark, to indicate the beginning and ending of each character. sexadecimal -Pertaining to the number system that has a radix of 16. sexatdecimal notation -Also called dekahexadecimal notation. A scale of notation for numbers with base 16. sexless connector-Also called hermaphroditic connector. An interconnecting device in which the mating parts are exactly alike at their mating surfaces. s f e r i c s - 1. Contraction of the term atmospherics, meaning interference. 2. Radio interference from atmospherics, or static. s f e r i c s receiver -Also called lightning recorder. A type of radio direction finder that electronically measures the direction of arrival, intensity, and rate of occurrence of atmospherics. In its simplest form the instrument consists of two orthogonally crossed antennas. Their output signals are connected to an oscillograph so that one loop measures the east-west components. These are combined vertically to give the azimuth. sg -Abbreviation for screen-grid electrode (of a vacuum tube). shaded-pole motor -A single-phase induction motor provided with one or more auxiliary short-circuited

stator windings that are displaced magnetically from the main winding. s h a d i n g - 1. A brightness gradient in the reproduced picture not present in the original scene, but caused by the camera tube. 2. Compensating for the spurious signal generated in a camera tube during the trace intervals. 3. Controlling the directivity pattern of a transducer through the distribution of phase and amplitude of the transducer action over the active face. s h a d i n g coil-See shading ring. shading compensation-Dynamic sensitivity control of the picture signal to reduce the amount of video level change from center to edge of the picture. s h a d i n g ring - 1. A heavy copper ring sometimes placed around the central pole piece of an electrodynamic loudspeaker to act as a shorted turn for cancellation of the hum voltage of the field coil. 2. A copper ring set into part of the pole piece of a small alternating-current motor to produce the lagging component of a rotating magnetic field for starting purposes. s h a d i n g signal-A signal that increases the gain of the amplifier in a television camera while the electron beam is scanning a dark portion. s h a d o w attenuation --Attenuation of radio waves over a sphere in excess of that over a plane when the distance over the surface and other factors are the same. s h a d o w factor-The ratio of the electric field strength that would result from propagation over a sphere to that which would result from propagation over a plane (other factors being the same). s h a d o w g r a p h --A device arranged in such a manner as to enable photography and/or visual observation of the silhouette of back-illuminated objects placed within the object field of the device and of gradations in luminous intensity resulting from variations in the opacity or in the index of refraction of media contained within the object field. s h a d o w mask-See aperture mask. s h a d o w m a s k tube-A type of color-generating cathode-ray tube that utilizes a shadow mask, a thin perforated electrode located close to the display screen. Each hole in the mask coincides with a triad of three phosphor dots, each representing red, blue, or green. A specific electron beam from the gun energizes phosphor dots of single color. shadow region -A region in which, under normal propagation conditions, an obstruction reduces the field strength from a transmitter to the point at which radio reception or radar detection is ineffective or virtually so. shadow tuning indicator-A vacuum tube in which a moving shadow shows how accurately a radio receiver is tuned. shaft-The axial member to which torque is applied to cause rotation of an adjustable component. s h a f t angle encoder -An electromechanical device that has a means for counting equally spaced radii that represent angular increments around the periphery of a disk. Usually, the measurement is in degrees, minutes, and seconds, since 2n radians is not a prime number. Usually the disc is divided into an even number of equal increments. s h a f t position encoder --Also called converter or coder. An analog-to-digital converter that transduces a mechanical analog shaft rotation to an electrical digital representation. s h a k e d o w n test -An equipment test carried out during the installation work. s h a k e r -An electromagnetic device capable of imparting known and/or controlled vibratory acceleration to a given object.

s h a k e table

- shield coverage

s h a k e table-A laboratory tester in which an instrument or component is subjected to vibration that stimulates operating conditions. s h a k e - t a b l e test-A laboratory test in which a device or component is placed in a vibrator to determine the reliability of the device or component when subjected to vibration. s h a n k - 1. The part of a phonograph needle that is clamped into position in the pickup or cutting head. 2. The cylindrical or rodlike portion of a connector or contact. 3. That part of a fastener lying between the head and the extreme opposite end. 4. See cantilever. S h a n n o n limit -The maximum signal-to-noise ratio improvement that can be achieved by the best modulation technique, as implied by Shannon’s theorem relating channel capacity to signal-to-noise ratio. S h a n n o n ’ s theorem -See sampling theorem. s h a p e d - b e a m antenna- An antenna whose directional pattern over a certain angular range is designed to a specific shape for some particular use. s h a p e d - b e a m display tube-A cathode-ray tube in which the beam is first deflected through a matrix, then repositioned along the axis of the tube, and finally deflected into the desired position on the faceplate. A typical tube is the Charactron. s h a p e factor-1. For a filter, the ratio (usually maximum) comparing a high-attenuation-level bandwidth and a low-attenuation-level bandwidth. 2. The ratio of the 60-dB bandwidth to the 6-dB bandwidth. Defines the selectivity of an amplifier stage. 3. A factor used to take the shape of a coil into account when its inductance is computed. s h a p i n g -Adjustment of a plan-position-indicator pattern set up by a rotating magnetic field. shaping network- 1. An electrical network designed to be inserted into a circuit to improve its transmission or impedance properties, or both. See also corrective network. 2. A network inserted in a telegraph circuit for improving the waveshape of the signals. s h a r e d data-Data in memory or on a secondary storage device that is used by more than one task. s h a r e d file-A direct-access device that two systems may use at the same time; a shared file may link two systems. s h a r e w a r e -Software that is freely shared on public networks and BBSs. Users are frequently asked, on the honor system, to remit a small amount of money to the software developer. sharp-cutoff tube-The opposite of a remotecutoff tube. A tube in which the control-grid spirals are uniformly and closely spaced. As the grid voltage is made more and more negative, the plate current decreases steadily to cutoff. to a limited range of s h a r p tuning-Response frequencies. shaving -In mechanical recording, the removal of material from the surface of a recording medium for the purpose of obtaining a new surface. s h e a r wave-1. Also called a rotational wave. A wave, usually in an elastic solid, that causes an element of the solid to change its shape but not its volume. 2. A wave in which particle displacement is at right angles to the direction of propagation. s h e a t h - 1. The external conducting surface of a shield transmission line. 2. A metal wall of a waveguide. 3. Part of a discharge in a rarefied gas, in which there is a space charge due to an accumulation of electrons or ions. 4. The outer covering or jacket of a cable. s h e a t h - r e s h a p i n g converter -A converter in which the pattern of the wave is changed by gradual

686 reshaping of the waveguide sheath and the metal sheets mounted longitudinally in the guide. sheet grating -A three-dimensional grating consisting of thin metal sheets extending along the inside of a waveguide for about one wavelength. It is used to stop all but the predetermined wave, which passes unimpeded. sheet-metal contact-A contact made by stamping and bending sheet metal rather than by the machining of metal stock. It is available in a wide variety of configurations and is usually less expensive than machined contacts. sheet resistance -The electrical resistance of a thin sheet of material with uniform thickness as measured across opposite sides of a unit square pattern. Expressed in ohms per square. s h e e t resistivity- Also called ohms per square. 1. The electrical resistance measured across the opposite sides of a square pattern of deposited film material. 2. The resistance of a unit area of printed and fired thick-film material. Expressed in ohms per square per unit of film thickness. Sheffer-stroke function -The Boolean operator that gives a truth-table value of true only when both of the variables that the operator connects are not true. shelf aging -The change with time of the properties of a stored component or material. shelf corrosion -Consumption of the negative electrode of a dry cell as a result of local action. shelf life -1. The length of time under specified conditions that a material or component retains its usability. 2. The time period that an item can be stored, under specified conditions, and still meet specifications. 3. The length of time a battery is expected to retain charge when stored. shell-I. A group of electrons having a common energy level that forms part of the outer structure of an atom. 2. The outer section of a plug or receptacle that mechanically supports the assembly and in some cases provides coupling and locking. 3. That part of a phonograph pickup which carries the cartridge. The head shell can often be detached from the pickup arm. shell-type transformer -A transformer in which the magnetic circuit completely surrounds the windings. shelving equalizer- An equalizer whose boost or cut characteristic response curve resembles a shelf. Maximum boost or cut occurs at the indicated frequency and remains constant at all frequencies beyond. SHF -Abbreviation for superhigh frequency. shield-1. A device designed to protect a circuit, transmission line, etc., from stray voltages or currents induced by electric or magnetic fields, consisting, in the case of an electric field, of a grounded conductor surrounding the protected object. At high frequencies this will provide magnetic shielding as well. At low frequencies (through the audio range) magnetic shielding is accomplished by surrounding the object with a material of high magnetic permeability. See braid, 2. 2.Any barrier to the passage of interference-causing electrostatic or electromagnetic fields. An electrostatic shield is formed by a conductive layer (usually foil) surrounding a cable core. An electromagnetic shield is a ferrous metal cabinet or wire-way. 3. In cables, a metallic layer placed around a conductor or group of conductors to prevent electrostatic or electromagnetic interference between the enclosed wires and external fields. 4. A metallic covering, usually copper or aluminum, placed around or between electric circuits, around cables or their components, to suppress the effects of undesired signals that may originate from adjacent or external sources. The shield may be braided wires, foil wrap, foil backed tape, a metallic tube, or conductive vinyl or rubber. shield coverage -See shield percentage.

587

shielded building -In modem practice, a building in which shielding was incorporated in the basic architec!mal design. Shielded buildings often employ structural steel members as an integral part of RFI shielding. shielded cable -1. A single- or multiple-conductor cable surrounded by a separate conductor (the shield) intended to minimize the effects of adjacent electrical circuits. 2. A cable in which each insulated conductor is enclosed in a conducting envelope so constructed that substantially every point of the surface of the insulation is at ground potential with respect to ground under normal operating conditions. shielded-conductor cable -A cable in which the insulated conductor OK conductors are enclosed in a conductiing envelope or envelopes, almost every point on the surface of which is at ground potential with respect to ground. s h i e l d e d enclosure-A room, hangar, or box that is shielded or screened so as to provide a controlled electromagnetic environment. shielded joint-A cable joint having its insulation SO enveloped by a conducting shield that substantially every point on the surface of the insulation is at ground potential, or at some predetermined potential with respect to the ground. shielded line-A transmission line whose elements confine propagated radio waves to an essentially h i t e space inside a tubular conducting surface called the sheath, thus preventing the line from radiating radio waves. shielded pair-A two-wire transmission line surrounded by a metallic sheath to isolate the pair from electrical interference. shielded room-An enclosed area made free from electracal interference that would affect the sensitivity of electrical equipment. s h i e l d e d transmission line -A transmission line whose elements confine the propagated electrical energy inside a conducting sheath. shielded wire- An insulated wire covered with a metal shield -usually of tinned, braided copper wire. shielded X-ray tube-An X-ray tube enclosed in a grounded metd container, except for a small opening through which the X-rays emerge. shield effectiveness-The relative ability of a shield to screen out undesirable radiation. shield factor-Ratio between the noise (or induced current or voltage) in a telephone circuit when a source of shielding is present and when it is not. shield grid-In a glass tube, a structure that shields the control electrode from the anode or cathode, or both. It prevents the radiation of heat from them and the depositing of thermionic activating material on them. It also reduces the electrostatic influence of the anode, and may be used as a control electrode in some applications. shield-grid thyratron -A thyratron that contains a shield grid. usually operated at the same potential as the cathode. shielding - 1. The practice of confining the dielectric field of an electric cable to the inside of the cable insulation or insulated condluctor assembly by surrounding the insulation or assembly with a grounded conducting medium called a shield 2. Metal covering used on a cable; also a metal can, case partition, or plates enclosing an electronic circuit or component. Shielding is used to prevent undesirable radiation, pickup of signals, magnetic induction, stray current, ac hum, or radiation of an electrical signal. 3. A physical barrier, usually electrically conductive, designed to reduce the interaction of electnc or magnetic fields on devices, circuits, or portions of circmts.

shielded building

- shift register

shielding effectiveness-The relative reduction of radiated electromagnetic energy levels occasioned by the use of an enclosure either to contain or exclude the energy. shield percentage -Also called shield coverage. The physical area of a circuit or cable actually covered by shielding material, expressed in percent. shield wire-A wire employed for reducing the effects of extraneous electromagnetic fields on electric supply or communication circuits. shift -1. Displacement of an ordered set of computer characters one or more places to the left or right. If the characters are the digits of a numerical expression, a shift is equivalent to multiplying a power of the base. 2. The process of moving information from one place to another in a computer; generally, a number of bits are moved at once. A word can be shifted sequentially (generally referred to as shifting left or right), or all bits of a word can be shifted at the same time (called parallel load or parallel shift). 3. In a computer, an operation whereby a number is moved one or more places to the left or right. The number 110, for instance, becomes 1100 if shifted one place left or 11 if shifted one place right. The operation is of considerable use in digital computer operations. 4. The difference between the mark and space frequencies. For example, if the mark frequency is 2125 Hz and the space frequency is 2295 Hz, the dBerence of 170 Hz is referred to as the shift. The 170Hz and 850-Hz shifts have become two widely used standards. shift counter-1. A shift register in which the first stage, through logic feedback, produces a pattern of 1s or Os as a function of the state of other stages in the register. The pattern of 1s and Os so produced is termed a ring code. 2. See ring counter, 2. shift-frequency modulation --A form of frequency modulation in which the modulating wave shifts the output frequency between predetermined values and the output wave is coherent, with no phase discontinuity. shift-in character-In a computer, a code extension character that can be used by itself to bring about a return to the character set in effect before substitution of another set was caused by a shift-out character. shift out -In a computer, to move information within a register toward one end so that, as the information leaves this one end, Os are entered into the other end. shift-out character-In a computer, a code extension character that can be used by itself to cause substitution of some other character set for the standard set, usually to access additional graphic characters. shift pulse-A drive pulse that initiates the shifting of characters in a register. shift register- 1. A digital storage circuit in which information is shifted from one flip-flop of a chain to the adjacent flip-flop on application of each clock pulse. Data may be shifted several places to the right or left, depending on additional gating and the number of clock pulses applied to the register. Depending on the number of positions shifted, the rightmost characters are lost in a right shift, and the leftmost characters are lost in a left shift. See dynamic shift register; static shift register. 2. A program, entered by the user into the memory of a programmable controller, in which the information data (usually single bits) is shifted one or more positions on a continual basis. There are two types of shift registers: asynchronous and synchronous. 3. A register in which binary data bits are moved as a contiguous group a prescribed number of positions to the right or to the left. 4. A memory in which data words are entered serially and shifted to successive storage locations. The data word can be read when it has been sequentially shifted to the output. 5. A digital circuit consisting of flip-flops, which is used

ship error - short-circuit protection (automatic) to convert parallel data (where several binary digits arrive at once) to serial (where the same digits travel one after another), or vice versa. ship error-A radio direction-finder error that occurs when radio waves are reradiated by the metal structure of a ship. ship-heading marker-& a PPI scope, an electronic radial sweep line indicating the heading of the ship on which the equipment is installed. ship’s emergency transmitter-A ship’s transmitter to be used exclusively on a distress frequency for distress, urgency, or safety purposes. ship station-A radio station operated in the maritime mobile service and located on board a vessel that is not permanently moored. ship-to-shore communication-Communication by radio between a ship at sea and a shore station. shock-1. An abrupt impact applied to a stationary object. It is usually expressed in gravities (g). 2. An acceleration transient of short duration and nonrepetitive occurrence. 3. Sudden stimulation of the nerves and convulsive contraction of the muscles caused by a discharge of electricity though the body. shock absorber-A device for dissipating vibratory energy, to modify the response of a mechanical system to an applied shock. shock excitation-See impulse excitation. shock-excited oscillations-See free oscillations. shock hazard -A hazardous condition that exists at a part of a ground-fault circuit interrupter if (a)there would be current of 5 milliamperes or more in a resistance of 500 ohms connected between the part in question and the grounded supply conductor, and (b) the device would not operate to open the circuit to the 500-ohm resistor within a specified time. shock isolator-Also called a shock mount. A resilient support that tends to isolate a system from applied mechanical shock. Shockley diode -A four-layer controlled semiconductor rectifier diode Without a base connection, used as a trigger or switching diode. shock motion-In a mechanical system, transient motion characterized by suddenness and by significant relative displacements. shock mount-See shock isolator. shockover capacitor-A capacitor connected between the grid and cathode of a thyratron to prevent premature firing. shock pulse-Usually a single disturbance that is characterized by an increase and a decrease of acceleration in a relatively short period. shock test (mechanical)-A test to determine the ability of a device to withstand suddenly applied forces of specified magnitude and duration. shodop -Acronym for short-range Doppler. shoran -Acronym for short-range air navigation. A precision distance-measuring system employing the pulse timing principle to measure the distance from an aircraft to one or more fixed responder ground stations. Fundamentally, the system consists of a mobile transmitterreceiver-indicator unit and a fixed receiver-transmitter unit (transponder). Pulses are sent from the mobile transmitter and returned to the originating point by the transmitter. The indicator measures the time interval required for the travel of a pulse between stations and converts this information into distance to the nearest thousandth of a mile. shore effect-The bending of radio waves toward the shore line when traveling over water, due presumably

688 to the slightly greater velocity of radio waves over water than over land. This effect causes errors in radio directionfinder indications. shore-to-ship communication -Communication by radio between a shore station and a ship at sea. short-See short circuit. short base-line system -A system that uses continuous waves and that has a base-line length that is short in comparison to the target distance. short check-See flash test. short circuit-Also called a short. 1. An abnormal connection of relatively low resistance between two points of a circuit. The result is excess (often damaging) current between these points. 2. An accidental or intentional nearzero resistance connection between two sides of a circuit. 3. An abnormal connection of relatively low impedance, whether made accidentally or intentionally, between two points of different potential. 4. A low-resistance path in a system that allows the current to flow outside of the proper circuit in an appliance, junction box, or in the wires. Due to a failure in insulation or improper hookup, the current takes the short low-resistance path rather than flowing through the entire circuit. 5. An abnormal condition that occurs when there is an unwanted electrical connection between two wires. It results in a flow of excess current. short-circuit current-1. The current a power supply delivers when its output terminals are shortcircuited. 2. An electronic regulator’s output current with the output terminal shorted to the negative supply. Shortcircuited current and maximum regulator output current depend on the pass circuitry. The maximum output current is also limited by the maximum allowable package power dissipation and, hence, by quiescent current. short-circuit driving-point admittance-The driving-point admittance between the j terminal of an n-terminal network and the reference terminal when all other terminals have zero alternating components of voltage with respect to the reference point. short-circuit feedback admittance (of an short-circuit electron-device transducer) -The transfer admittance from the output terminals to the input terminals of a specified socket, the associated filters, and the electron device. short-circuit forward admittance (of an short-circuit electron-device transducer) -The transfer admittance from the input terminals to the output terminals of a specified socket, the associated filters, and the electron device. short-circuit impedance- 1. The driving-point impedance of a line or four-terminal network when its far end is short-circuited. 2. The input impedance to a line or four-terminal network when the far end or output terminals are shorted. short-circuitingor grounding device- A power or stored-energy operated device that functions to shortcircuit or ground a circuit in response to automatic or manual means. short-circuit output admittance (of an electron-device transducer)-The short-circuit driving-point admittance at the output terminals of a specified socket, the associated filters, and the electron device. short-circuit output capacitance (of an nterminal electron device) -The effective capacitance determined from the short-circuit output admittance. short-circuit parameters-In an equivalent circuit of a transistor, the resultant parameters when independent variables are selected for the input and output voltages. short-circuit protection(automatic) -A currentlimiting system that enables a power supply to continue

689

short-circuit t r a n s f e r admittance

operating without damage into any output overload, including short circuits. The output voltage must be restored to normal when the overload is removed, as distinguished from a fuse or circuit-breaker system, which opens at overload and must be reclosed to restore power. short-circuit transfer admittance-The transfer admittance from terminal j to terminal I of an n-terminal network when all terminals except j have zero complex alternating components off voltage with respect to the reference point. short-circuit transfer capacitance (of an electron device) -The effective capacitance determined from the short-circuit transfer admittance. s h o r t code-A system of instructions that causes an automaton to behave as if it were another, specified automaton. s h o r t - c o n t a c t switch -A selector switch in which the movable contact is wider than the distance between its chps, so that the new circuit is made before the old one is broken. s h o r t - d i s t a n c e navigational aid -An equipment or system that provides navigational assistance to a range not exceeding 200 miles (322 km). shorted-Prevented from operating by a short circuit. s h o r t e d ouU-Made inactive by connecting a heavy wire or other low-resistance path around a device or portion of a circuit. short-flash light source- An electronic flash tube in which the flash recurs at a frequency extending to many thousands per second. A stroboscopic light source is a short-flash light source. s h o r t - g a t e gain -Video gain on a short-range gate. shorting noise-A noise that occurs in wirewound potentiometric transducers, even when no current is drawn from the device. It is due to the shorting out of adjacent turns of the wire as the slider traverses the winding. The portion of the interturn current that flows through the slider appears as noise. shorting switch-A switch type in which contact is made for a new position before breaking contact with the previous position. Classified as a make-before-break switch. short-range navigation -A precision positionfixing system using a pulse transmitter and receiver in connection with two transponder beacons at fixed points. short-range navigation aid -A navigation aid that is usable only at distances within radio line of sight. short-slot coupler- A 3-dB coupler. short-time duty-A service requirement that demands operation at a substantially constant load for a short, specified time. s h o r t time limits-Values of minimum and maximum trip time measured a t various percentages of overload. short-time rating-The rating that defines the load that a machine, apparatus, or device can carry at approximately the room temperature for a short, specified tlme. s h o r t w a v e -Abbreviated sw. Radio frequencies from 1.6 to 30 MHz, which fall above the commercial broadcasting band and are used for sky-wave communication over long distances. s h o r t w a v e c o n v e r t e r -An electronic unit designed to be connected between a receiver and its antenna system to permit reception of frequencies higher than those the receiver ordinarily handles. s h o r t w a v e transmitiler-A radio transmitter that radiates shortwaves, which ordinarily are shorter than 200 meters.

-shu

s h o t effect -Noise voltages developed by the random travel of electrons within a tube. The effect is characterized by a steady hiss from a radio, and by snow or grass in a television picture. s h o t g u n mike- Also called a hyperdirectional or long-reach mike. An extremely unidirectional microphone, used for spotting a speaker or soloist from a considerable distance. s h o t noise-1. Noise generated due to the random passage of discrete current carriers across a banier or discontinuity, e.g., a semiconductor junction, as well as by thermal agitation in a base resistor. Shot noise is characteristic of all transistors and diodes and is directly proportional to the square root of the applied current. 2. Noise voltages developed in a thermionic tube as a result of random variations in the number and velocity of electrons emitted by the cathode. The effect is characterized by the presence of a steady hiss in audio reproduction and of snow or grass in video reproduction. The shot noise (German, schottefleekt) concept stems from the random manner in which electrons in a vacuum tube collide with the plate (anode)-not unlike the sound effect produced by casting a handful of BB-shot against a wall, with their slightly differing and overlapping impact times. Additionally, the electrons from a vacuum-tube cathode are not emitted uniformly, producing fluctuation noise. 3. Noise that is inherent in an electric current because it consists of a stream of finite particles, i.e.; electrons. 4. The noise generated by a charge crossing a potential barrier. For medium and high frequencies it is the dominant noise mechanism in bipolar devices. Shot noise has a constant spectral density. shrinkable tubing - 1. A nonmetallic tubing that is fabricated to allow a nonreversible decrease in its diameter on the application of heat. It is used to provide insulation or mechanical protection to conductors, cables, splices, and terminations. 2. Plastic or elastomeric tubing used to protect wires, cables, and splices from mechanical damage. The tubing shrinks to a predetermined size on application of heat or solvent evaporation. shunt- 1. A precision low-value resistor placed across the terminals of an ammeter to increase its range. The shunt may be either internal OK external to the instrument. 2. Any part connected, or the act of connecting any part, in parallel with some other part. 3. In an electric circuit, a branch whose winding is in parallel with the external OK line circuit. 4. An alternate path in parallel with a part of a circuit. 5. To place a circuit element in parallel with another. 6. To bypass a portion of a circuit. 7. A deliberate shorting-out of a portion of an electric circuit. 8. A key-operated switch that removes some portion of an alarm system from operation, allowing entry into a protected area without initiating an alarm signal. A type of authorized access switch. 9. A calibrated low resistance connected in parallel with the input terminals of an ammeter, to enable measurement of a wider range of currents. s h u n t calibration--A. procedure in which a parallel resistance is placed across a (similar) element to obtain a known and deliberate electrical change. shunt-fed vertical antenna-A vertical antenna connected to the ground at the base aqd energized at a suitable point above the grounding point. s h u n t feed-See parallel feed. s h u n t field-Part of the magnetic flux produced in a machine by the shunt winding connected across the voltage source. shunt-field relay-A special polarized relay with two coils on opposite sides of a closed magnetic circuit. The relay operates only when the currents in its two windings flow in the same direction.

s h u n t i n g effect

- side thrust

s h u n t i n g effect -A reduction in signal amplitude caused by the load that an amplifier or measuring instrument imposes on the signal source. For dc signals the shunting effect is directly proportional to the output impedance of the signal source and inversely proportional to the input impedance of the amplifier. switch that shunting or d i s c h a r g e switch-A serves to open or to close a shunting circuit around any piece of apparatus (except a resistor), such as a machine field, a machine armature, a capacitor, or a reactor. s h u n t leads-Those leads that connect the circuit of an instrument to an external shunt. The resistance of these leads must be taken into account when the instrument is adjusted. s h u n t loading -Loading in which reactances are applied in parallel across the conductors of a transmission circuit. s h u n t neutralization -See inductive neutralization. s h u n t peaking network-See peaking network. s h u n t regulator-A device placed across the output of a regulated power supply to control the current through a series-dropping resistance in order to maintain a constant output voltage or current.

Shunt regulator.

s h u n t T-junction -See H-plane T-junction. s h u n t wire-A conductor joining two parts of an electric circuit to divert part of the current. s h u n t - w o u n d generator-A direct-current generator in which the field coils and armature are connected in parallel. shunt-wound motor- 1. A direct-current motor that has its field (stationary member) and armature (rotating member) circuit connected in parallel. Its speed can be regulated by varying either the applied armature or field voltage. 2. A motor whose armature and field windings are connected in parallel. It has a fairly constant speed, but a low starting torque. shutoff -A provision whereby a recorder will automatically go into the stop mode at the end of a tape. In some recorders, the automatic shutoff can be made to turn off the entire unit as well as any other components powered by it. shutter-A movable cover that prevents light from reaching the film or other light-sensitive surface in a still, movie, or television camera except during the exposure time. s h u t t l e -A high-speed tape-running mode that permits fast cuing or rewinding of the tape. sibilance-The strong emphasis in pronunciation of the letters “s” and “sh” in speech. It can be exaggerated by microphones having peaks in their high-frequency response. SIC -Abbreviation for semiconductor integrated circuit.

690

side armature-An armature that rotates about an axis parallel to that of the core, with the pole face on a side surface of the core of a relay. sideband attenuation -Attenuation in which the relative transmitted amplitude of one or more components of a modulated signal (excluding the carrier) is smaller than the amplitude produced by modulation. sideband power-The power contained in the sidebands. This is the power to which a receiver responds when receiving a modulated wave, not the carrier power. sidebands- 1. The frequency bands on both sides of the carrier frequency. The frequencies of the wave produced by modulation fall within these bands. 2. The wave components lying within such bands. During amplitude modulation with a sine-wave carrier, the upper sideband includes the sum (carrier plus modulating) frequencies, and the lower sideband includes the difference (carrier minus modulating) frequencies. 3. The modulation bands of frequencies that are both above and below the carrier frequency during modulation. 4. A band of frequencies on each side of the carrier frequency of an amplitudemodulated wave. Each sideband contains all of the information that was in the modulating wave. (The upper sideband contains frequencies that are the sums of the carrier and modulation frequencies, and the lower sideband contains the difference frequencies.) sideband splatter- 1. Those portions of the modulation sidebands that lie beyond the limits of the assigned channel. 2. In radio communications, interference on other channels caused by spurious sidebands resulting from overmodulation. side circuit -A circuit arrangement for deriving a phantom circuit. In four-wire circuits, the two wires associated with the “go” channel form one side circuit, and those associated with the return channel form another. See also phantom circuit. side-circuit loading coil-A loading coil for introducing a desired amount of inductance into a side circuit while introducing a minimum amount of inductance into the associated phantom circuit. side-circuit repeat coil -See side-circuit repeating coil. side-circuit repeating coil -Also called sidecircuit repeat coil. A device that functions as a transformer at a terminal of a side circuit, and acts simultaneously as a device for superposing one side of a phantom circuit on the side circuit. side e c h o -An echo due to a side lobe of an antenna. side frequency-One of the frequencies of a sideband. side lobe-A portion of the beam from an antenna, other than the main lobe. It is usually much smaller than the main lobe. See figure on page 691. side-lobe blanking -A technique that compares relative signal strengths between an omnidirectional antenna and the radar antenna. side-lobe cancellation-A technique designed to exclude or greatly attenuate jamming signals introduced through the side or back lobes of a receiving antenna. side-looking airborne radar -A high-resolution airborne radar system in which the beam from the antenna is directed at right angles to the direction of flight. siderial day-The time it takes for the earth to rotate exactly 360” about its axis with respect to the “fixed” stars. The siderial day contains 1436.07 minutes. Compare solar day. sideswiper- A telegraph key that operates from side to side rather than up and down. side thrust- 1. In disc recording, the radial component of force on a pickup arm caused by the stylus drag. 2. The tendency of a stylus to skate toward the center of a

sidetone

SIDE LOBES

Side lobes.

record, causing increased wear on the inner groove wall. With low tracking weight, side thrust can cause the stylus to jump the record’s groove. sidetone- 1. The reproduction, in a telephone receiver, of sounds received by the transmitter of the same telephone set (e.g., hearing one’s own voice in the receiver of a telephone set when speaking into the mouthpiece). 2. That portion of a speaker’s voice that is fed back to his or her receiver. sidetone t e l e p h o n e set-A telephone set with no balancing network for reducing sidetone. siemens- 1. International standard unit of conductance that replaces and is identical with the term mho. The reciprocal of resistance in ohms. 2. The unit of electric conductance of a conductor in which a current of 1 ampere is produced by an electric potential difference of 1 volt. s i g h t check-To verify the sorting or punching of punched cards by looking through the pattern of punched holes. sign - 1. A symbol that distinguishes negative from positive quantities. 2. A binary indicator of the position of the magnitude of a number relative to zero. signal-1. A visible, audible, or other conveyor of infomation. 2. The intelligence, message, or effect to be conveyed over a communication system. 3. The physical embodiment of a message or of information. 4. An electrical wave used to convey information. 5. An alerting signal; that is, an acoustic device (such as a bell) or a visual device (such as a lamp) that calls the attention. 6. To transmit an information signal or alerting signal. 7. The event, phenomenon, or electrical quantity that conveys information from one point to another. 8. A current used to convey infoimation, either digital, analog, audio, or video. 9. An electrical impulse of a predetermined voltage, current, polarity, and pulse width. 10. Any electronic visual, audible, or other indication used to convey infomation. In semiconductors, an electrical quantity (typically voltage, current, or light level) corresponding to some physical quantity. Signals are coded in frequency or amplitude to separate them from unwanted noise. signal attenuation --The reduction in the strength of electrical signals. signal averaging -A technique for extracting a signal waveform (generally a time-varying voltage) from a background of unwanted noise. Simple frequencydomain filtering with passive or active circuit elements is the most widely used method for accomplishing this result. But this type of filtering is effective only when the frequency spectrum of the signal and the frequency

- signal encodin

spectrum of the noise do not overlap. A signal averager is a special kind of filter, sometimes referred to as a comb filter. It can be used effectively only if the desired signal, with its contaminating noise, can be repeated a number of times. In addition. a synchronization of that pulse must have a fixed time relationship to the desired signal, preferably, but not necessarily, ahead of the signal. signal-averaging computer- An electronic averager that filters out signals of interest from background noise. signal bias -A form of teletypewriter signal distortion brought about by the lengthening or shortening of pulses during transmission. When marking pulses are all lengthened, a marking signal bias results; when marking pulses are all shortened, a spacing signal bias results. signal-carrier FM recording-A method of recording in which the input signal is frequency modulated onto a carrier, and the carrier is recorded on a single track at saturation and without bias. signal conditioner- A device placed between a signal source and a readout device for the purpose of conditioning the signal. Some examples are damping networks, attenuator networks, preampbfiers, excitation and demodulation circuits, converters for changing one electrical quantity into another (such as voltage to current), instrument transformers, equalizing or matching networks, and filters. signal conditioning-I. To process the form or mode of a signal so as to make it intelligible to, or compatible with, a given device, including such manipulation as pulse shaping, pulse clipping, digitizing, and linearizing. 2. Any operation that prepares a transducer signal for subsequent display or control functions. Depending on the application, a transducer signal might require any one or a combination of several conditioning operations such as filtering, amplification, isolation, integration. differentiation, and rectification. For extracting low-level signals from electrical noise, an instrumentation amplifier is often the best choice. signal conductor- An individual conductor used to transmit an impressed signal. signal converter-A circuit that reduces, filters, and (if necessary) rectifies incoming signals to logic system levels. signal delay-The transmission time of a signal through a network. The time is always finite, and it may be undesired or purposely introduced. signal diode-1. A semiconductor diode used for the purpose of extracting or processing information contained in an electrical signal that varies with time and may be either analog or digital in nature. 2. A diode that exhibits an asymmetrical voltage-current characteristic and is used for signal detection. signal-distortion generator-An instrument furnished and designed to apply distortion on a signal for the purpose of ranging and adjusting teletypewriter equipment or for furnishing a clear signal. signal dropout-The loss of signal that occurs when the signal becomes too weak to be usable. signal electrode-The electrode from which the signal output of a camera tube is taken. signal element-Also called a unit interval. That part of a signal which occupies the shortest interval of the signaling code. It is considered to be of unit duration in building up signal combinations. signal encoding device -A system component located at the protected premises that will initiate the transmission of an alarm signal, supervisory signal, trouble signal, or other signals the central station is prepared to receive and interpret.

signal enhancement - signal-shield ground signal enhancement-Ensemble averaging of time-domain signals, whereby a set of time domain samples are digitized and then averaged. In order to enhance the signal due to averaging, the time function must be repetitive, and the start of the ensemble average must have a known relationship to some repetitive event (trigger). Such a repetitive signal is the vibration from one rotation of an engine (where the firing of spark plug 1 serves as the trigger). signal filtering -The shaping of amplitude or phase characteristics with respect to frequency, for the purpose of meeting an operational requirement. This usually is accomplished by analog methods. signal-frequency shift-In a frequency-shift facsimile system, the numerical difference between the frequencies corresponding to the white and black signals at any point in the system. signal generator- 1. Also called a standard voltage generator. A device that supplies a standard voltage of known amplitude, frequency, and waveform for measuring purposes. 2. An instrument that provides ( a ) Calibrated and variable frequency over a broad range. (b) Calibrated and variable output level over a wide dynamic range. (e) One or more forms of calibrated modulation. Not all frequency sources or synthesizers are signal generators. Sweepers, test oscillators, and traditional frequency synthesizers cannot be classified as signal generators because they usually lack a calibrated output or some form of calibrated modulation. 3. A portable test oscillator that can be adjusted to provide a test signal at some desired frequency, voltage, modulation, or waveform. signal ground -The ground return for low-level signals, such as inputs to audio amplifiers or other circuits, that are susceptible to coupling through ground-loop currents. signal highlighting-Identifying the connection points of a net in a printed circuit board. signaling-1. The process by which a caller on the transmitting end of a line informs a particular party at the receiving end that a message is to be communicated. Signaling is also that supervisory information that lets the caller know that the called party is ready to talk, that his or her line is busy, or that he or she has hung up. Signaling also holds the voice path together while a conversation goes on. 2. Indicating to the receiving end of a communication circuit that intelligence is to be transmitted. 3. In a circuit-switched telecommunications network, the exchange of information that is concerned with the establishment, control, and management of a telephone connection. signaling channel-A tone channel used for signaling purposes. signaling key-A key used in wire or radiotelegraphy to control the sequence of current impulses that form the code signals. signal injector- A test instrument, usually small, that contains an audio-frequency pulse oscillator. A signal injected at points in the circuitry aids in troubleshooting. signal intelligence-A generic term that includes both communications intelligence and electronics intelligence. signal interpolation-See interpolation. signal lamp-A lamp that indicates, when lit or out, the existence of certain conditions in a circuit (e.g., signal lamps on switchboards, or pilot lamps in radio sets). signal leakage-Interference in a given playback channel that has its origin in the recording system. Such interference occurs during simultaneous record/reproduce

692 and has a leading time displacement with reference to the signal on the tape. signal level-1. The difference between the measure of the signal at any point in a transmission system and the measure of an arbitrary reference signal. (Audio signals are often stated in decibels-thus, their difference can be conveniently expressed as a ratio.) 2. The magnitude of signal compared with an arbitrary reference magnitude. signal line-One of a set of signal conductors in an interface system used to transfer messages among interconnected devices. signal matching-Inserting buffers near the target system when the target microprocessor is replaced for emulation, so that the signals at the target microprocessor are reproduced exactly. signal-muting switch -A switch used on a record changer to ground (mute) the signal from the pickup during a change cycle. signal-noise ratio-See signal-to-noise ratio. signal parameter-That parameter of an electrical quantity whose values or sequence of values conveys information. signal plane-A conductor layer intended to carry a signal, rather than serve as a ground or other fixed-voltage function. signal plate-A metal plate that backs up the mica sheet containing the mosaic in one type of cathode-ray television camera tube. The electron beam acts on the capacitance between this plate and each globule of the mosaic to produce the television signal. signal plus noise and distortion-A radioreceiver sensitivity measurement based on the signal input required to produce 50 percent of the rated output at a 12decibel ratio (4 : 1 voltage ratio) of signal plus noise and distortion to noise and distortion alone. signal-point stereo microphone -A housing containing two, usually directional, microphones angled so that each picks up sound from one side of the stereo field, with both picking up sounds from the middle. signal processing-A broad class of electronic functions that enhance the representations of physical or electrical phenomena. Temperature, pressure, vibration, acceleration, and flow are examples of physical properties that rely on signal processing enhancements. The detection and conversion of rf, X-ray, or ultrasonic energy into images and sound is another form of signal processing. signal processing equipment -Any equipment or circuit used to intentionally change the characteristics (but not the overall level) of a signal. Includes such devices as equalizers, limiters, phasers, flangers, and delay lines. signal reconditioning-The act of partially or completely restoring the original form of a distorted signal. signal regeneration-The process of demodulating a received signal to recover its baseband data (thus removing received noise but creating bit errors) and remodulating the baseband signal onto a carrier for retransmission. signal report-A report given in numerical values of signal strength and quality. signal-separation filter-A bandpass filter that selects the desired signal or channel from a composite signal. signal-shaping network- An electric network inserted into a telegraph circuit, usually at the receiving end, to improve the waveshape of the signals. signal-shield ground- A ground technique for all shields used for the protection from stray pickup of leads carrying low-level, low-frequency signals.

1593 signal shifter-A variable-frequency oscillator for shifting amateur transmitters to a less crowded frequency .within a given band. signal splitter-A passive device that enables two 1sr more TV sets to divide a TV signal between them with proper balancing and isolaition. Available in either 75- or 300-ohm impedances. signal strength-1. The strength of the signal produced by a transmitter a i a particular location. Usually it is expressed as so many millivolts per meter of ithe effective receiving-antenna length. 2. The intensity of the television signal measured in volts, millivolts, microvolts, or decibels, usi.ng 0 dB as a reference. Equal to 1000 microvolts in rf systems; generally 1 volt in video systems. signal-strength meter- Also called an S meter. A meter connected in the AVC circuit of a receiver and calibrated in dB or arbitrary “S” units to read the strength of a received signal. signal-to-distortionratio -The ratio of desired to undesired signal in a transmitted single-sideband signal. signal-to-noise ratio -Abbreviated SNR or s/n ratio. Also called signal-noise ratio. 1. Ratio of the magnitude of the signal to that of the noise (often expressed in decibels). 2. In television transmission, the ratio in decibels of the maximum peak-to-peak voltage of The video television signal (including the synchronizing pulse) to the m s voltage of the noise at any point. 3. The ratio of the amplitude of a signal after detection to the amplitude of the noise accompanying the signal. It may also be considered as the ratio, at any specific point of a circuit, of signal power to total circuit-noise power. 4. Ratio of the root-mean-square facsimile signal level to the root-mean-square noise level. 5. The difference, measured in decibels, between a specified signal reference level and the level of unwanted noise. The higher the ratio, the better the equipment. 6. The span, measured in decibels, of signal intensity between a device’s overload point at the upper limit and its background noise at the l.ower Iimit (In tape recording, the s/n ratio usually lies between &e pennissible lirnit of saturation distortion and the tape’s background hiss.) 7. The ratio, in decibels, between a reference power output (usually an amplifier’s rated power) and the hum and noise power in the output of the amplifier. The higher this ratio, the better. 8. The ratio, usually in decibels, between the level of the loudest undistorted tone that can be recorded and the noise that is generated and recorded when no signal is present. 9. The ratio of the power in a desired signal to the undesirable noise present in the absence of a signal. 10. The difference between the nominal or maximum operating level and the noise floor; usually specified in decibels. 11. The ratio of the peak value of the video signal to value of the noise. Usually expressed in decibels. signail tracer-A test instrument used for tracing a signal through a circuit in order to find faulty wiring or components. signa! tracing -The process of locating a fault in a circuit by injecting a test signal at the input and checking each stage, usually from the output backwards. effective (root-mean-square) ve with characteristics that pennit it to carry intelligence. SignaU-wewet envelope-The contour of a signal wave that is composed of a series of wave cycles. signa! winding -Aim called an input winding. In a saturable reactor, the control winding to which the independent variable (signal wave) is applied. signature (target)-The characteristic pattern of the target displayed by detection and classification equipment.

signal shifter - significant digits (of a number) signature analysis- Abbreviated SA. 1. A synchronous process, whereby activity at an electrical node (referenced to a clock signal) is monitored for a particular stimulus over a given time. The analysis that follows the nodal monitoring is based on data compression. The long, complex pattern of a data stream is reduced to a 16-bit, 4-digit “signature.” Correct signatures for a particular circuit are determined empirically from tests on a known-good product. 2. A means of isolating digital logic faults at the component level applicable to all digital systems. The technique involves the tracing of signals and the conversion of lengthy bit streams into 4-digit hexadecimal “signatures.” Using logic diagrams and schematics specially annotated with correct signatures at each trace node, and guided by troubleshooting trees, a circuit can be traced back to a point in the circuit that has a correct input signature and incorrect output signature. Signatures are traced under the direction of a test PROM. 3. A patented troubleshooting technique (Hewlett-Packard Go.) based on the principle that a good digital circuit in a known (initialized) state will produce the same output when stimulated repeatedly by the same input. If the repeated output of a device is not the one it has been designed to produce, it has failed. 4. A specific digitalcircuit-testing troubleshooting technique that makes use of coded representations of serial bit streams. Using a known input signal, a signature-analysis system generates such a coded representation at each point on a knowngood pc board. The signabre at each point on a board under test should then be the same as the signature at the corresponding point on the known-good board. 5. A technique for compressing large amounts of digital data into a relatively short data word, or signature. If the signature matches a reference signature it can be assumed, to an extremely high probability, that the data stream is valid. Signature analysis, therefore, can be used to verify the integrity of data streams. signature analyzer -An instrument that conlpares stored patterns (signatures) against actual received patterns. signature testing -Comparison of the actual output digital signatures, such as transition counts, with the expected correct signatures recorded from a -known-good device. sign bit -I. In complementary arithmetic, the leftmost bit of a number. If the sign bit is 1, the number is negative; if it is 0, the number is positive. 2. The leftmost bit of a computer word, which is sometimes used to indicate whether the number it contains is positive or negative. A 0 usually means a positive number, and a 1 a negative number. sign-control flip-flop -In computers, a flip-flop in the arithmetic unit used for storing the sign of the result of an operation. sign digit-A character (+ or -) used to designate the algebraic sign of a number. significance -Weight. In positional representation, the factor by which a digit must be multiplied to obtain its additive contribution to the value of a number; the factor is determined by the digit position. significant digits (of a number]-l. A set of digits from consecutive columns, beginning with the most significant digit other than zero, and ending with the least significant digit whose value is known or assumed to be relevant. The digits of a number can be ordered according to their significance, which is greater when occupying a column corresponding to a higher power of the radix. 2. A digit that contributes to the precision of a number. Significant digits are counted from the first digit on the left that is not zero and continue to the last accurate digit on the right. (A right-hand zero may be counted if it is

sign position

- silicon dioxide

an accurate part of the numeral.) For example, 2500.0 has five significant digits, 2500 probably has only two (it is not known that the last two digits are accurate) but 2501 has four, and 0.0025 has two. sign position-A position, normally at one end of a number, that contains an indicator of the algebraic sign of the number. silent alarm-A remote alarm without an obvious local indication that an alarm has been transmitted. silent-alarm system-An alarm system that signals a remote station by means of a silent alarm. silent discharge -The gradual and nondisruptive discharge of electricity from a conductor into the atmosphere. It is sometimes accompanied by the production of ozone. silent period--An hourly period during which ship and shore radio stations must remain silent and listen for distress calls. silica gel -A moisture-absorbent chemical used for dehydrating waveguides, coaxial lines, pressurized components, shipping containers, etc. silicon -1. A metallic element often mixed with iron or steel during smelting to provide desirable magnetic properties for transformer-core materials. In its pure state, it is used as a semiconductor. 2. A brittle, gray, crystalline chemical element that, in its pure state, serves as a semiconductor substrate in microelectronics. It is naturally found in compounds, such as silicon dioxide. silicon bilateral switch -A device that has characteristics similar to those of the silicon unilateral switch, but exhibits the same characteristics in both directions.

694 state, blocks a voltage applied in either direction. The device is enabled to conduct in the forward direction when an appropriate signal is applied to the gate electrode. When such conduction is established, it continues even with the control signal removed until the anode supply is removed, reduced, or reversed. The SCR is the solidstate equivalent of the thyratron tube. 2. A semiconductor device that functions as an electrically controlled switch for dc loads. The SCR is one type of thyristor. 3. A reverse-blocking triode thyristor that can be triggered into conduction in only one direction. Terminals are anode, cathode, and gate. 4. A three-junction semiconductor device that is normally an open circuit until an appropriate gate signal is applied to the gate terminal, at which time it rapidly switches to the conducting stage. Its operation is similar to that of a gas thyratron, which conducts current in one direction only.

ANODE

ANODE P N

P

N\ CATHODE

GATE

CATHODE

GATE

Junctions

Symbol.

"ON" STATE

I

I

&'VERSE BREAKDOWN VOLTAGE

I

I

"OFV'STATE

Anode characteristic.

Junctions.

I

Syrnbo1.

Anode 2 characteristic.

Silicon bilateral switch.

silicon capacitor-See varactor. silicon cell -A solid-state device composed of silicon that is used to convert radiation into electrical energy. silicon compiler-A software package that takes over chip creation from design to mask production. silicon controlled rectifier -Abbreviated SCR. Also called reverse-blocking triode thyristor. 1. A fourlayer pnpn semiconductor device that, when in its normal

Silicon controlled recaper.

silicon controlled switch-Abbreviated SCS. A four-terminal pnpn semiconductor switching device; it can be triggered into conduction by the application of either a positive or negative pulse. silicon detector-See silicon diode. silicon diffused epitaxial mesa transistor -A silicon transistor that has high voltage and power ratings and low storage time and saturation voltage. silicon diode-Also called a silicon detector. A crystal detector used for rectifying or detecting UHF and SHF signals, It consists of a metal contact held against a piece of silicon in a particular crystalline state. silicon diode array tube-A highly sensitive vidicon-type tube used in CCTV cameras designed for low light level applications. silicon dioxide-1. A compound that results from oxidizing silicon quartz. Selective etching of silicon dioxide makes possible selective doping for the generation of components in monolithic integrated circuits. 2. An abundant material found in the form of quartz and agate and as one of the major constituents of sand. The silicates of sodium, calcium, and other metals can be readily fused, and on cooling do not crystallize but instead form transparent material glass.

silicon double-base diode - s~iicont

695 ANODE

ANODE

I CATHODE

I CATHODE Symbol.

Junctions.

The thickness of SOS films is comparable with diffusion depths commonly used in MOSLSI fabrication. Consequently, doping impurities penetrate completely through the silicon, so that the only component of the pn junction is that normal to the surface. Since the principal area contributions to a pn junction come from the underside and side walls of a diffusion well, the SOS vertical junction area- and, hence, capacitance -is reduced considerably. 4. A technology whereby MOSWTs are deposited on a sapphire substrate to increase the transistor switching speed. Silicon is grown on a passive insulating base (sapphire) and then seIectively etched away to form a solid-state device.

SO, \

ALUMINUM

I

GATE ELECTRODE

i

Anode characteristic.

Silicon controlled switch.

SUBSTRATE SAPPHIRE

Silicon-on-sapphire transistor. silicon double-base diode -See unijunction transistor. silicone-A member of the family of polymeric materials characterized by a recurring chemical group That contains silicon and oxygen atoms as links in the main chain. These compounds are presently derived from silica (sand) and methyl chloride. One of their important properties is resistance to heat. silicon foundw-A facility that fabricates an integrated circuit from a design supplied by an independent party 1 silicon gate- 1. An MOS process that uses silicon rather than metal as one of the transistor elements. This permits the use of lower operating voltages and increases the dynamic response of the device. 2. MOS technology That uses silicon as the metal for the gate of the transistor. An alternative is aluminum gate. 3. One of several methods for fabricating metal-oxide semiconductor circuits. silicon-gate MOS - A process using polycrystalline silicon to replace the metd. layer as the gate electrode. It offers high speed and low threshold. silicon monoxide-A dielectric material often used in the fabrication of a microelectronic device to form an insulator, substrate, or a thin-film capasitor dielectric. silicon nitride-A compound that is deposited on the surface of a silicon monolithic integrated circuit to improve the stability of the integrated circuit. Silicon nitride is relatively impervious to some ions that penetrate silicon dioxide; best stability is obtained through the use of a combination of silicon nitride and silicon dioxide. Charge storage at the interface between layers of silicon nitride and silicon dioxide has resulted in memory devices in which the retention times are extremely long. silicon on sapphire- Abbreviated SOS. Also called spinel. 1. A semiconductor manufacturing process in which a silicon layer is grown on a sapphire substrate. 'The silicon layer is divided into a number of electrically isolated islands for individual transistors. Silicon on sapphire is used for high-performance LSI circuits. 2. A semiconductor manu€acturing process that uses an insulated material (sapphir'e) instead of silicon as a substrate on which the epitaxial layer is grown. With the process, MOS or bipolar performance can be significantly improved. over that of conventional devices. 3. A fabrication technique in which thin crystalline films of silicon are deposited! on a single crystal alumina (sapphire) substrate.

silicon oxide- 1. A dielectric material commonly used in the surface passivation of microelectronic circuits. Silicon oxide contains various combinations of silicon monoxide and silicon dioxide. 2. Silicon monoxide or dioxide or a mixture, the latter of which can be deposited on a silicon IC as insulation between metalization layers. silicon photodiode -Semiconductor pn or pin junction that utilizes absorbed photon energy in the range of 1.06 to 1.03 electronvolts to excite carriers from one energy level to a higher state. The resultant change in the charge across the junction is monitored as a current in the external photodiode circuit. silicon planar transistor --A silicon transistor produced by the planar process and consisting of a series of etchings and diffusions to produce a transistor with a thin oxide layer within the planes of a silicon substrate. silicon rectifier- 1. One or more silicon rectifying cells or cell assemblies. 2. Semiconductor diode that converts alternating current to direct current and which can be designed to withstand large currents and high voltages. silicon rectifying cell -An elementary two-terminal silicon device that consists of a positive and a negative electrode and conducts current effectively in only one direction. silicon solar cell -A photovoltaic cell designed to convert light energy into power for electronic and communication equipment. It consists essentially of a thin wafer of specially processed silicon. silicon steel -Steel containing 3 percent to 5 percent silicon. Its magnetic qualities make it desirable for use in the iron cores of transformers and in other ac devices. silicon surface-barrier detectors -Silicon radiation detectors based on a rectifying contact at the silicon's surface. silicon symmetrical switch --A thyristor modified by the addition of a semiconductor layer to malce the device into a bidirectional switch. It is used as an ac phase control for synchronous switckng and control of motor speed. silicon target -A high-sensitivity TV image pickup tube of the direct readout type utilizing a silicon diode array photoconductive target. Suitable for low-light applications. High sensitivity extends through the visible range,

silicon transistor - simple steady-state vibration

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Silicon solar cell.

with extended sensitivity to the near-infrared region. Has low lag and high bum resistance. silicon transistor-A transistor in which silicon is used as the semiconducting material. silicon unijunction transistor-See unijunction transistor. silicon unilateral switch -Abbreviated SUS. A device similar to the silicon-controlled switch, except that a Zener junction is added to the anode gate so that the silicon unilateral switch is triggered into conduction at approximately 8 volts. The SUS can also be triggered by application of a negative pulse to the gate.

ANODE

CATHODE

Svrnbol.

Junctions.

Anode characteristic.

Silicon unilateral switch.

Silicon Valley- Also called Silicon Gulch. The area around Sunnyvale, California, where most of the American semiconductor manufacturers are located. silk-covered wire-A wire covered with one or more layers of fine floss silk. It is a better insulator than cotton. Also, it is more moisture-resistant and permits more turns of wire within a given space.

696 silk screen-A screen of a closely woven silk mesh stretched over a frame and used to hold an emulsion outlining a circuit pattern and used in screen printing of film circuits. Used generally to describe any screen (stainless steel or nylon) used for screen printing. silver -A precious metal that is more conductive than copper. Because it does not readily corrode, it is used for contact points of relays and switches. Its chemical symbol is Ag. silvered-mica capacitor-A mica capacitor that has a coating of silver deposited directly on the mica sheets instead of using conducting metal foil. silvering -See silver spraying. silver migration-A process by which silver in contact with an insulating surface, under conditions of high humidity and with an electrical potential applied, is removed ionically from one location and redeposited as a metal in another location. This transfer results in reduced insulation resistance and dielectric failure. silver oxide cell -A small dry cell giving a constant voltage of 1.5 volts. Used in low-current applications, such as hearing aids, calculators, and electric watches. It consists of a pure zinc anode, a depolarizing silver oxide cathode, and a potassium hydroxide or sodium hydroxide electrolyte. silver solder-A solder that is composed of copper, silver, and zinc. It has a melting point lower than that of silver, but higher than that of lead-tin solder. silver soldering -Brazing with a silver-based filler metal. silver spraying -Also called silvering. Metallizing the surface of an original master disc recording by using a dual spray nozzle in which ammoniated silver nitrate and a reducer are combined in an atomized spray to precipitate the metallic silver. silverstat -An arrangement of closely spaced contactors. Sometimes used as a step-by-step device to unbalance the arms of a resistance bridge. silverstat regulator-A multitapped resistor whose taps are connected to single-leaf silver contacts. Variation of voltage causes a solenoid to open or close these contacts, shorting out more or less of the resistance in the exciter circuit as a means of regulating the output voltage to the desired value. simple buffering-A technique for buffer control such that the buffers are assigned to a single data control block and remain assigned to it until it is closed. simple-gate IC -An integrated circuit that consists of one or more gate circuits formed on a single chip. The input and output of each gate are brought out to separate pins on the integrated-circuit package. simple harmonic current-Also called sinusoidal current. A symmetrical alternating current whose instantaneous value is equal to the product of a constant and the sine or cosine of an angle having a value varying linearly with time. simple harmonic electromotiveforce -A symmetrical alternating electromotive force that is equal to the product of a constant and the cosine or sine of an angle that varies linearly with time. simple harmonic motion -A periodic motion whose displacement varies as a sinusoidal function of time. simple quad -See s-quad. simple scanning -Scanning of only one scanning spot at a time. simple sound source-A source that radiates sound uniformly in all directions under free-field conditions. simple steady-state vibration - A periodic motion made up of a single sinusoid.

697 simple target-h radar, a target whose reflecting surface does not cause the amplitude of the reflected signal to vary with the aspect of the target (e.g., a metal siphere). simple tone - 1. A sound wave whose instantaneous sound'pressure is a simple sinusoidal function of time. 2. Also called a pure tone. A sound sensation characterized by its singleness of pitch. simplex- 1. Transmission in one direction only. 2. A transmission facility in which the transmission is restricted to only one direction. 3. A form of communications satellite operation that involves a communication in only one direction at a tirne (mainly for facsimile, television, and some data). simplex channel -A path for electrical transmission of information in one direction between two or more terminals. simplex coil-A repeating coil used on a pair of wires to derive a commercial simplex circuit. simplexed circuit-A two-wire metallic circuit from which a simplex circuit is derived, the metallic and simplex circuits being capable of simultaneous use. simplex mode -Operation of a communication channel in one direction only, with no capability for reversing. simplex modem-A two-wire modem that can transmit in only one direction. sirnplebx modern with backward channelTwo-wire modem that can transmit simultaneously in both directions, with the primary direction being reasonably high speed and the secondary (or backward) direction being rather low speed. simplex operation-Communication that takes place in only one direction at a time between two stations. Included in this classification are ordinary transmitreceive or press-to-talk operation, voice-operated carrier, and other forms of manual or automatic switching from transmit to receive. simplex software -One-way transmission of data. A program that can be in the form of ROM, floppy disk data. cassette data, or hard-copy (firmware), or in the form of a machine code or high-].eve1language in RAM. simplex transmission -Data transmission in one direction only. simulate-1. To use the behavior of another system to represent certain behavioral features of a physical or abstract system. 2. To represent the functioning of a device, system, or computer program by another; e.g., to represent one computer by another, to represent the behavior of a physical system by the execution of a computer program, or to represent a biological system by a mathematical model. To represent, by imitation, the fianctions of one system or process by means of another. See emulate. s ~ ~ w l ~-Also t i ~ ncallled digital simulation. 1. A type of problem in which a physical model and the conditions to which the model may be subjected are all represented by mathematical formulas. 2. The substitution of instrumentation (often a computer) for actual operational conditions, so that valid data can be obtained. 3. Modeling of the operation of a logic circuit by a computer program containing (device models and topology information about their interconnections. 4. The technique of utilizing representative or artificial data to reproduce in a model various conditions that are likely to occur in the actual performance of a system. Frequently used to test the behavior of a system under operating policies. 5 . Representation of either an abstract or a physical system's features by computer operations. Often the operzting envisonment of a program must be simulated during

simple target - simultaneous lo the software testing. 6. Modeling a target microprocessor with a software interpreter so that object code can be checked as if it were actually executing in the target microprocessor. Simulation usually can't duplicate timing problems, glitches, or microprocessor idiosyncrasies. InpuUoutput devices are often simulated so microcomputer development can proceed before the actual devices are available. 7. Representation of physical systems by computers. simulator- 1. A device that represents a system or phenomenon and that reflects the effects of changes in the original so that it may be studied, analyzed, and understood from the behavior of that device. 2. A cross-computer program that allows the user to test the object program by simulating the action of the microcomputer when the actual circuitry is unavailable. Simulators often provide certain kinds of diagnostic information unavailable with a debugger program running on the actual microcomputer: warning of the overflow of a processor stack or of an attempt by the program to write into a location in the ROM, for example. They usually allow manipulation and display of the simulated microcomputer memory and CPU registers; setting of breakpoints, whereby processing can be stopped at a certain program address or when the program reads or writes into a specified memory Location; and tracing, in which each instruction in a certain address range is printed out as it is executed. Often they provide timing information, such as the number of instructions or machine cycles executed from program start to stop. 3. Program that helps to evaluate a microprocessor by duplicating all logic operations within the software of a large computer. Software simulators are sometimes used in the debug process to simulate the execution of machinelanguage programs using another computer (often a limesharing system). These simulators are especially useful if the actual computer is not available. They may facilitate the debugging by providing access to internal registers of the CPU that are not brought out to external pins in the hardware. 4. A device or a computer program that simulates the operation of another device or computer. simulator program -A program that causes one computer to imitate the logical operation of another computer for purposes of measurement and evaluation. Primarily used to exercise program logic independent of hardware environment. Extremely useful for debugging logic prior to committing it to ROM. simulcast- 1. To broadcast a program simultaneously over more than one type of broadcast station, e.g., to broadcast a stereophonic program over an AM and FM station. 2. A program so broadcast. simulcasting -Broadcasting a stereo program over an AM and FM station. An AM and Fh.I tuner are required for stereo reception. simultaneous-Pertaining to the occurrence of events at the same instant of time. simultaneous access-See parallel access. simultaneous computer-A computer in which there is a separate unit to perform each portion of the complete computation concurrently, the units being interconnected in a manner that depends on the computation. At different times during a run, a given interconnection carries signals that represent different values of the same variable. For example, ;he simultaneous computer is a differential analyzer. simultaneous lobing-In radar, a direction-determining technique utilizing the received energy of two concurrent and partially overlapped signal lobes. The relative phase of power of the two signals received from a target is a measure of the angular displacement of the target from the equiphase or equisignal direction.

simultaneous transmission - single-degree-of-freedom system

simultaneous transmission-Transmission of control characters or data in one direction at the same time that information is being received in the opposite direction. SlNAD or sinad -Abbreviation for signal-to-noise and distortion. 1. A measurement of the signal-to-noise ratio of a receiver system in which the signal level measurement includes the system noise and distortion: (s n d)/n. sine-The sine of an angle of a right triangle is equal to the side opposite that angle divided by the hypotenuse (the long side opposite the right angle). sine galvanometer -An instrument resembling a tangent galvanometer except that its coil is in the plane of the deflecting needle. The sine of the angle of deflection will then be proportionate to the current. sine law-The law which states that the intensity of radiation in any direction from a linear source varies in proportion to the sine of the angle between a given direction and the axis of the source. sine potentiometer-A dc voltage divider (potentiometer) whose output is proportionate to the sine of the shaft-angle position. sine wave- 1. A wave that can be expressed as the sine of a linear function of time, space, or both. 2. A waveform (often viewed on an oscilloscope) of a pure alternating current or voltage. It is drawn on a graph of amplitude versus time or radial degrees and follows the rules of sine and cosine values in relation to angular rotation of an alternator. It can be simulated by means of an electronic oscillator. 3. The only waveform that cannot be considered to be a pulse. All other waveforms consist of more than one frequency, all harmonically related. A sine wave has a single frequency and therefore occupies a very small bandwidth. It passes through circuitry of any bandwidth with no change in waveform, but it may be changed in amplitude.

+ +

,414

sine-wave modulated jamming-A jamming signal consisting of a cw signal modulated by one or more sine waves. singing -1. An undesired self-sustained oscillation at a frequency in or above the passband of a system or component. 2. An unwanted self-sustained audiofrequency oscillation in an audio system or device. singing margin-Also called gain margin. The excess of loss over gain around a possible singing path at any frequency, or the minimum value of such excess over a range of frequencies. singing point-1. The condition of a circuit or transmission path where the sum of the gains exceeds the sum of the losses. When expressed in decibels, it is the gain that can be added to the circuit equivalent before singing will begin. 2. The amount of total gain in the transmission system (most commonly used in connection with two-wire repeaters) that causes the system to begin to

698

lose efficiency of performance because the self-oscillating point is too closely approached. 3. The singing point of a circuit that is coupled back to itself is the point at which the gain is just sufficient to make the circuit break into oscillation. singing-stovepipe effect-Reception and reproduction of radio-signal modulation by ordinary pieces of metal, such as sections of stovepipe, in contact with each other. It is caused by mechanically poor connections, such as rusty bolts or faulty welds, that act as nonlinear diodes and produce intermodulation distortion when subjected to strong radiated fields near transmitters. single-address code -An instruction that contains the location of the data as well as the operation or sequence of operations to be performed on this data. single amplitude -With reference to vibratory conditions, the peak displacement of an oscillating structure from its average or mean position. single-anode tank-See single-anode tube. single-anode tube -Also called a single-anode tank. An electron tube with one anode (used chiefly for pool-cathode tubes). single-assignment language-A programming language that allows only one value to be assigned to a variable in a single expression. single-axis gyro-A type of gyro in which the spinning rotor is mounted in a gimbal arranged so as to tilt about only one axis relative to the stable element. single-board microcomputer- Also called monoboard microcomputer. A single printed circuit board containing, as a minimum, processor, memory (ROM and/or RAM), and input/output -usually a combination of serial and parallel ports. May also include a counter/timer function and bus interconnection scheme. A single-board microcomputer family may also include other functional system elements (such as memory and YO functions) on circuit boards of the same format as the microcomputer board. single-button carbon microphone-A microphone having a carbon-filled buttonlike container on one side of its flexible diaphragm. As the sound waves move the diaphragm, the resistance of the carbon changes, and the microphone current constitutes the desired audiofrequency signal. single-carrier FM recording -The method of recording in which the input signal is frequency modulated onto a carrier and the carrier is recorded on a single track at saturation and without bias. single-channel -A carrier-only or single-tone modulated radio control transmitter and matching receiver installation. single-channel monopulse tracking s y s t e m See monopulse tracking. single-channel simplex-Nonsimultaneous communication between stations over the same frequency channel. single circuit -A telegraph circuit capable of nonsimultaneous two-way communication. single-circuit system-An alarm circuit that routes only one side of the circuit through each sensor. The return may be through either ground or a separate wire. single-conversion receiver- A receiver employing a superheterodyne circuit in which the input signal is downconverted once. single crystal-A piece of material in which the crystallographic orientation of all the basic groups of atoms is the same. single-degree-of-freedom system-A system for which only one coordinate is required to define the configuration of the system.

699

single-dial control -Control of a number of different devices or circuits by means of a single adjustment (e.g., in tuning all variable-capacitor sections of a radio receiver). single-ended -Unbalanced, such as grounding one side of a circuit or transmission line. single-ended amplifier- An amplifier in which only one tube or transistor normally is employed in each stage-o'r if more than one is used, they are connected in parallel so that operation is asymmetric with respect to ground. singleended input -Amplifier input configuration in which all analog inputs are referenced to system ground. single-ended input impedance -The impedance between one amplifier input terminal and ground (with the other input terminal, if any, grounded for ac) when the amplifier is balanced. single-ended input voltage -The signal voltage applied to one amplifier input terminal with the other input terminal at signal ground. single-ended output voltage -The signal voltage between one amplifier output terminal and ground. single-ended push-pull amplifier circuit -An amplifier circuit having two transmission paths designed to operate in a complementary manner and connected to provide ar single unbalanced output. (No transformer is used.) Signal -As opposed to a differencenal that is at ground potential when it is at zero level. single-ended tube-A metal tube in which all electrodes -including the control grid -are connected to base pins and there is no top connection. The letter S after the first numerals in a receiving-tube designation (e.g., 6SP.17) indicates a single-ended tube. single-ended voltage gain -Within the linear range of an amplifier, the ratio of a change in output voltage to the corresponding change in single-ended input voltage. single-frequency duplex-A method that provides communications in opposite direction over a singlefrequency carrier channel, lbut not at the same time. The change between transmitting and receiving conditions is controlled automatically by the voices of the communicating parties. single-frequency siniplex-A system of singlefrequency carrier communications in which the change from transmission to reception is accomplished by manual rather than automatic means. single-grip terminal -A solderless terminal designed to permit a crimp to the wire only. le-groove stereo-See monogroove stereo. le-gun color tube-A color picture tube with a single electron gun that produces only one beam, which is sequentially deflected across the phosphor dots. single harmonic dktortion-The ratio of the power at the fundamental frequency measured at the output of the transmission system considered to the power of any single harmonic observed at the output of the system because of its nonlinearity, when a singlefrequency signal of specified power is applied to the input of the system. It is expressed in decibels. single-hop lpropagatiion-Transmission in which the radio waves are reflected only once in the ionosphere. single in-line package-See SIP. s i n g ~ e - ~ ~ n photosensitive ct~o~ semiconductor--Two layers of semiconductor materials with an electrode connection to each material. Light energy controls the amount of current.

single-dial control - single sampling

single-line diagram -Also called single-line drawing. A form of schematic diagram in which single lines are used to show component interconnections even though two or more conductors are required in the actual circuit. single-line t e l e p h o n e -A telephone that provides access to one telephone line. single-loop feedback-A loop in which feedback may occur only through one electrical path. single-mode fiber- 1. A fiber waveguide that supports only one mode of propagation. 2. An optical glass fiber that consists of a step core of very small diameter, approximately 6 pm, and a cladding approximately 20 times the thickness of the core. Tremendous information rates (great bandwidth) are possible with single-mode fibers. The primary disadvantages of this type of fiber are cost of manufacture, difficulty in launching signals into the fiber, and difficulty in splicing and general handling in the field. single-operand instruction -An instruction containing a reference to one register, memory location, or device. single-phase circuit -Either an alternating-current circuit with only two points of entry, or one with more than two points of entry but energized in such a way that the potential differences between all pairs of points of entry are either in phase or 180" out of phase. A singlephase circuit with only two points of entry is called a single-phase two-wire circuit. single-phase synchronous generator-A generator that produces a single alternating electromotive force at its terminals. single phasing-The tendency of the rotor (of a motor tach generator) to continue to rotate wheii one winding is opened and the other winding remains excited. single-point ground -See uniground. single-point grounding -A grounding system that attempts to confine all return currents to a network that serves as the circuit reference. It does not imply that the grounding system is limited to one earth connection. To be effective, no appreciable current is allowed to flow in the circuit reference; Le., the sum of the above return currents is zero. single-polarity pulse -A pulse that departs from normal in one direction only. single pole-A contact arrangement in which all contacts in the arrangement connect, in one position or another, to a common contact. single-pole, double-throw- Abbreviated SPDT. A three-terminal switch or relay contact for connecting one terminal to either of two other terminals. single-pole-piece magnetic h e a d -A magnetic head with only one pole piece on one side of the recording medium. single-pole, single-throw -Abbreviated SPST. 1. A two-terminal switch or relay contact that either opens or closes one circuit. 2. A switch with only one moving and one stationary contact. Available either normally open (no) or normally closed (nc). single rail-The method of data transfer in a computer on only one line or wire. The device at the destination must be able to handle the data in either the high-level or low-level value. The return path is by way of common or ground. single-rank binary -A flip-flop that requires no more than one full clock pulse from a single clock system to transfer the logic from a synchronous input to the output of the binary. It contains only one memory stage. single sampling pian-The plan that consists of a single sample size with associated acceptance and rejection criteria.

single-shield solid enclosure

- sinker

700

single-shield solid enclosure -An all-metal enclosure providing higher attenuation than cell-type units. It is usually a rigid, free-standing enclosure. single-shot -See monostable. single-shot blocking oscillator-A blocking oscillator modified to operate as a single-shot trigger circuit. single-shot multivibrator -Also called a singletrip multivibrator. 1. A multivibrator modified to operate as a single-shot trigger circuit. See also monostable multivibrator. 2. A monostable multivibrator that, after being triggered to the quasi-stable state, will “flop” back by itself to the stable state after a certain period of time. single-shot trigger circuit-Also called a singletrip trigger circuit. A trigger circuit in which the pulse initiates one complete cycle of conditions, ending with a stable condition. single sideband -Abbreviated SSB. An AM radio transmitter technique in which only one sideband is transmitted. The other sideband and the carrier are suppressed. This gives SSB a 6 : 1 efficiency advantage over AM, and, thus, greater range per watt of output power. SSB occupies half of a conventional AM (double-sideband) channel. single-sideband filter-A bandpass filter in which the slope on one side of the response curve is greater than on the other side. So called because it is used in systems to suppress a carrier frequency and transmit one or both sidebands. single-sideband modulation -1. Modulation whereby the spectrum of the modulating wave is translated in frequency by a specified amount, either with or without inversion. 2. A form of amplitude modulation in which only one of the two sidebands is transmitted. Either of the two sidebands may be transmitted, and the carrier may be transmitted, reduced, or suppressed. single-sideband suppressed carrier -Modulation resulting from the partial or complete elimination of the carrier and all components of one sideband from an amplitude-modulated wave. single-sideband s y s t e m -A type of radiotelephone service in which one set of sidebands (either the upper or lower) is completely suppressed and the transmitted carrier is partially suppressed. single-sideband transmission -Transmission of only one sideband, the other sideband being suppressed. The carrier wave may be transmitted or suppressed. single-sideband transmitter -A transmitter in which only one sideband is transmitted.

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CAnniEn OSCILUTOR

BAUNCEO MODUUTOR

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Limn AMPLIFIER

AUDIO INPUT

Single-sideband transmitter.

single-signal receiver -A superheterodyne receiver equipped for single-signal reception. A highly selective filter is placed in the intermediate-frequency amplifier, and provision is included for varying the selectivity of the receiver to suit the requirements of the band condition. single-signal reception -Use of a piezoelectric quartz crystal and associated coupling circuits as a crystal

filter to provide the high degree of selectivity required for reception in a crowded band. single step-Pertaining to a method of computer operation in which each step is carried out in response to a single manual operation. single-stroke bell-A bell that is struck once each time its mechanism is activated. single-stub transformer -A shorted section of coaxial line connected to a main coaxial line near a discontinuity so that impedance matching at the discontinuity is achieved. single-stub tuner-A section of transmission line that is terminated by a movable short-circuitry plunger or bar and that is attached to a main transmission line to provide impedance matching. single sweep- The operating mode for a triggeringsweep oscilloscope in which the sweep must be reset for each operation, thus preventing unwanted multiple display; it is particularly useful for trace photography. In the interval after the sweep is reset and before it is triggered, the oscilloscope is said to be armed. single throw-A contact arrangement in which each contact form included is a single contact pair. single-throw circuit breaker-A circuit breaker in which only one set of contacts need be moved to open or close the circuit. single-throw switch-A switch in which only one set of contacts need be moved to open or close the circuit. single-tone keying -Keying in which the carrier is modulated with a single tone for one condition, either marking or spacing, but is unmodulated for the other condition. single-track magnetic system -A magneticrecording system whose medium has only one track. single-track recorder-A tape recorder that records or plays only one track at a time on or from the tape. See also monaural recorder. single-trip multivibrator-See single-shot multivibrator. single-trip trigger circuit-See single-shot trigger circuit. single-tuned amplifier-An amplifier characterized by resonance at a single frequency single-tuned circuit -A circuit that may be represented by a single inductance and capacitance, together with associated resistances. single-turn potentiometer-A potentiometer in which the slider travels the complete length of the resistive element with only one revolution of the shaft. single-unit semiconductor device -A semiconductor device having one set of electrodes associated with a single carrier stream. single-wire line-A transmission line that uses the ground as one side of the circuit. single-wound resistor -A resistor in which only one layer of resistance wire or ribbon is wound around the base or core. sink-In communication practice: 1. A device that drains off energy from a system. 2. A place where energy from several sources is collected or drained away. 3. Anything into which power of some kind is dissipated. 4. The component or network into which energy (usually current) flows. 5. A device that switches ground or minus to a load. The current flows from the load into the sensor. See interface, 2. sinker-An nf region that extends down from the collector contact area on an integrated transistor to the n+ island under the collector for the purpose of reducing the collector resistance.

5'01

s i n k load

s i n k load-A load wiith a current whose direction is away from its input. A sink load must be driven by a current si&. sins --Acronym for ship's inertial navigational system; especially applicable to submarine use. sinter-A ceramic matixial or mixture fired so that it is not completely fused but is a coherent mass. sintered plate -A powder that holds the active plate material used for both the anode and cathode in secondary cells. This provides a large surface area for the active material, allowing better cycle life, higher discharge rates, and better efficiency than the pocket-type plate design. sintering - 1. The process in which metal or other powders are bonded by cold-pressing them into the dieslred shape and then heating them so that a strong, cohesive body is formed. 2. The welding together of powdered particles at temperatures below the melting or fusion point. Particles are fused together to form a mass, but the mass, as a whole, does not melt. sinusoid -A curve having ordinates proportional to the sine of the abscissa. sinusoidal -Varying in proportion to the sine of an angle or time function (e.g., ordinary alternating current). sinusoidal current -See simple harmonic current. sinusoidal electromagnetic wave -In a homogeneous medium, a wave with an electric field strength proportionate to the sine (or cosine) of an angle that is a linear function of time, distance, or both. sinusoidal field-A ffield in which the magnitude of the quantity at any point varies as the sine or cosine of an independent variable such as time, displacement, or temperature. sinusoidal quantity -A quantity that varies in the manner off a sinusoid. sinusoidal vibration -A cyclical motion in which the object moves linearly. The instantaneous position is a sinusoidal function of time. sinusoidal wave -A, wave whose displacement varies as the sine (or cosine) of an angle that is proportional to time, distance, or both. SIP- Abbreviation for single in-line package. 1. A package having a single row of external leads, usually mounted vertically with leads through the printed circuit board, but can be surface mounted with Beads bent in gullwing fashion. 2. A package for electronic components that is suited for automated assembly into printed circuit boards. The SIP is characterized by a single row of external connecting terminals, or pins, which are inserted into the holes of the printed1 circuit board.

Single in-line package.

SI s y s t e m -International

System of Units. Includes

m k s and mksa units.

site error-In navigation, the error that occurs when the radiated field is distorted by objects near navigational equipmen;.

- skin antenna

situation-display tube -A large cathode-ray tube used for displaying tubular and vector information having to do with the various functions of an air-defense mission. six-phase circuit -A combination of circuits energized by alternating electromotive forces that differ in phase by one-sixth of a cycle (60"). size control-On a television receiver, a control that varies the size of the picture either horizontally or vertically. skating -The tendency of a pivoted toneann to be pulled to the center spindle. It is caused by friction between the stylus and the record surface. skating force-A frictional force between a pickup stylus and the record material, tending to move the pickup toward the center of the record. It is present only when the cartridge is offset at an angle to reduce tracking error, and is a function of tracking force, offset angle, stylus size and shape, record material, and recorded amplitude. In a stereo recording, the effect of skating force is to increase the stylus-to-groove contact force on the left channel and decrease it on the right channel. skein winding -A method of winding single-phase motors in which each pole is a long skein of wire, formed by winding around two headless nails or bolts (smooth) set some distance apart on a piece of wood. The entire pole is wound in place by twisting the coil to form a concentric chain. No internal connection is made between coils of the same pole. The winding is measured with a single turn of wire; then, using this endless wire, the location of the winding pins can be found. skeletal coding -Sets of computer instructions in which some addresses and other parts are undetermined. These items usually are determined by routines designed to modify them according to given parameters. s k e w - 1. In facsimile. the nonrectangular received frame due to asychronism between the scanner and recorder. Numerically it is the tangent of the angle of this deviation. 2. The motion characterized on a magnetic tape by an angular velocity between the gap center line and a line perpendicular to the tape center line. 3. In magnetic thin film, the deviation of the easy axis during fabrication. 4. The angular displacement of a printed character, character group, or other data from the intended or ideal placement. 5. A measure (expressed in percent) of the departure of each individually received DTMF signal frequency from its nominal value. A function of component tolerances, aging, environmental conditions, and certain types of transmission-multiplexing equipment, skew is measured at the DTMF receiver. 6. The time difference between the logic-state changes on different input pins within a particular test pattern. 7. The time difference of corresponding digital information on separate lines, measured at the rising or falling edges of the digital data. s k e w e d distribution -A frequency distribution of any natural phenomenon in which zero or infinity is one of its limits. skewing-The time delay or offset betweec two signals with respect to each other. s k e w n e s s - A statistical measure of the asymmetry existing in a distribution. s k e w ray-A ray that is skewed to the axis of an optical fiber. If the fiber is straight, a skew ray travels along a helical path around, but not crossing, the fiber's axis. skiatron -1. A dark-trace oscilloscope tube. See also dark-trace tube. 2. A display employing an optical system with a dark-trace tube. skin antenna -A flush-mounted aircraft antenna made by isolating a portion of the metal skin of the aircraft with insulating materials.

skin d e p t h

-slap-back

skin depth-Also called depth of penetration. In a current-canying conductor, the depth below the surface at which the current density has decreased one neper below the current density at the surface; that is, the field has decreased to 1 / (36.8 ~ percent) of its surface value. skin effect -Also called radio-frequency resistance. 1. The tendency of rf currents to flow near the surface of a conductor. Thus, they are restricted to a small part of the total sectional area, which has the effect of increasing the resistance. 2. The phenomenon that occurs when an alternating current forces the ac current to flow mostly in the outer parts of a conductor. 3. The phenomenon in which the depth of penetration of electric currents into a conductor decreases as the frequency increases. 4. A characteristic of current in a conductor whereby as the frequency increases more and more current flows near the conductor surface and less at the center. skinner-A wire brought out at the end of a cable prepared for soldering to a terminal. skinning -Peeling the insulation from a wire. skin tracking-Radar tracking of an object without the aid of a beacon or other signal device on board the object. s k i p - 1. A digital-computer instruction to proceed to the next instruction. 2. In a computer, a “blank” instruction. 3. To ignore one or more of the instructions in a sequence. 4. Term referring to propagation of radio signals over considerable distances due to reflection back to earth from the ionosphere. skip distance -The distance separating two points on the earth between which radio waves are transmitted by reflection from the ionized layers of the ionosphere. s k i p fading -Fading due to fluctuations of ionization density at the place in the ionosphere where the wave is reflected, which causes the skip distance to increase or decrease. skip-if-set instructions -In computers, a class of instructions in which provision is made for examining particular logic conditions. Usually they are used in conjunction with a jump (branch) instruction. For example, a skip-if-word-register-ready instruction would allow the program to check for a ready condition of the word register and then permit the program to continue along one of two different paths, depending on the condition of the word register. s k i p keying-The reduction of the radar pulserepetition frequency to a submultiple of that normally used, to reduce the mutual interference between radars or to increase the length of the radar time base. s k i p zone-Also called zone of silence. A ringshaped space or region within the transmission range wherein signals from a transmitter are not received. It is the distance between the farthest point reached by the ground wave and the nearest point at which the refracted sky waves come back to earth. skirt selectivity-A measure of the resolution capability of a spectrum analyzer when displaying signals of unequal amplitude. A unit of measure would be the bandwidth at some level below the 6-dB down points. SKU -Stockkeeping unit. Abbreviation used in many computer reports to define an individual stock item. s k y error -See ionospheric error. sky hook- Amateur term for antenna. s k y noise- 1. Noise produced by radio energy from stars. 2. Background microwave radiation coming from deep space. It can be a noise source for dish antennas and sets a lower boundary for the possible noise temperature of any dish antenna of approximately 16 to 20 K. Sky wave -See indirect wave; ionospheric wave.

702

Skirt selectivity.

sky-wave correction -In navigation, a correction for sky-wave propagation errors applied to measured positional data. The amount of the correction is established on the basis of an assumed position and on the height of the ionosphere. sky-wave station error-In sky-wave-synchronized loran, the station-synchronization error due to the effect of the ionosphere on the synchronizing signal transmitted from one station to the other. sky-wave-synchronized loran -A loran system in which the range is extended by using ionospherereflected signals for synchronizing the two ground stations. sky-wave transmission delay -The longer time taken by a transmitted pulse when carried by sky waves reflected once from the E layer compared with the same pulse carried by ground waves. slab-A relatively thick crystal from which blanks are cut. slab line-A double-slotted coaxial line whose outer shield has been unwrapped and extended to infinity in both directions so that the resulting configuration is a cylindrical conductor between two parallel conductors. slab wafer-A slice of semiconductor material that has straight edges, as opposed to a conventional rounded wafer that has 21 percent less area than a square with comparable dimensions. Slant range-1. In radar, the line-of-sight distance from the measuring point to the target, particularly an aerial target. 2. Line-of-sight distance between two points not at the same elevation. slap-back-An echo effect wherein the original signal reappears as distinct echoes that decay in level each time they appear. One way of creating slap-back is to feed the output signal from the play head back into the record head, at a slightly lower level. For example, if the sound “la” is originally fed to the recorder, then “la-la-la ... la” will be heard, with each “la” slightly lower in level until the signal fades away.

YO3 slave-I. A component in a system that does not act independently, but only under the control of another similar component. 2. A device that follows an order given by a master remote control. slave antenna-A directional antenna that is positioned in azimuth and elevation by a servo system. The iinfomation controlling the servo system is supplied by a tracking or positioning system. slave drive-See follower drive. slaved tracking -A method of interconnecting two ox more regulated power supplies so that the master supply operates to control other power supplies called slaves. slave operation-A method of interconnecting two or more stabilized power supplies so that coordinated control of the assembly by controlling the master supply alone is achieved, and essentially proportional outputs are obtained from all units. slave irelay-See auxiliary relay, 2. slave station- 1. A radionavigational station whose emissions are controlled by a master station. 2. A device on a communication facility that is prevented from initiating transmission in mder to organize and control communications between tvio or more stations. slave sweep-A time base that is synchronized or higgered by a waveform from an external source. It is used in navigational systems for displaying or utilizing the same infomation at different locations, or in displaying or utilizing different information with a common or related time base. slaving -The use of a torque to maintain the orientation of the spin axis of a gyro relative to an external reference such as a pendu1u.m or magnetic compass. sleeping sickness --In transistors. the gradual appearance of leakage. sieeve -1. A cylindrical contacting part, usually placed in back of the tip or ring of a plug and insulated from it. 2. An iron core (usually a thin-walled cylinder) used as an electromagnetic shield around an inductor. 3. A lead tube placed over cable conductors that have been spliced. 4. A tube of woven cotton pushed over a twisted wire joint in a cable. 5. A brass or copper tube or paired tubes for fastening line or drop wires together by twisting, crimping, or rolling. 6. A tube of copper or iron placed over a relay winding to make the relay slow acting. sleeve antenna-A vertical half-wave antenna whose Power half is a metallic sleeve through which the concentric: feed line mns. The upper radiating portion, which is one-quarter wavelength, is connected to the center of the line. ~ ~ e e v ~ l ~antenna d i ~ o -lA~ dipole antenna with a coaxial sleeve around the center. s ~ e e w ~ - s tantenna ~b -An antenna consisting of half of a sleeve-dipole antenna projecting from an extended conducting surface. sleewe wire-1. A third conductor when associated with a pair. 2. Wire that connects to the sleeve of a plug 01jack. By extension, it is common practice to designate by this term the conductors having similar functions or arrangements in circuits where plugs or jacks may not be involved. -Any preformed tubular insulation, of braided or extruded construction, that is intended for placement over portions of cables or conductors during their installation to insulate them or hold them together. slewing - 1. Rapid change of a mechanism associated with either end of a data-transmission system when it stops following one target and takes up another. 2. In random-sampling-oscilloscope technique, the process of incrementally delaying successive samples or a set of samples with respect to the signal under examination.

slave - slide switch slewing rate-See slew rate. Slew range-1. The high-speed range in which a motor can run continuously but cannot stop, start, or reverse without losing step count. 2. The maximum stepping rate at which a stepper motor will run without losing synchronism with the field. slew rate- Also called rate limit or voltage velocity limit. 1. The maximum rate of change of the output voltage of an amplifier operated within its linear region. 2. The maximum rate of change of the output voltage of a closed-loop amplifier under large-signal conditions (the conditions that exist when an ac input voltage causes saturation of an amplifier stage, resulting in current limiting of that stage). 3. The maximum rate at which an amplifier output can be driven between limits in response to a step change in input voltage while accurately reproducing the input waveform. Usually measured in volts per second or volts per microsecond. For example. a OS-V/ps slew rate means that the output rises or falls no faster than 0.5 V every microsecond. Slew rate is caused by current limiting and saturation of an opamp internal stage. That limited current is the maximum current available to charge the compensation capacitance network. 4. The rate at which the output can be driven from limit to limit under overdrive conditions. Generally specified in volts per microsecond. 5. The rate at which an amplifier follows a fast-rising waveform. Usually measured in volts per microsecond. 6. In a sample-andhold circuit, the fastest rate at which the sample hold output can change. Specified in volts per microsecond. slew torque-See running torque. SLlc -Acronym for Subscpiber Line Interface Circuit. 1. In digital transmission of voice, the circuit that performs some or all of the interface functions at the central office. See BORSCHT. 2. An analog device incorporated in a telephone transmission network and in the interface of a telephone with a central office. It also performs conversions from the two-wire subscriber loop to the four-wire central-office switch, and vice versa. slice -1. A single wafer cut from a silicon ingot and forming a thin substrate on which have been fabricated all the active and passive elements for multiple integrated circuits. A completed slice usually contains hundreds of individual circuits. See also chip, 2. 2. Those parts of a waveform between two given amplitude limits on the same side of the zero axis. 3. A type of chip architecture that permits the cascading or stacking of devices to increase word bit size. slicer-Also called an amplitude gate or a clipperlimiter. A transducer that transmits only portions of an input wave lying between two amplitude boundaries, slicked switch-An dacritized mercury switch in which the rolling surface has been treated with an oily material. slideback-The technique of applying a dc voltage to one input of a differential amplifier in order to change the vertical position on the CRT screen of the signal applied to the other input. slideback voltmeter-A vacuum-tube voltmeter that measures effective voltage values indirectly by measuring the change in grid bias voltage required to restore the plate current of the vacuum tube to the value it had before the unknown voltage was applied to the grid circuit. slider -A sliding contact. slide-rule dial-A tuning dial in which a pointer moves in a straight line over a straight scale. So called because it resembles a slide rule. slide switch -A switch that is actuated by sliding a control lever from one position to another.

slide wire - slow-releasing relay

Slide switch. slide wire-A bare resistance wire and a slider that can be set anywhere along the wire to provide a continuously variable resistance. slide-wire bridge - A simplified Wheatstone bridge in which the resistance ratio is determined by the position of a slider on a resistance wire. slide-wire rheostat-A long single-layer coil of a resistance wire with a sliding contact. The resistance is varied by moving the slider. sliding contact-See wiping contact. sliding load-A length of transmission line containing a matched electrical load at a distance from the connector end that can be varied. sliding short-A length of transmission line containing an electrical short at a distance from the connector end that can be varied. slip- 1. The difference between the synchronous speed of a motor and the speed at which it operates. Slip may be expressed as a percentage or decimal fraction of synchronous speed or directly in revolutions per minute. 2. Distortion produced in a recorded facsimile image as a result of slippage in the mechanical drive system. 3. A method of interconnecting multiple wiring between switching units so that trunk 1 becomes the first choice for the first switch, trunk 2 becomes the first choice for the second switch, and so on. slip process-See wet process. slip ring-A device for making electrical connections between stationary and rotating contacts. See also collector rings. slip-ring motor -Term usually applied to an induction motor with a wound secondary. (The correct term is a wound rotor motor.) slip speed -The speed difference between speed at any load and the synchronous speed. slope- 1. The essentially linear portion of the gridvoltage, plate-current characteristic curve of a vacuum tube. This is where the operating point is chosen when linear amplification is desired. 2. See roll-off, 1. 3. The rate of attenuation of frequencies beyond the passband of a crossover network. Usually either 6 dB or 12 dB per octave of frequency. slope-based linearity-A manner of expressing nonlinearity as the deviation from a straight line for which only the slope is specified. slope detection- A discriminator operation on one of the slopes of the response curve for a tuned circuit. It is rarely used in FM receivers because the linear portion of the response curve is too narrow for large-signal operation. Slope detector-A detector in which slope detection is employed. Slot - 1. One of the grooves formed in the iron core of a motor or generator armature for the conductors forming the armature winding. 2. A unit of time in a time-division multiplex (TDM) frame during which a subchannel bit or character is carried to the other end of the circuit and extracted by the receiving TDM unit. 3. That longitudinal position in the geosynchronous orbit into which a communications satellite is parked. Above the United States, communications satellites are typically

704 positioned in slots that are based at two- to three-degree intervals. slot antenna-A radiating element formed by a slot in a conducting surface. slot armor-An insulator in the slot of a magnetic core of a machine; it may be on the coil or separate from it. slot cell-A formed sheet of insulation that is separate from the coil and placed in the slot of a magnetic core. slot coupling-A method of transferring energy between a coaxial cable and a waveguide by means of two coincident narrow slots, one in the sheath of the coaxial cable. E - or H-waves are launched into the guide, depending on whether the cable and guide are parallel or perpendicular to each other. slot-discharge resistance-See corona resistance. slot effect-The minimum voltage of rated frequency applied to the control-voltage winding of a motor tach generator necessary to start the rotor turning at noload conditions with rated voltage and frequency on the fixed-voltage winding. slot insulation-Flexible sheet-type insulation inserted into the slots of armatures and stators to insulate the windings from the core. slot radiator-A primary radiating element in the form of a slot cut in the walls of a metal waveguide or cavity resonator or in a metal plate. slotted line-See slotted section. slotted rotor plate-See serrated rotor plate. slotted section-Also called a slotted line or slotted waveguide. A section of a waveguide or shielded transmission line, the shield of which is slotted to permit examination of the standing waves with a traveling probe. slotted SWR measuring equipment -A device in which standing and/or reflected waves are measured with a slotted line and a detecting probe. slotted waveguide -See slotted section. slow-acting relay -See slow-operating relay. slow-action relay- See time-delay relay. Slow death -The gradual change of transistor characteristics with time. This change is attributed to ions that collect on the surface of the transistor. slowed-down video -A technique of transmitting radar data over narrow-bandwidth circuits. The radar video is stored over the time required for the antenna to move through one beam width, and is subsequently sampled at such a rate that all range intervals of interest are sampled at least once each beam width or once per azimuth quantum. The radar-return information is quantized at the gap-filler radar site. slow memory-See slow storage. slow-operate, fast-release relay-A relay designed specifically for a long make and short release time. slow-operate, slow-release relay-A slowspeed relay designed specifically for both a long make and a long release time. slow-operating relay-Also called slow-acting relay. A relay that is slow to attract its armature after its winding is energized. A copper slug, or collar, at the armature end of the core delays the operation momentarily after the operating circuit is completed. Such a relay is often marked SO on circuit diagrams. slow-release relay-See slow-releasing relay. slow-releasing relay- Also called a slow-release relay. A slow-acting relay in which a copper slug, or collar, at the heelpiece end of the core delays the restoration momentarily after the operating circuit is opened. Such a relay is often marked SR on circuit diagrams.

705

slow-scan television -Abbreviated SSTV. slow-speed relay-A relay designed specifically for long operate or release time, or both. slow storage -Also called slow memory. Computer storage in which the access time is relatively long. See also secondary storage. slow-wave circuit-A microwave circuit in which the phase velocity of the waves is considerably below the speed of light. Such waves are used in traveling-wave tubes. slow-wave structure-A circuit composed of selected inductance and capacitance that causes a wave to be propagated at a speed slower than the speed of light. SLSl -Abbreviation for super large-scale integration (lO0,OOO transistors per chip). 1. A heavy rnetail ring or short-circuited windn a relay core to delay operation of the relay. 2. A metallic core that can be moved along the axis of a coil for tuning purposes. tuner- A waveguide tuner containing one or more longitudinally adjustable pieces of metal or dielectric. slug tuning-Varying the frequency of a resonant circuit by introducing a slug of material into the electric or magnetic fields, or both. slumber switch - A circuit arrangement whereby a iadio or a recorder automatic shutoff provision can be made to turn off the apparatus itself as well as any other equipment plugged into its ac outlet. SMAC -Abbreviation for Scene Matching Area Correlator. An optical terminal homing system that matches images with stored maps. usiness computer- 1. A system with a price tag low enough to fit the budget of a small business, simple enough for clerks and typists to operate, yet sophisticated enough to perfom a variety of complex transactions. 2. A coDputer that is affordable by a small business, rather than a relatively low-performance system for business. small-scale integration-See SSI. small-outline transistor -See SOT. small signal -That value of an ac voltage or current which. when halved or doubled, will not affect the characteristic being measured beyond the normal accuracy of the measurement of that characteristic. small-signal analysis -Consideration of only s m d excursions from the no-signal bias, so that a vacuum tube or transistor can be represented by a linear equivalent circuit. small-signal characteristics-The characteristics of an amplifier operating in the linear amplification region. small-signal current gain (current-transfer ratio) -The output current of a transistor with the output circuit shorted. divided by the input current. The current components are understood to be small enough that linear relationships hold between them. small-signal drain-to-source on-state resistance -The small-signal resistance between the drain amd source terminals of a field-effect transistor with a specified gate-to-source voltage applied to bias the device to the on state. For a depletion-type device, this gate-tosource voltage may be zero. small-signal gain--The gain characteristics of an amplifier operating in the linear amplification region. Small-signal gain is typically measured at least 10 dB below the input power level that creates 1 dB gain compressi~on. srnall-,signal open-circuit forward-transfer impedance-In a transistor, the ratio of the ac output voltage to the ac input current when the ac output current is zero.

slow-scan television - S-meter small-signal open-circuit input impedanceIn a transistor, the ratio of the ac input voltage to the ac input current when the ac output current is zero. small-signal open-circuit output admittance-In a transistor, the ratio of the ac output current to the ac voltage applied to the output terminals when the ac input current is zero. small-signal open-circuit output impedanceIn a transistor, the ratio of the ac voltage applied to the output terminals to the ac output current when the ac input current is zero. small-signal Open-circuit reverse-transfer impedance-In a transistor, the ratio of the ac input voltage to the ac output current when the ac input current is zero. small-signal open-circuit reverse-woltage transfer ratio-In a transistor, the ratio of the ac input voltage to the ac output voltage when the ac input current is zero. small-signal power gain -In a transistor, the ratio of the ac output power to the ac input power under specified small-signal conditions. Usually expressed in dB. small-signal short-circuit forward-current transfer ratio-In a transistor, the ratio of the ac output current to the ac input current when the ac output voltage is zero. small-signal short-circuit f o ~ a r d - t r a ~ ~ e r admittance-In a transistor, the ratio of the ac output current to the ac input voltage when the ac output voltage is zero. small-signal short-circuit input admittanceIn a transistor, the ratio of the ac input current to the ac input voltage when the ac output voltage is zero. small-signal short-circuit input impedanceIn a transistor, the ratio of the ac input voltage to the ac input current when the ac output voltage is zero. small-signal short-circuit output admittance-In a transistor, the ratio of the ac output current to the ac output voltage when the ac input voltage is zero. small-signal short-circuit reverse-transfer admittance-In a transistor, the ratio of the ac input current to the ac output voltage when the ac input voltage is zero. small-signal transconductance-In a transistor, the ratio of the ac output current to the ac input voltage when the ac output voltage is zero. smart terminal-1. See intelligent terminal. 2. A computer terminal that can do more than simply send data to a computer and display data from a computer. Depending on how many chips are built into it, a smart terminal can edit and temporarily store up to several thousand words, produce graphics, and even change the color of the background on its monitor. smear- 1. Television-picture distortion in which objects appear stretched out horizontally and are blurred. 2. Small frequency and time distortion introduced into a radio signal by a dispersive reflector such as the moon. smectic phase-A parallel arrangement of liquid crystal molecules arranged in layers. The physical appearance of the smectic state is that of a highly viscous, turbic fluid. S-meter-A meter provided in some communications receivers to give an indication of the relative strength of the received signal in terms of arbitrary units. It is calibrated in “S” units and decibels. Nominally, each S unit equals 6 dB.Above S9, most meters are calibrated in 10-dB increments. Sometimes a manufacturer will specify what input level (usually between 50 and 100 @VIis required for a reading of S9. S-meters are intended to be relative, rather than absolute, indicators. They are useful

smileys

- snap-action contacts

706

to an extent in comparing the strength of two stations, or the performance of two antennas at one location. See also signal-strength meter. smileys- Also called emoticons. Little symbols in a text message meant to be viewed sideways; used to express emotion. Smileys are often used in e-mail messages and newsgroup postings. Examples include :) (happy), :-( (sad), :-i (mad), :-o (wow!), :-@ (yell), and ;-) (wink). S m i t h chart-A special polar diagram used in the solution of transmission-line and waveguide problems. It consists of constant-resistance circles, constant-reactance circles, circles of constant standing-wave ratio, and radius lines that represent constant line-angle loci. s m o k e detector-A device that detects visible or invisible products of combustion. See also ionization smoke detector; photoelectric beam-type smoke detector; photoelectric spot-type smoke detector; resistance-bridge smoke detector. smooth-To apply procedures that bring about a decrease in or the elimination of rapid fluctuations in data. s m o o t h i n g -Averaging by a mathematical process or by curve fitting, such as the method of least squares or exponential smoothing. s m o o t h i n g c h o k e - An iron-core choke coil that filters out fluctuations in the output current of a vacuumtube rectifier or direct-current generator. s m o o t h i n g circuit- Also called ripple filter. A combination of inductance and capacitance employed as a filter circuit to remove fluctuations in the output current of a vacuum-tube or semiconductor rectifier or direct-current generator. s m o o t h i n g factor-The factor expressing the effectiveness of a filter in smoothing out ripple voltages.

s m o o t h i n g filter- 1. Also called ripple filter. A filter used to remove fluctuations in the output current of a vacuum-tube or semiconductor rectifier or direct-current generator. 2. A low-pass filter in the vertical-deflection amplifier of a spectrum analyzer. It is used to smooth amplitude fluctuations in order to display spectral density and the average level of random signals as single lines. (The time constant of a smoothing filter is generally variable.) SMPTE-Abbreviation for the Society of Motion Picture and Television Engineers. (Formerly it was the SMPE, Society of Motion Picture Engineers.) SMT -Abbreviation for surface-mount technology. The mounting of components on the surface of a printed circuit board; as contrasted with through-hole mounting, in which component leads extend through the board. s n a k e -A tempered steel wire, usually of rectangular cross section. The snake is pushed through a run of conduit or through an inaccessible space such as a partition and used for drawing in wires. snap-acting switch-A switch in which there is a rapid motion of the contacts from one position to another position, or their return. This action is relatively independent of the rate of travel of the actuator. snap-action-1. In a mercury switch, the rapid motion of the mercury pool from one position to another. 2. A rapid motion of the contacts from one position to another position, or their return (differential storing of energy). This action is relatively independent of the rate of travel of the actuator. snap-action contacts -A contact assembly such that the contacts remain in one of two positions of equilibrium with substantially constant contact pressure

Smith chart.

707 during the initial motion of the actuating member until a point is reached at which stored energy causes the contacts to move abruptly to a new position of equilibrium. snap magnet-A permanent magnet used in thermostatic, pressure, and other control instruments to provide quick make-and-break action at the contact and thereby minimize sparking. The magnet pulls the armature in suddenly against the spring to close the contacts and hold them closed until the spring is compressed enough to make them fly apart. snap-off diode -A planar epitaxial passivated silicon diode that is processed in such a way that a charge is stored close to the junction when the diode conducts. Upon application of a reverse voltage, the stored charge forces the diode to switch quickly to its blocking state, or snap off. s n a p s h o t - 1. In a computer, a dynamic printout of selected data in storage that occurs at breakpoints and checkpoints during the computing operations, as opposed to a static printout. 2. A printout of intermediate results part way though a program run. s n a p s h o t dump-A selective dynamic dump carried out at various points in a machine run. s n a p s h o t routine -Special type of debugging routine that includes provisions for dynamic printout of selected data at various checkpoints in a computing operation. snap-strate-A scribed substrate that can be processed by gang deposition in multiples of circuits and snapped apart aftemard. snap switch-A switch (e.g., a light switch) in which the contacts are separated or brought together suddenly as the operating knob or lever compresses or ri:leases a spring. snap waractor -See step-recovery diode. s n e a k circuit-That part of a complete electrical circuit which carries an unintentional (sneak) current. Sneak currents may prevent proper operation of interconnected equipment. s n e a k current -A leakage current that enters telephone circuits from other circuits; it is not strong enough to cause immediate damage, but it can produce harmful heating effects if permitted to continue. s n e a k path -In computers, an unwanted circuit through a series-parallel configuration. Snell’s law-The sine of the angle of incidence divided by the sine of the angle of refraction equals a constant called the index of refraction when one of the media is air. s ~ ~ ~-Also ~ ~ called s csnooperscope. o ~ ~ 1. An instrument for seeing in the dark by means of infrared radiation. A high-aperture lens forms an image of distant objects on the photocathode of an infrared-sensitive image tube, the visible final image being viewed through a magnifier (eyepiece). The scene must be illuminated with infrared if such a tube is to be usable. These instruments find extensive use in warfare and also for operations in rooms that have to be kept dark because film emulsions are exposled. 2. A snooperscope attached to a rifle and used to aid in the sighting a.nd shooting of targets in lowlight-level conditions. sniwet-A straight, jagged, or broken vertical black line that appears near the right edge of the screen of a television receiver, caused by discontinuity in the platecurrent characteristic of the horizontal amplifier tube under conditions of zero bias. snisritz-A small pulse of noise. See also glitch. snoopgrscope - 1. A night viewing device to permit a user to see objects in total darkness. It consists of an infrared source, an infrared image converter, and a battery-operated high-voltage dc-to-dc converter. Infrared

snap magnet

- soak timer

radiation sent out is reflected back to the snooperscope, where it is then converted into a visible image on the fluorescent screen of the image-converter tube. 2. An instrument used for viewing in low levels of illumination by means of infrared radiation. A high-aperture lens forms an image of distant objects on the photocathode of an infrared-sensitive image tube, the visible final image being viewed through a magnifier. The scene must be illuminated with infrared energy. 3. See also sniperscope. snow -Also known as sparklies. 1. A speckled background caused by random noise on an intensity-modulated display, such as alternate dark and light dots appearing randomly in a television picture (usually indicative of a weak signal). 2. Heavy random noise in a video picture. snowflake transistor -A high-speed, mediumpower switching transistor for use as a thin-film or core driver. It employs a six-pointed emitter geometry that permits the optimum ratio of emitter periphery to emitter area. snow static-Precipitation static caused by falling snow. SNR -Abbreviation for signal-to-noise ratio. I. Expressed in decibels, it relates how much louder a signal is than the background noise. It is measured at the speaker, and is used in sensitivity ratings. Often, (s n)/n is used, as it is easier to measure; it is the ratio of the signal and background noise to the background noise, and will yield an apparently higher sensitivity than the s/n ratio. 2. Usable information in a signal (optical or electrical) compared to the noise that tends to interfere with the transmission of the information. Also abbreviated sln ratio. SIn ratio-See SNR. snubber capacitor-A capacitor incorporated in a rapidly switched LC circuit to reduce EM1 by lowering the circuit resonant frequency and characteristic impedance. snubber circuit -1. A form of suppression neiwork that consists basically of a series-connected resistor and capacitor connected in shunt with an SCR. The snubber circuit combined with the effective circuit series inductance controls the maximum rate of change of voltage and the peak voltage across the device when a stepped forward voltage is applied to it. 2. A circuit designed to reduce the sensitivity of a solid-state relay to spikes and other high-dV/dt transients in the load circuit voltage. Snubbers prevent false firing of solid-state relay sviitching elements. One such circuit is often referred to as an RC circuit. SO -Abbreviation for small outline (package). Similar to a miniature plastic Bat pack, but with gull-wing lead forms primarily or wholly constructed for surface mounting. Typical lead spacing is 0.05 inch. SOA- Abbreviation for safe operating area. s o a k - 1. In an electromagnetic relay, the condition that exists when the core is approximately saturated. 2. To increase the current through a relay winding until the core is saturated with flux, and then hold the magnetization at that level for a certain time. soakage-The inability of a capacitor to come up to voltage instantaneously without voltage lag or creep during or after charging. The lower the soakage, the lower the lag and creep. s o a k time - 1. The period of time required following activation for the electrolyte in a cell or battery to be sufficiently absorbed into the active materials. 2. The length of time a ceramic material (such as a substrate or thick-film composition) is held at the peak temperature of the firing cycle. s o a k timer-A reset timer, usually dial-adjustable, as applied in a temperature-control system for controlling

+

s o a k value

- software maintenance

the length of time the temperature is held at a predetermined level. s o a k value-The voltage, current, or power applied to the coil of the relay coil to ensure that a condition approximating magnetic saturation exists. s o c k e t - 1. An opening that supports and electrically connects to vacuum tubes, bulbs, or other devices or components when they are inserted into it. 2. Also known as the female contact. A mechanical electrical connector. s o c k e t adapter-A device placed between a tube and its socket so that the tube can be used in a socket designed for some other base, or so that current or voltage can be measured at the electrodes while the tube is in use. socket connector-A connector that contains socket contacts and that receives a plug connector containing male contacts. s o c k e t contact -A hollow female contact designed to mate with a male contact. It is normally connected to the live side of a circuit. sodar- Acronym for sound detecting and ranging. A device that detects large changes in temperature overhead by the amount of sound returned as echoes (the colder the atmosphere, the louder the echoes). The sound, which is within the range of human hearing, is launched upward, and the echoes are changed into oscilloscope patterns. sodium amalgam-oxygen cell -A fuel-cell system in which materials functioning in the dual capacity of fuel and anode are consumed continuously. Low operating temperatures and high power-to-weight ratios are significant characteristics of the system. sodium-vapor lamp -A gas-discharge lamp containing sodium vapor. It is used chiefly for highway illumination. sofar-Acronym for sound fixing and ranging. An underwater sound system with which air and ship survivors can be located within a square mile and as far as 2000 miles (3200 km) away. Survivors drop a TNT charge into the water. The charge, which is timed to explode at 3000 to 4000 feet (914 to 1220 m), sets up underwater sound waves that can be picked up by hydrophones at shore stations. soft copy-Alphanumeric or graphical data, or both, presented in nonpermanent form, such as on a video screen. soft error-1. An occasional random loss of data in a memory. The reason for the error is normally not identifiable, nor is it repeatable on a device tester. 2. A dynamic error normally caused by some transient condition. Retrying the failed operation will often result in successful completion. 3. Alteration of the information in a memory cell resulting from an alpha particle striking the cell. soft key-A key on the terminal keyboard that may be labeled on the lower part of the terminal screen and whose function can be programmed. soft magnetic material -Also called low-energy material. Ferromagnetic material that, once having been magnetized, is very easily demagnetized (i.e., requires only a slight coercive force to remove the resultant magnetism). soft phototube-A gas phototube. soft radiation -Term applied to radiation composed of particles or photons that will not easily penetrate a material because of their low energy levels. soft soldering -Process of joining two metals with a fusible alloy or solder that melts below 800°F (427°C). See hard soldering. soft start-A method of increasing the duty cycle of the switching element in a power supply from zero to its normal operating point during system startup. Using soft start eliminates output voltage overshoot and magnetizing

708 current imbalances in the transformer. See also warm boot. soft tube -1. A high-vacuum tube that has become defective because of the entry of a small amount of gas. 2. An electronic tube into which a small amount of gas has purposely been put to obtain the desired characteristics. software- 1. Programs, routines, codes, and other written information for use with digital computers, as distinguished from the equipment itself, which is referred to as hardware. 2. A set of computer programs, procedures, rules, and associated documentation concerned with the operation of a data-processing system, e.g., compilers, monitors, editors, utility programs. 3. A computer program or set of programs held in some storage medium and loaded into readwrite memory (RAM)for execution. 4. The set or package of programs that instructs a computer to perform certain predefined functions. 5. The user program that controls the operation of a programmable controller. 6. Totality of programs and routines used to extend the capabilities of computers, such as compilers, assemblers, narrators, routines, and subroutines. 7. The computer programs, procedures, and documentation concerned with the operation of a computer system, e.g., assemblers, compilers, operating systems, diagnostic routines, program loaders, manuals, library routines, and circuit diagrams. Software is the name given to the programs that cause a computer to carry out particular operations. Contrasted with hardware. 8. The modifiable (to some extent) binary bit patterns in the memory of a computer that control the operation of the processing portion of the computer. Software programs are usually written in one of three general classes of language: machine, assembler, or higher level. 9. A computer’s programs. If a particular bit of data manipulation is done through a program rather than by special circuitry, it is said to be “in software.” Doing things in software is cheap and flexible, since a program can be easily changed. 10. An expression for programs and also tapes or disks with recorded data. There are various kinds of software, including applications and executive. The executive is the “heart” of the system and is responsible for scheduling and controlling activity in the system. Applications or task programs perform specific functions whose activity is controlled by the executive. 11. Programs that control the operation of computer hardware. Operating systems, executives, monitors, compilers, editors, utility routines, and user programs are considered software. software buffer-A location or set of locations in memory given by name by the resident program and used to hold information until it can be used. software compatible -Describes an MPU that executes the same software as another one. software documentation -Program listings a n d or technical manuals describing the operation and use of programs. software house-A company that offers software programs and support service to users. Such support can range from simply supplying manuals and other information to a complete counseling and computer parttime programming service. software interrupt-The interruption of a userlevel program in response to the acknowledgment of a hardware interrupt by the operating system. In high-levellanguage programs, software interrupts can safely occur only at the end of a program line. software list-A document that defines all the next lower level modules that are contained in the module being documented. software maintenance -1. Improvements and changes made in software. 2. The task of keeping software up to date and working properly.

'709

software programmable

software programmable- A system whose functions are defined by a program, generally supplied by the manufacturer, that may be redefined or updated by changing or replacing the program. software tool-A computer program, rules, and associated documentation that assist a data-processing technologist in designing, developing, maintaining, and imanaging data and software. sofhnrire or computer numerical control-A numerical control system wherein a dedicated storedprogram computer is used to perform some or all of the basic numerical control functions. The control program can be read in and stored from data on tape, cards, manual switches, etc. Changes in the response, sequence, and/or functions can be made by reading in a different control program. soft X-rays -X-rays with comparatively long wavelengths and, hence, poor penetrating power. solar absorber-A surface that has the property of converting solar radiation into thermal energy. solar absorption index- A quantity that relates The angle of the sun at different latitudes and local times with ionospheric absorption. solar battery-A series of solar cells arranged to collect solar radiation and to generate a given amount of electrical energy. solar cell- I. A device capable of converting light or other radiant energy directly into electrical energy. 2. Silicon photovoltaic cell that can be used to generate electricity from direct sunlight. Such cells are especially usefu€ in space vehicles, for which no other source of electricity is available. 3. A photovoltaic cell designed to respond to wavelengths in solar radiation. Basically a semiconductor diode that absorbs light and converts it to electrical power. This ability depends on the material of the serniconductor and on the photovoltaic effect. In rhis effect a photon of solar radiation is absorbed by the semiconductor material by giving up its total energy to produce an excess charge carrier (electron or hole). The absorption can happen only if the photon energy is greater than the energy of the bandgap of the material-the difference between the conduction band and the valence band (the excited state and the ground state).

f-0

SUNLIGHT

N.TYPE SILICON

-

\

P-TYPE SILICON NP JUNCTION

Sohzr cell.

solar concentrator-- A device that increases the intensity of solar energy by optical means. solar constant-The standard intensity of solar iadiation impinging on the earth's atmosphere at the mean distance between earth and sun. It is the energy equivalent of 1.353 kilowatts of electricity per square meter. Under clear skies some 80 to 90 percent of this radiation reaches the ground; under heavy clloud cover, 10 percent or less. The average energy rate at the earth's surface is about 1 kW per square meter.

- soldering

solar day-A day that contains exactly 24 hours (1440 minutes). During a solar day the sun rotates slightly more than 360" about its axis with respect to "fixed" stars. Compare siderial day. solar-energy conversion-The process of changing solar radiation into electrical or mechanical power, either directly or by using a heat engine. solar furnace-An optical system that is designed to produce a high temperature in a specified area by the optical direction and concentration of solar radiatkon on that area. The system usually consists of a collecting system that may have reflective optics concentrators, or a combination of both, and a tracking system that keeps the collecting and directing system properly oriented to the sun. solar noise -Electromagnetic radiation from the sun at radio frequencies. solar radiation-Radiation from the sun that is made up of a very wide range of wavelengths, from the long infrared to the short ultraviolet, with its greatest intensity in the visible green at about 5000 angstroms (500 nm). The solar radiation received on the earth's surface is restricted to the visible and near infrared, since the air strongly absorbs the wavelengths located at either end of the spectrum. solar simulation -The simulaaon of solar radiation in the infrared and ultraviolet spectrum for the analysis of extraterrestrial sunlight and its effects on spacecraft, materials, and components. solder- 1. A readily meltable metal or alloy that produces a bond at a junction of two metal surfaces. True solder must have a lower melting point than the metals being joined and must also be capable of uniting with the metals to be joined. 2. An alloy that melts at relatively low temperatures and is used to join or seal metals with higher melting points. Solder alloys melt over a range of temperatures; the temperature at which a solder begins to melt is the solidus, and the temperature at which it is completely molten is the liquidus. solderability-The ability of a conductor to be "wetted" by hot solder and to form a strong low-resistance bond with the solder. solder bumps -The round solder balls bonded to a transistor contact area and used to make connection to a conductor by face-down bonding techniques. solder contact-A contact having a cup, hollow cylinder, eyelet, or hook to accept a wire for a conventional soldered termination. solder cup -The end of a terminal or similar device into which a contact is inserted before being soldered. solder darn -A dielectric composition screened across a conductor to limit molten solder from spreading farther onto solderable conductors. solder eye -A solder-type terminal provided with a hole at its end through which a wire can be inserted prior to being soldered. A ring-shaped contact termination of a printed-circuit connector for the same purpose. solder eyelet-An eyelet, or hole, in a contact through which a wire may be mechanically connected to the contact prior to soldering. solder flux-A substance that transforms a passive, contaminated metal surface into an active, clean, solderable surface. Generally, all such fluxes should prevent oxidation during heating, lower interfacial surface tensions, be thermally stable, 3e easily displaced by molten solder, be noninjuious to components, remove easily if desired, remove oxide, and penetrate films. solder ground - A conducting path to ground due to dripping or overhanging solder. soldering -1. The joining of metallic surfaces (e.g., electrical contacts) by melting B metal or an alloy (usually

soldering dross - solid conductor tin and lead) over them. 2. A process of joining metallic surfaces with solder, without the melting of the base metals. A soldered connection has metallic continuity and therefore excellent long-term reliability. See soft soldering; hard soldering. soldering dross-Usually a combination of tin oxide and lead oxide in a ratio closely resembling the parent metal. In practice this floating mass of tarnish also contains other metal reaction products- sulfides and organic residues such as burned flux, etc. Dross contains the metallic impurities picked up during soldering. This occurs only when the impurity concentrations exceed the solubility limits and when intermetallics are formed that float to the surface. soldering fluid-A liquid used with wave solder systems that can be intermixed with solder to reduce the surface tension of solder, promote wetting, and eliminate the formation of dross. See also soldering oils. soldering gun -1. A pistol-shaped soldering tool having a trigger switch to turn it on. Operates from 117 volts ac and has an integral stepdown transformer with a single-turn secondary that quickly heats the copper soldering loop. 2. Category of soldering tool. Pistol-grip guns have trigger action control of low or high tip temperatures for general use, with output ranges commonly rated at 100/140, 145/210, or 240/325 watts; temperaturecontrolled guns designed for solid-state electronics work with interchangeable power heads for varying fixed-tip temperatures. soldering iron -1. A soldering tool consisting of a heating element to heat the tip and melt the solder, plus a heat-insulated handle. 2. An electrically heated coppertipped tool that heats the work and melts solder to make a soldered joint. soldering-iron tip- A high-purity copper-substrate form, iron plated 0.006 to 0.030 inch (0.254to 1.127 mm) thick, hot tin dipped in the working area, with the remaining surface immunized by nickel-chromium plating. The working area of the tip is usually fabricated for access and maximum heat transfer to the work point. soldering oils-Liquid compounds formulated for use as the oil in oil intermix wave-soldering equipment and as pot coverings on still solder pots. solder joint -The point of bonding between solder and component surfaces. solderlessconnection-The joining of two metallic parts by pressure only, without soldering, brazing, or using any method that requires heat. solderless connector-A device for clamping two wires firmly together to provide a good connection without solder. A common form is a cap with tapered internal threads that are twisted over the exposed ends of the wires. solderless contact-See crimp contact. solderless lug-A terminal lug that holds the conductor it terminates by compressing it under a screw. solderless terminals-Small metal parts used for joining a wire to another wire or to a stud by the method of crimping. solderlesswrap- Also called wire wrap. A method of connection in which a solid wire is tightly wrapped around a rectangular, square, or V-shaped terminal by means of a special tool. solderless wrapped c o n n e c t i o n -Also called wire-wrapped connection or wrapped connection. A connection made by wrapping wire that is under tension around a square or rectangular terminal. solder lug-Device to which wire is secured by soldering. Solder lugs are attached to a printed circuit board, termination strip, chassis, or electrical component.

710

solder m a s k - A printed-circuit-board technique in which everything is coated with a plastic except the contacts to be soldered. solder short-A defect that occurs when solder forms a short-circuit path between two or more conductors. sole-In a magnetron or a backward-wave oscillator, an electrode used to carry a current that produces a magnetic field in the desired direction. solenoid -1. An electric conductor wound as a spiral with a small pitch, or as two or more coaxial spirals. 2. An electromagnet having an energized coil approximately cylindrical in form and an armature whose motion is reciprocating within and along the axis of the coil. 3. A coil of wire surrounding a movable iron bar that is located in such a way that when the coil is energized the core is drawn into it. 4. An electromagnet with a movable steel core (plunger), used to translate electrical energy into linear mechanical motion. The wire coil is wound on a cylindrical or rectangular tube, and the similarly shaped plunger (which may be solid or laminated steel) extends about half way into the tube, in its deenergized position. When the coil is energized by direct current, the plunger is drawn into the tube by magnetic attraction, and the external mechanism connected to the plunger is activated accordingly. Solenoids designed for operation on alternating current are constructed like the dc types, except that the plunger is equipped with the “shading” coil that maintains the magnetic field between alternations of the current, to reduce hum and eliminate chatter. 5. An electromagnet with a movable core, or plunger, which, when it is energized, can move a small mechanical part a short distance. 6. A device that converts electrical energy into mechanical work by providing force only during a linear closing stroke.

Solenoid.

solenoid valve- 1. A combination of an electromagnet plunger and an orifice to which a disc or plug can be positioned to either restrict or completely shut off a flow. (Orifice closure or restriction occurs when the electromagnet actuates a magnet plunger.) 2. A combination of two basic functional units: (a) a solenoid (electromagnet) with its plunger (or core), and (b) a valve containing an orifice in which a disc or plug is positioned to stop or allow flow. The valve is opened or closed by movement of the magnetic plunger (or core), which is drawn into the solenoid when the coil is energized. solid-A state of matter in which the motion of the molecules is restricted. They tend to remain in one position, giving rise to a crystal structure. Unlike a liquid or gas, a solid has a definite shape and volume. solid circuit -A semiconductor network fabricated in one piece of material by alloying, diffusing, doping, etching, and cutting, and using jumper wires as necessary. solid conductor -An electrical conductor consisting of a single wire.

711

solid electrolyte

solid electrolyte-A. solid semiconductor in direct contact with a thin nonconductive oxide coating. solid-electrolyte fuel cell -A self-contained fuel cell in which oxygen is the oxidant and hydrogen is the fuel. The oxidant and fuel are kept separated by a solid electrolyte that has a crystalline structure and a low conductivity. solid-electrolyte tantalum capacitor-Also called solid tantalum capacitor. A tantalum capacitor with a solid semiconductor electrolyte instead of a liquid. A wire anode is used for low capacitance values, and a sintered pellet for higher values.

SINTERED TANTALUM PELLET (ANODE) TANTALUM PENTOXIDE

BOTTOM OF CASE

MAGNESIUM DIOXIDE (SOLI0 ELECTROLYTE, CATHODE)

NICKEL LEA0

i

(POSITIVE)

Hermetically sealed. SINTERED TANTALUM LE,T; (ANODE) DIPPED EPOXY COATING ,.,re n

\

/’

TANTALUM PENTOXIDE / (DIELECTRIC) - -

WCLU

NICKEL LEAD (POSITIVE)

\.

MAGNESIUM DIOXIDE (SOLID-ELECTROLYTE)

N I C K E ~LEAD (NEGATIVE)

T A ~ A L U MWIRE WELDED TO TANTALUM PELLET

Epoxy dipped.

Solidelectrolyte tantalum capacitor.

solid logic technology-The use in computers of miniaturized modules that make possible faster circuitry because of the reduced distances current must travel. solidly grounded -Also called directly grounded. Grounded through an adequate grounded connection in which no impedance has been inserted intentionally. solid metal mask-A thin sheet of metal with an etched pattern used in contact printing of film circuits. solid silicon circuit-Semiconductor circuit that employs a single piece of silicon material in which the various circuit elements (transistors, diodes, resistors, and capacitors) are formed by diffusion in the planar configuration. By combining oxide masking, diffusion, metal deposition, and alloying, a complex network with active and passive components is made completely within a die that is part of a single semiconductor wafer. Often, thin-film devices are applied to the surface of the silicon wafer to provide passive circuit elements beyond the range of solid silicon technology. External

- soli

connections are made through small wires soldered, welded, or thermocompression-bonded to selected points of the surface. solid state-1. Pertaining to circuits and components using semiconductors. 2. The physics of materials in their solid form. Examples of solid-state materials are transistors, diodes, solid-state lasers, metals, and alloys, etc. 3. Technology utilizing solid semiconductors in place of vacuum tubes for amplification, rectification, and switching. 4. A silicon or germanium semiconductor device, such as a diode, transistor, or integrated circuit; or circuits, equipment, or systems made from such devices. 5. A circuit or system that does not rely on vacuum or gas-filled tubes to control or modify voltages and currents. 6. The electronic components that convey or control electrons within solid materials, e.g., transistors, germanium diodes, and integrated circuits. 7. Refers to the electronic properties of crystalline materials, generally semiconductors. As opposed to vacuum and gas-filled tubes that function by flow of electrons through space, or by flow through ionized gases, solid-state devices involve the interaction of light, heat, magnetic field, and electric currents in crystalline materials. Compared with earlier vacuum-tube devices, solid-state components are smaller, less expensive, more reliable, use less power, and generate less heat. solid-state atomic battery-A device in which a radioactive material and a solar cell are combined. The radioactive material emits particles that enter the solar cell, which in turn produces electrical energy. solid-state bonding -The process of forming a metallurgical joint between similar or dissimilar metals by causing adjoining atoms at the joint interface to combine by interatomic attraction in the solid state. (This process is different from diffusion bonding in that no atomic diffusion is required.) The adjoining surfaces to be bonded must be atomically clean and must be brought within atomic distances before such a bond can become established. solid-state circuit- A complete circuit formed from a single block of semiconductor material. See also monolithic integrated circuit. solid-state component -A component whose operation depends on the control of electric or magnetic phenomena in solids (for exaaple, a transistor, crystal diode, or ferrite). solid-state computer- A computer built primarily from solid-state electronic circuit elements. solid-state device-1. Any element that can control current without moving parts, heated filaments, or vacuum gaps. All semiconductors are solid-state devices, although not all solid-state devices (for example, transformers) are semiconductors. 2. An electronic device that operates by virtue of the movement of electrons within a solid piece of semiconductor material. 3. Electronic component that controls electron flow through a solid material such as a crystal; for example, a transistor, diode, or integrated circuit. solid-state imaging system -An imaging system that uses a mosaic of tiny light-sensitive semiconductors (phototransistors) to produce individual outputs that are then converted into a coherent video signal. solid-state integrated circuits-The class of integrated components in which only solid-state materials are used. solid-state lamp - 1. A pn junction that emits light when forward biased. Made from a complex compound of gallium, arsenic, and phosphorus called gallium arsenide phosphide. Its light output is typically at 670 nanometers. It characteristically looks like a forward-biased diode with a breakdown voltage in the region of 1.6 volts. 2. An

solid-state laser - sonic altimeter electroluminescent semiconductor that emits low-intensity radiation in the green or red regions. Used as an indicator lamp. solid-state laser-A laser using a transparent substance (crystalline or glass) as the active medium, doped to provide the energy states necessary for lasing. The pumping mechanism is the radiation from a powerful light source, such as a flash tube. Ruby lasers are solidstate lasers. solid-state physics-The branch of physics that deals with the structure and properties of solids, including semiconductors (i.e., a material whose electric resistivity is between that of insulators and conductors). Generally used semiconductors are silicon and germanium. solid-state relay -Abbreviated SSR. 1. A relay that employs solid-state semiconductor devices as components. 2. A factory-built and packaged product used for switching an ac load. It has an isolated input/output construction that permits the current to be switched electronically without moving parts. Optical and transformer coupling are among the methods used to achieve input/output isolation and permit coupling from the control circuit to the trigger circuit. SSRs are used in place of electromechanical relays when there is a need for compatibility with digital logic drive circuits, where an electromagnetic coil and contacts would cause interference problems. 3. An o d o f f control device in which the load current is conducted by one or more semiconductors, e.g., a power transistor, SCR, or triac.

- .

I

PHOTOTRANSISTOR

712

solo manual -See swell manual. Sommerfeld formula -An approximate wavepropagation relationship that may be used when distances are short enough that the curvature of the earth may be neglected in the computations. Sommerfeld’s equation -Equation for groundwave propagation that relates field strength at the surface of the earth at any distance from a transmitting antenna to the field strength at unit distance for given ground losses. Sonalert-A solid-state tone-emitting device (P. R. Mallory & Co., Inc.). sonar- Acronym for sound navigation and ranging. Also called active sonar if it radiates underwater acoustic energy, or passive (listening) sonar if it merely receives the energy generated from a distant source. 1. Apparatus or technique of obtaining information regarding underwater objects or events through the transmission and reception of acoustic energy. Two well-known uses are to detect submarines and fish. 2. A system that uses underwater sound, at sonic or ultrasonic frequencies, to detect and locate objects in the sea. Sonar signals can also be used as a communication medium. The various systems generally may be divided into three basic classifications: passive (listening only), echo-ranging (active), and communication.

-

PULSE

PING

((((((((((

’GR lZH-1

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I

Solid-state relay. CATHODE.RAY TUBE

solid-state s w i t c h -A no-contact switch that completes a circuit by means of solid-state components. solid-state watch-A timepiece that uses a quartz crystal or other precise frequency resonator in conjunction with low-power MOS integrated circuits. Employs liquid crystals or light-emitting diodes to indicate hours, minutes, seconds, data, months, days of the week, etc., in a digital andlor alphanumeric format. solid tantalum capacitor-See solid-electrolyte tantalum capacitor. solidus- The highest temperature at which a metal or alloy is completely solid. solid wire-Wire that consists of a single conductor, not of multiple strands. solion -Contraction of solution ion. An electrochemical sensing and control device in which ions in solution carry electric charges to give amplification corresponding to that of vacuum tubes and transistors. solion integrator -A precision electrochemical cell housed in glass and containing four small platinum electrodes in a solution of potassium iodide and iodine. The integrator anode and cathode make up the covers of a small cylindrical volume (less than 0.00025 in?, or 0.0041 cm3) for storing electrical information in the form of ions. The integrator cathode contains a fixed amount of hydraulic porosity for completing the internal-solution path to the other two electrodes.

Sonar.

sonar b a c k g r o u n d noise-In sonar, the total noise presented to the final receiving element that interferes with the reception of the desired signal. sone-1. A unit of loudness. A simple tone of frequency 1000 hertz, 40 dB above a listener’s threshold, produces a loudness of 1 sone. The loudness of any sound that is judged by the listener to be n times that of the 1sone tone is n sones. 2. A value for loudness. May be used for overall evaluation of a sound or of a frequency band. The sone scale is linear (in contrast to decibels, which are logarithmic). sones per b a r k -Loudness density defined as a function of subjective pitch. When loudness density is integrated over subjective pitch, the result is total loudness. sonic- 1. Pertaining to the speed of sound. 2. Utilizing sound waves. sonic altimeter- An altimeter that determines the height of an aircraft above the earth by measuring the time the sound waves take to travel from the aircraft to the ground and back, based on the fact that the velocity of sound at sea level is 1080 feet per second (329 m/s) through dry air at 0°C (32°F).

sonic applicator

713

sonic applicator-A self-contained electromechanical transducer for local application of sound for therapeutic purposes. sonic cleaning -The cleaning of contaminated materials by the action of intense sound waves produced in the liquid into which the material is immersed. sonic delay line-A device in which electroacoustic transducers and the propagation of an elastic wave through a medium are used to produce the delay of an electrical signal. sonic drilling-The cutting or shaping of materials with an abrasive slurry driven by a reciprocating tool attached to an electromechanical transducer. sonic frequencies-Vibrations that can be heard by the human ear (from about 15 hertz to approximately 20,000 hertz). sonic motion detector-A sensor that detects the motion of an intruder by his or her disturbance of an audible sound pattern generated within the protected area. sonic soldering-The method of joining metals by the use of mechanical vibration to break up the surface oxides. sonic speed-,% speed of sound. sonic thermocouple-A thermocouple so designed that gas moves past the junction with a velocity of mach 1 or greater, resulting in maximum heat transfer to the junction. sonne- Also called consol. A radionavigational aid that provides a number of rotating characteristic signal zones. A bearing may be determined by observation (and interpolation) of the instant when transition occurs from one zone to the following zone. sonobuoy-Also called a radiosonobuoy. 1. A device used to locate a submerged target (e.g., a submarine). By means of a hydrophone system in the water, a sonobuoy detects the noises and converts them into radio signals, which are transmitted to a receiver in an airplane. Each sonobuoy transmits on one of several possible frequencies, and the receiver in the airplane has a channel selector so the operator can switch from one to another. 2. A passive sonar device (to distinguish it from an active sonar system, which transmits a signal and listens for an echo) that uses hydrophones to convert acoustic signals from natural phenomena, such as wave motion, or from ships or submarines into electrical signals. These signals are filtered and sent to the surface for transmission to a surface vessel or aircraft for further processing.

( ( ( 1 ) ) ) RADIO SIGNALS I ANTENNA

I

WWER AND SIGNAL CABLE

- SOT

of a substance resulting from its exposure to ultrasonic waves. sonometer-A frequency meter whose operation depends on its mechanical resonance with the vibrations of a variable length of stretched wire. sonoptography-The use of sound waves to obtain a 3D image of an object. No lenses are required. In essence, a two-stage process in which the diffraction pattern of an object irradiated by sound waves is biased by a coherent sound wave and recorded. The resultant pattern, like the hologram, then is interrogated with a suitable coherent light source to obtain a three-dimensional image. s o n o r a d i o g r a p h y -The diagnostic procedure that uses ultrasonic energy to probe the body and, with the help of laser beams, a reflecting membrane to produce a three-dimensional picture. s o p h i s t i c a t e d -A piece of equipment, system, etc., that is complex and intricate, or requires special skills to operate. s o p h i s t i c a t e d vocabulary-An advanced and elaborate set of computer instructions, enabling the computer to perform such intricate operations as linearizing, extracting square roots, selecting the highest number, etc. sorption -The combination of absorptive and adsorptive processes in the same material. sort-- 1. To arrange items of information according to rules that depend on a key or field contained by the items. 2. A function performed by a program, usually part of a utility package; items in a data file are arranged or rearranged in a logical sequence designated by a keyword or field in each item in the file. 3. A procedure designed to arrange a group of elements in random order into some kind of a sequence. Examples include the bubble sort, the selection sort, and the partition sort. 4. The process of arranging data in a specific order. sorter-A machine that sorts cards according to the position of coded holes. SOS- 1. A distress signal used in radiotelegraphy. 2. Abbreviation for silicon on sapphire. A CMOS technology in which a layer of silicon is epitaxially grown on a sapphire wafer, with specific regions subsequently etched away between individual transistors. Each device is thus totally isolated from other devices. Since sapphire is an insulator, SOS is a subset of SO1 (silicon-on-insulator) technology. Both SO1 and SOS technologies provide for high levels of radiation hardness. SOT- Abbreviation for small outline transistor. A small plastic package with gull wing leads for mounting discrete semiconductor devices on printed circuit boards.

BON

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Sonobuoy.

sonoluminescence -1. The creation of light in liquids by sonically induced cavitation. 2. The luminescence

SOT- small outline transistor (SOT 23 size).

sound

- sound-reflection coefficient

sound -1. Also called a sound wave. An alteration in pressure, stress, particle displacement or velocity, etc., propagated in an elastic material, or the superposition of such propagated alterations. 2. Also called a sound sensation. The auditory sensation usually evoked by the alterations described in (1) above. 3. An undulatory motion of air or other elastic medium, which can produce the sensation of hearing when incident on the ear. (Sound requires a medium for propagation, for unlike electromagnetic waves, sound cannot travel through a vacuum.) sound absorption -The conversion of sound energy into some other form (usually heat) in passing through a medium or on striking a surface. sound-absorption coefficient-The incident sound energy absorbed by a surface or medium, expressed in the form of a fraction. sound analyzer-A device for measuring the amplitude and frequency of the components of a complex sound. It usually consists of a microphone, an amplifier, and a wave analyzer. sound articulation -The percent of articulation obtained when the speech units are fundamental sounds (usually combined into meaningless syllables). sound bars- Alternate dark and light horizontal bars caused in a television picture by audio-frequency voltage reaching the video-input circuit of the picture tube. sound board -A hardware adapter that dramatically adds digital sound reproductions capabilities to IBMcompatible computers. sound carrier -The frequency-modulated carrier that transmits the sound portion of television programs. sound concentrator-A parabolic reflector used with a microphone at its focus to obtain a highly directive pickup response. sound-effect filter -A filter, usually adjustable, designed to reduce the passband of a system at low andor high frequencies in order to produce special effects. sound energy-The total energy in a given part of a medium, minus the energy that would exist there if no sound waves were present. s o u n d - e n e r g y density-At a point in a sound field, the sound energy contained in a given infinitesimal part of the medium, divided by the volume there. The commonly used unit is the erg per cubic centimeter. s o u n d - e n e r g y flux-The average rate at which sound energy flows through any specified area for a given period. The commonly used unit is the erg per second. sound-energy flux density-See sound intensity. sounder- See telegraph sounder. sound field-A region in any medium containing sound waves. s o u n d film -Motion-picture film having a sound track along one side of the picture frames for simultaneous reproduction of the sounds that accompany the film. A beam of light is projected through the sound track and is modulated at an audio rate by the variations in the width or density of the track. A phototube and amplifier then convert these modulations into sound. sound gate-A mechanical device through which filmis passed in a projector to convert the sound track into audio signals that can be amplified and reproduced. In a television camera used for pickups, a sound gate provides the sound accompaniment for the motion picture being televised. Associated with the sound gate are an exciter lamp, a lens assembly, and a phototube. sound head-The part of a sound motion-picture projector that converts the photographic or magnetic sound track on the film into audible sound signals.

714 sounding-Determination of the depth of water or the altitude above the earth. sound intensity- Also called specific sound-energy flux or sound-energy flux density. The average rate of sound energy transmitted in a specified direction through a unit area normal to this direction at the point considered. The common unit is the erg per second per square centimeter, although sound intensity expressed in watts per square centimeter may occasionally be used. sound intensity level-The amount of sound power passing through a unit area. sound level-A measure of the overall loudness of sounds on the basis of approximations of equal loudness of pure tones. It is expressed in decibels with respect to 0.0002 microbar. sound-level meter -An instrument -including a microphone, amplifier, output meter, and frequencyweighting networks -for the measurement of noise and sound levels. The measurements approximate the loudness level obtained for pure tones by the more elaborate ear-balance method. sound-on-sound recording -1. A method by which material previously recorded on one track of a tape may be recorded on another track while simultaneously adding new material to it. 2. A method of tape recording in which an original sound track may be impressed with an added sound track for special effects, such as one performer appearing to play two instruments, etc. sound-powered t e l e p h o n e set -1. A telephone set in which the transmitter and receiver are passive transducers; operating power is obtained from the speech input only. The voice sound waves operate a moving coil or variable-reluctance transmitter to produce the current waves transmitted to the telephone line. No external power is used, but the output level is lower than that of a battery-powered phone. 2. A telephone set whose transmitter is a dynamic microphone. It requires no power other than that of the voice of the user. sound-power level -1. The ratio, expressed in decibels, of the sound power emitted by a source to a standard reference power of watt. 2. The number of watts of acoustic power radiated by a noise source. sound power of a source-The total sound energy radiated by the source per unit of time. The common unit is the erg per second, but the power may also be expressed in watts. sound pressure -The instantaneous pressure minus the static pressure at some point in a medium when a sound wave is present. sound-pressure level -Abbreviated SPL. 1. In decibels, 20 times the logarithm of the ratio of the pressure of a sound to the reference pressure, which must be explicitly stated (usually, either 20 pPa, 2 x microbar, or 1 microbar). 2. The pressure of an acoustic wave stated in terms of newtondsquare meter, dyneskquare centimeter, or microbars. (One microbar is approximately equal to one millionth of the standard atmospheric pressure.) sound probe-A small microphone (or tube added to a conventional microphone) for exploring a sound field without significantly disturbing it. sound recordings-Records, tapes, or other sonic components upon which audio intelligence is inscribed or recorded or can be reproduced. sound-recording s y s t e m -A combination of transducing devices and associated equipment for storing sound in a reproducible form. sound-reflection coefficient -Also called acoustical reflectivity. Ratio at which the sound energy reflected from a surface flows on the side of incidence to the incident rate of flow.

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sountd-reproducing system -A combination of transducers and associate'd equipment for reproducing prerecorded sound. sound sensation -See sound, 2. sound-sensing detection s y s t e m -An alarm system that detects the audible sound caused by an attempted forcible entry into a protected structure. The system consists of microphones and a control unit containing an amplifier, accumulator, and a power supply. The unit's sensitivity is adjustable so that ambient noises or normal sounds will not initiate an alarm signal. However, noises above this preset level or a sufficient accumulation of impulses will initiate an alarm. Sound sensor -A sensor that responds to sound; a microphone. sound spectrum -The frequency components included within the range of audible sound. sound stage-The area between the two or more speakers of a stereo or quad setup where subjective sound images or imaginary speakers seem to be, providing a wide area of apparent sound source. sound takeoff -Th'e connection or coupling at which the 4.5-MHz frequency-modulated sound signal in a television receiver is obtained. sound track-The narrow band that carries the sound in a movie film. It is usually along the margin of the film, and more than one band may be used (e.g., for stereophonic sound). sound-transmission coefficient (of an interf a c e or s e p t u m ) -Also called acoustical transmittivity. The ratio of the transmitted to the incident sound energy. Its value is a function of the angle of incidence of the sound. sound wave -See sound, 1. sound-with-sound- 1. A special provision in some recorders that allows the record head for one channel to be used for listening to that track while adding new material in exact synchronism on the adjacent track. Playing and mixing both simultaneously produces a composite sound withouit the degradation of one sound otherwise caused by a dubbing step in sound-on-sound mixing. 2. A process by which a program is recorded on one track, then monitored as a second program is recorded on another track. source- 1. The device that supplies signal power to a transducer. 2. In a field-effect transistor, the electrode that corresponds to the cathode of a vacuum tube. 3. Supply of energy, or device upstream from a sink. See also sink. 4. Terminal that usually sources carriers. In MQS devices, which are usually symmetrical, it can be interchanged with the drain terminal in a circuit. 5. The working-current terminal (at one end of the channel in a FET) that is the source of holes (p-channel) or free electrons (n-channel) flowing in the channel. Corresponds to the emitter in a bipolar transistor. 6. The device that switches positive dc to a load. The current flows from the sensor into the load. 7. The origin of radiant energy, such as a light-emitting diode. 8. Userwritten instruction statemisnts prior to translation by a computer into machine-executable form. 9. One of the three regions that form a field-effect transistor. Majoritycarriers (electrons in an n-channel FET or holes in a p-channel FET) originate at the source and flow across the channel to the drain ais a result of the electric field applied between source and drain. source address-In computer systems having a source-destination architecture, the source address is the address of the device address or memory location from which data is being transferred. source code - 1. A nonexecutable computer program written in a high-level language. A compiler or

sound-reproducing s y s t e m - s ~ u r c rec e assembler must translate the source code into object code (machine language) that the computer can understand and process. 2. Virtually any computer language, from assembly to high-level, that doesn't fit the definition of object code. source connector-One of three classifications of fiber-optic connectors that interconnect a light source (typically a LED) to a fiber-optic cable. A metal connector shell that is mounted on a circuit board or attached to a panel provides heat sinking and EM1 protection. See bundle connector. source-cutoff current -"he current into the source terminal of a depletion-type transistor with a specified gate-to-drain voltage applied to bias the device to the off state. source data automation -The methods of recording information in coded forms on paper tapes, punched cards, or tags that can be used repeatedly to produce many other records without rewriting. source document -A paper containing information that is to be read into the computer. source electrode-One of the electrodes in a field-effect transistor. It is analogous to the emitter in a transistor or the cathode in a vacuum tube. Represented by the symbol S. source impedance--. The impedance that a source of energy presents to the input terminals of a device. 2. The impedance that a meter or other instrument sees; i.e., the impedance of the driving circuit when measured from the input terminals of the meter. sourcing -Redesign or modification of existing equipment to eliminate a source of electromagnetic interference. When sourcing is not feasible, engineers are forced to resort to suppression, filtering, or shielding. source language- 1. The language used to prepare a problem as the input for a computer operation. 2. In a computer, the language from which a statement is translated. 3. The original language used by the programmer, on which a translator program operates. 4. In general, any language that is to be translated into another (target) Ianguage; usually, however, it refers to the language used by a programmer to program a system. source load-A load with a current whose direction is toward its input. A source load must be driven by a current source. source machine-The computer used to translate the source program into the object program. source module-In a computer, a series of statements expressed in the symbolic language of an assembler or compiler and constituting the entire input to a single execution of the assembler or compiler. source program- 1. A computer program written in a language designed for ease of expression of a class of problems or procedures by humans. A generator, assembler, translator, or compiler routine translates the source program into an object program in machine language. 2. The original program, as written by the programmer, from which a working program system is derived. 3. A program, in either hard-copy or stored form, written in a high-level language (source language) other than machine language, which requires translation by the assembler, compiler, or interpreter program before it can be run on the computer. 4. A program written by a human, either in assembly or in a high-level language. source recording -The recording of information in machine-readable form, such as punched cards or tape, magnetic tape, etc. Once in this form, the information may be transmitted, processed, or reused without a need for manual processing.

source statement - spacing interval source statement -A computer program written in other than machine language, usually in threeletter mnemonic symbols that suggest the definition of the instruction. There are two kinds of source statements: executive instructions, which translate into operating machine code (op code), and assembly directives, which are useful in documenting the source program but generate no code. sourceltape switch-A control found on control amplifiers with tape monitor jacks, and on recorders with monitor heads; allows comparison of the signal being fed to the tape (source) with the signal just recorded. source terminal --The terminal electrically connected to the region from which majority carriers flow into the channel of a field-effect transistor. s o u t h pole -In a magnet, the pole into which magnetic lines of force are assumed to enter after emerging from the north pole. space- 1. An impulse that, in a neutral circuit, causes the loop to open or causes the absence of a signal, whereas in a polar circuit it causes the loop current to flow in a direction opposite to that for a mark impulse. A space impulse is equivalent to a binary 0. 2. In some codes, a character that causes a printer to leave a character width with no printed symbol. 3. The signaling state used to represent a binary 0. See mark. 4. One of two states describing the condition of a teleprinter’s loop. The space is characterized by an open-loop condition. The mark state indicates a closed loop. space attenuation-1. The loss of energy, expressed in decibels, of a signal in free air caused by such factors as absorption, reflection, scattering, and dispersion. 2. Reduction of a TV satellite signal strength due to the fact that the beam spreads out after leaving the antenna. It is a major factor in path loss. space c h a r g e -1. The negative charge caused by the cloud of electrons that forms in the space between the cathode and plate of a vacuum tube because the cathode emits more electrons than are attracted immediately to the plate. 2. An electrical charge distributed throughout a volume or space. s p a c e - c h a r g e debunching-In a microwave tube, a process in which the bunched electrons are dispersed due to the mutual interactions between electrons in the stream. s p a c e - c h a r g e effect -Repulsion of electrons emitted from the cathode of a thermionic vacuum tube by electrons accumulated in the space charge near the cathode. s p a c e - c h a r g e field -The electric field that occurs inside a plasma due to the net space charge in the volume of the plasma. s p a c e - c h a r g e grid -A grid, usually positive, that controls the position, area, and magnitude of a potential minimum or of a virtual cathode adjacent to the grid. s p a c e - c h a r g e region -The region around a pn junction in which holes and electrons recombine, leaving no mobile charge carriers and a net charge density different from zero. See also depletion layer. s p a c e - c h a r g e tube-A tube in which the space charge is used to greatly increase the transconductance. A positively charged grid is placed next to the cathode, in front of the control grid. This enlarges the space charge, moving it out to where the control grid can have a greater effect on it and hence on the plate current. space coordinates -A three-dimensional system of rectangular coordinates. The x and y coordinates lie in a reference plane tangent to the earth, and the z coordinate is perpendicular. space current-The total current between the cathode and all other electrodes in a vacuum tube.

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spaced antenna-An antenna system used for minimizing local effects of fading at shortwave receiving stations. So called because it consists of several antennas spaced a considerable distance apart. spaced-antenna direction finder- A direction finder comprising two or more similar but separate antennas coupled to a common receiver. space detection and tracking system -A system that can detect and track space vehicles from the earth and report the orbital characteristics of such vehicles to a central control facility. space diversity-See space diversity reception. space diversity gain-The improvement in radio reception, expressed in decibels, obtained by combining the signals from two receiving antennas physically separated by not less than 5 wavelengths. space diversity reception -Also called space diversity. 1. Diversity reception from receiving antennas placed in different locations. 2. A method of diversity radio reception in which the receiving antennas are physically separated, vertically or horizontally, by 5 wavelengths or more. spaced-loop direction finder- A spaced-antenna direction finder in which the individual antennas are loops. space factor-Ratio of the effective area utilized to the total area in a winding section. space harmonics -Harmonics in the distribution of flux in the air gap of a resolver. They may be determined as a percent of fundamental by a Fourier analysis of the flux distribution antenna. Space harmonics cause angular inaccuracy. space-hold-In a computer, the normal no-traffic line condition by which a steady space is transmitted. space pattern-On a test chart, a pattern designed for the measurement of geometric distortion. The EIA hall chart is an example. space permeability -The factor that expresses the ratio of magnetic induction to magnetizing force in a vacuum. In the cgs electromagnetic system of units, the permeability of a vacuum is arbitrarily taken as unity. space p h a s e -Reaching corresponding peak values at the same point in space. space quadrature -The difference in the position of corresponding points of a wave in space, the points being separated by one-quarter of the wavelength in question. space radio station-An amateur radio station located on an object that is beyond, is intended to go beyond, or has been beyond the major portion of the earth’s atmosphere. spacer cable-A means of primary power distribution that consists of three partially insulated or covered phase wires and a high-strength messenger-ground wire, all mounted in plastic or ceramic insulating spacers. transition, or space-to-mark transition -The switching, from a spacing impulse to a marking impulse. (Teletypewriter term.) space wave-The radiated energy consisting of the direct and ground waves. spacing -The distance between stereo microphones or speakers. spacing end distortion -End distortion that lengthens the spacing impulse by advancing the markto-space transition. (Teletypewriter term.) spacing interval -The interval between successive telegraph signal pulses. During this interval, either no current flows or the current has the opposite polarity from that of the signal pulses.

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spacing pulse -In teletypewriter operation, the signal interval during which the selector unit does not operate. spacing wave- Also called back wave. In telegraphic communication, the emission that takes place between the active portion of the code characters or while no code characters are being transmitted. spacistor- 1. A semiconductor device consisting of one pn junction and four electrode connections. It is characterized by a low transient time for carriers to flow from the input to the output. 2. Multiple-terminal solidstate device, similar to a transistor, that achieves highfrequency operation up to about 10,000 MHz by injecting electrons or holes into a space-charge layer that rapidly forces these carriers to a collecting electrode. spade connector-A terminal with a slotted tongue and nearly square sides. spade contact -A contact with fork-shaped female members designed to dovetail with spade-shaped male members. Alignment in this type of connection is very critical if good conductivity is to be achieved. spade lug-A solder lug that has an open end so that it can be slipped under the head of a binding screw. spade tips-Notched, flat metal strips connected to the end of a cord or wire so that it can be fastened under a binding screw. spade-tongue terminal -A slotted-tongue terminal designed to be slipped around a screw or stud without removal of the nut. spaghetti- 1. Heavily varnished cloth tubing sometimes used to provide insulation for circuit wiring. 2. A form of tubular insulation that can be slipped over wires before they are connected to terminals. span - 1. The part or space between two consecutive points of support in a conductor, cable, suspension strand, or pole line. 2. The reach or spread between two established limits, such as the difference between high and low values in a given range of physical measurements. span adjustment-See sensitivity adjustment. s-palrameters -Abbreviation for scattering parameters. A group of measurements taken at different frequencies that represent the forward and reverse gain and the input and output reflection coefficients of a microwave component when the input and output ports of the component are terminated in specified impedances -usually 50 ohms. s p a r k - 1. The abrupt, brilliant phenomenon that characterizes a disruptive discharge. 2. A single, short electricd discharge between two electrodes. 3. The brief flash of light from the arc. 4. The bridging or jumping of a gap between two electrodes by a current of electricity. s p a r k capacitor-A capacitor connected across a pair of contact points, or across the inductance that causes the spar!k, for the purpose of diminishing sparking at these points. s p a r k coil- An induction coil used to produce spark discharges. s p a r k duration - 1. The time between the moment when the electrons first jump a gap and the moment when the cmlsnt ceases to flow across it. 2. The length of time a spark is established across a spark gap or the length of time current flows in a spark gap. s p a r k electrodes--The conductive element on each side of a spark gap through which current flows to and from the gap. s p a r k e n e r g y -The amount of energy dissipated between the electrodes of a spark gap. This is normally expressed as a steady-state wattage as though dissipated for a full second. Normally expressed in milliwatt seconds or millijioules.

spacing pulse - s p a r k suppression spark frequency-The total number of sparks occurring per second in a spark transmitter (not the frequency of the individual waves). s p a r k gap-The arrangement of two electrodes between which a disruptive discharge of electricity may occur, and such that the insulation is self-restoring after the passage of a discharge. s p a r k - g a p modulation -Modulation in which a controlled spark-gap breakdown produces one or more pulses of energy for application to the element in which the modulation is to take place. spark-gap modulator-A modulator employed in certain radar transmitters. A pulse-forming line is discharged across either a stationary or a rotary spark gap. s p a r k - g a p oscillator-A type of oscillator consisting essentially of an interrnpted high-voltage discharge and a resonant circuit. sparking -Intentional or accidental spark discharge, as between the brushes and commutator of a rotating machine, between the contacts of a relay or switch in a solid tantalum capacitor, or at any other point, in which a circuit is broken. sparking voltage-The minimum voltage at which a spark discharge occurs between electrodes of a given shape at a given distance apart under given conditions. s p a r k killer -Also called spark suppressor. An electric network, usually a capacitor and resistor in series, connected across a pair of contact points (or across the inductance that causes the spark) to diminish sparking at these points. s p a r k lag-The interval between attainment of the sparking voltage and passage of the spark. sparklies-Also known as snow, 1. Weak-signal noise that appears as dot or streak interference in a satellite TV picture. Loss of lock in an FM[ video demodulator causes this. In extreme cases, tearing or loss of the picture may result. 2. Small black and/or white blips or dots in a television picture, indicating an insufficient signal-to-noise ration. sparkover-Breakdown of the air between two electrical conductors, permitting the passage of a spark. s p a r k plate--In an automobile radio, a metal plate insulated from the chassis by a thin sheet of mica. It bypasses the noise signals picked up by the wiring under the hood. s p a r k plug-An assembly that includes a pair of electrodes and insulator. it provides a spark gap in an engine cylinder. spark-quenching device --See spark suppressor. s p a r k recorder -A recorder in which the recording paper passes through a spark gap formed by a metal plate underneath and a moving metal pointer above the paper. Sparks from an induction coil pass through the paper, periodically burning small holes that form the record trace. s p a r k source-A device used to produce a shortcircuit pulse of luminous energy by an electrical discharge between two closely spaced electrodes either in air or in a controlled atmosphere at a pressure usually greater than half an atmosphere. s p a r k spectrum -The spectrum produced in a substance when the light from a spark passes between terminals made of that substance or through an atmosphere of that substance. s p a r k suppression-The use of a capacitor or resistor across contacts that break currents in inductive circuits, to prevent excessive sparking when the contacts break. A capacitor and resistor in series may also be used. s p a r k suppressor -Also called a spark-quenching device, spark killer, or an arc suppressor. An electric network, such as a capacitance and resistance in series or

s p a r k test - specific repetition rate a diode connected across a pair of contacts, to diminish sparking (arcing) at these contacts. s p a r k test-A test performed on wire and cable to determine the amount of detrimental porosity or defects in the insulation. s p a r k transmitter- A radio transmitter in which the source of radio-frequency power is the oscillatory discharge of a capacitor through an inductor and a spark gap. spatial c o h e r e n c e -The phase relationship of two wave trains in space. spatial distribution -The directional properties of a speaker, transmitting antenna, or other radiator. spatial frequency-The number of black and white line pairs displayed on a screen per degree of visual angle. Spatial frequency is expressed as cycles per degree or as lines per inch for a given viewing distance. SPDT- Abbreviation for single-pole, double-throw. A three-contact switching arrangement that connects a circuit to one of two alternate connections. s p e a k e r -Abbreviated spkr. Also called a loudspeaker. An electroacoustic transducer that radiates acoustic power into the air with essentially the same waveform as that of the electrical input.

Speaker. s p e a k e r efficiency-Ratio of the total useful sound radiated from a speaker at any frequency to the electrical power applied to the voice coil. s p e a k e r impedance-The rated impedance of the voice coil of a speaker. speaker-reversal s w i t c h -A switch for connecting the left channel to the right speaker and vice versa on a stereo amplifier. It is a means of correcting for improper left-right orientation in the program source. s p e a k e r system-A combination of one or more speakers and all associated baffles, horns, and dividing networks used to couple the driving electric circuit and the acoustic medium together. s p e a k e r voice coil -In a moving-coil speaker, the part that is moved back and forth by electric impulses and is fastened to the cone in order to produce sound waves. s p e a k i n g arc-A dc arc on which audio-frequency currents have been superimposed. As a result, the arc reproduces sounds in a manner similar to a speaker, and its light output will vary at the audio rate required for sound-film recording. special-effectsgenerator-An apparatus used in the production of videotapes, this unit makes possible smooth switching of camera inputs and provides a wide variety of screen techniques, such as split and wipes.

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special-event station -Station licensed at a specific land location for operation related to the celebration of an event, past or present, that is unique, distinct, and of general interest to either the public or to amateur radio operators, for the purpose of bringing public notice to the amateur radio service. special-function key-A key on a keyboard that often has no predefined purpose but that can be programmed to send one or more useful commands. special-purpose computer -A computer designed to solve a restricted class of problems, as contrasted with a general-purpose computer. special-purpose language -A programming language that is designed to satisfy a single specific objective. special-purpose logic -Proprietary features of a programmable controller that allow it to perform logic not normally found in relay ladder logic. special-purpose motor- A motor possessing special operating characteristics and/or special mechanical construction designed for a particular application and not included in the definition of a general-purpose motor. special-purpose relay-A relay whose application requires special features not characteristic of generalpurpose or definite-purpose relays. s p e c i f i c acoustic impedance- Also called unitarea acoustic impedance. The complex ratio of sound pressure to particle velocity at a point in a medium. imaginary specific acoustic reactance-The component of the specific acoustic impedance. specific acoustic resistance-The real component of the specific acoustic impedance. specifications- 1. A published set of instructions for doing work in a uniform, standard manner. 2. Detailed description of the characteristics of a component, device, or system. 3. A clear, complete, and accurate statement of the technical requirements descriptive of a material, an item, or a service, and of the procedure to be followed to determine if the requirements are met. specific coding -Digital-computer coding in which all addresses refer to specific registers and locations. specific conductance-See electrolytic conduction. specific conductivity -The conducting ability of a material in mhos per cubic centimeter. It is the reciprocal of resistivity. s p e c i f i c damping of a n instrument-See relative damping of an instrument. dielectric s p e c i f i c dielectric strength -The strength per millimeter of thickness of an insulating material. specific gravity-The weight of a substance compared with the weight of the same volume of water at the same temperature. specific h e a t -1. The capacity of a material to be heated at a given temperature (expressed as calories per degree Celsius per gram) compared with water, which has a specific heat of 1. 2. The amount of heat required to raise a specified mass by one unit of a specified temperature. s p e c i f i c inductive capacity-See dielectric constant. saturation specific magnetic moment -The moment of a magnetic material per unit weight. It is expressed in terms of emdgram. specific program -Digital-computer programming for solving a specific problem. specific repetition rate-In loran, one of a set of closely spaced repetition rates derived from the basic rate and associated with a specific set of synchronized stations.

719 Specific resistance--The resistance of a conductor. It is expressed in ohms per unit length per unit arm, usually circular mil feet. See also resistivity, 1. speciific routine -- A digital-computer routine expressed in specific computer coding and used to solve a specific inathematical, logical, or data-handling problem. specific sound-energy flux -See sound intensity. spectral- 1. Being a function of wavelengths. 2. Pertaining to or as a function of wavelength. Spectral quantities are evaluated at a single wavelength. spectral bandwidth -The difference between the wavelengths of single-peak devices at which the radiant intensity is 50 percent (unless otherwise stated) of the maximum value. spectral characteristic -1. The relationship between the radiant sensitivity of a phototube and the wavelength of the incident radiant flux. It is usually shown by a graph. 2. The relation, usually shown by a graph, between the emitted radiant power per wavelength interval and the wavelength. spectral coherence-A measure of the extent to which the output of a photodetector is restricted to a single wavelength or band of wavelengths; color response. spectrum analyzer s p e c t r a l contour plotter-A that presents a three-dimensional contour plot of analog signals, heart sounds, brain waves, etc. spectral density-A value of a function whose integral over a frequency interval represents the contributions of the signal components within that frequency interval. spectral e n e r g y distribution-Abbreviated SED. A plot of energy as a function of wavelength for a given light. spectral intensity-A function that precisely defines the spectrum and has the units of voltage squared per unit frequency. spectral output (of a light-emitting diode)-A description of the radiant-energy or light-emission characteristic versus wavelength. This information is usually given by stating the wavelength at peak emission and the bandwidth between balf-power points or by means of a curve. spectral purity-A measure of how much the spectrum of the output of a signal generator deviates from that of a pure sine wave. spectral radiant flux-The radiant flux per unit wavelcngth interval, usually in watts per nanometer. s p e c t r a l radiant reflectance-That fraction of the power in a light beam that is reflected from a surface. In less precise usage, called reflectivity. s p e c t r a l response-Also called spectral sensitivity characteristic. 1. The relative amount of visual sensation produced by one unit of radiant flux of any one wavelength. The human eye or a photocell exhibits greatest spectral response to the wavelengths producing yellowgreen light. 2. The variation of responsivity of the detector with the wavelength of the impinging radiation. spectral sensitivity-The color response of a photosensitive device. splectral sensitivity characteristic-See spectral response spectral voltage density-The nns voltage corresponding to the energy contained in a frequency band having a width of 1 hertz. For the spectral voltage density at a given frequency, the band is centered on the given frequency. spectrogram - A machine-made graphic representation of sounds in terms of their component frequencies. Time is shown on the horizontal axis, frequency on the vertical axis, and intensity by the darkness of the mark.

specific resistance

- spectrum

s p e c t r o g r a p h -An instrument with an entrance slit and dispersing device that uses photography to obtain a record of the spectral range. The radiant power passing through the optical system is integrated over time, and the quantity recorded is a function of the radiant energy. spectrometer- A test instrument that determines the frequency distribution of the energy generated by any source and displays all components simultaneously. spectrophotoelectric- 1. Pertaining to the dependence of photoelectric phenomena on the wavelength of the incident radiation. 2. Characteristic of the relationship between photoelectric activity and the wavelength of incident radiation. spectrophotometer- An instrument for measuring spectral transmittance or reflectance. s p e c t r o p h o t o m e t r i c analysis-The detection and measurement, relative to wavelength, of spectral reflectance, spectral transmittance, or spectral emittance. spectrophotometry- 1. A process of making comparisons between parts of light spectra by means of a photometric device in combination with a spectrometer. 2. Study of the reflection or transmission properties of specimens as a function of wavelength. spectroradiometer -An instrument for measuring the radiant energy from a source at each wavelength through the spectrum. Spectral regions are separated either by calibrated filters or by a calibrated monochromator. The detector is usually an energy receiver, such as a thermocouple. spectroscope- An instrument used to disperse radiation into its component wavelengths and to observe or measure the resultant spectrum. spectroscopy- 1. The branch of optics that deals with radiations in the infrared, visible, and ultraviolet regions of the spectrum. 2. The measurement and interpretation of the electromagnetic radiation absorbed or emitted when molecules, atoms, or ions change from one internal energy level to another. Such a change could be caused by incident radiation of the kind supplied by a laser. In the case of molecules, the wavelength corresponding to the energy transitions that occur are mainly established by mechanical motions like rotation and vibration. These motions show up in the infrared region of the spectrum-from beyond the red end of the visible region at 0.8 pm to about 100 pm, where the microwave region begins. The molecules’ electrical properties determine the intensities of the energy transitions. In order to determine whether a given type of molecule is present, it is only necessary to pass a range of IR wavelengths through the substance and note the position and intensity of the peaks and valleys of the detected beam. Use of a spectrum “dictionary” then shows what materials are present. 3. The branch of science dealing with the theory and interpretation of spectra. spectrum -1. A continuous range of electromagnetic radiations, from the longest known radio waves to the shortest known cosmic rays. Light, which is the visible portion of the spectrum, lies about midway between these two extremes. 2. The frequency components that make up a complex waveform. The band of frequencies necessary for transmission of a given type of intelligence. 3. The range of frequencies considered in a system. 4. The distribution of the amplitude of the components of a timedomain signal as a function of frequency. 5. The wavelengths or frequencies associated with any system one may wish to describe, such as the visible spectrum, the infrared spectrum, the entire electromagnetic spectrum, etc. 6. The entire range of electromagnetic energy used in transmission of voice, data, and television. When applied to light, and/or lasers, it includes the frequencies from shortwave ultraviolet through infrared energy.

spectrum analysis

- speed regulation

720

spectrum analysis -1. The study of energy distribution across the frequency spectrum for a given electrical signal. 2. The process of determining the magnitude of frequency components of a signal, Le., magnitude of the Fourier transform. spectrum analyzer- 1. A scanning receiver that automatically tunes through a selected frequency spectrum and displays on a CRT or a chart a plot of amplitude versus frequency of the signals present at its input. A spectrum analyzer is, in effect, an automatic Fourier analysis plotter. 2. A test instrument that shows the frequency distribution of the energy emitted by a pulse magnetron. It also is used in measuring the Q of resonant cavities and lines, and in measuring the cold impedance of a magnetron. 3. Test equipment that displays the energy present at all input signal frequencies over a finite period of time. Spectrum analyzers can be synchronized with a sweeping oscillator to display the frequency response of audio equipment or sound systems. 4. An instrument that displays the power or voltage of a time-domain signal as a function of frequency. MIXER

SWEEP

OSCILLATOR

AMPLIFIER WIDTH

Spectrum analyzer.

spectrum intervals-Frequency bands represented as intervals on a frequency scale. spectrum level-For a specified signal at a particular frequency, the level of that part contained within a band 1 hertz wide, centered at the particular frequency. spectrum locus -The locus of a point representing the colors of the visible spectrum in a chromaticity diagram. spectrum-selectivity characteristic -A measure of the increase in the minimum input-signal power over the minimum detectable signal required to produce an indication on a radar indicator, if the received signal has a spectrum different from that of the normally received signal. s p e c t r u m signature analysis-The evaluation of electromagnetic interference from transmitting and receiving equipment in order to determine operational and environmental compatibility. spectrum utilization c h a r a c t e r i s t i c s -The compiled data of either transmitters or receivers that describes operational parameters such as bandwidth, sensitivity, stability, antenna pattern, power output, etc. Also describes the capabilities of the equipment to either reject or suppress unwanted electromagnetic energy. specular reflection -Reflection of light, sound, or radio waves from a surface so smooth that its inequalities are small in comparison with the wavelength of the incident rays. As a result, each incident ray produces a reflected ray in the same plane.

SPEDAC -Acronym for solid-state, parallel, expandable, differential-analyzer computer. A high-speed digital differential analyzer using parallel logic and arithmetic, solid-state circuitry, and modular construction and capable of being expanded in computing capacity, precision, and operating speed. speech amplifier -A voltage amplifier made specifically for a microphone. s p e e c h audiometer -An audiometer for measuring either live or recorded speech signals. s p e e c h clipper -1. A speech-amplitude-limiting circuit that permits the average modulation percentage of an amplitude-modulated transmitter to be increased. 2. Circuit using one or more biased diodes to limit the wave crests of speech frequency signals. Used in speech amplifiers of transmitters to maintain a high average modulation percentage. s p e e c h compression- 1. A modulation technique that makes use of certain properties of the speech signal in transmitting adequate information regarding quality, characteristics, and the sequential pattern of a speaker’s voice over a narrower frequency band than otherwise would be necessary. 2. A means of boosting the average level of voice signals to provide increased “talk power” of higher average modulation levels. speech frequency-See voice frequency. speech-interference level-A value for rating the effect of background noise on the intelligibility of speech. speech interpolation -The method of obtaining more than one voice channel per voice circuit by giving each subscriber a speech path in the proper direction only at the times when his or her speech requires it. s p e e c h inverter -An apparatus that interchanges high and low speech frequencies by removing the carrier wave and transmission of only one sideband in a radiotelephone. This renders the speech unintelligible unless picked up by apparatus capable of replacing the carrier wave in the correct manner. See also scrambler circuit. speech level-The energy of speech (or music), measured in volume units on a volume indicator. s p e e c h scrambler- 1. A device to provide privacy to voice communications via wire or radio. (The simplest is an inverter that changes low frequencies to high, and vice versa at the receiving end.) 2. See scrambler circuit. s p e e c h synthesizer-A system used in research to generate speech from electrical signals in order to study human vocal patterns. speed calling -A feature that allows numbers to be dialed with abbreviated codes. speed control-The act of precisely increasing or decreasing the speed of a driven gear or shaft by an electrical or mechanical means. speed limit-A control function that prevents the controlled speed from exceeding prescribed limits. speed of light-The speed at which light travels: 186,284 miles per second, or 3 x IO8 d s . speed of sound-Also called sonic speed. The speed at which sound waves travel through a medium (in air and at standard sea-level conditions, about 750 miles per hour or 1080 feet per second, or 329 d s ) . speed of transmission -Also called rate of transmission. The instantaneous rate of processing information by a transmission facility. Usually measured in characters or bits per unit time. speed-ratio control -A control function that maintains a preset ratio of the speeds of two drives. speed regulation-A figure of merit indicating the change in motor speed from no load to full load expressed

speed regulator

721 as a percentage of full-load speed. Speed regulation is generally established at rated speed. speed regulator-A regulator that maintains or varies the speed of a motor at a predetermined rate. speedup capacitor-- 1. A capacitor used in RCTL to permit faster turn-on of the transistor in response to a change in input; it also helps overcome the storage delay of the transistor itself. 2. See commutating capacitor. spelling checker-A program that checks the words in a computer file against a previously recorded list, querying or correcting words not on that list. s p h e r e gap-A spark gap with spherical electrodes. It is used as an excess-voltage protective device.

spherical wave- A wave in which the wavefronts are concentric spheres. sphygmocardiograph -A device for simultaneous recording of heartbeat and pulse. sphygmogram-A graphic recording of the movements, forms, and forces of an arterial pulse. s p h y g m o m a n o m e t e r -An instrument for measuring blood pressure, especially that in the arteries. spider-Highly flexible ring, washer, or punched flat member used in a dynamic speaker to center the voice coil on the pole piece without appreciably hindering the in-and-out motion of the voice coil and its attached diaphragm. spider bonding -A method used for connecting an integrated-circuit chip to its package leads or to a filmtype substrate for hybrid constructions. ‘instead of running individual wires from each bonding pad on the chip to the corresponding package lead, a preformed lead frame is placed over the chip, and all connections are made by a single operation of a bonding machine. spider-web antenna-An all-wave receiving antenna having several lengths of doublets connected somewhat like the web of a spider to give favorable pickup characteristics over a wide range of frequencies. spider-web coil -A flat coil having an open weave somewhat like the bottom of a woven basket. It was used in older radio receivers. spike- Also called a transient. 1. An abrupt transient that comprises part of a pulse but exceeds its average amplitude considerably. 2. A pulse of short duration and of greater amplitude than an average pulse. 3. A distortion in the form of a pulse waveform of relatively short duration superimposed on an otherwise regular or desired pulse waveform. 4. A burst of extra voltage in a power line, lasting only a fraction of a second. s p i k e discriminator-A circuit used in a transponder to discriminate against pulses of extremely short duration, such as might be caused by ignition noise. energy -The radio-frequency spike-leakage energy per pulse transmitted through tr and pre-tr tubes before and during the establishment of the steady-state radio-frequency discharge. s p i k e noise-In a chopper, the static field noise caused by insulating material; can be observed if the chopper is followed by a wideband amplifier. spiking- Short, multiple, irregular bursts of laseroutput radiation. Spiking is characteristic of pulse lasers, especially flash-pumped solid-dielectric types (e.g., ruby, neodymium in glass). The spike duration is typically 0.2 to 2 microseconds. spill-The redistribution and hence loss of information from a storage element of a charge-storage tube. spillover positions- Storage positions in which backlogged traffic that accumulates when a send channel is inoperative or unusually busy is held for transmission immediately on the availibility of a channel. spin block-A loop created when a process keeps checkmg the state of a flag or status bit while waiting for an event to occur. spindle-The upward-projecting shaft used on a phonograph turntable for positioning and centering the record. spinel-See silicon on sapphke. spinner -1. An automaticallyrotatable radar antenna, together with its associated equipment. 2. The part of a mechanical scanner that is rotated about an axis; generally, use ofthe term is restricted to cases of relatively high-speed rotation. spinning electron-An electron that spins with an angular momentum.

‘NSULAToR9s

SPARK GAP \ INSULATOR

Sphere gap.

sphere-gap voltmeter- An instrument for measuring high voltages. It clonsists of a sphere gap, and the electrodes are moved together until the spark will just barely pass. The voltage can be calculated from gap spacing and the electrode diameter, or read directly from a calibrated scale. spherical aberration- 1. Image defects (e.g., blurring) due to the spherical form of a lens or mirror. These defects cause a blurred image because the lens or mirror brings the central and marginal rays to different focuses. Common types of spherical aberration are astigmatism and curvature of the field. 2. The optical error introduced by the fact that incident rays at different distances from the optical axis are focused at different points along the axis by reflection from spherical mirror surfaces or refraction by spherical lenses. spherical candlepower-In a lamp, the average candlepower in all directions in space. It is equal to the total luminous flux of ithe lamp, measured in lumens, divided by 4n. spherical coordinates-A system of polar coordinates that originate in the center of a sphere. All points lie on the surface of the sphere, and the polar axis cuts the sphere at its two poles. of spherical-earth ;attenuation -Attenuation radio waves over an imperfectly conducting spherical earth in excess of the attenuation that would occur over a perfectly conducting plane. spherical e a r t h factor-Ratio between the electrical field strengths that would result from propagation over an imperfectly conducting spherical eaah and a perfectly conducting plane. spherical stylus---A cartridge stylus whose shape is conical, with the downward-facing point of the cone rounded to a specified radius of curvature, usually 0.5 or 0.7 mil (12.7 or 17.8 pm).

- spinning electron

spinthariscope

- splitter

s p i n t h a r i s c o p e -An instrument for viewing the scintillations of alpha particles on a luminescent screen. spin wave-A moving magnetic disturbance in a ferrite. The presence of an alternating magnetic field with its frequency near that of the natural precessional frequency of a spin tends to increase the precession angle. This increase in precession angle is passed from atom to atom by dipole and exchange interactions. spin-wave amplitude -The difference between the precession angles of two spins. spiral distortion -In camera tubes or image tubes using magnetic focusing, a form of distortion in which image rotation varies with distance from the axis of symmetry of the electron optical system. spiral four-A quad in which the four conductors are twisted about a common axis, the two sets of opposite conductors being used as pairs. spiral scanning -Scanning in which the maximum radiation describes a portion of a spiral, with the rotation always in one direction. spkr- Abbreviation for speaker. SPL -Abbreviation for sound-pressure level. splashproof -A device or machine so constructed and protected that external splashing will not interfere with its operation. splashproof motor-An open motor in which the ventilating openings are so constructed that drops of liquid or solid particles falling on it, or coming toward it in a straight line at any angle not greater than 100" from the vertical, cannot enter either directly or by striking and running along a surface of the motor. splatter -Adjacent-channel interference due to overmodulation of a transmitter by abrupt peak audio signals. It is particularly noticeable for sounds containing highfrequency harmonics. splice- 1. A device used for joining two or more conductors. 2. A joint connecting conductors with good mechanical strength and good conductivity; a terminal that permanently joins two or more wires. 3. Nonseparable junction joining optical conductor to optical conductor. 4. An in-line connection between two wires that results in a single conductor. 5. A physical join between pieces of tape 6. A connection of two cables in which each pair in one cable is connected to the corresponding pair in the other. splice insulation -Insulation used over a splice. splicer-Any device that holds magnetic recording tape ends in place for properly aligned splices. Many splicers are automatic to some extent, emitting the tape and trimming the edges of the splice by means of built-in cutting edges. splicing block- 1. A nonautomatic recording tape splicer consisting of an elongated block of metal or plastic with a shallow groove to hold the tape and a narrow slot, usually diagonal, across the middle of the block to guide the cutting blade. Splices are made with a special splicing tape that generally needs no edge trimming. 2. A tool for tape editing consisting of a nonmagnetic metal block with a guide channel that holds magnetic recording tape in precise alignment. Additional straight and diagonal grooves provide a path for a razor blade to follow for cutting the tape so it can be spliced effectively. splicing Ioss-See coupling loss, 1. splicing tape -A pressure-sensitive, nonmagnetic tape designed for joining two pieces of magnetic tape; characterized by high flexibility and an adhesive that will not flow out from under the splice and, thus, cause adhesion between adjacent layers on the reel. spline-A piecewise curve adhering to certain continuity conditions at the node points.

722

split- 1. Of radar tracks, the separation of radar data from a single track to such a degree that one or more additional tracks can be initiated manually or automatically; a similar condition exists when a raid is separated to such an extent that it can be represented on a situation display as two or more raids. 2. Initiation of split tracks, raids, or groups by a direction center track monitor or by programming means. split-anode magnetron-A magnetron with an anode divided into two segments, usually by parallel slots. split-conductor cable-A cable in which each conductor is composed of two or more insulated conductors normally connected in parallel. split fitting-A conduit fitting, bend, elbow, or tee split longitudinally so that it can be positioned after the wires have been drawn into the conduit. The two parts are held together usually by screws. split frequency-The frequencies between the 10W z channels assigned by the FCC for use by U.S. broadcasters. split gear-A type of gear designed to minimize backlash. The method consists of splitting one gear of a meshing pair and so connecting a spring between the two halves that pressure is exerted on both sides of the teeth of the other gear. split hydrophone-A direction hydrophone in which the electroacoustic transducers are divided and arranged so that each division can induce a separate electromotive force between its own terminals. split image-Two or more scenes appearing on a television screen as a result of trick photography at the studio. split-phase -Characteristic of any device (such as an induction motor) that derives a second phase from a single-phase alternating current source by using a capacitive or inductive reactor. split-phase motor- 1. A single-phase induction motor having an auxiliary winding connected in parallel with the main winding, but displaced in magnetic position from the main winding so as to produce the required rotating magnetic field for starting. The auxiliary circuit is generally opened when the motor has reached a predetermined speed. 2. A singlephase induction motor that is momentarily converted to two-phase (polyphase, self-starting) motor by inclusion of an additional primary power winding displaced 90" from the main windings to provide required starting torque. Occasionally the auxiliary windings are designed to operate full time rather than momentarily. split projector-A directional projector in which electroacoustic transducing elements are divided and arranged so that each division can be energized separately through its own terminals. split rotor plate-See serrated rotor plate. split-sound system -An early television receiver IF system in which the audio and video IF signals were separated right after the mixer stage and amplified in separate IF stages. Replaced by the more current intercarrier sound system. split-stator capacitor- A capacitor comprising two isolated stators that function in series with a common rotor. split-stator variable capacitor-A variable capacitor with a rotor section common to two separate stator sections. Used for balancing in the grid and plate tank circuits of transmitters. split-streaming -See bandsplitting. splitter-1. A device with one input that provides two or more outputs to allow multiple receiver hookups to one antenna. Can be passive (an antenna coupler) or active, providing gain. 2. A passive device similar

723 to an antenna coupler but designed to match a 75-0hm impedance. 3. A device that takes a signal and splits it

into two or more identical but lower power signals. split transducer-A directional transducer in which electroacoustic transducing elements are divided and arranged so that each division is electrically separate. split winding -An equal division of a winding that will allow series or paraliel external connection of the divided winding (four external leads) of a servomotor. spoiler-A rod grating mounted on a parabolic reflector to cause the radiation pattern to change from a pencil beam to a cosecant-squared pattern. When the reflector and gating are rotated through 90” with respect to the feed antenna, one pattern changes to the other. spontaneous emission- 1. Emission occurring without stimulation or quenching after excitation. 2. Radiation produced when a quantum mechanical system falls spontaneously from an excited state to a lower state. Emission of this radiation occurs in accordance with the laws of probability and without regard for the presence ojf similar radiation at the same time. spoofing-The defeat or compromise of an alarm system by tricking or fooling its detection devices, such as by short circuiting part or all of a series circuit, cutting wires in a parallel circuit, reducing the sensitivity of a sensor, or entering false signals into the system. Spoofing contrasts with circumvention. spool -A flanged form serving as the foundation on which a coil is wound. spooler-A system program that permits I/O transfers to be queued for an YO device, thereby permitting the requesting task to continue executing even when it cannot immediately use the VO device. Spoolers are commonly used with very slow sequential-output-only devices, such as printers. spooling -Abbreviation for simultaneous peripheral operations online. Process of allowing programs using slow output devices to complete execution rapidly. Data is temporarily stored in buffers or queues for later low-speed transmission concurrent with normal system operation. s p o r a d i c E ionization -Ionization that appears in the atmosphere at E-layer heights, is more noticeable at higher latitudes, and occurs at all times of the day. It may be caused by particle radiation from the sun. sporadic E layer-A portion that sometimes breaks away from the normal I? layer in the ionosphere and exhibits unusual erratic characteristics. sporadic propagation -Abnormal and unpredictable radio transmission that only occurs occasionally. Caused by unusual intense ionization in some part of the E layer of the ionosphere. sporadic reflections- Also called abnormal reflections. Sharply defined, intense reflections from the sporadic E layer. Their frequencies are higher than the critical frequency of the layer, anjd they occur anytime, anywhere, and at any frequency. spot- 1. The area instantaneously affected by the impact of an electron beam of a cathode-ray tube. 2. See land, 2. 3. The smallest luminescent area of the screen surface instantaneously excited by the impact of an electron beam. spot beam -A satellite beam that covers a relatively small geographical area. -See yield-strength-controlled bonding. spot distortion -Undesirable asymmetry or defect in the spot shape. spot j a m m i n g -Jamming of a specific frequency or channel. spot noise factor--See spot noise figure.

split transducer

- spread spectrum transmission

spot noise figure- Also called spot noise factor. Ratio of the output noise of a transducer to the portion attributable to the thermal noise in the input termination when the termination has a standard noise temperature (290°K). The spot noise figure is a point function of input frequency. spot projection -In facsimile: 1. An optical method in which the scanning or recording spot is delineated by an aperture between the light source and the subject copy or record sheet. 2. The optical system in which the scanning or recording spot is the size of the area being scanned or reproduced. spot protection -Protection of objects such as safes, art objects, or anything of value that could be damaged or removed from the premises. spot size-The smallest area of light that can be produced by a CRT. spot speed-1. In facsimile, the length of the scanning line times the number of lines per second. 2. In television, the product of the length (in units of elemental area, i.e., in spots) of the scanning line and the number of scanning lines per second. spottiness- Bright spots scattered irregularly over the reproduced image in a television receiver due to human-made or static interference entering the television system at some point. spot welding- 1. A resistance welding process whereby welds are made between two or more overlapping sheets of metal by pressing them together between two electrodes arranged to conduct current to the outer surfaces of the overlapped sheets. The tips of one or both of the electrodes are restricted in area to approximately the diameter of the spot weld desired. 2. Resistance welding in which the current is directed through the entire area under the electrode tip. Welding is usually performed by a rocker-arm type spot welder. spot wobble -An externally produced oscillating movement of an electron beam and its resultant spot. Spot wobble is used to eliminate the horizontal lines across the screen and thus make the picture more pleasing. s p r a y fluxing - A specialized wave-solder fluxing technique in which a fine stainless-steel screen drum is rotated in liquid flux. The amount of flux transferred is controlled by the rotational speed of the drum and air pressure. The drum contains air jets. See ulso brush fluxing; foam fluxing; wave fluxing. spray-gun soldering -Soldering fluxed and heated parts by blowing molten solder on them from a gas or electrically heated gun. spreader- 1. An insulating crossarm used to hold the wires of a transmission l i e apart. 2. The crossarm separating the parallel wire elements of an antenna. spread groove -A groove cut between recordings. The groove, which has an abnormally high pitch, separates the recorded material but still enables the stylus to travel from one to the next. spreading anomaly-That part of the propagation anomaly that is identifiable with the geometry of the ray pattern. spreading IOss-The transmission loss suffered by radiant energy. The effect of spreading, or divergence, is measured by this loss. spreadsheet-1. A computer program that sets up an electronic spreadsheet in which the lines and columns are automatically calculated according to formulas chosen by the user. When one number is changed, the program will automatically change all the sums and multiples that are affected. 2. A program that provides automatic calculations on any numbers and formulas that are input. spread spectrum transmission - 1. A communications technique that involves transmitting information

s p r i n g - sputtering that has been multiplied by a pseudo-random noise (PN) sequence that essentially spreads it over a relatively wide frequency bandwidth. The receiver detects and uses the same PN sequence to “despread” the frequency bandwidth and decode the transmitted information. This communications technique allows greater signal density within a given transmission bandwidth and also provides a high degree of signal encryption and security in the process. 2. A communications technique in which many different signal waveforms are transmitted in a wide band. Power is spread thinly over the band so narrow-band radios can operate within the wide band without interference. spring -A resilient, flat piece of metal forming or supporting a contact member in a jack or a key. spring-actuated stepping relay -A stepping relay in which cocking is done electrically and operation is produced by spring action. spring contact-1. A relay or switch contact, usually of phosphor bronze and mounted on a flat spring. 2. A device employing a current-canying cantilever spring that monitors the position of a door or window. spring contact probe-Also called spring pin or spring probe. The element that provides the electsical connection between a particular node on the product to be tested and the verifier electronics. Usually spring loaded to allow some thickness, lead length, and other product variations. spring curve-A plot of the spring force on the armature of a relay versus armature travel. spring-finger action-The design of a contact, as used in a printed circuit connector or a socket contact, permitting easy stress-free spring action to provide contact pressure and/or retention. spring pile-up- An assembly of all contact springs operated by one armature lever. spring-return s w i t c h -A switch that returns to its normal position when the operating pressure is released. spring stop-In a relay, the member used to control the position of a pretensioned spring. spring stud-In a relay, an insulating member that transmits the armature motion from one movable contact to another in the same pileup. s p r o c k e t holes-Holes punched on each line of a perforated tape used as a timing reference and for driving certain transports. s p r o c k e t pulse- 1. A pulse generated by one of the magnetized spots that accompany every character recorded on magnetic tape. During read operations, sprocket pulses permit regulation of the timing of the read circuits and provide a count of the number of characters read from the tape. 2. A pulse generated by a sprocket or driving hole in a paper tape; this pulse serves as the timing pulse for reading or punching the tape. SPST- Abbreviation for single-pole, single-throw. A two-contact switching arrangement that opens or closes one circuit; the circuit may be normally open or normally closed. spurious Counts-See spurious tube counts. spurious emanations -Unintentional and unde sired emissions from a transmitting circuit. spurious emission-See spurious radiation. spurious modulation -Undesired modulation of an oscillator; for example, frequency modulation resulting from mechanical vibration. spurious pulse-In a scintillation counter, a pulse not purposely generated or directly due to ionizing radiation. spurious pulse mode- An unwanted pulse mode that is formed by the chance combination of two or more pulse modes and is indistinguishable from a pulse interrogation or reply.

724

spurious radiation -Also called spurious emission. Emissions from a radio transmitter at frequencies outside its assigned or intended emission frequency. Spurious emissions include harmonic emissions, parasitic emissions, and intermodulation products, but exclude emissions in the immediate vicinity of the necessary band, which are a result of the modulation process for the transmission of information. spurious response- 1. Any undesired response from an electric transducer or similar device. 2. The sensitivity of a circuit to signals of frequencies other than the frequency to which the circuit is tuned. 3. In electronic warfare, undesirable signal images in the intercept receiver as a result of mixing of the intercepted signal with harmonics of the receiver local oscillators. 4. A characteristic of a spectrum analyzer wherein displays appear that do not conform to the calibration of the radio-frequency dial. 5. Response of a frequency-selective system to an undesired frequency. spurious-response attenuation -The ability of a receiver to discriminate between a desired signal to which it is resonant and an undesired signal at any other frequency to which it is simultaneously responsive. spurious-response ratio -Ratio of the field strength at the frequency that produces a spurious response to the field strength at the desired frequency, each field being applied in turn to produce equal outputs. Image ratio and intermediate-frequency response ratio are special forms of spurious-response ratio. spurious-response rejection -The ability of an FM tuner to reject spurious signals falling outside the tuned frequency, or the immunity of the tuner itself to the production of spurious signals as the result of intermodulation, etc. spurious signal- 1. An unwanted signal generated either in the equipment itself or externally and heard (or seen) as noise. 2. Undesired signals appearing external to an equipment or circuit. They may be harmonics of existing desired signals, high-frequency components of complex waveshapes, or signals produced by incidental oscillatory circuits. 3. An undesired false signal. spurious transmitter output- Any component of the radio-frequency output that is not implied by the type of modulation and the specified bandwidth. s p u r i o u s transmitter output, conducted-A spurious output of a radio transmitter that is conducted over a tangible transmission path such as a power line, control circuit, radio-frequency transmission line, waveguide, etc. spurious transmitter output, extraband-A spurious transmitter output that lies outside the specified band of transmission. s p u r i o u s transmitter output, inband-A spurious transmitter output that lies within the specified band of transmission. spurious transmitter output, radiated -A spurious output radiated from a radio transmitter. (The associated antenna and transmission lines are not considered part of the transmitter.) spurious tube counts- Also called spurious counts. The counts in radiation-counter tubes other than background counts and those caused directly by the radiation to be measured. They are caused by electrical leakage, failure of the quenching process, etc. spurt tone -A short-duration audio-frequency tone used for signaling or dialing selection. sputtering- Also called cathode sputtering. 1. A process sometimes used in the production of a metal master disc. In this process the original is coated with an electric conducting layer by means of an electric discharge in a vacuum. 2. A thin-film technique in which

725 material for the 6lm is ejected from the surface of the bulk source when the source is subjected to ion bombardment. 3. Dislocation of surface atoms of a material bombarded by high-energy atomic particles. 4. A method of depositing a thin film or material onto a subsBate. The substrate is placed in a large demountable vacuum chamber having a cathode made of the metal or ceramic to be sputtered. The chamber is then operated so as to bombard the cathode with positive ions. As a result, small particles of the material fall uniformly on the substrate. 5. A deposition process wherein a surface, or target, is immersed in an inert-gas plasma and is bombarded by ionized molecules that eject surface atoms. The process is based on the disintegration of the target material under ion bombardment. Atoms broken away h m the target material by gas ions deposit on the part (substrate), forming a thin film. SQ-A matrix system developed by CBS, Inc. S-quad-Also called simple quad. An arrangement of two parallel paths, each of which contains two elements in series. square-A unit area, Le., the ratio of length/ width = 1. uare-law demodulator- See square-law detector. square-law detection-Detection in which the output voltage is substantially proportional to the square of the input voltage over the useful range of the detector. square-law detector- Also called square-law demodulator. A detector in which the output signal current is proportional to the square of the radio-frequency input voltage. Operation of this circuit depends on nonlinearity of the detector characteristic, rather than on rectification. square-law scale meter-A meter in which the deflection is proportionall to the square of the applied energies. square-loop ferrite-A ferrite with a rectangular hysteresis loop. square-loop material-Ferromagnetic material having a squareness ratio approaching 1. Compare rectangular loop. squereness -The ratio of the residual induction to the maximum induction obtained at the maximum magnetizing field being used. It can be considered as a figure of merit of the flatness of the decaying magnetizing curve. squareness ratio- 1. For a magnetic material in a symmetrically cyclically magnetized condition, the ratio of the flux density at zero magnetizing force to the maximum flux density. 2. The ratio of the flux density to the maximum flux density when the magnetizing force has changed halfway from zero toward its negative limiting value. square wave -1. A square- or rectangular-shaped periodic wave that alternately assumes two fixed values for equal lengths of time, the transition time being negligible in comparison with the duration of each fixed value. 2. An ac periodic waveform in which voltage alternates rapidly from a positive peak value to the negative peak value, and vice versa, after a delay. square-wave amplifier- A resistance-coupled amplifier (in effect, a wideband video amplifier) that amplifies a square wave with a minimum of distortion. square-wave generator-A signal generator for producing square or rectangular waves. It is useful for testing the frequency response of wideband devices. See also square-wave testing. s q ~ ~ r e - ~response-In av~ camera tubes, the ratio of the peak-to-peaksignal amplitude given by a test pattern consisting of alternate black and white bars of equal widths to the difference in signal between large areas of black and white having the same illuminations

SQ

- squelch circuit

1.1+3 1+3+5

1

1

1

+3

+3 + 5

= = =

FUNDAMENTAL FUNDAMENTAL PLUS THIRD HARMONIC FUNDAMENTAL PLUS THIRD PLUS FIFTH HARMONIC

Square wave showing harmonic composi~n.

as the bars. Horizontal square-wave response is measured if the bars are perpendicular to the horizontal scan, and vertical square-wave response is measured if they are parallel. square-wave testing-The use of a square wave signal to test the frequency response of a wideband device. The output wave seen on an oscilloscope will show how much the square wave was distorted in passing through the device. Squaring circuit - 1. A circuit that changes a sine wave or other wave into a square wave. 2. A circuit that contains nonlinear elements and that produces an output voltage proportional to the square of the input voltage. squawker -The midrange speaker of a three-way system. squeal - 1. Audible tape vibrations, primarily in the longitudinal node, caused by a frictional excitation at the heads and guides. 2. In a radio receiver, a high-pitched tone heard together with the wanted signal. squealing-The high-pitched noise heard along with the desired intelligence in a radio receiver. It is due to interference between stations or to oscillation in one of the receiver circuits. squeegee-The part of a screen printer used in thick-film circuit manufacturing that pushes the composition across the screen and through the mesh onto the substrate. squeezable waveguide- In radar, a variablewidth waveguide for shifting the phase of the radiofrequency wave traveling through it. squeeze section -A length of waveguide whose critical dimension can be altered to correspond to changes in the electrical length. squeeze track -A variable-density sound track in which variable width with greater signal-to-noise ratio is obtained by means of adjusting masking of the recording light beam and simultaneously increasing the electric signal applied to the light modulator. squegger- A self-quenching oscillator in which the suppression occurs in the grid circuit. squegging-A self-blocking condition in an oscillator circuit. squegging oscillator-See blocking oscillator, 1. Squelch-To automatically quiet a receiver by reducing its gain in response to a specified characteristic of the input. squelch circuit-1. A circuit for preventing a radio receiver from producing an audio-frequency output in the absence of a signal having predetermined characteristics. A squelch circuit may be operated by signal energy in the receiver passband, by noise quieting, or by a combination of the two (ratio squelch). It may also be

squib

- stabilized master oscillator

operated by a signal having modulation characteristics (selective squelch). 2. A circuit that silences a receiver in the absence of signals above a certain level of signal strength. This squelch threshold is usually adjustable and will stop background noise from reaching the speaker but will activate the receiver when an intelligible signal is detected. squib -Contained powder charge and initiating device that, when energized, produces heat and pressure. squint-In radar, an ambiguous term meaning either the angle between the two major-lobe axes in a lobeswitching antenna or the angular difference between the axis of antenna radiation and a selected geometric axis such as the axis of the reflector. squint angle-The angle between the physical axis of the antenna center and the axis of the ratliated beam. squirrel-cage induction motor- An induction motor in which the secondary circuit, usually the rotor, consists of a squirrel-cage winding (two discs connected along their circumference with copper bars) arranged in slots in the iron core. squirrel-cage motor-A rugged electric motor that basically consists of two components: a wound stator and the rotor assembly, which most typically consists of a laminated cylindrical iron core with slots for conductors. The unit rotates when a moving magnet field induces a current in the shorted rotor conductors. squirrel-cage winding -A permanently shortcircuited winding that is usually uninsulated and has its conductors uniformly distributed around the periphery of the machine, and is joined by continuous end rings. squitter-In radar, random firing (intentional or otherwise) of the transponder transmitter in the absence of interrogation. SRAM -Abbreviation for static random-access memory. A readwrite memory in which the data are latched and retained. SRAMs do not lose their contents as long as power is on. This memory does not need to be refreshed as does a DRAM. S/rf meter -An indicator on some CB transceivers to indicate relative strength of an intercepted signal when receiving, and the relative rf power output when transmitting. SSB -See single sideband. SSFM-A system of multiplex in which singlesideband subcarriers are used to frequency modulate a second carrier. SSI -Abbreviation for small-scale integration. 1. A classification of ICs by size, applicable to chips that contain less than 12 gates or circuits of equivalent complexity. 2. A circuit of under 10 gates, generally involving one metallization level implementing one circuit function in monolithic silicon. 3. The earliest form of integratedcircuit technology. A typical SSI circuit contains from one to four logic circuits. SS loran -Sky-wavesynchronized loran. Loran in which the slave station is controlled by the sky wave from the master station rather than the ground wave. This method is used with unusually long base lines. SSPM-A system of multiplex in which singlesideband subcarriers are used to phase-modulate a second carrier. SSR -Abbreviation for solid-state relay. S S W - Abbreviation for Slow Scan Television. 1. Sending still images (usually black and white) by means of audio tones over telephone lines or on the MF/HF bands. Transmission times vary from a few seconds to several minutes. 2. A television system that employs a slow rate of horizontal scanning suitable for transmission of printed matter, photographs, and illustrations.

726

stability- 1. The ability of a component or device to maintain its nominal operating characteristics after being subjected to changes in temperature, environment, current, and time. It is usually expressed in either percent or parts per million for a given period of time. 2. The ability of a power supply to maintain a constant output voltage (or current) over a period of time under fixed conditions of input, load, and temperature. Usually expressed in terms of a voltage (or current) change over a fixed length of time. 3. The ability to maintain effectiveness within reasonable bounds in spite of large changes in environment. 4.For a feedback-control system or element, the property such that its output will ultimately attain a steady-state dc level within the linear range and without continuing external stimuli. 5. The overall ability of a resistor to maintain its initial resistance value over extended periods when subjected to any combination of environmental conditions and electrical stresses. 6. The ability of a motor-control system to operate at or near a constant speed over a wide load range without oscillations in speed (hunting). 7. A measure of deviations from a rated output over long periods. 8. Fluctuations in accuracy, or drift, over a given period. stability factor-The measure of the bias stability of a transistor amplifier. It is defined as the change in collector current, I C , per change in cutoff current, IC. stabilivolt-A gas-filled tube containing a number of concentric, coated iron electrodes. It is used as a source of practically constant voltage for apparatus drawing only small currents. stabilization-1. The introducing of stability into a circuit. 2. A process by means of which the output of electromechanical transducers is optimized by adjusting magnetic and mechanical parameters for its maximum magnetic permanency, to maintain its output stable under changing environmental and external conditions. 3. The reduction of variations in voltage or current not due to prescribed conditions. 4. The treatment of a permanentmagnet material designed to increase the permeance of its magnetic properties. This process may include such conditions as heat, shock, or demagnetizing fields so that the magnet will produce a constant magnetic field. Stabilization generally refers only to magnetic stability wherein if the disturbing influence were removed and the magnet remagnetized, any magnetic changes can be completely restored. Flux changes caused by internal structural changes are permanent in character and cannot be restored simply by remagnetization. stabilization b a k e -A preconditioning performed on finished material to ensure reliability in commercial end use. In semiconductors this procedure accelerates any inherent metallurgical and/or chemical degradation within the device and takes care of over 95 percent of the failures due to infant mortality. In addition, it acts to stabilize such semiconductor parameters as current gain (beta), breakdown voltage, and diode leakage. stabilization network- A network used to prevent oscillation in an amplifier with negative feedback stabilized feedback-See negative feedback. stabilized flight-A type of flight in which control information is obtained from inertia-stabilized references such as gyroscopes. stabilized local oscillator- An extremely stable radio-frequency oscillator used as a local oscillator in the superheterodyne radar receiver in a moving-target indicator system. stabilized master oscillator-The master oscillator in complex microwave systems that acts as the frequency reference for all rf signals within the system. Usually crystal and temperature controlled for maximum frequency stability.

stabilized shunt-wound motor

727

stabilized shunt-wound motor- A shunt-wound motor to which a light series winding has been added to prevent a rise in speed, or to reduce the speed when the load increases. stabilized winding -Also called tertiary winding. An auxiliary winding used particularly in star-connected transformers to (a) stabilize the neutral point of the fundamental frequency voltage, (b) protect the transformer and the system from excessive third-harmonic voltages, or (c) prevent telephone interference caused by thirdharmonic currents and voltages in the lines and earth. stabistor- A voltage-limiting semiconductor. A diode designed to break over and conduct at a certain voltage. This is the normal forward conduction of a diode and is also characteristic of Zener diodes, which avalanche into conduction when breakdown (backward) voltage is exceeded. stable element-In navigation, an instrument or device that maintains a desired orientation independently of the vehicle motion. stable oscillation-A response that does not increase indefinitely with time; the opposite of an unstable oscillation. stable platform -Also called a gyrostabilized platform. A gyro instrument that provides accurate azimuth, pitch, and roll attitude information. In addition to serving as reference elements, they are used for stabilizing accelerometers, star trackers, and similar devices in space. stable strobe-A series of strobes that behaves as if caused by a single jammer. s t a c k - 1. That portion of a computer memory and/or registers used to temporarily hold information, usually the contents of the internal registers within a microprocessor chip. 2. See pileup, 1. 3. A block of successive memory locations that is accessible from one end on a lastin first-out basis (LIFO). The stack is coordinated with the stack pointer, which keeps track of storage and retrieval of each byte of information in the stack. A stack may be any block of successive information locations in the readwrite memory. 4.A series of extra data registers, found especially in calculators using reverse Polish notation. The stack is used as a “first-in, last-out”

- s t a c k e d - b e a m radar

type of memory. Data is shifted into the stack by pressing an operational key, and is shifted down by pressing an operational key. The lowest registers and any subsequent registers on a nonrandody accessible basis allow storage of intermediate results prior to their reuse with a later completing operation. Thus, access to parentheses (brackets) is automatic on pressing the ENTER key. A four-level stack (X, Y, Z, t) has the capability of three levels of parentheses (three sets of brackets). 5. A data area allocated to a process from which individual stack frames are allocated. 6. A region of memory that works by special rules. Each time the computer stores a word there, it goes on top of the stack and all the previously stored words move down one level. When a computer takes a word off the top of the stack, everything moves up one level, until the stack is empty. The computer has access only to the top of the stack. Piling a word on the stack is called a push, and taking a word off is called a pull or a pop. 7. A sequence of memory locations used in LIFO (last-in, first-out) fashion that stores, or stacks, computer words when the computer receives an interrupt request. A stack pointer specifies the last-in entry (or where the next-in entry will go). 8. A dynamic, sequential data list, usually contained in system memory, having special provisions for program access from one end or the other. Storage and retrieval of data from the stack is generally automatically performed by the processor. 9. A last-in, first-out structure that preserves the chronological ordering of information. Stacks are necessary for subroutines and interrupt management. A stack is manipulated by two basic instructions: push and POP. s t a c k e d array- 1. An antenna system consisting of two or more antennas connected together and placed with respect to each other to increase the gain in a specific direction or directions. 2. A group of several identical microwave antennas placed one above the other to increase the gain of an antenna. They are connected in proper phase relationship, so that their signals are additive. s t a c k e d - b e a m radar -A three-dimensional radar system in which elevation information is derived by

LATERAL OR

Stable plagom.

s t a c k e d - d i o d e laser - stand-alone

728

emitting narrow beams placed one above the other to cover a vertical segment, azimuth information is obtained by horizontal scanning of the beam, and range information is obtained from the echo-return time. s t a c k e d - d i o d e laser- A type of laser used when a great amount of power is required. Avoiding the bulk of large numbers of optical lenses, this instrument offers high output intensity and a small emitting region at reasonable drive currents. stacked dipole antenna- Antenna in which the antenna directivity is increased by providing a number of identical dipole elements, excited either directly or parasitically. The resultant radiation pattern will depend on the number of dipole elements used, the spacing and phase difference between the elements, and the relative magnitudes of the currents. s t a c k e d h e a d s -Also called inline heads. An arrangement of magnetic recording heads used for stereophonic sound. The two heads are directly in line, one above the other. s t a c k frame-A contiguous data area allocated for every activation of a routine; holds parameter values, local variables, temporary variables, and return-linkage information. s t a c k pointer-1. A register that comes into use when the microprocessor must service an interrupt- a high-priority call from an external device for the central processing unit to suspend temporarily its current operations and divert its attention to the interrupting task. A CPU must store the contents of its registers before it can move on to the interrupt operation. It does this in a stack, so named because information is added to its top, with the information already there being pushed further down. The stack thus is a last-in, first-out type of memory. The stackpointer register contains the address of the next unused location in the stack. 2. The counter or register used to address a stack in the memory. stage -1. A term usually applied to an amplifier to mean one step, especially if part of a multistep process; or the apparatus employed in such a step. 2. A hydraulic amplifier used in a servovalve. Servovalves may be singlestage, two-stage, three-stage, etc. 3. A single section of a multisection circuit or device. s t a g e - b y - s t a g e elimination -A method of locating trouble in electronic equipment by using a signal generator to introduce a test signal into each stage, one at a time, until the defective stage is found. stage efficiency -Ratio of useful power (alternating current) delivered to the load to the power at the input (direct current). stagger -Periodic positional error of the recorded spot along a recorded facsimile line. staggered h e a d s -An infrequently used arrangement of magnetic recording heads for stereophonic sound. The heads are 17/32 inch (30.95 mm) apart. Stereo tapes

SHARP CUTOFF ON

recorded with staggered heads cannot be played on recorders using stacked heads, and vice versa. staggered tuning-A means of producing a wide bandwidth in a multistage IF amplifier by tuning to different frequencies by a specified amount. staggering-The offsetting of two channels of different carrier systems from exact sideband-frequency coincidence in order to avoid mutual interference. staggering advantage -A reduction in intelligible crosstalk between identical channels of adjacent carrier systems as a result of using slightly different frequency allocations for the different systems. stagger time-The interval between the times of actuation of any two contact sets. stagger-tuned amplifier- An amplifier consisting of two or more stages, each tuned to a different frequency. stagnation t h e r m o c o u p l e -A type of thermocouple in which a high recovery factor is achieved by stagnating the flow in a space surrounding the junction. This results in a high response time as compared with an exposed junction. staircase-A video test signal containing several steps at increasing luminance levels. The staircase signal is usually amplitude modulated by the subcarrier frequency and is useful for checking amplitude and phase linearities in video systems. staircase generator -A special-purpose signal generator that produces an output that increases in steps; thus, its output waveform has the appearance of a staircase. staircase signal -A wavefonn consisting of a series of discrete steps resembling a staircase. stall torque-1. The torque that the rotor of an energized motor produces when restrained from motion. 2. The torque developed by a servomotor at speed in excess of 1 rpm but less than 0.5 percent of the synchronous speed with a rated voltage and frequency of the proper phase relationship applied to both windings. 3. See holding torque. stalled-torque control-A control function used to control the drive torque at zero speed. StalO-Acronym for stabilized local oscillator. A highly stable oscillator, usually stabilized by feedback from a very high-Q LC circuit such as a high-Q cavity. Used as part of a moving-target indication device in conjunction with a radar. stamped printed wiring -Wiring that is produced by die stamping and that is bonded to an insulating base. stamper- A negative (generally made of metal by electroforming) from which finished records are molded. stand-alone- 1. Pertaining to a device that requires no other piece of equipment along with it to complete its own operation or function. 2. A system or piece of equipment that is capable of doing its job without being

I----

OVERALL DUE 10 21RESPONSER 25-MHZ I SOUND TRAPS

TRAPS ON THE INOIVIOUAL RESPONSE

1,

Staggered tuning.

729 connected to anything else. 3. Self-contained, not rquiring any special add-ons or supports, e.g., a stand-alone word processor. 4. Word-processing equipment that contains all the necessary Components within itself, allowing it to operate entirely by itself. This and shared logic are the two major types of word-processing equipment. stand-alone system -A microcomputer software development system that runs on a microcomputer without connection to anotheir computer or a time-sharing system. 'This system includes an assembler, editor, and debugging aids. It may include some of the features of a prototyping kit. stand-alone terminal -See intelligent terminal. standard- 1. An exact value, or a concept established by authority, custom, or agreement, that serves as a model or rule in the measurement of a quantity or in the establishment of a procedure, 2. A device used to maintain continuity of value in the units of measurement by periodic comparison with higher-echelon or national standards. 3. An agreement on a definition. By referencing standards, which may be either test methods or physical or electrical descriptions, a component or system having desired properties may be obtained. 4. A specification for data communication that is widely accepted and implemented by communications vendors. Standards may be formal (published by a recognized standards organization) or de facto (accepted without formal publication). standard antenna -An open single-wire antenna, including the lead-in wire, having an effective height of four meters. standard beam approach-Abbreviated SBA. A VHF, 40-MHz continuous-wave low-approach system using a localizer and markers. The two main-signal lobes are tone-modulated with the Morse-code letters E and T (e and -). These modulations form a continuous tone when the aircraft is on its course. The airborne equipment is usually instrumented for visual reference, but may be used aurally in some applications. standard broadcast band-The band of frequencies extending from 530 to 1710 kilohertz. standard broadcast channel-The band of frequencies occupied by the carrier and two sidebands of a broadcast signal. The carrier frequency is at the center, with the sidebands extending 5 kHz on either side. standard broadcast station-A radio station operated on a frequency between 530 and 1710kHz for the purpose of transmitting programs intended for reception by the general public. standard candle-A unit of candlepower equal to a specified fraction off the visible light radiated by a group of 45 carbon-filament lamps preserved at the National Bureau of Standards, the lamps being operated at a specified voltage. The standard candle was originally the amount of light radiated by a tallow candle of specified composition and shape. standard capacitor-A capacitor whose capacitance is not likely to vary. It is used chiefly in capacitance bridges. stanidard cell - 1. A, primary cell that serves as a standard of voltage. 2. Predefined circuit elements that may 'be selected and arranged to create a custom or semicustom integrated circuit more easily than through original (custom) design. Cell libraries provide the building blocks from which designers create ASICs (applicationspecific integrated circuits). standard component-A component that is regularly produced by some manufacturer and is carried in stock by one or more distributors. standard defiectim- 1. In a galvanometer having an attached scale, one scale division. 2. In a galvanometer

stand-alone system

- standard luminosity curve

Standard cell.

without an attached scale, 1 millimeter when the scale distance is 1 meter. standard deviation -1. A measure of the variation of data from the average. It is equal to the root mean square of the individual deviations from the average. 2. A measure of dispersion of data or of a variable. The standard deviation is computed by finding the difference between the average and actual observations, squaring each difference, summing the squared differences, finding the average squared difference (called the variance), and then taking the square root of the variance. 3. A statistical measure used most often when analyzing experimental data. The standard deviation of a set of data is the measure of the dispersion of data values about the mean. standard electrode potential-An equilibrium electrode potential for an electrode in contact with an electrolyte in which all of the components of a speciiied chemical reaction are in their standard states. The standard state for an ionic constituent is unit ion activity. standard error-Applied to statistics such as the mean to provide a distribution within which samples of the statistics are expected to fall. standard eye-An observer that has red and infrared luminosity functions. standard facility-In programming actions, a basic communications electronics functional entity that is engineered to satisfy a specific communications electronics operational requirement. An associated standard facility equipment list describes the facility functionally and indicates the material required for the standard facility. standard-frequency service- A radiocommunication service that transmits for general reception specified standard frequencies of known high accuracy. standard-frequency signal -One of the highly accurate signals broadcast by the National Bureau of Standards radio station WWV on 2.5, 5 , 10, 15, 20, and 25 MHz. standard-gain horn -A waveguide device that has essentially flared out its waveguide dimensions to specific lengths that match (with certain gain) the incoming energy to the atmosphere. The applications include using these horns for reflectors and lenses, pickup horns for sampling power, and receiving and transmitting antennas. standardization-The process of establishing by common agreement engineering criteria, terms, principles, practices, materials, items, processes, equipment, parts, subassemblies, and assemblies to achieve the greatest practicable uniformity of items of supply and erigineering practices, to ensure the minimum feasible variety of such items and practices, and to effect optimum interchangeability of equipment parts and components. standard luminosity curve- An empirically derived function that describes the response of the eye to radiation of different wavelengths. (The terms luminous

standard m i c r o p h o n e

- standing wave

and illumination indicate that this function is taken into account.) standard m i c r o p h o n e -A microphone whose response is known for the condition under which it is to be used. standard noise temperature-A standard reference temperature (T) for noise measurements, taken as 290 K. standard observer-A hypothetical observer who requires standard amounts of primaries in a color mixture to match every color. standard pitch -The tone A at 440 hem. standard play- An arbitrary description given to identify a spool of “thick” recording tape with a specified playing time according to reel size. For example, a 7-inch (17.8-cm) spool will hold 1200 ft (366 m) of standardplay tape; a 5-inch (12.7-cm) spool will hold 600 ft (182 m). The actual playing time is then dependent on tape speed. standard propagation -Propagation of radio waves over a smooth, spherical earth of uniform dielectric constant and conductivity, under standard atmospheric refraction. standard r e f e r e n c e temperature-In a thermistor, the body temperature for which the nominal zeropower resistance is specified. standard refraction -The refraction that would occur in an idealized atmosphere; the index of refraction decreases uniformly with height at the rate of 39 x per Kilometer. standard register of a motor meter-Also called a dial register. A four- or five-dial register, each dial being divided into ten equal parts numbered from 0 to 9. The dial pointers are geared so that adjacent ones move in opposite directions at a 10-to-1 ratio. standard resistor- Also called a resistance standard. A resistor that is adjusted to a specified value, is only slightly affected by variations in temperature, and is substantially constant over long periods of time.

Standard resistor.

standard rod gap-A gap between the ends of two half-inch square rods. Each rod is cut off squarely and mounted on supports so that it overhangs the inner edge of each support by a length equal to or greater than half the gap spacing. It is used for approximate measurements of crest voltages. standard seawater conditions-Seawater with a static pressure of 1 atmosphere, a temperature of lYC, and a salinity such that the velocity of sound propagation is exactly 1500 meters per second.

730

standard source-In fiber optics, the reference optical power source to which emitting and detecting devices are compared for calibration purposes. standard s p h e r e gap-A gap between two metal spheres of standard dimensions. It is used for measuring the crest value of a voltage by observing the maximum gap spacing at which sparkover occurs when a voltage is applied under known atmospheric conditions. standard subroutine-In a computer, a subroutine that is applicable to a class of problems. standard television signal -A signal that conforms to accepted specification. standard test conditions-The environmental conditions under which measurements should be made when disagreement of data obtained by various observers at different times and places may result from making measurements under other conditions standard test-tone power-One milliwatt (0 dBm) at 1000 hertz. standard voltage generator-See signal generator, l. standard volume indicator- A volume indicator with the characteristics prescribed by the American Standards Association. standby- 1. The condition of equipment that will permit complete resumption of stable operation within a short period of time. 2. A duplicate set of equipment to be used if the primary unit becomes unusable because of malfunction. standby battery-A storage battery held in reserve to serve as an emergency power source in event the regular power facilities at a radio station, hospital, etc., fail. standby power generator- An alternating-current generator, held in reserve and used to supply the necessary ac power requirements when there is failure of commercially supplied ac power. s t a n d b y power supply-Equipment that supplies power to a system in the event the primary power is lost. It may consist of batteries, charging circuits, auxiliary motor generators, or a combination of these devices. s t a n d b y redundancy- That redundancy wherein the alternative means of performing the function is inoperative until needed and is switched upon failure of the primary means of performing the function. standby register-A register in which accepted or verified information can be stored to be available for a rerun in the event of a mistake in the program or a malfunction in the computer. standby transmitter-A transmitter installed and maintained ready for use whenever the main transmitter is out of service. s t a n d i n g current-The current present in a circuit in the absence of signal. standing-on-nines carry-A system of executing the carry process in a computer. If a carry into a given place produces a carry from there, the incoming cany information is routed around that place. standing wave -Also called stationary wave. 1. The distribution of current and voltage on a transmission line formed by two sets of waves traveling in opposite directions, and characterized by the presence of a number of points of successive maxima and minima in the distribution curves. At points where the voltages of the two waves add, there will be a voltage antinode; at points where the voltages subtract, there will be a voltage node. The nodes and antinodes do not move, and the resultant wave is called a standing wave. 2. The combination of two waves having the same frequency and amplitude and traveling in opposite directions. Standing waves are indicated by a stationary set of nodes spaced

73 1 one-half wavelength apart along the propagation direction of the waves. The modes of optical resonators are standing waves produced as the radiation travels back and forth between highly reflecting walls. standing-wave detector -See standing-wave meter. standing-wave indicator--See standing-wave meter. standing-wave loss factor-Ratio of the transmission loss in a waveguide when it is unmatched compared with the loss when it is matched. standing-wave meter- Also called a standingwave indicator or detector. An instrument for measuring the standing-wave ratio in a transmission line. It may also include means for finding the location of maximum and minimum amplitudes. standing-wave ratio-Abbreviated S W . The ratio of current (or voltage) at a loop (maximum) in the transmission line to the value at a (minimum) node. It is equal to the ratio of the characteristic impedance of the line to the impedance of the load connected to the output end of the line. standing-wave-ratio bridge -Abbreviated S W bridge. .A bridge for measuring the standing-wave ratio on a transmission line to check the impedance match. standing waves-'The behavior of air pressure waves in an enclosed room or box, giving rise to resonances that occur. They are created by the effects of multiple sound reflections between opposite walls, and cycle at frequencies determined by the distance between them. In effect, the room acts as a resonator. standoff insulator-1. An insulator used to hold a wire or other radio component away from the structure on which it is mounted. 2. An insulator used to support a high-voltage lead, such as an antenna feeder, at some distance from the mounting surface. star chain-A group of navigational radio transmitting stations comprising a master station about which three or more slave stations are symmetrically located. star-connected circuit-A polyphase circuit in which all current paths within the region that limits the circuit extend from each of the points of entry of the phase conductors to a common conductor (which may be the neutral conductor). ar connection-See wye connection. Stark effect-The splitting or shifting of spectral lines or energy levels due to an applied electric field. starlight --A scene illumination of 1/10,000 of a footcandle. star network-A set of three or more branches with one teminal OF each connected at a common node. starquad cable-Four wires laid together and twisted as a group. start bit--In asynchronous transmission, the first bit used to indicate the beginning of a character; normally, a space condition that serves to prepare the receiving equipment for the reception and registration of the character. start; dialing signal-A signal transmitted from the incoming end of a circuit, after receipt of a seizing signal, to indicate that tlhe circuit conditions necessary for receiving the numerical routine information have been established.arli element-In certain serial transmissions, the initial element of a character, used for the purposes of synchronization. In Baud.ot teletypewriter operation, the start element is one space bit. tatter- 1. An auxiliary electrode used to initiate conduction in a glow-discharge cold-cathode tube. 2. Sometimes referred to as a trigger electrode. A control electrode whose principal function is to establish sufficient ionization to reduce the anode breakdown voltage

standing-wave detector

- stat-

in a gas tube. 3. An electric controller for accelerating a motor from rest to normal speed. starter b r e a k d o w n voltage-The voltage required to initiate conduction across the starter gap of a glowdischarge cold-cathode tube, all other tube elements being held at cathode potential before breakdown. starter gap-The conduction path between a starter and the other electrode to which the starting voltage is applied in a glow-discharge cold-cathode tube. starter voltage drop-The voltage drop across the starter gap after conduction is established there in a glowdischarge cold-cathode tube. starting anode-The anode that establishes the initial arc in a mercury-arc rectifier tube. starting circuit breaker-A device whose principal function is to connect a machine to its source of starting voltage. starting current of an oscillator-The value of oscillator current at which self-sustaining oscillations will start under specified loading. starting electrode-The electrode that establishes the cathode spot in a pool-cathode tube. starting reactor-A reactor for decreasing the starting current of a machine or device. starting torque- Also called pull-in torque. 1. The maximum load torque with which motors can start and come to synchronous speed. 2. The torque necessary to initiate motion of a system. starting voltage-The voltage necessary for a gaseous voltage regulator to become ionized or to start conducting. As soon as this happens, the voltage drops to the operating value. start lead-Also called inside lead. The inner termination of a winding. startover-A program function that causes an inactive computer to become active. start-record signal -In facsimile transmission, the signal that starts the converting of the electrical signal to an image on the record sheet. start signal-The signal that converts facsimiletransmission equipment from standby to active. start-stop multivibrator -See monostable multivibrator; flip-flop multivibrator. start-stop system-A system in which each group of code elements that represents an alphabetical signal is preceded by a start signal and followed by a stop signal. The start signal prepares the receiving mechanism to receive and register the character. The stop signal causes the receiving mechanism to come to rest in preparation for reception of the next character. start-stop transmission -The method of transmission used in a start-stop system. start-up -The time between equipment installation and the full operation of the system. start-without-error rate-Stepping rate at which a stepper motor with no external load inertia can start and stop without losing a step. start-without error torque- Also called pull-in torque. Force moment produced by a stepper motor when started at a fixed frequency or step rate. starved amplifier -An amplifier employing pentode tubes in which the screen voltage is set 10 percent below the plate voltage and the plate-load resistance is increased to 10 times the normal valne. Thus, the amplification factor is greatly increased-often a stage gain of 2000 is achieved. stat--A prefix used to identify electrostatic units in the cgs system. See also statampere; statcoulomb; statfarad; stathenry; statmho; statohm; statvolt.

statampere

- staticizer

statampere -The cgs electrostatic unit of electric current, equal to 3.3356 x lo-*' ampere (absolute). statcoulomb-The cgs electrostatic unit of charge, equal to 3.3356 x lo-'' coulomb (absolute). state- 1. The condition of a circuit, system, etc. 2. The condition at the output of a circuit that represents logical 0 or logical 1. 3. A condition or set of conditions considered together, especially one of the two normal sets of operating conditions of a gate or flip-flop. 4. The logical 0 or 1 condition in PC memory or at a circuit's input or output. state code-A coded indication of what state the CPU is in -responding to an interrupt, servicing a DMA request, executing an I/O instruction, etc. state diagram -A representation of the stable states of a process, and the vectored paths by which the process passes to and from these states. state m a c h i n e -A sequential-logic system whose outputs depend on previous and present inputs (for example, a counter), as opposed to processes that are functions of present inputs alone. statement -In computer programming, a meaningful expression or generalized instruction written in a source language. state of charge-The condition of a storage cell or battery in terms of the remaining capacity. state table-Also called state transition table. A list of the outputs of a logic circuit based on the inputs and previous outputs. Such a circuit has memory and cannot be described by a simple truth table. state transition table -See state table. s t a t f a r a d -The cgs electrostatic unit of capacitance, equal to 1.11263 x lo-'* farad (absolute). stathenry-The cgs electrostatic unit of inductance, equal to 8.98766 x lo-" henrys (absolute). static-1. See atmospherics. 2. A form of information storage in shift registers and memories whereby information will be retained as long as power is applied. 3. Capable of maintaining the same state indefinitely (with power applied) without any change of condition. Not requiring a continuous refreshing. 4. A state in which a quantity does not change appreciably within an arbitrarily long time interval. 5. In bum-in, the quality of a test wherein the device is subject to either forward or reverse bias applied to appropriate terminals; voltages are unvarying throughout test. statically balanced arm-A type of tonearm whose masses are first balanced about the pivot, then deliberately unbalanced by approximately 1 gram in order to provide the required tracking force. static analysis -Examination of a program (usually via computer) for errors and inconsistencies, without actual execution. static behavior -The behavior of a control system or an individual unit under fixed conditions (as contrasted to dynamic behavior, under changing conditions). static breakdown voltage-The voltage at which a transient suppressor begins to conduct when subjected to slow-rising dc. Does not account for transient rise-time rates. static burn-in --High-temperature test with device subjected to unvarying voltage rather than to operating conditions; either forward or reverse bias. static cell-A memory cell; basically a crosscoupled flip-flop. Some power is consumed at all times through the two loads. Some newer designs reduce the power required to maintain the state of the flip-flop by using high-resistance polysilicon load resistors. static characteristic-The relationship between a pair of variables such as electrode voltage and electrode

732 current, all other voltages being maintained constant. This relationship is usually represented by a graph. static c h a r g e - 1. The accumulated electric charge on an object. 2. An electric charge held on the surface of an object. static check-Of a computer, consists of one or more tests of computing elements, their interconnections, or both, performed under static conditions. static control-A control system in which control functions are performed by solid-state devices. static convergence-Convergence of the three electron beams at the center of the aperture mask in a color picture tube. The term static applies to the theoretical paths the beams would follow if no scanning forces were present. static decay-In a storage tube, decay that is a function only of storage surface properties, such as lateral or transverse leakage. static detector-A device used to detect presence of static charges of electricity, which could cause explosions in hazardous atmospheres. static device- As associated with electronic and other control or information-handling circuits, the term static refers to devices with switching functions that have no moving parts. static dump--In a computer, a dump performed at a particular time with respect to a machine run, often at the end of the run. static electricity-Stationary electricity --.e., in the form of a charge in equilibrium, or considered independently of the effects of its motion. static electrode potential -The electrode potential measured when there is no net current between the electrode and electrolyte. s t a t i c eliminator -1. A device for reducing atmospheric static interference in a radio receiver. 2. One of a broad range of devices that neutralize nonconductive materials by producing a region of ionized air through which the charged material can pass. Induction static bars consist of a row of grounded metallic points or tufts placed as close as possible to the moving material without touching it. Radioactive static bars employ a coating of radioactive substance facing toward the material to be discharged at a distance of about 1 inch. Electrical static bars have a series of points maintained at high voltage, most frequently capacitively coupled to the voltage source so that they are shock-free even when touched. A small power unit energizes the electrical bars, which are about 1 inch (2.54 cm) from the moving material. Ionizing air guns and blowers also neutralize static. See antistatic sprays. static error-An error that does not depend on the time-varying nature of a variable. staticfield -A field that is present between the poles of either a permanent magnet or an electromagnet that has a direct current passing through its coils. static focus-The focus attained when the electron beam is theoretically at rest or is at the position it would occupy if scanning energy were not applied. static forward-current t r a n s f e r ratio-In a transistor, the ratio, under specified test conditions, of the dc output current to the dc input current. static input resistance-In a transistor, the ratio of the dc input voltage to the dc input current. staticize -1. In a computer, to perform a conversion of serial or time-dependent parallel data into a static form. 2. Occasionally, to retrieve an instruction and its operands from storage prior to executing the instruction. staticizer-A storage device that is able to take information sequentially in time and put it out in parallel.

733

static line regulation -The output voltage variation of a power supply as the line voltage is varied slowly from rated minimum to rated maximum, with the load current held at the nominal value. static: load regulation -The output voltage variation of a power supply as load current is varied slowly from 0 to 100 percent of rating, with the input line voltage held at the nominal value. static: machine-A machine for generating an electric charge, usually by induction. static measurement-A measurement taken under conditions in which neither the stimulus nor the environmental conditions fluctuate. static memory- 1. A type of semiconductor memory in which the basic storage element can be set to either of two states, in which it will remain so long as the power stays on. See also dynamic memory. 2. A type of semiconductor readwrite random-access memory that does not require periodic refresh cycles. 3. An MOS memory that uses a flip-flop as a storage element. It does not need to be refreshed, does not require a clock, and does not lose its contents as long as power is applied. static MOS array-A circuit made up of MOS devices that does not require a clock signal. static noise -Noise resulting from lightning, aurora, or other atmospheric discharges. static power conversion equipment -Any equipment that converts electrical power from one form to another without the use of moving parts such as rotors or vibrators. Static implies the use of semiconductors. static pressure- Also called hydrostatic pressure. The pressure that would exist at a certain point in a medium With no sound waves present. In acoustics, the commonly used unit is the microbar. statio printout-In a computer, a printout of data that is not one of the sequential operations and occurs after conclusion of the machine run. static RAM--Memory that does not require refreshing because of the cell circuit design although it is still volatile, losing data on removal of power. SRAM is more expensive than DRAM, but is faster and requires less control circuitry. static register-A computer register that retains its information in static form. static, regulator-A transmission regulator in which the adjusting mechanism is in self-equilibrium at any setting, and control power must be applied to change the setting. s t a t i c sensitivity-In phototubes, the direct anode current divided by the incident radiant flux of constant value. static shift register-A shift register in which logic flip-flops are used for storage. This technique, in integrated form, results in greater storage-cell size and consequently in shorter shift-register lengths. Its primary advantage is that information is retained as long as power is supplied to the device. A minimum clock rate is not required, and, in fact, the device can be undocked. static skew-1. A measure of the distance that the ouqput from one track is ahead or behind @e., leading or lagging) the output of another track as a tape is transported over the read head. 2. The long-term or average misalignment of a drive's read head as referenced to a master skew tape. Results from gap scatter and misadjustment. static storage-In computers, storage in which the information does not change position (e.g., electrostatic storage, flip-flop storage, binary magnetic-core storage, etc.). The opposite of dynamic storage.

static line regulation - status line static subroutine -A digital-computer subroutine involving no parameters other than the address of the operands. static s w i t c h -A semiconductor switching device in which there are no moving parts. static torque-See locked-rotor torque. static transconductance-In a transistor, the ratio of the dc output current to the dc input voltage. station -1. One or more transmitters, receivers, and accessory equipment required to carry on a definite radiocommunication service. The station assumes the classification of the service in which it operates. 2. An input or output point in a communications system, such as the telephone set in a telephone system or the point at which a business machine interfaces the channel on a leased private line. stationarity-The absence of variations with time in the special intensity and amplitude distribution of random noise. stationary appliance- An appliance that is not easily moved from one place to another in normal use. stationary battery-A storage battery designed for service in a permanent location. stationary contacts -Those members of contact pairs that are not moved directly by the actuating system. stationary field-A constant field-i.e., one in which the scalar (or vector) at any point does not change during the time interval under consideration. stationary wave -See standing wave. station authentication -Security measure designed to establish the authenticity of a transmitting or receiving station. station battery-The electrical power source for signaling in telegraphy. station break- 1. A cue given by the station originating a program, to notify network stations that they may identify themselves to their audiences, broadcast local items, etc. 2. The actual time taken in (1) above. station license-The instrument of authorization for a radio station in the amateur radio service. station-to-station call -A telephone call in which the calling party does not specify that he or she wishes to reach a particular person at the called point. statistical multiplexer-See ITDRI. statistical multiplexing -Multiplexing by providing bandwidth on the multiplexed data line only for those channels that have data available for transmission. No bandwidth is wasted on terminals that are not sending data. s t a t m h o -The cgs electrostatic unit of conductance, mho (absolute). equal to 1.11263 x statohm-The cgs electrostatic unit of resistance, equal to 8.98766 x lo-" ohms (absolute). stator- 1. The nonrotating part of the magnetic structure in an induction motor. It usually contains the primary winding. 2. The stationary plates of a variable capacitor. 3. The conducting surfaces Of a switch. Similar to the commutator in electrical rotating mecl-ianisms. stator of an induction watthour meter-A voltage circuit, one or more current circuits, and a magnetic circuit combined so that the reaction with currents induced in an individual, or a common, conducting disc exerts a driving torque on the rotor. stator plates-The fixed plates of a variable capacitor. status-The present condition of a device. Usually indicated by flag flip-flops or special registers. See flag. status line-A simple method of representing some state of a device in an interconnection scheme.

status register - step generator

status register-Register used in a computer to hold status information inside a functional unit, such as an MPU, a PIC, a DMAC, or an FDC. A typical MPU’s status register provides carry, overflow, sign (“negative”), zero, and interrupt. It could also include parity, enable (interrupts), or mask. status word register-A group of binary numbers that informs the user of the present condition of the microprocessor. statvolt-The cgs electrostatic unit of voltage, equal to 299.796 volts (absolute). stave -One of the number of individual longitudinal elements that comprise a sonar transducer. s t a y cord-A component of a cable, usually a hightensile textile, used to anchor the cable ends at their points of termination to keep any pull on the cable from being transferred to the electrical connection. s t e a d y state-1. A condition in which circuit values remain essentially constant, occurring after all initial transients or fluctuating conditions have settled down. 2. A term used to specify the current through a load or electric circuit after the inrush current is complete. A stable run condition. 3. A characteristic of a condition exhibiting only minor change over an arbitrarily long period. steady-state deviation -The difference between the final value assumed by a specified variable after the expiration of transients and its ideal value. steady-state oscillation -Also called steady-state vibration. Oscillation in which the motion at each point is a periodic quantity. s t e a d y - s t a t e regulation- Slow changes in the output voltage of a power supply following an inputvoltage and/or load-impedance variation; it is usually expressed in volts (AV) or as a percentage of the nominal output. s t e a d y - s t a t e value-The value of a current or voltage after all transients have decayed to negligible values. s t e a d y - s t a t e vibration -See steady-state oscillation. steatite-A ceramic consisting chiefly of a silicate of magnesium. Because of its excellent insulating properties -even at high frequencies -it is used extensively in insulators and as a circuit substrate. steer-To adjust by electrical means the polar response pattern of an antenna or the direction of current in a circuit. steerable antenna- 1. An antenna whose major lobe can be readily shifted in direction. 2. A multielement antenna in which the phase relationship between the elements is electronically adjustable. Thus, the antenna beam can be steered in direction and adjusted for beam width. J.K-’. Stefan-Boltzmann c o n s t a n t - 1.38 x The constant of proportionality between blackbody radiated power and temperature. Stefan-Boltzmann law-The total emitted radiant energy per unit of a blackbody is proportionate to the fourth power of its absolute temperature. Steinmetz coefficent-A factor by which the 1.6 power of the magnetic flux density must be multiplied to give the approximate hysteresis loss of an iron or steel sample in ergs per cubic centimeter per cycle when that sample is undergoing successive magnetization cycles having the same maximum flux density. stenode circuit -A superheterodyne receiving circuit in which a piezoelectric unit is used in the intermediate-frequency amplifier to balance out all frequencies except signals at the crystal frequency, thereby giving very high selectivity.

734 step-To

use the step-and-repeat method.

step and repeat-1. A method of dimensionally positioning multiples of the same or intermixed functional patterns on a given area of a photoplate or a film by repetitions, or contact or projection printing of a single original pattern of each type. 2. A method of positioning multiples of the same pattern on a mask or wafer. 3. A process wherein the conductor or resistor pattern is repeated many times in evenly spaced rows onto a single film or substrate. step-and-repeat camera -A type of camera that has scales or other arrangements by which successive exposures can be lined up and equally spaced on a sheet of film. It is used in manufacturing microcircuits. step-and-repeat fix technique-A mechanical technique that provides for linear indexing of a movable platform carrying a wafer or photographic plate. Applications of this technique are in the testing of a device wafer, and in the masking operation that is part of the process of fabricating microelectronic devices. step-and-repeat printer-A projection printer that is capable of reproducing a multiplicity of images from a master transparency on a single support coated with a photosensitive layer by indexing the receiving material from position to position. Such accessories or attachments find use in microcircuit production. step angle- Also called increment. The nominal angle through which the rotor shaft of a stepper motor moves between adjacent step positions. The angle is specified in degrees. For a 200-step per revolution motor, the step angle is 1.8”. step-by-step automatictelephone system -A switching system that employs successive step-by-step selector switches that are actuated by current impulses from a telephone dial. step-by-step switch -A bank-and-wiper switch in which the wipers are moved by individual electromagnetic ratchets. step calibration -Also called interval calibration. Often confused with sense step, that is, the application of a calibration resistor to produce a deliberate electrical unbalance. step counter-In a computer, a counter used in the arithmetical unit to count the steps in multiplication, division, and shift operations. step down -To decrease the value of some electrical quantity, such as a voltage. step-down transformer-A transformer in which the voltage is reduced as the energy is transferred from its primary to its secondary winding. step fiber-A glass optical fiber that has a core of uniform optical density. That is, there is a step function change between the optical density of the cladding and the optical density of the core. When attenuation of signal was the primary practical problem, step fiber was acceptable, and still is acceptable, for limited information rate application. step function-1. A signal characterized by instantaneous changes between amplitude levels. The term usually refers to a rectangular-front waveform used for making tests of transient response. 2. An essentially nonperiodic waveform that has a transistion from one voltage level to another, the time of which is negligible compared with the total duration of the waveform. response -See transient resstep-function ponse, 2. step generator -A device for testing the linearity of an amplifier. A step wave is applied to the amplifier input and the step waveform observed, on an oscilloscope, at the output.

735 step input-A sudden but sustained change in an input signal. step load change-An instantaneous change in the magnitude of the load current. stepped index fiber- 1. A fiber composed of a core glass of one index of refraction and a different cladding material of a lower index of refraction. The fiber is characterized by a sharp change in index of refraction at the interface of the two materials. 2. An optical fiber that confines most photons to the fiber's core because they ricochet off the surface, back toward the center. Since the photons skip from side to side at different angles while other photons are traveling more or less unimpeded straight down the center of the fiber, the photons constituting a piece of a message gradually become more and more scattered and eventually deteriorate into meaningless noise unless picked up, amplified, and retransmitted by repeaters every few hundred yards or so. stepped oxide-A technique of forming the Si02 layer of each electrode in two thicknesses so that a twolevel potential well can be formed with one voltage. (MIS technology term.) stepper -Photo equipment used to transfer a reticle pattern onto a wafer. Because of its limited field of view, low throughput, and high cost, such equipment is usually used only for feature size smaller than 1.5 microns, where resolution and line-width control are critical. stepper motor-1. A motor whose normal operation consists of discrete angular motions of essentially uniform magnitude, rather than continuous rotation. 2. A digital device that converts electrical pulses into proportionate mechanical movement. Each revolution of the motor shaft is made in a series of discrete identical steps. The design of the motor usually provides for clockwise and/or counterclockwise rotation. (Thus, the stepper is ideally suited for many positional and control applications.) 3. Electromagnetical prime mover that rotates through fixed angles in response to applied pulses. The motor accordingly permits use of digital signals to control mechanical motion or position. In addition, the high holding torque associated with each step permits a stepping motor to replace devices such as brakes and clutches, with a gain in system reliability. 4. A device that converts pulsating direct current into rotary mechanical motion. Each dc pulse rotates the stepper a certain fraction of one revolution. The rotor is magnetically held at its last position. 5. A bidirectional permanent-magnet motor that turns through one angular increment for each pulse applied to it. 6. An electric motor that moves incrementally. 7. A device that translates electrical pulses into precise mechanical movement. The output shaft may deliver rotary or linear motion. steppers-Specially designed electric motors that revolve from pole to pole under control of sequentially energized field windings. Two principle designs are currently available: variable reluctance and permanent magnet. stepping-See zoning, 1. stepping rate-A measure of stepper motor speedthe number of steps through which the motor rotates in a specified time, usually 1 second. stepping relay- Also called rotary stepping switch (or relay) or stepping switch. 1. A multiposition relay in which moving wiper contacts mate with successive sets of fixed contacts in a series of steps, moving from one step to the next in successive operations of the relay. 2. A switch that electromechanically steps its wipers across a bank of contacts. stepping switch -See stepping relay. step-recovery diode-Also called snap varactor. 1. A varactor in which forward voltage injects carriers

step input

- sterance

Stepping relay. across the junction, but before the carriers can combine, the voltage reverses and carriers return to their origin in a group. The result is the abrupt cessation of reverse current and a harmonic-rich waveform. 2. A special form of pn junction in which the charge storage and switching characteristics are optimized for use in microwave-frequency multipliers and comb generators. The device stores charge while in forward conduction, and a large reverse bias current can be obtained until all the charge is removed. The device impedance then goes from a low value to a very high one in transition times as low as 50 picoseconds. step response-Motor-shaft rotational response of a stepper motor to a step command related to time. step-servo motor-A device that, when properly energized by dc voltage, indexes in definite angular increments. steps per revolution-The total number of steps required for the output shaft of a dc stepping motor to rotate 3 W , or one complete revolution. Steps per revolution is calculated by dividing the step angle into 360". steps per second-The number of angular movements accomplished by the motor of a dc stepping motor in 1 second. This figure replaces the rpm figure of a standard drive motor. step stress test -A test consisting of several stress levels applied sequentially for periods of equal duration to a sample; during each period a stated stress level is applied, which is increased from one step to the next. step-strobe marker-A form of strobe marker in which the discontinuity is in the form of a step in the time base. step up-To increase the value of an electrical quantity, such as a voltage. step-up transformer-A transformer in which the voltage is increased as the energy is transferred from the primary to the secondary winding. step voltage-The potential difference between two points on the earth's surface separated by a distance of one pace, or about 3 feet or 91.4 cm, in the direction of maximum potential gradient. step-voltage regulator -A device consisting of a regulating transformer and a means for adjusting the voltage or the phase relation of the system circuit in steps, usually without interrupting the load. steradian -1. The unit of solid angular measure, being the subtended surface area of a sphere divided by the square of the sphere's radius. There are 4n steradians in a sphere. The steradian is the unit of solid angular measurement often used in problems of illumination. 2. The solid angle described by a unit area on a sphere from a point source at unity distance and located at the center of the sphere, e.g., 1 sq ft illuminated at a distance of 1 ft. sterance-Describes the intensity per unit area of a source.

Sterba antenna

- stimulated emission

Sterba antenna -A series-fed array of adjacent, broadside-firing, transposed square loops that have halfwave sides and are spaced a distance of approximately one-half wavelength. Sterba curtain -A stacked dipole antenna array that consists of one or more phased half-wave sections and a quarter-wave section at each end. The array can be oriented for either vertical or horizontal radiation and can be fed at either the center or the end. stereo--A prefix denoting having or dealing with three dimensions. stereo-See stereophonic. stereo adapter-Also called a stereo control unit. A device used with two sets of monophonic equipment to make them act as a single stereo system. stereo amplifier -An audio-frequency amplifier with two or more channels, for a stereo sound system. stereo broadcasting-See stereocasting. stereo cartridge -A phonograph pickup for reproduction of stereophonic recordings. Its high-compliance needle is coupled to two independent voltage-producing elements. stereocasting -Also called stereo broadcasting. Broadcasting over two sound channels to provide stereo reproduction. This may be done by simulcasting, multicasting, or multiplexing. s t e r e o c e p h a l o i d microphone-Two or more microphones arranged to simulate the acoustical patterns of human hearing. stereo control unit -See stereo adapter. stereo microphones- Two or more microphones spaced as required for stereo recording. stereophonic- 1. Designating a sound reproduction system in which sound is delivered to the listener through at least two channels, creating the illusion of depth and of locality of source. 2. A two-channel recording and reproduction system more popularly referred to as stereo. At the recording studio, separate microphones are used for each recorded channel. The correct reproduction of stereo signals in the home gives to the listener a sense of direction of sound and, thus, realism. 3. A multiplechannel sound system or recording in which each channel carries a unique version of the total original performance. When the channels are blended acoustically, they recreate the breadth and depth of the original, adding a new dimension to reproduced sound. At least two channels are required for playback, although more than two may be used in recording. 4. Using two or more channels to create a spatial effect. stereophonic reception -Reception involving the use of two receivers having a phase difference in their reproduced sounds. The sense of depth given to the received program is analogous to the listener's being in the same room as the orchestra or other medium. s t e r e o p h o n i c s e p a r a t i o n -The ratio of the electrical signal caused in the right (or left) stereophonic channel to the electrical signal caused in the left (or right) stereophonic channel by the transmission of only a right (or left) signal. s t e r e o p h o n i c sound s y s t e m -A sound system with two or more microphones, transmission channels, and speakers arranged to give depth to the reproduced sound. s t e r e o p h o n i c subcarrier-A subcarrier employed in FM stereophonic broadcasting that has a frequency that is the second harmonic of the pilot subcarrier frequency. s t e r e o p h o n i c s u b c h a n n e l -The band of frequencies from 23 to 53 kilohertz containing the stereophonic subcarrier and its associated sidebands. s t e r e o p h o n i c s y s t e m -A sound-reproducing system in which a plurality of microphones, transmission

736 channels, and speakers (or earphones) are arranged to afford a listener a sense of the spatial distribution of the sound sources. stereo pickup-A phonograph pickup used with stereo records, wherein a single stylus actuates two transducer elements, one of which reproduces the left channel and the other the right channel. stereo recording -The impressing of signals from two channels onto a tape or disc in such a way that the channels are heard separately on playback. The result is a directional, three-dimensional effect. s t e r e o s c o p e - A small instrument containing a picture support and a pair of magnifying lenses, so arranged that the left eye sees only the picture taken with the left lens of the stereo camera, and the right eye only the right picture. If the camera lenses are separated by the interocular distance, and if the focal lengths of camera and stereoscope lenses are equal, then a true-to-scale, or orthoscopic, reproduction of the scene will be obtained. Stereoscopes are used extensively in photogrammetry for plotting the contour lines in a terrain recorded by aerial photography. stereoscopic-Imagery giving the illusion of being three-dimensional. stereoscopic television -A system of television broadcasting in which the images appear to be threedimensional. stereo separation -A stereo receiver's ability to keep the audio information in each channel separate from the other. stereosonic s y s t e m -A recording technique using two closely spaced directional microphones with their maximum directions of reception 45" from each other. In this way, one picks up sound largely from the right and the other from the left, similar to middle-side recording. stick-CB radio term for any nondirectional antenna. s t i c k circuit-A circuit used to maintain energization of a relay or similar unit through its own contacts. s t i c k i n e s s -The condition of physical interference with the operation of the moving part of an electrical indicating instrument. sticking-In computers, the tendency of a flip-flop to remain in, or to spontaneously switch to, one of its two stable states. stiff -A voltage source whose value is largely independent of the current drawn having a relatively low impedance. stiff ness f a c t o r -The angular lag between the input and output of a servosystem. stilb-Abbreviated sb. The unit of luminance (photometric brightness) equal to 1 candela per square centimeter. still -Photographic or other stationary illustrative material used in a television broadcast. stimularity- -An arbitrary measure of sensitivity to stimulation. It is proportional to the quantum efficiency relative to incident radiation. stimulated emission - 1. The emission of radiation by a system going from an excited electron energy level to a lower energy level under the influence of a radiation field. The emitted radiation is in phase with the stimulating radiation and produces a negative absorption condition. 2. Radiation similar in origin to spontaneous emission, but determined by the presence of other radiation having the same frequency. Since the phase and amplitude of the stimulated wave depend on the stimulating wave, this radiation is coherent with the stimulating wave. The rate of stimulated emission is proportional to the intensity of the stimulating wave. 3. In a laser, the emission of light caused by a signal applied to the laser

737

stimulus

such that the response is directly proportional to, and in phase coherence with, the electromagnetic field. stimulus- 1. See excitation, 1. 2. An input parameter to a unit under test, e.g., voltage or current. See ulso measurand. stirring effect -The circulation in a molten conductive charge due to the combined motor and pinch effects. stitch bond - 1. A wire bond made by laying the wire on the bonding pad and using thermocompression or ultrasonic scrubbing to form the joint. Note that in thermocompression wire bonding, the first termination is a ball bond, while subsequent terminations of the same wire are stitch bonds. 2. A bond made with a capillarytype bonding tool when the wire is not formed into a ball prior to bonding. stitch bonding-A bonding technique in which wire is fed through a capillary tube. A bent section of the wire is bonded to the cantact area by the capillary. The capillary is removed and a cutter severs the wire, forming a new bend for the next bonding operation.

lOOL MOTION FORMS

FLEXIBLE CIRCUIT PAD

Stitch bonding.

stitching-The process of welding thermoplastic materials by successive applications of two small electrodes that are connected to the output of a radiofrequency generator; a mechanism similar to that of a conventional sewing machine is used. stitch wire -A semiautomatic system of point-topoint interconnections in which gold-plated steel pins are pressed into holes in conventional printed-circuit boards. Teflon-insulated 30 AWG nickel wire is bonded to the pins. Electronic components are then soldered to terminal projections on the opposite side of the board. SBL -Abbreviation for Schottky transistor logic. stocliastic -The characteristic of events changing the probabilities of various responses. stochastic process -A random process. stock reel -Also called supply reel or storage reel. On a tape recorder, the reel from which unrecorded or unplayed tape is taken as the machine records on or plays it. stoichiometric impiiriW-A crystalline imperfection caused in a semiconductor by a deviation from the stoichiometric composition. stopband -That part of the frequency spectrum that is subjected to specified attenuation of signal strength by a filter. (The part of the s,pectrum between the passband and the stopband is called the transition region.) stop bit - 1. A signal following a character or block that prepares the receiving device to receive the next character or block. 2. In asynchronous transmission, the last bit, used to indicate the end of a character (normally a mark condition) that serves to return the line to its idle or rest state. Stop-copy-SSee copyguard.

- storage capacity

stop-cycle timer-A timer that runs through a single cycle and then stops until the starting signal is reinitiated. stop element-Also called stop signal. In certain types of serial transmission, the last element of a character, used to ensure that the next start element will be recognized. stop instruction-A machine operation or routine that requires some manual action other than operation of the start key to continue processing. stop opening-In a camera, the size of the apemre that controls the amount of light passing through the lens. stopping potential-The voltage required to stop the outward movement of electrons emitted by photoelectric or thermionic action. stop-record signal-A facsimile signal used for stopping the conversion of the electric signal into an image on the record sheet. stop signal -The signal that transfers facsimile equipment from active to standby. storage- I. The act of storing information. See also store, 1 and 2. 2. A computer section used primarily for storing information in electrostatic, ferroelectric. magnetic, acoustic, optical, chemical, electronic, electrical, mechanical, etc., form. Such a section is sometimes called a memory, or a store, in British terminology. 3. In an oscilloscope, the ability to retain the image of an electrical event on the cathode-ray tube (CRT) for further analysis after that event ceases to exist. This image retention may be for only a few seconds with variable persistence storage, or it may be for hours with bistable storage. 4. The retention of data so that the data can be obtained at a later time. 5. A computer-oriented medium in which data is retained. Primary storage is the internal storage area where the data and program instructions are retained for active use in the system-normally core storage. Auxiliary or external storage is for less active data. These may include magnetic tape, disk, or drum. 6. Synonymous with memory. storage access time-In a computer. the time required to transfer information from a storage location to the local storage register or other location, where the information then becomes available for processing. storage allocation-The assignment of specific sections of computer memory to blocks of data or instructions. storage battery-Two or more storage cells connected in series and used as a unit.

NEGATIVE PLATES

CONTAINER

SEPARATORS

Liauio

ELECTROLYTE

Storage battery.

storage capacity - 1. The amount of information that a storage (memory) device can retain. It is often expressed as the number of words the device can retain (given the number of digits and the base of the standard word). In the case of comparisons among devices that

storage cell - storage tube use different bases and word lengths, the capacity is customarily expressed in bits. For example, a 1 K semiconductor memory can store 1024 bits, a 2 K semiconductor memory can store 2048 bits. Fixed memories usually contain instructions and therefore their capacity is sometimes expressed as the number of words of a certain length that they can hold. For example, 256 x 4 means that the memory can store 256 four-bit words, which makes it a 1 K memory (1024 bits), The same 1 K memory could be a 128 x 8 memory. 2. The number of items of data that a storage device is capable of containing. Frequently defined in terms of computer words, or by a specific number of bytes or characters. storage cell-1. Also called a secondary cell. A cell that, after being discharged, can be recharged by sending an electric current through it in the opposite direction from the discharging current. 2. An elementary unit of storage (e.g., binary cell, decimal cell). 3. A cell that converts chemical energy into electrical energy by a reversible chemical reaction and that may be recharged by passing a current through it in the direction opposite to that of its discharge. storage counter-A counter in which a series of current pulses charge a capacitor, with each pulse raising the voltage to a higher level. A comparator circuit determines when the capacitor voltage reaches a predetermined level. Special techniques are frequently used to linearize the charging curve of the capacitor. storage CRT-A CRT that can retain a visual image for some length of time so that it is not necessary to refresh to avoid flicker. Thus, the picture can be written at a slower rate. The absence of refresh eliminates the refresh memory and reduces display-deflection and videobandwidth requirements. The resultant system is available at a price less than that of most other systems. However, it does have deficiencies, such as low luminance and contrast and the need to rewrite an entire picture if any element is changed. storage cycle -1. The periodic sequence of events that occur when information is transferred to or from a computer storage device. 2. Storing, sensing, and regeneration from parts of the storage sequence. storage device-1. A device into which data can be inserted, in which it can be retained, and from which it can be retrieved 2. A device used for storing data within a computer system, e.g., core storage, magnetic disk unit, magnetic tape unit, etc. storage element - 1. An area that retains information distinguishable from that of adjacent areas on the storage area of charge-storage tubes. 2. The smallest part of a digital-computer storage facility, used for storage of a single bit. storage integrator-In an analog computer, an integrator used to store a voltage in the hold condition for future use while the rest of the computer assumes another computer control state. storage key-In a computer, an indicator that is associated with a storage block or blocks and that requires tasks to have a matching protection key in order to use the blocks. storage laser- Any laser that stores unusually high energy prior to discharge. For example, a storage diode laser is a laser in which some carriers are electrically excited for a time longer than the lasing period. storage life -Also called shelf life. 1. The minimum length of time over which a device, system, or transducer can be exposed to specified environmental storage conditions without changing the performance beyond a specified tolerance. 2. The period during which a battery can be stored and remain suitable for use. 3. The length

738 of time an item can be stored under specified conditions and still meet specified requirements. storage location-1. A computer storage position that holds one machine word and usually has a specific address. 2. A position in storage where a character, byte, or word may be stored. storage medium -Any recording device or medium into which data can be copied and held until some later date, and from which the entire original data can be obtained. storage node- Also called a storage electrode. The structure in a DRAM cell on which the cell’s charge is stored. storage oscilloscope - 1. An instrument that has the ability to store a CRT display in order that it may be observed for any required time. This stored display may be instantly erased to make way for storage of a later event. 2. An oscilloscope used as the output device of analog and digital computers or in the analysis of nonperiodic events and the monitoring of slow signals.

STORAGE CRT

STORAGE

-0

Storage oscilloscope.

storage print-In computers, a utility program that causes the requested core image, core memory, or drum locations to be recorded in either absolute or symbolic form on either the line printer or the delayed printer tape. storage protection-Also called memory protection. In a computer, an arrangement by which access to storage is prevented for reading, writing, or both. storage register- A collection of electronic circuits that allows data (usually one or more computer words) to be stored until needed. storage surface-The part of an electrostatic storage tube on which storage of information takes place. storage temperature-The temperature of the medium immediately adjacent to the device at which the device, without power applied, may be stored indefinitely without deterioration. storage time- 1. The time during which the output current or voltage of a pulse is falling from maximum to zero after the input current or voltage has been removed. 2. An increase in the time needed to turn off a transistor that has been driven into saturation. It results from the fact that a transistor in heavy conduction has many excess charge carriers moving in the collector region. When the base signal is changed to the cutoff level, collector current continues until all the excess charge carriers have been removed from the collector region. storage tube- 1. An electron tube into which information can be stored and later read out, usually a cathode ray tube with a storage screen that will retain charges impressed on it and that can control an electron beam in some way, allowing changes to be read out. 2. A CRT

store

'739 that stores images on a separate storage screen behind the viewing screen in the tub]:. Images then remain on the viewing screen until the stimage screen is erased. Since a storage tube does not have to be refreshed, it can display an extremely large amount of data without flicker. 3. A cathode-ray tube combined with an electrostatic storage unit that is used to introduce, store, and retrieve information translated into electric charge form. 4. A CRT that retains an image for a considerable period without redrawing. store - I. To retain information in a device from which the information can later be withdrawn. 2. To introduce information into the device in (1) above. 3. A British synonym for storage. See storage, 2. store and forward- 1. A data communications technique that accepts packets, stores them until they are validated and complete, and then forwards them to the next node on the packet path. 2. Process of message handling used in a message-switching system. 3. Communications system in which messages received at intermediate routing points are recorded for later retransmission to a further routing point or the ultimate recipient. stored energy-The amount of energy stored in the primary of an electonic ignition system. In an inductive system the stored energy is

w,:= 1/2L12 where W,= energy stored in the primary field, in joules L = priniary inductance, iin henrys I = current in the primary winding, in amperes In a capacitor discharge system,

W,= 1/2CE2 where W,=enNergy stored in the primary capacitor, in joules C = primary capacitance, in farads E = peak primary voltage, in volts

stored-energy welding -A method of welding in which electric energy is accumulated (stored) electrostatically, electromagnetically, or electrochemically at a relatively slow rate and is then released at the required rate for welding. stored program-A set of instructions in the computer memory specifying the operations to be performed and the location of the data on which these operations are to be performed. stored-program computer -Also called generalpurpose computer. 1. A computer in which the instructions specifying the program to be performed are stored in the memory section along with the data to be operated on. 2. A digital computer that, under control of its own instructions, can synthesize, and sometimes alter, stored instructions as though they were data and can subsequently execute these new instructions. stored program !logic-A program stored in a memory unit containing logical commands to the remainder of the memory so that the same processes are performed on all problems. stored-response testing -Comparison of the actual output responses of the device under test with the expected correct output responses stored within the tester. The expected correct responses can be recorded from a known-good device or determined by manual analysis or software simulation. Stored-response testing often implies storage of the actual logic states, although such digital signatures as transition counts could be the stored responses.

- strain-gage alarm s y s t e m

stored routine--In computers, a series of stored instructions for directing the step-by-step operation of the machine. stored writing rate (of a storage oscilloSCOpe)-The highest rate of spot movement that will leave behind a stored image on the face of the cathode-ray tube. Faster spot movement will not leave an image. as in step-response displays with no vertical edges or sine-wave displays with the zero-crossing edges missing. store transmission bridge -A transmission bridge that consists of four identical impedance coils (the two windings of the back-bridge relay and the live relay of a connector, respectively) separated by two capacitors. It couples the calling and catled telephones together electrostatically for the transmission of voice-frequency (alternating) currents, but separates the two lines for the transmission of direct current for talking purposes (talking current). storm loading -The mechanical loading imposed on the components of a pole line by wind, ice, etc., and by the weight of the components themselves. straight dipole-A half-wave antenna consisting of one conductor, usually centerfed. straightforward circuit-A circuit in which signaling is performed automatically and in one direction. straightforward trunking -In a manual telephone switchboard system, that method of operation in which one operator gives the order to another operator over the trunk that later carries the conversation. straight-line capacitance-The variable-capacitor characteristic obtained when the rotor plates are shaped so that the capacitance varies directly with the angle of rotation. straight-line code-The repetition of a sequence of instructions, with or without address modification, by explicitly writing the instructions for each repetition. Generally straight-line coding will require less execution time and more space than equivalent loop coding. If the number of repetitions is large, this type of coding is tedious unless a generator is used. The feasibility of straight-line coding is limited by the space required as well as the difficulty of coding a variable number of repetitions. straight-line f r e q u e n c y -The variable-capacitor characteristic obtained when the rotor plates are shaped so that the resonant frequency of the tuned circuit containing the capacitor varies directly with the angle of rotation. straight-line tracking arm-See radial tonearm. straight-line wavelength -The variable-capacitor characteristic obtained when the rotor plates are shaped so that the wavelength of resonance in the tuned circuit containing the capacitor varies directly with the angle of rotation. strain -The physical deformation, deflection, or change in length resulting from stress (force per unit area). The magnitude of strain is normally expressed in microinches per inch. strain anisotropy-A force that directs the magnetization of a particle along a preferred direction relative to the strain. strain gage-1. A resistive transducer whose electrical output is proportional to the amount it is deformed under strain. 2. A measuring element for converting force, pressure, tension, etc., into an electrical signal. 3. A device for measuring the expansion or contraction of an object under stress, compsising wires that change resistance with expansion or contraction. See also load cell. 4. A sensor that produces a voltage or resistance change when a mechanical force is applied. strain-gage alarm system-An alarm system that detects the stress caused by the weight of an intruder as

strain-gage based

- streaming

Strain gage, 1. he or she moves about a building. Typical uses include placement of the strain-gage sensor under a floor joist or under a stairway tread. strain-gage based -An instrument or transducer with a sensing element composed of bonded or unbonded strain gages. strain-gage sensor -A sensor that, when attached to an object, will provide an electrical response to an applied stress on the object, such as a bending, stretching, or compressive force. strain-gage t r a n s d u c t i o n -The conversion of the measurand into a change in resistance caused by strain in four or, more rarely, two arms of a Wheatstone bridge. strain insulator -A single insulator, an insulator string, or two or more strings in parallel designed to transmit the entire pull of the conductor to, and insulate the conductor from, the tower or other support. strain pickup-A phonograph pickup cartridge using the principle of the strain gage. strain-sensitive cable- An electrical cable that is designed to produce a signal whenever the cable is strained by a change in applied force. Typical uses including mounting it in a wall to detect an attempted forced entry through the wall, fastening it to a fence to detect climbing on the fence, or burying it around a perimeter to detect walking or driving across the perimeter. strain wire -Wire having a composition such that it exhibits favorable strain-gage performance. Also the strain-sensitive filments that constitute the transfer electrical elements in certain transducers. strand - 1. One of the wires or groups of wires of any stranded conductor. 2. A bundle of wires that are twisted together to form a flexible cable capable of withstanding large tensile stress. stranded conductor- 1. A conductor composed of a group of noninsulated wires, usually twisted. 2. See stranded wire. s t r a n d e d wire- Also called stranded conductor. A conductor composed of a group of wires or any combination of groups of wires. The wires in a stranded conductor are usually twisted or braided together. stranding-The twisting together of small wires to form a single larger conductor. Used to provide long flexing life, limpness, ease of handling, or vibration resistance. s t r a n d i n g effect-The property of a stranded conductor to exhibit a higher dc resistance than does a solid conductor of the same material and cross-sectional area. It is due to the relatively longer distance that current must travel when following a stranded conductor’s helically configured wires. strand lay-The distance of advance of one strand of a spirally stranded conductor in one turn, measured axially.

740

strap- 1. A wire or strip connected between the ends of the segments in the anode of a cavity magnetron to promote operation in the desired mode. 2. A bare or insulated conductor run from terminal to terminal of the same or adjacent components. 3. A connecting link or wire between two terminals. 4. To interconnect two or more terminals with strapping wire. strapping -1. In a multicavity magnetron, the connecting together of resonator segments that have the same polarity, so that undesired modes of oscillation are suppressed. 2. An interconnecting strap or straps. stratification -The separation of nonvolatile components of a thick film into horizontal layers during firing, due to large differences in density of the component. It is more likely to occur with a glass-containing conductor paste, and under prolonged or repeated firing. stratosphere-A calm region of the upper atmosphere characterized by little or no temperature change throughout. It is separated from the lower atmosphere (troposphere) by a region called the tropopause. stray capacitance -1. The capacitance introduced into a circuit by the leads and wires connecting the circuit components. 2. Any of the small unintentional capacitances that exist between wires or components in a circuit, particularly capacitance to ground. 3. The capacitance introduced into a circuit by the relative proximity of cables, wires, components, etc. stray current-A portion of the total current that flows over paths other than the intended circuit. stray-current corrosion-Corrosion that results when a direct current from a battery or their external source causes a metal in contact with an electrolyte to become anodic with respect to another metal in contact with the same electrolyte. Accelerated corrosion will occur at the electrode where the current direction is from the metal to the electrolyte and will generally be in proportion to the total current. s t r a y field -The leakage magnetic flux that spreads outward from an inductor and does no useful work. stray magnetic field -Stray magnetic flux from nearby transformers or inductors that can link with conductors or other inductors to produce undesired and interfering noise voltages. s t r a y s -See atmospherics. streaking -Distortion in which televised objects appear stretched horizontally beyond their normal boundaries. It is most apparent at the vertical edges, where there is a large transition from black to white or white to black, and is usually expressed as short, medium, or long streaking. Long streaking may extend as far as the right edge of the picture and, in extreme low-frequency distortion, even over a whole line interval. stream deflection amplifier -A fluidic device that utilizes one or more control streams to deflect power stream, altering the output. streamer b r e a k d o w n -Breakdown caused by an increase in the field due to the accumulation of positive ions produced during electron avalanches. streaming -1. The production of a unidirectional flow of currents in a medium where sound waves are present. 2. A nonstop save-and-restore technique wherein data is transmitted between a tape backup system and Winchester disk in a continuous stream without starting and stopping between data blocks. When all of the data has been transferred, the streaming drive stops. This technology allows for low-cost drives, since the requirement for search and overwrite of a single record is eliminated. A streaming drive does not need highperformance start/stopability, and the expensive servo electronics inherent in that function are also eliminated. 3. A modem’s condition when it is sending a carrier

;74 4 signal on a multidrop communication line and hasn’t been polled. s t r e n g t h of a simple! sound source-The rms magnitude of the total air flow at the surface of a simple source in cubic meters per second (or cubic centimeters per second), where a simlple source is taken to be a spherical source whose radius is small compared with one-sixth wavelength. s t r e n g t h of a sound source-The maximum instantaneous rate of volume displacement produced by the source when emitting a sinusoidal wave. Stress-The force producing strain in a solid. s t r e t c h e d display-A PPI display having the polar plot expanded in one rectangular dimension. The equalrange circles of the normal PPI display become ellipses. stria--A defect in optical materials, such as glass, plastic, or crystals, consisting of a more or less sharply defined streak of material having a slightly different index of refraction than the main body of the material. striation t e c h n i q u e --Rendering sound waves visible by using their individual ability to refract light waves. striking an arc -Starting an electric arc by touching two electrodes together momentarily. striking distance-The effective separation of two conductors having an insulating fluid between them. striking potential- 1. The voltage required to start #anelectric arc. 2. The lowest grid-to-cathode potential at ,which plate current begins flowing in a gas-filled triode. striking voltage -The value of voltage required to start current in a gas tube. string- 1. In a list of items, a group of items that are already in sequence according to a rule. 2. A connected sequence of entities, such as characters, in a command string. 3. A contiguous set of memory addresses each of which contains a single alphanumeric character. Strings are often enclosed in quotes when written in program statements. 4. A line of symbols of indefinite length .treated as a single unit. 5 . The way a computer sees text. 16. A sequence of characters. string electrometeir -An electrostatic voltagemeasuring instrument consisting of a conducting fiber stretched midway between and parallel to two conducting plates. The electrostatic field between the plates displaces the fiber laterally in proportion to the voltage between the plates. string-shadow instrument -An instrument in which the indicating means is the shadow (projected or viewed though an optical system) of a filamentary conductor whose position in a magnetic or an electric field depends on the measured quantity. strip -To remove insulation from a wire or cable. strip (chartrecorder- 1. An instrument for recording variations in the measurement of a quantity over time, using a moving pen on a long strip of paper. 2. Data recorder that provides a record in the form of a graph on a strip of paper. Used to measure parameters whose values do not change rapidly with time (one typical device has a specified response time of 0.25 second, full scale). Strip chad recorders are available in multipen models. strip contacts--Formed contacts in a continuous length, or strip, for use in an automatic installation machine. striping-In flowcharting, the use of a line across the uppe:r portion of a symbol to indicate the presence of a detailed representation elsewhere in the same set of flowcharts. striplime- I. Also called microstrip. Layout and interconnection method used for circuits that operate at very high frequencies, usually above 1 gigahertz. 2. Strip transmission line. 3. A type of microwave transmission line used in integrated circuits, consisting of a narrow,

s t r e n g t h of a simple sound source PRESSURIZED

ON-OFF

VELOCITY/ACCELERATION FEEDBACK

- strobe RECTILINEAR

POSITION FEEDBACK

SIGNAL INPUT

Strip chart recorder.

flat conductor sandwiched between, and insulated from, wider flat grounded conductors. 4. A type of transmission line configuration that consists of a single nmow conductor parallel and equidistant to two parallel ground planes. 5. A microwave conductor on a substrate. strip-loaded diffused optical waveguide -A three-dimensional optical waveguide constructed from a two-dimensional diffused optical waveguide on whose surface has been deposited a dielectric strip of a lower refractive index material, thus confining the electromagnetic fields of the propagating mode to the vicinity of the strip, hence achieving a three-dimensional guide. stripper-A hand-operated or motor-driven tool for removing insulation from wires. stripping -1. A process using either acids or plasma to remove the resist coating of a wafer after the exposure, development, and etching steps. 2. Removing the insulation from a wire. 3. Removing the outer sheath or covering of a cable or wire, thus exposing the insulated wires. strip printer-A peripheral device used with a programmable controller to provide a hard COPY of process number, status, and functions. strip transmission line -A microwave transmission line in the form of a thin, narrow rectangular strip adjacent to a wide ground-plane conductor or between two wide ground-plane conductors. Separation of the conductors usually is achieved by using a low-loss dielectric material on which the conductors are formed by etching. strobe-1. An intensified spot in the sweep of a deflection-type indicator, used as a reference mark for ranging or expanding the presentation. 2. An intensified sweep on a plan-position indicator or B-scope. Such a strobe may result from certain types of interference or it may be purposely applied as a bearing or heading marker. 3. On a console oscilloscope, a line representing the azimuth data generated by a jammed radar site. 4. See electronic flash. 5. An input to a counter or register that permits the asynchronous entry of parallel data. 6. A selection signal that is active when data is correct on a bus. 7. A control signal used to effect information transfers at the hardware level. strobe hold time-The time necessary to strobe parallel data into a counter or register completely. strobe marker-A small bright spot, a short gap, or other discontinuity produced on the line trace of a radar display to indicate the part of the time base that is receiving attention. strobe pulse-Also called sample pulse. 1. A pulse used to gate the output of a core-memory sense amplifier into a trigger in a register. 2. A pulse of duration less than the time period of a recurrent phenomenon, used for making a close investigation of that phenomenon. The frequency of the strobe pulse bears a simple relation to

strobe release time - stud welding that of the phenomenon, and the relative timing is usually adjustable. 3. A pulse that enables a system for a fixed period only. strobe release time-The time that must elapse after the strobe input is disabled before a clocking transition will be recognized by a counter. Strobolume -A trade name used to describe a highintensity electronic stroboscope manufactured by General Radio Company. stroboscope- 1. A light that flashes at a frequency that can be adjusted to coincide with any repeating motion. When the flashing rate is synchronized with the motion, the moving device appears to be stopped. Since the flashing rate is known, the speed of the device can be determined without physically contacting the device. A flashing rate slightly different from the synchronized rate makes the device appear to operate in slow motion. With the stroboscope, such characteristics of motion as whip, vibration, rotation, or chatter can be observed readily. 2. Device that administers brief flashes of light for the purpose of observing the behavior of an object during a short interval of time. One of the most effective means for accomplishing this purpose is a gaseous tube energized by the discharge of a capacitor. Light flashes as short as 1 microsecond have been produced in this fashion. By illuminating moving machinery with intermittent flashes of light at the correct frequency, the machine can be made to appear stationary; by reducing or increasing the flash rate slightly, the machine will appear to move slowly in the forward or reverse direction. Many turntable platters carry a band of dots or lines around their rims, or on their under surfaces, lit by a neon lamp. When the platter speed is adjusted to exactly 331h or 45 rpm, the dots or lines appear to stand still. stroboscopic disc -A printed disc having several rings, each with a different number of dark segments. The pattern is placed on a rotating phonograph turntable and illuminated at a known frequency by a flashing discharge tube. The speed can then readily be determined by noting which pattern appears to stand still or rotate the slowest.

Stroboscopic disc.

stroboscopic light source -An electronic flash tube capable of repeated operation at hundreds or thousands of flashes per second for long periods. stroboscopic tachometer-A stroboscope with a scale calibrated in flashes or in revolutions per minute. The stroboscopic lamp is directed onto the rotating device being measured, and the flashing rate is adjusted until the device appears to be standing still. The speed can then be read directly from the scale. strobotron- 1. A type of glow lamp that produces intense flashes of light when fed with accurately timed voltage pulses. It is used in electronic stroboscopes for visual inspection of high-speed moving parts. 2. A

742 specified cold-cathode gas tube used to apply a shortduration, high-power arc for a stroboscope. stroke -In character recognition, a straight line segment or arc that forms a part of a graphic character. stroke centerline-In character recognition, a line equidistant from the two stroke edges. stroke edge- In character recognition, the region of discontinuity between a side of a stroke and the background, determined by averaging, over the length of the stroke, the irregularities produced by the printing and detection processes. stroke pattern-The pattern, formed by a charactergeneration CRT system, in which the characters are composed of a sequence of line segments (strokes) generated by the electron beam motion with time intervals between successive coordinates. The characters are formed within a rectangle by different combinations of vertical, horizontal, and diagonal strokes, coupled with intensity control signals. stroke speed -Also called scanning-line frequency or scanning frequency. The number of times per minute that a fixed line, perpendicular to the direction of scanning, is crossed in one direction by a scanning or recording spot in a facsimile system. stroke width -In character recognition, the distance, measured in the direction perpendicular to the stroke centerline, between the two edges of a stroke. structured logic design -A method of describing chip design through a hierarchical structure by which each level of component functions can be described by a lower level of functions. structured programming -Also called top-down programming. 1. A systematic procedure for writing programs in modular form with a clear logical structure. Such programs are easy to understand and modify. 2. A set of conventions and rules that, when followed, yields programs that are easy to write, test, modify, and read. 3. Techniques concerned with improving the programming process through better organization of programs and better programming notation to facilitate correct and clear description of data and control structures. stub- 1. A short length of transmission line or cable joined as a branch to another transmission line or cable. 2. A short section of transmission line, open or shorted at the far end, connected in parallel with a transmission line to match the impedance of the line to that of an antenna or transmitter. stub angle-A right-angle elbow for a coaxial rf transmission line, the inner conductor being supported by a quarter-wave stub. stub cable-A short branch from a principal cable. The end is often sealed until used. Pairs in the stub are referred to as stubbed-out pairs. stub matching-Using a stub to match a transmission line to an antenna or load. stub-supported coaxial- A coaxial cable whose inner conductor is supported by short-circuited coaxial stubs. stub tuner-A stub terminated by movable shortcircuiting means and used for matching impedance in the line to which it is joined as a branch. stuck-at-I, stuck-at-0-A particular fault model in which a faulty node remains at a logical 1 or 0 state regardless of the inputs applied. stud-Threaded or serrated insert or post used for connecting wires or terminals. stud welding-A process in which the heat of an electric arc drawn between the fastener and the work melts a quantity of metal, after which the two heated parts are brought together under pressure.

'743

stunt box- 1. A device for controlling the nonprinting functions of a Teletype terminal. 2. A mechanical unit that allows a teletype operator to add control features to the teleprinter; for example, an automatic nonoverline control that prevents printing over a message already typed. Controlling a remote device is another use for the stunt box. stutte!r--In facsimile, a series of undesired black ;mdwhite lines sometimes produced when the signal amplitude changes sharply. STV-See subscription TV. lus;-Also called a needle. 1. The needlelike object used in a sound recorder to cut or emboss the record grooves. Generally it is made of sapphire, stellite, or steel. 'The plural is styli. 2. The pointed element that contacts the record sheet in a facsimile recorder. 3. A small piece of industrial-grade diamond or artificial sapphire, conically shaped, that tracks the groove in a phonograph record. Stylus motion is transmitted through the supporting cantilever to the generating elements in the cartridge. Styli come in several shapes, such as elliptical or spherical. 4. A hand-held object that provides coordinate input to the display device. stylus alignment-The position of the stylus with respect to the record. The correct position is perpendicular. h!; drag-Also called needle drag. The friction between the reproducing stylus and the surface of the recording medium. stylus force-Also called vertical stylus force or tracking force, and formerly called needle pressure or stylus pressure. The downward force, in grams or ounces, exerted on the disc by the reproducing stylus. stylus oscillograph -An instrument in which a pen or stylus records, on paper or another suitable medium, the value of an electrical quantity as a function of time. stylus p r e s s u r e -See stylus force. stylu:; radius-The radius in mils of the spherical tip that contacts the groove wall of a phonograph record. In an elliptical stylus there are two radii. The smaller radius applies to the sides of the stylus looking down on it, and the larger radius applies to the curvature that contacts the V groove, looking along the groove. s u b a s s e m b l y - 1. Parts and components combined into a unit for convenience in assembling or servicing. A subassembly is only pari of an operating unit; it is not complete in itself. 2. A portion of a complete equipment that has one particular function in a single unit for ease of replacement. 3. A part of a complete assembly. Several subassemblies are usually required to complete an assembly. A subassemlbly is not normally capable of delivering an output by itself. subatomic -Smaller than atoms--.e., electrons or protons. subatomic particles-The particles that make up the atom -i.e., protons, electrons, and neutrons. subcarrier-1. A carrier used to generate a modulated wave that is applied, in turn, as a modulating wave to modulate another camer. 2. The carrier used in stereo broadcas,tingto accommodate the subchannel stereo components. Frequency is 38 kHz and is suppressed at the transmitter, leaving only the sidebands, but is reformed at the receiver for detection of the stereo components by doubling the synchronized 19-kHz pilot tone. 3. A second signal "'piggybacked" onto a main signal bo carry additional information. In satellite television transmission, the video picture is transmitted over the main carrier. The corresponding audio is sent via an F'M subcarrier. Some satellite transponders carry as many as four special audio or data subcaniers whose signals may or may not be related to the main programming. 4. A carrier wave that

stunt box

-subharmonic

modulates another higher-frequency carrier. In satellite transmissions, a 6.8 MHz audio subcarrier is often used to modulate the C-band carrier. In television, a 3.58 MHz subcarrier modulates the video carrier on each channel. subcarrier band -A band associated with a given subcarrier and specified in terms of maximum subcarrier deviation. subcarrier c h a n n e l -The channel required to convey the telemetric information of a subcarrier band. subcarrier discriminator tuning unit -A device that tunes the discriminator to a particular subcarrier. subcarrier frequency shift-The use of an audiofrequency shift signal to modulate a radio transmitter. subcarrier oscillator- 1. In a telemetry system, the oscillator that is directly modulated by the measurand or its equivalent in terms of changes in the transfer elements of a transducer. 2. In a color television receiver, the crystal oscillator operating at the chrominance subcarrier frequency of 3.579545 MHz. subcarrier substrate-A small substrate of a film circuit that is mounted in turn onto a larger substrate. subcarrier transmission --A subdivision of carrier transmission designed to increase the capacity of the telephone system. The term id used in other circumstances in a similar fashion to indicate a transmission modulated upon a carrier or subcarrier of a communication channel. subchannel-In a telemetry system, the route for conveying the magnitude of one subcommutated measurand. subchassis-The chassis on which closely associated components, such as those of an amplifier or power supply, are mounted. A subchassis is a building block, easily changed and usable in a variety of systems. subcircuit -A group of physically realizable components that performs a specific function, typically treated as a black box. subclutter visibility-The characteristic that relates to how well a radar equipped with a moving-target indicator can see through clutter. subcommutation-In a computer. the act of connecting one data source to a sampled data system less frequently than other data sources. subcommutation frame--In PGM systems, a recurring integral number of subcommutator words that include the single subcommutation frame synchronization word. The number of subcommutator words is equal to an integral number of primary commutator frames. The length of a subcommutation frame is equal to the total number of words or bits generated as a direct output of the subcommutator. subcycle generator -A frequency-reducing device used in telephone equipment to furnish ringing power at a submuItiple of the power-supply frequency. subdivided capacitor-A capacitor in which several capacitors, known as sections, are mounted so that they may be used individually or in combination. s u b e l e m e n t -A distinguishable portion of a circuit element (e.g., the emitter, collector, and base are subelements of an integrated bipolar transistor). subfigure -User-defined symbols :hat are used repetitively in a drawing. subframe-A complete sequence of frames during which all subchannels of a specific channel are sampled once. s u b h a r m o n i c - 1. A sinusoidal quantity whose frequency is an integral submultiple of the fundamental frequency of its related periodic quantity. A wave with half the frequency of the fundamental of another wave is called the second subharmonic of that wave; one with a third of the fundamental frequency is called a third subharmonic, etc. 2. A harmonic signal whose frequency is less than

s u b j a m m i n g visibility

- substitution method

that of the fundamental, being the fundamental frequency divided by an integral number. 3. A fractional multiple of the fundamental frequency. s u b j a m m i n g visibility-The characteristic that relates to the ability of a particular radar antijam technique to see through jamming signals. s u b j e c t copy- Also called copy. In facsimile, the material in graphic form to be transmitted for reproduction by the recorder. s u b m a r i n e cable-A cable designed for service under water; usually a lead-covered cable with a steel armor applied between layers of jute. submerged-resistor induction furnace-A furnace for melting a metal. It comprises a melting hearth, a descending melting channel closed through the hearth, a primary induction winding, and a magnetic core that links the melting channel and primary winding. submersible transformer -A transformer so constructed that it will operate when submerged in water under predetermined conditions of pressure and time-e.g., a subway transformer. subminiature tube-A small electron tube used generally in miniaturized equipment. subminiaturization -The technique of packaging discrete miniaturized parts, using assembly techniques that result in increased volumetric efficiency (e.g., a hybrid circuit). submultiple resonance-Resonance at a frequency that is a submultiple of the frequency of the exciting impulses. subnanosecond -Less than a nanosecond. s u b p a n e l - An assembly of electrical devices connected together that forms a simple functional unit in itself. subprogram -An independently compilable part of a larger computer program. subrefraction -Atmospheric refraction that is less than standard refraction. subroutine- 1. In computer technology, the portion of a routine that causes a computer to carry out a well-defined mathematical or logical operation. 2. Usually called a closed subroutine. One to which control may be transferred from a master routine, and returned to the master routine at the conclusion of the subroutine. 3. A set of instructions and constants necessary to direct a computer to carry out a well-defined mathematical, special, or logical operation. A subroutine usually resides in mass storage and can be called by the computer whenever that specific function must be performed. It may be used over and over in the same program and in different programs. 4. A subprogram (group of instructions) reached from more than one place in a main program. The process of passing control from the main program to a subroutine is a subroutine call, and the mechanism is a subroutine linkage. Often data or data addresses are made available by the main program to the subroutine. The process of returning control from the subroutine to the main program is subroutine return. The linkage automatically returns control to the original position in the main program or to another subroutine. See also nesting. 5. A short program segment that performs a specific function and is available for general use by other programs and routines. 6. Computer program segment identified by name and bracketed by a “subroutine” and a “return” statement. Execution is transferred to a subroutine when a subroutine call occurs. Subroutines save memory space at the expense of execution speed. subroutine call -See subroutine, 4. s u b r o u t i n e linkage-See subroutine, 4. subroutine reentry-In a computer, initiation of a subroutine by a program before the subroutine has completed its response to another program that called for

744 it. This can occur when a control program is subjected to a priority interrupt. subroutine return -See subroutine, 4. subscriber line-1. A line that connects a central office and a telephone station, private branch exchange, or other end equipment. 2. A telephone circuit from the central office to a subscriber’s telephone. s u b s c r i b e r loop-See local loop, 1. subscriber multiple -A bank of manual-switchboard jacks that provides outgoing access to subscriber lines and usually has more than one appearance across the switchboard. subscriber’s drop-The line from a telephone cable to a subscriber’s building. s u b s c r i b e r ’ s equipment-That portion of a central station alarm system installed in the protected premises. subscriber set-Also called a customer set. An assembly of apparatus for originating or receiving calls on the premises of a subscriber to a communication or signaling service. subscript-A notation for use in a computer to specify one member of an array in which each member is referenced only in terms of the array name. s u b s c r i p t e d variable-1. A variable with one or more following subscripts enclosed in parentheses. 2. A variable that has one or more numbers attached to it, indicating its place in a series or array. subscription television-Abbreviated STV. 1. See pay television. 2. An over-the-air or broadcast pay TV service in which scrambled signals are sent to decoder boxes on TV sets for which viewers pay a fee to receive movies and sports programming. subscription television broadcast program A television broadcast program intended to be received in intelligible form by members of the public only for a fee. subset-1. In a telephone system, the handset or deskset at the station location. 2. Also known as a modem, data set, or subscriber set. A modulatioddemodulation device designed to make business-machine signals compatible with communications facilities. 3. The subscriber’s telephone instrument. Subsidiary Communications Authorization See SCA. subsonic frequency -See infrasonic frequency. s u b s o n i c s p e e d - A speed less than the speed of sound. substation -1. Any building or outdoor location at which electric energy in a power system is transformed, converted, or controlled. 2. A junction point where several transmission and distribution lines are tied together. s u b s t e p - A part of a computer step. s u b s t i t u t e -In a computer, to replace one element of information by another. s u b s t i t u t e c h a r a c t e r -An accuracy-control character, intended to be used in place of a character determined to be invalid, in error, or not representable on a particular device. substitution emulation -See emulation. substitution interference measurement-A measurement in which the noise level of the source being measured is compared to a known level from a calibrated source; for example, an impulse generator for broadband noise or a sine-wave generator for cw. substitution m e t h o d -A three-step method of measuring an unknown quantity in a circuit. First, some circuit effect dependent on the unknown quantity is measured or observed. Then a similar but measurable quantity is substituted in the circuit. Finally, the latter

745 quantity is adjusted io produce a like effect. The unknown value is then assumed to be equal to the adjusted known value. substrate-Also called base material. 1. The supporting material on or in which the parts of an integrated circuit are attached or made. The substrate may be passive (thin film, hybrid) or active (monolithic compatible). 2. A material on the surface of which an adhesive substance is spread for bonding or coating; any material that provides a supporting surface for other materials, especially materials used to support printed-circuit patterns. 3. The physical material )upon which an electronic circuit is fabricated. Used primarily for mechanical support but may serve a useful thermal or electrical function. Also, a material on whose surface an adhesive substance is spread for bonding or coating, or any material ?hat provides a supporting surface for other materials. 4. The base or support layer of a transistor or monolithic chip, which usually constitutes a major proportion of the total volume. When composed of ceramic, glass, or sapphire, the substrate functions mainly as a support during the operations of fabrication and encapsulation. However, when composed of heavily doped semiconductor material it normally performs the additional function of a distributed low-resistance connection to the physically lowest region of the device. 5. That part of an integrated circuit that acts as a support. 4. A slab of insulating material used for strnctural support of thick-film depositions and assembly components, usually high-purity (96 to 99 percent) alumina. See alumina. 7 . The material on which the chips and other components are mounted, comparable to a printed circuit board. Substrate materials in common use include glass, sapphire, silicon, alumina, beryllia, and porcelainized steel. 8. The underlying material on which a microelectronic device is built. ase material -The supporting material on which the elements of a thick-film circuit are deposited or attached. subsurface wave -An electromagnetic wave propagated through water or land. Operating frequencies for communications may be limited to approximately 35 kHz due to attenuation of high ffrequencies. subsynchronous--aving a frequency that is a submultiple of the driving frequency. s ~ ~ s y n c ~ r oreluctance no~s motor- A form of reluctance motor with more salient poles in the primary winding. 4 s a result, the motor operates at a constant average speed that is a submultiple of its apparent synchronous speed. subsystem -1. A major, essential, functional part of a system. The subsystem usually consists of several componeiots. 2. A part or division of a system that in itself has the properties of a system. 3. An organization of computer components (e.g., a tape drive and controller) that comlprises a functional unit that is part of a larger system. subtractive filter-An optical filter that is of a certain color and eliminates that color when placed in the path of white light. subtractive process-A printed circuit manufacturing process in which a conductive pattern is formed by the removal of portions of the surface of a metal-clad insulator by chemical means (etching). subtractor -An operational amplifier circuit in which the output is proportional to the difference between its two input voltages or between the net sums of its positive and negative inputs. subvoice-grade c h a n n e l -A channel whose bandwidth is less than that of a voice-grade channel. Such a channel usually is a subclhannel of a voice-grade line.

(According to common usage, a telegraph channel is excluded from this definition.) subwoofer-A speaker that is specifically made to reproduce the lowest of audio frequencies, between approximately 20 Hz and 100 Hz. success ratio-The ratio of the number of successful attempts to the total number of trials. It is frequently used as a reliability index. suckout-A hole in the response pattern of a tuned circuit due to the self-resonance of components at certain frequencies. sudden commencement -Magnetic stoms that start suddenly (within a few seconds) and simultaneously all over the earth. sudden ionospheric disturbances -The sudden increase in ionization density in lower parts of the ionosphere, caused by a bright solar chromospheric emption. It gives rise to a sudden increase of absorption in radio waves propagated through the low parts of the ionosphere, and sometimes to simultaneous disturbances of terrestrial magnetism and earth current. The change takes place within one or a few minutes, and conditions usually return to normal within one or a few hours. Suhl effect-When a strong transverse magnetic field is applied to an n-type semiconducting filament, the holes injected into the filament are deflected to the surface. Here they may recombine rapidly with electrons and, thus, have a much shorter life, or they may be withdrawn by a probe as though the conductance had increased. suicide control -A control function that uses negative feedback to reduce and automatically maintain the generator voltage at approximately zero. sulfating-The accumulation of lead sulfate on the plates of a lead-acid storage battery. This reduces the energy-storing ability of the battery and causes it to fail prematurely. sulfation-The lead sulfate that forms on battery plates as a result of the battery action that produces electric current. sulfonated polystyrene sensor -Also called Pope cell. An ion-exchange device with good response, accuracy, and long-term stability whose resistance changes exponentially with humidity and temperature. sum-The combination of two electrical signals of the same electrical polarity. The total electhicad energy produced by combining the two different signals of a stereo program. sum channel-A combination of left and right stereo channels identical to the program, which may be recorded or transmitted monophonically. s u m m a r y p u n c h -A punch-card machine that may be attached to another machine in such a way that it will punch information produced, calculated, or summarized by the other machine. s u m m a r y recorder -In computers, output equipment that records a summary of the information handled. summation check-A redundant computer check in which groups of digits are summed, usually without regard to overflow. The sum is then checked against a previously computed sum to verify the accuracy of the computation. summation frequency-A frequency that is the sum of two other frequencies that are produced simultaneously. summation tone -A combination tone, heard under certain circumstances, whose pitch corresponds to a frequency equal to the sum of the frequencies of the two components. summing junction -The input terminal of an operational amplifer that is inverted and has both input and feedback connected to it.

summing point

- superposition theorem

Summing amplr3er.

summing point- 1. A mixing point whose output is obtained by adding its inputs (with the prescribed signs). 2. The input terminal to which the feedback loop from the output of an amplifier is returned. sum of products-A general form of Booleanalgebraic expression that can be implemented readily through the use of electronic gate circuits. sum operand-In a calculator, automatically adds first factors of any sequence of multiplication or division problems. Used when obtaining average unit price and standard deviation. superband -The frequency band from 216 to 300 MHz, used for fixed and mobile radios and additional television channels on a cable system. supercardioid -Similar to cardioid but with a narrower response lobe. supercardioid microphone -A microphone having a cardioid “polar pattern” with an unusually high discrimination between sounds from the front and rear. supercommutation-1. Commutation at a higher rate by connection of a single data input source to equally spaced contacts of the commutator (cross patching). Corresponding cross patching is required at the decommutator. 2. The connection of one data source of a computer to a sampled-data system more frequently than other data sources are connected. superconducting -Exhibiting superconductivity. superconductivity- 1. The ability of certain alloys and metals, such as lead, tin, and vanadium, to conduct electricity with zero resistance. In general, electrical resistance falls as the temperature of a conductor decreases. For certain metals and alloys, resistance abruptly drops to nil when the temperature reaches a specific point near absolute zero. In recent years, superconductivity has been achieved at temperatures as high as -140°C. 2. The decrease in resistance of certain materials (lead, tin, thallium, etc.) as their temperature is reduced to nearly absolute zero. When the critical (transition) temperature is reached, the resistance will be almost zero. superconductors -Materials that exhibit superconductivity. These are materials in which the resistance drops to almost zero at a temperature near absolute zero.

746 Superconductivity is exhibited by many of the metallic elements, their alloys, and intermetallic compounds. super-emitron-See image iconoscope. supergroup-In carrier telephony, five groups (60 voice channels) multiplexed together and handled as a single unit. A basic supergroup occupies the 312 to 552 kHz band. superhet -Slang for a superheterodyne receiver. superheterodyne receiver- 1. A receiver in which the incoming modulated rf signals are usually amplified in a preamplifier and then fed into the mixer for conversion into a fixed, lower carrier frequency (called the intermediate frequency). The modulated IF signals undergo very high amplification in the IF-amplifier stages and are then fed into the detector for demodulation. The resultant audio or video signals are usually further amplified before being sent to the output. 2. A receiver that converts the incoming signal to an intermediate frequency and amplifies the signal at an intermediate frequency before detection. superheterodyne reception-A method of receiving radio waves in which heterodyne reception converts the voltage of the intermediate, but usually superaudible, frequency, which is then detected. superhigh frequency- Abbreviated SHF. The frequency band extending from 3 to 30 GHz (100 to 10 mm). superimpose-In a tape recorder, to record one or more signals over another without erasure, so that when a tape is played back, all recordings can be heard simultaneously. (Particularly useful if one wishes to have a spoken commentw with a musical background.) Supermalloy -Trade name of Arnold Engineering Company for a magnetic alloy with a maximum permeability greater than 1,000,000. supermode laser -A frequency-modulated laser whose output is passed through a second phase modulator driven 180” out of phase and with the same modulation index as the first modulator. All of the energy of the previously existing laser modes is compressed into a single frequency, with nearly the full power of the laser concentrated in that signal. superposed circuit- An additional channel obtained in such a manner from one or more circuits normally provided for other channels that all channels can be used simultaneously, without mutual interference. superposed ringing-Also called superimposed ringing. Party-line telephone ringing accomplished by using a combination of alternating and direct currents; direct current of both polarities is used to provide selective ringing. superposition -The process of adding two or more signals together and having each signal retain its unique identity. superposition theorem -When a number of voltages (distributed in any manner throughout a linear network) are applied to the network simultaneously, the current that flows is the sum of the component currents

OSClLMTOA

Superheterodyne receiver.

‘747 that would flow if the same voltages had acted individually. Likewise, the potentiall difference that exists between any two points is the complonent potential difference that would exist there under the same conditions. superpower-A comparatively large power (sometimes over 1,000,000 watts) used by a broadcasting station in its antenna. superradiance-In lasers, a rapid increase in intensity of fluorescent line emission with increasing excitation (pump) power. This intensity increase and associated line narrowing are attributed to coherent reinforcement of spontaneously emitted photons during a single pass through the active region. superrefraction-Abnormally large refraction of radio waves in the lower layers of the atmosphere, leading to abnomal ranges of operation. superregeneration-1. A form of regenerative amplification frequency used in radio-receiver detecting circuits. (Oscillationsare alternately allowed to build up and are quenched at a superaudible rate. 2. Method used to produce greater regeneration than otherwise possible without the harmful effects of oscillation. See also quench frequency. superregenerative detector -A detector that functions on superregeneration to achieve extremely high sensitivity with a minimum of amplifier stages. superregenerativereceiver -A receiver in which the regeneration is varied in such a manner that the circuit is periodically rendered oscillatory and nonoscillatory. supersensitive relay-A relay that operates on extremely small currents (usually less than 250 microamperes). nic -Faster than the speed of sound (approxmph or 1200 kmih). These speeds are usually referred to by the term mach or mach number. Mach 1 equals the speed of sound; mach 2, twice the speed of sound, etc. supersonic communication-Communication through water by manually keying the sound output of echo-ranging equipment used on ships. supersonic frequency- See ultrasonic frequency. supersonics- 1. The general term covering phenomena associated with speeds higher than that of sound (e.g., aircraft and projectiles that travel faster than sound). 2. The general term covering the use of frequencies above the range of normal hearing. supersonic sounding -A system of determining ocean depths by measuring the time interval between the production of a supersonic wave just below the surface of the water and the arrival of the echo reflected from the bottom. The sounds are transmitted and received by either magnetostriction or piezoelectric units, and electronic equipment is employed to provide a continuous indication of depth (sometimes with a permanent recording). ersync signal-A combination horizontal- and vertical-sync signal transmitted at the end of each scanning line in commercial television. superturnstile antenna -A stacked antenna array in which each element is a batwing antenna. ertweeter-A tweeter used usually in four-way or five-way systems only ‘ior extremely high frequencies. Super Video Graphics Array-See SVGA. superwised lines-Interconnecting lines in an alarm system that are electrically supervised against tampering. See also line supervision. emisor-I. A routine or routines carried out in iresponse to a requirement for changing or interrupting the ilow of operation through a central processing unit, or for performance of input-output operations; therefore, the medium for coordinating the use of resources and maintaining the flow of operations through the central

superpower

- support software

processing unit. Hence, a control routine executed in supervisor state. 2. A program that helps manage the operation of a computer system. supervisory alarm system -An alarm system that monitors conditions or persons or both and signals any deviation from an established norm or schedule. Examples are the monitoring of signals from guard patrol stations for irregularities in the progression along a prescribed patrol route, and the monitoring of production or safety conditions such as sprinkler water pressure, temperature, or liquid level. supervisory circuit -An electrical circuit or radio path that sends information on the status of a sensor or guard patrol to an annunciator. For intrusion alarm systems, this circuit provides line supervision and monitors devices. See also supervisory alarm system. supervisory control- 1. A system by which selective control and automatic indication of remote units is provided by electrical means over a relatively small number of common transmission lines. (Cmier-current channels on power lines can be used for this purpose.) 2. An arrangement for selectively controlling remotely located equipment by electrical means. supervisory control signaling -Characters or signals that actuate equipment or indicators at a remote terminal automatically. supervisory signal-A signal for attracting the attention of an attendant in connection with switching apparatus, etc. supervoltage-A voltage applied to X-ray tubes operating between 500 and 2000 kilovolts. supplementary group -In wire communications, a group of trunks that provides direct connection of local or trunk switching centers by way of other than a fundamental route. supplementaryinsulation-An independent insulation provided in addition to the functional insulation to ensure protection against electrical shock hazard in the event that functional insulation should fail. supply port-In a fluidic device, the pox? at which power is provided to an active device. supply reel - 1. In a tape recorder, the feed reel from which the tape unwinds while playing or recording. 2. On a tape recorder, the reel generally on the left side of the recording head stack. It has a full reel of tape prior to beginning of the recording. supply voltage -The voltage obtained from a power supply to operate a circuit. support chips- 1. Integrated circuits, exclusive of the microprocessor unit (the central processing unit of the microcomputer), that are required to complete a system. These chips must be compatible with the selected microprocessor and are generally part of the same family as the microprocessor unit. The degree of the support chip’s flexibility and availability is what will determine the total capability of a microcomputer system and, thus, becomes a significant factor in the selection of one system over another. 2. Semiconductor chips required to make the MPU functional, such as a clock generator. Includes chips that directly interface with the MPU to enhance its function, such as a DMA or a dedicated MCU supplied by a manufacturer as a standard part. Also includes chips that are not connected directly to the MPU but which enhance its function, such as a modem. A support chip may or may not contain memory. A memoiy with YO ports would be considered a support chip, whereas a c h p containing only memory would be classified as a memory device. support software-A library of software tools used selectively or in total to produce software. This library

suppressed carrier - surface resistance may consist of compiler, link, editors, source update programs, etc. suppressed carrier- 1. That type of system which results in the suppression of the carrier frequency from the transmission medium. The intelligence of a carrier wave after modulation is contained in either sideband, and normally only one sideband is transmitted; the other sideband and carrier frequency are suppressed. The intelligence is recovered at the receiving end by inserting a carrier frequency from a local source that, when combined with the incoming signal, produces the original frequencies with which the transmitting carrier was modulated. 2. A method of transmission in which one or more sidebands are transmitted but the carrier is not transmitted. suppressed-carrier operation -See suppressedcarrier transmission. suppressed-carrier transmission -Transmission in which the carrier frequency is either partially or totally suppressed. One or both sidebands may be transmitted. suppressed time d e l a y -Deliberate displacement of the zero of the time scale with respect to the time of emission of a pulse, in order to simulate electrically a geographical displacement of the true position of a transponder. suppressed-zero instrument -An indicating or recording instrument in which the zero position is below the end of the scale markings. suppression- 1. Elimination of any component of an emission-e.g., a particular frequency or group of frequencies in an audio- or radio-frequency signal. 2. Reduction or elimination of noise pulses generated by a motor or motor generator. 3. Elimination of unwanted signals or interference by means of shielding, filtering, grounding, component relocation, or sometimes redesign. 4. An optical function in online or offline printing devices by which they can ignore certain characters or character groups transmitted through them. 5. The reduction to an acceptable level of a certain frequency or frequencies. suppression pulse-The pulse generated in an airborne transponder by coincidence of the first interrogation pulse and the control pulse. This pulse, also known as a killer pulse, is used to suppress unwanted interrogations from the side lobes. suppressor- 1. A resistor used in an electron-tube circuit to reduce or prevent oscillation or the generation of unwanted rf signals. 2. A resistor in the high-tension lead of the ignition system in a gasoline engine. suppressor grid -A grid interposed between two positive electrodes (usually the screen grid and the plate) primarily to reduce the flow of secondary electrons from one to the other. s u p p r e s s o r pulse-The pulse used to disable an ionized flow field or beacon transponder during intervals when interference would be encountered. s u r f a c e acoustic wave-A sound or acoustic wave that travels on the surface of the optically polished surface of a piezoelectric material. This wave travels at the speed of sound but can pass frequencies as high as several gigahertz. Its amplitude decays exponentially with substrate depth. s u r f a c e analyzer -An instrument that measures or records irregularities in a surface. As a crystal-pickup stylus or similar device moves over the surface, the resulting voltage is amplified and fed to an indicator or recorder that magnifies the surface irregularities as high as 50,000 times. s u r f a c e asperities- Small projecting imperfections on the surface coating of a tape that limit and cause

748 variations in head-to-tape contact. A term useful in discussions of friction and modulation noise. s u r f a c e barrier-A barrier formed automatically at a surface by the electrons trapped there. surface-barrier transistor- Abbreviated SBT. A wafer of semiconductor material into which depressions have been etched electrochemically on opposite sides. The emitter- and collector-base junctions or metal-tosemiconductor contacts are then formed by electroplating a suitable metal onto the semiconductor in the etched depressions. The original wafer constitutes the base region. No longer manufactured. s u r f a c e conductance -Conductance of electrons along the outer surface of a conductor. surface-controlled a v a l a n c h e transistor-A transistor in which the avalanche breakdown voltage is controlled by an external field applied through surface insulating layers, and which permits operation at frequencies up to the 10-GHz range. s u r f a c e diffusion -The high-temperature injection of atoms into the surface layer of a semiconductor material to form the junctions. Usually a gaseous diffusion process. s u r f a c e duct-An atmospheric duct for which the lower boundary is the surface of the earth. surface electromagnetic waves- Waves that propagate along the interface between two different media without radiation, with exponentially decaying evanescent fields on both sides of the interface. s u r f a c e insulation -Also called oxalizing or insulazing. A coating applied to magnetic-core laminations to retard the passage of current from one lamination to another. surface leakage-The passage of current over the surface of an insulator rather than through it. Surface leakage in new components is very low, but when a component is installed in equipment and exposed to dust, dirt, moisture, and other degrading environments, leakage current can increase and cause problems. s u r f a c e mounting -1. Connecting discrete components directly to foil patterns without using holes. 2. A packaging technique that attaches components directly to a circuit board rather than using leads, thus saving space. surface noise-Also called needle scratch. 1. In mechanical recording, the noise caused in the electrical output of a pickup by irregular contact surfaces in the groove. 2. Noise generated by contact of a phonograph stylus with minute particles of dust or other irregularities in a record groove. Can also be caused by excessive wear of a disc or by poor-quality coating on recording tape. s u r f a c e of position-Any surface defined by a constant value of some navigational coordinate. s u r f a c e recombination rate-The rate at which free electrons and holes recombine at the surface of a semiconductor. surface recording-Storage of information on a coating of magnetic material such as that which is used on magnetic tape, magnetic drums, etc. Surface reflection -Also called Fresnel loss. The part of the incident radiation that is reflected from the surface of a refractive material. It is directly proportional to the refractive index of the material and is reduced for a given wavelength by application of an appropriate surface coating. s u r f a c e resistance-The ratio of the direct voltage applied to an insulation system to the current that passes across the surface of the system. In this case, the surface consists of the geometric surface and the material immediately in contact with it. The thin layer of moisture at the interface between a gas and a solid usually has the greatest effect on surface resistance.

surface resistivity - susceptibility

749 surface resistivity-- 1. The resistance between opposite edges of a surface film 1 cm square. Since the length and width of the path are the same, the centimeter terms cancel. Thus, units of surface resistivity are actually ohms. To avoid confusion with usual resistance values, surface resistivity is normally given in ohms per square. It is measured by determining the resistance between two straight conductors I cm alpart, pressed upon the surface of a slab of the material. Water-absorbent materials usually show a lower resistivity than nonabsorbent ones. 2. The resistance of the surface of an insulating material to the dc current. surface states -Discontinuities and contaminants at the surface of a semiconductor device, which tend to change the surface characteristics and promote device parameter instability. surface-temperature resistor- A platinum resistance thermometer designed for installation directly on the surface whose temperature is being measured. surface wave- I. A subclassification of the ground wave. So called because it travels along the surface of the earth. 2. A wave that travels along the interface between two media without radiation, such as an electric wave on the surface of a wire surrounded by air. 3. A radio wave that reaches the reception point from the transmitter by traveling along the surface of the earth rather than by reflection from the ionosphere. surface-wave filter-A filter whose operation is based on the use of the interlaced, deposited electrode pairs and acoustic surface waves on a single crystal substrate. The device operates on traveling-wave principles, not a lumped-element concept.

METALLIZED INTERDIGITAI

Surface-wave device.

surface-wave transmission line -Abbreviated SWTL. Ideally, a nonradiating broadband transmission line that functions by guiding electromagnetic energy in the surrounding air. A surface line allows coupling to the field anywhere along the guide (in contrast to an ordinary waveguide, in which the internal fields are completely screened from external space by metal walls). 1% noncontacting device can be used to couple some or all of the energy to or from the line. surfing - 1. Casually iroaming around the Internet. 2. Exploring the World Wide Web. Commonly called surfing the Net. surfing the Net -Navigating the Internet; usually, random Web browsing. surge - 1. Sudden current or voltage changes in a circuit. 2. A transient variation in the current and/or potential at a point in the circuit. 3. An oversupply of voltage from the power company, lasting as long as several seconds. A strong surge can damage electronic equipment. surge admittance--Reciprocal of surge impedance.

surge-crest ammeter -A special magnetometer used with magnetizable links to measure the crest value of transient electric currents. surge current rating-The maximum current pulse that can be carried by a semiconductor diode for the specified length of time, repetition frequency, waveform, and temperature. surge generator-See impulse generator, 1. surge impedance-See characteristic impedance. surge-limiting capacitor -A capacitor intended to limit the maximum voltage across the terminations by acting as a low impedance to surges. surge suppressor-Also called voltage clipper or thyrector. A two-terminal device (pnp) that will conduct in either direction above a specified voltage and polarity, but otherwise acts as a blocking device to current. It essentially is a back-to-back diode with avalanche characteristics for protecting circuitry from high alternating voltage peaks or transients. surge voltage (or current)- 1. A large, sudden change of voltage (or current), usually caused by the collapse of a magnetic field or by a shorted or open circuit element. 2. The maximum voltage (or current) to which the capacitor should be subjected under any conditions. This includes transients and peak ripple at the highest line voltage. surge-voltage recorder-See Lichtenberg figure camera. surround-The part of a speaker cone by which its outside edge is anchored, usually corrugated. surround sound- 1. A system of audio reproduction that uses four or more speakers to simulate the full three-dimensional effect of a live musical performance or cinematic environment. 2. An audio system that includes front and rear channels and sometimes a front and center channel to stimulate the full three-dimensional effect of a live performance. surveillance- 1. Systemic observation of air, surface, or subsurface areas by visual, electronic, photographic, or other means. 2. Control of premises for security purposes through alarm systems, closedcircuit television (CCTV), or other monitoring methods. 3. Supervision or inspection of industrial processes by monitoring those conditions that could cause damage if not corrected. See nlso supervisory alarm system. surveillance radar-In air traffic control systems, a radar set or system used in a ground-controlied approach system to detect aircraft within a certain radius of an airport and to present continuously to the radar operator information as to the position, in distance and azimuth, of these aircraft. surveillance radar station --In the aeronautical radionavigation service, a land station employing radar to detect the presence of aircraft. survivability-The measure of the degree to which an item will withstand hostile human-made environments and not suffer abortive impairment of its ability to accomplish its designated mission. SUS-See silicon unilateral switch. susceptance- 1. The reciprocal of reactance, and the imaginary part of admittance. It IS measured in siemens. 2. The component of (sinusoidal) current in quadrature with the terminal voltage of a circuit, divided by that voltage. susceptance standard -A standard with which small, calibrated values of shunt capacitance are introduced into 50-ohm coaxial transmission arrays. susceptibility- 1. Ratio of the induced magnetization to the inducing magnetic force. 2. The undesired response of an equipment to emissions, interference, or

susceptibility meter

- sweep j a m m e r

transients, or to signals other than those to which the equipment is intended to be responsive. susceptibility meter -A device for measuring low values of magnetic susceptibility. susceptiveness-The tendency of a telephone system to pick up noise and low-frequency induction from a power system. It is determined by telephone-circuit balance, transpositions, wire spacing, and isolation from ground. suspension -A wire that supports the moving coil of a galvanometer or similar instrument. suspension galvanometer- An early type of moving-coil instrument in which a coil of wire was suspended in a magnetic field and would rotate when it carried an electric current. A mirror attached to the coil deflecting a beam of light, causing a spot of light to travel on a scale some distance from the instrument. The effect was a pointer of greater length but no mass.

SUSPENSION

MAGNET

-

Suspension galvanometer.

sustain-In an organ, the effect produced by circuitry that causes a note to diminish gradually after the key controlling the note has been released. sustained oscillation -1. Oscillation in which forces outside the system but controlled by it maintain a periodic oscillation at a period or frequency that is nearly the natural period of the system. 2. Continued oscillation due to insufficient attenuation in the feedback path. sustained start-An electrical signal for starting a timer that is of any duration longer than the timer setting. sustaining current -The current required to maintain ionization across a spark gap. SVGA- Abbreviation for Super Video Graphics Array. An enhancement from VGA monitors. SVGA monitors can display a resolution up to 1028 x 768 and up to 16.7 million colors. SW-Abbreviation for shortwave. swamping resistor- In transistor circuits, a resistor placed in the emitter lead to mask (minimize the effects of) variations caused in the emitter-base junction resistance by temperature variations. swamp resistance-A small amount of resistance, provided by a resistor with a negative or small positive resistance-temperature coefficient, placed in series with the coil of an electrical indicating instrument to reduce the overall temperature coefficients of the instrument. The resistor also may be used for adjustment of the terminal resistance of the meter. swap-Refers to the process of moving part of a program from the main memory to external storage (tape

750 or disk) so that another piece of program can be moved from external storage to main memory. Swapping reduces computer efficiency, but it allows the system to get along with less memory. swapping - 1. A time-sharing term referring to the transfer of a currently operating program from system memory to an external storage device, the replacement of that program by a program of higher priority, and the restoration of the temporarily stored program following execution of the higher-priority program. 2. A feature of an operating system that permits suspended tasks to be moved to secondary storage in order to generate enough memory space so that the next task of the ready list can be loaded into memory (if it is not already resident) and executed. The task will be swapped back into system memory when it is scheduled to resume execution. This movement to and from secondary storage may occur many times to a given task before its executing is complete. sweating -Soldering by assembling and heating parts previously coated with solder. SWECS- Abbreviation for small wind energy conversion systems. A system with a generating capaEky less than 100.000 kW. sweep-The crossing of a range of values of a quantity for the purpose of delineating, sampling, or controlling another quantity. Examples of swept quantities are the displacement of a scanning spot on the screen of a cathode-ray tube, and the frequency of a wave. sweepable equalizer -An equalizer whose center frequency is continuously variable over a given frequency range, but the Q is not variable. sweep accuracy-The accuracy of the trace horizontal displacement in an oscilloscope compared with the reference independent variable, usually expressed in terms of average rate error as a percent of full scale. sweep amplifier- An amplifier stage designed to increase the amplitude of the sweep voltage. sweep circuit-A circuit that produces, at regular intervals, an approximately linear, circular, or other movement of the beam in a cathode-ray tube. sweep delay -The time between the application of a pulse to the sweep-trigger input of an oscilloscope and the start of the sweep. s w e e p - d e l a y a c c u r a c y -The accuracy of an indicated sweep delay in an oscilloscope, usually specified in error terms. sweep expander-See sweep magnifier. sweep-frequency generator- 1. A signal source capable of changing frequency automatically and in synchronism with a display device. The frequency sweep can be obtained by either mechanical or electronic means. 2. An oscillator that generates an audio or radio frequency that is repetitively swept, low to high or high or low, over a preset band of frequencies to provide a test signal for wideband devices. sweep-frequency record -A test record on which a series of constant-amplitude frequencies have been recorded. Each frequency is typically repeated 20 times per second, starting at 50 Hz and continuing up to 10 kHz or higher. sweep generator -Also called timing-axis oscillator. A circuit that applies voltages or currents to the deflection elements in a cathode-ray tube in such a way that the deflection of the electron beam is a known function of time against which other periodic electrical phenomena may be examined, compared, and measured. sweeping receivers -Automatically and continuously tuned receivers designed to stop and lock on when a signal is found or to continually plot band occupancy. sweep jammer-An electric jammer that sweeps a narrow band of electronic energy over a broad bandwidth.

75 1

sweep linearity -The maximum displacement error of the independent variable between specified points on the display area in an oscillioscope. sweep lockout -A means for preventing multiple sweeps when operating an oscilloscope in a single-sweep mode. sweep magnifier -As0 called sweep expander. A circuit or control for expanding part of the sweep display of an oscilloscope. sweep oscillator- An oscillator used to develop a sawtooth voltage that can be amplified to deflect the electron beam of a cathode-ray tube. See also sweep generator. s w e e p , switching -The alternate display of two or more time bases or other sweeps using a single-beam GIRT. Comparable to dual- or multiple-trace operation of a deflection amplifier. sweep test-Pertaining to cable, checking the frequency response by generaRing an rf voltage whose frequency is varied back and forth through a given frequency range at a rapid constant rate while observing the results on an oscidloscope. s w e e p - t h r o u g h -A jamming transmitter that sweeps through a radio-frequency band and jams each frequency briefly, producing a sound like that of an aircraft engine. sweep voltage-The voltage used for deflecting an electron beam. It may be applied to either the magnetic deflecting coils or the electrostatic plates. swell manual-Also called solo manual. In an organ, the upper manual normally used to play the melody. See UZSQ manual, 2. swept resistance-The portion of the total resistance of a potentiometric transducer over which the slider travels when the device is operated through its total range. swim -The phenomenon in which the constructs on a CRT screen appear to move about their normal position. It can be observed when the refresh rate is slow and is not some multiple or submultiple of Line frequency. In some cases, swim is a result of instability in the digitalto-analog converters in the display controller swimrfling -Lateral shifting of a thick-film conductor pattern on molten glass crossover patterns. swing- 1. The variation in frequency or amplitude of an electricd quantity. 2. The total variation of voltage, currentl 0.1 frequency. 3. The arc traversed by the needle of a meter. ~ w ~ n permeability g ~ ~ c -See ~ reversible permeability. swing,@r- 1. A swinging short. 2. See swing short. swinging -1. Momentary variations in frequency of a received wave. 2. Existing only for short periods. swinging arm-A type of mounting and feed used to move the cutting head at a uniform rate across the recording disc in some recorders. All phonograph pickups are of the swinging-arm type. swinging c h o k e - 1. ,4filter inductor designed with an air gap in its magnetic circuit so its inductance decreases as the current through it increases. When used in a power-supply filter, a swinging choke can maintain approximately critical inductance over wide variation in load current 2. An audio-frequency choke whose core is operated saturated with flux. It is used at the input of a power-supply filter for improved voltage regulation. Its inductance is at a maximum for small currents, and charges (swings) to a minimum for large currents. swing short- Also called swinger. A come-and-go (intermittent) short produced by a pair of wires swinging together in the wind.

sweep linearity - s w i t c h s w i s s - c h e e s e packaging -Also called imitation 2D. A high-density packaging technique in which passive and active components are inserted into holes punched in printed circuit board substrates and attached by soldering or thennocompression bonding or by means of conductive epoxy adhesive. switch - 1. A mechanical or electrical device that completes or breaks the path of the current or sends it over a different path. 2. In a computer, a device or programming technique by means of which selections are made. 3. A device that connects, disconnects, or transfers one or more circuits and is not designated as a controller, relay, or control valve. The term is also applied to the functions performed by switches. 4. A mechanical component for opening or closing (intempting or completing) one or more electrical circuits. In electronics, as opposed to the electrical industry, switches tend to be low-voltage, low-current units scaled to the size of the equipment in which they function. Switches suitable for opening and closing 120- and 240-volt ac line current and various dc and signal-level voltages under 100 volts dc predominate. 5. A mechanical or electronic device designed for conveniently interrupting, completing, or changing connections in electrical circuits whenever desired or necessary. Mechanical types may control more than one circuit by incorporating multiple-contact elements that are controlled by the same actuator. Electronic switches ordinarily control only a single electrical circuit. switchboard- 1. A manually operated apparatus at a telephone exchange. The various circuits from subscribers and other exchanges terminate here, so that operators can establish communications between two subscribers on the same exchange or on different exchanges. 2. A single large panel or an assembly of panels on which are mounted the switches. circuit breakers, meters, fuses, and terminals essential to the operation of electrical equipment. 3. An attended console where telephone subscribers' lines appear for answering and calling. An operator interconnects lines and trunks and supervises the connections. switch detector-A detector that extracts inforination from the input waveform only at instants determined by a selector pulse. switched capacitor -A technique commonly used in analog signal processing to create filtering and signal conditioning circuits. switched line-Also called dial-up line. A c o m u nications link for which the physical path may vary with each usage, such as the public telephone network. s w i t c h e d network- Also called public switched network and switched message network. 1. The network by which switched telephone service is provided to the public. 2. A multipoint network with circuit switching s. The telephone network is a switched network, as are Telex and TWX. switcher-1. A catchall term for a power source that employs switching techniques to achieve higherefficiency regulation. Can include line switchers and conventional transformer/rectifies ac-operated power sources employing switching regulator techniques. 2. A device that allows the pictures from a number of cameras to be viewed on one monitor. 3. See switching power suppIy. switch-fader-A control that p e m t s each of two or more cameras to be selectively fed into the distribution system. The fader permits gradual transition from one camera to another. s w i t c h gear-A general term covering switching, interrupting, control, metering, protective, and regulating devices; also assemblies of these devices and associated interconnections, accessories, and supporting structures,

switch hook

- switching transistor

used primarily in connection with the generation, transmission, and distribution of electric power. s w i t c h hook-A switch associated with the structure on a telephone set that supports the receiver or handset. The switch is operated when the receiver or handset is removed from or replaced on the support. switching- 1. Making, breaking, or changing the connections in an electrical circuit. 2. The action of turning a device on and off. switching amplifier- 1. One whose output stage rapidly switches output power between transistor saturation and cutoff. Average output current is varied by controlling switching frequency, pulse amplitude, duty cycle, or any combination of these factors. Usually, however, switching amplifiers control power by modulating either pulse width or pulse frequency. Switching rates can be varied up to about 100 kHz. Since a switching amplifier controls output power by varying on-off time ratio of the output pulses, amplifier heat dissipation varies little from a nominal rating and is much less than that of amplifiers that consume unused power. However, switching amplifiers generate transients that can upset the operation of nearby electronic circuits. 2. See class D amplifier. switching center -1. A location at which data from an incoming circuit is routed to the proper outgoing circuit. 2. A group of equipment within a relay station for automatically or semiautomatically relaying communications traffic. 3. A location where an incoming calymessage is automatically or manually directed to one or more outgoing circuits. 4. See switching office. switching characteristics- An indication of how a device responds to an input pulse under specified driving conditions. switching circuit-A circuit that performs a switching function. In computers, this is performed automatically by the presence of a certain signal (usually a pulse signal). When combined, switching circuits can perform a logical operation.

F 2 T

Simple switch.

Vacuum tube.

Triac.

Switching circuits.

switching coefficient-The derivative of applied magnetizing force with respect to the reciprocal of the

752 resultant switching time. It is usually determined as the reciprocal of the slope of a curve of reciprocals of switching times versus the values of applied magnetizing forces, which are applied as step functions. switching control-An installation in a wire system where telephone or teletypewriter switchboards are installed to interconnect circuits. switching current -The current through a device at the switching voltage point. switching device -Any device or mechanism, either electrical or mechanical, that can place another device or circuit in an operating or nonoperating state. switching differential-The difference between the operate and release points of a switch, caused by hysteresis. It can be in units of amperes, volts, inches, gausses, etc. See hysteresis. switching diode -A diode that has a high resistance (corresponding to an open switch) below a specified applied voltage but changes suddenly to a low resistance (closed switch) above that voltage. switching equipment -Equipment located in the telephone company offices that makes the interconnection between the station equipment of two or more subscribers. switching hysteresis-The principle associated with sensors, such that the operate point is not at the same level as the release point. In solid-state sensors it is accomplished with negative-resistance devices, and in mechanical switches it results from the storing of potential energy before the transition occurs. switching mode -A way of utilizing a vacuum tube or transistor so that (except for negligibly small transition times) it is either in cutoff or saturation. A transistor operated in this mode can switch large currents with little power dissipation. switching off ice -Also called switching center. A location where either toll or local telephone traffic is switched or connected from one line or circuit to another. switching pad -A transmission-loss pad automatically inserted into or removed from a toll circuit for different desired operating conditions. switching power supply- Also called switcher. A power supply (usually dc output) that achieves its output regulation by means of one or more active power-handling devices that are alternately placed in the off and on states. Distinguished from linear or dissipative power supplies, in which regulation is achieved by power-handling devices whose conduction is varied continuously over a wide range that seldom (if ever) includes the full off or full on condition. See figure on page 753. switching regulator-A power supply design that achieves efficient regulation by commuting the input voltage into a filter circuit. switching time- 1. The interval between the reference time and the last instant at which the instantaneous-voltage response of a magnetic cell reaches a stated fraction of its peak value. 2. The interval between the reference time and the first instant at which the instantaneous integrated-voltage response reaches a stated fraction of its peak value. 3. The time for a multiplexer to change from one channel to the next with the new output signal remaining within a specified percentage of its final value. Expressed for a maximum voltage transition. switching transients-Transient voltage spikes that appear at a multiplexer’s output when the multiplexer is switched from one channel to another and one of the switches is turned off. Such spikes may cause inaccurate measurements if output is sampled, digitized, or integrated during this time. switching transistor -A three-terminal device with one terminal controlling the electrical impedance

switching trunk

753 HIGH-FREOUENCY AC VOLTAGE

CHOPPED DC VOLTAGE

UNREGULATED DC VOLTAGE

- symbolic code

REGULATED DC VOLTAGE

SERIES-PASS

REMOTE SENSlFlG LINES

Schematic. OC OUTPUT

AC INPUT

t

I TRANSFORMER-

Block diagram

Switching power supply.

between the other two. Typical transistor switching circuits include inverters, converters, switching voltage regulators, and relay and solenoid drivers. switching trunk-A trunk that runs between alongdistance office and a local exchange office and is used for completing a long-distance call. switching voltage -The maximum forward voltage a device can sustain without breaking over into full conduction. switchplate-A small plate attached to a wall to cover a push-button or other type of switch. s w i t c h register-A physical register made up of a number of manual switches, typically equal to the number of bits in the computer, and generally located on the computer control panel. The switch register is used to manually enter addresses and data into the computer’s memory and to manually intervene in program execution. The function performed by a physical switch register can also be implemented by software, with switches being set through a terminal device or a memory location. s w i t c h room -That part of a telephone central office building that houses switching mechanism and associated apparatus. switchtail ring counter-A type of ring counter in which the output of one stage is inverted before being applied as an input to the next stage. An even number of states equal to 2n (where n is the number of flip-flops) normally is produced. For example, a modulo-10 counter can be made from five flip-flops. Each flip-flop changes states on every fifth count. Decoding of all 10 states is accomplished conveniently with 10 two-input gates. A switchtaill ring counter will contain the complement of the information it contained initially after n clock pulses, and will contain the initial information again after 2n clock pulses.

sequence of switches through s w i t c h train -A which connection must be made when a circuit between a calling telephone and a called telephone is established. SWL-Shortwave listener; one who tunes the shortwave bands as a hobby. SWR -Abbreviation for standing-wave ratio. SWR bridge -See standing-wave-ratio bridge. SWR meter-An external or built-in circuit that measures the standing-wave ratio at the transceiver end of the antenna transmission line. S W L -Abbreviation for surface-wave transmission line. syllabic companding -Companding in which the effective gain variations are made at speeds allowing response to the syllables of speech but not to individual cycles of the signal wave. syllable articulation -Also called percent of syllabic articulation. The percent of articulation obtained when the speech units considered are syllables (usually meaningless and usually of the consonant-vowelconsonant type). symbol - 1 . A simplified design representing a part in a schematic circuit diagram. 2. A letter representing a particular quantity in formulas. symbolic- 1. Having to do with the representation of something by a conventional sign. 2. Represented by the usual alphanumeric symbols. symbolic address -Also called a floating address. In digital-computer programming, a label chosen in a routine to identify a particular word, function, or other information independent of the location of the information within the routine. symbolic code- Also called pseudocode. A code by which programs are expressed in source language; that is, storage locations and machine operations are

symbolic coding - synchro differential motor referred to by symbolic names and addresses that do not depend on their hardware-determined names and addresses. Contrasted with computer code. symbolic coding -In digital computer programming, any coding system using symbolic rather than actual computer addresses. symbolic debugger -A system software interactive debugging utility in which the debugging software has access to program symbol tables, and a programmer can refer to memory location names rather than absolute addresses. This is a valuable facility for use with relocatable code or paged systems in which task code may not be loaded at the same memory address each time it executes. symbolic deck-A deck of cards punched in programmer coding language rather than binary language. symbolic execution-Reconstructing the logic and actions along a program path via symbolic rather than actual data. symbolic language-Human-oriented programming language. Any programming language prepared in coding other than a specific machine language, and which thus must be translated by compiling, assembly, etc. symbolic-language programming-Also called assembly-language programming. The writing of program instructions in a language that facilitates the translation of programs into the binary code through the use of mnemonic convention. symbolic layout editors-Software design tools that allow the designer to place symbols representing circuit elements (for example, transistors, logic gates, or even registers) instead of having to redesign them each time they are used. symbolic logic-A special computer or control system language composed of symbols that the instrumentation can accept and handle. Combinations of these symbols can be fed in to represent many complex operations. symbolic programming -A program using symbols instead of numbers for the operations and locations in a computer. Although the writing of a program is easier and faster, an assembly program must be used to decode the symbol into machine language and assign instruction locations. symbol table -A table constructed by an assembler or compiler to bind symbolic labels to their actual addresses. symmetrical-Balanced; Le., having equal characteristics on each side of a central line, position, or value. symmetrical alternating quantity-An alternating quantity for which all values separated by a half period have the same magnitude but opposite sign. symmetrical avalanche rectifier -An avalanche rectifier that can be triggered in either direction. After triggering, it presents a low impedance in the triggered direction. symmetrically cyclically magnetized condition -The condition of a cyclically magnetized material when the limits of the applied magnetizing forces are equal and of opposite sign. symmetricaltransducer (with respect to specified terminations) -A transducer in which all possible pairs of specified terminations can be interchanged without affecting the transmission. symmetricaltransistor-A transistor in which the collector and emitter are made identical, so either can be used interchangeably. sync- 1. Short for synchronous, synchronization, synchronizing, etc. 2. The maintenance of correct time relationships between events, i.e., synchronization. syncable -Capable of being synchronized.

754 sync compression- 1. The reduction in gain applied to the sync signal over any part of its amplitude range with respect to the gain at a specified reference level. 2. The reduction in the amplitude of the sync signal, with respect to the picture signal, occurring between two points of a circuit. sync generator-1. An electronic device that supplies pulses to synchronize a television system. 2. A device for generating a synchronizing signal. synchro- 1. A small motorlike device containing a stator and a rotor and capable of transforming an angular-position input into an electrical output, or an electrical input into an angular output. When several synchros are correctly connected together, all rotors will line up at the same angle of rotation. 2. A range of ac electromechanical devices that are used in data transmission and computing systems. A synchro provides mechanical indication of its shaft position as the result of an electrical input, or an electrical output that represents some function of the angular displacement of its shaft. Such components are basically variable transformers. As the rotor of a synchro rotates it causes a change in synchro voltage outputs. Major types or classes of synchros include torque synchros, control synchros, resolvers, and induction potentiometers (linear synchro transmitters).

I

, Synchro.

synchro control differential generator-A rotary component for modifying the synchro control generator output signal to correspond to the addition or subtraction from the generator shaft angle. Usually used with a synchro control generator and synchro control transducer. synchro control generator-A rotary component for transforming the shaft angle to a corresponding set of electrical signals for ultimate retransformation to the shaft position in a remote location. synchro control transformer-A rotary component that accepts signals from a generator or differential generator for reconversion to the shaft angle with the aid of a servomechanism. Often used by itself as an angleto-signal transducer, but usually with a synchro control generator and synchro control differential generator. synchro differential generator-A synchro unit that receives an order from a synchro generator at its primary terminals, modifies this order mechanically by any desired amount according to the angular position of the rotor, and transmits the modified order from its secondary terminals to other synchro units. synchro differential motor-A motor that is electrically similar to the synchro differential generator except that a damping device is added to prevent oscillation. Its rotor and stator are both connected to synchro generators, and its function is to indicate the sum of or difference between the two signals transmitted by the generators.

755

synchro generator - synchronous demodulator

synchiro generator-A synchro that has an elec~licaloutput proportional to the angular position of its rotor. Synchroguide -A type of control circuit for horizontal scanning in which the sync signal, oscillator voltage pulse, and scanning volltage are compared and kept in synchronism. synchiro motor-A synchro in which the rotor-shaft position is dependent on the electrical input. synchronism- 1. The phase relationship between two or more quantities of the same period when their phase difference is zero. 2. Applied to the synchronous motor, &e condition under which the motor runs at a speed that is directly related to the frequency of the power applied to the motor and is not dependent upon other variables. synchronization - 1. The precise matching of two waves or functions. 2. The process of keeping the electron beam on the television screen in the same position as the scanning beam at the transmitter. 3. In a carrier, that degree of matching in frequency between the carrier used for modulation and the carrier used for demodulation that is sufficiently accurate to permit efficient functioning of the system. 4. The maintenance of correct time relationships between events. Examples in recording include synchronization of sound and film for motion-picture use, synchronization of a slide-changing projector with a tape by means of signals recorded on the tape, and selective synchronization, used to synchronize several tracks when they are recorded one at a time. synchronization error -In navigation, the error due to imlperfect timing of two operations (may or may not include the signal transmission time). ~ y n c ~ r o n ~ z amode-The tio~ level at which data on a communications link is synchronized. Start-stop mode denotes character-by-character synchronization; synchronous mode denotes frame-by-frame (or block level) synchronization. s ~ ~ c h ~ o npulses i ~ a -Pulses t ~ ~ ~originated by the transmitting equipment and introduced into the receiving equipment to keep the equipment at both locations operating in step. s ~ ~ c h r o n ~1.z To ~ - adjust the periodicity of an electrical system so that it bears an integral relationship t(o the frequency of the periodic phenomenon under investigation. 2. To lock one element of a system into step with another. The term usually refers to locking a receiver to a transmitter, but it can refer to locking the data terminal equipment bit rate to the data set frequency. 3. In television, to maintain two or more scanning processes in phase. synchronized sweep-A sweep that would freerun in the absence of an applied signal, but is synchronized by the presence of the signal. s y ~ c h ~ o nwaveformsiz~~ A condition whereby the timing of one waveform is related to the timing of another waveform. synchronizer- 1. The component of a radar set that generates the timing voltage for the complete set. See also timer, 3.2!. A computer stor,agedevice used to compensate for a difference in a rate of flow of information or time of occurrence of events when information is being transmitted from one device to another. synchronizing-pulse selector-A circuit used to separate synchronizing pulses from commutated pulse trains. synchronizing reactor -A current-limiting reactor that is connected momentarily across the open contacts of a circuit-i.nterruptingdevice for synchronizing purposes.

synchronizing relay-A relay that functions when two alternating-current sources are in agreement within predetermined limits of phase angle and frequency. synchronizing separator-See amplitude separator. synchronizing signal -See sync signal. synchronous-1. In step or in phase, as applied to two devices or machines, 2. A term applied to a computer in which the performance of a sequence of operations is controlled by equally spaced clock signals or pulses. 3. Having a constant time interval between successive bits, characters, or events. The term implies that all equipment in the system is in step. 4. Operation of a switching network by a clock pulse generator. More critical than asynchronous timing but requires fewer and simpler circuits. 5. Describes modems, terminals, and transmissions in which all bits are of equal duration. Synchronous transmissions must always be associated with a clocking signal to keep the receiver and transmitter in step. 6. A communications protocol in which the data characters and bits are transmitted at a fixed rate with the transmitter and receiver synchronized. This eliminates the need for start-stop elements and provides greater transmission efficiency. 7. Term used to describe a device or system in which all events occur in a predetermined timed sequence. synchronous booster converter-A synchronous converter connected in series with an ac generator and mounted on the same shaft. It is used for adjusting the voltage at the commutator of the converter. synchronous capacitor-A rotating machine running without mechanical load and designed so that its field excitation can be varied in order to draw a leading current (like a capacitor) and thereby modify the power factor of the ac system or influence the load voltage through such change in power factor. synchronous clock- An electric clock driven by a synchronous motor, for operation on an ac power system in which the frequency is accurately controlled. synchronous communication - A method of transferring serial binary data between computer systems or between a computer system and a peripheral device; binary data is transmitted at a fixed rate, with the transmitter and receiver synchronized. Synchronization characters are located at the beginning of each message or block of data to synchronize the flow. synchronous communications satellite-A communications satellite whose orbital speed is adjusted so that the satellite remains above a particular point on the surface of the earth. synchronous computer-A digital computer in which all ordinary operations are controlled by clock pulses from a master clock. synchronous converter -A synchronous machine that converts alternating current to direct current and vice versa. The armature winding is connected to the collector rings and commutator. synchronous data communications-A serial YO hardware protocol in which the transmitter and receiver are synchronized to a common clock signal. synchronous demodulation -In a color television receiver, the process of separately detecting the I and Q sidebands of the color subcarrier system. synchronous demodulator -Also called a synchronous detector. 1. A demodulator in which the reference signal has the same frequency as the carrier or subcarrier to be demodulated. It is used in color television receivers to recover either the I or the Q signals from the chrominance sidebands. 2. A double-balanced, full-wave demodulator. The basic operation is similar to that of the chroma demodulation system except that the

synchronous detector

- synchrotron

45.75-MHz reference carrier is generated inside of the IC rather than in a separate crystal oscillator referenced to burst signal as is done with the chroma. The only signals that are detected are the ones that are in phase with the demodulation signal produced by the carrier generator. Signals that are not synchronized with the IF carrier, such as the adjacent-channel video and sound carriers and random noise, are not detected. This requires less extensive trapping of interfering signals in earlier IF stages. 3. A detector sensitive to signals close to or at a particular frequency that is the same as the frequency of a control signal, applied independently. The synchronous detector is also phase-sensitive and is used in bridge and other null circuits as an antinoise device. synchronous detector -See synchronous demodulator. synchronous device-A device that transfers information at its own rate and not at the convenience of any interconnected device. synchronous gate-A time gate in which the output intervals are synchronized with the incoming signal. synchronous generator-A circuit designed to synchronize an externally generated signal with a train of clock pulses. The generator produces precisely one output pulse for each cycle of the input signal. The output pulse thus has a width equal to that of the period of the clock pulse train. synchronous idle character - A communication control character used to provide a signal for synchronization of the equipment at the data terminals. synchronous induction motor-A motor with the rotor laminations cut away, exposing the rotor and definite poles. Also, a motor that has definite poles, but the poles are permanent magnets. This term is also applied to a wound-rotor (slip-ring) motor that is started as an induction motor and, when near synchronism, has dc applied to two of the rings to operate as a true synchronous motor. synchronous inputs- 1. Those inputs of a flip-flop that do not control the output directly, as do those of a gate, but only when the clock permits and commands. Called J and K inputs or ac set and reset inputs. 2. Inputs to a flip-flop that affect the output only at the time the clock signal changes from a particular level to the other level. synchronous inverter-See dynamotor. synchronous logic -The type of digital logic used in a system in which logical operations take place in synchronism with clock pulses. synchronous machine-1. A machine that has an average speed exactly proportionate to the frequency of the system to which it is connected. 2. A system whose operation is tied to data-independent timing or a system clock. synchronous modem- A line-termination unit that uses a derived clocking signal to perform bit synchronization with incoming data. synchronous motor - 1. An induction motor that runs at synchronous speed. Its stator windings have the same arrangement as in nonsynchronous induction motors, but the rotor does not slip behind the rotating magnetic stator field. 2. Type of ac electric motor in which rotor speed is related directly to frequency of power supply. 3. A motor that runs at a speed in step with the power-station frequency (fundamental or harmonic of the alternator speed). Often started as an induction motor and converted to synchronous operation as it approaches synchronous speed. 4. An alternating-current motor that operates at a speed determined solely by the frequency

756 of the supply power and does not slow down as its load increases. synchronous multiplexer -A multiplexer that can time-interleave two data streams into one higher-speed stream. In a system using these types of multiplexers, all peripheral equipment in the system must be under the control of a master synchronizing device or clock. synchronous operation-Operation of a system under the control of clock pulses. synchronous rectifier-A rectifier in which contacts are opened and closed at the correct instant by either a synchronous vibrator or a commutator driven by a synchronous motor. synchronous shift register- Shift register that uses a clock for timing of a system operation and in which only one state change per clock pulse occurs. synchronous speed-A speed value related to the frequency of an ac power line and the number of poles in the rotating equipment. Synchronous speed in revolutions per minute is equal to the frequency in hertz divided by the number of poles, with the result multiplied by 120. synchronous system-1. A system in which the sending and receiving instruments are operating continuously at substantially the same frequency and are maintained in a desired phase relationship. 2. A system in which all events are synchronized by a common clock pulse. synchronous torque- 1. The maximum load torque with which a motor can be loaded after it comes to synchronous speed. These torques are usually higher than starting torques. 2. Torque that a synchronous motor develops after dc field excitation is applied; the total steady-state torque available to drive the load. synchronous transfer- An I/O transfer that takes place in a certain amount of time without regard to feedback from the receiving device. synchronous transmission - 1. Data transmission in which characters and bits are transmitted at a fixed rate, with the transmitter and receiver synchronized by a clock source. This eliminates the need for individual start bits and stop bits surrounding each byte, thus providing greater efficiency. Compare with asynchronous transmission. 2. Transmission in which the sending and receiving instruments operate continuously at the same frequency and are held in a desired phase relationship by correction devices. synchronous vibrator- An electromagnetic vibrator that simultaneously converts a low dc voltage to a low alternating voltage and applies it to a power transformer, from which a high alternating voltage is obtained and rectified. In power packs, it eliminates the need for a rectifier tube. synchroscope- 1. An instrument used to determine the phase difference or degree of synchronism of two alternating-current generators or quantities. 2. An oscilloscope on which recurrent pulses or waveforms may be observed, and which incorporates a sweep generator that produces one sweep for each pulse. synchro system-A system for obtaining remote indication or control by means of self-synchronizing motors such as selsyns and equivalent types. synchro-torque receiver- A relatively low-impedance positioning device that generates its own torque when driven by a suitable synchrc-torque transmitter. synchro-torque transmitter-A positioning device that generates electrical information of sufficient power to drive a suitable torque receiver. synchrotron -A device for accelerating charged particles (e.g., electrons) in a vacuum. The particles are guided by a changing magnetic field while being

757 accelerated many times in a closed path by a radiofrequency electric field. synchirotron noise-Radio noise caused by the acceleration of charged particles to high speeds. synchirotron radiation -Also called magnetic bremsstrahlung. The radiation produced by relativistic electrons as they travel in a region of space containing magnetic fields. sync level-The levell of the peaks of the synchronizing signal. s y n c limiter-A circuit used in television circuits to prevent sync pulses from exceeding a predetermined amplitude. sync pulse-Part of the sync signal in a television system. s y n c section-A color TV circuit comprising a lreyer, burst amplifier, phase detector, reactance tube, subcarrier oscillator, and quadrature amplifier. sync separator-The circuit that separates the picture signals from the control pulses in a television system. s y n c signal -Also called a synchronizing signal. The signal employed for synchronizing the scanning. In television it is composed of pulses at rates related to the line and field frequencies. sync-signal generator -A synchronizing signal generator for a television receiver or transmitter. syntax-1, The rules that govern the structure of (expressionsin a language. 2. The grammar of a programming language, that is, d e s about how commands may be used and how they fit together. 3. Set of grammatical rules defining valid constructs of a language. 4. Structure of expressions in a language and the rules governing the structure of a language. 5 . The way in which words are put together to form valid computer commands. synthesis-The combination of parts to form a whole. synthesizer- 1. A device that can generate a number of crystal-controlled frequencies for multichannel communications equipment. 2. A system for generating a precise and stable frequency whose accuracy is determined by quartz crystal oscillators, instead of inductance/capacitance tuned circuits. As compared with the latter, a synthesizer circuit can result in a tuner or transmitter whose frequency setting is known with great accuracy and that is free from drift or other tuning errors. True digital tuners (as opposed to those which tune conventionally but have digital frequency displays) use synthesizers in order to advance in discrete steps from one exact channel frequency to another without passing through the unwanted frequencies in between. s y n t h e s i z e r f r e q u e n c y meter- A device for measuring frequency by utilizing a synthesized crystalbased signal for the internally generated signal. s y n t h e t i c display generation--Logical andnumerical processing to display collected or calculated data in symbok form. s y n t h e t i c s p e e c h --.Artificially reproduced acoustic signals that are recognizable as human speech. syntony -The condition in which two oscillating circuits have the same resonant frequency. system -1. An assembly of component parts linked together by some form of regulated interaction into an organized whole. 2. A collection of consecutive operations and procedures required to accomplish a specific objective. 3. A collection of units combined to work a larger integrated unit having the capabilities of all the separate units. 4. The complete computer assembly, with GBU, memory, YO,plus any required devices or peripherals for the application intended. 5. A set of interconnected

synchrotron

noise - system of units

elements constituted to achieve a given objective by performing a specific function. system analysis- The examination of an activity, procedure, method, technique, or business to determine what must be accomplished and how the necessary operations may best be accomplished by using electronic data-processing equipment. s y s t e m a t i c distortion -Distortion of a periodic or constant nature, such as bias or characteristic distortion; the opposite of fortuitous distortion. systematic error- 1. The magnitude and direction of the tendency of a measuring process to measure some quantity other than the one intended. 2. An error of the type that has an orderly character that can be corrected by calibration. s y s t e m a t i c inaccuracies--Those inaccuracies due to inherent limitations in the equipment. system bus-A general-purpose backbone used to connect processors, memory, and peripherals to form a computer system. s y s t e m deviation-The instantaneous difference between the value of a specified system variable and the ideal value of the same system variable. system effectiveness-A measure of the degree to which an item can be expected to fulfill a set of specified mission requirements, which may be expressed as a function of availability, dependability, and capability. s y s t e m element-One or more basic elements, together with other components necessary to form all or a significant part of one of the general functional groups into which a measurement system can be classified. system engineering-A method of engineering analysis whereby all the elements in a system, including the process itself, are considered. system failure rate-The number of occasions during a given time period on which a given number of identical systems do not function properly. system ground-One common point to which the grounds for various pieces of equipment in a system are connected. The system ground is generally the best point to connect to earth ground. system input unit-A device defined as a source of an input job stream. system integration-The process of matching physical, electrical, and logical characteristics of different components so that they work together. s y s t e m layout-In a microwave system, a chart or diagram showing the number, type, and termination of circuits used in the system. system library-The assemblage of all cataloged data sets at an installation. s y s t e m macroinstruction-A predefined macroinstruction that makes available access to operating system facilities. system master tapes-Magnetic tapes that contain programmed instrucfions necessary for preparation of a computer before programs are run. s y s t e m network diagram -A diagram showing each station and its relationship to the other stations in a network of stations and to the control point@). system noise-The output of a system when it is operating with zero input signal. three electron beams s y s t e m of beams-The emitted by the triple electron-gun assembly in a color tube. They occupy positions equidistant from a common axis and are spaced 120" apart around the axis. system of units-An assemblage of units for expressing the magnitudes of physical quantities.

system output unit - system support s y s t e m output unit-An output device that is shared by all jobs and onto which specified output information is transcribed. system o v e r s h o o t -The largest value of system deviation following the dynamic crossing of the ideal value as a result of a specified stimulus. s y s t e m reliability-The probability that a system will perform its specified task properly under stated conditions of environment. s y s t e m residence volume-The volume in which the nucleus of an operating system and the highest-level index of the catalog are located. system resonance-The fundamental resonance of the woofer/enclosure combination. Related to the lowfrequency performance of the systems, but not without ambiguity, especially when comparing different types of enclosures. Not to be confused with free-air resonance of the woofer. systems analyst-A person skilled in solving problems with a digital computer. He or she analyzes and develops information systems. systems-implementation languages-Essentially compilers with assemblerlike features. These allow the programmer to take advantage of compiler-level languages, but revert to assembler languages when necessary. s y s t e m software-1. Software that is intimately associated with the operating system, e.g., kernel routines,

758 system services, and system support software. 2. All the programs that tie together and coordinate the devices that make up the computer system. It includes such programs as loaders, compilers, interpreters, and input/output routines. 3. That collection of programs which controls the computer and helps people use the computer. Generally, supervisory and support modules, as opposed to application programs. This includes assemblers, editors, debuggers, operating systems, compilers, I/O drivers, loaders, and other utility programs. 4. A program that acts to assist the applications program and is usually not visible to the user. It takes the form of controlling and utilizing the internal resources of the computer. It keeps track of time, sequences, and events, and performs the input and output functions. This is the program that is used for general applications and, when made part of a memory medium such as disk, tape, semiconductor, or bubble memory, is referred to as the system firmware. s y s t e m s programs -Computer programs provided by a computer manufacturer. Examples are operating systems, assemblers, compilers, debugging aids, and input/output programs. system support-Functions such as language translators, debugging tools, diagnostics, and libraries that enable a system user or programmer to write and test tasks in an efficient manner.

T

T- 1. Symbol for transformer or absolute temperature. 2. Abbreviation for prefix tera- (10”). tab-- 1. See land, 2. 2. A nonprinting spacing action on a typewriter or tape preparation device, the code of which is necessary to the tab sequential format method of programming. 3. Term used to describe construction of wound capacitors whereby the two electrode foils, separated by dielectric, are positioned one above the other with a margin of dielectric completely surrounding the edges of both foils. Foil tabs, placed in the wound capacitor during winding, span the margin for connection to the leads. table -1. A collection of data, each item of which is uniquely identified by a label, its position with respect to the other items, or some other means. 2. A set of data values. table lockup-1. A computer technique that stores a table of data in a computer so that the data can be used during the running of the program. 2. In a computer, a method of controlling the location to which a jump or transfer is made. It is used especially when there is a large number of alternatives, as in function evaluation in scientific computations. tablet -An input device that digitizes coordinate data indicated by stylus position. tab sequential format-A means for identification of a computer word by the number of tab characters in the block preceding the word. The initial character in each word is a tab character. Words must be presented in a certain order, but all characters in a word except the tab character may be omitted when the command that word represents is not desired. tabuliate-1. To arrange data into a table. 2. To print totals. tabulated cylinder-Translation of a curve along a direction line with upper and lower limits on the distance of trans1ation. tabulator-A machine (e.g., a punch-card machine) that reads information from one medium and produces lists, totals, or tabulations on separate forms or continuous paper strips. tachometer- 1. An instrument used to measure the frequency of mechanical systems by the determination of angular velocity. 2. A transducer that gives an electric output signal proportional to the rotational speed of a shaft. 3. A device for mieasuring rate by counting the number of pulses that occur in a given period. 4. An instrument designed to measure the rate of rotation of components such as shafts. t a c h o m e t e r generator-A smallgenerator attached to a rotating shaft for the purpose of generating a voltage proportional to the shaft speed. In speed-control circuits, a tachometer may be coupled to the shaft of the motor whose speed is to be controlled. A change of motor speed will produce a change of tachometer output voltage. This

MOTOR WHOSE SPEED IS TO BE MEASUAEO

OC OR AC TACHOMETER

DC VOLTMETER (WITH DC TACHOMETER) OR FREOUENCY METER (WITH AC TACHOMETERI CALIBRATED IN RPM

Tachometer. change of voltage can be used as an error signal to restore the speed to the desired value. tacky state-The condition of a material when it exhibits an adhesive bond to another surFace. TACS -Abbreviation for Total Access Comunication System. An analog cellular radio protocol used in the United Kingdom. tactical-1. Of or relating to combat tactics. 2. Of or occurring at the battlefront. 3. Using or being weapons of force employed at the battlefront. tactical air navigation-A short-range UHF airnavigation system that presents accurate information to a pilot in two dimensions, distance and bearing from a selected ground station. tactical call sign -Call sign that identifies a tactical command or tactical communication facility. tactical communications system -Systems that provide internal communications within tactical air elements, composed of transportable and mobile equipment assigned as unit equipment to the supporting tactical unit. tactical frequency-Radio frequency assigned to a military unit to be used in the accomplishment of a tactical mission. tag -1. A label attached to a piece of data in a dataflow computer that says where the data is to be used in a program. 2. Also called a sentinel. In digital-computer programming, a unit of information whose composition differs from that of other members of the set so that it can be used as a marker or label. Tagged Image File Format -Abbreviated TIFF. A high-resolution bit-mapped graphics format for storing scanned images on B M PCs and compatibles and Macintosh computers. tail- 1. A small pulse following the main pulse and in the same direction, or the slow decay following the main body of the pulse. 2. The free end of wire extending beyond the bond impression of a wire bond from the heel. tail clipping -A method of sharpening the trailing edge of a pulse. tailing-See hangover, 1.

tailor-made

- tantalum (electrolytic) capacitor

tailor-made -Also called custom. Referring to a program or programs that are specially written for one particular task, for one set of people. Tailor-made software is usually commissioned by an individual customer, and not sold to anyone else. tail pull-The act of removing the excess wire left when a wedge or ultrasonic bond is made. tail pulse -A pulse in which the decay time is much longer than the rise time. tails-out-1. Storage of a nonreversing tape on the takeup reel rather than on the supply reel, to avoid the tape-distorting interval winding stresses and uneven wind of high-speed rewinding. 2. In the case of reversing tapes (Le., cassettes or four track open-reel tapes), storing the tape wound on whichever reel (or hub) it ends up on after having been played or recorded. tail-warning radar set-A radar set placed in the tail of an aircraft to warn of aircraft approaching from the rear. t a k e u p reel -1. The reel that accumulates the tape as it is recorded or played on a tape recorder. 2. The reel on a tape recorder that is on the right side of the head stack and is empty prior to beginning the recording. talbot-A unit of luminous energy in the mksa system equal to 1 lumen-second. talk-back- A voice intercommunicator; an intercom. talker echo-An echo that reaches the ear of the person who originated the sound. talking battery-The dc voltage supplied by the central office to the subscriber’s loop to operate the carbon transmitter in the handset. talking path-The transmission path of a telephone circuit, making up the tip and ring conductors and the equipments connected to them. talk-listen s w i t c h -A switch on an intercommunication unit to switch the speaker as required to function either as a reproducer or as a microphone. talk-off -The tendency of a dual-tone multifrequency (DTMF) system to respond falsely to otherthan-valid DTMF signals. Talk-off criteria are generally specified very subjectively- sometimes in such broad terms as “good” or “poor.” tally light-Signal lights installed at the front and back of television cameras to inform performers and crew members when a particular camera is on the air. tamper device- I. Any device, usually a switch, that is used to detect an attempt to gain access to intrusion alarm circuitry, such as by removing a switch cover. 2. A monitor circuit to detect any attempt to modify the alarm circuitry, such as by cutting a wire. tamper switch -A switch that is installed in such a way as to detect attempts to remove the enclosure of some alarm system components, such as control box doors, switch covers, junction box covers, or bell housings. The alarm component is then often described as being “tampered.” tandem -See cascade. tandem office-In a telephone system, an office that interconnects the local end offices over tandem trunks in a densely settled exchange area where it is not economical to provide direct interconnection between all end offices. The tandem office completes all calls between the end offices but is not connected directly to subscriber’s stations. tandem transistor-Two transistors in one package and internally connected together. tangent-A straight line that touches the circumference of a circle at one point. t a n g e n t galvanometer -A galvanometer consisting of a small compass mounted horizontally in the center

760 of a large vertical coil of wire. The current through the coil is proportional to the tangent of the angle at which the compass needle is deflected. tangential component -A component acting at right angles to a radius. tangential pickup arm-A pickup arm that maintains the longitudinal axis of the stylus tangent to the record grooves throughout the entire movement of the arm across the record. tangential sensitivity- A term generally applied as an indication of quality in a receiving system. This term can be used to define the minimum signal level that can be detected above the background noise. However, it is usually expressed as that signal power level that causes a 3-dB rise above the noise-level reading. tangential sensitivity on look-through -The strength of the target signal, measured at the receiver terminals, required to produce a signal pulse having twice the apparent height or the noise. tangential wave path -In radio-wave propagation of a direct wave over the earth, a path that is tangential to the surface of the earth. The tangential wave path is curved by atmospheric refraction. tangent of loss angle-The ratio of the equivalent series resistance and the capacitive reactance of a capacitor obtained at a sinusoidal alternating voltage of specified frequency. tangent sensitivity -The slope of the line tangent to the response curve at the point being measured. t a n k -1. A unit of acoustically operating delay-line storage containing a set of channels. Each channel forms a separate recirculation path. 2. See tank circuit, 2. tank circuit-1. A circuit capable of storing electrical energy over a band of frequencies continuously distributed about a single frequency at which the circuit is said to be resonant or tuned. The selectivity of the circuit is proportionate to the ratio between the energy stored in the circuit and the energy dissipated. This ratio is often called the Q of the circuit. 2. Also called a tank. A parallel-resonant circuit connected in the plate circuit of an electron-tube generator. tantalum (electrolytic) capacitor -An electrolytic capacitor with a tantalum foil or sintered-slug anode.

TINNED NICKEL LEAO

~1

TANTALUM HALO

FLUOROCARBON TFE FLUOROCARBON

-

ELECTROLYTE \ SILVER TANTALUM

TFE FLUOROCARBON TINNED

COPPER LEAO

-

U Tantalum capacitor.

'761

tantalum-foil electrolytic capacitor

tantallum-foil electrallytic capacitor -A capacitor that consists of two tantalum foil electrodes with an oxide on the anode, separated by layers of absorbent paper saturated with an operating electrolyte. tantalum oxide-A dielectric material used in capacitors; it is formed electrochemically in a thin film on surfaces of tantalum metal. T-antenna -Any antenna consisting of one or more horizontal wires, with the lead-in connected approximately in the center. tap -- 1. A fixed electrical connection to a specified position on the element of a potentiometer, transformer, etc. 2. A branch. Applied to conductors, such as a battery tap, and to miscellaneous general use. 3. A connection of the terminal end of one conductor to another conductor at some point along its run; the process of making such a connection. Also, a connection or connection point brought out of a winding, as in a transformer, at some point between the ends of the winding, for controlling output ratios. 4. Connection on the phone line that lets a third party listen to what is being said in a telephone conversation. tap center -A connection to the electrical midpoint of a coil, resistor, or transformer winding. tap conductor -A conductor, usually short but longer than a pigtail, that serves to connect utilization equipment to the serving circuit. tap crystal- A compound semiconductor that stores current when stimulated by light and then gives up energy in the form of flashes of light when subjected to mechanical tapping. e - 1. Plastic ribbons with one side coated metallically to receive impressions from a recording head, or, if already recorded, to indiuce signals in a playback head. Tape is regularly wound on reels or packaged in magazines or cartridge form. 2. See punched tape. 3. A ribbon of flexible material- e.g., friction, magnetic, punched, etc. 4. A strip of material, which may be punched, coated, or impregnated with magnetic or optically sensitive substances, used for data input, storage, or output. The data is stored serially in several channels across the tape trans. the reading or writing motion. Tape has a far versely 1o higher storage capacity than disk storage of similar volume, but it takes much longer to write or recover data to tape than to disk.

COMPONENTS

\APE

Tape-and-reelpackaging.

tape cable-Also called flat flexible cable. A form of flexible multiple conductor in which parallel strips of metal are imbedded in an insulating material.

- tape-on surface-temperature resistor

tape cartridge-A magazine or holder for a length of magnetic tape that by its design avoids the necessity for manual threading or handling. Usually compatible only with one specific type of machine. See also tape magazine. tape character -Information consisting of bits stored across the several longitudinal channels of a tape. tape-controlled carriage -A pager-feeding device automatically controlled by a punched paper tape. tape Copy-A message received in tape form as the result of a transmission. tape deck- I. The basic assembly of a tape recorder, consisting of the tape-moving mechanism (the tape transport) and a head assembly. Some decks also include recording and playback preamplifiers; these properly are called tape recorders. Some have playback-only preamplifiers; these have no standard name but are often called tape players. 2. A tape recorder that does not include power amplifiers or speakers. tape distributor-A machine that reads prerecorded paper tape. tape drive- 1. A mechanism for moving tape past a head; tape transport. 2. The motor and associated mechanism that pulls the tape past the playing or recording heads. tape feed-A mechanism that feeds the tape to be read or sensed by a computer or other data-handling system. tape guides- Grooved pins of nonmagnetic material mounted at either side of the recording-head assembly. Their function is to position the magnetic tape on the head as it is being recorded or played. tape head-The transducer on a tape recorder past which the tape runs during record or replay. It applies a magnetic field to the tape during the recording process and provides electrical output during replay. tape hiss- Sibilant background noise heard when a tape is played. Although some of this noise is directly attributable to irregularities of the oxide coating, some also is contributed by the recording circuitry. tape lifters-A system of movable guides that automatically divert tape from contact with the recorder heads during the fast forward or rewinding mode of operation, thus preventing head wear. tape limited-Pertaining to a computer operation in which the time required for the reading and writing of tapes is greater than the time required for computation. tape loop-A length of magnetic tape with the ends joined together to form an endless loop. Used either on a standard recorder, a special message-repeater unit, or in conjunction with a cartridge device, it enables a recorded message to be played back repetitively; there is no need to rewind the tape. tape magazine-Also called a tape cartridge. A container holding a reel of magnetic recording tape, which can be played without being threaded manually. tape mark-A special record indicating end of file. tape monitor- 1. A circuit that permits the checking of recordings by taking the signal directly from the tape a moment after the recording is made. This is only possible on three-head recorders. 2. An interruption in the signal path of a preamplifier, from which the selected input signal is supplied to an external tape recorder, and to which the playback output of the recorder is returned for further amplification and processing. Tape monitor circuits allow one to listen to a tape as it is recorded, ensuring it is being recorded properly. They also allow the use of external signal processing devices such as equalizers, noise reducers, and expanders, and are sometimes known as external processor loops for that reason. tape-on surface-temperature resistor-A surface-temperature resistor installed by adhering the

tape parity

- target

sensing element to the surface with a piece of pressuresensitive tape. tape parity-Parity error that occurs when information is transferred to or from magnetic tape. tape-path center line-The locus or path traced by an imaginary point, located on the recording tape midway between its edges, as it travels from reel-to-reel through guides, past heads, and between capstan and pressure rollers. For correct tracking and minimum tape distortion, the entire path should lie in a single plane located above the motor board at a height compatible with head-gap locations. tape perforator-A device that records a teletypewriter or data message by punching holes in paper tape, under control of either a local keyboard or an incoming signal. tape phonograph- See tape player. tape player -Sometimes called a tape phonograph or a tape reproducer. A unit for playing recorded tapes. It has no facilities for recording. tape punch-A peripheral device that generates (punches) holes in a paper tape to produce a hard copy of PC memory contents. taper -In communication practice, a continuous or gradual change in electrical properties with length-e.g., as obtained by a continuous change of cross section of a wavelength or by the distribution and change of resistance of a potentiometer or rheostat. tape reader- 1. A peripheral device for converting information stored on punched paper tape to electrical signals for entry into PC memory. 2. A unit that is capable of sensing data from punched tape. tape recorder -A mechanical-electronic device for recording voice, music, and other audio-frequency material. Sound is converted to electrical energy, which in turn sets up a corresponding magnetic pattern on iron oxide particles suspended on paper or plastic tape. During playback, this magnetic pattern is reconverted into electrical energy and then changed back to sound through the medium of headphones or a speaker. The recorded material may be converted to a visual display by the use of an oscilloscope, other visual indicator, or a graphic recorder. See also videotape recording. tapered potentiometer-A continuously adjustable potentiometer whose resistance varies nonunifonnly along the element, being greater or less for equal slider movement at various points along the resistance element. tapered transmission line -See tapered waveguide. tapered waveguide -Also called a tapered transmission line. A waveguide in which a physical or electrical characteristic changes continuously with distance along the axis of the guide. tape relay-A method in which perforated tape is used as the intermediate storage in the process of relaying messages between transmitting and receiving stations. tape-relay station -A component of a communications center that carries out the function of receiving and forwarding messages by means of tape relay. tape reproducer- See tape player. tape reservoir-That part of a magnetic tape system used to isolate the tape storage inertia (i.e., tape reels, etc.) from the drive system. taper pin -A pin-type contact having a tapered end designed to be inserted into a tapered hole. tape skew-The deviation of a tape from following a linear path when transported across the heads, causing a time displacement between signals recorded on different tracks and amplitude differences between the outputs from

762 individual tracks owing to variations in azimuth alignment. The adjectives static and dynamic are used to distinguish between the steady and fluctuating components of the tape skew. tape speed-The speed at which tape moves past the head in the recording or playback mode. The standard tape speed for home use is 7112 ips (19.05 c d s ) or half this speed (33/4 ips). One-fourth or even one-eighth this speed is also used, but usually only for music when special high-quality tape is utilized. The professional recording speed for music mastering is usually 15 ips (38.1 cmis). tape-speed errors- Any variation in tape speed from the normal speed over the record or reproduce head, regardless of cause. tape-speed variations-See flutter, 1. tape splicer-A device for splicing magnetic tape automatically or semiautomatically. tape station -See tape unit. tape threader-A device that makes easier the threading of magnetic recording tape onto the reel. tape-to-card -Pertaining to equipment or methods used to transfer data from magnetic or punched tape to punched cards. (No longer in use.) tape-to-head speed-The relative speed of the tape and head during normal recording or replay. (The tape-to-head speed coincides with the tape speed in conventional longitudinal recording, but it is considerably greater than the tape speed in systems where the heads are scanned across or along the tape.) tape-to-tape converter-A device for changing from one form of inputloutput medium or code to another, i.e., magnetic tape to paper tape (or vice versa) or eightchannel code to five-channel code. tape transmitter- 1. A machine actuated by previously punched paper tape and used for high-speed code transmission. 2. A facsimile transmitter designed for transmission of subject copy printed on narrow tape. tape transport-See transport. tape-transport m e c h a n i s m -See motor board. tape unit-Also called tape station. A device that contains a tape drive and the associated heads and controls. tape-wound core-Also known as bimag. A magnetic core consisting of a plastic or ceramic toroid around which is wound a strip of thin magnetic tape possessing a square hysteresis-loop characteristic. A tape-wound core is used principally as a shift-register element. tap lead-The lead connected to a tap on a coil winding. tapped control -A rheostat or potentiometer having a fixed tap at some point along the resistance element, usually to provide fixed grid bias or automatic tone compensation. tapped line-A delay line in which more than two terminal pairs are associated with a single sonic-delay channel. tapped resistor-A wirewound fixed resistor having one or more additional terminals along its length, generally for voltage-divider applications. tapped winding -A coil winding with connections brought out from turns at various points. See figure on page 763. tapper bell -A single-stroke bell designed to produce sound of low intensity and relatively high pitch. tap switch -A multicontact switch used chiefly for connecting a load to any one of a number of taps on a resistor or coil. target - 1. In a camera tube, a structure employing a storage surface that is scanned by an electron beam to generate an output-signal current corresponding to the charge-density pattern stored thereon. 2. Also called an

target acquisition - T-circulator

763

llzpped winding. anticathode. In an X-ray tube, an electrode or part of an electrode on which a beam of electrons is focused and from which X-rays are emitted. 3. In radar, a specific object of radar search or surveillance. 4. Any object that reflects energy back to the radar receiver. 5. In image pickup tubes, a structure employing a storage surface that is scanned by an electron beam to generate a signal output current corresponding to a charge-density pattern stored thereon. The structure may include the storage surface that is scanned by an electron beam, the backplate, and the intervening dielectric. target acquisition -In radar operation, the first appearance of a recognizable and useful signal returned from a new target. target capacitance-In camera tubes, the capacitance between the scanned area of the target and backplate. target cutoff voltage-In camera tubes, the lowest target voltage at which any detectable electrical signal, corresponding to a light image on the sensitive surface of the tube, can be obtained. target discrimination -The characteristic of a guidance system that permits it to distinguish between two or more targets in close proximity. target fade-The loss or decrease of signal from the target due to interference or other phenomena. target glint -See scintillation, 2. target identification -A visual procedure by which a radar target is positively identified as either hostile or friendly. target integration-A system of increasing the sensitivity of a TV camera when viewing a static scene by cutting off the beam for a predetermined number of frames and reading out the information in the first frame after beam turn-on. target language -The language into which some other language is to be properly translated. In computers, any language (such as object code) into which another language (such as source code) is translated. target noise-Reflections of a transmitted radar signal from a target that has a number of reflecting elements randomly oriented in space. target reflectivity-The degree to which a target reflects electromagnetic energy. target scintillation-The apparent random movement of the center of reflectivity of a target observed during the course of an operation. target seeker-In a missile homing system, the element that senses some feature of the target so that the resulting infomation can be used to direct appropriate maneuvlers to maintain a collision course. target signature-The characteristic pattern of a given taxget when displayed by detection and classification equipment. target system- 1. The computer that is being emulated on another system. 2. The microcomputer under development: the prototype. target voltage-In a camera tube with low-velocity scanning, the potential difference between the thermionic cathode and the backplate.

tariff -The published rate for utilization of a specific unit of equipment, facility, or type of service provided by a communications common carrier. Also the vehicle by which the regulating agency approves or disapproves such facilities or services. Thus, the tariff becomes a contract between customer and common carrier. task-1. A unit of work for the central processing unit as determined by the control program; therefore, the basic multiprogramming unit under the control program. 2. A software module in which code is executed in a sequential manner. task control block-The consolidation of the control information that has to do with a task. t a s k d i s p a t c h e r -The control-program function that selects a task from the task queue and gives control of the central processing unit bo that task. tasking -The capability of a computer to process more than one set of instructions, or task, at a time. t a s k list-A system data structure containing a list of tasks within the system. t a s k management-Those functions of the control program by which the use of the central processing unit and other resources by tasks is regulated. t a s k queue-A queue that contains control information for all tasks in a system at any given time. task state -The status of a task; it may be undefined, ready to execute, executing, or suspended awaiting some event. taut-band galvanometer- A galvanometer whose moving coil i s suspended between two taut ribbons. taut-band suspension -In an indicating instrument, a mechanical arrangement in which the moving element is suspended by means of a thin, flat conducting ribbon at each end. The ribbons normally are in tension sufficient to maintain the lateral motion of the moving element within limits that permit the freedom of useful motion for any mounting position of the instrument. A restoring torque is produced within the ribbons when the moving element rotates. TBC -Abbreviation for time base corrector. A device that corrects time base stability errors (errors in the rate at which a signal is occurring) during tape playback. TC - 1. Abbreviation for teleconferencing. The use of telecommunications to link physically separated individuals or groups for purposes of holding a meeting. The technology can range from a simple speakerphone to elaborate custom-designed teleconference rooms equipped with two-way audio, graphics, and video. See also teleconference. 2. Abbreviation for temperature coefficient. T carrier -A the-division-multiplexed service, normally supplied by the telephone company, that usually operates a digital transmission facility at an aggregate data rate of 1.544 Mbps and above. TC capacitor -Abbreviation for temperature-compeusating capacitor. Tchebychev filters-Filter networks that are designed to exhibit a predetermined ripple in the passband (ripple amplitudes from 0.01 dJ3 to 3 dB are common) in exchange for which they provide a more rapid attenuation above cutoff -which, unlike their passband response, is monotonic. T c h e b y c h e v function- A mathematical function whose curve ripples within certain bounds (See ripple, 2). This produces an amplitude response more square than that of the Butterworth function, but with less desirable phase and time-delay characteristics. There is an entire family of Tchebychev functions (0.1 ripple, 0.5 ripple, etc.). T-circulator -A circulator consisting of three identical rectangular waveguides joined asymmetrically to form

TCR -telegraph c h a n n e l a T-shaped structure, with a ferrite post or wedge at the center of the structure. Power that enters any waveguide emerges from only one adjacent waveguide. TCR -Abbreviation for temperature coefficient of resistance. TDD/lT-Acronym for tone dialing for the deafkeletype. A method by which the hearing impaired can type messages over normal phone lines using special equipment. TDM -See time-division multiplexing. TDMA- Abbreviation for time division multiple access. A method of sharing a transmission medium by dividing the time into “slots” and allocating those slots to users on a network. TDR -Abbreviation for time-delay relay. teach box-A hand-held control with which a robot can be programmed. tearing -Distortion observed on the television screen when the horizontal synchronization is unstable. Groups of horizontal lines are displaced in an irregular manner, creating the appearance of parts of the image having been torn away. teaser transformer-A transformer of two Tconnected, single-phase units for three-phase to two-phase or two-phase to three-phase operation; it is connected between the midpoint of the main transformer and the third wire of the three-phase system. teasing-In the life testing of switches, the slow movement of rotor contacts making and breaking with stator contacts. technical control board-In a switch center or relay station, a testing position at which there are provisions for making tests on switches and associated access lines and trunks. technical load-The portion of the operational power load of a facility that is required for communications-electronics, tactical-operations, and ancillary equipment. It includes power for lighting, air conditioning, or ventilation necessary for full continuity of communications-electronics operation. technician -A person who works directly with scientists, engineers, and other professionals in every field of science and technology. Technicians’ duties vary greatly, depending on their field of specialization. But in general, the scientist or engineer does the theoretical work, and the technician translates theory into action. technician license-A class of amateur radio license issued in the United States by the FCC for the primary purpose of operation and experimentation on frequencies above 50 MHz. technology- 1. To organize the means for satisfying needs and desires. 2. Know-how applied to get a job done. tecnetron -A high-power multichannel field-effect transistor similar to a triode tube in that it has anode and cathode connections on opposite ends of a small germanium rod (and a grid connection between them). TED -Abbreviation for transferred electron device. A gate-controlled, Gunn-effect unit. The triode TED consists of an anode, cathode, and Schottky barrier gate. The device resembles a Gunn diode. It has a threshold and a negative-resistance region that produces oscillation at the transit-time frequency, which depends on the anodecathode spacing. tee junction-Also spelled T-junction. A junction of waveguides in which the longitudinal guide axes form a T. The guide that continues through the junction is called the main guide; the one that terminates at a junction, the branch guide. telautograph- Also called a telewriter. A writing telegraph instrument in which the movement of a pen in the transmitting apparatus varies the current and thereby

764 causes the corresponding movement of a pen at the remote receiving instrument. tele- -A prefix, from Greek, that means distant or at a distance. telecamera -Abbreviation for a television camera. telecardiophone- An amplifying stethoscope that permits heart sounds to be heard at a distance. telecast- Abbreviation for television broadcasting-specifically, a television program, or the act of broadcasting a television program. telecasting -The broadcasting of a television program. telecommand -One-way transmission to modify, initiate, or terminate functions of a device at a distance. telecommunication -1. All types of systems in which electric or electromagnetic signals are used to transmit information between or among points. Transmission media may be radio, light, or waves in other portions of the electromagnetic spectrum; wire; cable; or any other medium. 2. Data transmission between a computing system and remotely located devices via a unit that performs the necessary format conversion and controls the rate of transmission. 3. Pertaining to the art and science of telecommunication. 4. Any transmission, emission, or reception of signs, signals, writing, images, or sounds, or intelligence of any nature by wire, radio, visual, or other electromagnetic systems. 5. Generally refers to the reception and/or transmission of information -whether in digital or analog form-by telephone, telegraph, and the like. 6. The transmissiodreception between terminals, or between terminals and computers, of (digitized) information or messages over telephone lines or by wireless transmission. 7. Communication by electrical transmission, such as television, radio, telephone and telegraph, that is carried over a distance. 8. The conversion and transmission of information from a computer to another device at a distance. 9. The process of moving data from one point to another. 10. Synonym for data communication. The transmission of information from one point to another. telecommunication lines-Telephone and other communication lines that are used to transmit messages from one location to another. teleconference-1. A conference between persons who are remote from one another but linked together by a telecommunications system. 2. Electronically linked meeting conducted among groups of people in geographically separated locations. Three forms of teleconference currently exist. A typical video mode includes an audio system, a facsimile device, and a storage unit for the display of prepared material. An audio teleconference lacks live-video capability but nonetheless usually utilizes graphic-display equipment. In a computer teleconference, data is transmitted by keyboard and then printed out. 3. A meeting conducted via telephone lines between two or more groups of individuals who are physically separated. It provides a low-cost technique of bringing people together via telephone channels and also overcomes problems imposed by distance and time. telegenic-The suitability of a subject or model for televising. telegram -Any written matter that is transmitted by telegraphy. t e l e g r a p h - 1. A system that employs interruptions or polarity changes of direct current for the transmission of signals. 2. A system of communication using coded signals. telegraph channel- 1. The transmission media and intervening apparatus involved in the transmission of telegraph signals in a given direction between two intermediate telegraph installations. A means of one-way transmission of telegraph signals. 2. A communication

765 path that is suitable for transmitting telegraph signals between two points. The required bandwidth depends on the signaling speed. telegiraph circuit -A complete circuit over which signal currents flow between transmitting and receiving apparatus in a telegraph system. It sometimes consists of an overhead wire or cable and a return path through the ground. t e l e g r a p h concentirator-A switching arrangement by means of which a number of branch or subscriber lines or station sets may be connected to a lesser number of trunk lines, operating positions, or instruments through the medium of manual or automatic switching devices to obtain more efficient use of facilities. t e l e g r a p h distributor- A device that effectively associates one direct current or carrier telegraph channel in rapid succession with the elements of one or more signal-sending or signal-receiving devices. telegraph-grade circuit -A circuit suitable for transmission by teletypewriter equipment. Normally the circuit is considered to employ dc signaling at a maximum speed of 75 bauds. telegraph key -A single-pole, single-throw switch that can be rapidly operated by hand so as to form the dots and dashes of telegraph code signals by opening and closing contacts to modulate current. telegraph-modulated waves -Continuous waves whose amplitude or frequency is varied by means of telegraphic keying. t e l e g r a p h repeater -Apparatus that receives telegraph signals from one line and retransmits corresponding signals on another line. t e l e g r a p h selector-A device that performs a switching operation in response to a definite signal or group of successive signals received over a controlling circuit. telegraph signal distortion -The time displacement of transitions between conditions, such as marking and spacing, with respect to their proper relative positions in perfectly timed signals. The total distortion is the algebraic sum of the bias and the characteristic and fortuitous distortions. t e l e g r a p h sounder-A telegraph receiving instrument in which an electromagnet attracts an armature each time a pulse arrives. This armature makes an audible sound as it hits against its stops at the beginning and end of each current impulse, and the intervals between these sounds we translated from code into the received message by the operator. t e l e g r a p h transmission speed -The rate at which signals are transmitted. This may be measured by the equivalent number of dot-cycles per second or by the average number of letters or words transmitted and received per minute. t e l e g r a p h transmitter -A device for controlling a source of electric power in order to form telegraph signals. t e l e g r a p h wave -A completely random two-level signal.

telegraphy- 1. A system of telecommunication for the trarismission of graphic symbols, usually letters or numerals, by the use of a signal code. It is used primarily for record communication. 2. Any system of telecommunication for the transmission of graphic symbols or images for reception in record form, usually without gradation of shade values. 3. The science of communicating at a distance by means of coded current pulses sent over wire circuits. teleQectrocardiograiph -A device for transmission and remote reception of electrocardiograph signals. teleifnatics-Also called telematique. 1. A capability in telecommunications, computers, and semiconductors.

telegraph

circuit

- t e l e p h o n e carrier current

2. The integration of computer-processing applications with telecommunications capabilities. telemeter- 1. To transmit analog or digital reports of measurements and observations over a distance (e.g., by radio transmission from a guided missile to a control or recording station on the ground). 2. A complete measuring, transmitting, and receiving apparatus for indicating, recording, or integrating the value of a quantity at a distance by electric translating means. telemetering -A measurement accomplished with the aid of intermediate means that allow perception, recording, or interpretation of data at a distance from a primary sensor. The most widely employed interpretation of telemetering restricts its significance to data transmitted by means of electromagnetic propagation. telemeter service--Metered telegraph transmission between paired telegraph instruments over an intervening circuit adapted to serve a number of such pairs on a shared-time basis. telemetry-I. The science of sensing and measuring information at some remote location and transmitting the data to a convenient location to be read and recorded. 2. The transmission of measurements obtained by automatic sensors and the like over communications channels. 3. The practice of transmitting and receiving the measurement of a variable for readout or other uses. The term is most commonly applied to electric signal systems. 4. Transmission and collection of data obtained by sensing conditions in a real-time environment. 5. Transmission of coded analog data, often realtime parameters, from a remote site. telemetry beacon-A system whereby two or more reply pulses are transmitted by the beacon for the transmission of data from the test vehicle to the ground station. telemetry cable-Cable used for the transmission of information from instruments to the peripheral recording equipment. telemetry frame-In PCM systems, one complete sampling of words or channels oE information at a given rate; in time-division multiplexing, one complete commutator revolution. telemetry f r a m e rate-The frequency derived from the period of one frame. teleoperator -A mobile robot controlled by a human operator. Teleoperators are most often used in areas that would be hazardous to buman beings. t e l e p h o n e -Combination of apparatus for converting speech energy into electrical waves, transmitting the electrical energy to a distant point, and there reconverting the electrical energy to audible sounds. t e l e p h o n e address -The complete 10-digit number that specifies the location of a particular telephone. Consists of a 3-digit area code, a 3-digit central office code, plus a 4-digit station number. t e l e p h o n e answering machine-A device that answers a telephone in the subscriber’s absence, plays a recorded message, and then records messages from callers before disconnecting. When the subscriber returns he or she can rewind and play back all messages recorded in his or her absence, or the subscriber can interrogate the telephone answering machine remotely by sending appropriate tones from another telephone and then listening to the recorded messages. t e l e p h o n e capacitor-A fixed capacitor connected in parallel with a telephone receiver to bypass rf and higher audio frequencies and thereby reduce noise. t e l e p h o n e carrier current- -A carrier current used for telephone communication so that more than one channel can be obtained on a single pair of wires.

telephone central office - teletypewriter code telephone central off ice-A switching unit, installed in a telephone system that provides service to the general public, that has the necessary facilities for terminating and interconnecting lines and trunks. telephone channel-1. A channel suitable for the transmission of telephone signals. 2. A communication path suitable for carrying voice message traffic between two points. telephone circuit-A complete circuit over which audio and signaling currents travel between two telephone subscribers communicating with each other in a telephone system. telephone company- Any common carrier providing public telephone system service. There are about 2500 telephone companies in the United States. telephone current-An electric current produced or controlled by the operation of a telephone transmitter. telephone instrument -A subscriber’s complete telephone set. telephone jack-See phone jack. telephone network-The arrangement of trunks, subscriber lines, centralized switching locations, etc., used to switch calls and make connections between various customers. telephone number-In the United States, a sevendigit number assigned to a telephone. It contains a threedigit central office code. telephone pickup-Any of several devices used to monitor telephone conversations, usually without direct connection to the telephone line and operating on the principle of mutual magnetic coupling. telephone plug -See phone plug. telephone receiver-The portion of the telephone instrument held closely to the human ear that converts the analog electrical speech signal into sound waves. telephone relay- 1. A relay used in telephone system switching equipment. 2. Any high-density, multipole relay intended for signal level switching in communications and data processing. These relays may have selfwiping contacts, that is, bifurcated pole blades that scrape over mating surfaces to remove minor oxide buildup. telephone repeater -An assemblage of amplifiers and other equipment employed at points along the line to rebuild the signal strength in a telephone circuit. telephone ringer- An electric bell that operates on low-frequency alternating or pulsating current and is used for indicating a telephone call to a station being alerted. telephone system-A group of telephones plus the lines, trunks, switching mechanisms, and all other accessories required to interconnect the telephones. telephone transmitter- 1. A microphone used in a telephone system. See also microphone. 2. A transducer that uses voice sound pressure on a diaphragm to translate the acoustic message into an analog electrical signal. telephone wire-A general term referring to many different types of communication wire. It refers to a class of wires and cables, rather than a specific type. telephony- 1. The transmission of speech current over wires, enabling two persons to converse over almost any distance. 2. A telecommunications system for transmitting speech or other sounds. telephoto- Also called telephotography. A photoelectrical transmission system for point-to-point or air-to-ground transmission of high-definition pictorial information. telephotography-See telephoto. telephoto lens-A lens system that is physically shorter than its rated focal length. It is used in still, movie, and television cameras to enlarge images of objects photographed at comparatively great distances.

766 telepoint-A cordless telephone system in which a subscriber can make but not receive phone calls in public areas that have been equipped with telepoint base stations. The system is not mobile-the user must remain essentially in a fixed location throughout the duration of the call. Both service and equipment are less expensive than cellular. teleprinter-1. See printer, 1. 2. Trade name used by Western Union for its telegraph terminal equipment. 3. See teletypewriter. teleprocessing - 1. A form of information handling in which the data-processing system operates in conjunction with communication facilities (originally a trademark of International Business Machines Corp.). 2. The processing of data that is received from or sent to remote locations by way of telecommunication lines. Such systems are essential to hook up remote terminals or connect geographically separated computers. teleprompter-A device mounted on the front of a camera that projects copy on a semireflective mirror placed directly in front of the lens so the performer can read lines while appearing to look at the camera. teleran -A navigational system in which radar and television transmitting equipment are employed on the ground, with television receiving equipment in the aircraft, to televise the image of the ground radar PPI scope to the aircraft along with map and weather data. telering-A frequency-selector device for the production of ringing power. telerobotics-Remote operation systems that mimic human movements through machinery. telesis -Progress intelligently planned and directed; the attainment of desired ends by the application of intelligent human effort to the means. telesynd-Telemeter or remote-control equipment that is synchronous in both speed and position. Teletype- 1. A trademark of Teletype Corporation for a series of teleprinter equipment such as tape punches, reperforators, page printers, etc., used in communications systems. Now often incorrectly used as a generic term to indicate any similar piece of equipment. 2. A peripheral electromechanical device for inserting or recording a program into or from a PC memory in either a punched paper tape or printed ladder diagram format. teletypewriter-Also known as a teleprinter. 1. See printer, 1. 2. A generic term referring to the basic equipment made by Teletype Corporation and to teleprinter equipment. The teletypewriter uses eletromechanical functions to generate codes (Baudot) in response to a human input to a manual keyboard. 3. A keyboard machine that can transmit and receive alphabetical, numerical, and certain control (nonprinting) characters as a train of pulses on two wires. Attachments can be fitted for punching paper tape and printing on a roll of paper at the same time, also for reading tape and printing the message that is read. 4. A keyboard printing unit that is often used to enter information into a computer and to accept output from a computer. The widest usage of the teletypewriter is as an input/output device in minicomputer systems, a remote terminal in a time-sharing system, and an operator console for computer systems. teletypewriter code -A special code in which each code group is made up of five units, or elements, of equal length that are known as marking or spacing impulses. The five-unit start-stop code consists of five signal impulses preceded by a start impulse and followed by a stop impulse. Each impulse except the stop impulse is 22 milliseconds in length; the stop impulse is 32 milliseconds (based on 60-word-per-minute operation).

teletypewriter exchange service - television c

767

teletypewriter exchange service- 1. A commercial service that provides teletypewriter communication on the same basis as telephone service, through central switchboards to stations in the same city or other cities. 2. Abbreviated TWX. A public teletypewriter exchange (switched) service in the United States and Canada formerly owned by AT&T but now belonging to Western Union. Baudot and ASCII-coded machines are used. teletypewriter signal distortion-With respect to a stop-start teletypewriter signal, a shift of the transition points of the signal pulses from their proper positions in relation to the beginning of the start pulse. The magnitude of the distortion is expressed as a percentage of a perfect unit pulse length. teletypewriter switching system -A total message switching system whose terminals are teletypewriter equipment. teletypewriter test tape -A tape perforated so that it contains the identification of the transmitting station followed by repetitions of the letters RY and a test that consists of letters and figures. televise-The act of converting a scene or image field into a television signal for transmission. television -Abbreviated TV. 1. A telecommunication system for transmission of transient images of fixed or moving objects. 2. A system €or converting visual images into electrical signals that can be transmitted (by radio or wire) to distant receivers, where the signals are reconverted to the original visual images and displayed on a CF!T. television and radar navigation-A navigational system that (a) employs ground-based search radar

equipment along an airway to locate aircraft flying near that airway; (b) transmits, by television means, information pertaining to these aircraft and other information to the pilots of properly equipped aircraft; and (c) provides information to the pilots appropriate for use in the landing approach. television bandwidth-The range of frequencies within which a television broadcast transmission must fall, generally assigned to be from 54 to 890 MHz. television broadcast band -The frequencies assignable to television broadcast stations in the band extending from 54 to 806 MHz. These frequencies are grouped into channels, as follows: channels 2 through 4, 54 to 72 MHz; channels 5 and 6,76 to 88 MHz; channels 7 through 13, 174 to 216 MHz; and channels 14 through 69, 470 to 806 MHz. television broadcast station-A radio station for transmitting visual signals, and usually simultaneous aural signals, for general reception. television camera -Abbreviated TV camera. A camera that contains an electronic image tube in place of a photographic film. The image formed on the tube face by a lens is scanned rapidly by a moving electron beam. The beam current varies with the local brightness of the image, which is transmitted to the viewer's set, where it controls the brightness of the scanning spot in a cathode ray tube. The scanning spots at the camera and the viewing tube must be accurately synchronized. television channel -A band of frequencies 6 megahertz wide in the television broadcast band, assigned to television broadcasting stations. The channel for associated sound signals may or may not be considered part

Television channels Channel number

Band (megahertz)

Channel number

Band (megahertz)

Channel number

Band (megahertz)

2 3 4 5 6 7 8 9 10 11 12 13 14 45 16

54-60 60-66 66-72 76-82 82-88 174-1 80 180-1 86 186-192 192-198 198-204 204-210 210-216 470-476 476-482 482-488 488-494 494-500 500-506 506-512 512-51 8 518-524 524-530 530-536 536 -542 542 -548 548-554 554-560

29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

560-566 566-572 572-578 578-584 584-590 590-596 596-602 602-608 608-614 614-620 620-626 626-632 632-638 638-644 644-650 650-656 656-662 662-668 668-674 674-680 680-686 686-692 692-698 698-704 704-710 710-716 716-722 722-728

57 58 59 60 67 62 63 64 65 66 67 68 69 70* 71* 727? 7475" 7677" 78* 79' 80* 81 82* 83"

728-734 734-740 740-746 746-752 752-758 758-764 764-770 770 - 776 776-782 782-788 788-794 794-800 800-806 806-812 812-81 8 818-824 824-830 830-836 836-842 842-848 848 - 854 854-860 860-866 866 -872 872-878 878-884 884-890

17 18 19 20 21 22 23 24 25 26 27 28

"The frequencies between 806 and 890 MHz, formerly allocated to television broadcasting,are now allocated to the land mobile services. Operation, on a secondaly basis, of some television translatorsmay continue on these frequencies.

television engineering

- temperature coefficient of resistance

of the television channel. There are a total of 12 VHF and 56 UHF television channels, beginning with channel 2 and ending with channel 69. Former UHF channels 70 through 83 are now either used by repeaters or are directly assigned to the land mobile service. Frequency ranges begin at 54 MHz and extend to 806 MHz. television engineering -See radio engineering. television interference-Abbreviated TVI. Interference in the reception of the sound and/or video portion of a television program by a transmitter or another device. television monitor-A television receiver that receives the signals generated by a television camera directly, or remotely through a radio link. It may be used to check image and sound reception continuously, as a closed-circuit television system for security and surveillance, or in editing. television pickup station-A land mobile station used for the transmission of television program material and related communications from the scenes of events occurring at points removed from television broadcast station studios to the television broadcast stations. television picture monitor- A special-purpose television set for displaying picture signals in broadcast or closed-circuit television systems. Applications are in studio master control, for tape monitoring, for control of picture quality in studios and intercity network relays, and for the display of pictures for audiences. television radar air navigation -A system in which aircraft positions are determined by ground radar, and the resulting PPI display, superimposed on a map, is transmitted to the aircraft by television. By this means, each pilot can observe the position of his aircraft in relation to others. television receive only -Abbreviated TVRO. Small satellite earth stations designed to receive satelliterelayed television programming, but having no provision for transmitting to the satellite. Typically small home systems. television receiver- A radio receiver for converting incoming electric signals into television pictures and the associated sound. television reconnaissance- Air reconnaissance by optical or electronic means to supplement photographic and visual reconnaissance. television relay system -A system of two or more stations for transmitting television relay signals from point to point, using radio waves in free space as a medium. Such transmission is not intended for direct reception by the public. television repeater-A repeater used in a television circuit. television screen -In a television receiver, the fluorescent screen of the picture tube. television signal -The audio signal and video signal that are broadcast simultaneously to produce the sound and picture portions of a televised scene.

VIDEO

3 579545 MH2

CARRIER

COLOR SUBCARRIER

768

television transmitter- The aggregate radio-frequency and modulating equipment necessary to supply to an antenna system the modulated radio-frequency power by which all component parts of a complete television signal (including audio, video, and synchronizing signals) are concurrently transmitted. televoltmeter -A telemeter that measures voltage. telewattmeter-A telemeter that measures power. telewriter-See telautograph. telex -1. An audio-frequency teleprinter system used in Great Britain to provide teletypewriter service over telephone lines. 2. An automatic teleprinter exchange service available worldwide through various common carriers. Western Union is the carrier in the United States. It is similar to TWX. Only Baudot equipment is provided, but business machines may be used also. 3. A dial-up telegraph service enabling its subscribers to communicate directly and temporarily among themselves by means of start-stop apparatus and circuits of the public telegraph network. The service operates worldwide. Computers can be connected to the telex network. telluric current-See earth current, 1. telpak-A communications-carrier service for the leasing of wideband channels between points. Telstar -A low-altitude active communications satellite used for microwave communication and satellite tracking. tempco -Abbreviation for temperature coefficient. temperature coefficient-Abbreviated TC or tempco. 1. A factor used to calculate the change in the characteristics of a substance, device, or circuit element with changes in its temperature. 2. The percentage change in the output voltage (or current) of a regulated power supply due to a variation of ambient temperature. The values are usually expressed as a percentage per degree Celsius and restricted to the specified ambient range of the unit. 3. A measure of a sensor's sensitivity, specifically the rate at which a parameter (such as resistance or voltage) changes with temperature. It is usually expressed as a percent per degree (either Fahrenheit or Celsius), and may be positive or negative. temperature coefficient of capacitance-Often referred to as the TC characteristic. The amount of capacitance change of a capacitor per degree change in temperature. For capacitors that exhibit a relatively linear capacitance change with temperature, the temperature coefficient is commonly expressed in parts per million per degree Celsius (ppm/"C). Capacitors with a nonlinear capacitance change are more often described in terms of percent capacitance change for a given temperature. temperature coefficient of frequency-The rate at which the frequency changes with temperature, generally expressed in hertz per megahertz per degree Celsius at a given temperature. temperature coefficient of permeability-A coefficient expressing the change in permeability as the temperature rises or falls. It is expressed as the rate of change in permeability per degree. temperature coefficient of resistance -Abbreviated TCR. 1. The ratio of the change in resistance (or resistivity) to the original value for a unit change in temperature. The temperature coefficient over the temperature range from t to t l , referred to the resistance R, at temperature t , is determined by the following ratio:

>

0

I

2

3

FREOUENCY (MHz)

Television signal.

4

5

where t is the temperature, preferably in degrees Celsius. The value will be positive unless otherwise indicated by a negative sign. 2. The maximum change in resistance per

769 unit change in temperature, usually referred to in parts per million (ppm) per degree Celsius and specified over a temperaiture range. The temperature is that of the resistor itself, not ambient temperature. temperature coefficient of voltage drop -The change in the voltage drop of a glow-discharge tube, divided by the change in ambient temperature or in the temperature of the envelope. temperature coefficient value -The expected percentage change per degree of temperature difference from a specified temperature. temperature-compensated zener diode-A positive .temperature-coefficientreversed-bias zener diode (pn junction) connected in series with one or more negative-temperature forward-biased diodes within a single package. temperature-compensating capacitorAbbreviated TC capacitor. A capacitor whose capacitance varies with temperature in a known and predictable manner. Normally this characteristic is specified with a P or N (positive or negative: to indicate the direction of change) followed by a number that indicates the change in parts per million per degree Celsius (centigrade). Such capacitors are used extensively in oscillator circuits to compensate for changes due to temperature variations in the values of other components. temperature compensation -The process whereby the effects of an increase or decrease in ambient temperature are canceled (e.g., as in the case of an oscillator that is required to maintain a stable output frequency regardless of ambient temperature changes). temperature control -1. A switch actuated by a thermostat responsive to changes in temperature; used to maintain temperxture within certain limits. 2. A control device responsive to temperature. temperature cycling -A type of accelerated test in which systems or devices are subjected alternately to high and low temperatures to simulate diurnal temperature fluctuations. temperature derated voltage -The maximum voltage that may be applied continuously to the terminals of a capacitor at a stated temperature between the rated and the maximum temperature. temperature derating -Lowering the voltage, current, or power rating of a device or component when it is used at elevated temperatures. t e m ~ e r a t ~ rdetectore An instrument used to measure the temperature of a body. Any physical property that is dependent on temperature may be employed, such as the differential expansion of two bodies, thermoelectromotive force at the junction of two metals, change of resistance of a metal, or the radiation from a hot body. t e m ~ ~ r a t ~ r ~ - ~-The ~ m i condition ted of a cathode when all the electrons emitted from it are drawn away by a strong positive field, The only way to increase the flow of electrons is to raise the cathode temperature. temperature retay-A relay that functions at a predetermined temperature. temperature rise-Also called T rise. 1. The difference between the initial and final temperature of a component or device. Temperature rise is expressed in degrees Celsius or Fahrenheit, usually referred to an ambient temperature., and equals the hot-spot temperature minus the ambient temperature. 2. Temperature change of a terminal from a no-load condition to a full-current load. t e m ~ e r a t u saturation r~ -See filament saturation. t e m i ~ e ~ asensort ~ ~ ~ See thermistor; thermocouple, 3. ~ ~ ~ ~ e r ashock-A t u r e rapid change from one temperature extreme to another.

temperature coefficient of voltage drop - terminal temperature-wattage characteristic -In a thermistor, the relationship, for a specific ambient temperature, between the temperature of the thermistor and the applied steady-state power. t e m p o r a r y magnet --A magnetized material having a high permeability and low retentivity. t e m p o r a r y memory-A read and write memory containing information that can be changed by the internal circuitry of the electronic switching system. t e m p o r a r y storage- 1. Internal storage locations in a computer reserved for intermediate and partial results. 2. Memory locations or registers reserved for immediate and partial results obtained during the execution of a program. TEM wave -Abbreviation for transverse electromagnetic wave. tens complement- 1. An arithmetic process employed in a computer to perform decimal subtractions through the use of addition techniques. The tenscomplement negative of a number is obtained by individually subtracting each digit in the number from 9 and adding 1 to the result. 2. The radix complement in decimal notation. tensilized tape -A variety of polyester backing that has been “prestretched” to prevent further severe elongation when subjected to excessive tension. A tape that does not stretch before breaking can be spliced back together without loss of program material. tensiometer -A device for determining the tautness of a supporting wire or cable. tension -1. Mechanical-the condition of strain that tends to stretch. 2. Electrical-the potential or electrostatic voltage. tension arm-An arm, or feeler, over which a recording tape rides as it enters or leaves the heads. It is lightly spring loaded to take up any tape slack and maintain a uniform tension in order to reduce flutter. Should the tape end or break, the arm causes the transport to shut off. tenth-power width-In a plane containing the direction of the maximum of a lobe, the full angle between the two directions in that plane, about the maximum, in which the radiation intensity is one-tenth the maximum value of the lobe. tera--Abbreviated T. Prefix for the numerical quantity of 1012. terabyte -A unit of memory equal to approximately 1 trillion bytes. terahertz-One million megahertz, or 1012hertz. Letter symbol: THz. teraohm-One million megohms, or !012 ohms. t e r a o h m m e t e r - An instrument used to measure extremely high resistance. terminal -1. A point of connection for two or more conductors in an electrical circuit. 2. A device attached to a conductor to facilitate connection with another conductor. 3. A point in a system or communication network at which data can be either inserted or removed. 4. A device that permits access to a central computer, usually inclnding a typewriterlike keyboard and either CRT or typing device (teletypewriter) on which the operator’s input and the computer’s output can be displayed. 5. Any device capable of sending and/or receiving information over a communications channel. 6. The means by which data is entered into a computer system and by which the decisions of the system are communicated to the environment it affects. A wide variety of terminal devices have been built, including teleprinters, special keyboards, light displays, cathode-ray tubes, thermocouples, pressure gauges and other instrumentation, radar units, and telephones. 7.

terminal area

- terminating

A device designed to terminate a conductor that is to be affixed to a post, stud, chassis or another conductor, or the like, to establish an electrical connection. Types of terminals include ring, tongue, spade, flag, hook, blade, quickconnect, offset, and flanged. terminal area- 1. A portion of a microelectronic circuit used for making electrical connections to the conductor pattern-e.g., an enlarged pad (area) on a semiconductor die. 2. A portion of a printed circuit used for making electrical connections to the conductive pattern, such as the enlarged portion of conductormaterial surrounding a component mounting hole. terminal block- An insulating base or slab equipped with one or more terminal connectors for the purpose of making electrical connections thereto. terminal board-Also called a terminal strip. 1. An insulating base or slab equipped with terminals for connecting wiring. 2. Board fabricated from an insulating material containing a single or multiple row or mangement of termination points for the purpose of making connections. 3. An insulated mounting for terminal connections. Terminal strips are available with threaded holes to accept threaded screws or with threaded studs to accept fastening washers and nuts. If terminal areas are separated by an insulating barrier, the terminal strips are called barrier blocks.

Terminal boards.

terminal box-A housing in which cable pairs are brought out to terminations for connections. terminal brush-A brush with long bristles for cleaning fuses and terminals in a terminal box. terminal connector-A connector that joins a conductor to a lead, terminal pad (solid or laminated block), or round terminal stud of electrical apparatus. terminal cutout pairs-Numbered, designated pairs brought out of a cable at a terminal. terminal emulation-1. A situation in which special software makes a computer behave as though it were a terminal connected to another computer. 2. The process by which an asynchronous terminal, such as a PC, can communicate with a synchronous computer system, such as a mainframe or minicomputer. This is done by imitating (emulating) the operations of the mainframe's or mini's synchronous terminals. terminal equipment-1. At the end of a communications channel, the equipment essential for controlling the transmission and/or reception of messages. 2. Telephone and teletypewriter switchboards and other centrally located equipment to which wire circuits are terminated. 3. Assemblage of communications-type equipment required to transmit and/or receive a signal on a channel or circuit, whether it be delivery or relay. 4. In radio relay systems, usually refers to equipment used at points where intelligence is inserted or derived, as distinct from equipment used to relay a reconstituted signal. 5. Any equipment at the end of communicationslines that sends and/or receives certain signals for specific services.

770 For example, telephones and teletypewriters are terminal devices; so are many datasets. terminal guidance- 1. Guidance applied to a guided missile between midcourse guidance and arrival at the target. 2. Electronic, mechanical, visual, or other assistance given an aircraft pilot to facilitate arrival at, landing upon, or departure from an air landing or air-drop facility. terminal hole-Also called component hole. A hole used for the attachment and electrical connection of component terminations, including pins and wires, to a printed board. terminal impedance- 1. The complex impedance seen at the unloaded output or input terminals of transmission equipment or a line in otherwise normal operating condition. 2. See terminal resistance. terminal leg -See terminal stub. terminal lug-1. A threaded lug to which a wire may be fastened in a terminal box. 2. A cylindrical piece of metal, either solid or hollow and of two or more diameters, that can be stacked, flared, swaged, or pressed into a hole for the purpose of connecting leads or external wires to the conductive pattern. terminal mode-Condition of a PC when it is connected to a host computer. terminal p a d -An alternate term for terminal area. terminal pair-An associated pair of accessible terminals (e.g., the input or output terminals of a device or network.) terminal repeater- 1. An assemblage of equipment designed specificallyfor use at the end of a communication circuit-as contrasted with the repeater, which is designed for an intermediate point. 2. Two microwave terminals arranged to provide for the interconnection of separate systems, or separate sections of a system. terminal resistance- Also called termiual impedance. The total resistance measured between the input terminals of a meter. For an ac meter, it is the effective dc resistance measured by the voltage-doubling or substitution technique with rated end-scale input of the appropriate frequency applied. terminal resistor-A resistor used as a terminating device. terminal room-In telephone practice, a room associated with a central office, private branch exchange, or private exchange that contains distributing frames, relays, and similar apparatus. terminal station -The microwave equipment and associated multiplex equipment employed at the ends of a microwave system. terminal strip-See terminal board. terminal stub-Also called terminal leg. A piece of cable that comes with a cable terminal for splicing into the main cable. terminal unit-Abbreviated TU. 1. An apparatus that terminates the considered interface system and by means of which a connectiou (and translation, if required) is made between the considered interface system and another external interface system. 2. The RTTY equivalent of a modem. It contains a modulator, demodulator, and loop power supply. 3. Equipment usable on a communication channel for either input or output. terminal VHF omnirange-Veq high frequency omnirange, normally low powered, complete with a locd monitoring device that will automatically shut down the facility if it is not operating properly. terminated line- A transmission line terminated in a resistance equal to the characteristic impedance of the line, so that there is no reflection or standing waves. terminating -The closing of the c i r d t at either end of a line or transducer by connection to some device.

77 1 Terminating does not imply any special condition, such as the elimination of reflection. terminating capacitor -A capacitor sometimes used as a terminating device for a capacitance sensor antenna. The capacitor alllows the supervision of the sensor antenna, especially if a long wire is used as the sensor. terminating device-A device that is used to terminate an electrically supervised circuit. It makes the electrical circuit continuous and provides a fixed impedance reference (end of line resistor) against which changes are measured to detect an alarm condition. The impedance changes may be caused by a sensor, tampering, or circuit trouble. termination- 1. A load connected to a transmission line or other device. To avoid wave reflections, it must match the characteristic impedance of the line or device. 2. A waveguide technique; the point at which energy flowing along a waveguide continues in a nonwaveguide mode of propagation. 3. The terminals at an antenna to which the transmission line is connected (screw terminals, solder connections, coaxial connector, etc.). termination block-A nonconductive material on which are provided several termination points. ternary- 1, A numerical system of notation using the base 3 and employing the characters 0, 1, and 2. 2. Able to assume three distinct states. ternairy code-A code in which each element may be any one of three distinct kinds or values. ternary gates-Ternary circuits that operate on three logic states at a time-that is, in base 3 arithmetic instead of base 2. ternary incremental representation-A type of incremental representation in which the value of an increment is rounded to one of three values plus or minus one quantum or zero. ternary pulse-code modulation-A form of pulse-code modulation in which each element of information is represented by one of three distinct values, e.g., positive pukes, negative pulses, and spaces. terrain-avoidance radar- Airborne radar that provides a display of terrain ahead of a low-flying airplane to permit horizontal avoidance of obstacles. terrailn-clearance indicator-A device for measuring the distance from an aircraft to the surface of the sea or earth. terraiin error-In navigation, the error resulting from distortion of the radiated field by the nonhomogeneous characteristics of the terrain over which the radiation in question has been propagated. terrain-following radar- Airborne radar that provides a display of terrain ahead of a low-flying aircraft to permit manual control, or signals for automatic control, to maintain constant altitude above the ground. terrestrial interference-Abbreviated TI. Interference of earth-based microwave communications with reception of satellite broadcasts. terrestrial-reference flight -Stabilized flight in which control information is obtained from terrestrial phenomena (e.g., flight in which basic information derived from the magnetic field of the earth, atmospheric pressure, and the like is fed into a conventional automatic pilot). ay coil-A third coil used in the output transformer of an audio amplifier to supply a feedback voltage. tertiary winding-1. A winding added to a transformer, in addition to the conventional primary and seconday windings, k~suppress third harmonics or to make connections to a power-factor-correcting device. 2. See stabilized winding. tesla -The SI unit of magnetic flux density, equal to 1 weber per square meter. Letter symbol: T.

terminating capacitor

- test pattern

Tesla coil -An air-core transformer used for developing high-voltage discharge at a very high frequency. It has a few turns of heavy wire as the primary and many turns of fine wire as the secondary. test-A procedure or sequence of operations for determining the manner in which equipment is functioning or the existence, type, and location of any trouble. test bed-A test site that either contains or simulates all hardware and software interfaces. test bench-Equipment designed specifically for making overall bench tests on equipment in a particular test setup under controlled conditions. test board -A switchboard equipped with testing apparatus arranged so that connections can be made from it to telephone lines or central office equipment for testing purposes. test clip-A spring clip fastened to the end of an insulated wire to enable quick temporary connections when circuits or devices are being tested. test driver-Tool providing the facilities needed to execute a program, e.g., inputs or files, and commands. May also evaluate outputs and produce reports. testing level-The value of power used for reference, represented by 0.001 watt working into 600 ohms. test jack- 1. A jack that makes a circuit or circuit element available for testing purposes. 2. In recent practice, a jack that is multiplied with the operating jack on the switchboard. test language-A procedure or programming language designed or adapted for the development of test specifications and routines. test lead-1. A flexible, insulated lead wire that usually has a test prod on one end. It is ordinarily used for making temporary electrical connections. The insulation normally is rubber; the standard colors are red and black. 2. A flexible insulated lead used chiefly for connecting meters and test instruments to a circuit under test. test loop -A cycle of tests that can be repeated over and over, e.g., to locate intermittent faults. test oscillator-A test instrument that can be set to generate an unmodulated or tone-modulated radiofrequency signal at any frequency needed for aligning or servicing receivers and/or amplifiers. test pattern-A geometric pattern containing a group of lines and circles, used for testing the performance of a television receiver or transmitter by revealing the following video-signal characteristics: horizontal linearity, vertical linearity, contrast, aspect ratio, interlace, streaking, ringing, vertical resolution, and horizontal resolution. The camera is focused on the chart, and the pattern is viewed for fidelity at the monitor.

Test pattern.

test point - thermal compression bonding

test point- 1. A connection to which no instrument is permanently connected, but which is intended for temporary, intermittent, or future connection of an instrument. 2. A convenient, safe access to a circuit or system. test prod-A sharp metal point used for making a touch connection to a circuit terminal. It has an insulated handle and a means for electrically connecting the point to a test lead. test program -1. A software component that implements a test procedure. 2. A particular group of test sequences or test patterns. test record -A phonograph disc designed to test the quality and characteristics of turntables, pickups, amplifiers, etc. test routine-In a computer: 1. A synonym for check routine. 2. Generally both the check and the diagnostic routines. test s e q u e n c e - A group of test steps or test patterns. test set -1. One or more instruments required for servicing of a particular type of equipment. 2. Also called analyzer, circuit verifier, and tester. An assembly of instruments that electrically simulate and monitor electronic equipment. Some test sets are used to service equipment. test to failure -The practice of inducing increased electrical and mechanical stresses in order to determine the maximum capability of a device so that conservative use in subsequent applications w ill thereby increase its life through the derating determined by these tests. test tone-A tone used in circuit identification for purposes of locating trouble or making adjustments. tetrad-A group of four, especially a group of four pulses used to express a digit in the scale of 10 or 16. tetrode-A four-electrode electron tube containing an anode, a cathode, a control electrode (grid), and one additional electrode that is ordinarily a screen grid. tetrode junction transistor- See double-base junction transistor. tetrode transistor-A junction transistor with two electrode connections to the base to reduce interelement capacitance (in addition to the normal emitter and collector elements, each having one connection). Te value-The temperature at which the resistance of a centimeter cube is 1 megohm. TE wave- Abbreviation for transverse electric wave. text-1. In U.S. ASCII and communications, a sequence of characters treated as an entity if it is preceded by one STX communication control character and terminated by one EXT communication control character. 2. The control sections of an object or load module, considered together. 3. The part of a message or transaction between the control information of the header and that of the trace section or tail that constitutes the information to be processed or delivered to the addressed location. 4. The main part of the message that is sent from a data source (host) to a data link (terminal). It is usually preceded by a header and followed by an “End of Text” signal. text editing-A general term that encompasses any rearrangement or change perfomed on textual material, such as deleting, adding, or reformatting. text fonts-A complete set of one-character type. Tflip-flop- 1. Also called binary. A type of flip-flop whose outputs change state each time the input-signal voltage falls from 1 to 0 and remain unchanged when the input-signal voltage rises from 0 to 1. Thus, there is one change in output state for every two changes in input signal, and the frequency of the output is half the frequency of the input. 2. A flip-flop with only one input. When a pulse appears on the input, the flip-flop changes

772 states. (Used in ripple counters.) 3. Also called toggle or trigger flip-flop. A circuit that performs the divide-by-two function; frequently used in counting applications. thallofide cell-A photocondncting cell that has thallium oxysulfide as the light-sensitive agent. THD- Abbreviation for total harmonic distortion. theoretical acceleration at stall -A figure of merit derived from the stall-torque to rotor-inertia ratio, which indicates how rapidly a motor will accelerate from stall. theoretical Cutoff-See theoretical cutoff frequency. theoretical cutoff frequency- Also called theoretical cutoff. The frequency at which, disregarding the effects of dissipation, the attenuation constant of an electric structure changes from zero to a positive value or vice versa. theoretical electrical travel -The shaft travel over which the theoretical function characteristic of a precision potentiometer extends, as determined from the index point. theremin -An electronic musical instrument consisting of two radio-frequency oscillators that beat against each other to produce an audio-frequency tone, in a manner similar to a beat-frequency audio oscillator. The pitch and volume are varied by hand capacitance. thermal-A general term for all forms of thermoelectric thermometers, including a series of couples, thermopiles, and single thermocouples. thermal agitation-1. Movement of the free electrons in a material. In a conductor they produce minute pulses of current. When these pulses occur at the input of a high-gain amplifier in the conductors of a resonant circuit, the fluctuations are amplified together with the signal currents and heard as noise. 2. Also called thermal effect Minute voltages arising from random electron motion, which is a function of absolute temperature expressed in kelvins. 3. In a semiconductor, the random movement of holes and electrons within a crystal due to the thermal (heat) energy. thermal-agitation voltage-The potential difference produced in circuits by thermal agitation of the electrons in the conductor. thermal alloying-The act of uniting two different metals to make one common metal by the use of heat. thermal ammeter-See hot-wire ammeter. thermal breakdown - 1. A form of breakdown in which decomposition or melting occurs due to the temperature rise resulting from the applied electric stress. 2. A runaway condition in a dielectric, the loss factor of which increases with temperature. Dielectric loss heats the material, producing an increase in tempemture. Therefore, the dielectric loss increases still more, producing a further increase in temperature, and so on. thermal circuit breaker-A circuit breaker whose operation depends on temperature expansion due to electrical heating. thermal coefficient of resistance-The change in the resistivity of a substance due to the effects of temperature only. Usually expressed in ohms per ohm per degree change in temperature. thermal compensation -A method employed to reduce or eliminate the thermal effects on one or more of the performance parameters of a transducer. thermal c o m p r e s s i o n bonding -Diffusion bonding whereby two carefully prepared surfaces are brought into intimate contact under carefully controlled conditions of temperature, time, and clamping pressure. Plastic deformation is induced by the combined effects of pressure and temperature, which in turn results in atom movement causing the development of a crystal lattice bridging the

773

gap between the facing surfaces and results in bonding. (Time is a critical factor in controlling the ambient temperature at the area to be bonded and the size of the bond that is formed.) Generally, the process is performed under a protective atmosphere of inert gas to keep the surfaces to be bonded clean while they are being heated. thermal conduction-1. The transfer of thermal energy by processes having no net movement of mass and having rates proportional to the temperature gradient. 2. The rate of flow of heat through a material by thermal conductilon. thermal conductivity-A measure of the ability of a substance to conduct heat. Expressed in terms of calories of heat conducted per second per square centimeter per centimeter of thickness per degree Celsius difference in temperature from one surface to the other. thermal conductor--A material that readily transmits heat by conduction. thermal contraction -The shrinkage exhibited by most metals when cooled. thermal converter- Also called thermocouple converter, thermoelectric converter, thermoelectric generator, or thermoelement. One or more thermojunctions in thermal contact with, or an integral part of, an electric heater, so that the electromotive force developed by thermoelectric action at the output terminals gives a measure of the input current in the heater. thermal cutout -1. An overcurrentprotective device that contains a heater element that affects a fusible member and thereby opens the circuit. 2. A heat-sensitive switch that automatically opens the circuit of an electrical device when the operating temperature of the device exceeds a predetermined value. thermal derating factor-The factor by which the power dissipation rating must be reduced with an increase of ambient or case temperature. thermal detector -See bolometer. thermal drift-A change in the output of a ~ g u iated power supply over a. period of time, due to changes in internal ambient temperatures not normally related to environmental changes. Thermal drift is usually associated with changes in line voltage and/or load changes. thermal effect-See thermal agitation, 2. thermal emf -The electromotive force generated when thle junction of two dissimilar metals is heated. See d S 0 Seebeck emf. thermal endurance- An indication of the relative life expectancy of a prodluct when exposed to operating temperatures much higher than no& room temperature. therimal equilibrium-The condition that exists when a system and its surroundings are at the same temperature. ~ h e r ~expansion al - 1. Physical expansion resulting from an increase in temperature; it may be linear and volumetric. 2. The expansion of a material when subjected to heat. thermal flasher- An electric device that automatically opens rand closes a circuit at regular intervals, owing to alternate heating and cooling of a bimetallic strip heated by a resistance element in series with the circuit being controllled. thermal generation-The creation of a hole and a free electron by freeing a bound electron through the addition of heat energy. thermal instrument-An instrument that depends on the heating effect of an electric current for its operation (e.g., tkiennocouple and hot-wire instruments). thermal ionization-Ionization due to high temperature (e.g., in the electrically conducting gases of a flame). thermal junction -See thermocouple.

thermal conduction

- thermal radiiation

thermal lag-The t h e expended in raising the entire mass of a cathode structure to the temperature of the heater. thermal life-The operating life of a device under varying ambient temperatures. thermal microphone-A microphone depending for its action on the variation in the resistance of an electrically heated conductor that is being alternately increased and decreased in temperature by sound waves. thermal noise-Also called resistance, Johnson, and white noise. 1. Random circuit noise associated with the thermodynamic interchange of energy necessary to maintain thermal equilibrium between the circuit and its surroundings. See also Johnson noise. 2. Noise generated by the random thermal motion of charged particles. 3. A voltage, produced by the random motion of free electrons in a conductor, whose value is instantaneously fortuitous with time and whose spectral components uniformly embrace the electromagnetic gamut -albeit the bandwidth of m y practical circuits limit both the noise spectrum and magnitude as well. Thermal noise is characterized by a normal distribution of levels. 4. A type of electromagnetic noise produced in conductors or in electronic circuitry that is proportional to temperature. 5. Noise that occurs in all transmission media and communications equipment as a result of random electron motion (which is a function of temperature). Thermal noise sets the lower limit for the sensitivity of a receiving system. thermal noise level-The equivalent rms voltage value, over a stated bandwidth, of all energy components generated by a resistor at a stated resistor temperature with no externally supplied current through the resistor. thermal oxidation-The formation of a self-oxide on the exposed surfaces of a semiconductor. thermal printer-1. A nonimpact printing device that utilizes a special heat-sensitive paper. The paper passes over a matrix of dot heating elements. As data is fed to the printer, dot elements relating to specific characters are heated, which changes the color of the paper at that point to reveal individual characters. 2. A printer that forms characters in a dot matrix by selectively heating printhead elements as they move across the paper.

.c\

THERMAL PRINTING WIRE ON HEAD REPLACEABLE THERMAL PRINTING HEAD

.

.

w ,, \

,

\

HEAT~ENSITIVEPAPER

PRINTING HEAD IN PRINTER

Thennal (maaiw) printer.

thermal protector- A current- and temperatureresponsive device used to protect another device against overheating due to overload. thermal radiation-Commonly known as heat. 1. Radiation produced by the action of heat on molecules

thermal rating

- thermionic converter

774

or atoms. Its frequency extends between the extremes of infrared and ultraviolet. 2. The process of electromagnetic emission in which the radiated energy is extracted from the thermal excitation of atoms or molecules. thermal rating - 1. A statement of the permissible temperature rating, beyond which unsatisfactory performance occurs. 2. The maximum or minimum temperature at which a material or component will perform its function without undue degradation. t h e r m a l regenerative cell -A fuel-cell system in which there is continuous regeneration of the reactants from the products formed during the cell reaction. t h e r m a l relay-A relay that responds to the heating effect of an energizing current, rather than to the electromagnetic effect. Delay between the start of the energizing current and the switching response is generally predictable and sometimes adjustable. thermal resistance-1. Ratio of the temperature rise to the rate at which heat is generated within a device under steady-state conditions. 2. The resistance of a substance to the conductivity of heat. 3. That change in the electrical resistance of a material when subjected to heat. 4. Of a semiconductor device, the quotient of the temperature difference between two specified points or regions and the heat flow between these two points or regions under conditions of thermal equilibrium. thermal resistivity-Thermal resistance of a unit cube of material. t h e r m a l resistor-An electronic device that makes use of the change in resistivity of a semiconductor with changes in temperature. See thermistor. thermal response time-The time from the occurrence of a step change in power dissipation until the junction temperature reaches 90 percent of the final value of junction-temperature change, when the device-case or ambient temperature is held constant. thermal runaway- 1. A regenerative condition in a transistor, whereby heating at the collector junction causes collector current to increase, which in turn causes more heating, etc. The temperature can rapidly approach levels that are destructive to the transistor. 2. An unstable condition common in bipolar transistors occurring because collector current and gain both increase with device temperature. Permanent damage can result if circuit precautions are not taken. permanent change t h e r m a l sensitivity set-A in sensitivity due to temperature effects only. Usually expressed as the difference in sensitivity at room temperature before and after a temperature cycle over the operating temperature range of the transducer.

thermal shock-1. A sudden, marked change in the temperature of the medium in which a component or device operates. 2. The effect of heat or cold applied at such a rate that nonuniform thermal expansion or contraction occurs within a given material or combination of materials. In connectors, the effect can cause inserts and other insulation materials to pull away from metal parts. t h e r m a l telephone receiver- Also called thermophone. An electroacoustic transducer, such as a t e l e phone receiver, in which the temperature of a conductor is caused to vary in response to the current input, thereby producing sound waves as a result of the expansion and contraction of the adjacent air. thermal time constant-1. The time from the occurrence of a step change in power dissipation until the junction temperature reaches 63.2 percent of the final value of junction-temperature change, when the devicecase or ambient temperature remains constant. 2. In a thermistor, the time required for 63.2percent of the change from initial to final body temperature after the application of a step change in temperature under zeropower conditions. thermal time-delay relay-A type of relay in which the time interval between energization and actuation is determined by the thermal storage capacity of the actuator critical operating temperature, power input, and thermal insulation. thermal time-delay s w i t c h -1. An overcurrent protective device containing a heater element and thermal delay. 2. A switch whose contacts control a load circuit and are delayed from operating for a predetermined time interval. Operation of the contacts is by the effect of heat generated by current through a heater. t h e r m a l tuning -Adjusting the frequency of a cavity resonator by using thermal expansion to vary its shape. t h e r m i c -Pertaining to heat. thermion-An ion, either positive or negative, that has been emitted from a heated body. Negative thermions are electrons (thermoelectrons). thermionic- 1. Pertaining to the emission of electrons by heat. 2. Pertaining to the emission of electrons or ions from an incandescent body. thermionic c a t h o d e -See hot cathode. thermionic converter- Also called thermionic generator or thermoelectron engine. A device that produces electrical power directly from heat. One type contains a heated cathode to emit electrons and a cold anode to collect them, thereby causing a current. Both electrodes are enclosed in a vacuum or gas-filled envelope.

EXCESS HEAT RADIATED AWAY ENVELOPE THERMAL CONDUCTION LOSSES ELECTRON FLOW

OUCTION LOSSES RADIATION LOSSES FROM CATHODE TO ANODE

HEAT ENERGY INPUT

ECTRON CMJLING AT THE CATHODE CAUSED BY ELECTRONS BOILING OFF

Thermionic converter.

thermionic current

775 thermionic current-Current due to directed movements of thermions (e.g., the flow of electrons from the cathode to the plate in a thermionic vacuum tube). thermionic detector-A detector circuit in which a thermionic vacuum tube delivers an audio-frequency signal when fed with a modulated radio-frequency signal. thermionic diode-A diode electron tube that has a heated cathode. thermionic emission- 1. Emission of electrons from a solid body as a result of elevated temperature. See also Edison effect. 2. 'That portion of the emission of electrons from a hot cathode in a vacuum tube which is due solely to the elevated temperature of the cathode. thermionic energy Conversion-The direct production *ofelectricity by means of the electron emission from a heated substance. thermionic generatar- See thermionic converter. thernnionic grid emission -Also called primary grid emission. The current produced by the electrons thennionically emitted from a grid. Generally it is due to excessive grid temperatures or to contamination of the grid wires by cathode coating material. thermionic rectifier-A rectifier utilizing a thermionic vacuum tube to convert alternating current into unidirectional current. thermionic tube-See hot-cathode tube. thermionic work function-The energy required to transfer electrons from a given metal to a vacuum or some other adjacent medium during thermionic emission. thermistor- Also called thermal resistor. 1. A thermally sensitive solid-state semiconducting device made by sintering lnixtures of the oxide powders of various metals. (Made in many shapes, such as beads, disks, flakes, washers, and rods, to which contact wires are attached.) As its temperature is increased, the electrical resistanrx (typically) decreases. The associated temperature coe,fficient of resistance is extremely high, nonlinear, and most frequently negative. The large temperature coefficients and the nonlinear resistance temperature characteristics of thermistors enable them to perform many unique regulatory functions. 2. A passive semiconductor device whose electrical resistance varies with temperature. Its temperature coefficient of resistance is high, nonlinear, and usually negative. 3. A solid-state semiconducting structure (basically one of the bolometers) that changes electrical resistance with temperature. Materially, some kind of ceramic composition is used. It is of much higher electrical resistance than metallic bolometers and, hence, requires much higher voltages to become useful. 4. A resistor with a high temperature coefficient of resistance, exhibiting a definite, reliable, repeatable response to temperature change. Negative temperature coefficient (TC) types show an exponential decrease in resistance as temperature increases. Positive TC types show an increase

- thermocompression bonding

in resistance with increasing temperature. 5 . A resistor that is sensitive to temperature changes. It will change in ohmic value as a function of changing temperature.

4

E

D WIRE

A

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Bead.

a Road.

Washer.

20

e 2 =

04

02

04

01

10

4

10

40

MILLIAMPERES

Typical characteristic.

Thermistors.

thermoammeter- Also called a thennocouple ammeter. An ammeter that is actuated by the voltage generated in a thermocouple through which the current to be measured is sent. It is used chiefly for measuring radio-frequency currents. thermocompensator-In pH meters, a temperatwesensitive device sometimes used to make electronic adjustments in the circuit that are required due to changes in the temperature of the solution. thermocompression bond -A bond formed by two elements through the simultaneous application of heat and pressure. No additional materials are used to assist the fusing. Common types of thermocompression bonds are wedge, ball (nailhead), and stitch. See ball bond; stitch bond. thermocompression bonding- 1. A method of interconnecting ICs in a circuit by bonding thin gold wires between conducting patterns of a circuit and to the IC chip's metal preforms by means of heat and pressure. 2. The joining of two materials by the combined effects of heat and pressure. FORCE

FORCE

i

i DUCTILE LEAD MATERIAL (TYPICALLY 0 0007 TO 0 0015111OR 17 a TO SCISSORS CUTOFF)

SUBSTRATE HOLDER

I

d, SUBSTRATE

I

Capillary

Wedge

Thennocompressionbonding.

thermocouple

- thermoelectric manometer

thermocouple -Also called thermal junction. 1. Temperature transducer comprising a closed circuit made of two different metals. If the two junctions are at different temperatures, an electromotive force is developed that is proportional to the temperature difference between the junctions. This is called the Seebeck effect. 2. Dissimilar metals that, when welded together, develop a small voltage dependent on the relative temperature between the hotter and the colder junction. Banks of thermocouples connected together in series of parallel make up a thermopile. Either may be thought of as a weak battery that converts radiant to electrical energy. 3. A device for measuring temperature in which two electrical conductors of dissimilar metals are joined at the point of heat application and a resulting voltage difference, directly proportional to the temperature, is developed across the free ends and is measured potentiometrically. 4. A pair of dissimilar-metal wires, joined so that when their junction is heated, the thermoelectric effect causes a voltage to be generated that is proportional to the temperature.

HEATER FILAMENT

FILAMENT SUPPORT WIRE GLASS

Thermocouple.

thermocouple ammeter-See thermometer. thermocouple contact - A contact of special material used in connectors employed in thermocouple applications. Materials often used are iron, constantan, copper, chromel, alumel, and others. thermocouple converter-See thermal converter. thermocouple instrument-An electrothermic instrument in which one or more thermojunctions are heated by an electric current, causing a direct current to flow through the coil of a suitable direct-current mechanism such as one of the permanent-magnet, moving-coil type. thermocouple junction -A pair of electrically dissimilar metals that make intimate contact and generate a voltage related to temperature. thermocouple lead wire- An insulated pair of wires used from the thermocouple to a junction box or to the recording instrument. thermocouple thermometer -See thermoelectric thermometer. thermocouple vacuum gage -A vacuum gage that depends for its operation on the thermal conduction of the gas present. The pressure being measured is a function of the electromotive force of a thermocouple whose measuring junction is in thermal contact with a heater carrying a constant current. Thermocouple vacuum

776 gages ordinarily are used over a pressure range of lo-' to mm Hg. thermocouple wire-A wire drawn from special metals or alloys and calibrated to established specifications for use as a thermocouple pair (e.g., iron, constantan, alumel, etc.). thermodynamics- 1. The study of the relationship between heat and other forms of energy. 2. Examination of the processes whereby heat energy is converted into other forms of energy. thermoelectric arm -Also called thermoelectric leg. The portion of a thermoelectric device having the electric current density and the temperature gradient approximately parallel or antiparallel and having electrical connections made at its extremities to a part in which the opposite relation between the direction of the temperature gradient and the electric current density exists. thermoelectric converter - A device capable of converting heat energy directly into electrical energy. See also thermal converter. thermoelectric cooler-1. A device utilizing the Peltier phenomenon to provide a silent, nonmoving cooler having a controllable cooling rate. 2. A solid-state device that cools as current passes through it. thermoelectric couple-A thermoelectric device in which there are two arms of unlike composition.

HOT JUNCTIONS

I

COLD JUNCTION

/

Thennoelectric couple.

thermoelectric device-A general term for thermoelectric heat pumps and generators. thermoelectric effect -The electromotive force produced by the difference in temperature between two junctions of dissimilar metals in the same circuit. thermoelectric engine -See thermoelectric converter. thermoelectricgenerator -See thermal converter. thermoelectric heating device-A thermoelectric heat pump used for adding thermal energy to a body. thermoelectric heat pump-A device in which the direct interaction of an electrical current and heat flow is used to transfer thermal energy between bodies. thermoelectricity- 1. The d m t conversion of heat into electricity. 2. The reciprocal use of electricity to create heat or cold. See also Peltier effect; Seebeck effect; Thomson effect. 3. Electricity produced by the agency of heat alone. See also thermocouple. thermoelectric junction -1. A thermojunction, as in a thermocouple. 2. A junction between dissimilar wires in a thermocouple or thermopile. A potential difference is created at that junction by the application of heat. thermoelectric leg-See thermoelectric arm. thermoelectric manometer-A manometer (pressure-measwing instrument) that depends on the variation of thermoelectromotive force (voltage due to heat) with pressure.

777 thermoelectric series- A series of metals arranged in the order of their thermoelectric powers. thermoelectric solar cell-A solar cell that uses a thermoelectric converter, consisting of two sheets of metal with a semiconductor sandwiched between them, to generate electricity. thermoelectric thermometer- Also called a tthermocciuple thermometer. A thermometer employing one or more thermocouples, of which one set of measuring junctions is in thermal contact with the body whose temperature is to be measured, while the temperature of the reference junctions is either known or otherwise taken into account. thernroelectromotive force -1. The voltage developed due to the differences in temperature between parts of a circuit containing two or more different metals. 2. The algebraic sum of the Peltier emf at a thermocouple junction and the Thomson emf in the thermocouple metals. thermoelectron -The electron emitted from a heated body. thermoelectron engine-See thermionic converter. thermoelement -A device consisting of a thermocouple and a heating element arranged for measuring small currents. See also thermal converter. thermogalvanometer- An instrument for measuring small high-frequency currents from their heating effect. Generally it consists of a dc galvanometer connected to a thennocouple that is heated by a filament carrying the current to be measured. thernnograrn-High-resolution images resulting from a series of thermal scans using a bolometer. h --Radiation chart that plots heat emitted by the body. thermography- 1. The process of recording the distribution of temperature over the surface of an object by detecting the heat radiation from it. The detection may be by the effect of radiation on an infrared-sensitive phosphor or by the use of cholesteric liquid crystals that exhibit brilliant colors with temperature change. 2. The recording of a scanned pattern on a photographic medium, utilizing the infrared radiation naturally emitted by the object, as well as infrared receptors, such as photoelectric cells. 3. The technique of producing pictures from heat. t ~ ~ r r ~ o j ~ n c-One t i o n of the contact surfaces between the two conductors of a thermocouple. The thermojunction in thermal contact with the body under measurement is called the measuring junction, and the other thermojunction is called the reference junction. ~ h ~ r ~ o j battery ~ n ~ -At ~ nuclear-type ~ n battery that converts heat into electrical energy directly by the thermoelectric or the Seebeck effect. thermoluminescence- 1. The production of light in a material by moderate heat. 2. An alternative term for incandescence. thermomagnetic- 1. Pertaining to the effect of temperature on the magnetic properties of a substance. 2. Pertaining to the effect of a magnetic field on the temperature distribution in a conductor. thermometer -An instrument for measuring temperature. Electrical versions depend on the change in resistance of a material with temperature, the voltage produced in a thermocouple, or various other effects of temperature. therrnophone-An electroacoustic transducer in which sound waves of calizulable magnitude are produced by the expansion and contraction of the air adjacent to a conductor whose temperature varies in response to a current input. See also thermal telephone receiver.

thermoelectric series

- thermostatic switch

thermopile -A group of thermocouples connected in series. Specifically: 1. A device used to measure radiant power or energy. 2. A source of electric energy. 3. Battery of thermocouples, consisting of alternate rods of antimony and bismuth suitably joined and connected to a galvanometer. Thermopiles are used for the measurement of heat where thermometers cannot be employed. thermoplastic -1. A term describing plastic materials that can be made to flow repeatedly by applying heat. Lowering the temperature causes hardening. See thermosetting. 2. A type of plastic that can be remelted a number of times without any important change in properties. For example, nylon, lexan, and PVC are thermoplastic plastics. Such plastics are resilient after molding. 3. A classification of resin that can be readily softened and resoftened by repeated heating. thermoplastic flow test-For an insulating material, a measure of the resistance to deformation when subjected to heat and pressure. thermoplastic material -A plastic material that can be softened by heat and rehardened into a solid state by cooling. This remelting and remolding can be done many times. thermoplastic polyesters-Family of plastics with excellent dimensional stability, electrical properties, toughness, and chemical resistance. thermoplastic recording-A recording process in which information is placed onto plastic tape electronically. A special electron gun, fed by a digital or scanner input, writes a charge in narrow bands on a moving film coated with a plastic that has a low melting point. The film is heated by an rf heater that melts the plastic coating, permitting it to be deformed by electrostatic and surfacetension forces in proportion to the charge laid down by the beam of the electron gun. The ridges cool quickly and form a diffraction grating that can then be viewed, projected by suitable optics, or read out by a flying-spot scanner. The system operates in a high vacuum. thermosetting-1. A term describing plastic materials that are capable of becoming essentially insoluble or infusible when cured. Once cured, these materials do not soften or flow. See thermoplastic. 2. A term used to describe materials that are processed using steam or radiation. After processing the materials cannot be made to flow under the application of heat. 3. A classification of resin that cures by chemical reaction when heated and, when cured, cannot be resoftened by heating. thermosetting material--Plastic that hardens when heat and pressure are applied. Unlike a thermoplastic, it cannot be remelted or remolded. thermosetting plastic-A type of plastic in which an irreversible chemical reaction takes place while it is being molded under heat and pressure. This type of plastic cannot be reheated or softened without adversely affecting its properties. Melamine and diallyl-phthalate are thermosetting plastics. thermostat-A mechanism that can be set to operate at definite temperatures and can convert the expansion of heated metal or fluid into sufficient movement and power to operate small devices, control electric circuits or small valves, etc. thermostatic switch -1. A temperature-operated switch that receives its operating energy by thermal conduction or convection from the device being controlled or operated. 2. A switch whose function is controlled by variations of temperature and whose contacts make or break a load circuit automatically when the temperature of the ambient space in which its sensing element is placed or the temperature of the smface on which it is fixed reaches a predetermined value.

t h e r m o s t a t wire

- thick-film resistor

Thermostat. t h e r m o s t a t wire- Single or multiple-conductor wire, bare soft solid-copper conductor, usually PVC insulated. May be twisted and/or jacketed. May have enameled or nylon covered conductors and may have a metal armor covering. May also have asbestos insulations. It is used to transmit electrical signals between the thermostat and the heating or cooling unit. t h e t a -Brain wave signals whose frequency is approximately 3.5 to 7.5 Hz. The associated mental state is fuzzy, unreal, uncertain, daydreamlike, or ambiguous. t h e t a polarization-The state of the wave whereby the E vector is tangential to the meridian lines of some given spherical frame of reference. Thevenin’s theorem-The current that will flow through an impedance 21when connected to any two terminals of a linear network between which an opencircuit voltage E and impedance 2 previously existed is equal to the voltage E divided by the sum of 2 and Z1. thick film-1. Pertaining to a film pattern usually made by applying conductive and insulating materials to a ceramic substrate by a silk-screen process. Thick films can be used to form conductors, resistors, and capacitors. 2. Successive layering of resistive, dielectric, and conductive inks on a substrate by a type of screening process. 3. Technology using pastes to form conductor, resistor, and insulator patterns; usually screened onto the substrate and cured by firing at temperatures of 800°C to 900°C. While less expensive than thin films, thickfilm resistors exhibit somewhat poorer matching and temperature coefficients. 4.A layer of resistive, dielectric, or conductive paste that is deposited on a substrate by screen printing, then fired at an elevated temperature to drive off the binder and sinter the solids. By definition, the thickness is greater than lo4 angstroms (O.OOO4 inch),

778 although characteristically it is O.OOO4 to 0.001 inch (6.3 to 25 pm). thick-film assembly-Network deposited on a ceramic substrate, in combination with discrete active elements, forming a complete hybrid functional circuit. thick-film circuit- 1. A microelectronic assembly in which the passive circuit elements and their interconnections are defined on a ceramic substrate by using the silk-screen process. The active elements are added as discrete chips or packaged devices. 2. Conductive, resistive, andor capacitive network deposited on a substrate using a metallic or resistive film that is more than 5 micrometers in thickness. 3. A completed assembly of a thick-film substrate and possible add-on components, with its appropriate terminations and packaging. 4. A microcircuit whose passive components consist of a ceramic-metal combination deposited on a given substrate by screening and firing processes. thick-film hybrid integrated circuits-The physical realization of a hybrid integrated circuit fabricated on a thick-film network. thick-film hybrids- 1. A hybrid circuit in which conductive and resistive pastes are deposited on a substrate and heated. Heating hardens the paste and fuses it to the substrate. Once hardened, the resistive pastes become thick-film resistors, named because the thickness is about 1 mil (25 pm). Capacitors, discrete semiconductors, and ICs are then added to the circuit. 2. A thick-film circuit with add-on components other than encapsulated chips. thick-film network-A thick-film circuit that does not have add-on components. thick-film process- 1. A method in which electronic circuit elements -resistors, conductors, capacitors, etc. -are produced by applying specially formulated pastes to a ceramic substrate in a defined pattern and sequence. The substrate containing the “green pattern” is fired at a relatively high temperature to mature the circuit elements and bond them integrally to the substrate. The term thick film distinguishes this technology from thin-film practice, in which circuit elements are made by evaporation or sputtering in a high-vacuum environment. Circuits produced by this technology are identified by several descriptive phrases: thick-film passive circuits or thick-film hybrid circuits when active devices are included. 2. A method of manufacturing hybrid circuits by screen deposition of conductive, resistive, or insulating films thicker than 0.005 inch (127 pm). Thick-film structures generally contain only conductors, resistors, and capacitors, with any other required components added as discrete devices. thick-film resistor-A fixed resistor whose resistance element is a film considerably more than 0.001 inch (25 pm) thick.

FILM CAPACITOR TRANSISTOR CHIP

RESISTOR CAPACITOR CHIP

0CONDUCTOR Thick-film hybrid integrated circuit.

779

thick-film resistor, conductor, and dielectric compostions

thick-film resistor, conductor, and dielectric compostions-The principal materials for making thick-film circuits, available in paste form and consisting of mixtures of metal, oxide, and glass powders. thick-film resistor network-A combination of several resistors manufactured by incorporating the use of precious metal inks, screen printed and 6red onto alumina substrates. thick films-Layers of resistive, dielectric, and conductive inks that are deposited on a substrate. The deposition process, similar to graphic silk screening, employs a fine-mesh screen to hold the pattern for the components that are to be deposited. The pattern is produced by photographic means, and wherever the inks are not to be deposited, the holes in the mesh are blocked by an emulsion. thick-film substrate-A supporting material (commonly alumina) on which circuit elements such as conductors, resistors, inductors, and capacitors have been realized by a printing and firing technique. thickness vibration -Vibration of a piezoelectric crystal in the direction of its thickness. thin film-I. A film of conductive or insulating material, usually deposited by sputtering or evaporation, that may be made in a pattern to form electronic components and conductors on a substrate or used as insulation between successive layers of components. 2. The deposition of thin layers of a substance on an insulatin,gbase in a vacuum by a microelectronic process. 3. A conductive, resistive, and/or capacitive passive network deposited on a substrate using a metallic or resistive film that is less than 5 micrometers in thickness. 4.Metal film used to fabricate conductors and resistors, usually a few hundred angstroms thick. Commonly used resistor materials are nickel-chromium, tantalum nitride, and silicon-chromium. These films are usually deposited using sputtering, vacuum evaporation, or electron-beam techniques. 5. A method of manufacturing hybrid circuits in which evaporation or sputtering techniques are used to deposit very thin films of material onto a substrate. These film structures generally contain only conductors, resistors, and capacitors, with any other required components added as discrete devices. thin-film assembly-Passive or active network deposited on a suitable substrate using vapor or vacuum deposition techniques. The components may be produced individually, they may be totally integrated, or they may be combined as hybrids with the advantages of extremely small size and weight plus a low cost for a high-volume production. Thin-film assembly requires considerable engineering effort and sophisticated production equipment. thinfilm capacitor-A capacitor utilizing a metal oxide as the dielectric or insulating material. Both the electrodes and the dielectric are deposited in layers on a substrate. This device is usually associated with microelectronics and integrated and thin-film circuits. thin-film circuit- 1. A microcircuit in which the component element and interconnections are fabricated from thin deposited fihns of metal, semiconductor, and dielectric material, generally on an insulating substrate such as ceramic or sapphire. The term thin is usually taken to imply films having a thickness on the order of 1 micrometer. 2. A circuit whose passive components are deposited on a given substrate by sputtering or vacuum processes. thin-film deposition (chemical vapor type) -A technique that involves a decomposition and reaction between gases on the surface of a heated substrate such that a solid layer is nucleated and grown. Metals are generally derived from the decomposition of the

- thin-film optical modulator

metal halides. Insulators may be formed by reacting metal halides with oxygen (oxides), ammonia (nitrides), diborane (borides), etc. thin-film deposition (evaporation type) --Popular technique for depositing thin film in vacuum, accomplished by heating the source material in a low-pressure chamber so that it vaporizes and then condenses onto all cooler surfaces in line of sight from the source. thin-film deposition (sputtering type) -Evaporation produced by ion bombardment of the source material, known as cathode sputtering. thin-film deposition materials (conductorsand resistors)-Metals such as aluminum, gold, chromium, nickel, platinum, tungsten, alloys, and cermets deposited as electrical conductors and resistors on silicon or other substrates. thin-film deposition materials (inorganic dielectrics) -Film compounds produced by various vacuum evaporation processes and deposited on substrates to perform electrical functions. Examples include silicon monoxide, ZnS, CaF,SiOz, A1203, Si3&, and other chemical compounds. thin-film deposition materials (organic dielectrics) -Insulating film compounds produced when organic vapors are heated under conditions in which polymerization and deposition occur. Examples are parylent, butadene, acrolein, and &vinylbenzene. thin-film deposition materials (semiconductors) -Polycrystalline films deposited by vacuum or flash evaporation to produce high-purity single-crystal silicon or other semiconductor substances. thin-film formation-A process that is either additive, by pattern formation through masks, or subtractive, by selective etching of predeposited films from a substrate. thin-film hybrid integratedcircuit -The physical realization of a hybrid integrated circuit fabricated on a thin-film network. thin-film hybrids-Hybrid circuits that are made by placing the substrate in a vacuum chamber and depositing films of conductive and resistive material on the entire substrate. The material is photoetched in selected patterns to form conductive interconnections and thin-film resistors. These resistors are approximately 0.1 mil (25 pm) thick. Unencapsulated components are then added either by soldering or chemical bonding. thin-film integrated circuit -1. An integrated circuit consisting of a passive substrate on which the various passive elements (resistors and capacitors) are deposited in the form of thin-patterned films of conductive or nonconductive material. Active components (transistors and diodes) are attached separately as individually packaged devices or in unpackaged (chip) form, or may be fomed integrally by thin-film techniques. See also hybrid thinfilm circuit. 2. A device consisting of a number of electrical elements entirely in the form of thin films deposited in a pattern on a supporting material. 3. The physical realization of a number of electric elements entirely in the form of thin films deposited in a patterned relationship on a structural supporting material. thin-film memory-In a computer, a storage device made of thin disks of magnetic material deposited on a nonmagnetic base. Its operation is similar to the core memory. See also core memory, 1; storage, 2. thin-film microelectronics-Circuits made up of two-dimensional passive and essentially two-dimensional active elements mounted or deposited on thin wafers of an insulating substrate material. thin-film optical modulator-A device made of mulitlayered films of material of different optical characteristics capable of modulating transmitted light

thin-film optical multiplexer

- t h r e e - p h a s e current

by using electroacoustic, electro-optic, or magneto-optic effects to obtain signal modulation. Thin-film optical modulators are used as component parts of integrated optical circuits. thin-film optical multiplexer-A multiplexer consisting of layered optical materials that make use of electroacoustic, electro-optic, or magneto-optic effects to accomplish the multiplexing. Thin-film optical multiplexers may be component parts of integrated optical circuits. thin-film optical s w i t c h -A switching device for performing logic operations using light waves in thin films, usually supporting only one propagation mode, making use of electroacoustic, electro-optic, or magnetooptic effects to perform switching functions, such as are performed by semiconductor gates (AND, OR, NOT). Thin-film optical switches may be component parts of integrated optical circuits. thin-film optical waveguide- An optical waveguide consisting of thin layers of differing refractive indices, the lower indexed material on the outside or as a substrate, for supporting usually a single electromagnetic wave propagation mode with laser sources. The thin-film waveguide lasers, switches, modulators, filters, directional couplers, and related components need to be coupled from their integrated optical circuits to the optical waveguide transmission media, such as optical fibers and slab dielectric waveguides. combination of thin-film resistor network-A several resistors manufactured by deposition of appropriate alloys and metals onto glass silicon and alumina substrates using vacuum techniques. thin films-Resistive materials of submicrometer thickness made of nichrome or tantalum (or other exotic metal). They are deposited onto a substrate by vacuum deposition or by rf sputtering under a vacuum. Thin-film resistors provide excellent tolerances, are very stable with temperature changes, but are costly to apply, necessitating the use of expensive vacuum equipment. thin-film semiconductor- A semiconductor produced by the deposition of an appropriate single-crystal layer on a suitable insulator. thin-film solar cell -A solar cell that is lightweight and flexible due to its construction by vacuum deposition of a semiconductor material (e.g., gallium arsenide or cadmium sulfide) onto a thin plastic or metal substrate. It is used as a power source in spacecraft because of its light weight. think time-The time the user of a time-sharing system spends sitting at his or her terminal but not using the computer. thin-walled conduit -Metallic tubing used to enclose insulated wires in an electrical circuit. thin-wall ring magnet-A type of ceramic permanent magnet in which the axial length is greater than the wall thickness or the wall thickness is less than 15 percent of the outside diameter. third harmonic-A sine-wave component having three times the fundamental frequency of a complex wave. third-harmonic distortion-The rms thirdharmonic voltage divided by the rms fundamental voltage. This value often is used as a measure of distortion in an essentially symmetrical system, such as ac-biased recording. third-party traffic -Amateur radiocommunication by or under the supervision of the control operator at an amateur radio station on behalf of anyone other than the control operator. thixotropic- 1. A property of a paste or liquid that describes its ability to flow more readily when agitated or sheared. Thixotropy of a paste is a necessary condition for

780 screen ability. 2. Description of materials that are gel-like at rest but fluid when agitated. thixotropy -The property of a coating compound that provides low viscosity during agitation, but will thicken to reduce runoff when allowed to stand for a short period. Thomson bridge-See Kelvin bridge. T h o m s o n coefficient-The ratio of the voltage between two points on a metallic conductor to the difference in temperature between the same points. T h o m s o n effect-The production or absorption of heat (in addition to the Z2R loss) by a current between two points within a temperature gradient in a homogeneous conductor. Whether the heat is given off or absorbed depends on the direction of the current. T h o m s o n electromotive f o r c e -The voltage that exists between two points that are of different temperatures in a conductor. T h o m s o n h e a t -The thermal energy absorbed or produced due to the Thomson effect. thoriated filament -A tungsten vacuum-tube filament to which a small amount of thorium has been added to improve emission. The thorium comes to the surface and is primarily responsible for the electron emission. thread-See chip, 1. t h r e e - a d d r e s s -Pertaining to an instruction format that contains three address parts. t h r e e - a d d r e s s code -Also called instruction code. In computers, a multiple-address code that includes three addresses, usually two addresses from which data is taken and one address where the result is entered. Location of the next instruction is not specified, and instructions are taken from storage in preassigned order. t h r e e - a d d r e s s instruction - 1. In computers, an instruction that includes an operation and specifies the location of three registers. See also three-address code. 2. An instruction that can separately specify two sources and a destination. three-channel stereo-A stereo recording or reproduction system that uses three spaced microphones for recording and three sound reproducers for playback. three-conductor jack-Receptacle having three through circuits: tip, ring, and sleeve. three-layer diode-Also called diac. A twoterminal voltage-controlled device exhibiting a bilateral negative resistance characteristic. The device has symmetrical switching voltages ranging from 20 to 40 volts and is specifically designed for use as a trigger in ac power-control circuits such as those using triacs. three-level maser (or laser)-A maser or laser system that involves the ground state and two other energy levels. Laser action usually takes place between the intermediate and ground states. The pump populates the intermediate state by way of the highest state. When applied to a maser, this pump brings the population of the highest state and the ground state into equilibrium. Maser action may take place either between the upper and intermediate levels or between the intermediate and ground levels, depending on the relaxation times of the different transitions. t h r e e - p h a s e circuit -A combination of circuits energized by alternating electromotive forces that differ in phase by one-third of a cycle, or 120 electrical degrees. In practice, the phases may vary several degrees from the specified angle. t h r e e - p h a s e current -A current delivered through three wires -each wire serving as the return for the other two, and the three current components differing in phase successively by one-third of a cycle, or 120 electrical degrees.

three-phase, four-wire system

'781 three-phase, four-wire system-An ac supply system comprising four conductors: three connected as in a three-phase, three-wire system and the fourth to the neutral point of the supply, which may be grounded. three-phase motor- 1. An ac motor operated from a three-phase circuit. 2. A fme polyphase induction motor with three or more power windings designed specifically to operate from a three-phase power source. It is selfstarting. three-phase, seven-wire system - A system of ac supply from groups of three single-phase transformers connected in a Y. Thus, a three-phase, four-wire, grounded-neutral system of a higher voltage for power is obtained. the neutral wire being common to both systems. three-phase, three-wire system -An ac supply system comprising three conductors, between successive pairs of which are maintained alternating differences of potential successively displaced in phase by one-third of a cycle. three-plus-one instruction-In digital computer programming, a four-address instruction in which one of the addnesses always specifies the location of the next instruction to be performed. three-pole switch -An arrangement of three singlepole switches coupled together to operate three contacts simultanleously. three-position relay- Sometimes called a centerstable polar relay. A relay that may be operated to three distinct positions. three-pulse cascade canceler-A moving-target indicator technique in which two 2-pulse cancelers are cascaded together. This improves the velocity response. three-quarter bridge-A bridge connection in which one of the diode rectifiers has been replaced by a resistor.

Three-quarter bridge.

three-state-See tristate. three-state logic-A logic family that may be in one of three states rather than the usual two-high, low, or high impedance. In the high-impedance state the output voltage is unaltered. Logic: in a high-impedance state may be easily and permanently connected to a bus. three-way speaker system -A sound-reproducing system using three separate speakers, each designed for a specific portion of the audio spectrum (high, low, and middle frequencies). The Ihigh- and low-frequency speakers are known as the tweeter and woofer, respectively. three-way switch -A switch that can connect one conductor to any one of two other conductors. three-wire system-A system of electric supply comprising three conductors, one of which (known as the neutral wire) is maintained at a potential midway between the potential of the other two (referped to as the outer conductors). Part of the load may be connected directly between the outer conductors, the remainder being divided

- threshold value

as evenly as possible into two parts, each of which is connected between the neutral and one outer conductor. There are thus two distinct supply voltages, one being twice the voltage of the other. threshold -1. The point at which an effect is first produced, observed, or otherwise indicated. 2. In a modulation system, the smallest value of carrier-to-noise ratio at the input of the demodulator for all values above which a small percentage change in the input carrier-to-noise ratio produces a substantially equal or smaller percentage change in the output signal-to-noise ratio. 3. That point at which an indication exceeds the background or ambient. 4. A minimal signal-to-noise input required to allow a video receiver to deliver an acceptable picture. threshold current-1. The minimum current at which a gas discharge becomes self-sustaining. 2. The minimum forward current for which the laser is in a lasing state at a specified temperature. threshold decoding - A decoding procedure so arranged that the decision on the symbol that was transmitted is based on a majority count of the paritycheck equations involving that symbol. threshold element-A device that performs the logic threshold operation, but in which the contribution to the output determination by the truth of each input statement has a weight associated with that statement. threshold field-The least magnetizing force in a direction that tends to decrease the remanence, which, when applied either as a steady field of long duration or as a pulsed field appearing many times, will cause a stated fractional change of remanence. threshold frequency-The frequency at which the quantum energy is just sufficient to release photoelectrons from a given surface. threshold af audibility-Also called threshold of detectability or threshold of hearing. For a specilied signal, the minimum effective sound pressure of a signal capable of evoking an auditory sensation in a specified fraction of the trials. The characteristics of the signal, the manner in which it is presented to the listener, and the point at which the sound pressure is measured must all be specified. This threshold is usually expressed in decibels relative to 0.0002 microbar. threshold of detectability-See threshold of audibility. threshold of discomfort- Also called threshold of feeling. For a specified signal, the minimum effective sound-pressure level that, in a specified fraction of the trials by a battery of listeners, will stimulate the ear to the point at which the sensation of feeling becomes uncomfortable. This threshold is customarily expressed in decibels relative to 0.0002 microbar. threshold of feeling -See threshold of discomfort. threshold of hearing --See threshold of audibility. threshold of luminescence -See luminescence threshold. threshold of sensitivity-The smallest stimulus or signal that will result in a detectable output. This phrase is frequently used to describe the voltage point at which an operations monitor or event marker will trigger. threshold signal -In navigation, the smallest signal capable of producing a recognizable change in the positional information. threshold-triggered flip-flop- A flip-flop whose state changes when the actuating signal passes through a certain voltage level, regardless of the rate at which the voltage changes. threshold value -1. The minimum input that produces a corrective action in an automatic control system. 2. The minimum level for which there is a measurable output.

threshold voltage

- thyristor

threshold voltage- 1. The level of input voltage at which a binary logic circuit changes from one logic state to the other. 2. The voltage at which a pn junction begins to conduct current. 3. In a solid-state lamp, the voltage at which emission of light begins. 4.The minimum gate voltage needed to turn on an MOS enhancement-mode device. throat- 1. Part of the flare or tapered parallel-plate guide immediately adjacent to and connected to the main run of a waveguide. 2. The smaller cross-sectional area of a horn. t h r o a t microphone-A microphone worn around the throat and actuated by vibrations of the larynx as the user talks. It is used in jet airplanes, tanks, and other places where background noise would drown out the conversation. t h r o u g h connection- 1. Electrical continuity between patterns on double-sided or multilayer boards established by means of plated-through holes or jumper wires. 2. An electrical connection between conductive patterns on opposite sides of an insulating base, e.g., plated-through hole or clinched jumper wire. through path-The transmission path from the loop input signal to the loop output signal in a feedback control loop. throughput-1. A measure of the efficiency of a system; the rate at which the system can handle work. 2. The speed with which problems or segments of problems are performed in a computer. Throughput varies from application to application and is meaningful only in terms of a specific application. 3. The total useful information processed or communicated over a given period expressed in bits per second, packets per second, or some similar measurement. This quantity is frequently used for system comparisons. For example, a communication system with a throughput of 50 messages per second is superior to a system with a throughput of 30 messages per second. 4. The total amount of data that can be manipulated per second. Throughput takes into consideration such machine characteristics as basic architecture, execution speed, logic capability, and software sophistication, but i s more directly related to the size of a computer’s real addressable memory t h r o u g h p u t rate-1. The highest rate at which a multiplier can switch fiom channel to channel at its specified accuracy. This rate is determined by the settling time. 2. An d d converter or a data-acquisition system can convert a finite number of points in any given time. Throughput rate is an expression of that quantity and depends both on the time required to make a conversion and the time required to set up the unit to make the next conversion. In a data-acquisition system, throughput rate includes the effects of the composite delay arising from switching and settling times of the MUX, settling time of the amplifier, and acquisition time of the sample-and-hold. t h r o u g h repeater-A microwave repeater that is not equipped to provide for connections to any local facilities other than the service channel. t h r o u g h t r a n s f e r function -The transfer function of the through path in a feedback control loop. throw-1. In an electric motor or generator, the number of core slots spanned between the bottom leg of a coil and the top leg of the same coil. 2. Movement of a contact from one stationary point to another. A singlethrow switch has a normally open or a normally closed circuit per pole. A double-throw switch has a normally open and a normally closed circuit per pole. throwing power-Referring to the ability of an anode used in an impressed-current cathodic-protection system to distribute its current over a large surface. It is principally dependent upon the anode voltage, current,

782 surface area, position of the anode with respect to the cathode, and the salinity and flow velocity of the water. throw-out spiral -See lead-out groove. thru-hole connection -Also called feed-thru connection and plated-through hole. A conductive material used to make electrical and mechanical connections between the conductive patterns on opposite sides of a printed circuit board. thru repeater-In a microwave system, a repeater station that is not equipped to be connected to any local facilities other than the service channel. thumbwheel switch -A rotating numeric switch used to input numeric information to a controller. thump-1. A low-frequency transient disturbance in a system or component. 2. The noise caused in a receiver by telegraph currents when the receiver is connected to a telephone circuit on which a direct-current telegraph channel is superimposed. 3. A brief, unwanted lowfrequency noise (transient) that may occur when system power is turned on or off and is due to a lack of control in certain amplifier stages at that time. thyratron -1. A hot-cathode gas tube in which one or more control electrodes initiate the anode current, but do not limit it except under certain operating conditions. 2. A gas-filled triode in which a sufficiently large positive pulse applied to the control grid ionizes the gas and initiates conduction. Thereafter, the grid has no further effect, but conduction can be halted by reducing the plate voltage to zero (or less), or by reducing plate current to a value too small to maintain ionization.

-P Cross-section.

Schematic symbol

Thyratron.

thyratron gate-In computers, an AND gate consisting of a multielement gas-filled tube in which conduction is initiated by the coincident application of two or more signals. Conduction may continue after one or more of the initiating signals have been removed. thyratron inverter- An inverter circuit in which thyratron tubes convert the dc power to ac power. thyrector-A silicon diode that acts as an insulator until its rated voltage is reached, and as a conductor above that voltage. It is used for ac surge-voltage protection. thyristor -1. A bistable device comprising three or more junctions. At least one of the junctions can switch between reverse and forward voltage polarity within a single quadrant of the anode-to-cathode voltage-current characteristics. Used in a generic sense to include silicon controlled rectifiers and gate-control switches, as well as multilayer two-terminal devices. (Many countries use the term thyristor in place of the term pnpn-type switch.) 2. Member of a family of semiconcuctor switching devices of which the silicon controlled rectifier (SCR) and the triac are the most commonly used. Thyristors are fabricated from four alternate layers of positive (p) and negative (n) semiconductor material. 3. An SCR or triac

thyrite -time constant

7’83

Symbol. JunctlQnS.

Characteristic

Thyrector. (which is a form of SCR) that can be used for switching both positive and negative half cycles of ac. 4. A member of a class of semiconductor devices (made of at least four alternate p-n-p-n layers) that snap to a completely 011 state for working current when a momentary pulse of control current is received and can (typically) be turned off only by intempting the working current. Thyristors are mostly high-power devices. 5. A bistable semiconductor device comprising three or more junctions that can be made conductive at any instant when the anode (or principal) voltage is positive. The term thyristor may be used either as a generic term or as an abbreviation for reverse-blocking triode thyristor. 6. A device with turn-on characteristics that can be controlled by externally applied voltage or current. These devices generally consist of several interconnected layers of p- and n-type semiconductor material. thyrite -A silicon-carbide ceramic material with nonlinear resistance characteristics. Above a critical voltage, the resistance falls considerably. THz-Letter symbol for terahertz (10” hertz). tickler-A small coil connected in series with the anode circuit of an electron tube and inductively coupled to a grid-circuit coil. The tickler coil is used chiefly in regenerative detector circuits, to establish feedback or regeneration. tie cable- 1. A cable between two distributing frames ar distributing points. 2. A cable between private branch exchanges. 3. A cable between a private branch exchange switchboard and the main office. 4. A cable connecting two other cables. tie line- 1. See interconnection, I. 2. A privateline communication channel of the type communications common carriers provide for joining two or more points. tie point- 1. An insulated distributing point (other than an active terminal connection) where junctions of component leads are made in circuit wiring. 2. An insulated terminal to which two or more wires are connected. tier airray- An array of antenna elements, one above the other. ties-- 1. Electrical con.nectionsor straps. 2. Tie wires. tie tirunk-A telephone line or channel directly connectiug two private brmch exchanges. tie wiire-Wire that connects a number of terminals together. tie wires-Short pieces of wire used to tie open-line wires to insulators. TIFF-See tagged image file format. .TIF files-Tagged image file format files. Bit-mapped graphic images popular among desktop publisheirs. TIG --Abbreviation for tungsten inert-gas welding. A technique using a tungsten electrode, generally without a filler material. Popular for light-metal gages and highprecision work. tight coupling -See close coupling.

tilt- 1. In radar, the angle between the axis of radiation in the vertical plane and a reference axis, which is normally the horizontal. 2. See wave tilt. 3. The angle an antenna makes with the horizontal. 4. A deviation from the ideal low-frequency response; unsatisfactory low-frequency response. tilt angle-In radar, the angle between the vertical axis of radiation and a reference axis (normally the horizontal). tilt controls -In a color television receiver employing the magnetic-convergence principle, the three controls used to tilt the vertical center rows in the three colored patterns produced by a dot-generator signal. tilt error -1 , In navigation, the ionospheric error component due to nonuniform height. 2. The difference between the true tilt and the mechanical tilt. The sign is such that when it is algebraically added to the mechanical tilt, the result is the true tilt. See aZso antenna tilt error. tilting-1. Forward inclination of the wavefront of radio waves traveling along the ground. The amount of tilt depends on the electrical constants of the ground. 2. Changing the angle of a television camera to f0kW a moving object being televised. 3. Changing the vertical angle of a directional antenna. TIM -Abbreviation for transient intermodulation distortion. timbre -Also called tone color or musical quality. 1. The character of a musical tone that distinguishes one musical instrument from another playing the same note. The difference between two steady tones having the same pitch and degree of volume is called the difference in timbre. Timbre depends mostly on the relative intensity of the different harmonics and the frequencies of the most prominent harmonics. 2. The tonal quality of sound based on the pitch and the relative mix of fundamental and harmonic frequencies. time-The measure of the duration of an event. The fundamental unit of time is the second. time assignment speech interpolation-Telephone switching equipment whereby a person is connected to idle circuits when he starts talking, and is disconnected when he stops talking. time base-A voltage generated by the sweep circuit of a cathode-ray-tube indicator. Its waveshape is such that the trace is either linear with respect to time or, if nonlinear, is still at a known timing. time clock- A loosely used term sometimes referring to time switches, sometimes to interval timers, or to any type of timer. time-code generator-A timer with an absolute time reference having digital outputs suitable for machine interpretation. Dial or numeric display may be included. time-compression multiplexing -A method of providing the appearance of full-duplex communication over a single twisted-pair half-duplex copper loop. Data are buffered at each end and sent across the line at double the subscriber data rate, with the two ends taking turns. time constant-1. The rime required for an exponential quantity to change by an amount equal to 0.632 times the total change that will occur. Specifically: ( a )In a capacitor-resistor circuit, the number of seconds required for the capacitor to reach 43.2 percent of its full charge after a voltage is applied. The time constant of a capacitor having a capacitance C in farads in series with a resistance R in ohms is equal to R x G . (b) In an inductor-resistor circuit, the number of seconds required for the current to reach 63.2 percent of its final value. The time constant of an inductor having an inductance L in henrys and resistance R in ohms is equal to L/R. 2. The time required for a motor to accelerate from 0 to 63.2 percent of its final no-load speed when the rated voltage, with the

time constant of a capacitor

- time flutter

proper phase relationship, is applied. 3. A measure of the rapidity with which a transducer responds to a change in temperature. It is the time required for the sensor to complete 63.2 percent of its exponential response to a step change in temperature and is highly dependent on the thermal conductivity of the medium measured. Time constant must match the speed of which it is a part. In general, small sensors respond more rapidly than large ones. time constant of a capacitor-The product of the insulation resistance and the capacitance of a capacitor. time constant of fall -The time required for a pulse to fall from 70.7 percent to 26.0 percent of its maximum amplitude, excluding spikes. time-current characteristics of a fue-The relation between the root-mean-square alternating current or direct current and the time for the fuse to perform the whole or some specified part of its interrupting function. Usually shown as a curve. timed acceleration-A control function that automatically controls the speed increase of a drive as a function of time. time date generator-A device used in surveillance that electronically produces a single-row display of day, time, and date information on any standard TV screen (or raster). timed deceleration-A control function that automatically controls the speed decrease of a drive as a function of time. time delay-1. The time required for a signal to travel between two points in a circuit. 2. The time required for a wave to travel between two points in space. 3. The total elapsed time or lag required for a given command to be effected after the command is given. 4. Also called envelope delay. The slope of the phaseversus-frequency curve at a specified frequency. In a loose sense, this is the time it takes a designated point in a wave to pass through a filter. time-delay circuit-A circuit that delays the transmission of an impulse signal, or the performance of a transducer, for a definite desired length of time. time-delay closing relay- See time-delay starting relay. time-delay generator- A device that accepts an input signal and provides a delay in time before the initiation of an output signal. time-delay relay -Also called slow-action relay. 1. A relay in which there is an appreciable interval of time between the energizing or deenergizing of the coil and the movement of the armature (e.g., slow-operating relays and slow-release relays). 2. A device in which a defined delay occurs between the application or removal of the control current and the switching of the load current. 3. An electronic device with either relay or solid-state output that performs a retarding function on receipt of instruction. 4. A reset timer with delayed contacts. 5. A relay with electromagnetic action that provides a specified time interval between the energizing of the coil and the actual contact closure. The timing interval can be preset and the delay may be achieved either by mechanical clockwork or electronic means. time-delay spectrometry- An acoustic measurement technique utilizing a real-time spectrum analyzer. time-delay starting relay--Also called time-delay closing relay. A device that functions to give a desired amount of time delay before or after any point or opemtion in a switching sequence or protective relay system. time-delay stopping or opening relay-A time-delay device that serves in conjunction with the device that initiates the shut-down, stopping, or opening operation in an automatic sequence.

784 time-derived channel-Any of the channels obtained by time-division multiplexing of a channel. time discriminator-A circuit in which the sense and magnitude of the output is a function of the time difference of, and relative time sequence between, two pulses. time-distribution analyzer- Also called time sorter. An instrument that indicates the number or rate of occurrence of time intervals falling within one or more specified ranges. The time interval is defined by the separation between members of a pulse pair. time-division data link-Radiocommunications that use time-division techniques for channel separation. time-division multiplex channel-A path established for a segment of time during which the central station equipment obtains a signal indicating the status of a signal-encoding device. time-division multiplexer-A device that samples all data input from different low-speed devices, and retransmits all the samples in an equal amount of time. time-division multiplexing-Abbreviated TDM. 1. Multiplexing by assigning each low-speed channel its own time slot during which it transmits data. 2. A process by which two or more channels of information are transmitted over the same link by allocating a different time interval for the transmission of each channel. 3. A signaling method characterized by the sequential and noninterfering transmission of more than one signal in a communication channel. Signals from all terminal locations are distinguished from one another by each signal occupying a different position in time with reference to synchronizing signals. 4. A system of multiplexing in which channels are established by connecting terminals one at a time at regular intervals by means of an automatic distribution. 5. The multiplexing technique that provides for the independent transmission of several pieces of information on a time-sharing basis by sampling, at frequent intervals, the data to be transmitted. 6. A data-communication technique for combining several lower-speed channels into one facility or transmission path at a higher speed; each low-speed channel is allotted a specific position in the signal stream based on time. Thus, the information on the low-speed input channels is interleaved at higher speed on the multiplexed channel. At the receiver, the signals are separated to reconstruct the individual low-speed channels. time domain-1. An analysis of a waveform in terms of how the parameter of interest, voltage for example, varies with time. (The sine wave can help to visualize this concept. At any instant in time the voltage has only a single unique value. But as time progresses, the voltage rise and fall describes the familiar smooth curve. A square wave, on the other hand, is a picture in the time domain of a voltage that repeatedly changes abruptly &om one value to another.) 2. A measurement technique where the results are plotted or shown against a scale of time, in contrast to frequency domain where the results are plotted on a scale of frequency. timed-release circuit -A circuit designed to automatically release other connected circuits after a preset interval. time-edit-To prevent the t h e code in a computer from being recorded or transmitted when no data samples are being passed, or, conversely, to record or transmit the time code with each data sample passed. time flutter-A variation in the synchronization of components of a radar system, leading to variations in the position of the observed pulse along the time base and reducing the accuracy with which the time of arrival of a pulse may be determined.

785

time frame--In telemetry, the time period containing all elements between corres>pondingpoints of two successive reference markers. time gain -See sensitivity-time control. time gate-A transducer that has an output during chosen time intervals only. time h a r m o n i c s --High-frequency components generated by nonlinearity in a resolver magnetic circuit. In ac resolvers with no dc components present, time harmonics are odd multiples of the fundamental frequency. Time harmonics appear as a component of null voltage. time-interval selector-A circuit that functions to produce a specified output pulse when and only when the time interval between two input pulses is between set nimits. time l a g -1. The interval between application of any force and full attainment lof the resultant effect. 2. The interval between two phenomena. time-lapse VTR-A videotape recorder that provides a continuous record of events over a period of from 12 to 48 hours on one reel of videotape. time-mark generator -A circuit that produces accurately spaced pulses for display on the screen of an oscilloscope. time modulation --Modulation in which the time of occurrence of a definite part of a waveform is made to vary in accordance with a modulating signal. time of persistence-The time that elapses between the instant of removal of the excitation and the instant at which the luminiance or radiance has dropped to a stated fraction of its initial value, usually 10 percent. time-out-The interval of time allotted for certain operations to occur (for e:tample, response to polling or addressing) before operation of the system is interrupted and must be started again. e pattern -A picture-tube presentation of horizontal mid vertical lines or rows of dots generated by two stable frequency sources operating at multiples of the line and field frequencies. hase -Reaching corresponding peak values at the same instants of time, though not necessarily at the same points in space. time pulse distributor-A device or circuit for allocating tinning pulses or clock pulses to one or more conducting paths or control lines in a specified sequence. time quadrature-Differing by a time interval corresponding to one-fourth the time of one cycle of the frequency in question. timer- 1. A special clock mechanism or motoroperated device used to perform switching operations at predetermined time intervals. 2. An assembly of electric circuits ,and associated equipment that provides the following: trigger pulses, sweep circuits, intensifier pulses, gate voltage, blanking voltages, and power supplies. 3. The part of a radar set that initiates pulse transmission and synchronizes this with the beginning of indicator sweeps, timing of gates, range markers, etc. See also synchronizer, 1. 4. An instrument that measures the interval between events. The term event may encompass anything from persons moving through a turnstile to oscillations in the highest-frequency radar bands. time resoluti~n --The smallest interval of time that can be measured with a given system. time response -An output, expressed as a function of time, that results from a specified input applied under specified operating conditions. timer motor-A synchronous clock motor having a definite output speed determined by the number of poles in the stator and the reduction of the associated gear train.

time f r a m e -timing lag time sequencing ---In a computer, switching signals generated by a program purely as a function of accurately measured elapsed time. time series analysis-Analysis of any variable classified by time, in which the values of the variable are functions of the time periods. time share-To use a device for two or more purposes on a time-sharing basis. t i m e sharing- I. A method of operation in which a computer facility is shared by several users for different purposes at (apparently) the same time. Although the computer actually services each user in sequence, the high speed of the computer makes it appear as if the users were all handled simultaneously. 2. A means of making more efficient use of a facility by allowing more than one using activity access to the facility on a sequential basis. 3. A computer system in which CPU time and system resources are shared simultaneously by several operators engaged in unrelated tasks and located at terminals remote from the central processing unit. The speed of the computer gives the appearance of simultaneously performing multiple jobs. Programs performing the individual jobs are swapped at high speeds under direction of the scheduling formulas or plan for the time-sharing system, thus assuring each user a system response within a few seconds (almost the exact opposite of a batch system). 4. The use of the same computer memory for two or more simultaneous tasks. time-sharing system-See TSS. time signals -Time-controlled radio signals broadcast by governrnent-operated radio station WWV at regular intervals each day on several frequencies. time signal service-Radiocommunication service for the transmission of time signals of stated high precision, intended for general reception. time slicing -1. The sharing of CPU time among several software processes by giving each process a defined interval (slice) of the CPU’s time. 2. A type of operation in which a computer works on one program for a short time, then goes to another program and works on that for a short time, and so forth. 3. A technique that shares microprocessor time among several processes. A quantum of time allocated to a process is termed a time slice. time sorter-See time-distribution analyzer. time stability-The degree to which a component value is maintained to a stated degree of certainty (probability) under stated conditions of use over a stated period of time. It is usually expressed in i percent or f per unit (ppm) change per 1000 hours of continuous use. t i m e switch-A clock-controlled switch used to open or close a circuit at one or more predetermined times. Usually refers to repeat cycle timers with a dial graduated with time of day (in 24-hour type) or with time and day (in 7-day type). Has means of adjusting the time when circuits are turned on or off, usually with pins or clips. Used for turning lights on at night, hinging bells in offices, schools, etc. time-to-digital conversion -The process of converting an interval of time into a digital number. time window -In random-sampling-oscilloscope technique, the part of the signal period that is displayed. timing-The procedure of adjusting the ignition distributor so the sparks will occur at the spark plugs at the correct time in relation to the position of the piston on the compression stroke. timing axis oscillator-See sweep generator. timing lag-The number of engine degrees retard in timing caused by electrical lag in the system. Generally stated as number of engine degrees per 1000 rpm engine speed.

timing light

-toggle switch

timing light-A stroboscope unit that is connected to the secondary ignition circuit of an internal-combustion engine to produce flashes of light in unison with the firing of a specific spark plug. By directing these flashes of light on the whirling timing marks, the marks appear to stand still. By adjusting the distributor, the timing marks may be properly aligned, thus setting the timing. timing-pulse distributor- Also called waveform generator. A computer circuit driven by pulses from the master clock. It operates in conjunction with the operation decoder to generate timed pulses needed by other machine circuits to perform the various operations. timing relay-A form of auxiliary relay used to introduce a definite time delay in the performance of a function. timing signal -Any signal recorded simultaneously with data to provide a time index. timing tape-A variety of leader tape having printed indications of intervals of 7 1 / ~inches (19.05 cm) along its length to facilitate measuring off a desired number of seconds' worth of leader. tinkertoy- An attempt at modularization whereby wafers, with one or more component parts printed or mounted on them, are stacked vertically, with interconnecting wiring stiff enough to provide support running through holes around the periphery of the wafer. tin-lead-An alloy used for the majority of soldering operations in the electronics industry. Usually, an alloy close to the eutectic composition (62 percent tin, 38 percent lead) is chosen to permit usage of the lowest possible soldering temperature, thereby reducing risk of damage to temperature-sensitive components. with metallic tin to permit easy tinned-Covered soldering. tinned wire-A copper wire that has been coated with a layer of tin or solder to prevent corrosion and to simplify soldering. tinning - A process of coating a conductor surface with solder. tinsel -Flat ribbons of bronze, silver, or copper alloy spiraled around a textile core of cotton, nylon, etc. Used in telephone and electronics applications as conductors in line cords, microphone cords, and retractile cords. tinsel conductor-A type of electrical conductor comprising a number of tiny threads, each thread having a fine, flat ribbon of copper or cadmium bronze closely spiraled about it. Used for small cables requiring limpness and extra-long flex life (e.g., used with headsets or handsets). tinsel wire-1. A very flexible conductor made by wrapping one or more thin ribbon conductors over a nylon string core. Used to make telephone cords. 2. A lowvoltage stranded wire in which each strand is a very thin conductor ribbon spirally wrapped around a textile yam. Insulation is generally a textile braid. Intended usage is for severe flexing. tint-A mixture of a color with white light. tip- 1. The contacting part at the end of a plug or probe. 2. Also called tip side. The end of the plug used to make circuit connections in a manual switchboard. The tip is the connector attached to the positive side of the common battery that powers the station equipment. By extension, it is the positive battery side of a communications line. tip and ring-Traditional telephone terminology for positive and negative. In old-style telephone switchboards, the tip (positive) wire was the one that connected to the tip of the plug; the ring (negative) wire was connected to a slip ring in the jack. tip jack-Also called a pup jack. A small single-hole jack for a single-pin contact plug.

786 tip mass-The effective mass at the tip of the stylus of a pickup cartridge. (Modern techniques have reduced this mass toward 1 milligram or below.) tipoff -The last portion of a vacuum-tube bulb to be melted and sealed after evacuation of the bulb. tip-ring-sleeve (TRS) phone plug-A threeconductor phone plug commonly used for balanced audio connections. tip side-Also called a tip wire. The conductor of a circuit associated with the tip of a plug or the tip spring of a jack. See also tip, 2. tip-sleeve (TS) phone plug -A two-conductor phone plug (or jack) commonly used for unbalanced audio connections. tip wire-See tip side. T-junction-See tee junction. TM wave -Abbreviation for transverse magnetic wave. Tm,," wave-In a rectangular waveguide, the transverse magnetic wave for which m and n are the number of half-period variations of the magnetic field along the longer and shorter transverse dimensions, respectively. TNC -A threaded connector for miniature coax; TNC is said to be short for threaded-Neill-Concelman. (Contrast with BNC.) T-network-A network composed of three branches. One end of each branch is connected to a common junction point. The three remaining ends are connected to an input terminal, an output terminal, and a common input and output terminal.

9 T-network.

TO can -Abbreviation for transistor-outline metalcan package. TO-5-A small cylindrical IC package about 0.375 inch (9.5 mm) in diameter and made of metal; it can have up to 12 pins protruding from the bottom of the can. to-from indicator- An instrument that forms part of the omnirange facilities and is used for resolving the 180" ambiguity. toggle- 1. A flip-flop. The term implies that the flipflop will change state upon receipt of a clock pulse, and is used mainly with reference to flip-flops connected as a counter, in which the process of changing state is called toggling. 2. To use switches to enter data into the memory of a computer. 3. To change states abruptly in such a way that the process goes to completion once a critical point is reached, even if the actuating cause is removed; in logic circuits, a change of state of a flip-flop or Schmitt trigger, 4. See T flip-flop. 5 . The ability, through the use of a windowing program, to allow a user to switch back and forth between different PC applications programs, as well as between PC and mainframe or mini applications. toggle frequency-In a digital circuit, the number of times per second that the circuit changes state. toggle rate-Twice the frequency at which a flipflop completes a full cycle encompassing both states. Usually used to denote the maximum input frequency that a flip-flop can follow. toggle switch -1. A switch with a projecting lever whose movement through a small arc opens or closes

787 one or more electric circuits. 2. A panel-mounted switch with an extended lever; normally used for o d o f f switching. 3. A switch having a lever (toggle), the movement of which results either directly or indirectly in the connection or disconnection of the switch terminations in a specified manner. Any indirect action through an actuating mechanism should be such that the speed of connection andor disconnection is independent of the speed of lever movement. tokamak-A doughnut-shaped plasma confinement device for research into the problems associated with nuclear fusion. tokern -1. A group of bits used in some bus networks to signal network access by a particular station. 2. The information package that contains a piece of data and a description of its location in a computer program. tokeni passing-A protocol that gives a terminal permission to transmit on a token ring LAN. A unique bit pattern, called a token, circulates around the ring from terminal to terminal. The terminal that possesses the token has permission to transmit token ring network-A local area network (LAN) in a circle configuration. Messages are sent when one computer attaches a message to a special bit pattern (called a token) as it travels around the circle. tolerance- 1. A permissible deviation from a specified value. A frequency tolerance is expressed in hertz or as a percentage of the nominal frequency; an orientation tolerance, in minutes of airc; a temperature tolerance, in degrees Celsius; and a dimensional tolerance, in decimals or Fractions. 2. A pedssible deviation from specified capacitance (resistance, inductance, etc.) values, characteristics, and physical dimensions. 3. A specified allowance for error from a desired or measured quantity. 4, Maximum error or variation from the standard permissible in a measuring instrument. 5 . Maximum electrical or mechanical variation from specifications that can be tolerated without impairing the operation of a device. toll -- 1. In public switched systems, a charge for a connection beyond an exchange boundary, based on time and distance. 2. Any part of telephone plank circuits, or services for which toll charges are made. toll call- 1. Telephone call to points beyond the area within which telephone calls are covered by a flat monthly rate or are charged for on a message unit basis. 2. A telephone call, subject to charge, for a destination outside of the local service area of the calling station. toll center-Also called toll office and toll point. 1. The basic to41 switching entity; a central office where channels and toll-message circuits terminate. While this is usually one particular central office in a city, larger cities may have several central offices where toll-message circuits terminate, 2. A major telephone distribution center that distributes calls from one major metropolitan area to another. toll-free number-See enterprise number. toll office -See toll center. tdl point-See toll center. toll restriction-The action of preventing restricted telephones from making calls to toll or other restricted points. H restrictor counts the first three digits dialed and diverts calls to forbidden codes either to a busy tone, a recorded announcement, o r an operator. toll-terminal b - O n a toll connection, that part of the overall transmission loss attributable to the facilities from the toll center through the tributary office to and including the subscriber’s equipment. Bone -1. A sound wave capable of exciting an auditory sensation having pitch. 2.A sound sensation having pitch.

tokamak

- tone Signaling

tonearm -1. The pivoted arm of a record player that extends over the record and holds the pickup cartridge. Wires from the cartridge run through the arm to the preamplifier, usually located on the underside of the turntable mounting board. 2. The portion of a record player that supports the phono cartridge and maintains it in the correct relationship to the record surface and the spiral groove. On conventional pivoted tonearms, the cartridge is mounted at an offset angle and with a slight overhang beyond the turntable center to reduce the tracking error. The mass of the c h d g e and the forward portion of the arm is balanced by an adjustable countemeight, and the desired vertical tracking force is supplied by a slight mass unbalance or a spring. tone bunt -A single sine-wave frequency, 50 to 500 microseconds long. having a rectangular envelope, used for testing the transient response of speakers. tone channel-An intelligence or signaling circuit in which on-off or frequency-shift modulation of a frequency (usually an audio frequency) is used as a means of transmission. tone control-1. A control, usually part of a resistance-capacitance network, used to alter the frequency response of an amplifier so that the listener can obtain the most pleasing sound. In effect, a tone control accentuates or attenuates the bass or treble portion of the audio-frequency spectrum. 2. A circuit designed to increase or decrease the amplification in a specific frequency range, with little or no effect at other frequencies. Bass tone controls usually affect frequencies below a turnover frequency that may vary between 100 and 1OOOHz. Treble tone controls are typically hinged to affect frequencies above 1500 Hz. The range of a tone control (the maximum amount by which it can vary the amplification within its operating range) is typically about f15 dB, but may be as low as &7 dB or as great as f20 dB. (Equalizers can provide tone control over five or more frequency bands.) tone dialing -See pushdown dialing. tone generator-A device for providing an audiofrequency current suitable for testing audio-frequency equipment or for signaling. tone keyer-An instrument device that converts direct-current impulses to audio tones, for line transmission or for keying a transmitter. tone localizer-See equisignal localizer. tone-modulated waves- Waves obtained from continuous waves by amplitude-modulating them at an audio frequency in a substantially periodic manner. tone modulation--A type of code-signal transmission obtained by causing the radio-frequency carrier amplitude to vary at a fixed audio frequency. tone pad-An array of 12 or 16 numbered keys that generate the standard telephone dual-tone multifrequency (DTMF) dialing signals. toner- 1. Charged carbon particles, dry or suspended in a liquid solvent, used to produce a dark image on a light medium. 2. Minute, dry particles of resin and carbon black that are used to create images. In the electrostatic copying process, toner is capable of accepting an electrical charge. It is carried to the photoconductor by a developer medium and transferred to the surface of a copy sheet by a series of successively greater electrical charges. tone reversal-Distortion of the recorder copy in facsimile. It causes the various shades of black and white not to be in the proper order. tone signaling-The transmission of supervisory, address, and alerting signals over a telephone circuit by means of voice frequency tones. Also used in “touch tone” dialing.

tongue

- total h a r m o n i c distortion

tongue-The portion of a solderless terminal that projects from the barrel. Tonotron -A multimode, selective-erasure storage tube. tool function-In automatic control of machine tools, a command that identifies a specific tool and calls for the use of that tool. TO package-Can-type IC chip configuration, an outgrowth of the original TO transistor package. Most common are the TO-5, TO-18, and TO-47. The IC chip is mounted within the package, interconnected to terminals on the can, and then hermetically sealed. TO stands for transistor outline. top cap-A terminal in the form of a metal cap at the top of some vacuum tubes and connected to one of the electrodes. top-down programming -See structured programming. top-hat resistors-Film resistors having a projection on one side allowing a notch to be cut into the center of the projection to effectively form a serpentine resistance and thereby increase the resistivity. top-loaded vertical antenna -A vertical antenna that is larger at the top, resulting in a modified current distribution that gives a more desirable radiation pattern vertically. A series reactor may be connected between the enlarged portion of the antenna and the remaining structure. topology- 1. The physical arrangement and relationship of interconnected nodes and lines in a network. Linear bus, mesh, star, token ring, and point-to-point are the major LAN topologies. 2. The surface layout of the elements comprising an IC. tornadotron-A millimeter wave device that generates radio-frequency power from an enclosed, orbiting electron cloud excited by a radio-frequency field when subjected to a strong, pulsed magnetic field. torn-tape relay-A method of receiving messages in tape form, breaking the tape, and retransmitting the message in tape form. torn-tape switching center- A location at which operators tear off the incoming printed and punched paper tape and transfer it manually to a machine for transmission over the proper outgoing circuit. toroid- 1. A surface, or its closed solid, generated by any closed plane rotating about a straight line in its own plane -the resulting configuration being doughnut shaped. 2. A highly efficient type of coil wound on a ring or doughnut type of core. The toroid provides for high concentrated magnetic field within itself, and has a minimum magnetic flux leakage (external field). toroidal coil -A coil wound in the form of a toroidal helix. toroidal core-A ring-shaped core. toroidal permeability-Under stated conditions, the relative permeability of a toroidal body of the given material. The permeability is determined from measurements of a coil wound on the toroid such that stray fields are minimized or can be neglected. torque -A force that tends to produce rotation or twisting. torque amplifier-A device with input and output shafts and supplying work to rotate the output shaft so that its position corresponds to that of the input shaft but does not impose any significant torque on the latter. torque-coil magnetometer-A magnetometer that depends for its operation on the torque developed by a known current in a coil capable of turning in the field to be measured.

788

torque gradient-The torque required in inchounces to pull a specific energized synchro 1" away from its normal position. torque motors -A motor that is designed to provide its maximum torque under the condition of stall or lockedrotor. A second criteria of torque motors is that they must be capable of remaining in a stalled condition for prolonged periods. torque of an instrument -Also called deflecting torque. The turning moment produced on the moving element by the quantity to be measured or by some quantity dependent thereon acting throughthe mechanism. torquer-A device that produces torque about an axis of freedom in response to a signal input. torque-to-inertia ratio -See acceleration at stall. torr-The unit of pressure used in the measurement of a vacuum. It is equal to '/760 of a standard atmosphere, and for practical purposes may be considered equivalent to one millimeter of mercury (mm Hg). torsiometer-An instrument for measuring the amount of power that a rotating shaft is transmitting. torsion galvanometer -A galvanometer in which the force between the fixed and moving systems is measured by the angle through which the supporting head of the moving system must be rotated to return the moving system to zero. torsion-string galvanometer-A sensitive galvanometer in which the moving system is suspended by two parallel fibers that tend to twist around each other. total capacitance-The capacitance between a given conductor and all other conductors in a system when all other conductors are connected together. total combined regulation -The change in output of a regulated power supply arising from simultaneous changes in all of the specified operating conditions, when the direction of such changes is such as to make their effects additive. It may be stated as a percentage of the specified output and/or as an absolute value. total connected load-The total current drawn in amperes, or power consumption in watts, of all of the utilization equipment connected to all or any given segment of a wiring system. t o t a l distortion-The sum total of all forms of signal distortions. total emission-The magnitude of the current produced when electrons are emitted from a cathode under the influence of a voltage such that all the electrons emitted are drawn away from the cathode. total emissivity-The ratio of radiation emitted by a surface to the radiation emitted by the surface of a blackbody under identical conditions. Important conditions that affect emissivity of a material are surface finish, color, temperature, and wavelength of radiation. Emissivity may be expressed for radiation of a single wavelength (monochromatic emissivity), for total radiation of a specified range of wavelengths (total spectral emissivity), or for total radiation of all wavelengths (total emissivity). total excursion -The application of a stimulus, in a controlled manner, over the span of an instrument. total flux-The luminous flux emitted by a light source in all directions. total harmonic distortion -Abbreviated THD. 1. The ratio of the power at the fundamental frequency, measured at the output of the transmission system considered, to the power of all harmonics observed at the output of the system because of its nonlinearity, when a single-frequency signal of specified power is applied to the input of the system. It is expressed in decibels. 2. The square root of the sum of the squares of the rootmean-square harmonic voltages divided by the root-meansquare fundamental voltage. 3. The ratio of the sum of

789 the amplitudes of all signals harmonically related to the fundamental and the amplitude of the fundamental signal. 4. A measure of the distortion produced in an audio system as a result of the production, by the system, of fiarmonics or multiples of the original audio signal. total iinternal reflection -When light passes from one medium to another that is optically less dense (e.g., from glass to air), the ray is bent away from the normal. ]if the incident ray meets the surface at such an angle that the refracted ray must be bent away at an angle of more than 90”, the light cannot emerge at all, and is totally internally reflected. totalizing -To register a precise total count from mechanical, photoelectric, electromagnetic, or electronic inputs or detectors. total losses of a ferromagnetic part-Under stated conditions, the power absorbed and then dissipated as heat when a body of ferromagnetic material is placed in a time-varying magnetic field. total losses of a transformer-The losses represented by the sum of the no-load and Ioad loses. total luminous flux-The total light emitted in all directions by a light source. totally enclosed motor-A motor so enclosed as to prevent the free exchange of air between the inside and the outside of the case, but not sufficiently enclosed to be termed airtight. nbalanced currents-See push-push currents. total range of an instrument-Also called the range of an instrument. The region between the limits within which the quantity measured is to be indicated or recorded. total regulation-The arithmetic sum of changes in output of a regulated power supply arising from changes in each of the specified operating conditions (current, voltage, or power) when such changes are applied individually and in a manner to make their effects additive. It may be stated as a percentage of the specified output andor as an absolute value. total resistance -The dc resistance of a (precision) potentiometer between the input terminals with the shaft positioned so as to give a maximum resistance value. total !spectralemissivity-See total emissivity. total telegraph distortion -Telegraph transmission impairment expressed in terms of time displacement of mark-space and space-mark transitions from their proper positions and given in percent of the shortest perfect pulse, called the unit pulse. total transition time-In a circuit, the time interval between the point of 10 percent input change and the point of 90 percent output change. It is equal to the sum of the delay time and rise (or fall) time. totem pole amplifier-A push-pull amplifier circuit that provides a single-ended output signal without the use of a transformer. Used mainly in the output stages of transistor audio amplifiers. TO-3 -A large metal IC housing, approximately 1.5 x 11 inch (3.8 x 2.5 cm) having up to eight pins. When properly heat-sided, this case is used where highpower dissipation takes place. call -See pushdown dialing. control-A control circuit that actuates a circuit when two metal areas or a preselected area are bridged by one’s finger or hand. t o u c h s c r e e n -A touch-sensitive display screen, whereby users can interact with a computer and select options by simply pointing with a finger instead of using a pointing device such as a mouse. Typically used in a kiosk.

total internal reflection

- TP tape

t o u c h sensitivity-The sensitivity of a capacitance sensor at which the alarm device will be activated only if an intruder touches or comes in very close proximity (about 1 cm or 0.39 in) to the protected object. Touch-Tone-A service mark of the American Telephone and Telegraph Company that identifies its push-button (DMTF) dialing service. The signal form is multiple tones in the audio-frequency range.

HIGH GROUP (HzJ

Touch-Tone frequencies.

Touch-Tone dialing -Push-button telephone dialing in which the direct-current pulsing technique of the rotating dial is replaced by a combination of tones to provide proper automatic switching. Touch-Tone t e l e p h o n e set -Designation for a telephone set using a push-button multifrequency dial. Each digit consists of combining one lower frequency with one higher frequency, e.g., the digit 8 consists of combining 852 Hz and 1336 Hz. t o u c h voltage-The potential difference between a grounded metallic structure and a point on the earth’s surface equal to the normal maximum horizontal reach (approximately 3 feet or 0.91 m). tourmaline -A strongly piezoelectric natural or synthetic crystal. tower-A structure usually used when an antenna must be mounted higher than 50 feet (15.24 m). tower loading-The load placed on a tower by its own weight, the weight of the wires and insulators with or without ice covering, the wind pressure acting on both the tower and the wires, and the tension in the wires. tower radiator-A metal tower structure used as a transmitting antenna. Townsend criterion -The relationship expressing the minimum requirement for breakdown in terms of the ionization coefficients. T o w n s e n d d i s c h a r g e -An electrical discharge in a gas at moderate pressure (above about 0.1 millimeter of mercury). It corresponds to corona, and is free from space charges. T o w n s e n d ionization coefficient-The average number of ionizing collisions made by an electron as it drifts a unit distance in the direction of an applied electric force. T-pad-A pad made up of resistance elements arranged in a T-network (two resistors inserted in one line, with a third between their junction and the other line). T P tape-See triple-play tape.

tr

- tracking error

tr- 1. Abbreviation for transient response. 2. Abbreviation for transmit-receive. trace -1. The pattern on the screen of a cathode-ray tube. 2. Software used for extremely detailed testing of the validity of an application program or other software. Data is stored in RAM as a program executes; when the program halts, a predetermined number of steps are available for examination. traceability- 1. Symbol identification that permits symbols to be traced throughout a software system. Also, continuity between program versions. See also auditing. 2. The ability to track a manufactured item through the steps of its manufacture. trace interval-The interval corresponding to the direction of sweep used for delineation. trace line-The visible or recordable path traced on the screen of a CRT by a moving spot. tracer- 1. A radioisotope that is mixed with a stable material to trace the material as it undergoes chemical and physical charges. 2. A thread of contrasting color woven into the insulation of a wire for identification purposes. 3. In automatic machine control, a sensing element that is made to follow the outline of a contoured template and produce the desired control signals. 4. See signal tracer. trace routine- Special type of debugging routine that develops a sequential record of specified events in the execution of a program. tracer program- Analysis tool that searches programs for unreachable (dead) code. trace width -The distance between two points on opposite sides of a trace on an oscilloscope at which luminance is 50 percent of maximum. If the trace departs from a well-behaved (approximately Gaussian) form, it should be smoothed for the purpose of measurement. tracing -The process of determining from what location in a telephone or computer network a call has originated. tracing distortion -The nonlinear distortion introduced in the reproduction of a mechanical recording when the curve traced by the reproducing stylus is not an exact replica of the modulated groove. tracing routine-See trace routine. track - 1. A path that contains reproducible information left on a medium by recording means energized from a single channel. 2. In electronic computers, that portion of a moving-type storage medium accessible to a given reading station (e.g., film, drum, tapes, disks). See also band, 3 ; channel, 3. 3. To follow a point of radiation to obtain guidance. 4. The path on the magnetic tape along which a single channel of sound is recorded. 5. One of the ring-shaped sequence of sectors defined on the magnetic surface of a disk or drum. A floppy disk has 77 tracks, numbered from 0 to 76. Tracks are arranged concentrically. 6. The actual line of movement of an aircraft or a rocket over the surface of the earth; a projection of the history of the flight path on the surface. 7. The trace of a moving target on a plan-position-indicator radar screen or an equivalent plot. See also tracking. trackability-How well the pickup system will track high amplitude and velocity modulation on a phonograph record at a given tracking weight. trackball-A data-entry device consisting of a sphere mounted in a small open-topped box. This sphere is hand operated by rotating it about either its x or y axis. The rotation is translated into digital data and stored in special input registers. The registers are then read by the host computer. The most common use of a trackball is in the control of cursor and tracking-symbol movements. It can also be used wherever it is desired to continuously vary display or process parameters.

790 track-command guidance -A missile guidance method in which both target and missile are tracked by separate radars and commands are sent to the missile to correct its course. track configuration -The number of separate recorded tracks that a machine can play or record. Thus, a two-track machine makes or plays two parallel tracks, each occupying slightly less than half the width of the tape. A four-track machine makes or plays four parallel tracks, two in the same playing direction on a twochannel machine, or four in the same playing direction on a quadraphonic machine. Monophonic machines can be full-track, half-track, or quarter-track. track-hold memory-A circuit that, in its track mode, develops an output that follows (ideally) the input exactly, or is proportional to it; and then, in its hold mode, maintains the output constant (ideally) at the value it had at the instant the circuit was commanded to change from track to hold. track homing-The process of following a line of position known to pass through an object. tracking - 1. The process of keeping a radio beam, or the cross hairs of an optical system, set on a target-usually while determining the range of the target. 2. The maintenance of proper frequency relationships in circuits designed to be simultaneously varied by ganged operations. 3. The accuracy with which the stylus of a phonograph pickup follows a prescribed path over the surface of the record. 4. The ability of a multigun tube to simultaneously superimpose information from each gun. Tracking error is the maximum allowable distance between the displays of any two guns. 5. The ability of an instrument to indicate at the division line being checked when energized by corresponding proportional values of actual end-scale excitation. 6. The interconnecting of power supplies in such a manner that one unit serves to control all units in series operation. In this manner, the output voltage of the slave units follows the variations of the master. 7. The difference at any shaft position between the output ratios of any two commonly actuated similar electrical elements expressed as a percentage of the single total voltage applied to them. 8. The process of following the movement of a satellite or rocket by radar, radio, and photographic observations. 9. The moving of a tracking symbol on the face of a CRT with a light-pen. The meaning can also be extended to include the movement of any graphical image on the screen, using any of the data entry devices. 10. The ability of a power supply to maintain a fixed ratio between multiple outputs regardless of variations in line, load, or ambient temperature. In supplies with symmetrical plusand-minus outputs, tracking maintains equal amplitudes of opposite polarity, referred to the common terminal. 11. The accuracy of indication of an analog meter having a nonlinear scale. tracking accuracy-The ability to indicate at a division line being checked when a meter is energized by corresponding proportional values of actual end-scale excitation, expressed as a percentage of actual end-scale value. Tracking accuracy is usually within one and onehalf times the rated full-scale accuracy of the meter. tracking antenna-A directional antenna system that automatically changes in position or characteristics to follow the motion of a moving signal source. tracking error- 1. In lateral mechanical recording, the angle between the vibration axis of the mechanical system of the pickup and a plane that contains the tangent to the unmodulated record groove and is perpendicular to the recording surface at the point of needle contact. 2. In horizontal recording, the angle between the body of a phonograph cartridge and the tangent of a groove at the

tracking filter - transaction file

791

point of a stylus contact. Ideally the angle should be zero, but can be maintained at less than 0.5" per inch (0.19" per centimeter) of playing radius in a well-designed tonearm. Excessive error can cause increased distortion on heavily recorded passages, especially near the inner grooves of th.e record.

Tracking error.

tracking filter-An electronic device that attenuates unwanted signals and passes the desired signal by the use of phase-lock techniques that reduce the effective bandwidth of the circuit and eliminate amplitude variations. tracking force-The downward force applied to a stylus by means of an adjustment on the tonearm. Sometimes specified as a recommended range or a single force, in grams. It is usually advisable to track near the upper rather than the lower suggested value, since distortional record damage from mistracking at too low a force is more objectionable than the slightly increased wear from the higher force. A large stylus has a large groove contact area, and thus can tolerate a higher tracking force. See also stylus force. tracking jitter-See jiitter, 2. tracking range- Also called lock-in range. The range of input frequency about f 0 under which a phaselocked loop, once locked, will remain locked. This is a function of loop gain, since the phase detector output is bounded and can drive the oscillator only over a certain €requency range, The tracking range may be controlled, if desired, by limiting the input signal to the oscillator. tracking resistance--See arc resistance. tracking spacing -The distance between the center Bine of adjacent tracks on a recording tape. In the typical case of longitudinal tracks 50 mils (1.27 mm) wide, the Eacking spacing is 70 mils (1.78 mm). tracking spot-A moving spot used for target indication on a radar. tracking weight-The downward force of a pickup stylus that ensures optimum reproduction of recorded groove modulation with minimum wear of groove wall and stylus. track-while scan-A radar system utilizing elecironic-computer techniques whereby raw data is used to track an assigned target, compute target velocity, and predict its future position without interfering with the scanning rate. t r a c k width-The width of the track on a recording tape, corresponding to a given record gap. The most common track widths encountered in longitudinal recording are 48 and 50 m i l s (2.22 and 1.27 mm), several such tracks being accommodated on a half-inch-wide (1.27 cm) tape. TRACON -Abbreviation for Terminal Radar Approach Control. An air traffic control facility that is

responsible for areas designated as terminal control areas, the exact size of which differs depending on the facility, but typically extends to about 30 miles (48 kilometers) from the airport tower. tractive force-The force that a permanent magnet exerts on a ferromagnetic object. traffic -1. Messages handled by communication or amateur stations. 2. The messages sent and received over a communication channel. traffic diagram-A chart or drawing that shows the movement and control of traffic over a communication system. traffic distribution-The routing by which communications traffic passes through a terminal to a switchboard or dialing center. traffic-flow security-Protection of the contents of messages by transmitting an uninterrupted flow of random text over a wire or radio link,with no indication that an interceptor may be used to determine which portions of this steady stream constitute encrypted messages and which portions are nearly random filler. traffic f o r e c a s t -Traffic level prediction on which communication system management decisions and engineering effort are based. trailer- 1. Tough, nonmagnetic tape spliced at the end of the recorded material on a tape that is expected to receive rough or frequent handling. Usually has one matte-finished surface for writing, and is often available in a variety of colors for coding purposes. See also leader. trailer record-A record that follows one or more records and contains information related to those records. trailers-Bright streaks at the right of large dark areas, or dark areas or streaks at the right of bright areas, in a televised picture. The usual cause is insufficient gain at low video frequencies. trailing b l a c k s -See following blacks. trailing edge-The transition of a pulse that occurs last, such as the high-to-low transition of a high clock pulse. trailing-edge pulse time-The time at which the instantaneous amplitude last reaches a stated fraction of the peak pulse amplitude. trailing reversal -See following blacks; following whites. trailing whites-See following whites. train-A sequence of units of apparatus linked together to forward or complete a telephone call. trainer- 1. The representation of an operating system by computers and its associated equipment and personnel. 2. Electronic equipment used for training operators of radar or sonar apparatus by simulating signals received under operating conditions in the field. train time-The period required for synchronous modems used on two- or four-wire leased lines to equalize the line and recover timing from the received data. This time, which applies primarily to full-duplex initialization, is especially important for multipoint operations. For either two- or four-wire circuits, actual transmission and reception cannot occur until both receiving and transmitting modems are synchronized. Train time is often referred to as RTS/CTS delay or poll response. It varies from 8.5 to about 40ms. Faster modems use longer equalization times, and have longer train times. tramlines-A pattern on an A-scope appearing as a number of horizontal lines above the baseline. The effect is produced by a continuous wave modulated with a lowfrequency signal. trans- Abbreviation for transmitter. Also abbreviated xmtr or xmitter. transaction file--In a computer, a 61e containing information relating to current activities or transactions.

transaction processing - transfer characteristic t r a n s a c t i o n processing -A processing method in which transactions are executed immediately after they are received by the computer. The largest single application for fault-tolerant computers, which involves repetitive, typically financial, tasks in banking, stock trading, and the like. transadmittance -From one electrode to another, the alternating components of the current of the second electrode divided by the alternating component of the voltage of the first electrode, all other electrode voltages being maintained constant. As most precisely used, the term refers to infinitesimal amplitudes. transceiver -The combination of radio transmitling and receiving equipment in a common housing, usually for portable or mobile use and employing some common circuit components for both transmitting and receiving. transceiving data link-Integrated data processing by means of punched cards, using transceivers as terminal equipment. The transmission path can be wire or radio. transconductance -Symbolized g,. Also called mutual conductance. An electron-tube rating equal to the change in anode current divided by the change in grid voltage causing the anode-current change. The unit of transconductance is the siemens; a more commonly used unit is the microsiemens siemens). transconductance amplifier- An amplifier that supplies an output current proportional to its input voltage. From its output terminals the amplifier appears to be a current source with a high outpnt impedance 2,. Its input impedance Zh >> Z,, and the output impedance 2, >> Z L , where Z , and Z L are the source and load impedances. transconductance meter- Also called a mutualconductance meter. An instrument for indicating the transconductance of a grid-controlled electron tube. transconductance tube tester-Also called a mutual-conductance or dynamic mutual-conductance tube tester. A tube tester with circuits set up in such a manner that the test is made by applying an ac signal of known voltage to the control grid, and the tube amplification factor or mutual conductance is measured under dynamic operating conditions. transconductor- An active or passive network whose short-circuit output current is a specific, accurately known, linear or nonlinear function of the input voltage, thereby establishing a predetermined relationship between input voltage and output current. transcribe- 1. To copy, with or without translating, from one external storage medium of a computer to another. 2. To copy from a computer into a storage medium or vice versa. transcriber-Equipment associated with a computing machine for the purpose of transferring input or output data from a record of information in a given language to the medium and language used by a digital computing machine, or from a computing machine to a record of information. transcription -1. An electrical recording (e.g., a high-fidelity, 33%-rpm record) containing part or all of a (radio) program. It may be either an instantaneous recording disc or a pressing. 2. A phonograph record, especially the 33 %-rpm 16-inch (40.6-cm) record, used to record broadcast programs. transdiode-A transistor so connected that the base and collector are actively maintained at equal potentials, although not connected together. The logarithmic transfer relationship between collector current and base-emitter voltage very closely approximates that of an ideal diode. transducer -1. A device that when actuated by signals from one or more systems or media can supply related signals to one or more other systems or media.

792 2. A device, component, machine, system, or combination of these that converts energy from one form to another. The energy may be in any form, such as electrical, mechanical, acoustical, etc. The term transducer is often restricted to a device in which the magnitude of an applied stimulus is converted into an electrical signal proportional to the quantity of the stimulus. 3. A device used to convert physical parameters, such as temperature, pressure, or weight, into electrical signals. 4. A device that converts information from one physical form to another. Examples include the phono cartridge (mechanical to electrical), speaker (electrical to acoustical), and microphone (acoustical to electrical). 5. A force-measuring device. It has the characteristics of providing an output, usually electrical, that serves as the measurement of load, force, compression, pressure, etc., when placed along the sensitive axis of the force cell. 6. An electromechanical device for translating a physical quantity such as pressure, temperature, displacement, acceleration, etc., into a proportional electrical quantity, such as voltage or current. 7.A device that converts something measurable into another form; often, a physical property such as temperature or flow into an electrical signal. Frequently used interchangeably with sensor. transducer-coupling system efficiency-The power output at the point of application, divided by the electrical power input into the transducer. transducer efficiency -Ratio of the power output to the electrical power input at the rated power. transducer equivalent noise pressure (of an

electroacoustic transducer or system used

f o r sound reception) -Also called equivalent noise pressure. For a sinusoidal plane-progressive wave, the rms sound pressure that, if propagated parallel to the principal axis of the transducer, would produce an open-circuit signal voltage equal to the rms of the inherent opencircuit noise voltage of the transducer in a transmission band having a bandwidth of 1 hertz and centered on the frequency of the plane sound wave. transducer gain-Ratio of the power that the transducer delivers to the load under specified operating conditions to the available power of the source. transducer insertion IoSS-SSee insertion loss. transducer loss-Ratio of the available power of the source to the power that the transducer delivers to the load under specified operating conditions. transducer p u l s e delay-The interval of time between a specified point on the input pulse and on its related output pulse. transfer- 1. To transmit, or copy, information from one device to another. 2. To jump. 3. The act of transferring. 4. In electrostatography, the act of moving a developed image, or a portion thereof, from one surface to another without altering its geometrical configuration (e.g., by electrostatic forces or by contact with an adhesive-coated surface). 5. In a computer, to terminate one sequence of instructions and start another. t r a n s f e r accuracy-The input-to-output error as a percentage of the input. Transfer accuracy depends on the source impedance, switch resistance, load impedance if the multiplexer is not buffered, and the signal frequency. transfer admittance- 1. The complex ratio of the current at the second pair of terminals of an electrical transducer to the electromotive force applied between the first pair, all pairs of terminals being terminated in any specified manner. 2. The reciprocal of transfer impedance. t r a n s f e r characteristic- 1. The relationship, usually shown by a graph, between the voltage of one electrode and the current to another electrode, all other electrode voltages being maintained constant. 2. The characteristics pertaining to the degree of output activity for an input stimulus, or vice versa. 3. Function that when

793 multiplied by an input magnitude will give a resulting output magnitude. 4. Relation ‘betweenthe illumination on a camera tube and the corresponding output-signal current, under specified conditions of illumination. transfer charge-The net electric charge moved from one terminal of a capacitor to another through an external circuit. t r a n s f e r check-In a computer, verification of bransmitted data by temporarily storing, retransmitting, and comparing. Also a check to see if the transfer or jump instimction was properly performed. t r a n s f e r circuit -A circuit that connects communication centers of two or more separate networks in order tO transfer the traffic between the networks. t r a n s f e r constant -Also called the image-transfer constant. One-half the natural logarithm of the complex ratio of the voltage times current entering a transducer to that leaving the transducer when it is terminated in its image impedance. t r a n s f e r contact -See break-make contact. t r a n s f e r control-See jump. t r a n s f e r current -The starter-gap current required to cause conduction across the main gap of a glowdischarge cold-cathode tube. t r ~ n s f eefficiency-The r percentage of total charge that is transferred in a charge-coupled device from one position to another during readout. t r a n s f e r factor-Number relating the input and output cuments of a transducer. See propagation cons:ant, 2. t r a n s f e r function -. 1. A characterization of a system (for example, mecjhanical structure of filter) by determining how the system responds to input energy at different frequencies. It may be measured by one of three -methods: ( a ) appllying a single sine wave and measuring the response to that sine wave, then varying the frequency of the sine wave and noting the change in the ~~ystem’s response, (b) applying specially shaped random noise (many frequencies simultaneously) and observing the system response, or (c) applying an impulse (also containing a broad range of frequencies). The transfer function can be derived by dividing the cross-spectral density by the power spectral density of the input or driven signal. 2. A mathematical expression that describes the relationship between the values of a set of conditions at ~ W Qdifferent times, typically at the beginning and end of a process. 3. The mathematical expression that relates the output and input of any characteristics of a filler as ,a function of frequency. The function usually is complex and therefore usually contains components corresponding to both attenuation and phase. 4. The mathematical expression of the relationship between a simple scale factor, representing the effects of any linear transmitting or recording medium when a waveform is evaluated as frequency components, and the frequency. function analyzer-An instrument that amplitude and phase response of the output of a circuit relative to the input over a range of frequencies. t r a n s f e r impedance --Ratio of the potential difference applied at one pair of terminals of a network to the resultant current at another pair of terminals (all terminals being tenninated in any specified manner). t r a n s f e r instruction -An instruction, signal, or operation that conditionally or unconditionally specifies the location of the next instruction and directs a computer to that instruction. slier loss -See coupling loss. sfer operation -- 1. An operation that moves datz from one storage location or one storage medium

transfer c h a r g e

- transformer-coupled am

to another. Transfer is sometimes taken to refer specifically to movement between different media; storage to movement within the same medium. 2. In a computer, transferring information from an accumulator to memory, or from memory to an accumulator; pushing into or popping out of the stack or moving infomation to the program counter, stack pointer, etc. transfer rate-The rate at which a transfer of data between the computer registers and storage. input, or output devices may be performed. It is usually expressed as a number of characters per second. transfer ratio-From one point to another in a transducer at a specified frequency, the complex ratio of the generalized force or velocity at the second point to that applied at the first point. transferred c h a r g e -The net electric charge moved from one terminal of a capacitor to another though an external circuit. transferred c h a r g e characteristic -The mathematical function that relates transferred charge to capacitor voltage. transfer switch-A form of air switch arranged so that a conductor connection can be transferred from one circuit to another without interrupting the current. transfer time-1. The time required for a transfer to be made in a digital computer. 2. In a relay, the total time -after contact bounce has ceased- between the breaking of one set of contacts and the making of another. Transfluxor-A trade name (RGA) for a binary magnetic core having two or more openings. Control of the transfer of magnetic flux between the three or more legs of the magnetic circuits provides ways to store information, gate electrical signals, etc. transform- 1. To convert a current or voltage from one magnitude to another, or from one type to another, 2. In digital-computer programming, to change information in structure or composition wlthout significantly altering the meaning or value. 3. To pass through a transformer. 4. To change data or equations from rectangular to polar coordinates, or vice versa. transformation point -The temperature at which an alloy or metal changes from one crystal state to another as it heats or cools. transformation ratio -The ratio between electrical output and input under certain specified conditions. transformer-1. An electrical device that, by electromagnetic induction, transforms electric energy from one or more circuits to one or more other circuits at the same frequency, but usually at a different voltage and current value. 2. An electrical device that changes voltage in direct proportion to the ratio of the number of turns of its primary and secondary windings.

Air core.

Iron core

Transformer.

transformer build -The amount of window area used in constructing a transformer. transformer-coupled amplifier-An amplifier whose stages are coupled together by transformers.

transformer-coupled solid-state relay

-transient response

transformer-coupled solid-state relay -A relay in which the control is applied to the primary of a lowpower transformer, and the resulting secondary voltage triggers the thyristor switch to the load. of a transformer t r a n s f o r m e r coupling -Use between stages of an amplifier, Le., to connect the anode circuit of one stage to the grid circuit of the following stage. t r a n s f o r m e r l e s s receiver-A receiver in which the power-line voltage is applied directly to seriesconnected tube heaters or filaments and to a rectifier circuit instead of first being stepped up or down in voltage by a power transformer. transformer load loss-Losses in a transformer that are incident to the carrying of the load. Load losses include Z"-Rloss in the windings due to load current, stray loss due to stray fluxes in the winding core, clamps, etc., and to circulating current, if any, in parallel windings. t r a n s f o r m e r loss -Expressed in decibels, the ratio of the signal power that an ideal transformer of the same impedance ratio would deliver to the load impedance to the signal power delivered by the actual transformer. high-quality insulating oil transformer oil -A in which windings of large power transformers are sometimes immersed to provide high dielectric strength, insulation resistance, and flash point, plus freedom from moisture and oxidation. transformer read-only store -In computers, a type of read-only store in which the presence or absence of mutual inductance between two circuits is the condition that determines whether a binary 1 or 0 is stored. t r a n s f o r m e r vault-An isolated enclosure, either above or below ground, with fire-resistant walls, ceiling, and floor for unattended transformers and their auxiliaries. transformer voltage ratio-The ratio of the root-mean-square primary terminal voltage to the rootmean-square secondary terminal voltage under specified conditions of load. transforming section-A length of waveguide or transmission line of modified cross section, or with a metallic or dielectric insert, used for impedance transformation. transhybrid loss- 1. The transmission loss at a given frequency measured across a hybrid circuit when connected to a given two-wire termination and balancing network. 2. The loss (isolation) between the transmit and receive branches of a four-wire line. Transhybrid loss is directly dependent on the degree of balance between the two-wire line and its balancing network. transient -1. A phenomenon caused in a system by a sudden change in conditions, and which persists for a relatively short time after the change. 2. A distinct line or series of lines perpendicular to the direction of scanning produced in the recorded copy immediately following a sudden change in density. 3. A momentaq surge on a signal or power line. It may produce false signals or triggering impulses and cause insulation or component breakdowns and failures. 4.Signal component of fast-rising leading side and usually of short duration. 5. A pulse, damped oscillation, or other temporary phenomenon occurring in a circuit or system. 6. Intermediate unstable state. 7. A change in a variable that disappears during transition from one steady-state operating condition to another. 8. Signals that exist for a brief period prior to the attainment of a steady-state condition. May include overshoots, damped sinusoidal waves, etc. transient analyzer- An electronic device for repeatedly producing a succession of equal electric surges of small amplitude and of adjustable waveform in a test circuit and presenting this waveform on the screen of an oscilloscope.

794

transient behavior-In a power supply, the general attitude of response in terms of amplitude and time. transient distortion- 1. Distortion due to the inability of a system to reproduce or amplify transients linearly. 2. Distortion of a transient signal component such as produced by resonance and lack of damping, the effect being overshoot or ringing following the fast-rising leading side of the signal component. transient intermodulation distortion-Abbreviated TIM 1. Distortion that occurs in an amplifier having a large amount of negative feedback in its main feedback loop and a certain amount of time or phase delay between the input and output signals. If a very fast transient musical signal or pulse is fed to such amplifiers, the feedback needed to reduce the amplitude of that signal at the input (and later) stages arrives too late, and an overload or momentary clipping occurs. At the instant of such clipping, other program-signal elements are also distorted or even obliterated. 2. Intermodulation distortion that occurs only momentarily during brief transients or signal peaks. transient m a g n i s t o r -A high-speed saturable reactor in which an alternating electric current in the form of a sine-wave carrier or pulses is passed through a signal winding and modulated by variations of current passing through a control coil. transient motion -Any motion that has not reached, or has ceased to be, a steady state. transient oscillation -A momentary oscillation that occurs in a circuit during switching. transient overshoot-The largest transient deviation of the measured quantity following the dynamic crossing of the final value as a result of the application of a specified stimulus. transient peak-inverse voltage -Under specified conditions, the maximum allowable instantaneous value of nonrecurrent reverse (negative) voltage that may be applied to the anode of an SCR with the gate open. t r a n s i e n t p h e n o m e n a -Rapidly changing actions occurring in a circuit during the interval between closing of a switch and settling to steady-state conditions, or any other temporary actions occurring after some change in a circuit or its constants. transient recovery time- Also called recovery time, transient response time, or response time. 1. The interval between the time a transient deviated from a specified amplitude range and the time it returns and remains within the specified amplitude range. The amplitude range is centered about the average of the steady-state values that exist immediately before and after the transient. 2. The time required for the output voltage of a power supply to come back to within a level approximating the normal dc output following a sudden change in load current. transient regulation -The degree of freedom of a system from variations in voltage and kquency caused by sudden changes, operational switching, emergency system faults, power transfers, etc. transient response- 1. The transient of a dependent variable resulting from an abrupt change of an independent variable with all other variables constant. 2. Also called step-function response. Commonly, the characteristic response of a system to a unit sweep or unit impulse. The elements of transient response most commonly specified are rise time, fall time, overshoot, undershoot, preshoot, and ringing. 3. (Input line changes) The transient of an output variable (voltage, current, or power) of an electronic power supply resulting from an abrupt specified change of input line voltage, with all other conditions held constant. 4. (Load changes) The transient of an output variable (voltage, current, or power) of an

transient response time

795 electronic power supply resulting from an abrupt specified change of load, with all conditions held constant. 5. Ability to respond to percussive signals cleanly and instantly. 6. The ability of an amplifier or transducer to handle and faithfully reproduce rapid changes in signal amplitudes. A very short rise time is a measure of this characteristic. 7. The closed-loop step function response of an amplifier under small-signal conditions. 8. The ability of an amplifier, microphone, or speaker to follow sildden changes in signal levels. transient response time -See transient recovery time. transient state-The condition in which a variable temporarily behaves in an erratic manner instead of changing smoothly and predictably. transistance- 1. The characteristic of an electrical element that makes possible the control of voltages, currents, or flux so as to produce gain or switching action in a circuit. Examples of the physical realization of transistance occur in transistors, diodes, and saturable reactors. 2. An electronic characteristic exhibited in the form of voltage or current gain or in the ability to control voltages or currents in a precise and nonlinear manner. (Examples of parts showing transistance: transistors, diodes, vacuum tubes.) 3. A function of transistors. An electrical property that causes applied voltage to create amplification or accomplish switching. transistor- 1. An active semiconductor device having three or more electrodes and capable of performing almost all the functions of tubes, including rectification and amplification. Germanium and silicon are the main materials used, with impurities introduced to determine the conductivity type (n-type has an excess of free electrons; p-tpe, a deficiency). Conduction is by means of electrons (elementary particles having the smallest negative electrical charge that can exist) and holes (mobile electron Pacancies equivalent to a positive charge). 2. A tiny chip of crystalline material, usually silicon, that ampt-ifies or switches electric current. It i s a three-terminal semiconductor device. A small current (base current) applied to one terminal can control a larger current (collector current) between the other two terminals. For elementary ]purposes, a transistor can be looked at as a resistor whose value can be changed from a high to a lraw value by applying a current to the base lead. 3. A three-terminal active semiconductor device that provides current amplification. A bipolar transistor is comprised of base, emitter, and collector and is a current-controlled device with a low input impedance. A field-effect transistor has gate, source, and drain electrodes and is a highimpedance, voltage-controlled device. The first transistor was invented at Bell Laboratories in 1947 by Nobel-Prize physicists John Bardeen, William Shockley, and Walter Wratain.

transistor action-The physical mechanism of amplification in a junction transistor. transistor amplifier -An amplifier in which the required amplification is produced by one or more transistors. transistor base-The region between an emitter and a collector of a transistor, into which minority carriers are injected. transistor chip-An unencapsulated transistor element of very small size used in microcircuits. transistor dissipation -The power dissipated in the form of heat by the collector. The difference between the power supplied to the collector and the power delivered by the transistor to the load. transistorized--Pertaining to equipment or a design in which transistors instead of vacuum tubes are used. transistor oscillator -An oscillator that uses a transistor in place of an electron tube. transistor-outlinemetal-can package-Abbreviated TO can. A type of package that resembles a transistor can, but generally is larger and has more leads. The pins are arranged in a circular pattern in the base. This type of package is often used for MSI, LSI, and MOS ICs. transistor parameters-The performance characteristics of a transistor or class of transistors. transistor pentode-A transistor designed for mixing, modulating, or switching and containing the equivalent of three emitters, a base, and a collector. transistor radio-A radio receiver that uses transistors in place of electron tubes. transistor region-The region around a pn junction in which the majority carriers from each side of the junction diffuse across it to recombine with their respective counterparts. transistor-resistor logic- Abbreviated TRL. An early form of logic-circuit design that was employed prior to the advent of monolithic circuits. The input elements are resistors; however, unlike RTL there is only one active output transistor. In discrete circuit designs, this logic form was the least expensive since it required a minimum number (one) of active devices. transistor seconds- Also called fallouts. Those transistors that remain after the firsts (units meeting rigid specifications for a specific application) have been removed from the production line. transistor symbols -Symbols used to represent transistors on schematic diagrams.

C (COLLECTOR)

I

E(EMITTER)[

f

r

-

- transistor-resistorlogic

C (COLLECTOR)

I

E (EMITTER)[

COLLECTOR

Npn.

Pnp.

Transistor symbols. CURfiENT

BASE

EMITTER

Tkansistor (typical).

transistor testers- Equipment and instmments that detect or measure leakage current, breakdown voltage, gain, or saturation voltage. Some testers are computer operated. transistor-transistor logic -Abbreviated TTL or T2L. Also called multiemitter transistor logic. 1. A logiccircuit design similar to DTL, with the diode inputs

-

transit angle translator replaced by a multiple-emitter transistor. In a four-input DTL, gate, there are four diodes at the input. A four-input TTL gate will have four emitters of a single transistor as the input element. TTL gates using npn transistors are positivelevel NAND gates or negative-level NOR gates. 2. A relatively high-speed and inexpensive bipolar logic circuit most commonly used in today’s logic designs. 3. Any logic gate circuit that uses a multiemitter npn transistor to perform the positive AND function, followed by one or more transistors to add power to (and possibly invert) the output. Operating speed is generally faster than that of DTL. 4. A widely used form of semiconductor logic. Its basic logic element is a multiple-emitter transistor. TTL is characterized by fairly high speed and medium power dissipation. transit angle-The product of angular frequency and the time taken for an electron to cross a given path. transition- 1. The process in which a quantummechanical system makes a change between energy levels, During this process, energy is either emitted or absorbed, usually in the form of photons, phonons, or kinetic energy of particles. Transitions that involve photons alone are called direct radiative transitions, whereas those that require a combination of a photon and a phonon are called indirect transitions. 2. The instance of changing from one state (such as a positive voltage) to a second state (such as a negative voltage) in a serial transmission. transitional function -A transfer function that represents a compromise made between the classical types of functions (Tchebychev, Butterworth, Gaussian, etc.) as a result of the fact that each classical function has certain advantages and disadvantages. In general, however, better functions than the transistional functions are available if the transfer function is optimized with respect to its own particular requirement. transition band -The range of frequencies that bound a passbandstopband interface. transition card-A card that signals the computer that the reading-in of a program has ended and that the carrying out of the program has started. transition counts-A particular digital signature used in logic-board testing. transition element -An element used for coupling different types of transmission systems, e.g., for coupling a coaxial line to a waveguide. transition error-In an encoder, the difference between the shaft angle at which a code-position change should occur and the angle at which it actually does occur. transition factor-See reflection factor, 1. transition frequency- Also called crossover frequency. 1. In a disc-recording system, the frequency corresponding to the point of intersection of the asymptotes to the constant-amplitude and the constant-velocity portions of its frequency-response curve. This curve is plotted with output-voltage ratio in decibels as the ordinate, and the logarithm of the frequency as the abscissa. 2. In a transistor, the product of the magnitude of the small-signal, common-emitter, forward-current transfer ratio times the frequency of measurement when this frequency is high enough that the magnitude is decreasing with a slope of approximately 6 dB per octave. transition layer-See transition region, 1. transition-layer capacitance-See depletionlayer capacitance. transition loss-At any point in a transmission system, the ratio of the available power from that part of the system ahead of the point under consideration to the power delivered to that part of the system beyond the point under consideration.

796

transition oscillator-A negative-transconductance oscillator employing a pentode tube with a capacitor connected between the screen and suppressor grids. The suppressor grid periodically divides the current between the screen grid and anode, thereby producing oscillations. transition point-A point at which the circuit constants change in such a way that a wave being propagated along the circuit is reflected. transition region -1. Also called transition layer. The region, between two homogeneous semiconductor regions, in which the impurity concentration changes. 2. The area, between the passband and the stopband, in which the attenuation of a filter is neither great nor small. The narrower the transition region, the more difficult is the design of the filter. 3. The region around a pn junction in which the majority carriers of each si& diffuse across the junction to recombine with their respective counterparts. transition temperature -The temperature below which the electrical resistance of a material becomes too small to be measured. transition time-The time required for a voltage change from one logic level to the opposite level, as measured between specified points on the transition waveform. The transition times from high to low level and from low to high level generally are different. transitron -A thermionic tube circuit whose action depends on the negative transconductance of the suppressor grid of a pentode with respect to the screen grid. transit time -1. The time taken for a charge carrier to cross a given path. 2. The average time a minority carrier takes to diffuse from emitter to collector in a junction transistor. 3. The time an electron takes to cross the distance between the cathode and anode. transit-time mode -A condition of oscillator operation, corresponding to a limited range of drift-space transit angle, for which the electron stream introduces a negative conductance into the coupled circuit. translate- 1. To change computer information from one language to another without significantly affecting the meaning. 2. To change one binary word to another, or to change to a different pair of binary signal levels, for the purpose of achieving compatibility between parts of a system. 3. To transform information in a way that preserves meaning, Le., from one code to another or from one language to another. translation -The conversion of a message to a different set of symbols. For example, in instrumentation, the changing of conventional algebraic expressions into machine language for computer programming. translational morphology-The structural characterization of an electronic component in which it is possible to identify the areas of patterns of resistive, conductive, dielectric, and active materials in or on the surface of the structure with specific corresponding devices assembled to perform an equivalent function. translation frequency- The 2220-MHz (2.2-GHz) frequency difference between an uplink and a downlink signal of a satellite TV system. translation loss- Also called playback loss. The loss in the reproduction of a mechanical recording, whereby the amplitude of motion of the reproducing stylus differs from the recorded amplitude in the medium. translator- 1. A device that transforms signals from the form in which they were generated into a useful form for the purpose at hand. 2. A television receiver and lowpower transmitter that receives television signals on one channel and retransmits them on another channel (usually a UHF channel) to valleys and like areas that cannot receive the direct signals. 3. In telephone equipment, the device that converts dialed digits into call-routing information. 4.In electric computers, a network or system

translator p a c k a g e - transmission security

797 that has a number of inputs and outputs and is connected so that input signals representing infomation expressed in a certain code result in oulput signals that represent the input information in a different code. 5. A generic term for any system that converts one language into another. translator p a c k a g e --A computer program that allows a user program (in binary) to be converted into a usable fornn for computer manipulation. See also program assembly. transliterate-To change the characters of one alphabet to the corresponding characters of another alphabet. translucent -Partially transparent. In optics the notion of imperfect, or diffused, light transmission is generally implied. Thus, a translucent material may conduct light but not clear images. transmissibility --Ratio of the response amplitude of the system in steady-state forced vibration to the excitation amplitude. The ratio may be between forces, displacements, velocities, or accelerations. transmission -1. Conveying electrical energy from point to point along a path. 2. The transfer of a signal, message, or other form of intelligence from one place to another by electrical means. 3. The dispatching of a signal, message, or other form of intelligence by wire, radio, telegraphy, telephony, facsimile, or other means; the signaling of data over communications channels. 4. A series of characters, messages, or blocks, including control information and user data, sent over a communication channel. transmission anomaly-The difference, in decibels, between the total loss in intensity and the reduction in intensity that would be due to an inverse-square divergence. transmission band The range of frequencies above the cutoff frequency of a waveguide, or the comparable useful frequency range for any other type of transmission device. transmission cable- 1. Two or more transmission lines. E the structure is Iflat, it is sometimes called flat transmission cable to differentiate it from a round structure, such as a jacketed group of coaxial cables. See transmission line. 2. A signal-carrying circuit composed of conductors and dielectric material with controlled electrical characteristics, used for the transmission of high-frequency or narrow-pulse type signals. transmission coefficient -For a transition or discontinuity between two bransmission media at a given frequency. the ratio of some quantity associated with the transmitted wave at a specified point in the second medium to the same quantity associated with the incident wave at a specified point in the first medium. transmission facility -1. The transmissionmedium and all the associated equipment required to transmit a message. 2. Cable andlor radio facility constituting interswitch trunks and subscriber access lines. transmission f a c t o r -- Ratio of flux transmitted to flux incident. Inverse of opacity. transmission function-The ratio of the output vloltage to the input voltage of a filter expressed in terms of magnitude and phase (or delay). transmission gain - 1. See gain. 2. The increase in the power of an electrical signal from one point in the circuit to another. transmission gate -The solid-state equivalent of a relay, having terminals that are connected to each other or not depending on the application of a separate control voltage. (In CMOS logic it is bidirectional.) transmission level-The level of signal power at m y point in a transmission system. It is equal to the ratio of the power at that point to the power at some point

-

in the system chosen as a reference point. This ratio is usually expressed in decibels. transmission line- 1. A material structure forming a continuous path from one place to another, and used for directing the transmission of electromagnetic energy along this path. 2. A conductor or series of conductors used for conveying electrical energy from a source to a load. 3. One or more insulated conductors arranged to transmit electrical energy signals from one locality to another. 4. A signal-carrying circuit with controlled electrical characteristics used to transmit high-frequency or narrow-pulse signals. transmission-line coupler -A coupler that allows the passage of electric energy in either direction between balanced and unbalanced transmission lines. transmission-line loss- 1. The difference in the amount of energy delivered at the output of a transmitter and the amount of energy absorbed by the antenna. For example, if a transmitter delivers 3 watts and the transmission line (coaxial cable) loss is 1 dB, the antenna will absorb approximately 2.4 watts since 20 percent of the available power is lost in the transmission line. 2. The power lost when a radio signal is fed from the antenna to the receiver through coaxial cable; expressed in decibels. transmission-line-tuned frequency meter- A frequency meter using a tuned length of wire or a coaxial cavity as the frequency-determining element. transmission link-The path over which information flows from sender to receiver. transmission IoSS-The decrease or loss in power during transmission of energy from one point to another. Usually expressed in decibels. transmission measuring set --A measuring instrument comprising a signal source and a signal receiver having known impedances, for measuring the insertion loss or gain of a network or transmission path connected between those impedances. transmission mode -A form of waveguide propagation along a transmission line characterized by the presence of transverse magnetic or transverse electromagnetic waves. Waveguide transmission modes are designated by integers (modal numbers) associated with the orthogonal functions used to describe the waveform. These integers are known as waveguide-mode subscripts. They may be assigned from observations of the tranverse field components of the wave and without reference to mathematics. transmission modes -Simplex transmission goes only one way; simplex with back-channel, one way with limited talk-back handshaking. Half-duplex transmission is bidirectional but in one direction at a time; full-duplex is simultaneously bidirectional. transmission modulation -Amplitude modulation of the current in the reading beam of a charge-storage tube as the beam passes through aperatures in the storage surface. The degree of modulation depends on the stored charge pattern. transmission primaries-The set of three primaries, either physical or nonphysical, each chosen to correspond in amount to one of the three independent signals contained in the color-picture signal. The I, Q, and Y signals. transmission regulator -A device that maintains the transmission substantially constant over a system. transmission response-The conversion of electrical energy traveling at the speed of light io sonic energy traveling at the speed of sound. transmission security-That part of communications security resulting from all measures intended for protection of transmissions from unauthorized interception, traffic analysis, and imitative deception.

transmission selective - transmitting voltage response transmission selective-The transmission of electromagnetic energy at wavelengths other than those that are reflected or absorbed. transmission speed -The number of information elements sent per unit time, usually expressed as bits, characters, word groups, or records per second or per minute. transmission system -1. An assembly of elements capable of functioning together to transmit signal waves. 2. One of two broad groups of communication means, distinguished by their information-carrying bandwidth and referred to as either wideband or narrowband transmission systems. The wideband system includes tropospheric scatter radio relay and submarine cables, and has an information bandwidth of more than four voice-frequency (3 to 4 kHz bandwidth) channels. The narrow-band system includes high-frequency radio (single sideband, amplitude modulated, ionospheric scatter) and landlines, and has an information-carrying bandwidth of four voice channels or less. transmission time -The absolute time interval between transmission and reception of a signal. transmission-type f r e q u e n c y meter-A frequency meter in which a tuned electrical circuit or a cavity is used to transmit the energy from the signal source under test to a detecting load. transmission wavemeter-A device that makes use of a cavity to transmit maximum power at resonance so that maximum deflection is obtained on a readout meter at the frequency of resonance. transmit-To send a program, message, or other information from one location to another. transmit current-The current drawn by a transceiver when in the transmit mode. transmit-on-alarm -A security device that activates only when triggered. Most security devices are of this nature; however, in multiplexing systems, it is usually impossible to determine whether or not transmit-on-alann devices are actuated or whether the transmitter has failed or the communication channel is inoperative. transmit-on-interrogation-The response of a security device that stores an alarm until it is interrogated in an appropriate manner. Used in multiplexed systems to avoid the problem of two simultaneous transmissions of alarm by two or more different stations. transmit-receive s w i t c h -Also called a tr switch, tr box, tr tube, or duplexing assembly. An automatic device employed in a radar to prevent the transmitted energy from reaching the receiver, but allowing the received energy to do so without appreciable loss. TO ANTENNA

RECEIVER

SWITCH FROM TRANSMITTER

Transmit-receiveswitch.

transmit-receive tube -See tr tube. transmittal mode-The method by which the contents of an input buffer are made available to the

798

program and the method by which records are made available by a program for output. transmittance-I. Of a material, the ratio of the radiant power transmitted through the material to the incident radiant power. 2. As a transfer function, a response function for which the variables are measured at different ports (terminal pairs). transmitted-carrier operation -Amplitudemodulated carrier transmission in which the carrier wave is transmitted. transmitted wave-See refracted wave. transmitter- 1. Equipment used to generate and amplify an rf carrier signal, modulate this carrier with intelligence, and radiate the modulated rf carrier into space. 2. In telephony, the microphone that converts sound waves into electrical signals at an audiofrequency rate. 3. Apparatus for converting electrical energy received from a source into radio-frequency electromagnetic energy capable of being radiated. 4.The device in a telephone handset used to convert speech to electrical energy. 5. A device that translates the low-level output of a sensor or transducer to a higher-level signal suitable for transmission to a site where it can be further processed. transmitter distributor -In teletypewriter operations, a motor-driven device that translates teletypewriter code combinations from perforated tape into electrical impulses and transmits these impulses to one or more receiving stations. transmitter f r e q u e n c y tolerance-The extent to which the carrier frequency of a transmitter may legally depart from the assigned frequency. transmitter start code -Usually a two-letter call that is sent to an outlying machine to automatically turn on its tape transmitter. transmitting antenna-A device for converting electrical energy into electromagnetic radiation capable of being propagated through space. transmitting current response -Of an electroacoustic transducer used for sound emission, the ratio of the sound pressure apparent at a distance of 1 meter in a specified direction from the effective acoustic center of the transducer to the current flowing at the electric input terminals. Usually expressed in decibels above a reference-current response of 1 microbar per ampere. transmitting efficiency (projector efficiency) Ratio of the total acoustic power output of an electroacoustic transducer to the electric power input. transmitting element-In fiber optics, the lightradiating side of the terminus in an optical conductor. transmitting loop loss-That part of the repetition equivalent assignable to the station set, subscriber line, and battery supply circuit that are on the transmitting end. transmitting power response (projector power r e s p o n s e ) -Of an electroacoustic transducer used for sound emission, the ratio of the effective sound pressure apparent at a distance of 1 meter in a specified direction from the effective acoustic center of the transducer to the electric power input. Usually expressed in decibels above a reference response of 1 microbar square per watt of electric input. transmitting station-A location at which the transmitter of a radio system and its antenna and associated equipment are grouped. transmitting voltage response-Of an electroacoustic transducer used for sound emission, the ratio of the sound pressure apparent at a distance of 1 meter in a specified direction from the effective acoustic center of the transducer to the signal voltage applied at the electric input terminals. Usually expressed in decibels above a reference-voltage response of one microbar per volt.

799 transollver-A servo unit with a three-phase stator and a two-phase rotor that can be used either as a control transmitter (with one rotor phase excited and the other shorted) or as a control transformer with the signal obtained from one phase oif the rotor, making sure the other phase is equally loaded to prevent unbalances. transainic speed -A speed of 600 to 900 miles per hour (965 to 1448 kmm), corresponding to about Mach 0.8 to 1.2, transparent -1. Implying clear and unimpeded transit of light. Window glass is a common example. 2. A computer process or function that is invisible to the user. transparent computer voice -Digitized and reconstructed voice that 80 percent of uncued listeners would not recognize as having come from a computer. transparent device -A device on a communications network that functions without making its presence known to the end terminals. transponder - 1. A combination receiver, frequency converter, and transmitter package designed to receive a signal and to retransmit it on another frequency. Broadcast and telecommunication satellites are equipped with transponders, which have a typical output of 5 to PO watts and operate over a frequency band with a 36 io 72megahertz bandwidth in the L, C, Ku, and sometimes Ka bands. Communication satellites typically have between 12 and 24 onboard transponders, although the INTELSAT VI has 50. 2. A component designed to r'eceive a signal and to retransmit it on another frequency. 3. A radio transmitter-receiver that transmits identifiable signals antomatically when the proper interrogation is received. See also pulse repeater. 4. A device (usually in the form of a radio transmitter) which sends a confirming or identifying message or releases a stored message after bein,g triggered by an interrogator. Used on communication satellites. 5. A microwave repeater that receives, amplifies. downconverts, and retransmits signals from a communication satellite. transponder dead time -The time interval between the start of a pulse and the earliest instant at which a new pulse can be received or produced by a transponder. t r a ~ s ~ ~ efficiency-A o~de~ ratio expressed as a percentage of the number of replies to the number of interrogations from a transponder. t ~ a n s ~ ~suppressed nde~ time delay-The overail1 fixed delay between recaption of an interrogation and the transmission of a reply. transport- Also called tape transport. 1. Platform or deck of a tape recorder on which the motor (or motors), ~ S mounted. It includes those reels, heads and C O ~ ~ Kare parts of the recorder other than the amplifier, preamplifier, speaker, and case. 2. That portion of a tape recorder which holds the reels of magnetic tape and draws the tape at a constant speed past the recording and playback heads. sportable transmitter- Sometimes called a portable transmitter. A transmitter designed to be readily carried from place to place, but normally not operated while in motion. t r a ~ s time-h p ~ ~ a.n automatic system, the time required to move an object, element, or information between two predetermined positions. t r a ~ s p Q s ~-The t ~ ~ ninterchanging of the relative positions of the conductors in an open-wire line to reduce noise, interference, and crosstalk. t ~ ~ ~ s ~ oblocks s i t~ Spreaders Q ~ used to space and reverse the relative positions of two conductors at fixed intervals. t ~ a ~ s ~ o ssection ~ t ~ o-A n length of open-wire line to which a fundamental transposition design or pattern is applied as a unit.

transolver - transverse

transradar -A bandwidth-compression system for use in long-range narrow-band transmission of radio signals from a radar receiver to a remote location. transrectification-The rectification that occurs in one circuit when an alternating voltage is applied to another circuit. transrectification characteristic -The graph obtained by plotting the direct voltage values for one electrode of a vacuum tube as abscissas against the average current values in the circuit of that electrode as ordinates, for various values of alternating voltage applied to another electrode as a parameter. The alternating voltage is held constant for each curve. and the voltages on other electrodes are maintained constant. transrectification factor- The change in average current of an electrode, divided by the change in the amplitude of the alternating sinusoidal voltage applied to another electrode (the direct voltages of this and other electrodes being maintained constant). transrectifier- A device, ordinarily a vacuum tube, in which rectification occurs in one electrode circuit when an alternating voltage is applied to another electrode. transresistance amplifier -An amplifier that supplies an output voltage proportional to an input current. The transfer function of the amplifier is eo/&,,= R,, where R, is the transresistaxe. transverse-beam traveling-wave tube --A traveling-wave tube in which the electron beam intersects the signal wave rather than moving in the same direction. transverse c r o s s t a l k coupling --Between a disturbing and a disturbed circuit in any given section, the vector summation of the direct couplings between adjacent short lengths of the two circuits, without dependence on intermediate flow in nearby circuits. transverse electric wave -Abbreviated TE wave. In a homogeneous isotropic medium, an electromagnetic wave in which the electric field vector is everywhere perpendicular to the direction of propagation. The dominant mode in a rectangular waveguide is TElo. transverse electramagneticwave -Abbreviated TEM wave. In a homogeneous isotropic medium, an electromagnetic wave in which the electric and magnetic field vectors both are everywhere perpendicular to the direction of propagation. This is the normal mode of propagation in coaxial line, open-wire line, and stripline. transverse-field traveling-wave tube -A traveling-wave tube in which the traveling electric fields that interact with the electrons are essentially transverse to the average motion of the electrons. transverse interference-Interference occurring across terminals or between signal leads. transverse magnetic E-mode-A type of mode in which the longitudinal component of the magnetic field is zero and the longitudinal component of the electric field is not zero. transverse magnetic: w a v e -Abbreviated TM wave. In a homogeneous isotropic medium, an electromagnetic wave in which the magnetic field vector is everywhere perpendicular to the direction of propagation. transverse magnetization -Magnetization of a recording medium in a direction perpendicular to the line of travel and parallel to the greater cross-sectional dimension. transverse recording -The technique of rotating heads that are oriented perpendicular to the edge and surface of the tape. transverse wave -A wave in which the direction of displacement is perpendicular to the direction of propagation at each point of the medium. When the direction of displacement forms an acute angle with the

trap

- traveling-wave tube

direction of propagation, the wave is considered to have both a longitudinal and a transverse component. trap- 1. A selective circuit that attenuates undesired signals but does not affect the desired ones. See also wave trap. 2. A crystal imperfection that can trap carriers. 3. An unprogrammed conditional jump to a known location, the jump being activated automatically by hardware; the location from which the jump occurs is recorded. 4. A device, usually a switch, installed within a protected area, which serves as secondary protection in the event a perimeter alarm system is successfully penetrated. Examples are a trip-wire switch placed across a likely path for an intruder, a mat switch hidden under a rug, or a magnetic switch mounted on an inner door. 5. A volumetric sensor installed so as to detect an intruder in a likely traveled corridor or pathway within a security area. 6. A CPU-initiated interrupt that is automatically generated when a predetermined condition, such as an illegal instruction, a breakpoint, a specified error, or power failure, is detected. Two vector locations are dedicated for each trap type. The vector locations contain the pc and ps for the trap service routine. 7. A method of catching computer program error when illegal instructions are executed or illegal memory locations are accessed. 8. A frequency-sensitive device that is used to attenuate specific signals that cause interference. TRAPAlT diode -Abbreviation for trapped plasma avalanche transit time diode. 1. A microwave avalanche diode that has either an n+pp+ or a p+nn+ structure. It may be manufactured from either silicon or germanium. When the diode is biased into breakdown, an electron-hole plasma fills the entire p or n region, and the voltage across the diode drops. A large current, induced by the low residual electric field, extracts the plasma from the diode. After the plasma is removed, the current drops and voltage rises. Energy stored in the resonant circuits of an oscillator raises the voltage above breakdown, and the cycle repeats. 2. A semiconductor microwave diode that, when its junction is biased into avalanche, exhibits a negative resistance at frequencies below the transittime frequency range of the diode due to generation and dissipation of trapped electron-hole plasma resulting from the intimate interaction between the diode and a multiresonant microwave cavity. TRAPATT oscillator -See trapped avalanche triggered transit (TRAPATT) oscillator. trapezoidal distortion-Distortion in which a televised picture has the shape of a trapezoid (wide at top or bottom) instead of a rectangle. It is due to the interaction between the vertical- and horizontal-deflection coils (or plates) of the cathode-ray tube. trapezoidal generator- An electronic circuit that produces a trapezoidal voltage wave. trapezoidal pattern-An oscilloscope pattern that indicates the percentage of modulation in an amplitudemodulated system.

Trapezoidal pattern.

800 trapezoidal wave -1. A trapezoidal-shaped waveform. 2. A square wave onto which a sawtooth has been superimposed. It is a voltage wave necessary to give a linear deflection current through the coils of a magnetically deflected cathode-ray tube. trapped avalanche triggered transit (TRAPAlT) oscillator- Oscillator device composed of a semiconducting diode in a coaxial resonating cavity. When the biasing current is applied to the diode, highfrequency waves are emitted into the cavity, where they are reflected back and forth and eventually produce a radio-frequency output. trapped flux-In a material in the superconducting state, magnetic flux linked with a closed superconducting loop. trapped plasma avalanche transit time diode -See TRAPATT diode. trapping-1. The holding of electrons or holes by any of several mechanisms in a crystal, thereby preventing them from moving. 2. In a computer, instructions that cause initiation by the central processing unit of an internal interrupt that transfers control to a subroutine which activates the desired operation of the instruction. Also, the subroutine can be changed, thereby causing the operation on the instruction to be changed. trap wire-A low-voltage wire used at hinge points where severe flexing occurs, usually in burglar alarm systems. It is made with tinsel conductor. traveling detector-A probe mounted on a slider and free to move along a longitudinal slot cut into a waveguide or coaxial transmission line. The traveling detector is connected to auxiliary measuring apparatus and used for examining the relative magnitude of any standing-wave system. traveling plane wave-A plane wave in which each frequency component has an exponential variation of amplitude and a linear variation of phase in the direction of propagation. traveling wave -The resulting wave when the electric variation in a circuit takes the form of translation of energy along a conductor, such energy being always equally divided between current and potential forms. traveling-wave amplifiers-A two-port amplifier in which the input signal excites a space-charge wave at one end of a slab of negative-differential-resistivity bulk material. The wave travels through the material between ohmic contacts that serve as a transmission line. The charge builds as it moves, so the output is a larger version of the input. traveling-wave magnetron-A traveling-wave tube in which the electrons move in crossed static electric and magnetic fields that are substantially normal to the direction of wave propagation. traveling-wavemagnetronoscillations -Oscillations sustained by the interaction between the space-charge cloud of a magnetron and a traveling electromagnetic field with approximately the same phase velocity as the mean velocity of the cloud. traveling-wave parametric amplifier-A parametric amplifier that has a continuous iterated structure incorporating nonlinear reactors and in which the signal, pump, and difference-frequency waves are propagated along the structure. traveling-wave phototube-A traveling-wave tube that has a photocathode and a window that admits a modulated laser beam, which causes the emission of a current-modulated photoelectron beam. This beam is then accelerated by an electron gun and directed into the helical slow-wave structure of the tube. traveling-wave tube -Abbreviated TWT. A tube in which a stream of electrons interacts continuously or

traveling-wave-tube amplifier - triad

801 ELECTRON GUN

INPUT /TRANSDUCER

ATTENUATOR

OUTPUT TRANSDUCER

COLLECTOR

i

ELECTADN BEAM

Traveling-wave tube.

repeatedly with a guided electromagnetic wave moving substantially in synchronism with it, and in such a way tliat there is a net transfer of energy from the stream to the wave. traveling-wave-tube amplifier-A power-amplifying piece of equipment yielding about 30 dB of gain over broad bandwidths. The units are built around certain TWTs in the most commonly used frequency bands, and they have external modulation circuitry incorporated. traveling-wave-tube interaction circuit-An extended electrode arrangement used in a travelingwave tube to propagate an electromagnetic wave in such a manner that the traveling electromagnetic fields are r'ztarded to the point at which they extend into the space occupied by the electron stream. tr box- See transmit-receive switch. -The resonant portion of a tr switch. 1. The higher part in harmonic music or voice; of high or acute pitlch. In music, the frequencies from middle C (261.63 hertz) upward. 2. The upper range of audio frequencies. treble boost-Delibeirate adjustment of the amplitude-frequency response OF a system or component to accentuate the higher audio frequencies. tree -A set of connecti-d branches without meshes. treeing -A progressive type of insulation failure in which branching hollow channels slowly penetrate the insulation at rather low appllied voltages. tree network- See hierarchical network. tremolo- 1. The amplitude modulation of an audio tlone, widely used in musical-instrument amplifiers to create effects that add bo the capability of the instrument itself. It is a musical effect characterized by a subaudio modulation of the musical tone. When amplitude modulation is wed, it is called tremolo; a frequency modulation effect is termed vibrato. 2. A warbling or fluctuating effect, approximately seven times per second, in the tone of an instrument characterized by a variation in intensity rather than pitch. See also vibrato. 3. A regular variation in the amplitude of a sound, generally at a frequency between 0.5 and 20 Hz. IF-- Abbreviation for tuned radio frequency. tri -Abbreviation for triode. triac -Also called bidirectional triode thyristor. 1. A bidirectional rectifier (esse:ntially two SCRs in parallel) that fmctions as an electrically controlled switch for ac loads and having an npnpn structure that can be triggered into either forward or reverse conduction by a pulse applied to its gate ellectrode. A triac will pass an alternating current. 2. A thyristor that can be triggered into conduction in either direction. Teminals are called main terminal 1 and gate. 3. A semiconductor device that functions as an electrically controlled switch for ac loads. The triac is one type of thyristor,

ANODE 2

GATE

ANODE 2

ANODE 1

Construction and connections

1 ANODE 2

ANODE 2

GATE[

IANODE

1

GATE

Symbol.

I

Junctions

"ON" STATE

Characteristic

TriaC.

triad -1. Three radio stations operated as a group for determining the position of aircraft or ships. 2. A group of three dots, one of each color-emitting phosphor, on the screen of a color picture tube. 3. A group of three bits or three pulses, usually in sequence on one wire or simultaneously on three wires. 4. Also called a triplex. A group of three insulated conductors twisted together without (or with) a sheath overall. Usually color-coded

triangulation

- trigger circuit

802

for identification. 5. In a color CRT, one set of red, green, and blue phosphors. triangulation -A method of finding the location of a third point by taking bearings from two fixed points a known distance apart. The third point will be at the intersection of the two bearing lines. triax -A type of shielded conductor that employs a shield and jacket over the primary insulation, plus a second shield and jacket over all. Aside from applications requiring maximum attenuation of radiated signals or minimum pickup of external interference, this cable can also be used to carry two separate signals. triaxial cable-1. A special form of coaxial cable containing three conductors. 2. A three-conductor cable with one conductor in the center, a second circular conductor shield concentric with the first, and a third circular conductor shield insulated from and concentric with the first and second, and a braid or impervious sheath overall. TriaxiaP speaker-Trade name applied to the three-way speakers manufactured by Jensen Sound Laboratories, Division of Pemcor, Inc., consisting of three electrically independent speaker elements mounted on a common (single) speaker frame.

MID-FREOUENCY

LOW-FREOUENCY

HIGH-FREOUENCV

MI0

MID-FREOUENCY’ LOW-FREOUE~CY HORN DIAPHRAGM

HIGH-FR~OUENCY HORN

Triaxiul speaker. tribo--A prefix meaning due to or pertaining to friction. triboelectric -Pertaining to electricity generated by friction. triboelectricity-Electrostatic charges generated due to friction between different materials. triboelectric series- A list of substances arranged so that any of them can become positively electrified when rubbed with one farther down the list, or negatively charged when rubbed with one farther up the list. triboluminescence-Luminescence that arises from friction. Usually occurs in crystalline materials. tributary circuit-A circuit that connects an individual drop, or drops, to a switching center. tributary station -A communications terminal consisting of equipment compatible for the introduction of messages into, or reception from, its associated relay station.

Triboelectric Series Positive Asbestos Rabbit fur Glass Mica Nylon Wool Cat fur Silk Paper Cotton Wood Lucite Sealing wax Amber Polystyrene Polyethylene Rubber balloon Sulfur Celluloid Hard rubber Vinylite Saran Wrap Negative

trickle c h a r g e -1. A continuous charge of a storage battery at a slow rate approximately equal to the internal losses and suitable to maintain the battery in a fully charged condition. 2. A continuous direct current, usually very low, that is applied to a battery to maintain it at peak charge or to recharge it after it has been partially or completely discharged. Usually applied to nickelcadmium (nicad) or wet-cell batteries. trickle charger-A device for charging a storage battery at a low rate continuously, or for several hours at one time. tricolor camera -A television camera designed to separate reflected light into three frequency groups, each corresponding to the light energies of the three primary colors. The camera transforms the intensity variations of each primary into amplitude variations of an electrical signal. tricolor picture tube-A picture tube that reproduces a scene in terms of the three light primaries. tricon-A radionavigational system in which an airborne receiver accepts pulses from a triplet (chain of three stations) in a variable time sequence so that the pulses arrive at the same time even though traveling over paths of various lengths. trigatron -An electronic switch in which breakdown of an auxiliary gap initiates conduction. trigger- 1. To cause, by means of one circuit, action to start in another circuit, which then functions for a certain length of time under its own control. 2. A pulse that starts an action or function; for example, a triggered sweep or delay ramp. 3. A timing pulse used to initiate the transmission of signals through the appropriate circuit signal paths. trigger action-The instantaneous initiation of main current flow by a weak controlling impulse in a device. trigger circuit-1. A circuit with two conditions of stability, with means for passing spontaneously or through application of an external stimulus from one to the other when certain conditions are satisfied. See also flip-flop, 1. 2. A circuit in which an electron tube performs the function of a relay. Impulses applied to the input of the

803 tube produce corresponding impulses in the output circuit, starting a chain of events. trigger countdown --.A process that reduces the repetition rate of' a triggering signal. trigger diode -A symmetrical three-layer avalanche diode used to control SCRs and triacs. It has a symmetrical switching mode and therefore fires whenever the breakover voltage is exceeded in either polarity of applied voltage. triggered blocking oscillator -A blocking oscillator that can be reset to iits starting condition by the application of a trigger voltage. triggered spark gap-A fixed spark gap in which the discharge passes between two electrodes and is struck (started) by an auxiliary electrode called the trigger, to which low-power pulses are applied. triggered sweep -In a cathode-ray oscilloscope, a sweep initiated by a signal pulse. trigger electrode-See starter, 2. trigger flip-flop -See T flip-flop. trigger gap-A gas-discharge device with three electrodes that can be triggered upon command. Two electrodes provide the main conduction path, and the third electrode serves as the trigger. triggering-The starting of circuit action, which then continues for a predetermined time under its own control. triggering signal -The signal from which a trigger is derived. trigger level - 1. In a transponder, the minimum receiver input capable of causing the transmitter to emit a reply. 2. The instantaneous level of a triggering signal ai. which a trigger is to be generated. Also the name of the control that selects the llevel. trigger point-The aimplitude point on the input pulse at which triggering of the sweep of a cathode-ray oscilloscope occurs. trigger pulse-A pulse used for triggering. trigger-pulse steering-In transistors, the routing or directing of trigger signals (usually pulses) through diodes or transistors (called steering diodes or transistors) so that the signals affect only one of several associated circuits. trigger' recognition--.In random-sampling-oscilloscope technique, the process of making a response to a suitably applied trigger, such as the time reference for the time window. trigistor -A bistable pnpn semiconductor component with characteristics comparable to those of a flip-flop or bistable multivibrator. un color picture tube-See tri-color picture tube. trim-To make a fine adjustment in a circuit or a ckcuit element. trim control--On soml- regulated power supplies, a control used to make minor adjustments of output voltage. trimmer capacitor-Also called a trimmer. 1. A small variable capacitor associated with another capacitor and used for fine adjustment of the total capacitance of the combination. 2. A small capacitor, usually adjustable by screwdriver, that is placed in parallel with a larger capacitor and used to tune the high-frequency end of the circuit more precisely. 3. A small adjustable circuit element connected in series or parallel with a circuit element of the same kind such that its adjustment sets the combination of the two to a desired value. trimmer potentiometer-A lead-screw-actuated potentiometer. trimmer resistor-A small rheostat used in place of a fixed resistor to permit adjustment of resistance values in a circuiit during initial calibration of an equipment or when recalibration is required.

trigger countdown

- triode thyristor

v Trimmer capacitor.

trimming - 1. The fine adjustment of capacitance, resistance, or inductance in a circuit. 2. The process of using abrasive or laser technique to accurately remove film material from a substrate to change (increase) the resistance value. Thick films are trimmed using either abrasives or lasers; thin-film resistors are laser trimmed. Automated laser trimming is possible using computercontrolled systems. 3. The process of cutting away a portion of a thick-film resistor in order to raise the nominal resistance value. Resistors can often be trimmed to within 1 percent of a desired value. Cutting is done with an air abrasive tool or with a laser beam. The width of the cut is called the kerf. trimming potentiometer-An electrical mechanical device with three terminals. Two terminals are connected to the ends of a resistive element. and one terminal is connected to a movable conductive contact that slides over the element, thus allowing the input voltage to be divided as a function of the mechanical input. It can hnction as either a voltage divider or rheostat. trim notch-The notch made in a resistor by trimming to obtain the design value. See kerf. trinistor -A three-terminal silicon semiconductor device with characteristics similar to those of a thyratron; used for controlling large amounts of' power. trinoscope-1. Any assembly of three kinescopes producing the red, green, and blue images required for tricolor television optical projection (e.g., for theater TV). 2. A color television viewing system with three kinescopes, three lenses, and three deflection yokes used to form the red, green, and blue images required for a tricolor television projection. triode -A three-electrode electron tube containing an anode, a cathode, and a control electrode (grid). triode amplifier- An amplifier in which only triode tubes are used. triode field-effect transistor -A field-effect transistor having a gate region, a sonrce region, and a drain region. Where no confusion is possible. the term may be abbreviated to field-effect triode. triode-heptode converter-A superheterodyne converter circuit that uses a triode local oscillator and a heptode converter, both contained in one envelope. triode-hexode converter - A superheterodyne converter circuit that uses a triode local oscillator and a hexode converter, both contained in one envelope. triode laser-A gas laser whose light output may be modulated by applying signal voltages to an integral grid. triode-pentode -A dual-purpose vacuum tube containing a triode and a pentode in the same envelope. triode pnpn-type switch -A pnpn-type switch having an anode, cathode, and gate terminal. triode thyristor -A three-electrode thyristor, of which one electrode is the gate. Commonly it has three terminals.

trip coil

- trouble-location problem

trip coil-An electromagnet in which a moving armature trips a circuit breaker or other protective device and thereby opens a circuit under abnormal conditions. trip computer-Digital and push-button dashboard electronic system (Chrysler Corp.) that displays readout of speed, miles, fuel, time, and performs computations involving any of these parameters. trip-free relay -See tripping relay. triple-conversion receiver-A communications receiver in which three different intermediate frequencies are employed to give better adjacent-channel selectivity and greater image-frequency suppression. triple detection -See double superheterodynereception. triple diffused -Pertaining to transistors fabricated within a monolithic substrate by three diffusion steps. triple-play tape -Abbreviated TP tape. Very thin recording tape of which it is possible to wind 3600 ft (1097 m) onto a 7-inch (17.8-cm) spool. This would give 180 minutes of playing time at 3 ips (9.525 c d s ) . triple-stub transformer-A microwave transformer consisting of three stubs placed a quarterwavelength apart on a coaxial line. The stubs are adjusted in length to compensate for impedance mismatch. triplet - 1. Three radionavigational stations operated as a group for the determination of position. 2. The waveform of the output voltage of a delay line when the input pulse has a width approximately equal to the resolution of the delay line. triplex-See triad, 4. triplex cable-A cable made up of three insulated single-conductor cables twisted together with or without a common insulating covering. triplexer-A dual duplexer that permits the use of two receivers simultaneously and independently in a radar system by disconnecting the receivers during the transmitted pulse. triplex s y s t e m -A system for simultaneously sending two messages in one direction and one message in the other direction over a single telegraph circuit. tripod -A three-legged camera support. tripping device -A mechanical or electromagnetic device used for opening (turning off) a circuit breaker or starter, either when certain abnormal electrical conditions occur or when a catch is actuated manually. tripping relay- Also called trip-free relay. A device that functions to trip a circuit breaker, contactor, or equipment, or to permit immediate tripping by other devices, or to prevent immediate reclosure of a circuit interrupter in case it should open automatically even though its closing circuit is maintained closed. trip protection circuit-A protective circuit that electrically interrupts the output when an overload occurs. trip voltage- Also called firing voltage. The voltage at which ionization occurs under any circumstances. trip-wire switch-A switch that is actuated by breaking or moving a wire or cord installed across a floor space. trisistor -A fast-switching semiconductor consisting of an alloyed junction pnp device in which the collector is capable of electron injection into the base. Its characteristics resemble those of a thyratron electron tube, and the switching time is in the nanosecond range. tristate- Also called three-state. 1. Logic systems utilizing three conditions on one line: a definite applied high voltage (logical 1); a definite low voltage (logical 0); and an open circuit or undefined state, permitting another part of the circuit to determine whether the line will be high or low. Usually refers to device outputs or systems using outputs of the tristate type. Useful in a

804 bus-organized system. 2. An output configuration found in several logic families that is capable of assuming three output states: high, low, and high impedance. The feature is useful for interconnecting large numbers of devices on the same wires while allowing only one to control the levels of the lines at a given time. tristate device-A device that has three states: on, off, and electrically disconnected. tristimulus values-The amounts of each of the three primary colors that must be combined to match a sample. tri-tet oscillator-A crystal-controlled, electroncoupled vacuum-tube oscillator that is isolated from the output circuit through use of the screen-grid electrode as the oscillator anode. Used for multiband operation because it generates strong harmonics of the crystal frequency. tritium-A radioactive isotope of hydrogen with an atomic number of 3. TRL -Abbreviation for transistor-resistor logic. Trojan h o r s e - 1. Software that, while performing a useful function, has hidden in it code for a program that performs security-breaching or fraudulent functions. 2. A program or data that seems innocuous when loaded into a system or network but later facilitates an attack by a hacker or a virus. trombone -An adjustable U-shaped coaxial line matching assembly. tropicalization -A chemical treatment developed to combat the fungi that ruin electronic equipment in hot, humid jungle regions. tropo -See tropospheric scatter communication. troposphere-The lower layer of the earth’s atmosphere, extending to about 60,000 feet (18,300 m) at the equator and 30,000 feet (9150 m) at the poles. In this area the temperature generally decreases with altitude, clouds form, and convection is active. tropospheric scatter -The propagation of radio waves by scattering as a result of irregularities or discontinuities in the physical properties of the troposphere. t r o p o s p h e r i c scatter communication -Also called tropo. A method or system of transmitting, within the troposphere, microwaves in the UHF or SHF bands to effect radiocommunication between two points on the earth’s surface separated by moderate distances of from 70 to 600 miles (112 to 965 km). Such a span or hop may be augmented by other spans in tandem to permit end-to-end or through circuits up to many thousands of miles. More specifically, this method of communication is now generally understood to embrace a radio system that permits communication over the distances indicated, with excellent reliability and good information capacity, using relatively high transmitted power, frequency modulation, and highly sensitive receiving apparatus. t r o p o s p h e r i c superrefraction -The phenomenon occumng in the troposphere whereby radio waves are bent sufficiently to be returned to the earth. tropospheric wave-A radio wave that is propagated by reflection from a place of abrupt change in the dielectric constant of its gradient in the troposphere. In some cases, the ground wave may be so altered that new components appear to arise from reflections in regions of rapidly changing dielectric constants; when these components are distinguishable from the other components, they are called tropospheric waves. trouble -Failure of a circuit or element to perform in a standard manner. trouble-location problem- A computer test problem whose incorrect solution supplies information on the location of faulty equipment. It is used after a check problem has shown that a fault exists.

805 t r o u b l e s h o o t -See troubleshooting. troubleshooting -Aka troubleshoot. 1. Locating and diagnosing malfunctions or breakdowns in equipment by means of systematic checking or analysis. 2. The work necessary to discover the cause of trouble; also implies the correction of the trouble by elimination of the cause. trouble unit-A weighting figure applied to indicate the expected performance of a telephone circuit or circuits in a given period of time. tr s w i t c h -See transmit-receive switch. ube-Transmit-receive tube. A gas-filled rf switching tube that permits use of the same antenna for both transmitting and receiving by preventing the transmitted power from damaging the receiver. (Usually, a tr unit consists of a cavity containing a discharge gap that connects the transmitter to the antenna, and a coupling circuit that connects the antenna to the receiver when the discharge gap is not fired, indicating that the transmitting tube is quiescent.) true bearing-A bewing given in relation to geographic north, as opposed to a magnetic bearing. true complement -See radix complement. true course-A course in which the direction of the e line is true rather than magnetic north. credit balance-In a calculator, when the answer is negative, the minius sign automatically appears in the display. true hloming -The following of a course in such a way that the true bearing of an aircraft or other vehicle is held constant. true north -Geographic north. true aihm-The actual value of the practical unit of resistance. It is equal to lo9 absolute electromagnetic units of resistance. true power-The average power consumed by a circuit during one complete cycle of alternating current. true radio bearing -See radio bearing. true random noise--A noise characterized by a noma1 or Gaussian distribution of amplitudes. true value-The value of a physical quantity that would be attributed to an object or physical system if that value could be determined with no error. truncate-1. To drop digits of a number of terms in a series, thereby lessening precision. For example, the value 3.14159265 (n)when truncated to five figures is 3.1415, whereas it could be rounded off to 3.1416. 2. To conclude a computational process according to some rule; for example, to stop the evaluation of a power series at a specified term. 3. The dropping of digits or characters from one end of a data itern, causing loss of precision or information. truncated paraboloid -A paraboloid reflector in which a portion of the top and bottom have been cut away to broaden the main radiated lobe in the vertical plane. truncation-The process of dropping one or more digits at the left or right of a number without changing any of the remaining digits. For example, in most operations the number 3847.39 would become 3847.3 when truncated one place at the right, whereas the same number would become 3847.4 when rounded correspondingly. See also round off. truncation error-The error resulting from the use of only a finite number of terms of an infinite series, or from the approximation of operations in the infinitesimal calculus by operations in the calculus of finite differences. trunk- 1. A single message circuit between two points, both of which are switching centers and/or individual message distribution points. 2. A communications channel between two different offices, or between groups

troubleshoot

- tube

of equipment within the same office. 3. A telephone line or channel between two central offices or switching devices, which is used in providing telephone connections between subscribers. 4. A major link in a communication system, usually between two switching centers. t r u n k circuit-A circuit that connects two switching centers. t r u n k facility-That part of a communication channel connecting two or more leg facilities to a central or satellite station. t r u n k group-Those trunks connecting two points, both of which are switching centers and/or individual message distribution points and which make use of the same multiplex terminal equipments. t r u n k hunting-A method by which an incoming call is switched to the next consecutive number if the first called number is busy. t r u n k loss-That part of the repetition equivalent assignable to the trunk used in the telephone connection. truth table- 1. A tabulation that shows the relation of all output logic levels of a digital circuit to all possible combinations of input logic levels in such a way as to characterize the circuit functions completely. 2. A matrix that describes a logic function by listing all possible combinations of inputs and by indicating the outputs for each combination. TSC -Abbreviation for transmitter start code. TSS -Abbreviation for time-sharing system. A computer operating system in which the processor's time is shared among simultaneous users, resulting in an interactive facility. TTL or T2L-Abbreviation for transistor-transistor logic. A bipolar technology used for producing logic gates. Positioned in the evolution of logic families after RTL (resistor-transistor logic) and DTL (diode-transistor logic) and before ECL (emitter-coupled logic) and CMOS. See gate. TTL or T2L compatible-The ability of a device or circuit to be connected directly to the input or output of TTL logic devices. Such compatibility eliminates the need for interfacing circuitry. TTL-compatible circuits -Circuits that meet the input/output interface standards of transistor-transistor logic (TTL) circuits. These can be TTL circuits themselves, or circuits made with other technologies that conform to TTL standards. TTY -An abbreviation of Teletype or teletypewriter unit. TU -See terminal unit. tuba-A powerful land-based radar jamming transmitter operated between 480 and 500 MHz. It was developed during World War II for use against night fighter planes. tube-A hermetically sealed glass or metal envelope in which conduction of electrons takes place through a vacuum or gas. tube bridge- An instrument used in the precise measurement of vacuum-tube characteristics. It contains one or more bridge-type measuring circuits, plus power supplies and signal sources for a14 possible electrode combinations. tube coefficients- Constants that describe the characteristics of a thermionic vacuum tube (e.g., amplification factor, mutual conductance, ac plate resistance). tube complement-The number and types of electron tubes required in an electronic equipment. tube count -A terminated discharge produced by an ionizing event in a radiation-counter tube. tube drop-The voltage measured across a tube, from plate to cathode, when the tube is conducting at its normal current rating.

tube electrometer - tuned resonating cavity tube electrometer-A thermionic vacuum tube adapted for use as an electrometer to measure potential difference. tube heating time-The time required for the coolest portion of a mercury-vapor tube to attain its operating temperature. tubing -Extruded nonsupported plastic materials designed as protection and electrical insulation for exposed components of electrical and electronic assemblies; as opposed to a coated, braided, or woven tube, termed sleeving. tube noise-Noise originating in a vacuum tube (e.g., from shot effect, thermal agitation, etc.). tube shield-A metallic enclosure placed over a vacuum tube to prevent external fields from interfering with the function of the tube. tube s o c k e t -A receptacle that provides mechanical support and electrical connection for a vacuum tube. tube tester-A test instrument for indicating the condition of vacuum tubes used in electronic equipment. tube voltage drop-The anode voltage in an electron tube during conduction. tubular capacitor-A paper, ceramic, or electrolytic capacitor shaped like a cylinder; leads or lugs project from one or both ends. tunable-cavity filter-A microwave filter in which tuning can be accomplished by adjustment of one or more screws that project into the cavity or by adjustment of the positions of one or more rectangular or circular irises in the cavity or waveguide. tunable e c h o box-An echo box consisting of an adjustable cavity operating in a single mode. When the echo box is calibrated, the setting of the plunger at resonance will indicate the wavelength. t u n a b l e magnetron-A magnetron that can be tuned mechanically or electronically over a limited band of frequencies. tuned- Adjusted to resonate or operate at a specified frequency. tuned amplifier-An amplifier in which the load is a tuned circuit. Thus, the load impedance and amplifier gain vary with the frequency. tuned-anode oscillator-See tuned-plate oscillator. tuned antenna- An antenna designed, by means of its own inductance and capacitance, to provide resonance at the desired operating frequency. tuned-base oscillator -A transistor oscillator comparable to a tuned-grid electron-tube oscillator. The frequency-determining device (resonant circuit) is located in the base circuit. tuned circuit -1. A circuit consisting of inductance and capacitance that can be adjusted for resonance at the desired frequency. 2. A circuit that is adjusted to be resonant at a particular frequency. tuned-collector oscillator- A transistor oscillator comparable to the tuned-plate electron-tube oscillator. The frequency-determining device is located in the collector circus. tuned dipole-A dipole antenna that resonates at its operating frequency. t u n e d filter-A resonant arrangement of electronic components that either attenuates signals at a particular frequency and passes signals at other frequencies, or vice versa. tuned-filter oscillator- An oscillator in which a tuned filter is used. tuned-grid oscillator- An oscillator whose frequency is determined by a parallel-tuned tank in the grid circuit. The tank is coupled to the plate to provide the required feedback.

806

tuned-grid, tuned-anode oscillator- See tunedgrid, tuned-plate oscillator. tuned-grid, tuned-plate oscillator -Also called tuned-grid, tuned-anode oscillator. An oscillator having parallel-resonant circuits in both the plate and the grid circuits. The necessary feedback is provided by the plateto-grid interelectrode capacitance.

TANK GRID

m GF + +-

PLATE TANK

6

B

+

Tuned-grid, tuned-plate oscillator.

tuned-plate oscillator- Also called tuned-anode oscillator. An oscillator whose frequency is determined by a parallel-tuned tank in the plate circuit. The tank is coupled to the grid to provide the required feedback. tuned radio-frequency amplifier- Abbreviated TRF amplifier. A tuned amplifier using resonant-circuit coupling and designed to operate at radio frequencies.

2tcned radio-ji-equency amplijier.

tuned radio-frequency receiver -Abbreviated TRF receiver. A radio receiver consisting of several amplifier stages that are tuned to resonate at the carrier frequency of the desired signal by a ganged variabletuning capacitor. The amplified signals at the original carrier frequency are fed directly into the detector for demodulation. The resultant audio-frequency signals are again amplified, and are then reproduced by a speaker. tuned radio-frequency transformer-Abbreviated TRF transformer. A transformer used for selective coupling in radio-frequency stages. tuned-reed f r e q u e n c y meter -A vibrating-reed instrument for measuring the frequency of an alternating current. tuned relay-A relay having mechanical or other resonating arrangements that limit the response to currents at one particular frequency. tuned resonating cavity-A resonating cavity half a wavelength long, or some multiple of a half wavelength, used in connection with a waveguide to produce a resultant wave with the amplitude in the cavity greatly exceeding that of the wave in the guide. For reception of waves, a detecting grating can be placed at the point of maximum amplitude in the cavity to

807 convert the energy to a form suitable for amplification in a telephone or televisioln circuit. A tuned cavity is a nonreflecting termination for a guide. tuned rope -Long lengths of chaff cut to the various lengths necessary for tunin.g to different wavelengths. tuned transformer-- A transformer whose associated circuit elements are adjusted as a whole to be resonant at the frequency of the alternating current supplied to the primary, thereby causing the secondary voltage to build up to higher values than would otherwise be obtained. tuner-In the broad sense, a device for tuning. Specifically, in radio-receiver practice: 1. A packaged unit capable of producing only the first portion of the functions 'of a receiver and delivering either rf, IF, or demodulated information to some other equipment. 2. That portion 'of a receiver that contains the circuits that are tuned to resonance at the received-signal frequency and those which are tuned to the local-oscillator frequency. 3. A radio or TV receiving circuit; a high-fidelity component containing such circuits. tungar rectifier-A gaseous rectifier containing argon gas. It is employed in battery chargers and lowvoltage power supplies. tungar tube -A phanotron (hot-cathode gas-filled rectifier tube) having a heated filament serving as the cathode and a graphite disc as the anode in a bulb filled with low-pressure argon. Used chiefly in battery chargers. tungsten-A metal used in the manufacture of filaments for vacuum tubes and in making contact points for switches and other parts where sparking may occur. After the tungsten is made ductile by rolling, swaging, and hammering, it is very tough. tungsten filament-. A filament used in incandescent lamps, and in thermionic vacuum tubes and other tubes requiring an incandescent cathode. Smaller tungsten filaments are operated in a vacuum, whereas those for larger lamps are used in an inert gas at about ordinary atmospheric pressure. tungsten lamp -An evacuated bulb containing a tungsten filament that is heated by passing an electric current through it. - 1. The adjustment relating to frequency of a circuit or system to secure optimum performance. Commonily, the adjustment of a circuit or circuits to resonance. 2. Making changes in a program to improve its performance without altering its results. tuninig capacitor-. 1. A variable capacitor for adjusting the natural frequency of an oscillatory or resonant circuit. 2. A variable capacitor that is intended to be mechanically actuated frequently throughout its life. make the circuit responsive to a particular frequency.

tuning core-Normally a molded iron core for permeability tuning, into which an adjusting screw has been cemented or molded. diode-A varactor diode used for rf tuning. des functions such as automatic frequency control and automatic fine tuning. eye-Slang for a cathode-ray tuning indicator. tuninlg fork- A two-pronged hard-steel device that vibrates at a definite natuxal frequency when struck or when set in motion by electromagnetic means. Used in some electronic equipment as an accurately controllable source of signals, because its vibrations can be formed

tuned rope -tunnel readily into audio-frequency signals by means of pickup coils. tuning-fork contact-A U-shaped female contact that resembles a tuning fork. It may be stamped or formed. tuning-fork drive-Control of an oscillator by continuous vibrations of a tuning fork. A high harmonic of the oscillating signal obtained from the fork is selected by filter circuits and is strongly amplified to determine the main oscillator frequency in a transmitter or other equipment. tuning in -Adjusting the tuning controls of a receiver to obtain maximum response to the signals of the station it is desired to receive. tuning indicator-A device that indicates whether or not a receiver is tuned accurately. It is connected to some circuit in which current or voltage is maximum or minimum when the receiver is accurately tuned to give the strongest output signal. tuning meter -A direct-current meter connected to a receiver circuit and used for determining whether the receiver is accurately tuned to a station. tuning probe- An essentially lossless probe of adjustable penetration extending through the wall of a waveguide or cavity resonator. tuning range-The frequency range over which a tuned circuit can be adjusted. tuning screw--A screw or probe inserted into a transmission line (parallel to the E field) to produce susceptance of magnitude and sign that depend on the depth of penetration of the screw. tuning stub-1. A short length of transmission line, usually with the free end shorted, connected to a transmission line to provide impedance matching. 2. A type of inductor element, usually adjustable, connected to a transmission line at intervals to improve the voltage distribution. tuning susceptance -The normalized susceptance of an atr tube in its mount due to its deviation from the desired resonance frequency. tuning wand -See neutralizing tool. tunnel action (in a pn junction)-A process whereby conduction occurs through the potential barrier due to the tunnel effect and in which electrons pass in either direction between the conduction band in the nregion and the valence band in the p-region. (Tunnel action, unlike the diffusion of charge carriers, involves electrons only, and for all practical purposes the transit time is negligible.) tunnel cathode-A metal-insulator-metal sandwich. Electrons tunnel from the metal substrate and appear in the metal film as hot electrons. Some of the hat electrons have sufficient energy to pass over the cathode surface barrier into the vacuum. tunnel diode-Also called Esaki diode. 1. A pn diode to which has been added a large amount of impurity. The tunnel diode has high-speed charge movement and a negative-resistance region above a minimum level of applied voltage. With the addition of suitable external circuits, it can be used as an oscillator or amplifier. 2. A two-layer device similar to the rectifier diode. As a small voltage is applied, current starts to flow. Increase the voltage a little more and current drops to zero. Add still a little more voltage and the current increases again. At still higher voltages it responds like an ordinary diode. That first surge of current is called tunneling. 3. -A heavily doped junction diode based on tunneling effect: the piercing of a potential barrier by a low-energy electron. Has a forward negative resistance, and is an excellent low-noise microwave amplifier. It has no upperfrequency limitation. 4. A diode utilizing the tunnel effect. It gives rise to negative differential conductance in a

tunnel effect

- turnover pickup

808

POSITIVE ELECTRODE

POSITIVE ELECTRODE

ELECTRODE

ELECTRODE

Junctions.

Symbol. I

Ip

VP

=

PEAK CURRENT

VV

vs

"

Characteristic.

Tunnel diode. certain range of the forward direction of the currentvoltage characteristic. tunnel effect-1. The piercing of a potential hill by a carrier, which would be impossible according to classical mechanics, but the probability of which is not zero according to wave mechanics, if the width of the hill is small enough. The wave associated with the carrier is almost totally reflected on the first slope, but a small fraction crosses the hill. 2. In a pn transition region, a process whereby conduction occurs through a potential barrier and in which electrons pass in either direction between the conduction band in the n-region and the valence band in the p-region. The tunnel effect, unlike the diffusion of charge carriers, involves electrons only and is for all purposes an instantaneous process. tunneling-An observed effect of the ability of certain atomic particles to pass through a barrier that they cannot pass over because of the required energy level. It is based on a law of quantum mechanics that predicts that the particles have a finite probability for tunneling according to their quantum-mechanical nature. tunnel rectifier-A tunnel diode that has a relatively low peak-current rating in comparison with other tunnel diodes employed in memory-circuit applications. tunnel resistor-A resistor containing a thin layer of metal plated across a tunneling junction, so that the characteristics of a tunnel diode and an ordinary resistor are combined. tunnel triode-A transistorlike device in which the emitter-base junction is a tunnel diode and the collectorbase junction is a conventional diode. tunneluminescence -The emission of light from a phosphor film deposited on the surface of a thin-film metal-oxide-metal sandwich. turbidimeter- See opacimeter. turbulence amplifier- 1. Fluidic digital element using laminar-to-turbulent flow transition to create the control effect. 2. A fluidic device in which the power jet is at a pressure such that it is in the transition region of laminar stability and can be caused to become turbulent by a secondary jet or by sound. turn -One complete loop of wire. turnaround time- 1. The interval between the time at which a job is submitted to a batch processing system

and the time at which the results are returned. 2. The actual time required to reverse the direction of transmission in a half-duplex circuit. For most communications facilities, time is required for line machine reaction. (A typical time is 200 milliseconds on a half-duplex telephone connection.) 3. The period required for half-duplex modems to reverse the direction of transmission on dialup or two-wire leased lines. This includes the time for reversing the echo suppressors used on the two-wire simplex paths between telephone central offices. These suppressors are placed between central offices to prevent signals from one transmission path from crossing over into another. Also, for synchronous modems, turnaround time covers line equalization and bit synchronization. A full-duplex modem has no turnaround time when used in a point-to-point link, since it can transmit and receive information simultaneously. turn factor-Under stated conditions, the number of turns that a coil of given shape and dimensions placed on a core in a given position must have for a coefficient of self-inductance of 1 henry to be obtained for the core. turnkey- 1. A computer console containing a single control, usually a power switch, that can be turned on and off only with a key. 2. A design and/or installation in which the user receives a complete running system 3. Pertaining to a computer system sold in a ready-to-use state. turn-off delay time-The time interval between occurrence of the trailing edge of a fast input pulse and the occurrence of the 90-percent point of the negative-going output waveform. turn-off reversal -A polarity reversal of the output of the electronic power supply occurring from the turning off of the power of a regulated power supply. turn-off thyristor-A thyristor that can be turned from the on state to the off state, and vice versa, with appreciable gain by applying control signals of appropriate polarities to the gate terminal. turn-off time-The time that a switching circuit (gate) takes to stop the current in the circuit it is controlling. turn-on d e l a y time-The time interval from the occurrence of the leading edge of a fast input pulse to the occurrence of the 10-percent point of the positivegoing output waveform, assuming that the rise time of the incoming pulses is 0.1 of the rise time of the element to be measured under loaded conditions. turn-on overshoot-Overshoots occurring from the turning on of power of a regulated power supply. turn-on reversal -A polarity reversal of the output of the power supply occurring from the turning on of the power supply of a regulated power supply. turnover Cartridge -A phonograph cartridge adapted, by the use of two styli, to play both large- and fine-groove records. turnover frequency- 1. In disc recording, the frequency below which constant-amplitude recording is used and above which constant-velocity recording is employed. 2. The knee of the tone control or filter frequency response curve. Though normally thought of as the frequency at which the control begins to have its effect, the turnover point is actually the frequency at which response has already been altered by 3 dB relative to the unfiltered signal. Some tone controls and filters offer a choice of turnover frequencies that are usually switch-selected. turnover pickup- Also called dual pickup. A pickup designed for playing both standard and microgroove records, using a single magnetic structure. See also turnover cartridge.

turns ratio - twin lead

Turntable.

turns ratio-The ratio of the number of turns in the primary winding to the number in the secondary winding of a transformer. turnstile antenna-An antenna composed of two dipole antennas normal to each other and with their axes intersecting at their midploints. Usually the currents are equal and in-phase quadrature. turntable-1. The round platter on which a phonograph record rests during cutting or playback. Also refers to the platter and its driving motor and associated parts, as a high-fidelity component. 2. In tape recording, the rotating flat disc on which the reel (or, in some professional machines, the tape “pie”) lies slightly raised above the recorder’s front or top panel. The turntable is usually fitted with a center spindle and gripping keys of some kind to keep the reel centered and prevent it from slipping against the rotation of the turntable. turntable rumble-See rumble, 1. turret-A revolving plate mounted at the front of some television cameras and carrying two or more lenses of different types to permit rapid interchange of lenses. turret tuner -A television-receiver tuner containing a separate set of resonating circuit elements for each channel. Each set is mounted on an insulating strip or strips placed on a drum rotated from the channel position for the desired channel. TW- Abbreviation for television. TW camera-An optical device, consisting of lens, electron beam tube, and preamplifier, that converts an optical image into an electrical signal. 7V c h a n n e l -See television channel. TWI -Abbreviation for television interference. TV recording -A permanent record of video signals recorded1 photographically, electronically, or by other means, and which may be displayed through a television system or projected as a motion-picture film. TVRO -See television receive only. WIT -See TV terminal. terminal -Abbreviated TVT. A keyboard and electromagnetic deflection-type display unit that utilizes an ordinary (or modified) TV set as a display. tweaking -1. The process of adjusting an electronic receiver circuit to optimize its performance. 2. The fine tuning of a circuit with overly critical adjustments,

repeated several times until no further improvement in performance is obtained. This usually requires cansiderable skill and is not recommended as a requirement in circuits for production or construction by a hobbyist with limited technical resources. tweeter-Also called a high-frequency unit. 1. A speaker intended to reproduce the very high frequencies, usually those above 3000 Hz, in a high-fidelity audio system. Units may be ionic, ribbon, electrostatic, or dynamic types. 2. A high-frequency speaker (driver) specializing in treble reproduction. twelve p u n c h -A punch in the top row of a card. twenty-one type repeater -A two-wire telephone repeater in which one amplifier serves to amplify the telephone currents in both directions. The circuit is arranged so that the input and output terminals of the amplifier are in one pair of conjugate branches, while the lines in the two directions are in another pair. twenty-two type repeater-A two-wire telephone repeater with two amplifiers. One amplifies the telephone currents being transmitted in one direction, and the other the telephone currents being transmitted in the other direction. twilight -A scene illumination of approximately one footcandle. twin axial cable-A single shielded twisted-pair cable that has low-loss signal transmission and high noise immunity. twin cable- 1. A cable composed of two parallel insulated stranded conductors having a common covering. 2. A pair of insulated conductors twisted and/or sheathed or held together mechanically and not identifiable from each other in a common covering. twin check-A continuous check of computer operations accomplished by duplication of equipment and automatic comparison of results. twin coaxial cable-A configuration containing two separate, complete coaxial cables laid parallel or twisted around each other in one complex. twinflex-British word for twisted pair of wires or twin lead. twin lead -Also called twin line. A type of transmission line covered by a solid insulation and comprising two parallel conductors, the impedance of which is determined

twin line

- two-pilot regulation

by their diameter and spacing. The three most common impedance values are 75, 150, and 300 ohms.

Twin lead.

twin line-See twin lead. twinning -1. The intergrowth of two crystal regions having opposite oriented axes. Two types of twinning may occur: electrical and optical. In electrical twinning, the electrical senses of the crystal axes are reversed and the twinned regions will interfere with one another piezoelectrically. It is this effect that limits the hightemperature utility of quartz as a piezoelectric material. 2. A defect of natural quartz crystals, in which both the right and left quartz are in the same crystal. twin-T network-See parallel-T network. twin triode-Two triode vacuum tubes in a single envelope. twin wire-A cable composed of two small, parallel, insulated conductors having a common covering. twist -1. The progressive rotation of the cross section of a waveguide about the longitudinal axis. 2. The deviation from a plane surface measured from one corner to the comer diagonally opposite. 3. The difference (in decibels) between DTMF high-group and low-group signal levels, mathematically defined as 10 log (highgroup power)/(low-group power). Measured at the DTMF receiver, it's a function of both the level difference generated by the signal source and the gain-frequency characteristic of the transmission facility. twisted joint-A union of two conductors wound tightly around each other. A sleeve may be used, and it and the conductors twisted. twisted pair-1. A cable composed of two small insulated conductors twisted together without a common covering. The two conductors of a twisted pair are usually substantially insulated, so that the combination is a special case of a cord. 2. Two insulated wires (signal and return) that are twisted around each other in a spiral pattern mainly to cancel the effects of electrical noise. Since both wires have nearly equal exposure to any electrostatic or electromagnetic interference, the differential noise is slight. twister -A piezoelectric crystal that generates a voltage when twisted. twistor -A computer memory element containing inclined helical windings of magnet wire on a nonmagnetic wire, with another winding over the helix. Information is stored in the form of polarized helical magnetization. two-address -In a computer, having the property that each complete instruction includes an operation and specifies the location of two registers, usually one containing an operand and the other the result of the operation. two-address code -A computer code that uses two address instructions. two-address instruction -A computer instruction that includes an operation and specifies the location of two registers.

8 10

two-conductor jack-Receptacle

having two cir-

cuits, tip and sleeve.

two-cored screened cable -British term for twoconductor shielded cable. two-dimensional circuitry-See thin-film integrated circuit. two-fluid cell -A cell having unlike electrolytes at the positive and negative electrodes. two-hole directional coupler-A directional coupler that consists of two parallel coaxial lines in contact, with holes or slots through their contacting walls at two points one-quarter wavelength apart. With this device, a portion of the rf energy traveling in one direction through the main line may be extracted, while energy traveling in the opposite direction is rejected. It is necessary that one end of the secondary line be terminated in its characteristic impedance. two-level system-A laser that uses only two electron energy levels. Electrons in the ground state (level 1) are pumped to the excited state (level 2). The electrons then surrender their energy by stimulated emission and return to the ground state. two-out-of-five code-A type of positional notation in which each decimal digit is represented by five binary digits; two of the five are of one kind (for example, 1s) and three are of the other kind (for example, Os). two-part code- A randomized code with an encoding section and a decoding section. In the encoding section, the plaintext groups are arranged in alphabetical or other significant order, accompanied by their code groups in nonalphabetical or random order. In the decoding section, the code groups are arranged in alphabetical or numerical order and accompanied by their meanings given in the encoding section. two-phase- Also called quarter phase. Having a phase difference of 90 electrical degrees, or one quartercycle. t w o - p h a s e current-Two currents delivered through two pairs of wires at a phase difference of one quarter-cycle (90") between them. t w o - p h a s e dynamic-Pertaining to a dynamic logic circuit that uses two clock signals to control the processing of information through the circuit or logic system. two-phase, five-wire system -An alternatingcurrent supply in which four of its conductors are connected as in a four-wire, two-phase system and the fifth is connected to the neutral points of each phase and usually grounded. Despite its name, it is strictly a fourphase, five-wire system. two-phase, four-wire system -A system of alternating-current supply comprising two pairs of conductors, between one pair of which is maintained an alternating difference of potential displaced in phase by one-quarter of a period from an alternating difference of potential of the same frequency maintained between the other pair. two-phase, three-wire system -An alternatingcurrent supply consisting of three conductors. Between one conductor (known as the common return) and each of the other two, alternating differences of potential that are 90" out of phase with each other are maintained. two-piece contact-A contact made of two or more separate parts joined by swedging, brazing, or other means of fastening to form a single contact. This type provides the mechanical advantages of two metals but also has the inherent electrical disadvantage of difference in conductivity. two-pilot regulation-The use of two pilot frequencies within a transmitted band so that the change in

811 attenuation due to twist can be detected and compensated for by a regulator. two-plus-one address-Pertaining to an instruction that contains two operand addresses and one control address. tWO-FlOrt network- A network with two ports. two-pulse canceler -A moving-target indicator canceler that compares the phase variation of two successive pulses received from a target. It discriminates against signals with radial velocities that produce a Doppler frequency equal to a multiplle of the pulse-repetition frequency. two-quadrant multiplier-Of an analog computer, a multiplier in which operation is restricted to a single sign (of one input variable only. twos cOmp!ement-Pertaining to a form of binary arithmetic used in a computer to perform binary subtractions with addition techniques. The twos-complement negative of a binary number is formed by complementing each bit in the number andl adding 1 to the result. twos-complement biinary -An alternate and more ,widely used code to represent negative values. With this code, zero and positive values are represented as in nat,mal binary, and all negative values are represented in a twos-coniplement form. That is, the twos complement of ,a number represents a negative value so that interface to ,a computer or microprocessor is simplified. two-source f r e q u e n c y keying -Keying in which the modulating wave shifts the output frequency between predetermined values derived from independent sources. two-state device -A mechanical or electronic device that, except during the time it is changing between states, is intended to be olperated in either of two states or conditions. two-terminal network-A network that is connected by only two terminals to an external system. two-terminal-pair network- Also called a fourpole, quadripole, or quadrupole network. A network with four accessible terminals grounded in pairs. One terminal of each pair may coincide with a network node. two-tone keying -Keying in which the modulating wave causes the carrier to be modulated with one frequency for the marking condition and a different frequency for the spacing condition. two-tone modulating -A method of modulating in which two different carrier frequencies are used for the two signaling conditions. two t r a c k (half track)-A tape format in which the width of the tape is recorded in two parallel magnetic tracks, separated by an unrecorded guard band. As compared with four-track recording, the two-track system gives improved dynamic range and can be edited without loss of program, since the tape is passed in a single direction only. two-track r e c o r d e r -See dual-track recorder. two-track recording -On quarter-inch-wide tape, the arrangement by which only two channels of sound may be recorded, either as a stereo pair in one direction or as separate monophonic tracks (usually in opposite directions). two-value capacitor motor -A capacitor motor that uses different values of effective capacitance for starting and running. two-wattmeter m e t h o d -A method of measuring total power in a balanced or unbalanced three-phase system by adding the reedings of two wattmeters, each with its current coil in olne phase and its voltage coil connected between it and the third phase.

two-plus-one address -

ves

two-way amplifier-An amplifier in which the right and left channels of a stereo system are both amplified simultaneously by the same tubes, using pushpull circuitry but feeding one signal to the input grids in parallel instead of push-pull. The parallel and push-pull signals are then separated by two output transformers in a matrixing circuit. two-way communication -Communication between radio stations, each having both transmitting and receiving equipment. two-way radio -Radiotelephone communications between fixed points (base stations) and portable units. two-way repeater-See repeater. two-way s w i t c h -A switch used for conholling electrical or electronic equipment, components, or circuits from either of two positions. two-way system -A speaker in whch the low and the high frequencies are reproduced separately by two electrically independent speaker elements, each of which is provided with a suitable sound-radiating system. two-way, three-way, etc. -Refers to the number of frequency bands into which a speaker’s output is divided. A two-way system divides the spectrum into two such bands, one of which is handled by a woofer or woofers, the other by a tweeter or tweeters. A threeway system would have one or more woofers, midrange speakers, and tweeters. Systems up to five-way are available. two-wire channel-A two-way circuit for transmission in either direction. two-wire circuit-1. A metallic circuit formed by two conductors insulated from each other. It is possible to use the two conductors as either a one-way transmission path, a half-duplex path, or a duplex path. Also used in contrast with a four-wire circuit to indicate a circuit using one line or channel for transmission of electric waves in both directions. 2. A communications circuit that uses a single pair of wires for both transmitted and received information. two-wire repeater-A repeater that can be used for transmission in both directions over a two-wire circuit. In carrier operation, it usually makes use of the principle of frequency separation for the two directions of transmission. two-wire system -1. A system of electric supply comprising two conductors, with the load connected between them. 2. A system in which all communication takes place over a two-wire circuit or the equivalent. TWT- Abbreviation for traveling-wave tube. TWX- See teletypewriter exchange service, 2. Twystron -A very high power, hybrid microwave tube combining the input section of a high-power klystron with the output section of a traveling-wave tube. It is characterized by high operating efficiency and wide bandwidths. .TXT files-Text files. These are usually just plain text that can be read by most programs. type acceptance-Equipment authorization granted by the FCC to ensure that equipment will function properly in the service for which it has been accepted. type A facsimile-Facsimile comunicaiion in which the images are built up of lines of constant-intensity dots. type A waves -Continuous waves. type A1 waves -Unmodulated, keyed, continuous waves. type A2 waves -Modulated, keyed, continuous waves. type & waves-Continuous waves modulated by music, speech, or other sounds.

type A4 waves

- type-printed telegraphy

type waves -Superaudio frequency-modulated continuous waves, as used in a facsimile system. type & waves -Superaudio frequency-modulated continuous waves, as used in television. type As waves -Composite transmissions and cases not covered by type A through type As waves. typebar-A linear type element that contains all printable symbols.

812

type B facsimile -Facsimile communication in which the images are built up of lines of dots having a varying intensity (e.g., in telephotography and photoradio). type B waves -Keyed, damped waves. type-printed telegraphy-Telegraphy in which the message is automatically printed at the receiving station.

U

ultor element -The element that receives the highest dc voltage in a cathode-ray tube. ultra-audible f r e q u e n c y -See ultrasonic frequency. ultra-audion -Any of several special vacuum-tube circuits employing regeneration. ultra-audion circuit-A regenerative detector circuit in which a parallel-resonant circuit is connected between the grid and the plate of a vacuum tube, and a variable capacitor is connected between the plate and cathode to control the amount of regeneration. ultra-audion oscillator-A variation of the Colpitts oscillator in which the resonant circuit employs a transmission-line section.

UART-See universal asynchronous receivedtransmitter. ubitron-An amplifier or oscillator in which an undulating electron beam interacts with an rf wave. The kinetic energy of the beam is converted into rf energy (0type interaction). The undulation of the beam is produced by a periodic magnetic field. This field gives the beam a transverse velocity component that interacts with the rf wave. U-bolt-A U-shaped bolt threaded on both ends, for fastening antennas to masits. UG-The two-letter designation that precedes the number on connectors for coaxial cable. It means Universal Government. UHF - 1. Abbreviation for ultrahigh frequency. 2. In television, a term used to designate channels 14 through 69. UJT -Abbreviation fcrr unijunction transistor. UL -Abbreviation for Underwriters Laboratories, Inc. UL certificated-For certain types of products that have met UL requirements and for which it is impractical to apply the UL Listing Mark or Classification Marking to the individual product, ,a certificate is provided that the manufacturer may use to identify quantities of material for specific job sites or to identify field-installed systems. UL listed -Signifies that production samples of the product have been found to comply with established Underwriters Laboratories’ requirements and that the manufacturer is authorized to use the Laboratories’ Listing Marks on the listed products that comply with the requirements, contingent on the followup services as a check of compliance. ultimately controlled variable -The quantity whose control is the end purpose of an automatic control system. ultimate sensitivity or threshold -One-half the dead band in a graphic recorder. When the instrument is balanced at the center of the dead band, it denotes the minimum change in measured quantity required to initiate pen response. u!timate trip current-The smallest value of current that will cause tripping of a circuit breaker under a given set of ambient conditions. ultimate trip limits-The values of overload of a circuit breaker at which the minimum and maximum limits of the time-current curve become asymptotic; Le., the limits of current that will trip or not trip the breaker “ultimately.” Minimum and maximum limits of ultimate trip are often called calibration. ultor- An adjective used to identify the picture-tube anode or element farthest from the cathode, the anode to which the highest voltage is applied, or the voltage itself (e.g.$ the ultor anode is the second anode of the picture tube, and the ultor voltage is the voltage applied to it).

FIF AC OUTPUl

P

Ultra-audion oscillator.

Ultrafax-A trade name of RCA for a system in which printed information is transmitted by radio, facsimile, and television at high speeds. ultrahigh frequency- Abbreviated UHF. Frequency band: 300 to 3000MHz. Wavelength: 100 to IO centimeters. ultrahigh-frequency canverter-A circuit used to convert UHF television signals to VHF in order to permit UHF television reception on a VHF receiver. ultrahigh-frequency generator- Any device for generating ultrahigh-frequency alternating currents (e.g., a conventional negative-grid generator; a positive-grid, or Barkhausen, generator; a magnetron; and a velocitymodulation, or electron-beam, generator such as the klystron). ultrahigh-frequency loop-Generally a singleloop antenna used in ultrahigh-frequency work to secure a nondirectional radiation pattern in the plane of the loop. The doughnut-shaped pattern is perpendicular to the loop.

813

ultrahigh-frequencytranslator

- ultrasonicfrequency

ultrahigh-frequency translator-A televisionbroadcast translator station that transmits on a UHF TVbroadcast channel. ultralinear amplifier-A class AB or B audio amplifier using pentodes or high-power-output beampower tubes whose screen voltages are taken from taps on a specially wound output transformer rather than from a fixed dc source. This form of operation results in a considerable decrease in distortion in high-fidelity systems. ultramicrometer-An instrument for measuring very small displacements by electrical means (e& by the variation in capacitance produced by the movement being measured). ultramicrowave-Having wavelengths of about lo-’ to iow4cm. ultrashort waves-Radio waves shorter than 10 meters in wavelength (about 30 MHz in frequency). ultrasonic-1. Having a frequency above that of audible sound- i.e., between sonic and hypersonic. 2. Sound waves that vibrate at frequencies beyond the hearing power of human beings (above 16,000 Hz). Commercial and military applications include ultrasonic cleaning, gauging, cutting, detection instruments, and welding. ultrasonic bond-A contact area where two materials are joined by means of ultrasonic energy and pressure. ultrasonic bonding- 1. A process for joining metal parts by the scrubbing action and energy transfer of a tool vibrating at an ultrasonic rate. This method is used to attach leads to pads on silicon devices. 2. A process involving the use of ultrasonic energy and pressure to join two materials. 3. A joining technique for wire and lead attachment that employs pressure plus an ultrasonically introduced scrubbing action to form a molecular bond.

ALUMINUM ORGOLD WIRE

ULTRASONIC VIBRATION

CAPILLARY TIP

\ A BO

Ultrasonic bonding.

ultrasonic brazing -See ultrasonic soldering. ultrasonic cleaner-A device using ultrasonic pressure waves to clean objects. ultrasonic cleaning-A method of cleaning that uses cavitation in fluids caused by applying ultrasonic vibrations to the fluid. ultrasonic cleaningequipment-Ultrasound used in the cleaning of metal and optical parts by virtue of its vibration rates. Large acoustic forces break off particles and contaminants from surfaces. ultrasonic cleaning tank-A heavy-gage, polished stainless-steel tank with transducers mounted on the bottom or sides. ultrasonic coagulation-The bonding together of small particles by the action of ultrasonic waves. ultrasonic cross grating-Also called grating. The two- or three-dimensional space grating produced

8 14

Ultrasonic cleaning tank.

when ultrasonic beams having different directions of propagation intersect. ultrasonic delay line- Also called an ultrasonic storage cell. A contained medium (usually a liquid such as mercury) in which the signal is delayed because of the longer propagation time of the sound waves in the medium. ultrasonic densitometer- An instrument device for determining the thickness or density of an object or material based on the time required for an ultrasonic signal to penetrate to a receiver and/or echo back to a receiver adjacent to another transmitter. ultrasonic detector-A device-either mechanical, electrical, thermal, or optical-for detecting and measuring ultrasonic waves. ultrasonic diagnosis-A method of obtaining information from within the body in a visual presentation without employing ionizing radiation. It differs from Xray in that the form of energy used is high-frequency sound, or ultrasound, which is inaudible. The sound is transmitted in very brief pulses followed by relatively lengthy “silent” intervals. Also, in contrast to X-ray techniques, in which the film is placed behind the tissue being examined, ultrasonic information is picked up at the original point of transmission in the form of echoes from internal structures. These returning echoes are converted to electrical energy and displayed in either a static or dynamic pattern, as desired, on a cathode-ray-tube screen. ultrasonic disintegrator- An apparatus for using the pressure wave produced by an ultrasonic generator to tear cells apart. ultrasonic drill-A special type of drill that has a magnetostrictive transducer attached to a tapered cone that serves as a velocity transformer. With an appropriate tool, practically any shape of hole can be drilled in brittle and hard material. ultrasonic flaw detector -Equipment comprising an ultrasonic generator, transducer, detector, and display; used to detect flaws or cracks in solids from the reflection pattern of ultrasonic signals observed on a cathode-ray tube. ultrasonicfrequency -Also called an ultra-audible frequency. 1. Any frequency above the audio range, but commonly applied to elastic waves propagated in gases, liquids, or solids. 2. Sound frequencies that are above the range of human hearing; approximately 20,000 Hz and higher.

ultrasonic generator

815

ultrasonic generator- A device for producing mechanical vibrations at frequencies above the range of human hearing. Typically, such a device consists of an rf oscilllator whose output is applied to a piezoelectric crystal. ultraisonic grating constant-The distance between diffracting centers of the sound wave producing particul,~light-diffraction spectra. ultralsonic immersion -Cleaning technique depending on cavitation (rapid formation of tiny bubbles in a cleaning liquid). Cavitation is created by ultrasonic, high-intensity sound waves. The agitation of imploding bubbles scrubs the immersed part. ultrasonic inspection -A nondestructive testing method of locating internal defects in a part by sending ultrasonic impulses (inaudible high-frequency sound waves of 0.5 to 11 megahertz) into the part and measuring the time required for these impulses to penetrate the material, be reflected from the opposite side or from the defect, ;and return to the sending point. ultrasonic level detector-A level detector consisting of an ultrasonic receiver and transmitter located in one wall of a container or vessel. With nothing to obstruct the beam, it is reflected from the opposite wall. When the level of the liquid or other material in the container reaches the beam, the liquid or material acts as a reflector, thus reducing the reflection time and indicating that a given level has been reached. ultraisonic light diffraction-The formation of optical (diffractionspectra when a beam of light is passed tbrough a longitudinal sound-wave field. The diffraction results from the periodic variation of the light refraction in the sound field. ultraisonic light modulator-A device containing a fluid that, by action of ultrasonic waves passing through the fluid, modulates a beam of light passed transversely through the fluid. ~ ~ ~ r a ~ material ~ o n i cdispersion -The production of suspensions or emulsions of one material in another by the actiton of high-intensity ultrasonic waves. u%trzisonic motion detector-A sensor that detects the motion of an intruder through the use of ultrasonic generating and receiving equipment. The device operates by filling a space with a pattern of ultrasonic waves; the modulation of these waves by a moving object is detected and initiates an alarm system. ultrasonic plating -The chemical or electrochemical deposition and bonding of one or more solid materials to the surface of another material by the use of vibrational wave energy. robe-A rod for directing ultrasonic force, used in a disintegration or foreign-body location application. ultraasonic rejection-The level of rejection of the 19-kHz oilot tone and 38-kHz voltage-controlled oscillator frequency in a stereo FM receiver.?he intrinsic rejection of a stereo decoder is the logarithmic ratio of the level of 19-kHz and 38-kHz reference tones with only the standard deemphasis filter at the decoder outputs. Itrasonics-The general subject of sound in the frequency range above 15 kilohertz. ultrasonic sealing -A film sealing method based on the application of vibratory mechanical pressure at ultrasonic frequencies (20 to 40 IcHz). Electrical energy is converted into ultrasonic vibrations by a magnetostrictive or piezoelectric transducer. The vibratory pressures at the film interface in the sealing area produce localized heat losses that cause the plastic surfaces to melt, thereby forming the seal. ~ ~ ~ r soldering~ ~ ~ o1. ~ A method i c of forming a nonporous, continuously metallic connection between

- ultraviolet

metal or alloy parts without necessarily employing chemicals or mechanical abrasives. Instead, vibrational wave energy, heat, and a separate alloy or metal having a melting point below 800°F (427°C) and also below that of the metals or alloys being joined are used. 2. Soldering in which the surface oxide coating of the base metal is removed by ultrasonic vibration. ultrasonic space grating-Also called grating. A periodic spatial variation in the index of refraction caused by the presence of acoustic waves within the medium. ultrasonic storage cell -See ultrasonic delay line. ultrasonic stroboscope-A light intempter in which the light beam is modulated by an ultrasonic field. ultrasonic therapy-The use of ultrasonic vibrations for therapeutic purposes. ultrasonic thickness gage- A thickness gage in which the propagation time of an ultrasonic beam through a sheet of material is translated into a measure of the thickness of the material. ultrasonic transducer-A device that takes the electrical oscillations produced by the ultrasonic generators and transforms them into mechanical oscillations. Typical transducer materials are piezoelectric (e.g., quartz or barium titanate) or magnetostrictive (e.g., nickel).

LIVE LEAD f--

GROUND LEAD

BAAaUM

T TAhAlE OUARTZ

Ultrasonic transducer.

ultrasonic waves -Waves having a frequency in the ultrasonic range. ultrasonic welding -1. A process that joins two pieces of metal by a form of diffusion bonding. The metals to be welded are clamped between a rigid anvil and a probe, which is vibrated at ultrasonic frequency. The vibration removes any surface oxide film by a simple mechanical scrubbing action, thus exposing the metal surfaces. Then plastic deformation caused by the imposed mechanical clamping load causes the atom movement necessary to joint the two crystal lattices, creating a strong, bonded, monolithic structure at the joint line. Some heat is generated by friction caused by the rubbing of the one surface upon the other. This heat undoubtedly aids the diffusion mechanism that occurs but is obviously insufficient to cause welding by itself. 2. Method of fusing two plastic parts by ultrasonic vibrations that are produced by mechanical motion of a converter, expanding and contracting some 20,000 times per second. The vibratory energy is channeled through a horn and applied to thermoplastic materials. This creates the frictional heat to produce a molecular interaction and weld materials. ultrasonic wire bonder-Equipment unit that fastens fine wire onto a substrate by use of ultrasonic energy. ultrasonography- A medical diagnostic technique in which pulses of ultrasonic energy are directed into the body, and returning echoes are detected. ultraviolet-I. Pertaining to electromagnetic radiations at wavelengths beyond the violet end of the spectrum of visible radiation. Because of the shorter wavelengths (200 to 4000 angstrom units), the photons of ultraviolet light have enough energy to initiate most chemical reactions and to degrade some plastics. 2. The invisible region

ultraviolet erasable PROM

- underload relay

of the spectrum immediately beyond the violet end and between the wavelengths of approximately 1000 to 3800 angstroms. ultraviolet erasable PROM -See UV erasable PROM. ultraviolet lamp -1. A lamp providing a high proportion of ultraviolet radiation (e.g., arc lamps, mercuryvapor lamps, or incandescent lamps in bulbs of a special glass that is transparent to ultraviolet rays). 2. A type of lamp that emits a great quantity of ultraviolet radiation. This may be an arc lamp encased in a bulb of a glass that is transparent to ultraviolet rays. ultraviolet r a y s -Radiation in the ultraviolet region. umbilical cable-A lifeline cable used for the main power supply to a missile in order to launch it. It is attached by means of a connector, which detaches as the missile becomes airborne. (Usually seen as a cable waving like a snake alongside the missile as it moves off the launching pad.) umbilical connector -A device for connecting cables to a rocket or missile prior to launch. It is removed (unmated) from the missile at the time of launching. umbrella antenna-An antenna in which the wires are guyed downward in all directions from a central pole or tower to the ground, somewhat like the ribs of an open umbrella. unamplified b a c k bias- A degenerative voltage developed across a fast time-constant circuit within an amplifier stage itself. unbalanced- 1. Lacking the conditions for balance. 2. Frequently, a circuit having one side grounded. 3. Differential mutual impedance or mutual admittance between two circuits that ideally would have no coupling. unbalanced circuit-A circuit whose two sides are electrically unlike. unbalanced line-A transmission line in which the voltages on the two conductors are not equal with respect to ground (e.g., a coaxial line). unbalanced output- An output in which one of the two output terminals is substantially at ground potential. unbalanced wire circuit-A circuit whose two sides are electrically unlike. unbianking-The turning on of the CRT beam. unblanking generator-A circuit for producing pulses that turn on the beam of a cathode-ray tube. unblanking pulse-A pulse that turns on the beam of a cathode-ray tube. unblocked record-A record contained in a file in which each block contains only one record or record segment. u n b o n d e d strain gage -A pressure-sensing element made up of resistance strain-gage wire elements arranged in a Wheatstone bridge. It can have two or four active arms, which respond to a pressure applied to the transducer. The unbonded strain-gage wires are suspended in air and are activated by a mechanism attached to a diaphragm or other pressure-responding element. unbundling-Kcing certain types of software and services separately from the hardware. uncertainty-A number or numbers assigned to a measurement as an assessment of all the errors associated with the process producing the measurement. See also accuracy. uncharged -Having a normal number of electrons and, hence, no electrical charge. unconditional-In a computer, not subject to conditions external to the specific instruction. unconditional jump-A computer instruction that interrupts the normal process of obtaining the instructions

816 in an ordered sequence and specifies the address from which the next instruction must be taken. unconditional transfer of control -In a digital computer that obtains its instructions serially from an ordered sequence of addresses, an instruction that causes the following instruction to be taken from an address that becomes the first of a new sequence. uncontrolled terminal-A user terminal that is online all the time and does not contain line-control logic for polling and calling. undamped natural frequency-The frequency at which a system with a single degree of freedom will oscillate, in the absence of damping, upon momentary displacement from the rest position by a transient force. undamped oscillations-Oscillations that have a constant amplitude for their duration. undamped wave- A wave whose amplitude does not change. undefined record-A record contained in a file in which the records have not been defined as being fixedlength records or variable-length records. underbunching-The condition whereby the buncher voltage of a velocity-modulation tube is lower than the value required for optimum bunching of the electrons. undercompounded-A generator in which the output voltage drops as the load is increased. undercurrent relay-A relay that functions when its coil current falls below a predetermined value. undercut-In a printed circuit board, the reduction of the cross section of a metal-foil conductor due to the removal of metal from beneath the edge of the resist by the etchant. undercutting-A cutting with too shallow a groove or with insufficient lateral movement of the stylus during sound disc recordings. underdamped-A degree of damping that is not sufficient to prevent oscillation in the output of a system following application of an abrupt stimulus. underdamping -1. In a system, the condition whereby the amount of damping is so small that the system executes one or more oscillations when subjected to a single disturbance (either constant or instantaneous). 2. Oscillation of the transducer output about a final steady value in response to a step change in the measurand. After an initial overshoot, the oscillation amplitude decreases. 3. See periodic damping. underflow- 1. In a computer, the generation of a quantity smaller than the accepted minimum (e.g., floating-point underflow). 2. Pertaining to the condition that arises when a machine computation yields a nonzero result that is smaller than the smallest nonzero quantity that the intended unit of storage is capable of storing. (Contrast with overflow.) 3. When a calculator’s capacity is exceeded, some of the least significant digits are discarded and the resulting display is sometimes zero. underglaze-A glass or ceramic glaze applied to a substrate prior to the screening and firing of a resistor. underground cable-A cable installed below the surface of the earth. under insulation -The insulation under wire that is brought from the center of a coil over the top or bottom wall. underlap-Recorded elemental areas that are smaller than normal -specifically,the space between the recorded elemental area in one recording line of a facsimile system and the adjacent elemental area in the next recording line, or the elemental areas in the direction of the recording line. underload relay-A relay that operates when the load in a circuit drops below a certain value.

817 undermodulation- Insufficient modulation of a transmitter due to misadjustment or to insufficient modulation signal. underpass-A semiconductor component that permits two conductors to cross each other without a short circuit between them. Generally, it is in the form of a low-value resistor covered by a silicon dioxide layer that isolates the top conductor; the resistor is part of the bottom conductor. underpower relay-A relay that functions when the power decreases below a predetermined value. underscan-Reducing the height and width of the video picture so that the edges, and, thus, portions of blanking, can be observed. undershoot- 1. The initial transient response to a unidirectional change in input, which precedes the main transition and is opposite in sense. See also precursor. 2. The crossing of the base line in the direction opposite to that of the principal pulse, but with insufficient amplitude to be considered a bipolar pulse. underthrow distortion -Distortion resulting when the maximum amplitude of the signal wavefront is less than the steady-state amplitude that would be attained by a prolonged signal wave. undervoltage protection-Also called low-voltage protection. The effect of a device to cause and maintain the interruption of power to the main circuit upon the reduction or failure of voltage. undervoltage relay-A relay that operates when its coil voltage falls below a predetermined value. underwater sound projector-An electroacoustic transducer designed to convert electric waves into sound waves, which are radiated in water for reception at a distance. ndienwiters Laboratories, Inc. -Abbreviated UE. 1. An independent, nonprofit product-safety testing and certification organization that operates laboratories for the examination and testing of devices, systems, and materids to ensure that they meet standards for safety. Acceptance is usually indicated by tags or by labels on devices showing the words “UL Approved” or “UL Listed.” 2. A corporation supported by some underwriters for the purpose of establishing safety standards on types of equipment and components. undistorted wave-A periodic wave in which both the attenuation and the velocity of propagation are the same for all sinusoidal components, and in which the same sinusoidal component is present at all points. undisturbed-one output-A 1 output of a magnetic cell to which no partial-read pulses have been applied since that cell was last selected for writing. undisturbed-zero output-A 0 output of a magnetic cell to which no partial-write pulses have been applied since that cell was last selected for reading. unflred tube-The condition of tr, atr, and pre-tr tubes when there is no radio-frequency glow discharge at either the resonant gap or the resonant window. unfrrrlableantenna -A device that can be unfolded to fonri a larger antenna. ungrounded-Not intentionally connected to ground except through high-impedance devices. ungrounded system -A system in which no point is directly connected to earth except through potential or ground-detecting transformers or other very high impedance devices. ~ n i a x ~ amagnetic l anisotropy-A property of magnetic thin film in which the direction of magnetization is always parallel to the easy axis unless an external force acts up09 it.

undermodulation

- unijunction transistor

uniconductor waveguide -A waveguide consisting of a rectangular or cylindrical metallic surface surrounding a uniform dielectric medium. unidirectional -Flowing in only one direction (e.g., direct current). Unidirectionalantenna -An antenna with a single, well-defined direction of maximum gain. unidirectional bus-A bus used by any individual device for one-way transmission of messages only, that is, either input only or output only. unidirectional Coupler-A directional coupler that samples only one direction of transmission. unidirectional current-A direct current; ie., one that is always positive or always negtitive-never alternating. unidirectional log-periodic antenna -A broadband antenna in which the cut-out portions of a logperiodic antenna are placed at an angle to each other to produce a unidirectional radiation pattern whose major lobe is in the backward direction, o f f the apex of the antenna. The impedance and the radiation pattern are essentially constant for all frequencies. unidirectional microphone-A microphone that is most sensitive to sounds arriving at it from one direction. unidirectional pulses -Single-polarity pulses that all rise in the same direction. unidirectional pulse train-A pulse train in which all pulses rise in the same direction. Unidirectional transducer-A transducer that responds to stimuli in only one direction from 2 reference zero or rest position. uniform corrosion-A form of corrosion that results from shifting anodic and cathodic areas evening out metallic thinning. In more complex cases, erosion constantly deprives the metal of its protective coating (e.g., oxides), exposing it to continuing corrosion. uniformfield -A field in which the scalar (or vector) has the same value at every point in the region under consideration at that instant. uniformity--In terms of magnetic tape properties, a figure of merit relating to the ability of the tape to deliver a steady and consistent output level upon being recorded with a constant input. Usually expressed in decibel variation from average at a midrange frequency. uniform line -A line with substantially identical electrical properties throughout its length. uniform plane wave-A plane wave with constantamplitude electric and magnetic field vectors over the equiphase surfaces. Such a wave can only be found in free space, at an infinite distance from the source. uniform precession-The condition in which the magnetic moments of all atoms in a sample are parallel and precess in phase about the magnetic field. Uniform precession occurs in the regions where the magnetic field is uniform. A spin wave is a phase distortion of this condition. uniform waveguide-A waveguide whose physical and electrical characteristics do not change with distance along its axis. uniground- Also called single-point ground. A single point in an electrical system connected to ground to eliminate noise currents. unijunctisn transistor- Abbreviated UJT. 1. Formerly called a double-base diode. A three-terminal semiconductor device that exhibits a stable negative-resistance characteristic between two of its terminals. It is this negative-resistance feature that makes the UJT suitable for the applications with which it is associated-thyristor trigger circuits, oscillator circuits, timing circuits, bistable

unilateral area track

- unipole I

818

EMITTER

A

RAW POWER

JUNCTION

IBASE1

II

H

1

I -

I

-

I

UNDIRECTIONAL} SWITCH

SYNCHRONIZER

UNlOlRECTlONAL

i

T

Static power supply.

Schematic.

Unijunction trcansistor.

circuits, etc. 2. A type of transistor that has easily controllable on-off characteristics and excellent voltage-sensing characteristics. 3. A three-terminal semiconductor having only one pn junction and exhibiting a stable open-circuit negative-resistance property. unilateralarea track-A sound trackin which only one edge of the opaque area is modulated in accordance with the recorded signal. However, there may be a second edge modulated by a noise-reduction device. unilateral bearing-A bearing obtained with a radio direction finder having unilateral response, eliminating the chance of a 180" error. unilateral conductivity-Conductivity in only one direction (e.g., in a perfect rectifier). unilateral element -A two-terminal element with a zero voltage-to-current characteristic (or the equivalent) on one side of the origin. unilateralization -A special case of neutralization in which the feedback parameters are completely balanced out. In transistors, these feedback parameters include a resistive in addition to a capacitive component. Unilateralization changes a network from bilateral to unilateral. unilateral network-1. A network in which any driving force applied at one pair of terminals produces a response at a second pair, but yields no response when the driving force is applied in the other direction. 2. A network that does not pass currents and signals equally well in both directions. For example, a network containing a rectifying element. unilateral switch -A semiconductor device similar to a miniature SCR. It switches at a fixed voltage that depends on its internal construction. unilateral transducer-See unidirectional transducer. uninterruptible power system-A solid-state power conversion system to provide regulated ac power to critical loads. Such a system provides uninte.rrupted power even during brownouts and blackouts. unipolar- 1. Having but one pole, polarity, or direction. With respect to amplifier power supplies, having an output that varies in only one polarity from zero and, therefore, always contains a dc component. 2. See neutral transmission. 3. Refers to transistors in which the working current flows through only one type of semiconductor

t 0

GENERATOR

Buffered power supply.

UniiatemptWe power system material, either n-type or p-type. In unipolar transistors, the working current consists of either positive or negative electrical charges, but never both. All MOS IC transistors are unipolar. Unipolar (MOS) IC transistors operate slower than bipolar IC transistors, but take up much less space on a chip and are much more economical to manufacture. unipolar field-effect transistor -A field-controlled majority-carrier device wherein the conductance of a semiconductor channel is modulated by a transverse electric field. The field is controlled by the combination of gate bias V,, and the net voltage Vd, between channel drain and source. unipolar pulse-A pulse that has appreciable amplitude in only one direction. unipolar transistor- 1. A transistor in which charge carriers are of only one polarity. See also fieldeffect transistor. 2. Transistor formed from a single type of semiconductor material, either n-channel or p-channel, as employed in field-effect transistors. CONTROL

UnQolar transistor. unipole- 1. An all-pass filter section with one pole and one zero. 2. A hypothetical antenna that radiates

819 and receives equally in all directions. See aZso isotropic antenna. cathaide -See indirectly heated cathode. unipotential electrostatic lens- A simple electrostatic lens having a focus that is controlled by a single potential difference. unit-I. A computer portion or subassembly that constitutes the means of accomplishing some inclusive operation or function (e.g., an arithmetic unit). 2. The specific magnitude of a quantity set apart by appropriate definitiom and serving as a basis for the comparison or measurement of like quantities; the lowest standard quantity in any system (of measurement. The unit of electrical energy, for example, is the kilowatthour. 3. One of the transceivers covered by a CB station license when more than one transceiver is used. 4. An assembly or device capable of independent operation. unit-area acoustic impedance -See specific acoustic impedance. unitary code-A code having only one digit, the number of times it is repeated determining the quantity it represents. unit charge-The electrical charge that will repel a force of 1 dyne on an equal and like charge 1 centimeter away in a vacuum, assuming each charge is concentrated at a point. United States of America Standards Institute-See American National Standards Institute. unit iintewal-See signal element. unit length-The basic element of time for determining code speeds in message transmission. unit load-The elecirical load imposed on a driver output by the receiver inputs. The actual values for a unit load are specified by the device manufacturer. The unit load is helpful to a logic system designer in determining bus drive requirements. unit magnetic pole-A pole with a strength such that when it is placed 1 centimeter away from a like pole, the force between the two is 1 dyne. unitor-In computers, a device or circuit that performs a function corresponding to the Boolean operation of union. See also OR gate. unit pulse-See baud. unit recordequipment -Equipment using punched cards as input data, such as collators, tabulating machines, etc. unit sequence starting relay-A device that functions to start the n e a available unit in a multipleunit equipment on the failure or on the nonavailability of the normally preceding unit. unit sequence switch-A switch used to change the sequence in which units may be placed in and out of service in multiple-unit equipment. unit step current (off voltage)-A current (or voltage) that undergoes an instantaneous change in magnitude from one constant level to another. unit substation transformer-A transformer that is mechanically and electrically connected to and coordinated in design with one or more switch-gear or motorcontroUed assemblies or combinations thereof. unit torque gradient-The torque gradient of a synchro, measured when the synchro is electrically connected to another synchro of the same size. unit under test -'4bbreviated UUT. Any system, set, subsystem, assembly, or subassembly undergoing testing. unitunnel diode-1. A diode similar to a tunnel diode, but specially treated to give peak reverse currents in the microampere region while providing high forward

unipotential cathode

- universe

conductance at low voltage levels. 2. A tunnel diode whose peak and valley point currents are approximately equal. unity coupling-Perfect magnetic coupling between two coils, so that all the magnetic flux produced by the primary winding passes through the entire secondary winding. unity gain-An amplifier or active circuit in which the output level is the same as the input level has unity gain. unity-gain bandwidth -The frequency at which the open-loop gain reaches unity, based on a 6-dB-peroctave crossing. It is a measure of the gain-frequency product of an amplifier. unity-gain crossover frequency- The frequency at which the curve of open-loop voltage gain of an amplifier crosses through unity gain, or zero decibels. unity power factor-A power factor of 1.0. It is obtained only when current and voltage are in phase (e.g., in a circuit containing only resistance, or in a reactive circuit at resonance). universal asynchronous reeeiverhransmitter-Abbreviated UART. 1. A device that will interface a word-parallel controller or data terminal to a bit-serial communication network. 2. A serial-to-parallel and parallel-to-serial converter. 3. An integrated circuit designed to handle serial/paraUel/serial conversion and transmission of data. 4. Commonly used LSI circuit that serves as a universal, single-package, TTL-compatible, full-duplex, serial communication line controller and data interface. 5. A sophisticated integrated circuit that accepts serial data and retransmits it as parallel data and vice versa. 6. A two-way, serial-to-parallel (and reverse) converter chip. UARTs are either dedicated or programmable; the latter permits selection of variables such as type of parity and word length. UART clock frequency is generally 16 times the baud rate. 7.A logic circuit that converts parallel information to an asynchronous serial format, and serial information to a paraliel format. Useful for connecting processors having parallel data buses to serial Ji'O lines. 8. A logic circuit that can connect a parallel I/O bus to either an asynchronous or a synchronous serial VO line. universal motor- 1. A series-wound motor designed to operate at approximately the same speed and output on direct current or on a single-phase alternating current of not more than 60 hertz and approximately the same rms voltage. 2. A motor with wound field and annature, with a commutator to make dc operation possible. When all windings are connected in series, it will operate on ac as well as dc, although the higher the ac frequency the more carefully the iron must be laminated to prevent excess eddy-current heating loss. universal output transformer- An output transformer having a number of taps on its winding. By proper choice of connections, it can be used between the audiofrequency output stage and the speaker of practically any radio receiver or audio amplifier. universal pattern-Circuit board pattern accommodating standard package configurations, such as DIPS. universal product code-See UPC. universal receiver -Also called an ac/dc receiver. A receiver with no power transformer and, thus, capable of operating from either ac or dc power lines without changes in its internal connections. universal shunt-See Ayrton shunt. universaltime- AbbreviatedUT. Also called Greenwich mean time and Greenwich civil time. A standard based on the rotation of the earth on its axis, with reference to the position of the sun. universe -See population.

UNlX

- urgency

UNIX- A complex and powerful multiuser computer operating system written in the C language originally developed, marketed, and trademarked by AT&T. It needs a computer with a large amount of RAM (random-access memory or storage capacity). UNIX allows a computer to handle multiple users and programs simultaneously and has TCP/IP built-in. It is the most common operating system for servers on the Internet. It also allows software. to be moved (known as porting) to computers of different sizes or types. UNIX is available in several related versions. unload-In a computer: 1. To remove the tape from the columns of a recorder by raising or lowering the recording head. 2. To remove a portion of the address part of an instruction. 3. See also dump. unloaded antenna-An antenna with no added inductance or capacitance. unloaded applicator impedance (dielectric heaters) -The complex impedance measured at the point of application and at a specified frequency without the load material in position. unloaded line-A line with no loading coils. unloaded Q (switching tubes) -Also called the intrinsic Q. The Q of a tube unloaded by either the generator or termination. unloading amplifier-An ampliiier capable of reproducing or amplifying a given voltage signal while drawing negligible current from the voltage source. unloading circuit-In an analog computer, a computing element or combination of computing elements capable of reproducing or amplifying a given voltage signal while drawing negligible current from the voltage source, thus decreasing the loading errors. unmodulated-Having no modulation; e.g., a carrier that is transmitted during moments of silence in radio programs, or a silent groove in a disc recording. unmodulated groove -Also called a blank groove. In mechanical recording, the groove made in the medium with no signal applied to the emitter. unoriented-A structure in which the crystallographic axes of the grains of a metal are not aligned to give directional magnetic properties. unpack-In a computer, to separate combined items of information, each into a separate machine word. unsaturated logic-A form of logic containing transistors operated outside the region of saturation; for example, current-mode logic (CML) and emitter-coupled logic (ECL). unserved energy-The amount of energy not delivered as a result of an equipment outage. untuned-Not resonant at any of the frequencies being handled. unusable samples- In random-sampling-oscilloscope technique, those samples not falling within the time window. unweighted noise-The measured noise level in electronic equipment, with a measuring device that is sensitive to a wide range of frequencies that extend beyond the audible spectrum. unwind-In a computer, to code all the operations of a cycle, at length and in full, for the express purpose of eliminating all red-tape operations. UPC-Abbreviation for universal product code. A product identification system designed to assign a unique number to every product in distribution. A 10-digit bar code, with the first 5 digits identifying the manufacturer, the second 5 identifying the item. Each digit is represented by the ratio of the widths of adjacent stripes and white areas. Used with optical checkout scanning devices that retrieve item price from a computer.

820 upconverter- 1. A device that increases the frequency of a transmitted signal. 2. A type of parametric amplifier that is characterizedby the frequency of the output signal being greater than the frequency of the input signal. update-1. To search a file (such as a particular record in a computer tape) and select one entry, then perform some operation to bring the entry up-to-date. 2. In a computer, to modify an instruction so that the address numbers in it are increased by a specified amount each time the instruction is executed. 3. Generally applied to computer files in which records are added, deleted, or amended to ensure that the latest information is contained in the file. update-response time -The interval between the entry of new data into a system and the display of that data. updating -The act of bringing information up to the current value. up/down counter- Also called reversible counter. A counter with the capability of counting in an ascending or descending order, depending on the logic present at the upldown inputs. uplink-1. Anrflinkfromasiteonthe earthorfrom an aircraft to a satellite. 2. The earth-to-geosynchronous satellite microwave link and related components, such as earth station transmitting equipment.The satellite contains an uplink receiver; uplink components in the earth station are involved with the processing and transmission of signals to the satellite. 3. The communicationspath from the earth to the satellite. 4. The earth station electronics and antenna that transmit information to a communication satellite for relay back to the ground. upload -1. The process of transferring communications instructions or data from terminals, including PCs, into a mainframe or host computer system. 2. To send a file from one computer to another via modem or other telecommunicationmethod. See also download. upper operating temperature -The maximum temperature to which a material can be subjected and still maintain specified operating characteristics within limits. upper sideband- 1. The higher frequency or group of frequencies produced by an amplitude-modulation process. 2. In carrier transmission,the band of frequencies that is higher than the carrier frequency. It is the sum of the instantaneous values of the carrier frequency and the modulating frequency. upset-duplex s y s t e m -A direct-current telegraph system in which a station between any two pieces of duplex equipment may transmit signals by opening and closing the l i e circuit and thereby upsetting the duplex balance. upset welding -A resistance-welding process wherein the weld is made simultaneously over the entire area of abutting surfaces or progressively along the joint with the aid of rolls or clamps that force the abutting surfaces together. The pressure is applied before heating starts and is maintained throughout the heating period. up time-1. The time during which an equipment is either operating or available for operation, as opposed to down time, when no productive work can be accomplished. 2. That element of active time during which an item is either alert, reacting, or performing a mission. up-time ratio-The quotient of up time divided by up time plus down time. urea plastic material -A thermosetting plastic material, with good dielectric qualities, used for radioreceiver cabinets, instrument housing, etc. urgency-The degree to which a process requires attention; determined by the process’s priority.

821

URL- Abbreviation for Uniform Resource Locator. An HTTP address used by the World Wide Web to specify a certain site. usable samples-In random-sampling-oscilloscope technique, those samples falling within the time window. USAlRT -Acronym for universal synchronous/asynchronous receiver/transmitter. See universal asynchronous receiverltransmitter. USASCII-Abbreviation for USA Standard Code for Information Interchange. The standard code, using a coded character set consisting of 7-bit coded characters (bits including parity check), for information interchange among data-processing communication systems and associated equipment. The USASCII set consists of control characters and graphic characters. Synonymous with ASCII. USASCSOCR-The United States of America Standard Character Set for Optical Characters. USASI -Abbreviation for United States of America Standards Institute, the successor to ASA (American Standards Association). USB-compatible -Universal Serial Bus Compatible. A new technology tlhat allows connection of many different kinds of peripherals to a PC using “hubs” to allow as many as 127 devices to be connected to a single attachment point. It can handle traffic up to 12 Mb/sec. scan-A paralkl reading method to prevent iguity in the readout of polystrophic codes at the code-position transitions by reading one to two sets of brushes, depending on the state of a control or selector bit. useful life-The total time a device operates between

selnet--A worldwide system of discussion groups, with comments passed among hundreds of thousands of machines. Usenet is completely decentralized, with over 10,000 discussion areas, called newsgroups. user-defined key-A key whose function or program can be changed, so that a command or sequence of c~mmandscan be executed with a single keystroke. Same as programmable key and soft-function key. Unlike a special-function key, a user-defined key may have a predefined purpose. user-friendly-Term used to describe computer hardware or software that is easy to use, by virtue

LBRL

- UVROM

of its design and the facilities that are offered to the user. user interface -The collection of screen formats, editing tools, commands, and software tools by which a user interacts with a computer. user-to-user service-A switching method that permits a direct user-to-user connection that does not include provision for message store-and-forward service. utilities-1. Programs used to perform a routine task. 2. Standard routines of often-used functions, usually supplied as par&of system software. utility-A (usually small) application or computer subroutine designed with a very particular task in mind, like converting between two formats. utility program- 1. A program providing basic conveniences, such as capability for loading and saving programs, for observing and changing values in a computer, and for initiating program execution. The utility program eliminates the need to rewrite a program every time a designer wants to perform a common function. 2. A computer program made available by the operating system to save programmers the bother of writing their own programs to do often-needed tasks. utility routine-A standard routine, usually part of a larger software package, that performs a service and/or program maintenance function, such as file maintenance, file storage and retrieval, media conversions, and production of memory and file printouts. utilization factor--In electrical power distribution, the ratio of the maximum demand of a system (or part of a system) to the rated capacity of the system (or part) under consideration. Utilogic-A line of digital ICs built around a basic AND and a basic NOR circuit. The AND has multiple emitter inputs; the NOR has emitter-follower inputs. The output for the AND is an emitter follower, and for the NOR, a totem-pole arrangement. A J-K binary element is also included in the line. UUT-Abbreviation for unit under test. UV erasable PROM -Abbreviation for ultraviolet erasable PROM. A programmable read-only memory that can be cleared (set to 0) by exposure to intense ultraviolet light. After being cleared, it may be reprogrammed. UVROM -An ultraviolet light erasable read-only memory. The memoIy is totally erased when exposed to ultraviolet light for a minimum of 20 minutes.

V

vacuum metalizing-A process in which surfaces V- 1. Letter symbol for volt. 2. Symbol for voltmeter. are given a thin coating of metal by exposing them to 3. Schematic symbol for vacuum tube. metallic vapor produced by evaporation under vacuum VCC-Symbol for the supply voltage to an integrated (one millionth of normal atmospheric pressure). circuit with respect to ground. vacuum phototube- 1. A phototube that is evacuVDD, VSS, VCC, V E E - I ~ an MOS circuit, the desated to such a degree that its electrical characteristics are ignation of the power-supply terminal serving the drain, essentially unaffected by gaseous ionization. 2. A photosource, collector, or emitter. The double subscript refers to tube that functions within a vacuum and therefore elimthe power-supply terminal, while a single subscript refinates the effect of gaseous ionization on its electrical erences the parameter at the element of a device. For properties. example, Vc is the voltage measured on the collector vacuum pickup-A handling instrument with a itself, while Vcc is the (constant) voltage supplied to small vacuum cup on one end, used to pick up chip the collector circuit. Note: In CMOS, the term VDDhas devices. been adopted as a convention referring to the positive vacuum range-For a communications system, the power-supply terminal, although it is actually applied to maximum range computed for an atmospheric attenuation the source of a p-channel transistor. of zero. VA--Letter symbol for voltampere. vacuum seal -An airtight junction between compovac -Abbreviation for vacuum. nent parts of an evacuated system. vaccine-A program to detect the presence of a vacuum switch-A switch in which the contacts computer virus. are enclosed in an evacuated bulb, usually to minimize vacuum -Abbreviated vac. Theoretically, an ensparking. closed space from which all air and gases have been vacuum tank-An airtight metal chamber that removed. However, since such a perfect vacuum is never contains the electrodes and in which the rectJfying action attained, the term is taken to mean a condition whereby takes place in a mercury-arc rectifier. sufficient air has been removed so that any remaining vacuum tight-See hermetic. gas will not affect the characteristics beyond an allowable vacuum tube-An electron tube evacuated to such amount. a degree that its electrical characteristics are essentially vacuum capacitor -A capacitor consisting usually unaffected by the presence of residual gas or vapor. of two concentric cylinders enclosed in a vacuum to raise vacuum-tube amplifier- An amplifier in which the breakdown voltage. electron tubes are used to control the power from the vacuum deposition-A process in which a sublocal source. stance is heated in a vacuum enclosure until the substance vacuum-tube characteristics-Data that shows vaporizes and condenses (deposits) on the surface of how a vacuum tube will operate under various electrical another material in the enclosure. This process is used in conditions. the manufacture of resistors, capacitors, microcircuits, and vacuum-tube keying -A code-transmitter keying semiconductor devices. The deposited material is called a system in which a vacuum tube is connected in series thin film. with the plate-supply lead going to the winding in the vacuum envelope-The airtight envelope that conplate circuit of the final stage. The grid of the tube is tains the electrodes of an electron tube. connected to its filament through the transmitting key so vacuum evaporation -A process in which a matethat when the key is open, the tube is blocked, interrupting rial is vaporized and the vapor deposits itself, through the plate supply to the output stage. Closing the key allows openings in a mask, onto a substrate to form a thin film. plate current once more through the keying tube and the vacuum gage-A device that indicates the absolute output tubes. gas pressure in a vacuum system (e.g., in the evacuated vacuum-tube modulator-A modulator in which parts of a mercury-arc rectifier). a vacuum tube is the modulating element. vacuum impregnation -Filling the spaces between vacuum-tube oscillator-A circuit in which a electric parts or turns of a coil with an insulating comvacuum tube is used to convert dc power into ac power pound while the coil or parts are in a vacuum. at the desired frequency. vacuum level-The degree of a vacuum, as detervacuum-tube rectifier-A tube that changes an mined by the pressure: rough vacuum (760 torr to 1 torr), alternating current to an unidirectional pulsating direct torr), high vacuum medium vacuum (1 torr to current. torr to torr), very high (hard) vacuum torr vacuum-tube transmitter-A radio transmitter in which electron tubes are utilized to convert the applied to torr), ultrahigh (ultrahard) vacuum (below electric power into radio-frequency power. torr). nnn bLL

vacuum-tube voltmeter

823

vacuum-tube voltmeter-Abbreviated VTVM. See electronic voltmeter. valence -A number representing the proportion in which an atom is able to combine with other atoms. It generally depends on the number and arrangement of electrons in the outermost shell of each type of atom. valence band- 1. In the spectrum of a solid crystal, the range of energy states containing the energies of the valence electrons that bind the crystal together. In a semiconductor material, it is just below the conduction hand, separated from it by the forbidden gap. 2. The band of atomic energy levels containing the valence electrons, i.e., those electrons in the outer shell of an atom. In an insulating or semiconductor material, the valence band energy level is below the conduction band. In a conducting material -for example, copper, aluminum, silver, gold, and lead- the valence-band energy level is above the conduction-band energy, thus allowing the electrons to be more free to move as an electric current. valence bond-Also called a bond. The bond formed between the electrons of two or more atoms. valence electrons- 1. The electrons of an atom in the outer shell that determine the chemical valency of the atom. 2. Electrons in the valence band of a semiconductor, where they are free to move under the influence of an electric field.

Yalence electrons.

valence shell-The electrons that form the outermost shell of an atom. validlate-To ensure {correctnessof data that has been (previously) or is being entered by any of a number of means, including check digit, batch total, numeric only field, and verification. validation -The process of verifying that execution of a system in its specified environment causes no operational problems. Includes prevention, diagnosis, recovery, and correction of errors. validity-Correctness; specifically, how closely repeated approximations approach the desired (i.e., correct) result. validity c h e c k - 1. A check to detennine that a code group actually represents a character in the particular code being used. 2. A computer input-data check based on known limits for variables in given fields. valley-A dip between two peaks in a curve. valley current--In a tunnel diode, the current measured at the positive voltage for which the current has a minimum value from which it will increase if the voltage is further increased.

;

-

1-1

I A

Valley current.

valley point-The point on the characteristic of a tunnel diode corresponding to the lowest voltage greater than the peak point voltage for which the differential conductance is zero. valley-point current-The current value at the valley point. valley-point emitter current -The currert flowing in the emitter of a unijunction transistor when the device is biased to the valley point. valley-point voltage -The voltage value at the valley point. valley voltage-In a tunnel diode, the voltage corresponding to the valley current. V a l U e - 1. The magnitude of a physical quantity. 2. The quantitative measure of a signal or variable. value analysis -The systematic use of techniques that serve to identify a required function, establish a value for that function, and finally to provide that function at the lowest overall cost. This approach focuses on the functions of an item rather than the methods of producing the present product design. value theory- The assignment of numerical significance to the worths of alternative choices. valve-1. A British term for a vacuum tube. 2. A device permitting current flow in one direction only (e.g., a rectifier). 3. A device or system that is capable of flow diversion, cutoff, or modulation. valve tube-See kenotron, 1. Van Allen radiation belts -Two doughnut-shaped belts of high-energy particles that surround the earth and are trapped in its magnetic field. They were first discovered by Dr. James A. Van Allen of Iowa State University. Van Atta antenna-A retrodirective array of antenna elements so interconnected that an incident wave produces a radiated beam from the array in the direction of the incident wave reversed over a significant range of angles of incidence, as in the case of an optical autocollimator. Versions of the array may contain amplifiers, circulators, and mixers, and may direct the transmitted beam, with or without modifications, in a direction or directions other than that of the incident wave reversed. Van Atta array-An antenna array designed so that the received signal is reflected back toward its source in a narrow beam to provide signal enhancement without

Van de Graaff accelerator

- variable connector

amplification. It consists of pairs of corner reflectors or other elements equidistant from the center of the array and connected together by means of low-loss transmission line. Van de Graaff accelerator -An electrostaticgenerator type of particle accelerator from which the voltage is obtained by picking up static electricity at one end of the machine (on a rubber belt) and carrying it to the other end, where it is stored.

-L

Motor

Van de Graangenerator.

vane-anode magnetron-A cavity magnetron in which the walls between adjacent cavities have parallel plane surfaces. vane attenuator-A waveguide device designed to preset attenuation in a circuit by sliding a resistive element from the side wall of the waveguide to the center for maximum attenuation. T h i s method of attenuation is used in precision calibrated attenuation readings, and resetting must be made. Some of its countless applications are calibrations of other attenuators, directional couplers, filters, and other lossy components, in antenna-pattern measurements, noise-level measurements, and for setting power levels to desired values. vane-type instrument-A measuring instrument in which the pointer is moved by the force of repulsion between fixed and movable magnetized iron vanes, or by the force between a coil and a pivoted vane-shaped piece of soft iron. vane-type magnetron-A cavity magnetron in which the walls between adjacent cavities have plane surfaces. V-antenna -A V-shaped arrangement of conductors, the two branches being fed equally in opposite phase at the apex. vapor pressure-The pressure of the vapor accumulated above a confined liquid (e.g., in a mercury-vapor rectifier tube). vaporware-A jocular term for products or components that have been announced by a vendor that do not yet exist and may never exist.

824 var -Letter symbol for voltampere reactive. The unit of reactive power, as opposed to real power in watts. One var is equal to one reactive voltampere. VAR -Abbreviation for visual-aural range, varactor -Also called varactor diode, silicon capacitor, voltage-controlled capacitor, and voltagevariable capacitor. 1. A two-terminal solid-state device that utilizes the voltagevariable capacitance of a pn junction. In the normal semiconductor diode, efforts are made to minimize inherent capacitance, while in the varactor, this capacitance is emphasized. Since the capacitance varies with the applied voltage, it is possible to amplify, multiply, and switch with this device. 2. Semiconductor diode that exhibits a change in capacitance with a change in applied voltage when operated in a reverse-biased condition. Varactors are used as voltage-variable capacitors in tuned circuits. varactor diode-A two-terminal semiconductor device in which use is made of the fact that its capacitance varies with the applied voltage. See also varactor. varactor-tuned oscillator- An oscillator in which a varactor diode is used in the frequency-determining networks that encompass the circuit’s active device@). varhour meter- Also called a reactive voltamperehour meter. An electricity meter that measures and registers the integral (usually in kilovarhours) of the reactive power of the circuit into which the meter is connected. variable-1. Any factor or condition that can be measured, altered, or controlled (e.g., temperature, pressure, flow, liquid level, humidity, weight, chemical composition, color). 2. A quantity that can take on any of a given set of values. 3. In a computer, a symbol whose numeric value changes from one iteration of a program to the next or within each iteration of a program. variable-area track- A sound track divided laterally into opaque and transparent areas. A sharp line of demarcation between these areas forms an oscillographic trace of the waveshape of the recorded signal. variable-capacitance diode -Abbreviated VCD. A semiconductor diode in which the junction capacitance present in all semiconductor diodes has been accentuated. An appreciable change in the thickness of the junctiondepletion layer and a corresponding change in the capacitance occur when the dc voltage applied to the diode is changed. variable-capacitance transducer -A transducer that measures a parameter or a change in a parameter by means of a change in capacitance. variable capacitor-1. A capacitor that can be changed in capacitance by varying the useful area of its plates, as in a rotary capacitor, or by altering the distance between them, as in some trimmer capacitors. 2. A capacitor whose capacitance can be varied by varying the separation between a pair of plates, or by varying the depth of insertion of interleaved plates. (Most widely used for tuning radio-frequency circuits.) variable-carrier modulation-See controlledcarrier modulation. variable-compression capacitor-A capacitor in which the capacitance can be varied by compressing a stack of electrode and dielectric layers. variable concentric capacitor- An air dielectric capacitor in which the capacitance can be varied by the axial movement of a rotor in a stator. variable connector- 1. A flowchart symbol representing a sequential connection that is not h e d , but which can be varied by the flowcharted procedure itself. 2. The device that inserts instructions in a program corresjmnding to the selection of paths appearing in a flowchart. 3. The computer instructions that cause a logical chain to take one of several alternative paths.

variable coupling - variable resistor

825 variable coupling --Inductive coupling that can be varied by moving the windings. varialble-cycle operaition-Computer operation in which any cycle is started at the completion of the previous cycle, instead of at specified clock times. varlalble-density track- A sound track of constant width antd usually, but not necessarily, of uniform light transmission on any instantaneous transverse axis. The average light transmission varies along the longitudinal axis in proportion to some characteristic of the applied signal. variable-depth sonair-A sensor that can be lowered by cable from a ship or helicopter, through the thermal layers, to detect submarines operating at deeper levels. variable disc capacitor-A solid-dielectric capacitor in which the capacitance can be varied by rotating a metal or metallized disc. variable-erase recording-The method of recording on magnetic tape by selective erasure of a prerecorded signal. variable field-A field in which the scalar (or vector) at any point changes during the time under consideration. variable-frequency oscillator-Abbreviated VFO, A stable oscillator whose frequency can be adjusted over a given range. warialble-frequency synthesizer -An instrument that translates the stability of a single frequency, usually obtained from a frequency standard, to any one of many other possible frequencies. In common usage, such instruments are called simply frequency synthesizers. wariable inductance-Also called variable inductor. A coil whose inductance can be varied.

START

n

\

COIL

/

COIL

FORM

variable point -Pertaining to a system of numeration in which the position of the radix point is indicated by a special character at that position. variable radio-frequencyradiosonde --A radiosonde whose carrier frequency is modulated by the magnitude of the meteorological variables being sensed. variable reluctance-Principle employed in certain phonograph pickups. Deflections of the stylus when playing a record make an armature vibrate between the poles of an electromagnet. The reluctance is the ratio of magnetic force to magnetic flux in a magnetic field. Variations due to stylus movement create variations in the current through the electromagnet. variable-reluctance microphone- Also called a magnetic microphone. A microphone that depends for its operation on the variations in reluctance of a magnetic circuit. variable-reluctance pickup-1. A phonograph cartridge that derives its electrical output signal from change effected in a magnetic circuit by means of some mechanical device such as a moving coil or magnet. 2. A type of cartridge that generates its signal from the relative motions of a magnetic field and a coil or coils (either the field or the coils may move, depending on cartridge design). The output is proportional to the velocity of the stylus motion. This requires an equalization circuit in the preamplifier to restore proper frequency balance, since records are cut with more nearly constant-amplitude than constant-velocity characteristics. 3. A phonograph pickup that depends for its operation on the variation of a resistance.

MOUNTING CLIP

OUTER COIL FORM

Variable-reluctancepickup.

A FINISH

‘CORE IUNOEA COIL)

\ ROD

varhbl8einductance.

variable-inductancepickup-A phonograph pickup in ahich the movement of a stylus causes the inductance to vary accordingly. variable-inductance transducer -A transducer in which the output voltage is a function of the change in a variable-inductance element. variable-length record-In a computer, pertaining to a file in which there is no constraint on the record length. (Opposite of fixed-length record.) variable monoergic -A type of emission in which the magnitude of the homogeneous particle or radiation energy is continuously variable over broad limits; e.g., the proton energy from some types of accelerators can be controlled by varying the high voltage. variable-mu pressure transducer- A device that converts mechanical input pressure to a proportional electrical output based on the change of the mu of its magnetic circuit due to the applied pressure (Villa~i effect). variable-mu tube --See remote-cutoff tube.

variable-reluctance stepping motor- -A motor with a soft-iron rotor that is made to step by sequential excitation of stator coils. It requires complementary equipment to furnish the sequencing pulses. variable-reluctance transducer- Also called a magnetic transducer. A transducer that depends fOF its operation on the variations in reluctance of a magnetic circuit. variable-resistance transducw -A transducer in which the signal output depends on the change in a resistance element. variable resistor -A wirewound or composition resistor whose resistance may be changed. See also potentiometer, 1; rheostat.

Variable resistors.

variable-speed motor

- vector cardiograph

variable-speed motor- A motor whose speed can be adjusted within certain limitations, regardless of load. variable-speed scanning -A scanning method whereby the optical density of the film being scanned determines the speed at which the scanning beam in the cathode-ray tube of a television camera is deflected. variable transformer- An iron-core transformer with provision for varying its output voltage over a limited range, or continuously from zero to maximum- generally by the movement of a contact arm along exposed turns of the secondary winding. variable tubular capacitor-A solid-dielectric capacitor in which the capacitance can be varied by the axial movement of an electrode within a tube. variable vane capacitor-A capacitor in which the capacitance can be varied by rotating the rotor vanes between the stator vanes. Variac -An autotransformer that contains a toroidal winding and a rotating carbon brush so that the output voltage is continuously adjustable from zero to line voltage plus 17 percent. Trade name of General Radio Company. variance-A measure of the fluctuations of data around the mean. variants- 1. Two or more cipher or code groups that have the same plain-language equivalent. 2. Two or more plaintext meanings that are represented by a single code group. variate-See random variable, 1. variation -The angular difference between a true and a magnetic bearing or heading. varicap-See varactor. varindor- An inductor whose inductance varies markedly with the current in the Winding. variocoupler-A radio transformer with windings that have an essentially constant self-impedance, but the mutual impedance between them is adjustable. variolosser- A device whose loss can be controlled by a voltage or current. variometer -A variable inductor consisting of a pair of series- or parallel-connected coils whose axes can be varied one with respect to the other. The change in mutual inductance causes a change in the total inductance. varioplex-A telegraph switching system that establishes connections on a circuit-sharing basis between a number of transmitters in one locality and corresponding receivers in another locality over one or more intervening channels. Maximum use of channel capacity is obtained by employing momentary storage of signals and allocating circuit time in rotation among the transmitters that have information in storage. varistor-From “variable resistor.” 1. A twoelectrode semiconductor device with a voltage-dependent nonlinear resistance that drops markedly as the applied voltage is increased. 2. A passive resistorlie circuit element whose resistance is a function of the current through it. The current through it is a nonlinear function of the voltage across its terminals; hence, a self-varying resistance. See aZso voltage-dependent resistor. 3. A voltage-dependent symmetrical resistor with a high degree of nonlinearity (the resistance does not change linearly as a function of the applied voltage). The value of the resistance is very high at voltages lower than nominal and very quickly changes to an extremely low value of resistance as the applied voltage is increased above the nominal voltage. The device is used as a voltage-transient or voltage-surge suppressor to improve the reliability of a voltage-sensitive circuit. It provides instantaneous response to high voltage, with good temperature stability and excellent clamping characteristics. The device is normally connected across its input terminals or across the

826 ac power source, providing protection with an effective low resistance somewhat above the normal input or line voltage values. One of the varistor’s main uses is to protect electronic equipment against lightning. It is also used to protect against sudden or transient surges of voltage in an ac power line. See also MOV. Varley loop-A type of Wheatstone-bridge circuit that gives, in one measurement, the difference in resistance between two wires of a loop. varmeter-Also called a reactive voltampere meter. An instrument for measuring reactive power in either vars, kilovars, or megavars. If the scale is graduated in kilovars or megavars, the instrument is sometimes designated a kilovarmeter or megavarmeter. varnished cambric-A linen or cotton fabric that has been impregnated with varnish or insulating oil and baked. It is used as insulation in coils and other radio parts. varying duty -A requirement of service that demands operation at loads and for intervals of time, both of which may be subject to wide variation. varying-speed motor-A motor that slows down as the load increases (e.g., a series motor, or an induction motor with a large amount of slip). varying voltage control-A form of armaturevoltage control obtained by impressing, on the armature, a voltage that varies considerably with a change in load and consequently changes the speed of the motor (e.g., by using a differentially compound-wound generator or a resistance in the armature circuit). V-beam system-A radar system for measuring elevation. The antenna emits two fan-shaped beams, one vertical and the other inclined, which intersect at ground level. Each beam rotates continuously about a vertical axis, and the time elapsing between the two echoes from the target provides a measure of its elevation. VCD -Abbreviation for variable-capacitance diode. v-chip-A semiconductor that blocks the display of violent and/or pornographic material on a TV. Transmitters have to incorporate a signal for the system to function. VCO -Abbreviation for voltage-controlled oscillator. VCR -1. Abbreviation for voltage-controlled resistor. 2. Abbreviation for videocassette recorder (or player). V-cut-A type of oscillator-crystal cut in which the major plane surfaces are not parallel to the X, Y, or 2 planes. VDR -See voltage-dependent resistor. VDT-Abbreviation for video display terminal. A CRT or gas-plasma tube display screen terminal or keyboard console that allows keyed or stored text to be viewed for manipulation or editing. VDU- 1. See video display unit. 2. Abbreviation for visual display unit. A display of data for use by human operators. Data is usually displayed as several rows of alphanumeric characters. vector-A quantity that has both magnitude and direction. Vectors commonly are represented by a line segment with a length that represents the magnitude and an orientation in space that represents the direction. See vector quantity. vector admittance-The ratio for a single sinusoidal current and potential difference in a portion of a circuit of the corresponding complex harmonic current to the corresponding complex potential difference. vector-ampere -“he unit of measurement of vector power. vector cardiograph- An instrument that measures both the magnitude and the direction of heart signals by displaying cardiograph signals on any desired set of axes, usually x, y, and z.

827

vector diagram -An arrangement of vectors showing the relationships between alternating quantities having the same frequency. vectored interrupt -1. An interrupt in a computer that carries its identity number or the address of its handler. 2. An interrupt scheme in which each interrupting device causes the operating system to branch to a different interrupt routine. This scheme is useful for a very fast interrupt response. vector field-In a given region of space, the total value of some vector quantity that has a definite value at each point of the region (e.g., the distribution of magnetic intensity in a region surrounding a currentcarrying conductor). vector function--A function that has both magnitude and direction (e.g., the magnetic intensity at a point near an electric circuit is a vector function of the current in that circuit). vector generator---That part of the display controller which draws vectors on the screen. Control codes within the display list specify whether the vector generators will move the beam in a blanked or unblanked mode. If the beam is unblanked, the vector will be drawn in a specified texture, vector impedance-The ratio for a simple sinusoidal current and potential difference in a portion of a circuit of the corresponding complex harmonic potentid difference to the corresponding complex current. vector interrupt-A term used to describe a microprocessor system in which each interrupt, both internal and external, has its own uniquely recognizable address. This enables the microprocessor to perform a set of specified operations that are preprogrammed by the user to handle each interrupt in a distinctively different manner. vector power-A vector quantity equal to the square root of the sum of the squares of the active and reactive powers. The unit is the vector-ampere. vector power factor--Ratio of the active power to the vector power. In sinusoidal quantities, it is the same as power factor. vector processing-A method for carrying out many repetitive mathematical operations with a single computer instruction. vector quantity-A quantity that has both magnitude and direction. Examples of quantities that are vectors are displacement, velocity, force, and magnetic intensity. vector refresh display-See calligraphic display. vector scan -Technique of displaying images on a screen, particularly suitable for precision drawings and animation. It is available only on special visual display units. Images are created by moving an electron beam in the CRT to any place on the screen, just as a pen is moved in any direction on paper. The positions are specified as IC and j~coordinates. vectorscope- 1. An oscilloscope with a circular time base of extreme stability (determined by the frequency of the color subcarrier). The instrument can be used to check the time delay between two signals because the phase difference at a particular frequency can be related to time difference. 2. Special synchroscope used in color TV camera and color encoder calibration. The vectorscope will graphically indicate on a CRT the absolute angles the different color signals describe in respect to a reference and to each other. These angles as read on the vectorscope represent the phase differences of the signals. vector s t r o k e display-See calligraphic display. velocimeter -A continuous-wave reflection Doppler system used to measure the radial velocity of an object.

vector diagram

- velocity pickup

velocity-A vector quantity that includes both magnitude (e.g., speed) and direction in relation to a given frame of reference. velocity error -The amount of angular displacement existing between the input and output shafts of a servomechanism when both are turning at the same speed. velocity filter -A storage-tube device that blanks all targets that do not move more than one resolution cell in less than a predetermined number of antenna scans. velocity hydrophone-A type of hydrophone in which the electric output is substantially proportional to the instantaneous particle velocity in the incident sound wave. velocity-lag error-A lag between the input and output of a device, proportional to the rate of variation of the input. velocity level-In decibels of a sound, 20 times the logarithm to the base 10of the ratio of the particle velocity of the sound to the reference particle velocity. The latter must be stated explicitly. velocity microphone-A microphone in which the electric output corresponds substantially to the instantaneous particle velocity in the impressed sound wave. It is a gradient microphone of order one, and is inherently bidirectional. velocity-modulated amplifier- Also called a velocity-variation amplifier. An amplifier in which velocity modulation is employed for amplifying radio frequencies. velocity-modulated oscillator- Also called a velocity-variation oscillator. An electron-tube structure in which the velocity of an electron stream is varied (velocity-modulated) in passing through a resonant cavity called a buncher. Energy is extracted from the bunched electron stream at a higher level in passing through a second cavity resonator called the catcher. Oscillations are sustained by coupling energy from the catcher cavity back to the buncher cavity. velocity modulation -Also called velocity variation. 1. Modification of the velocity of an electron stream by the alternate acceleration and deceleration of the electrons with a period comparable to that of the transit time in the space concerned. 2. Modulation of an electron stream by alternately accelerating and decelerating the electrons, thus grouping them into bunches. Velocity of light-A physical constant equal to 2.99796 x 10" centimeters per second. (More conveniently expressed as 186,280 statute miles per second, or 161,750 nautical miles per second, or 328 yards per microsecond.) velocity of propagation -1. The speed at which a disturbance (e.g., sound, radio, light waves) is radiated through a medium. 2. The ratio of the speed of the flow of an electric current in an insulated cabie to the speed of light, expressed in percentage. In the case of coaxial cables, this ratio is 65 to 66 percent, where the insulation is polyethylene. 3. The speed of transmission of electrical energy through a cable compared with its speed through air, expressed as a percentage of the speed in free space. Radio-frequency signals are transmitted in free space at a speed of 186,280 statute miles per second (2.99796 x 10' d s ) . Velocity of propagation is determined by the ratio of the dielectric constant of air to the square root of the dielectric constant of the insulation and is expressed in percent. 4. The speed with which a signal wave travels through a particular transmission. velocity pickup-A magnetic pickup whose output increase is a function of recorded velocity. (This differs from the ceramic pickup, whose output is a function of amplitude or deflection of the stylus.)

velocity resonance

- vertically polarized wave

velocity resonance-See phase resonance. velocity sorting -The selecting of electrons according to their velocity. velocity spectrograph-An apparatus for separating an emission of electrically charged particles into distinct streams in accordance with their speed, by means of magnetic or electric deflection. velocity transducer-A transducer that generates an output proportionate to the imparted velocities. velocity variation-See velocity modulation. velocity-variation amplifier- See velocity-modulated amplifier. velocity-variation oscillator-See velocity-modulated oscillator. Venn diagrams-Diagrams in which circles or ellipses are used to give a graphic representation of basic logic relations. Logic relations between classes, operations on classes, and the terms of the propositions are illustrated and &fined by the inclusion, exclusion, or intersection of these figures. Shading indicates empty areas, crosses indicate areas that are not empty, and blank spaces indicate areas that may be either. Named for English logician John Venn, who devised them. vent-A controlled weakness somewhere in the enclosure of an aluminum electrolytic capacitor to permit pressure relief in case of failure due to shorting or improper installation of the capacitor. vented baffle-An enclosure designed to properly couple a speaker to the air. ventilated transformer- A dry-type transformer that is so constructed that the ambient air may circulate through its enclosure to cool the transformer core and windings. venturi tube-A short tube with flaring ends and a constricted throat It is used for measuring flow velocity by measurement of the throat pressure, which decreases as the velocity increases. verification-The process of checking the results of one data transcription against those of another, both transcriptions usually involving manual operations. See also check. verifier- 1. Of computers, a device on which a record can be compared or tested for identity character by character with a retranscription or copy as it is being prepared. 2. A machine that is used to check the correctness of manually recorded data. verify-1. To check, usually with an automatic machine, one recording of data against another in order to minimize the number of human errors in the data transcription. 2. To make certain that the information being prepared for a computer is correct. vernier- 1. An auxiliary scale comprising subdivisions of the main measuring scale and, thus, permitting more accurate measurements than are possible from the main scale alone. 2. An auxiliary device used for obtaining fine adjustments. vernier capacitor-A variable capacitor placed in parallel with a larger tuning capacitor and used to provide a finer adjustment after the larger one has been set to the approximate desired position. vernier dial-A type of tuning dial used chiefly for radio equipment. Each complete rotation of its control knob moves the main shaft only a fraction of a revolution and thereby permits fine adjustment. vernitel-A precision device that makes possible the transmission of data with high accuracy over standard frequency-modulated telemetering systems. vertex-See node, 1. vertex plate-A matching plate placed at the vertex of a reflector.

828 vertical -In 45/45 recording, the signal produced by a sound arriving at the two microphones simultaneously and 180" out of phase, causing the cutting stylus to move vertically. vertical amplification-Signal gain in the circuits of an oscilloscope that produces vertical deflection on the screen. vertical-amplitude controls -See parabola controls. vertical antenna-A vertical metal tower, rod, or suspended wire that is used as a receiving andor transmitting antenna. vertical blanking-Blanking of a television picture tube during the vertical retrace. vertical-blankinginterval-The brief time between television fields required for the scanning electron gun to retrace from the bottom of the image to the top to begin scanning the next field. The interval occupies 16,667 milliseconds and occurs at the end of each 262.5 field scan lines. There are 21 usuable lines in this interval, which are devoted to 6 vertical synch pulses and 12 equalizing pulses, as well as additional horizontal pulse intervals. vertical-blanking pulse-In television, a pulse transmitted at the end of each field to cut off the cathoderay beam while it returns to the start of the next field. vertical-centeringcontrol-A control provided in a television receiver or cathode-ray oscilloscope to shift the entire image up or down on the screen. vertical compliance-The ability of a reproducing stylus to move vertically while in the reproducing position on a record. vertical-deflectionelectrodes-The pair of electrodes that move the electron beam up and down on the screen of a cathode-ray tube employing electrostatic deflection. vertical dynamic convergence- Convergence of the three electron beams at the aperture mask of a color picture tube during the scanning of each point along a vertical line at the center of the tube. vertical-field-blanking interval-See verticalblanking interval vertical field-strength diagram-A representation of the field strength at a constant distance from, and in a vertical plane passing through, an antenna. vertical frame transfer-A CCD configuration in which all charges accumulated during an integration period are rapidly moved out of the optically active area and to an identical optically shielded CCD area where the accumulation is read out at a slower pace during the next integration period. vertical-frequencyresponse-In an oscilloscope, the band of frequencies passed, with amplificationbetween specified limits, by the amplifiers that produce vertical deflection on the screen. vertical-hold control-See hold control. vertical-incidence transmission --The transmission of a radio wave vertically to the ionosphere and back. The transmission remains practically the same for a slight departure from the vertical (e.g., when the transmitter and receiver are a few kilometers apart). vertical-lateral recording-A technique of making stereo phonograph discs by recording one signal laterally, as in monophonic records, and the other vertically, as in hill-and-dale-transcriptions. vertical linearity control-A control that permits adjustment of the spacing of the horizontal lines on the upper portion of the picture to effect linear vertical reproduction of a television scene. vertically polarized wave -1. An electromagnetic wave with a vertical electric vector. 2. A linearly polarized wave with a horizontal field vector.

vertical MOS

829 vertical MOS-See VMOS. vertical polarization- 1. Transmission in which the transmitting and receiving antennas are placed in a vertical plane. so that the electrostatic field also varies in a vertical plane. 2. Transrnission of radio waves whose undulations vary vertically with respect to the earth. vertical quarter-wave stub-An antenna with a vertical portion that is electrically one quarter-wavelength Long. It is used generally with a ground plane at the base of the stub. vertical radiator -A transmitting antenna perpendicular to the earth’s surface. vertical recording -Also called hill-and-dale recording. Mechanical recording in which the groove modulation is perpendicular to the surface of the recording medium. vertical redundance-In a computer, an error condition that exists when a character fails a parity check, ie., has an even number of bits in an odd-parity system or vice versa. vertical resolution - 1. On a television test pattern, the number of horizontal wedge lines that can be clearly discerned by the eye before they merge together. 2. The number of horizontal lines that can be seen in the reproduced image of a television pattern. vertical retrace-1. The return of the electron beam from the bottom of the image to the top after each vertical sweep. 2. The return of the electron beam to the top of the picture tube screen or the pickup tube target at the completion of the field scan. vertical scanning -Scanning that proceeds in a series of vertical lines. vertical scrolling -The ability of a word processor to move vertically, a line at a time, up and down through a display page or more of text. This allows text that will not fit on a video display screen to be accessed for review or editing. Used in systems that have a display buffer (memoFj area) larger than the display screen capacity. vertical speed transducer -An instrument that furnishes an electrical output that is proportionate to the vertical speed of the aircraft or missile in which it is installed. arerticzal structured metal-oxide silicon power field-effect transistor-See VMOS power FET. vertical stylus force -See stylus force. vertical sweep-The downward movement of the scanning beam from top to bottom of the televised picture. vertical sync -The synchronizing pulses used to define tlhe end of one television field and the start of the next, occming at a rate of approximately 59.94 Hz (color) and 60 Bz (black and white). vertilcal-synchronizing pulse -Also called picture-synchronizing pulse. One of the six pulses transmitted at the end of each field in a television system. It maintains the receiver in field-by-field synchronism with the transmitter. vertical tracking-The phonograph pickup stylus motion ]path that is near vertical. Applies to hill-and-dale recordings on stereo discs. wertical tracking force -The minimum downward force at which a phonograph cartridge works without mistracking, i.e., a momentary hop by the stylus (making a raspy sound) or a jump into the next groove. high frequency- Abbreviated VHF. Fre9 band: 30 to 300MHz. Wavelength: 10 to 1

S.

large-scale intlegration-See VLSI. wery long range--A classification of ground radar sets by slant range, applied to those with a maximum range exceeding 250 miles (402 km).

- vibrating-reed meter

very low frequency-Abbreviated VLF. Frequency band: below 30 kHz. Wavelength: above 10,000 meters. very short range-Classification of ground radar sets by slant range, applied to those with a maximum range of less than 25 miles (40.2 km). vestigial -Pertaining to a remnant or remaining part. vestigial sideband -Amplitude-modulated transmission in which a portion of one sideband has been largely suppressed by a transducer having a gradual cutoff in the neighborhood of the carrier frequency.

PICTURE CARRIER

-0.25 MHZ 50 kHz

60

61

62 63 64 65 FREQUENCY IM MEGAHERTZ

65

Vestigial-sidebandtelevision channel. vestigial-sideband filter --A filter that is inserted between an AM transmitter and its transmitting antenna to suppress part of one of the sidebands. vestigial-sideband transmission -Also called asymmetric-sideband transmission. Signal transmission in which one normal sideband and the corresponding vestigial sideband are utilized. vestigial-sideband transmitter- A transmitter in which one sideband and only a portion of the other are transmitted. v/f converter-See voltage-to-frequency converter. VFO -Abbreviation for variable-frequency oscillator. VGA -Abbreviation for Video Graphics Array. A VGA monitor has a 480 x 640 display resolution and can display up to 256 colors simultaneously. A video standard for IBM PC and compatible computers. V-groove metal-oxide silicon -See VMOS. VHF- 1. Abbreviation for very high frequency. 2. In television, a term used to designate channels 2 through 13. VHF omnirange -Abbreviated VOR. -A specific type of range operating at VHF and providing radial lines of position in a direction determined by the bearing selection within the receiving equipment. A nondirectional reference modulation is emitted, along with a rotation pattern that develops a variable modulation of the same frequency as the reference modulation. Lines of position are determined by comparing the phase of the variable with that of the reference. VHLL -Abbreviation for very high-level language. Usually a problem or requirements description language, ranging in form from the highly abstract to plain English. VHSIC -Abbreviation for very high-speed integrated circuits. via -1. A vertical conductor or conductive path forming the interconnection between multilayer hybrid circuit layers. 2. Means of passing from one layer or side of a printed circuit board to the other. via hole-A plated-through hole that establishes electrical continuity but which is not intended for a component lead. See plated-through hole. vibrating bell --A bell having a mechanism designed to strike repeatedly and as long as it is actuated. vibrating-reed meter -Also called reed frequency meter. A frequency meter consisting of a row of steel

vibrating-reed relay

- videocassette recorder

reeds, each having a different natural frequency. All are excited by an electromagnet fed with the alternating current whose frequency is to be measured. The reed whose frequency corresponds most nearly with that of the current vibrates, and the frequency is read on a scale beside the row of reeds. vibrating-reed relay-1. A type of relay in which an alternating or a self-intempted voltage is applied to the driving coil so as to produce an alternating or pulsating magnetic field that causes a reed to vibrate. 2. A type of relay that is actuated by sound frequency. Can be triggered by an electrical resonant circuit, or simply by a mechanically induced sound vibration. vibrating-wire tranducer-A transducer that utilizes a thin wire suspended in a magnetic field; the change in tension of the wire reflects a frequency-modulating output. vibration-1. A continuously reversing change in the magnitude of a given force. 2. A mechanical oscillation or motion about a reference point of equilibrium. vibration analyzer-A device used to analyze mechanical vibrations. vibration-detection system- An alarm system that employs one or more contact microphones or vibration sensors that are fastened to the surfaces of the area or object being protected to detect excessive levels of vibration. The contact microphone system consists of microphones, a control unit containing an amplifier and an accumulator, and a power supply. The unit’s sensitivity is adjustable so that ambient noises or normal vibrations will not initiate an alarm signal. In the vibration sensor system, the sensor responds to excessive vibration by opening a switch in a closed-circuit system. vibration galvanometer- An ac galvanometer in which a reading is obtained by making the natural oscillation frequency of the moving element equal to the frequency of the current being measured. vibration isolator-A resilient support that tends to isolate a system from steady-state excitation or vibration. vibration meter -Also called a vibrometer. An apparatus comprising a vibration pickup, calibrated amplifier, and output meter, for the measurement of displacement, velocity, and acceleration of a vibrating body. vibration pickup-A microphone that responds to mechanical vibrations rather than to sound waves. In one type, a piezoelectric unit is employed; the twisting or bending of a Rochelle-salt crystal generates a voltage that varies with the vibration being analyzed. vibration sensitivity-The peak instantaneous change in output at a given sinusoidal vibration level for any one stimulus value within the range of an instnunent or equipment. It is usually expressed in percentage of full-scale output per vibratory “g” over a given frequency range. It may also be specified as a total error in percentage of full-scale output for a given vibratory acceleration level. vibration sensor-A sensor that responds to vibrations of the surface on which it is mounted. It has a normally closed switch that will momentarily open when it is subjected to a vibration with sufficiently large amplitude. Its sensitivity is adjustable to allow for the different levels of normal vibration, to which the sensor should not respond, at different locations. See also vibrationdetection system. vibration survey-A method of determining the natural frequency of a transducer by observation of the output waveform upon the application of a shock or tapping of sufficient magnitude to initiate oscillation of the instrument.

830 vibration &&-A test to determine the ability of a device to withstand physical oscillations of specified frequency, duration, and magnitude. vibration welding-Method of fusing two plastic parts by vibrating (rubbing) the mating surfaces together at relatively low frequencies, 90 to 120 Hz. vibrato -1. A musical embellishment that depends primarily on periodic variations of frequency, often accompanied by variations in amplitude and waveform. The quantitative description of vibrato is usually in terms of the corresponding modulation of frequency (typically 5 to 7 Hz), amplitude, or waveform, or all three. 2. Regular variation in the frequency of a sound, generally at a frequency between 2 and 15 times per second. This frequency modulation by a low-frequency oscillator is commonly used with guitars, organs, synthesizers, and the human voice. vibrator- 1. A vibrating reed that is driven like a buzzer and has contacts arranged to interrupt direct current to the winding(s) of a transformer, resulting in an alternating current being supplied from another winding to the load. 2. Electromagnetic device that is used to change a continuous steady current into a pulsating current. 3. An electromagnetic device for converting a direct voltage into an alternating voltage. vibrator power supply-A power supply incorporating a vibrator, step-up transformer, rectifier, and filters for changing a low dc voltage to a high dc voltage. vibratron-A triode with an anode that can be moved or vibrated by an external force. Thus, the anode current will vary in proportion to the amplitude and frequency of the applied force. vibrometer-See vibration meter. video -1. Pertaining to the bandwidth and spectnun position of the signal resulting from radar or television scanning. In current usage, video means a bandwidth on the order of several megahertz and a spectrum position that goes with a dc carrier. 2. A prefix to the name of television parts or circuits that carry picture signals. 3. Radar or television signals that actuate a cathode-ray tube. 4. Composite video contains color and luminance (brightness information) as well as horizontal and vertical synch pulses during the horizontal and vertical blanking intervals. One line of video, for instance, amounts to approximately 52 microseconds in visible horizontal scan time, and 63.5 microseconds for a complete line, including the color burst and horizontal synch. video adapter- An expansion board in a computer that provides enhanced display capabilities. video amplifier- 1. An amplifier that provides wideband operation in the frequency range of approximately 15 hertz to approximately 5 megahertz. 2. An amplifier designed for linear amplification over a wide range of frequencies from dc (zero) to over about 10 MHz. 3. A wideband amplifier used for passing picture signals. video band-The frequency band utilized to transmit a composite video signal. video carrier- 1. The television signal whose modulation sidebands contain the picture, sync, and blanking signals. 2. A frequency that is 1.25 MHz above the lower edge of the assigned 6-MHz frequency band of a TV channel. At channel 2, for instance, with a bandwidth of 54 to 60 MHz, the video carrier rests at 55.25 MHZ. videocassette-A plastic shell containing two reels and a given length of videotape. videocassette recorder- Abbreviated VCR. A device for recording and playing video images on magnetic tapes that are contained in plastic cases.

videocast

a3 1 VIDEO HEADS

HEADWHEEL

Vieocass8etterecorder. videocast- 1. To broadcast a program by means of television. 2. A program so broadcast. VideoCipher I, Il--Pi trademark for a video/audio encryption system developed by MIA-COM LINKABIT, Inc. VCI uses digital video and audio encryption; VCII uses analog video and digital audio encryption. video compression-1. The reduction of the number of bits needed to describe a video image. 2. A digital technique to compress several video channels into the bandwidth normally required by one channel. videai correlator-A radar circuit that enhances the capability for automatic target detection; supplies data for digital target plotting; and provides improved immunity to noise, interference, and jamming. video data digital processing -Digital processing of video signals for pictures transmitted by way of a television link. A computer is used to compare each scanned line with adjacent lines so that extreme changes resulting from electromagnetic interference can be eliminated. video detector -The demodulator circuit that extracts the picture information from the amplitudemodulated intermediate frequency in a television receiver. video dialtone-An FCC term for the new generation of home-distribution video systems that deliver compressed digital signals over switched networks to an interactive set-top box in the user premises. video digitizing-Thme process of capturing, converting, and storing video images for use by a computer. video disc-see optical video disc. video discrimination -A radar circuit that reduces the frequency band of the video-amplifier stage in which it is used. video display unit-Abbreviated VDU. A device for visual presentation of ~mnformation.A CRT is a typical video display unit. video freeze-A TV mode which makes it possible to “freeze” an image to study specific details at ease, e.g., to make notes of certain program information like phone numbers. video frequency- 1. The frequency of the signal voltage containing the piclue information that arises from the television scanning process. In the present United States television system, these frequencies are limited from approximately 30 Hz to 4 MHz. 2. A band of frequencies extending from less than 100 hertz to several megahertz. video-frequency amplifier--A device capable of amplifying those signals that comprise the periodic visual presentation. video-gain control-A control for adjusting the amplitude of a video signal. Two such controls are provided in the matrix section of some color television

- videotape recorder

receivers so that the proper ratios between the amplitudes of the three color signals can be obtained. video impedance--Of a detector diode, the output impedance measured at the video frequency when the diode is operating under specified bias conditions. video integration-A method of improving the output signal-to-noise ratio by utilizing the redundancy of repetitive signals to sum the successive video signals. video integrator-A device that uses the redundance of repetitive signals to improve the output signalto-noise ratio by summing the successive video signals. video inversion-A type of encoding or scrambling in which the transmitted downlink video signals are inverted. video mapping-The procedure whereby a chart of an area is electronically superimposed on a radar display. video masking-A method for the removal of chaff echoes and other extended clutter from radar displays. video mixer-A circuit or device used to combine the signals from two or more television cameras. video moir6-See moire effect. video monitor-A high-quality television set (without rf circuits) that accepts video baseband inputs directly from a TV camera, VTR, or satellite TV receiver with no rf modulator required. video pair cable-A transmission cable containing low-loss pairs with an impedance of 125 ohms. Used for TV pickups, closed circuit TV, telephone carrier circuits, etc. video recording (magnetic tape) --The methods of recording data having a bandwidth in excess of 100 kHz on a single track. video signal -1. The picture signal in a television system-generally applied to the signal itself and the required synchronizing and equalizing pulses. 2. In television, the signal that conveys all of the intelligence present in the image, together with the necessary synchronizing and equalizing pulses. 3. That portion of the composite video signal that varies in gray-scale levels between reference white and reference black. Also referred to as the picture signal, this is the portion that can be seen. 4. The picture signal. A signal containing visud information and horizontal and vertical blanking. See also composite video signal. 5 . The output from a video graphics adapter incorporating the red (R), green (G), and blue (B) signals and the luminance signal, or combinations of these signals, that pass to the video input of a monitor. video stretching-In navigation, a procedure whereby the duration of a video pulse is increased. video synthesizer -A video analog computer that accepts standard video signals from a camera, film chain, videotape or graphics generator, which it then processes and applies a combination of effects to in order to reshape and add motions (animation) to fixed graphics or live scenes. videotape-A wide magnetic tape designed for recording and playing back a composite black and white or color television signal. videotape recorder- Abbreviated VTR. 1. A device that permits audio and video signals to be recorded on magnetic tape and then played back without any processing, as with films, on a CCTV monitor. 2. A device that translates the electrical signals of a VTR television camera into corresponding magnetic variations, which are recorded on magnetic tape; the original image can be displayed on a television receiver at a later time by reconversion of the magnetic variations, stored on the tape, into appropriate electrical signals.

videotape recording

- viscometer

v i d e o t a p e recording -Abbreviated VTR. A method of recording television picture and sound signals on tape for reproduction at some later time. videotex- 1. A system that links TV screens to mass databases through television or telephone-based communication channels. 2. A generic term for interactive services delivered to personal computers or adapted television sets in the home or office. 3. Technology that connects computerized text and graphics to a television screen via telephone lines. 4. A terminal-oriented communication network that links users’ equipment to a computer that maintains a database of information services. Videotex services include shop-at-home catalogs, listings of community events, and message forwarding. videotext system -A system for the widespread dissemination of textual and graphic information by wholly electronic means for display on low-cost terminals (often suitably equipped television receivers) under the selective control of the recipient using control procedures easily understood by untrained users. vidicon- 1. A camera tube in which a charge-density pattern is formed by photoconduction and stored on that surface of the photoconductor which is scanned by an electron beam, usually of low-velocity electrons. 2. A vacuum tube capable of changing light images into electrical voltage variations corresponding to the brightness of those images; a particular type of cathoderay pickup tube used in some video cameras. viewer- A software application that permits visual display of content. See also browser; player. viewfinder -An auxiliary optical or electronic device attached to a television camera so the operator can see the scene as the camera sees it. viewfinder monitor -See electronic viewfinder. viewing angle-The angle through which an LCD display has acceptable contrast. viewing area-The area of the CRT face that can be directly seen by the user. Its size is determined by the size of the CRT and the area covered by the face mask. viewing mirror-A mirror used in some television receivers to reflect the image formed on the screen of the picture tube at an angle convenient to the viewer. viewing screen-The face of a cathode-ray tube on which the image is produced. viewing time-The time during which a storage tube presents a visible output that corresponds to the stored information. Villari effect-A phenomenon in which a change in magnetic induction occurs when a mechanical stress is applied along a specified direction to a magnetic material having magnetostrictive properties. vinyl resin-A soft plastic used for making phongraph records. virgin tape-See raw tape. virtual address-In a computer, an immediate, or real-time, address. virtual cathode-An electron cloud that forms around the outer grid in a thermionic vacuum tube when the inner grid is maintained slightly more positive than the cathode. virtual circuit-In packet switching, a network facility that gives the appearance to the user of an actual end-to-end circuit; a dynamically variable network connection in which sequential data packets may be routed differently during the come of a virtual connection. Virtual circuits enable transmission facilities to be shared by many users simultaneously. virtual connection -A packet-switched data path betyeen two terminals that performs as if the two devices were linked by a switched circuit.

832

virtual height-1. The height of the equivalent reflection point that will cause a wave to travel to the ionosphere and back in the same time required for an actual reflection. In determining the virtual height, the wave is assumed to travel at uniform speed and the height is determined by the time required to go to the ionosphere and back at the assumed velocity of light. 2. The apparent height of a layer of the ionosphere. It is determined from the time interval between the transmitted signals and the ionospheric echo at vertical incidence (the radio wave penetrating the ionosphere perpendicular to it). virtual image-The optical counterpart of an object, formed at imaginary focuses by prolongations of light rays (e.g., the image that appears to be behind an ordinary mirror). virtual memory- 1. The use of techniques by which the computer programmer may use the memory as though the main memory and mass memory were available simultaneously. 2. A technique that permits the user to treat secondary (disk) storage as an extension of core memory, thus giving the virtual appearance of a larger core memory to the programmer. 3. A technique for managing a limited amount of high-speed memory and a (generally) much larger amount of lower-speed memory in such a way that the distinction is largely transparent to a computer user. The technique entails some means of swapping segments of program and data from the lowerspeed memory (which would commonly be a drum or disk) into the high-speed memory, where it would be interpreted as instructions or operated on as data. The unit of program or data swapped back and forth is called a page. The high-speed memory from which instructions are executed is real memory, while the lower-speed memory (drums or disks) is called virtual memory. 4. Any of several schemes in which the user-visible address space is divided into several subspaces, so that each of the subspaces in use can be placed anywhere in main memory. In some schemes, parts of the virtual memory may be on a mass-storage device. virtual PPI r e f l e c t o s c o p e -A device for superimposing a virtual image of a chart onto the PPI pattern. The chart is usually prepared with white lines on a black background to the scale of the PPI range scale. virtual reality- Abbreviated VR. 1. A technology that is computer generated and allows the user to interact with data that gives the appearance of a three-dimensional environment. The user can enter and navigate the 3D world portrayed as graphic images, and change viewpoints and interact with objects in that world as if inside that world. A virtual reality environment can be experienced using a headset and electronic gloves, or simply viewed on a monitor. 2. Sophisticated, multidimensional imaging systems and high-speed processing capabilities that create environments that users can interact with and manipulate directly. virtual storage-Storage space that may be viewed as addressable main storage, but is actually auxiliary storage (usually peripheral mass storage) mapped into read addresses; the amount of virtual storage is l i i t e d by the addressing scheme of the computer. virus- 1. A software program that attaches itself to another program in computer memory or on a disk, and spreads from one program to another. Viruses may damage data, cause the computer to crash, display messages, or lie dormant. 2. Any destructive self-replicating program. 3. A computer program written to secretly reproduce itself across many computer systems. V i s e s can cause serious software damage. viscometer- Also called a viscosimeter. A device for measuring the degree to which a liquid resists a change in shape.

833 viscosimeter -See viscometer. viscosity- 1. The frictional resistance offered by one part tor layer of a liquid as it moves past an adjacent part or layer of the same liquid. 2. The property of a liquid that resiists internal flow; measured in units of poise or centipoise. Low-viscosity materials are usually thin, while high-viscosity materials are thick. viscous and magnetic damping -Damping by virtue of the viscosity of a fluid around the sensing element or of a magnetic field. wiscous-dampened arm -A phonograph pickup a m mounted on a liquid cushion of oil, which provides high damping to eliminate arm resonances. It also protects the record groove and stylus; the arm does not fall on the record when dropped, but floats down gently. visibility factor- Also called display loss. Ratio of the minimum input-signal power detectable by ideal instruments connected to the output of a receiver to the minimum signal power detectable by a human operator through a display connected to the same receiver. The visibility factor may include the scanning loss. visible emission -Also called visible light. Radiation that is characterized by wavelengths of about 0.38 to 0.77 micrometer. visible light --Electromagnetic wavelengths that can be seen by the human eye, ranging from 380 to 770 nanometers. visible radiation-Radiation with wavelengths ranging from about 0.4 and 0.7 micrometer, corresponding to the visible spectrum of light. visible spectrum--That region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees. It extends from about 400 to about 750 nanometers in wavelengths of the radiation. v i s h - T h e series of processes in which luminous energy incident on the eye is perceived and evaluated. visual-aural range-Abbreviated VAR. A special type of VNF range providing a pair of radial lines of position that are reciprocal in bearing and are displayed to the pilot on a zero-center, left-right indicator. This facility also provides a pair of reciiprocal radial lines of position located 90" from the above visually indicated lines. These are presented to the pilot as aural A-N radio-range signals, which provide a means for differentiating between the two visually indicated lines (and vice versa). visuall carrier frequency -The frequency of the television carrier that is modulated by the picture information. aU communication -Communication by optical signs such as flags and lights. visualiization-Graphic representation of abstract data usually relayed in texl, and numbers. visual radio range--Abbreviated VRR. A radio range whose course is fiollowed by means of visual instruments. visuall scanner- I. A device that generates an analog OIC digital signal by optically scanning printed or written data. 2. See scanner, 2. visual signal device -A pilot light, annunciator, or other device that provides a visual indication of the iconditioni of the circuit or system being supervised. visual storage tube--An electron tube that stores and visually displays infomation by means of a cathoderay beam scanning and charge storage mechanism. visual telephony -The transmission of picture information (television) by means of telephone lines. visual transmitter- Also called a picture transmitter. In tel~evision,the radio equipment for transmission of the picture signals only.

visual transmitter power- The peak power output during transmission of a standard television signal. vitreous -1. Having the nature of glass. 2. A term used in ceramic technology to indicate fired characteristics approaching being glassy, but not necessarily totally glassy. vitreous binder-A glassy material used in compounds to bind other particles together. This takes place after melting the glass and cooling. vitrification- 1. The progressive reduction in porosity of a ceramic m a t e d as a result of heat treatment or some other process. 2. The reduction of porosity in a ceramic product through the formation of a glassy bond. VLF -Abbreviation for very low frequency. VLSl -Abbreviation for very large-scale integration. Generally considered to be an IC with more than 1000 gates. VLsl circuit- Abbreviation for very large-scale integrated circuit. See gate array, 3. VMOS -1. Abbreviation for V-groove metal-oxide silicon -a variation of MOS technology. A manufacturing process (called isotropically etched double-diffusion MOS process) based on the technique of using V-shaped grooves in the silicon wafer to provide a third-dimensional surface. This allows for a smaller chip geometry than the (older) process using a two-dimensional area technique of manufacture. With smaller geometry, the same diameter wafer can, theoretically, yield more chips (roughly 50 percent more) and thereby reduce the unit cost per chip considerably. The cost of processing a wafer generally remains constant no matter how many chips it contains. 2. Abbreviation for vertical MOS. A semiconductor device in which current travels vertically in the semiconductor chip. A cross section shows a four-layer diffusion consisting of n+ at the top (source), p as the channel, n- as the drift region, and n+ as the drain. The layers' dimensions are precisely controlled by diffusion processes. Unlike conventional bipolar transistors, VMOS devices exhibit high density because of their short channel spacing: 1 pn compared with bipolar devices typical 5 P.

SOURCE GATE

SOURCE

90,

H

EPITAXIAL

DRAIN

Structure

Symbol.

VMOS transistor.

VMOS power FET

- void

VMOS power FET- Abbreviation for vertical structured metal-oxide silicon power field-effect transistor. In these semiconductor devices, current flows vertically from source to drain. This structure results in high current densities, low saturation resistance, excellent heat dissipation and power handling capabilities, low chip capacitance, and excellent wideband performance. vocabulary-A list of operating codes or instructions available for writing the program for a given problem and for a specific computer. vocoder -Abbreviation for voice-operated coder. A device used to compress the frequency bandwidth requirement of voice communications. It consists of an electronic speech analyzer, which converts the speech waveform to several simultaneous analog signals, and an electronic speech synthesizer, which produces artificial sounds in accordance with analog control voltages. vodas -Abbreviation for voice-operated device, antising. A system for preventing the overall voice-frequency singing of a two-way telephone circuit by disabling one direction of transmission at all times. voder -Abbreviation for voice-operation demonstrator. An electronic device capable of artificially producing voice sounds. It uses active devices in connection with electrical filters controlled through a keyboard. vogad -Abbreviation for voice-operated gain-adjusting device. A voice-operated device used to give a substantially constant volume output for a wide range of inputs. voice activated (sound activated)-Refers to a bug that radiates radio frequencies or a recorder that is activated only when sound is present in target area. voice analyzer- An electronic instrument for printing out waveforms corresponding to vocal characteristics; an aid in identifying speech problems as well as speakers. voice channel -A transmission path suitable for carrying analog voice signals (covering a frequency band of 250 to 3400 Hz) between two points. voice coder-A device that converts a speech signal into digital form prior to encipherment for secure transmission, and converts the digital signals back into speech at the receiving point. voice coil-Also called a speaker voice coil. 1. A coil attached to the diaphragm of a dynamic speaker and moved through the air gap between the pole pieces. 2. The moving coil in a dynamic speaker. It is suspended in the field of a permanent magnet and is fixed to the speaker diaphragm. voice/data system -An integrated communications system for transmission of both voice and digital data signals. voice filter -A parallel-resonant circuit connected in series with a line feeding several speakers. Its purpose is to remove the tubbiness of the male voice. The frequency of resonance is adjusted somewhere between 125 and 300 Hz. voice frequency-Also called speech frequency. 1. Any of the frequencies within the band of 32 to 16,000 Hz that are audible to the human ear. 2. Any of the frequencies within the band of 300 to 3500 Hz that are normally used for telephone communication. voice-frequency carrier telegraphy-Carrier telegraphy in which the carrier currents have frequencies such that the modulated currents may be transmitted over a voice-frequency telephone channel. VOiCe-freqUeflCy dialing -A method of dialing by which the direct-current pulses from the dial are transformed into voice-frequency alternating-current pulses.

834 voice-frequency telegraph system - A telegraph system by which many channels can be carried on a single circuit. A different audio frequency is used for each channel and is keyed in the conventional manner. Each frequency is generated by an oscillator. At the receiving end, the various audio frequencies are separated by filter circuits and are fed to their respective receiving circuits. voice-frequencytelephony -Telephony in which the frequencies of the components of the transmitted electric waves are substantially the same as the frequencies of corresponding components of the actuating acoustical waves. voice grade -A telephone circuit suitable for transmitting a bandpass from 300 to approximately 2700 Hz, or greater, with certain standards of noise and interference such that intelligible speech can be transmitted. voice-grade channel-1. A channel suitable for the transmission of speech, digital or analog data, or facsimile, generally with a frequency range of about 300 to 3000 hertz. 2. A telephone circuit normally used for speech communication, accommodating frequencies from 300 to 3000 Hz. voice-grade circuit-A switched (dial-up) or leased (dedicated) telephone circuit suitable for the transmission of speech, digital or analog data, or facsimile. generally with a frequency range of about 300 to 3000 hertz. voice-grade line -A local telephone loop, or trunk, having a bandpass of approximately 300 to 3000 Hz. voice mail-Sophisticated telephone voice messages that are recorded and translated into digital bits for storage and manipulation. Voice mail systems use specialized hardware and software and can be incorporated into a PBX or used as stand-alone systems. voice-operated coder-See vocoder. voice-operated device-A device that permits the presence of voice or sound signals to affect a desired control. voice-operated device, antising - A system for preventing the overall voice-frequency singing of a twoway telephone circuit by disabling one direction of transmission at all times. Acronym: vodas. voice-operated gain-adjusting device-A voice-operated device used to give a substantially constant-volume output for a wide range of inputs. voice-operated loss control and suppressor-A voice-operated device that switches the loss out of the transmitting branch and inserts the loss into the receiving branch under control of the subscriber’s speech. voiceprint-A speech spectrograph sufficiently sensitive and detailed to identify individual human voices. Voice recognition-The conversion of spoken words into computer text. Speech is first digitized and then matched against a dictionary of coded waveforms. The matches are then converted into text as if the words were typed on the keyboard. voice-recognition equipment vocabulary size -The number of utterances (words or short phrases) that can be distinctly recognized and digitally encoded. The larger the vocabulary, the more complex the source data that can be handled without special software. voice spectrum -The total fundamental frequency range of the human voice. voice synthesis-Technology that produces sound or voices by processing compressed digital signals and storing them in a memory in the same manner a human voice generates sound processed by the vocal tract and other organs. void -The absence of substance in a localized area.

83.5 volatile-1, A computer storage medium in which information cannot be retained without continuous power dissipation. 2. Capable of evaporating. volatile memory- 1. In computers, any memory that can return information only as long as energizing power is applied. The opposite of nonvolatile memory. 2. A readwrite memory whose content is irretrievably lost when operating power is removed. Virtually all types of readlwrite semiconductor rnemories are volatile. See also nonvolatile memory. volatile storage- 1. A computer storage device in which the stored information is lost when the power is removed. 2. A storage medium in which data cannot be retained without continuous power dissipation (e.g., acoustic delay lines, electrostatics, capacitors). volatile store-A storage device in which stored data is lost when the applied power is removed (e.g., an acoustic delay line). woiatility-With respect to memory, an inability to retain stored data in the absence of external power. Voldilcon-The trade name of Adage, Inc., for a family of high-speed, all-semiconductor, current-balancing devices that use digital logic and readout for high-speed precision measurement of analog signals. volt-Letter symbol: V. 1. The unit of measurement of electromotive force. It is the difference of potential required to make a current of 1 ampere flow through a resistance of 1 ohm. 2. The difference of electric potential between two points of a conductor carrying a constant current of 1 ampere when the power dissipated between these points is equal to 1 watt. Volta effect-See contact potential. voltage- 1. Electrical pressure; Le., the force that causes current through m electrical conductor. 2. Symbolized by E. The greatest effective difference of potential between any two conductors of a circuit. 3. The term most often used in place of electromotive force, potential, potential difference, or voltage drop, to designak electric pressure that exists between two points and is capable of producing a flow of current when a closed\ circuit is connected between the two points. 4. Standard unit of magnitude of an electrical signal, named after Count A. Volta, inventor of the battery about 1800. woltage amplification -Also called voltage gain. E. Ratio of the voltage across a specified load impedance connected to a transducer to the voltage across the input of the transducer. 2. The ratio of the voltage at the input of a device to Uhe voltage at the output from the device, expressed in decibels. voltage amplifier- An amplifier used specifically to increase a voltage. It is usually capable of delivering only a small current. voltage-amplifier tube -A tube that is designed primarily as a voltage amplifier. It has high gain, but delivers very little output power. voltage and power idirectional relay-A device that pennits or causes the connection of two circuits when the voltage difference between them exceeds a given value in a predetermined direction, and causes these two circuits to be disconnected from each other when the power flowing between them exceeds a given value in the opposite direction. voltage attenuation -Ratio of the voltage across the input of a transducer to the voltage delivered to a specified load impedance connected to the transducer. voltage balance relay-A device that operates on a given difference in voltage between two circuits.

volatile - voltage-controlled oscillator voltage breakdown -1. The voltage necessary to cause insulation failure. 2. A rapid increase of current flow, from a relatively low value to a relatively high value, upon the application of a voltage to a pn junction or dielectric. voltage-breakdown test-A test whereby a specified voltage is applied between given points in a device to ascertain that no breakdown will occur at that specified voltage. voltage calibrator -Test equipment that supplies accurate ac voltages for comparison on a scope screen with other waveforms to determine their voltage level. voltage coefficient of capacitance-Also called voltage sensitivity. The quotient of the derivative with respect to voltage of a capacitance characteristic at a point divided by the capacitance at that point. voltage coefficient of resistivity-The maximum change in nominal resistance value due to the application of a voltage across a resistor, after correcting for self-heating effects; usually expressed in percent or per-unit (ppm) change in nominal resistance per volt applied. voltage comparator- 1. An amplifying device with a differential input that will provide an output polarity reversal when one input signal exceeds the other. When operating with open loop and without phase compensation, operational amplifiers make fast and accurate voltage comparators. 2. A circuit that compares two analog voltages and develops a logic output when the voltages being compared are equal or one is greater or less than the reference level. voltage control-A method of varying the magnitude of voltage in a circuit by means of amplitude control, phase control, or both. voltage-controlled capacitor -See vmactor. voltage-controlled crystal oscillator- A crystal oscillator whose operating frequency can be changed by applying a controlling voltage to introduce a phase shift in the oscillator circuit. voltage-controlled oscillator-Abbreviated VCQ. 1. Any oscillator for which a change in tuning voltage results in a predetermined change in output frequency. Frequency tuning is accomplished by either changing the bias voltage on a varactor diode in the frequencydetermining resonant network or the bias voltage to the active device. The former approach, although more complex than the latter method of tuning, is capable of multioctave bandwidth. 2. A circuit that creates an ac output signal whose frequency is a function of the dc input voltage. 3. An oscillator whose frequency can be changed by means of an external control voltage. It is commonly found in synthesizers.

Voltage-controlled oscillator.

voltage-controlled resistor

- voltage gradient

voltage-controlled resistor -Abbreviated VCR. A three-terminal variable resistor in which the resistance value between two of the terminals is controlled by a voltage potential applied to the third. voltage corrector-An active source of regulated power placed in series with the output of an unregulated supply. The voltage corrector senses changes in the output voltage (or current) and corrects for these changes automatically by varying its own output in the opposite direction so as to maintain the total output voltage constant. voltage/current crossover-The characteristic of a power supply that automatically converts the mode of operation of a power supply from voltage regulation to current regulation (or vice versa) as required by preset limits. The constant-current and constant-voltage settings are independently adjustable over specified limits. The region near the intersection of the constant-voltage and constant-current curves is designated by the term “crossover characteristics.” voltage-dependent resistor -Abbreviated VDR. Also called varistor or metal oxide varistor (MOV). A special type of resistor whose resistance changes appreciably, nonlinearly, and consistently in response to voltage across its terminals. voltage-directional relay-1. A relay that functions in conformance with the direction of an applied voltage. 2. A device that operates when the voltage across an open circuit breaker or contactor exceeds a given value in a given direction. voltage divider- Also called a potential divider. 1. A resistor or reactor connected across a voltage and tapped to make a fixed or variable fraction of the applied voltage available. See also potentiometer, 1; rheostat. 2. High-voltage resistance string, tapped resistor, potentiometer, adjustable resistors, or a series arrangement of two or more fixed resistors connected across a voltage source. Of the total voltage, a desired fraction is obtained from the intermediate tap, movable contact, or resistor junction.

I INPUT VOLTAGE

OUTPUT VOLTAGE

836

voltage drop -1. The difference in voltage between two points due to the loss of electrical pressure as a current flows through an impedance. 2. The voltage developed across the component or conductor by current through the resistance or impedance of that component or conductor. 3. The voltage developed between the terminals of a circuit component by current through the resistance or impedance of that part. See IR drop. 4. The decrease in voltage as a current traverses a resistance. 5. The voltage measured across a resistance through which a current is flowing. 6. The voltage existing across each element of a series circuit. (Also true of a contact in series with its load where a voltage drop also exists.) The voltage present across the load will be the line voltage less the voltage drops across each element in series with the load. voltage endurance -See corona resistance. voltage f e e d -Excitation of a transmitting antenna by applying voltage at a point of maximum potential (at a voltage loop or antinode).

/

- - \

I1

VOLTAGE

\

\

FEED LINE

ENDFED

/

VOLTAGE

‘.-- - -

1 1 [i!

Voltage feed.

voltage feedback-A form of amplifier feedback in which the voltage drop across part of the load impedance is put in series with the input-signal voltage.

Voltage divider.

voltage doubler -A voltage multiplier that rectifies each half cycle of the applied alternating voltage separately, and then adds the two rectified voltages to produce a direct voltage having approximately twice the peak amplitude of the applied alternating voltage.

VOLTS

DC =

2 x PEAK VOLTS AC

Voltage doubler.

Voltagefollower.

voltage f r e q u e n c y converter-A circuit that produces an output frequency that varies with the voltage applied to its input. voltage gain -See voltage amplification. voltage generator-A two-terminal circuit element with a terminal voltage independent of the current through the element. voltage gradient-The voltage per unit length along a resistor or other conductive path.

voltage inverter - voltage-regulator diode

837 voltage inverter-A circuit having a response (output) proportional to a constant (the gain) times the input signal, but opposite in sign to it. In a unity-gain inverter, the output is -1 times the input. voltage jump- An abrupt change or discontinuity in the tube voltage drop during operation of glow-discharge tubes. voltage level-Ratio of the voltage at any point in a transmission system to an arbitrary value of voltage used as a reference. In television and other systems where waveshapes are not sinusoidal or symmetrical about a zero axis and where the sum of the maximum positive and negative excursions of the wave is important in system performance, the two voltages are given as peak-to-peak values. This ratio is usually expressed in dBV, signifying decibels referred to 1 volt peak-topeak. voltage limit-A control function that maintains a voltage between predetermined values. voltage loop-A point of maximum voltage in a stationary-wave system. A voltage loop exists at the ends of a half-wave antenna. voltage loss-The voltage between the terminals of a current-measuring instrument when the applied current has a magnitude corresponding to nominal endscale deflection. In other instruments, the voltage loss is the voltage between the terminals at rated current. voltage-measuring equipment-Equipment for measuring the magnitude of an alternating or direct voltage. voltage multiplier-- 1. A rectifying circuit that produces a direct voltage: approximately equal to an integral multiple of the peak amplitude of the applied alternating voltage. 2. A series arrangement of capacitors charged by rapidly rotating brushes in sequence, giving a high direct voltage equal to the source voltage multiplied by the number of capacitors in series. 3. A precision resistor used in series with a voltmeter to extend its measuring range.

R 0

8

-0

Voltage multiplier.

voltage node-1. A point having zero voltage in a stationary-wave system (e.g., at the center of a half-wavc antenna). 2. In a transmission system having standing waves, a point at which the voltage is a minimum. voltage offset -The amount of dc voltage present at an (instnunentation) amplitier’s output with a 0-volt input. Initial offset may be adjusted to zero; however, offsetvoltage shifts during operation can cause errors. Systems containing microcomputers can often correct offset with an auto-zero cycle, or the offset can be removed by a control adjustment. voltage plane-A conductor or portion of a conductor layer on or in a printed board that is maintained at other than ground potential. It can also be used as a common voltage source for heat sinking or for shielding. woltage quadrupler - A rectifier circuit in which four diodes are employed to produce a dc voltage of four times the peak value of the ac input voltage. voltage-range multiplier -Also called an instrument multiplier. 1. A series resistor installed external to

DC

VOLTS OC

=

4 x PEAK VOLTS AC

Voltage quadqler. the measurement device to extend its voltage range. 2. A precision resistor placed in series with a voltmeter to enable measurement of a high voltage with a voltmeter having a lower voltage range. voltage rating-Also called the working voltage. 1. The maximum voltage that an electrical device or component can sustain without breaking down. 2. The maximum sustained voltage that can be safely applied to a capacitor up to a specified temperature without risking capacitor failure. 3. The maximum voltage at which a given device may be safely maintained during continuous use in a normal manner. voltage ratio (of a transformer) -Ratio of therms primary terminal voltage to the rms secondary terminal voltage under specified load conditions. voltage-ratio box-See measurement voltage divider. voltage reference- A highly regulated voltage source used as a standard to which the output voltage of a power supply is continuously compared for purposes of regulation. voltage-reference diode-A diode that develops across its terminals a reference voltage of specified accuracy when biased to operate within a specified current range. voltage-reference tube-A gas tube in which the voltage drop is essentially constant over the operating range of current and is relatively stable at fixed values of current and temperature. voltage reflection coefficient-The ratio of the complex electric field strength or voltage of a reflected wave to that of the incident wave. voltage-regulating transformer-A saturatedcore type of transformer that holds the output voltage to within a few percent, with input variations up to f 2 0 percent. Considerable harmonic distortion results unless extensive filters are employed. voltage regulation-A measure of the degree to which a power source maintains its output voltage stability under varying load conditions. voltage regulator- 1. A circuit that holds an output voltage at a predetermined value or causes it to vary according to a predetermined plan, regardless of normal input-voltage change or changes in the load impedance. 2. A gas-filled electronic tube that has the property of maintaining a nearly constant voltage across its terminals over a considerable range of current through the tube. It is used in an electronic voltage regulator. 3. An electronic circuit used for controlling and maintaining a voltage at a constant level. voltage-regulator diode-1. A diode that develops across its terminals an essentially constant voltage throughout a specified current range. 2. A diode that is

voltage-regulator tube

- voltmeter sensitivity

normally biased to operate in the breakdown region of its voltage-current characteristic and that develops across its terminals an essentially constant voltage throughout a specified current range. voltage-regulator tube- Also called a VR tube. A glow-discharge cold-cathode tube in which the voltage drop is essentially constant over the operating range of current, and which is designed to provide a regulated direct-voltage output.

R

T POWER DC FROM SUPPLY

@

OUTPUT

Voltage-regulator tube.

voltage relay-A relay that functions at a predetermined value of voltage. voltage saturation-See plate saturation. voltage-sensitive resistor-A resistor (e.g., a varistor) whose resistance varies with the applied voltage. voltage sensitivity- 1. The voltage that produces standard deflection of a galvanometer when impressed on a circuit made up of the galvanometer coil and the external critical-damping resistance. The voltage sensitivity is equal to the product of the current sensitivity and the total circuit resistance. 2. See voltage coefficient of capacitance. voltage spectrum-A function that is the square root of the spectral intensity; it is expressed in terms of voltage in a unit frequency band. gas-filled glowvoltage-stabilizing tube -A discharge tube normally working in that part of its characteristic where the voltage is practically independent of current drop within a given range. voltage standard -An accurately known voltage source (e.g., a standard cell) used for comparison with or calibration of other voltages. voltage standing-wave ratio-Abbreviated VSWR. In a stationary-wave system (such as in a waveguide or coaxial cable), the ratio of the amplitude of the electric field or voltage at a voltage maximum to that at an adjacent voltage minimum. voltage stress-That stress found within a material when subjected to an electrical charge. voltage-to-frequency converter -Abbreviated v/f converter. An electronic circuit that converts an input voltage into a train of digital output pulses at a rate that is directly proportional to the input. voltage to ground-The voltage between any live conductor of a circuit and earth (or common reference plane). voltage transformer-See potential transformer. voltage transients-Unpredictable and usually unavoidable spikes and surges of electrical power. voltage tripler -A rectifier circuit in which three diodes are employed to produce dc voltage equal to approximately three times the peak ac input voltage. voltage-tunable magnetron -A high-frequency continuous-wave oscillator operating in the microwave region. Power outputs begin in the milliwatts range and extend through hundreds of watts. voltage-tunable tube- An oscillator tube whose operating frequency can be changed by varying one or

838 more of its electrode voltages (e.g., a backward-wave magnetron). voltage-tuned cavity oscillator -Primarily a cavity oscillator with the addition of a varactor diode to slightly modify the cavity’s resonant frequency. These oscillators are capable of FM and/or phase-locking. voltage-tuned crystal oscillator-A crystalcontrolled oscillator with a varactor diode in the frequency-determining network that is used to slightly vary the crystal frequency. voltage-type telemeter-A telemeter in which the translating means is the magnitude of a single voltage. voltage-variable capacitance diode- Another name for varactor diode. voltage-variable capacitor-See varactor. voltage velocity limit -See slew rate, 2. voltaic cell -An electric cell having two electrodes of unlike metals immersed in a solution that chemically affects one or both of them, thus producing an electromotive force. The name is derived from Volta, a physicist who discovered this effect. voltaic couple-mo dissimilar metals in contact, resulting in a contact potential difference. voltaic pile -A voltage source consisting of alternate pairs of dissimilar metal discs separated by moistened pads, forming a number of elementary primary cells in series. volt-ammeter- An instrument calibrated to read both voltage and current. voltampere-Letter symbol: VA. A unit of apparent power in an ac circuit containing reactance. It is equal to the potential in volts multiplied by the current in amperes, without taking phase into consideration. voltamperehour meter- An electricity meter that measures the integral, usually in kilovoltamperehours, of the apparent power in the circuit where the meter is connected. voltampere loss- See apparent power loss. voltampere meter- An instrument for measuring the apparent power in an alternating-current circuit. Its scale is graduated in voltamperes or kilovoltamperes. voltampere reactive -Also called wattless power. Component of the apparent power in an altematingcurrent circuit that is delivered to the circuit during part of a cycle, but is returned to the source during another part of the cycle. The practical unit of reactive power is the var, equal to 1 reactive voltampere. Volta’s law-When two dissimilar conductors are placed in contact, the same contact potential is developed between them, whether the contact is direct or through one or more intermediate conductors. volt box-See measurement voltage divider. volt-electron -An obsolete expression for electronvolt. voltmeter-I. An instrument for measuring potential difference between two points. Its scale is usually graduated in volts. If graduated in millivolts or kilovolts, the instrument is usually designated as a millivoltmeter or a kilovoltmeter. 2. An instrument used for the measurement of electric voltage. The instrument may be of the electrostatic or tube type, but usually consists of a moving-coil ammeter connected in series with a high resistance. The resistance of the meter being fixed, the current passing through it will be directly proportional to the voltage at the points where it is connected; thus, the instrument can be calibrated in volts. voltmeter-ammeter-A voltmeter and an m e t e r combined into a single case, but with separate circuits. voltmeter sensitivity-The ratio, expressed in ohms per volt, of the total resistance of a voltmeter to its full-scale reading.

839 volt-ohm-milliammeter-A test instrument with several ranges, for measwhg voltage, current, and resistance. VOlUm&-Also called power level. I. The magnitude (measured on a standard volume indicator) of a complex audio-frequency wave, expressed in volume units. In addition, the term volume is used loosely to signify either the intensity of a sound or the magnitude of an audiofrequency wave. 2. The amount or a measure of energy in an electrical or acoustical train of waves. 3. -A physical unit of storage media; for example, a reel of magnetic tape. A volume may contain part of a file, a complete file, or more than one file. Sections of one or more files may be contained in a volume, but not multiple sections of the same file. 4. The level of an audio signal or the intensity of a sound. 5. A unit of secondary storage media, such as a magnetic tape, disk pack, or flexible diskette. volume bar-When activated, a TV feature that displays a volume setting bar on-screen, showing the adjustment being made whenever volume levels are adjusted. volunie compressioni--Also called automatic volume compression. The limiting of the volume range to about 30 to 40 decibels at the transmitter to permit a higher average percentage modulation without overmoddation. Also used in recording to raise the signal-to-noise ratio. volunie compressor -Audio-frequency control circuit that limits the volume range of a (radio) program at the transmitter to permit using a higher average percent modulation without risk of overmodulation. volume conductivity-See conductivity, I. volume control --A variable resistor for adjusting the loudness of a radio receiver or amplifying device. volume equivalent--A measure of the loudness of speech reproduced over a complete telephone connection. It is expressed numerically in terms of the trunk loss of a working reference system that has been adjusted to give equal loudness. volume expander- A circuit that provides volume expansion. vosolume e x p a n s i o n -See automatic volume expansion. volume indicator -An instrument for indicating the volume of a complex electric wave such as that corresponding to speech. v o l u m e lifetime -The average time interval between the generation and recombination of minority carriers in a homogeneous semiconductor. volume limiter-An amplifier whose gain is automatically reduced when lthe average input volume to the amplifier exceeds a predetermined value, so that the output volume is maintained substantially constant. The normal gain is restored whenever the input volume drops below the predetermined limit. volume-limiting amplifier- An amplifier that reduces the gain whenever the input volume exceeds a predetermined value, so that the output volume is maintained substantially constant. The normal gain is restored whenever the input volume drops below the predetermined limit. volume magnetostriction -The relative volume change of a body of ferromagnetic material when the magnetization of the hody is increased from zero to a specified value (usually saturation) under specified conditions. volume range-1. Of a transmission system, the difference, expressed in dB, between the maximum and minimum volumes that the system can satisfactorily handle. 2. Of a complex audio-fpequency signal, the

volt-ohm-milliammeter

-

difference, expressed in dB, between the maximum and minimum volumes occurring over a specified period. volume recombination rate-The rate at which free electrons and holes recombine within the volume of a semiconductor. v o l u m e resistance-Ratio of the dc voltage applied to two electrodes in contact with or embedded in a specimen to the portion of the current between them distributed through the specimen. volume resistivity- 1. Ratio of the potential gradient parallel to the current in a material to the current density. See also resistivity, 1. 2. Also called specific insulation resistance. The electrical resistance between opposite faces of a 1-cm cube of insulating material, commonly expressed in ohm-centimeters. 3. The resistance of a material to dc current as a measure of volume. Expressed in ohm-centimeters. volumetric displacement -The change in volume required to displace the diaphragm of a pressure transducer from its rest position to a position corresponding to the application of a stimulus equal to the rated range of the transducer. volumetric efficiency--Also called packing iactor. The ratio of parts volume to total equipment volume, expressed in percent. In modules, it is usually taken as the volume of component bodies only (not including leads, other interconnecting media, insnIators, heat sinks. and so on) and based on nominal sizes of components and nominal outside module dimensions. volumetric radar -A radar capable of producing three-dimensional position data on several targets. volumetric sensor-A sensor with a detection zone that extends over a volume such as an entire room, part of a room or a passageway. Ultrasonic motion detectors and sonic motion detectors are examples of voIumetric sensors. volume unit-Abbreviated vu. 1. The unit of transmission measurement for measuring the level of nonsteady-state currents. Zero level is the steady-state reference power of 1 milliwatt in a cirmit of 600 ohms characteristic impedance. 2. A measure of the power level of the voice wave. Zero volume unit is equivalent to +4 dBm for simple electrical waves (single frequencies). 3. An arbitrary sound-level standard related to the decibel and used for calibrating recording levels. volume-unit 'rndicator-Also called a vu indicator or volume-unit meter. An instrument calibrated to read audio-frequency power levels directly in volume wits. volume-unit meter -See vu meter. volume velocity-The rate ab which a medium flows through a specified area due to a sound wave. Von Hippel b r e a k d o w n theory- Also called lowenergy criterion. Breakdown occurs at fields for which the rate of recombination of electrons and positive holes is less than the rate of collisional ionization. Assumes no distribution in electron energies. VOR -Abbreviation for VHF omnirange. vortex amplifier- 1. A fluidic device in which the angular rate of a vortex is controlled to alter the output. 2. A fluidic amplifier using momentum interaction to produce stream rotation and consequent output modification. vowel articulation-The percent of articulation obtained when the speech units considered are vowels, usually combined with consonants into meaningless syllables. VR -See virtual reality. V-ring -In commutator construction. a specially shaped insulating structure having one or more V-shaped sections. VRR- Abbreviation for visual radio range. VR tube -Abbreviation for voltage-regulator tube.

VSWR

- vu meter

VSWR -Abbreviation for voltage standing-wave ratio. VTF -Abbreviation for vertical tracking force. VTL -Abbreviation for variable threshold logic. VTM -See voltage-tunable magnetron. VTR -Abbreviation for videotape recording or videotape recorder. VTVM -Abbreviation for vacuum-tube voltmeter. VU -Abbreviation for volume unit. vu indicator- Abbreviation for volume-unit indicator. vulcanized fiber- A dense, homogeneous, cellulosic material that has been partially gelantinized by swelling with a zinc chloride solution. It may be made in the form of sheets, rods, coils, or tubes, and it may be used for electrical insulation as well as in mechanical applications. VU meter- Abbreviation for volume-unit meter. 1. A volume indicator with a decibel scale and specified dynamic and other characteristics. It is used to obtain correlated readings of speech power necessitated by the rapid fluctuations in a level of voice currents. 2. Strictly, a recording-level meter whose indicator needle’s motion is damped according to a specified standard to allow it to respond at a certain speed to sudden impulses without

-

840

overshooting the mark by more than a certain amount. The term vu meter is loosely applied to practically any recording-level indicator that uses an indicator needle, 3. A type of recording-level indicator that shows average signal levels in decibels relative to a fixed O-dB reference level or in percent of maximum recommended modulation. The term is frequently used for any level meter using this scale, but it applies mostly to meters having a specified, standard degree of damping.

PROGRAM

600n VU METER

II

r-

--,-- -

75M)i-I-

vu meter.

7

n I1

W

W- 1. Letter symbol for watt. 2. Symbol for energy or work. wafer-1. A thin semiconductor slice of silicon or germanium with parallel faces on which matrices of microcircuits or individual semiconductors can be formed. After processing, the wafer is separated into dice or chips containing individual circuits. 2. A single section of a wafer switch. 3. Slice of semiconductor crystal material used as substrate for monolithic ICs, diodes, and transistors. 4. The thin slice of semiconductor crystal from which many hundreds or tlhousands of single monolithic device chips are ultimately obtained. Normally all techniques, such as epitaxy, photolithography, diffusion, and passivation, are carried out on the wafer before it is scribed and broken into individual dice. 5. A thin slice, typically 5 to 30 mils thick, sawed from a cylindrical ingot (boule) of bulk semiconductor material (silicon or gallium arsenide), 4 to 8 or more inches in diameter. Arrays of ICs or discrete devices are fabricated in the wafers during the manufacturing process. Thi: wafer is then tested, scribed, and broken apart to produce semiconductor chips. wafer and die sorters-Equipment that automates the testing and sorting of semiconductor devices from wafer form. wafer fabrication-me process of epitaxial growth, impurity diffusion, oxide deposition, and metallization that forms the semiconductor devices on the wafer. wafer-handling equipment--Equipment used for processing silicon wafers using methods that include batch processing in a common carrier, air-bearing singlewafer processing, and a combination of batch and singlewafer processing. wafer probing-An electrical test of devices on the wafer, utilizing tiny probes to make contact with the metallized pads on the die. wafer socket -A vacuum-tube socket that consists of two punched sheets or wafers of an insulating material, separated by spring-metal (clipsthat grip the terminal pins of the inserted tube. wafer switch-A rotary multiposition switch with fixed terminals on ceramic or Bakelite wafers. The rotor arm, in the center, is positioned by a shaft. Several decks may be stacked onto one switch and rotated by a common shaft.

Wagner ground-A bridge with an additional pair of ratio arms, onto which the ground connection to the bridge is moved in order to effect a perfect balance, free from error. WAIS-See wide area information service. wait-A computer system service that causes a task to be suspended for a specified time or pending the occurrence of an event. waiting time- 1. In certain tubes (e.g., thyratrons), the time that must elapse between the turning on of their heaters and the application of plate voltage. 2. See access time, 1. Waldo -Mechanical hands that function as an extension of human hands, such as those used to handle radioactive materials. Now a scientific reality, the idea was first used in Robert A. Heinkin’s classic story “Waldo,” from whence came the name. walkie-lookie -A compact, portable television camera used for remote broadcasts. The resultant electrical pulses are transmitted by microwave radio to a local control point for retransmission over a standard television station. walkie-talkie -1. A two-way radio communication set designed to be carried by one person, usually strapped to the back, and capable of being operated while in motion. 2. A hand-held transceiver.

-0

SECTION A-A

Walkie-talkie, 2.

Wafer switch.

841

w a l k test light

- watthour-demand meter

walk test light-A light on motion detectors that comes on when the detector senses motion in the area. It is used while setting the sensitivity of the detector and during routine checking and maintenance. walkthrough --Programming by giving a robot instructions one by one, with the robot executing each before receiving the next. The speed of the robot is increased when programming i s satisfactory. A teach box is usually used. wall-attachment amplifier- 1. A family of fluidic elements that make use of flow-created low-pressure regions, causing fluid to adhere to an amplifier wall in a controlled manner. 2. A fluidic device in which the control of the attachment of a stream to a wall@) (Coanda effect) alters the output. wall box-A metal box placed in the wall and containing switches, fuses, etc. wall outlet-A spring-contact device to which a portable lamp or appliance is connected by means of a plug attached to a flexible cord. The wall outlet is installed in a box and connected permanently to the power-line wiring of a home or building. walls-The sides of the groove in a disc record. Walmsley antenna -An array of vertical rectangular loops with a height of one wavelength and a spacing of one-half wavelength. The loops are arranged in parallel planes and are series fed at the centers of the longer, vertical sides, with appropriate transpositions of the feed lines. Walsh radiator-A type of speaker driver invented by Lincoln Walsh, in which a gently sloping cone, moving up and down, so displaces the air with its sloped sides as to radiate a cylindrical wavefront in a 360" horizontal circle. wamoscope -Abbreviation for a wave-modulated oscilloscope. A cathode-ray tube that includes detection, amplification, and display of a microwave signal in a single envelope, thus eliminating the local oscillator, mixer, IF amplifier, detector, video amplifier, and associated circuitry in a conventional radar receiver. Tubes are available for a range of 2 to 4 GHz. WAN-Abbreviation for wide area network. A network that serves an area of hundreds or thousands of miles, using common-carrier-provided lines. Contrast with LAN. wander -See scintillation, 2. warble-tone generator -An oscillator whose frequency is varied cyclically at a subaudio rate over a fixed range. It is usually used with an integrating detector to obtain an averaged transmission or crosstalk measurement. warm boot-Also called soft start or warm start. 1. Partial restarting of a computer under operating system control without turning it off and on again. 2. Resetting the computer while power is on. See also soft start. warm-up time-1. In an indirectly heated tube, the time that elapses, after the heater is turned on, before the cathode reaches its optimum operating temperature. 2. The time, following power application to a device, required for the output to stabilize within specifications. warning net -Communications system established for the purpose of disseminating warning information of enemy movement or action to all interested commands. w a s h o u t emitter process-A process used in the manufacture of semiconductor devices. It involves use of the same mask for both the emitter diffusion and the deposition of the ohmic contact. The aluminum metallization for the contact is permitted to form in the same hole that was used for the diffusion. waste instruction -See no-operation instruction. watch -See radio watch.

842

watchdog -In control systems, a combination of hardware and software that acts as an interlock scheme, disconnecting the system's output from the process in event of system malfunction. water-activated battery-A primary battery that contains the electrolyte but requires the addition of (or immersion in) water before it becomes usable. water-cooled tube-A vacuum tube having an anode structure projecting through the glass envelope and constructed to permit circulation of water around the anode for cooling purposes during operation. water load-A matched waveguide termination in which the electromagnetic energy is absorbed in water. The output power is calculated from the difference in temperature between the water at the input and output. waterproof motor-A totally enclosed motor so constructed that it will exclude water applied in the form of a stream from a hose. Leakage may occur around the shaft, provided it is prevented from entering the oil reservoir and provision is made for automatically draining the motor. The means for automatic draining may be a check valve, or a tapped hole at the lowest part of the frame that will serve for application of a drain pipe. WATS -Abbreviation for Wide Area Telephone Service. Also called 800 or 888 service. 1. A service provided by telephone companies in the United States that permits a customer to make calls to or from telephones in a specific nonlocal zone for a flat monthly charge. 2. A service that, among other things, allows people almost anywhere in the United States to call-without charge to them-a certain number. A familiar arrangement has a business paying monthly fees for a so-called 800 number that can be dialed by the public. In-WATS allows a central customer to call out. watt-Letter symbol: W. 1. A unit of the electric power required to do work at the rate of 1 joule per second. It is the power expended when 1 ampere of direct current flows through a resistance of 1 ohm. In an alternating-current circuit, the true power in watts is effective voltamperes multiplied by the circuit power factor. (There are 746 watts in 1 horsepower.) 2. A measure of electrical or acoustical power. The electrical wattage rating of an amplifier describes the power it can develop to drive a loudspeaker. Acoustical wattage describes the actual sound produced by a loudspeaker in the given environment. (The two figures, in any given amplifier-speaker system, are necessarily very widely divergent inasmuch as the low efficiency of speakers necessitates their receiving relatively large amounts of amplifier power in order to produce satisfactory sound levels.) wattage rating-1. The maximum power that a device can safely handle. 2. The maximum power that the resistor can dissipate, assuming a specific life, a standard ambient temperature, and a stated long-term drift from its no-load value. Increasing the ambient temperature or reducing the allowable deviation from the initial value (more-stable resistance value) requires derating the allowable dissipation. With few exceptions, resistors are derated linearly from full wattage at rated temperature to zero wattage at the maximum temperature. watthour-A unit of electrical work indicating the expenditure of 1 watt of electrical power for 1 hour. Equal to 3600 joules. w a t t h o u r capacity-The number of watthours delivered by a storage battery at a specified temperature, rate of discharge, and final voltage. watthour constant of a meter-The registration, expressed in watthours, corresponding to one revolution of the rotor. watthour-demand meter-A combined watthour meter and demand meter.

watthour meter - waveform generator

843 watthour meter-1. An electricity meter that measures and registers the integral, usually in kilowatthours, of the active power of the circuit into which the meter is connected. This power integral is the energy delivered to the circuit during the iintegration interval. 2. A totalizing meter that registers the total electrical energy used, usually in kilowatthours. wattless componeflt- A reactive component. wattless power-Se,e reactive power. watt !oss--See power loss, 2. wattmeter -An instrument for measuring the magnitude of the active power in an electric circuit. Its scale is usually graduated in watts. If graduated in kilowatts or megawatts, the instrument is usually designated as a kilowattmeter or megawattmeter. attsecond-The amount of energy corresponding to 1 watt acting for 1 second. It is equal to 1 joule. wattseco~dconstant of a meter-The registration, in wattseconds, corresponding to one revolution of the rotor. wave -I. A physical activity that rises and falls, or advances and retreats, periodically as it travels through a medium. 2. Propagated disturbance, usually periodic, such as a radio wave or sound wave. If the periodic motion is regular and recurring, it is said to be aperiodic or damped. wave amplitude -The maximum change from zero of the characteristic of a wave. wave analyzer -An electric instrument for measuring the amplitude and frequency of the various components of a complex current or voltage wave. wave angle-The angle at which a wave is propagated from one point to another. wave antenna- Also called a Beverage antenna. A directional antenna composed of a parallel horizontal conductor one-half to several wavelengths long, and terminated to ground in its characteristic impedance at the far and. wawe band- 1. A band of frequencies, such as that assigned to a particular type of communication service. nd of frequencies comprising an electrical wave. band switch --A multiposition switch for the frequency band tuned by a receiver or r. clutter-CClutte:r caused on a radar screen by echoes from sea waves. wave converter-A. device for changing a wave from on12pattern to another (e.g., baffle-plate, grating, and sheath-reshaping converters for waveguides). wave duct- 1. A tubular waveguide capable of concentrating the propagation of waves within it. 2. A natural duct formed in air by atmospheric conditions. Waves of certain frequencies travel through it with more than average efficiency. wave equation-An equation that gives a mathematical specification of a wave process or describes the performance of a medlium through which a wave is passing. wave filter-A transducer for separating waves on the basis of their frequency. It introduces a relatively small insertion loss to waves in one or more frequency bands, and a relatively large insertion loss to waves of other frequencies. See aZso filter, 1. wave fluxing-A wave solder fluxing method. Flux is applied using the liquid wave principle to form a double-sided parabolic wave. Washing action of the wave promotes flux coverage of the underside surfaces, while capillary forces promote t h - h o l e penetration. See also brush fluxing; foam fluxing; spray fluxing. waveform-1. The shape of an electromagnetic wave. 2. A graphical representation of the relationship

between voltage, current, or power against time. It also provides a picture of the behavior of signals at given frequencies. 3. A geometrical shape as obtained by displaying a characteristic voltage or current as a function of time. 4. The variations in magnitude and polarity of a current or voltage with respect to time, plotted in graphic form. I

I

DC WAVEFORM

1

I

SAWTOOTH WAVEFORM

RANDOM VARYING WAVEFORM

PERIODIC ALTESNATING WAVEFORM

Waveforms,2.

wavef orm-amplitude distortion-Sometimes called amplitnde distortion. Nonlinear waveform distortion caused by unequal attenuation or amplification between the input and output of a device. waveform analyzer- 1. An instrument that measures the amplitude and frequency of the components in a complex waveform. 2. A frequency-selective voltmeter that can be used to determine the frequency and amplitude of each sine-wave component of a complex wave. 3. An instrument that measures the amplitude of a waveform over a specific period, with resolution usually in the low nanosecond range. waveform digitization-The earliest approach taken for speech synthesis. The technique relies on sampling of the waveform in the time domain at twice the highest frequency of interest (this is known as the Nyquist rate). Critical to the use of this technique is data compression; otherwise, memory requirements are prohibitive. waveform encoding -A synthesis technique that reproduces speech by reconstructing the original speech waveform. waveform error- A change in measurement accuracy of an average-reading ac meter, occurring when the waveform of the measured voltage or current departs from a pure sine-wave form. waveform generator-Also called arbitrary waveform generator. 1. See timing-pulse distributor. 2. An instrumentation that does not necessarily employ mathematically derived relationships between the output voltage and the time base to produce its output waveshape. Most generators of this type develop an output that follows a waveshape drawn out or copied manually from some existing natural phenomenon (e.g., an EKG trace or the stress versus elongation curve from a pull-to-fracture test of a metal sample) or specified via keyboard entries. The waveform may also follow tracings made manually on an accompanying digitizer tablet.

waveform influence

- wavelength

waveform influence-The change in meter indication of the applied current and/or voltage caused solely by a change in waveform from a specified waveform. waveform monitor -1. An oscilloscope designed for viewing signal waveforms. 2. An oscilloscope designed especially for viewing the waveform of a video signal. waveform recorder -A general-purpose, waveform-capturing instrument with high-speed, high-resolution analog-to-digital converters and digital memory. waveform synthesizer -Equipment for generating a signal of a desired waveform. wavefront-1. With respect to a wave in space, a continuous surface at every point of which the displacement from zero in the positive or negative direction is the same at any instant. In a periodic wave, the displacements of the points on a wavefront are in phase. For a surface wave, the wavefront is a continuous line whose points have the same properties as do the points in the wavefront of a wave in space. 2. That part of a signal-wave envelope between the initial point of the envelope and the point at which the envelope reaches its crest. 3. For a field of electromagnetic energy emanating from a source, the wavefront is a surface connecting all field points that are equidistant from the source. 4. A surface at right angles to rays that proceed from the wave source. The surface passes through those parts of the wave that are in the same phase and travel in the same direction. For parallel rays, the wavefront is a plane; for rays that radiate from a point, the wavefront is spherical. wave function-In a wave equation, a point function that specifies the amplitude of a wave. waveguide- 1. A system of material designed to confine direct electromagnetic waves in a direction determined by its physical boundaries. 2. A transmission line comprising a hollow conducting tube (rectangular or tubular) within which electromagnetic waves are propagated on a solid dielectric or dielectric-filled conductor. waveguide attenuator -A waveguide device for producing attenuation by some means (e.g., by absorption and reflection). waveguide connector-Also called a waveguide coupling. A mechanical device for electrically joining parts of a waveguide system together. waveguide coupling -See waveguide connector. waveguide critical dimension -The dimension of waveguide cross section that determines the cutoff frequency. waveguide cutoff frequency- Also called the critical frequency. The frequency limit of propagation, along a waveguide, for waves of a given field configuration. waveguide dummy load-Sections of waveguide for dissipating all the power entering the input flange. waveguide elbow-A bend in a waveguide.

@ .::....... ,