1.The Illustrated Dictionary ofElectronics

2. This page intentionally left blank. 3. The Illustrated Dictionaryof Electronics Eighth EditionStan Gibilisco Editor-in-ChiefMcGraw-Hill New York Chicago San Francisco Lisbon London MadridMexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto 4. Cataloging-in-Publication Data is on file with the Library of Congress abc McGraw-Hill Copyright 2001 by The McGraw-Hill Companies, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permission of the publisher.1234567890 AGM/AGM0987654321P/N 0-07-137237-7ISBN 0-07-137236-9The sponsoring editor for this book was Scott Grillo, and the production supervisor was Pamela Pelton. It was set in Bookman by Techbooks.Printed and bound by Quebecor/Martinsburg.McGraw-Hill books are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. For more information, please write to the Director of Special Sales, McGraw-Hill, Two Penn Plaza, New York, NY 10121-2298. Or contact your local bookstoreInformation in this book has been obtained by the publisherfrom sources believed to be reliable. However, neither thepublisher nor the authors guarantee the accuracy or complete-ness of any information published herein. Neither the publishernor the authors shall be responsible for any errors, omissions, ordamages arising out of use of this information. This work is pub-lished with the understanding that the publisher and authorsare supplying information but are not attempting to render pro-fessional services in any way, shape or form. If such services arerequired, the assistance of an appropriate professional shouldbe sought. This book is printed on recycled, acid-free paper containing a minimum of 50 percent recycledde-inked fiber. 5. To Tony, Tim, and Samuelfrom Uncle Stan 6. This page intentionally left blank. 7. ContentsPreface ixAcknowledgments xiDictionary 1Appendix A Schematic Symbols 773Appendix B Tables and Data 787 Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use 8. This page intentionally left blank. 9. Preface The Illustrated Dictionary of Electronics8th Edition has been revised, clarified, and up-dated, reflecting technological advances of recent years. New definitions have been added inthe fields of wireless technology, robotics, and artificial intelligence. Every effort has beenmade to be concise and accurate, without talking down to the reader. Many definitions contain cross references (indicated in ALL CAPITALS); these providerecommended additional information or allow comparison with related terms. Expressions ofspecial significance are printed in italics. Electronics abbreviations are included in the text;the full terms are stated as definitions. While an effort has been made to avoid superfluous mathematics, equations are some-times necessary to completely and effectively define a term. Mathematics beyond the high-school level has not been used. Appendix A contains the standard symbols used in electrical and electronic diagrams.These symbols are used in illustrations throughout this dictionary. Appendix B contains thefollowing data tables:1. Conversion between electrical systems2. Greek alphabet3. Mathematical functions and operations4. Prefix multipliers5. Resistor color codeSuggestions for future editions are welcome. Stan GibiliscoEditor-in-Chief Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use 10. This page intentionally left blank. 11. Acknowledgments Illustrations in this book were generated with CorelDRAW. Some clip art is courtesy of CorelCorporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7. Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use 12. This page intentionally left blank. 13. The Illustrated Dictionary ofElectronics 14. This page intentionally left blank. 15. A 1. Symbol for GAIN. 2. Symbol for AREA. 3. Sym- Abbe condenser 1. In microscopy, a special two-bol for AMPERE (SI unit for current). piece lens that has enhanced light-gathering ASymbol for negative terminal of filament-voltagepower. 2. A similar focusing device in an electro-source in a vacuum-tube circuit.magnetic antenna. A Symbol for positive terminal of filament-voltageabbreviated dialing In telephone systems, specialsource in a vacuum-tube circuit.circuits requiring fewer-than-normal dialing op- a 1. Abbreviation of ATTO- (prefix). 2. Abbreviation erations to connect subscribers.of AREA. 3. Abbreviation of ACCELERATION.abc 1. Abbreviation of AUTOMATIC BASS COM-4. Abbreviation of ANODE. 5. Obsolete abbrevia- PENSATION, a system for boosting the volume oftion of cgs prefix AB-. bass sounds at low amplifier gain. 2. Abbrevi- aA 1. Abbreviation of attoampere. 2. Obsolete foration of AUTOMATIC BIAS CONTROL. 3. Abbrevi-ABAMPERE. ation of AUTOMATIC BRIGHTNESS CONTROL. AAAS Abbreviation for American Association for the 4. Abbreviation of AUTOMATIC BRIGHTNESSAdvancement of Science. COMPENSATION. AAC Abbreviation of automatic aperture controlabcoulomb The unit of electrical quantity in the(NASA). cgs electromagnetic system. One abcoulomb AAS Abbreviation of advanced antenna systemequals 10 coulombs and is the quantity of elec-(NASA). tricity that flows past any point in a circuit in one AASR Abbreviation of airport and airways surveil-second when the current is one abampere.lance radar. aberration 1. Distortion from perfect shape in a AB Abbreviation of acquisition beacon (NASA).lens or reflecting mirror or antenna dish. 2. A A-B In sound and acoustics, the direct comparisonsmall error in the determination of the directionof two sources of sound by alternately turning on of a source of electromagnetic energy, on accountone and the other.of the motion of the source and/or the detecting ab- 1. Prefix that transforms the name of a practi-apparatus. 3. A small displacement in the appar-cal electrical unit to that of the equivalent electro-ent positions of the stars from month to month onmagnetic cgs unit (e.g., ABAMPERE, ABOHM, account of the earths orbital motion.ABVOLT). See individual entries of such cgsABETS Acronym for airborne beacon electronic testunits. 2. Abbreviation for ABSOLUTE.set (NASA). abac A graphic device for the solution of electronics abfarad The unit of capacitance in the cgs electro-magnetic system. One abfarad equals 109 faradsproblems. Also see ALIGNMENT CHART. abampere The unit of current in the cgs electro- and is the capacitance across which a charge ofmagnetic system. One abampere equals 10 1 abcoulomb produces a potential of 1 abvolt.amperes and corresponds to 1 abcoulomb per abhenry The unit of inductance in the cgs electro-magnetic system. One abhenry equals 109 henrysecond. Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use 16. 2 abhenry absolute errorand is the inductance across which a currentthat changes at the rate of 1 abampere per sec-ond induces a potential of 1 abvolt. ABL Abbreviation of Automated Biology Laboratory(NASA). abmho The obsolete unit of conductance and ofconductivity in the cgs electromagnetic system.Replaced with ABSIEMENS. abnormal dissipation Power dissipation higher orlower than the customary level, usually an over-load. abnormal oscillation 1. Oscillation where none isdesired or expected, as in an amplifier. 2. Oscilla-tion at two or more frequencies simultaneouslywhen single-frequency operation is expected.3. Oscillation at an incorrect frequency. 4. Parasiticoscillation. abnormal propagation 1. The chance shifting ofabsence-of-ground searching selector A rotarythe normal path of a radio wave, as by displace-switch that searches for an ungrounded contactments in the ionosphere, so that reception is de- in a dial telephone system.graded. 2. Unintentional radiation of energy fromabsiemens The unit of conductance or conductiv-some point other than the transmitting antenna. ity in the cgs electromagnetic system. Oneabsiemens equals 109 siemens and is the3. Propagation over a path or in a direction notexpected. conductance through which a potential of 1 ab- abnormal reflections Sharp, intense reflections at volt forces a current of 1 abampere.frequencies higher than the critical frequency ofabsolute 1. A temperature scale in which zero repre-the ionospheres ionized layer. sents the complete absence of heat. Units of mea- abnormal termination The shutdown of a running sure are same as units on Celsius and Fahrenheitcomputer program or other process. Caused byscales. See ABSOLUTE SCALE. 2. Independent ofthe detection of an error by the associated hard- any arbitrarily assigned units of measure or value.ware that indicates that some ongoing series ofabsolute accuracy The full-scale accuracy of a me-actions cannot be executed correctly. ter with respect to a primary (absolute) standard. abnormal triggering The false triggering or switch- absolute address In a digital computer program,ing of a circuit or device, such as a flip-flop, by the location of a word in memory, as opposed tosome undesirable source instead of the true trigger location of the word in the program.signal. Electrical noise pulses often cause abnor- absolute code A computer code in which the exactmal triggering. address is given for storing or locating the refer- abohm The unit of resistance and of resistivity in ence operand.the cgs electromagnetic system. One abohmabsolute coding In computer practice, coding thatequals 109 ohms and is the resistance across uses absolute addresses.which a steady current of 1 abampere produces aabsolute constant A mathematical constant thatpotential difference of 1 abvolt. has the same value wherever it is used. abort To deliberately terminate an operation, ex- absolute delay The time elapsing between theperiment, process, or project before it has run its transmission of two synchronized signals fromnormal course.the same station or from different stations, as in AB power pack 1. A portable dry-cell or wet-cell radio, radar, or loran. By extension, the time in-array containing both A and B batteries in oneterval between two such signals from any source,package. 2. An ac-operated unit in one packageas from a generator.for supplying A and B voltages to equipment nor- absolute digital position transducer A digital po-mally operated from batteries.sition transducer whose output signal indicates abrasion machine An instrument for determining absolute position. (See ENCODER.)the abrasive resistance of a wire or cable.absolute efficiency The ratio Xx/Xs, where Xx is abrasion resistance A measure of the ability of athe output of a given device, and Xs is the outputwire or wire covering to resist mechanical dam- of an ideal device of the same kind under theage.same operating conditions. ABS A basic programming abbreviation for the ab-absolute encoder system A system that permitssolute value (of a number, variable, or expres- the encoding of any function (linear, nonlinear,sion).continuous, step, and so on) and supplies a non- abscissa 1. The independent variable in a function.ambiguous output.2. The axis (usually horizontal) on the graph of a absolute error The difference indicated by the ap-function that indicates the independent variable. proximate value of a quantity minus the actual 17. 3absolute error absolute tolerancevalue. This difference is positive when the ap-proximate value is higher than the exact value,and it is negative when the approximate value islower than the exact value. Compare RELATIVEERROR. absolute gain Antenna gain for a given orientationwhen the reference antenna is isolated in spaceand has no main axis of propagation. absolute humidity The mass of water vapor perunit volume of air. Compare RELATIVE HUMID-ITY. absolute instruction A computer instruction that absolute Peltier coefficient The product of thestates explicitly and causes the execution of aabsolute Seebeck coefficient and absolute tem-specific operation.perature of a material. absolute magnitude For a complex number quan-absolute pitch A tone in a standard scale, deter-tity, the vector sum of the real and imaginary mined according to the rate of vibration, indepen-components (i.e., the square root of the sum ofdent of other tones in the range of pitch.the squares of those components). Also see AB-absolute pressure Pressure (force per unit area) ofSOLUTE VALUE and IMPEDANCE.a gas or liquid determined with respect to that of absolute maximum rating The highest value a a vacuum (taken as zero).quantity can have before malfunction or damageabsolute-pressure transducer A transducer actu-occurs.ated by pressure from the outputs of two different absolute maximum supply voltage The highest pressure sources, and whose own output is pro-supply voltage that can be applied to a circuitportional to the difference between the two ap-without permanently altering its characteristics.plied pressures. absolute measurement of current Measurementabsolute scale 1. A scale in which the zero valueof a current directly in terms of defining quan- indicates the lowest physically possible value thattities. 1. TANGENT GALVANOMETER method:a parameter can attain. 2. A standard scaleCurrent is proportional to the tangent of the an-for measurement of a quantity. 3. A universallygle of deflection of the needle of this instrument.agreed-upon scale for the determination of a vari-Deflection depends on torque, resulting from the able quantity. 4. The Kelvin temperature scale.magnetic field produced by current in the gal- 5. The Rankine temperature scale.vanometer coil acting against the horizontalabsolute Seebeck coefficient The quotient, as ancomponent of the earths magnetic field. integral from absolute zero to the given tempera-2. ELECTRODYNAMOMETER method: With thisture, of the Thomson coefficient of a material di-2-coil instrument, current is determined fromvided by its absolute temperature.the observed deflection, the torque of the sus- absolute spectral response The frequency outputpension fiber of the movable coil, and the coil di-or response of a device in absolute power unitsmensions.(such as milliwatts) as opposed to relative units absolute measurement of voltage Measurement (such as decibels).of a voltage directly in terms of defining quan-absolute system of units A system of units intities. 1. CALORIMETRIC method: A current- which the fundamental (ABSOLUTE) units arecarrying coil immersed in water raises the those expressing length (l), mass (m), charge (q),temperature of the water. The difference ofand time (t). All other physical units, includingpotential that forces the current through the coil practical ones, are then derived from these abso-then is determined in terms of the equivalent heat lute units.energy. 2. Disk-electrometer method: In thisabsolute temperature Temperature measured onsetup, a metal disk attached to one end of a either the Kelvin or Rankine scales, where zerobalance beam is attracted by a stationary disk represents the total absence of heat energy.mounted below it, the voltage being applied to theabsolute temperature scale 1. The Kelvin temper-two disks. The other end of the beam carries a ature scale, in which the divisions are equal inpan into which accurate weights are placed. At size to 1 Celsius, and the zero point is absolutebalance, the voltage is determined in terms of the zero, the coldest possible temperature, approxi-weight required to restore balance, the upper-disk mately 273.16 Celsius. 2. The Rankine temper-area, and the disk separation. ature scale, in which the divisions are equal in absolute minimum resistance The resistance be-size to 1 Fahrenheit, and the zero point is abso-tween the wiper and the nearer terminal of a po- lute zero or approximately 459.7 Fahrenheit.tentiometer, when the wiper is as close to that absolute tolerance The value of a component as itterminal as physically possible. All potentiome- deviates from the specified or nominal value. It isters have two such specifications, one for eachusually expressed as a percentage of the specifiedend terminal.value. 18. 4 absolute units A-B test absolute units Fundamental physical units (seeinto heat or other forms of energy. 2. Loss of all orABSOLUTE SYSTEM OF UNITS) from which all part of a skywave because of absorption by theothers are derived. See, for example, AMPERE,ionosphere. Also called ionospheric absorption orOHM, VOLT, and WATT. atmospheric absorption. absolute value The magnitude of a quantity with- absorption marker A small blip introduced ontoout regard to sign or direction. The absolute valuean oscilloscope trace to indicate a frequencyof a is written |a|. The absolute value of a posi- point. It is so called because it is produced by thetive number is the number itself; thus, |10| action of a frequency-calibrated tuned trap, simi-equals 10. The absolute value of a negative num- lar to an absorption wavemeter.ber is the number with its sign changed: |-10|absorption modulation Amplitude modulation of aequals 10. transmitter or oscillator by means of an audio- absolute-value circuit A circuit that produces afrequency-actuated absorber circuit. In its simplestunipolar signal in response to a bipolar input and form, the modulator consists of a few turns of wirein proportion to the absolute value of the magni-coupled to the transmitter tank coil and con-tude of the input. nected to a carbon microphone. The arrangement absolute-value computer A computer in which absorbs energy from the transmitter at a varyingdata is processed in its absolute form; i.e., everyrate as the microphone changes its resistance invariable maintains its full value. (Compare to accordance with the sound waves it receives.INCREMENTAL COMPUTER.) absolute-value device In computer practice, a de-vice that delivers a constant-polarity outputsignal equal in amplitude to that of the inputsignal. Thus, the output signal always has thesame sign. absolutezero Thetemperature 273.16C( 459.7F and 0 Kelvin). The coldest possibletemperature, representing the complete absenceof heat energy. absorbed wave A radio wave that dissipates in theionosphere as a result of molecular agitation.This effect is most pronounced at low andmedium frequencies. absorptance The amount of radiant energy ab-absorption spectrum For electromagnetic waves, asorbed in a material; equal to 1 minus the trans- plot of absorption coefficient (of the medium ofmittance. propagation) versus frequency. Also called EMIS- absorption The taking up of one material or me- SION SPECTRUM.dium by another into itself, as by sucking orabsorption trap See WAVETRAP.soaking up. Also, the retention of one medium (orabsorption wavemeter A resonant-frequency indi-a part of it) by another medium, through which cating instrument that is inductively coupled tothe first one attempts to pass. See, for example, the device under test.ABSORBED WAVE, ABSORPTION COEFFI-CIENT, DIELECTRIC ABSORPTION. CompareADSORPTION. absorption band See ABSORPTION SPECTRUM. absorption circuit A circuit that absorbs energyfrom another circuit or from a signal sourcees-pecially a resonant circuit, such as a wavemeteror wavetrap. absorption current In a capacitor, the current re-sulting from absorption of energy by the dielectricmaterial. absorption dynamometer A power-measuring in-strument in which a brake absorbs energy from arevolving shaft or wheel. absorption fading Fading of a radio wave, result-ing from (usually) slow changes in the absorptionof the wave in the line of propagation. absorptivity In audio and microwave technologies, absorption frequency meter See WAVEMETER. a measure of the energy absorbed by a given vol- absorption line See ABSORPTION SPECTRUM.ume of material. absorption loss 1. Transmission loss caused by A-B test Comparison of two sounds by reproduc-dissipation of electrical energy, or conversion of iting them in alternating succession. 19. 5abvolt accentuation abvolt The unit of potential difference in the cgs acceleration at stall The angular acceleration of aelectromagnetic system. One abvolt equals 108 V servomotor at stall, determined from the stalland is the difference of potential between any two torque and the moment of inertia of the motorspoints when 1 erg of work is required to move 1rotor.abcoulomb of electricity between them.acceleration derivative Acceleration (a) expressed abwatt The unit of power in the cgs electromagnetic as the second derivative of distance (s) with re-system. One abwatt equals 10 7 W and is thespect to time (t): a equals d 2s/dt 2.power corresponding to 1 erg of work per second.accelerationpotential See ACCELERATING ac 1. Abbreviation of ALTERNATING CURRENT.VOLTAGE.2. Abbreviation of ATTITUDE CONTROL. 3. Ab- acceleration switch A switch that operates auto-breviation of AERODYNAMIC CENTER. 4. A suf-matically when the acceleration of a body tofix meaning AUTOMATIC CALCULATOR orwhich it is attached exceeds a predetermined rateAUTOMATIC COMPUTER.in a given direction. a/c 1. Abbreviation of AIRCRAFT. 2. Abbreviation acceleration time The time required by a com-of AIR CONDITIONING. puter to take in or deliver information after inter- Ac Symbol for ACTINIUM. preting instructions. Compare ACCESS TIME. ACA Abbreviation of automatic circuit analyzer.acceleration torque During the accelerating pe- ac base current Symbol, IB(ac). The ac component of riod of a motor, the difference between the torquebase current in a bipolar transistor.demanded and the torque actually produced by ac base resistance Symbol, RB (ac). The dynamic the motor.base resistance in a bipolar transistor.acceleration voltage The potential between accel- ac base voltage Symbol, VB(ac). The ac componenterating elements in a vacuum tube, the value ofof base voltage in a bipolar transistor. It is the acwhich determines average electron velocity.input signal voltage in a common-emitter ampli- accelerometer A transducer whose output voltagefier or emitter-follower amplifier.is proportional to the acceleration of the moving ac bias In a tape recorder, the high-frequency cur- body to which it is attached.rent that passes through the recording head toaccentuation The emphasis of a desired band oflinearize operation. frequencies, usually in the audio-frequency spec- acc 1. Abbreviation of AUTOMATIC CHROMI-trum.NANCE CONTROL. 2. Abbreviation of AUTO-MATIC COLOR COMPENSATION. 3. Abbreviationof ACCELERATION. ac cathode current Symbol, IK(ac). The ac compo-nent of cathode current in an electron tube. ac cathode resistance Symbol, RK(ac). The dynamiccathode resistance in an electron tube. RK(ac)equals dVK/dIK for a constant value of VG. ac cathode voltage Symbol, VK(ac). The ac compo-nent of cathode voltage in an electron tube. It isthe ac output signal voltage in cathode-followerand grounded-grid amplifiers. accelerated life test A test program that simu-lates the effects of time on devices or apparatus,by artificially speeding up the aging process. accelerated service test A service or bench test inwhich equipment or a circuit is subjected to anextreme condition in an attempt to simulate theeffects of average use over a long time. accelerating conductor or relay A conductor orrelay that prompts the operation of a succeedingdevice in a starting mode according to establishedconditions. accelerating electrode In a cathode-ray tube orklystron, the electrode to which the acceleratingvoltage is applied. accelerating time The elapsed time that startswhen voltage is applied to a motor, and endswhen the motor shaft reaches maximum speed. accelerating voltage A positive high voltage appliedto the accelerating electrode of a cathode-ray tubeto increase the velocity of electrons in the beam. 20. 6 accentuator accuracy rating accentuator A circuit or device, such as a filter, RC(ac) equals dVC/dIC for a constant value of basetone control, or equalizer, used to emphasize a current IB (in a common-emitter circuit) or emit-band of frequencies, usually in the audio-ter current IE (in a common-base circuit).frequency spectrum. Also see ACCENTUATION. ac collector voltage Symbol, VC(ac). The ac compo- acceptable-environmental-range test A test tonent of collector voltage in a bipolar transistor.disclose the environmental conditions that equip- The ac output signal voltage in a common-emitterment can endure while maintaining at least theor common-base amplifier.minimum desired reliability. accompanying audio channel The RF signal that acceptable quality level Abbreviation, AQL. A per- supplies television sound. Also called Cochannnelcentage that represents an acceptable average ofsound frequency.defective components allowable for a process, or ac component In a complex wave (i.e., one con-the lowest quality that a supplier is permitted totaining both ac and dc), the alternating, fluctu-regularly present for acceptance. ating, or pulsating part of the combination. acceptance sampling plan A probabilistic methodCompare DC COMPONENT.of sampling a quantity of units from a lot, and de-accordion A printed-circuit connector contact withtermining from the sample whether to accept the a Z-shaped spring that allows high deflectionlot, reject the lot, or perform another sampling. with low fatigue. acceptance test A test performed on incomingac-coupled flip-flop A flip-flop that is operated byequipment or on submitted samples to determinethe rise or fall of a clock pulse.if they meet testers or suppliers specifications.ac coupling Transformer coupling or capacitive acceptor 1. Any device or circuit, such as a series- coupling, which transmit ac, but not dc. Compareresonant circuit, that provides relatively easy DIRECT COUPLING.transmission of a signal, in effect accepting thesignal. 2. A hole-rich impurity added to a semi-conductor to make the latter p-type. It is so calledbecause its holes can accept electrons. CompareDONOR. acceptor circuit See ACCEPTOR, 1. acceptor impurity See ACCEPTOR, 2. access 1. To gain entrance to something, such asthe interior of the cabinet of a high-fidelity ampli-fier. 2. In a computer, the action of going to a spe-cific memory location for the purpose of dataretrieval. 3. A port or opening into a piece ofequipment, placed there to make the equipmenteasy to maintain and repair. access arm A mechanical device that positions theread/write mechanism in a computer storage unit. access control register A register that is part of acomputer protection system that prevents inter-ference between different software modules. access method A method of transferring informa-tion or data from main storage to an input/out-put unit. access right The access status given to computersystem users that indicates the method of accesspermitted (e.g., read a file only or write to a file). access time The time required by a computer tobegin delivering information after the memory or accumulator 1. In a digital computer, a circuit orstorage has been interrogated.register device that receives numbers, totals accidental error An unintentional error commit-them, and stores them. 2. Storage battery.ted by a person making measurements andaccuracy 1. Precision in the measurement ofrecording data. quantities and in the statement of physical char- accidental triggering The undesired chance-acteristics. 2. Degree of precision. Usually ex-operation of a flip-flop or other switching circuit pressed, in terms of error, as a percentage of thecaused by a noise pulse or other extraneous sig-specified value (e.g., 10 V plus or minus 1%), as anal.percentage of a range (e.g., 2% of full scale), or as ac collector current Symbol, IC(ac). The ac compo- parts (e.g., 100 parts per million).nent of collector current in a bipolar transistor. accuracy rating The maximum error in an instru- ac collector resistance Symbol, RC(ac). The dy-ment, given as a percentage of the full-scalenamic collector resistance of a bipolar transistor. value. 21. 7accw ac magnetic bias ac generator 1. A rotating electromagnetic ma- accw Abbreviation of ALTERNATING-CURRENTchine that produces alternating current (e.g., aCONTINUOUS WAVE.dynamo or alternator). 2. An oscillator or com- ac/dc Abbreviation of ALTERNATING CURRENT/bination of an oscillator and an output ampli-DIRECT CURRENT. Pertains to equipment thatfier.will operate from either ac utility power or a dc ac grid voltage Symbol, VG(ac). The ac componentpower source. A notebook computer is a good ex-of control grid voltage in an electron tube. The acample.input signal voltage in a common-cathode ampli- ac directional overcurrent relay A relay thatfier or cathode follower.works on a specific value of alternating overcur- A channel The left channel of a two-channel stereorent that is rectified for a desired polarity.system. ac drain current Symbol, ID(ac). The ac component achieved reliability A statement of reliability basedof drain current in a field-effect transistor.on the performance of mass-produced parts or ac drain resistance Symbol, RD(ac). The dynamicsystems under similar environmental conditions.drain resistance in a field-effect transistor; RD(ac)Also called OPERATIONAL RELIABILITY.equals dVD/dID for a constant value of gate volt- achromatic 1. Without color. In a TV image, theage VG.tones from black through gray to white. The term ac drain voltage Symbol, VD(ac). The ac componentoccasionally refers to black-and-white television,of drain voltage in a field-effect transistor. The acalthough MONOCHROMATIC is more often usedoutput signal voltage in a common-source FETin this sense.amplifier. achromatic locus Also called achromatic region. ac dump The removal of all ac power from a systemAn area on a chromaticity diagram that containsor component.all points, representing acceptable reference ac emitter current Symbol, IE(ac). The ac compo-white standards.nent of emitter current in a bipolar transistor. achromatic scale A musical scale without acci- ac emitter resistance Symbol, RE(ac). The dynamicdentals.emitter resistance of a bipolar transistor; RE(ac) ACIA Abbreviation of asynchronous communica-equals dVE/dIE for a constant value of base cur-tions interface adapter.rent IB (in an emitter-follower circuit) or collector acicular Pertaining to the shape of magnetic parti-voltage VCC (in a common-base circuit).cles on recording tape. Under magnification, ac emitter voltage Symbol, VE(ac). The ac compo-these particles look like thin rods.nent of emitter voltage in a bipolar transistor. The acid A substance that dissociates in water solutionac input signal voltage in a common-base ampli-and forms hydrogen (H) ions (e.g., sulfuric acid).fier; the ac output signal voltage in an emitter-Compare BASE, 2.follower amplifier. acid depolarizer Also called acidic depolarizer. ac equipment An apparatus designed for opera-An acid, in addition to the electrolyte, used intion from an ac power source only. Compare DCsome primary cells to slow the process of polar-EQUIPMENT and AC/DC.ization. ac erasing In tape recording, the technique of us- ac line A power line that delivers alternating cur-ing an alternating magnetic field to erase materialrent only.already recorded on the tape. ac line filter A filter designed to remove extrane- ac erasing head Also called ac erase head. In tapeous signals or electrical noise from an ac powerand wire recording, a head that carries alternat-line, while causing virtually no reduction of theing current to erase material already recorded onpower-line voltage or power.the tape or wire. Also see AC ERASING. ac line voltage The voltage commonly delivered acetate Cellulose acetate, a tough thermoplasticby the commercial power line to consumers. Inmaterial that is an acetic acid ester of cellulose. Itthe United States, the two standards are 117 Vis used as a dielectric and in the manufacture ofand 234 V (~ about 5 percent). The lower voltagephotographic films.is used by most appliances; the higher voltage is acetate base 1. The cellulose acetate film thatintended for appliances and equipment thatserved as the base for the magnetic oxide coatingdraws high power, such as electric ovens, cook-in early recording tape. Most such tapes todaying ranges, clothes dryers, and amateur-radioare of polyester base. 2. The cellulose acetateamplifiers. In Europe, 220 V is the commonsubstrate onto which certain photosensitive ma-standard.terials are deposited for lithographic reproduc- aclinic line Also called magnetic equator. An imag-tion. Also see ACETATE and ANCHORAGE.inary line drawn on a map of the world or of an acetate tape Recording tape consisting of a mag-area that connects points of zero inclination (dip)netic oxide coating on a cellulose acetate film.of the needle of a magnetic compass.Also see ACETATE BASE. ACM Abbreviation for Association for Computing ac gate voltage Symbol, VG(ac). The ac componentMachinery.of gate voltage in a field-effect transistor. The ac ac magnetic bias See AC BIAS.input signal voltage. 22. 8 ac meter acoustic feedback ac meter A meter that is intended to work only on quencies. If one fork is struck and then broughtalternating current or voltage. Such meters in-near the other, the second fork will begin vibrating.clude iron-vane and rectifier types. If the second fork has a fundamental frequency that is a harmonic of the frequency of the first fork, the second fork will vibrate at its own resonant frequency. See HARMONIC, RESONANCE.acoustic coupling Data transfer via a sound link between a telephone and a pickup/reproducer. Was once common in computer terminals and facsimile machines. This scheme has been largely replaced by hard wiring and optical coupling.acoustic damping The deadening or reduction of the vibration of a body to eliminate (or cause to die out quickly) sound waves arising from it.acoustic delay line Any equivalent of a special transmission line that introduces a useful time delay between input and output signals. In one form, it consists of a crystal block or bar with an ac noise 1. Electromagnetic interference originat- input transducer at one end and an output trans-ing in the ac power lines. 2. Electrical noise of a ducer at the other. An electrical input signal inrapidly alternating or pulsating nature. the first transducer sets up sound waves that ac noise immunity In computer practice, the abil- travel through the interior of the crystal; theity of a logic circuit to maintain its state, despite piezoelectric reaction of the crystal to sound vi-excitation by ac noise. brations sets up an output voltage in the second acous Abbreviation for ACOUSTIC. transducer. The delay is caused by the time re- acoustic Pertaining to audible sound distur- quired for the acoustic energy to travel the lengthbances, usually in air (versus audio-frequency of the crystal bar.currents or voltages). acoustic absorption The assimilation of energyfrom sound waves passing through or reflected bya given medium. acoustic absorption loss That portion of soundenergy lost (as by dissipation in the form of heat)because of ACOUSTIC ABSORPTION. acoustic absorptivity The ratio of sound energyabsorbed by a material to sound energy strikingthe surface of the material. acoustic attenuation constant The real-numbercomponent of the complex acoustical propagationconstant, expressed in nepers per unit distance. acoustic burglar alarm An alarm that receives theacoustic depth finder A direct-reading device fornoise made by an intruder. The alarm device re- determining the depth of a body of water, or forsponds to the impulses from concealed micro- locating underwater objects via sonic or ultra-phones. sonic waves transmitted downward and reflected acoustic capacitance The acoustic equivalent of back to the instrument.electrical capacitance.acoustic dispersion Variation of the velocity of acoustic clarifier In a loudspeaker system, a set of sound waves, depending on their frequency.cones attached to the baffle that vibrate to absorbacoustic elasticity 1. In a loudspeaker enclosure,and suppress sound energy during loud bursts. the compressibility of air behind the vibrating acoustic communication Communications by cone of the speaker. 2. In general, the compress-means of sound waves. This can be through the ibility of any medium through which soundatmosphere, or it can be through solids or liq- passes.uids, such as a taut wire, a body of water, or theacoustic electric transducer A transducer, suchearth. as a microphone or hydrophone, that converts acoustic compliance COMPLIANCE in acoustic sound energy into electrical energy. Comparetransducers, especially loudspeakers. It is equiv- ELECTRICAL/ACOUSTIC TRANSDUCER. Alsoalent to electrical capacitive reactance. see ACOUSTIC TRANSDUCER. acoustic consonance An effect that occurs whenacoustic feedback A usually undesirable effecttwo objects are near each other but not in physical that occurs when sound waves from a loud-contact, and both have identical or harmonically speaker (or other reproducer) reach a microphonerelated resonant frequencies. An example is shown (or other input transducer) in the same system.by two tuning forks with identical fundamental fre- 23. 9 acoustic feedback acoustic radiatorThis can cause an amplifier to oscillate, with a re-sultant rumbling, howling, or whistling. acoustic filter Any sound-absorbing or transmit-ting arrangement, or combination of the two, thattransmits sound waves of desired frequency whileattenuating or eliminating others. acousticfrequencyresponse Thesound-frequency range as a function of sound intensity.A means of describing the performance of anacoustic device. acoustic generator A device that produces soundwaves of a desired frequency and/or intensity.Examples are electrical devices (headphones or acoustic line Baffles or other such structuresloudspeakers operated from a suitable oscillator, within a speaker that act as the mechanical equiv-buzzer, bell, or flame) and mechanical devicesalent of an electrical transmission line to enhance(tuning forks, bells, string, or whistles). the reproduction of very low bass frequencies. acoustic grating A set of bars or slits that are par- acoustic load A device that serves simultaneouslyallel to one another and arranged a fixed distanceas the output load of an amplifier and as a trans-apart so that an interference pattern forms asducer of electrical energy into acoustic energysound passes through. Used to determine the (e.g., headphones or a loudspeaker).wavelength of acoustic waves.acoustic memory In a computer, a volatile mem- acoustic homing system 1. A system that uses a ory element employing an acoustic delay line, of-sound signal for guidance purposes. 2. A guid-ten incorporating quartz or mercury as theance method in which a missile homes in ontransmission and delay element.noise generated by a target. acoustic mirage A type of sound distortion in acoustic horn A tapered tube (round or rectangu- which the listener experiences the illusion of twolar, but generally funnel-shaped) that directssound sources when there is only one. The phe-sound and, to some extent, amplifies it. So callednomenon is caused by the effect of a large tem-to distinguish it from a microwave horn.perature gradient in the air or water through acoustic howl See ACOUSTIC FEEDBACK. which the sound passes. acoustician 1. A person skilled in acoustics (anacoustic mode Crystal-lattice vibration withoutacoustics technician). 2. An AUDIOLOGIST. producing an oscillating dipole. acoustic impedance Unit, ACOUSTIC OHM. Theacoustic noise Interferential (usually disagreeable)acoustic equivalent of electrical impedance. Like sounds carried by the air (or other propagationthe latter, acoustic impedance is the total opposi- medium) to the ear or to an acoustic transducer.tion encountered by acoustic force. Also like elec- This is in contrast to electrical noise, which con-trical impedance, acoustic impedance hassists of extraneous current or voltage impulsesresistive and reactive components: ACOUSTIC and is inaudible until converted into sound.RESISTANCE and ACOUSTIC REACTANCE. acoustic ohm The unit of acoustic resistance, re- acoustic inductance Also called inertance. The actance, or impedance. One acoustic ohm equalsacoustic equivalent of electrical inductance. the volume velocity of 1 cm/s produced by a acoustic inertance See ACOUSTIC INDUCTANCE.sound pressure of 1 microbar (0.1 Pa). Also called acoustic inhibition See AUDITORY INHIBITION. acoustical ohm. acoustic intensity See SOUND INTENSITY. acoustic phase constant The imaginary-number acoustic interferometer An instrument that eval- component of the complex acoustic propagationuates the frequency and velocity of sound waves constant expressed in radians per second or radi-in a liquid or gas, in terms of a standing wave set ans per unit distance.up by a transducer and reflector as the frequencyacoustic phase inverter A bass reflex loudspeakeror transducer-to-reflector distance varies. enclosure. acoustic labyrinth A loudspeaker enclosureacoustic pressure 1. The acoustic equivalent ofwhose internal partitions form a maze-like path electromotive force, expressed in dynes peror tube lined with sound-absorbing material.square centimeter; also called acoustical pres-The tube effectively runs from the back of thesure. 2. Sound pressure level.speaker down to where it terminates in a MOUTH acoustic propagation The transmission of soundor PORT that opens at the front of the enclosure. waves, or subaudible or ultrasonic waves, as aThe labyrinth provides an extremely efficient re- disturbance in a medium, rather than as an elec-production system because of its excellent acous- tric current or electromagnetic field.tic impedance-matching capability. acoustic radiator A device that emits sound acoustic lens A system of barriers that refracts waves. Examples are the cone of a loudspeaker,sound waves the way that an optical lens does the diaphragm of a headphone, and the vibratingwith light waves. reed of a buzzer. 24. 10 acoustic radiometer ac plate resistance acoustic radiometer An instrument for measuringacoustic scattering The spreading of a soundthe intensity of a sound wave (see SOUND IN- wave in many directions as a result of diffraction,TENSITY) in terms of the unidirectional steady-reflection, or refraction.state pressure exerted at a boundary as a resultacoustic suspension A loudspeaker design thatof absorption or reflection of the wave. allows exceptional low-frequency reproduction acoustic reactance Unit, ACOUSTIC OHM. Thefor a fairly small physical size. An airtight enclo-imaginary-number component of ACOUSTIC sure is used to increase the tension on theIMPEDANCE. It can take the form of ACOUSTICspeaker cone.CAPACITANCE or ACOUSTIC INDUCTANCE. acoustic system 1. A coordinated array of acous- acoustic reflectivity The ratio Fr/Fi, where Fr istic components (e.g., acoustic filters, resonators,the rate of flow of sound energy reflected from aetc.) that responds to sound energy in a predeter-surface and Fi is the rate of flow of sound energy mined manner. 2. An audio-frequency system inincident to the surface. which sound energy is converted into electrical acoustic refraction The deflection of sound waves energy, processed, and then reconverted intobeing transferred obliquely between media that sound energy for a clearly defined purpose.transmit sound at different speeds. acoustic telegraph A telegraph that gives audible acoustic regeneration See ACOUSTIC FEEDBACK.signals, as opposed to visual signals or printed acoustic resistance Unit, ACOUSTIC OHM. The messages.real-number component of ACOUSTIC IMPE- acoustic transducer 1. Any device, such as head-DANCE. The opposing force that causes acoustic phones or a loudspeaker, for converting audio-energy to be dissipated in the form of heat. It is frequency electrical signals into sound waves. 2.attributed to molecular friction in the medium Any device, such as a microphone, for convertingthrough which sound passes. See ACOUSTIC sound waves into alternating, pulsating, or fluc-OHM. tuating currents. acoustic resonance In an enclosed chamber with acoustic transmission The direct transmission ofwalls that reflect sound waves, resonance that oc- sound energy without the intermediary of electriccurs at certain wavelengths because the echoes currents.combine in and out of phase. Speaker enclosures acoustic transmission system A set of compo-almost always have resonance at certain frequen- nents designed to generate acoustic waves.cies. This effect can be used to an advantage whenacoustic transmissivity Also called acousticit is necessary to get good bass (low-frequency) transmitivity. The ratio et/ei, where et is theresponse from a relatively small speaker.sound energy transmitted by a medium, and ei is acoustic resonator 1. A chamber, such as a box, the incident sound energy reaching the surface ofcylinder, or pipe, in which an air column resonatesthe medium. Acoustic transmissivity is propor-at a particular frequency. 2. A piezoelectric, mag-tional to the angle of incidence.netostrictive, or electrostrictive body that vibrates acoustic treatment Application of sound-absorb-at a resonant audio frequency that is governed bying materials to the interior of an enclosure orthe mechanical dimensions of the body when anroom to control reverberation.audio voltage at that frequency is applied. acoustic wave The traveling vibration, consisting of molecular motion, via which sound is trans- mitted through a gas, liquid or solid. Usually refers to sound waves in air.acoustic wave filter See ACOUSTIC FILTER.acoustoelectric effect The generation of a voltage across the faces of a crystal by sound waves trav- eling longitudinally through the crystal.acoustoelectronics A branch of electronics con- cerned with the interaction of sound energy and electrical energy in devices, such as surface-wave filters and amplifiers. In such devices, electrically induced acoustic waves travel along the surface of a piezoelectric chip and generate electrical en- ergy. Also called praetersonics and microwave acoustics.ac plate current Symbol, IP(ac). The ac component of plate current in a vacuum tube. acoustics 1. The physics of sound. The study and ac plate resistance Symbol, RP(ac). The dynamicapplications of acoustic phenomena. 2. The qual- plate resistance of an electron tube. RP(ac) equalsities of an enclosure or sound chamber (room,dEP/dIP, where EP is the plate voltage and IP is theauditorium, or box) that describe how soundplate current, for a constant value for grid volt-waves behave in it.age EG. 25. 11 ac plate voltage active chord mechanism ac plate voltage Symbol, EP(ac). The ac component ac source voltage Symbol, VS(ac). The ac compo-of plate voltage in an electron tube. The ac out- nent of source voltage in a field-effect transistor.put-signal voltage in a common-cathode ampli- The ac output-signal voltage in a source-followerfier. (grounded-drain) FET amplifier. ac power Symbol, Pac. Unit, watt (W). The power acss Abbreviation of analog computer subsystem.acting in an ac circuit, Pac equals EI cos q, whereac time overcurrent relay A device with a certainE is in volts, I in amperes, and q is the phase an- time characteristic, which breaks a circuit whengle. Compare DC POWER. Also see POWER.the current exceeds a certain level. ac power supply A power unit that supplies ac actinic rays Short-wavelength light rays in the vi-only (e.g., ac generator, vibrator-transformer, os- olet and ultraviolet portion of the spectrum thatcillator, or inverter). Compare DC POWERgive conspicuous photochemical action.SUPPLY.actinism The property whereby radiant energy acquisition 1. The gathering of data from trans- (such as visible and ultraviolet light, X-rays, etc.)ducers or a computer. 2. Locating the path of ancauses chemical reactions.orbiting body for purposes of collecting teleme- actinium Symbol, Ac. A radioactive metallic ele-tered data. 3. Orienting an antenna for optimum ment. Atomic number, 89. Atomic weight, 227.pickup of telemetered data.actinodielectric Exhibiting a temporary rise in acquisition and tracking radar An airborne orelectrical conductivity during exposure to light.ground radar, which locks in on a strong signalactinoelectric effect The property whereby cer-and tracks the body that reflects (or transmits)tain materials (such as selenium, cadmium sul-the signal. fide, germanium, and silicon) change their acquisition radar A radar that spots an oncoming electrical resistance or generate a voltage on ex-target and supplies position data regarding the posure to light. Also see ACTINODIELECTRIC.target to a fire-control or missile-guidance radar,actinometer An instrument for measuring the di-which then tracks the target. rect heating power of the suns rays or the actinic acr 1. Abbreviation of AUDIO CASSETTE RE-power of a light source.CORDER. 2. Abbreviation of AUDIO CASSETTEaction current A small transient current thatRECORDING SYSTEM. flows in a nerve in the human body as a result of ac reclosing relay The controlling component instimulation.an alternating-current circuit breaker. It causesactivate To start an operation, usually by applyingthe breaker to reset after a specified period ofan appropriate enabling signal.time.activation 1. Supplying electrolyte to a battery cell ac relay A relay designed to operate on alternatingto prepare the cell for operation. 2. Causing thecurrent without chattering or vibrating.acceleration of a chemical reaction. ac resistance Pure resistance in an ac circuit. Un- activation time In the activation of a battery celllike reactance and impedance, which are also(see ACTIVATION, 1), the interval between addi-forms of opposition to the flow of current, ac re-tion of the electrolyte and attainment of full cellsistance introduces no phase shift. voltage. acronym A word formed from letters or syllables activator A substance added to an accelerator (seetaken from other applicable words of a multiwordACCELERATOR, 3) to speed the action of the ac-term. Acronyms are convenient for naming newcelerator.devices and processes in electronics. Usually, a active Pertaining to a circuit or device that re-term is considered an acronym only when it is quires a power supply for its operation. This dif-spelled in all-capital letters; once the term is ac-fers from a passive circuit or device, whichcepted and popularized, it is written as a conven-operates with no external source of power.tional word and is no longer thought of as anactive antenna An antenna that uses a smallacronym. For example, LASER was once an whip, loop, or ferrite loopstick with a high-gainacronym for light amplification by the stimulated amplifier for receiving at very-low, low, medium,emission of radiation. By the popularization pro- and high radio frequencies (approximately 9 kHzcess, the acronym became a conventional wordto 30 MHz).from which other terms (such as the verb lase) active area The forward-current-carrying portionwere derived. of the rectifying junction of a metallic rectifier. acrylic resin A synthetic resin used as a dielectricactive arm See ACTIVE LEG.and in electronic encapsulations. It is made fromactive balance In telephone repeater operation, theacrylic acid or one of its derivatives. sum of return currents at a terminal network bal- ACS Abbreviation of automatic control system.anced against the local circuit or drop resistance. ac source current Symbol, IS(ac). The ac componentactive chord mechanism Abbreviation, ACM. Inof source current in a field-effect transistor. robots, an electromechanical gripper capable of ac source resistance Symbol, RS(ac). The dynamic conforming to irregular objects. It has a structuresource resistance in a field-effect transistor; RS(ac)similar to the human spine, with numerousequals dVS/dIS for a constant value of VG.small, rigid links connected by hinges. 26. 12 active communications satellite active repair time active communications satellite A satellite con- active file A computer file in use (i.e., one that istaining receivers (which pick up beamed electro- being updated or referred to).magnetic signals from a ground point and amplifyactive filter A bandpass, bandstop, highpass orthem) and transmitters (which send signals backlowpass filter, consisting of resistors, capacitors,to the surface of the earth). Also called active and operational amplifiers, arranged to pass a de-comsat. Compare PASSIVE COMMUNICATIONS sired frequency response. Commonly used at au-SATELLITE. dio frequencies. active component 1. A device capable of some dy- active infrared detection Detection of infrarednamic function (such as amplification, oscilla-rays reflected from a target to which they weretion, or signal control) that usually requires a beamed.power supply for its operation. Examples includeactive jamming Transmission or retransmissionbipolar transistors, field-effect transistors, and of signals for the purpose of disrupting communi-integrated circuits. Compare PASSIVE COMPO-cations.NENT. 2. In an ac circuit, a quantity that con- active junction A pn junction in a semiconductortains no reactance so that the current is in phase device that has been created by a diffusion pro-with the voltage.cess. active component of current See ACTIVE CUR-active leg An element within a transducer thatRENT.changes one or more of its electrical characteris- active computer A computer in an installation ortics in response to the input signal of the trans-network that is processing data. ducer. Also called active arm. active comsat See ACTIVE COMMUNICATIONSactive lines In a U.S. television picture, the linesSATELLITE. (approximately 488) that make up the picture. active control system A device or circuit thatThe remaining 37 of the 525 available lines arecompensates for irregularities in the operatingblanked and are called INACTIVE LINES.environment.active material 1. In a storage cell, the chemical active current In an ac circuit, the current compo- material in the plates that provides the electricalnent that is in phase with the voltage. This is in action of the cell, as distinguished from the sup-contrast to reactive current, which is not in phaseporting material of the plates themselves. 2. A ra-with the voltage, and is inactive, with respect to dioactive substance. 3. The phosphor coating of apower in the circuit. The active current is equal to cathode-ray tube screen. 4. The material used tothe average power divided by the effective voltage.coat an electron-tube cathode. active decoder An automatic ground-station de- active mixer A signal mixer using one or more ac-vice that gives the number or letter designation oftive components, such as transistors or in-a received radio beacon reply code.tegrated circuits. An active circuit provides active device 1. An electronic component, such as a amplification, input-output isolation, and hightransistor that needs a power supply, and/or thatinput impedance, in addition to the mixing ac-is capable of amplifying. 2. Broadly, any device (in-tion. Compare PASSIVE MIXER.cluding electromechanical relays) that can switch active modulator A modulator using one or more(or amplify) by application of low-level signals.active components, such as transistors or inte- active electric network A network containing onegrated circuits. An active circuit provides gain,or more active devices or components, usuallyinput-output isolation, and high input impe-amplifiers or generators, in addition to passive dance, in addition to modulation. Compare PAS-devices or components. SIVE MODULATOR. active element The driven or RF-excited elementactive network See ACTIVE ELECTRIC NET-in a multielement antenna or antenna array.WORK.active pressure The electromotive pressure that produces a current in an ac circuit.active pull-up An arrangement using a transistor as a pull-up resistor replacement in an integrated circuit, providing low output impedance and low power consumption.active RC network 1. A resistance-capacitance (RC) circuit that contains active components (transistors or integrated circuits), as well as pas- sive components (capacitors and resistors). 2. An RC network in which some or all of the resistors and capacitors are simulated by the action of ac- tive components.active repair time The time during which mainte- nance is done on a system and the system is out of operation. 27. 13active satellite adapterily in the same physical location as the trueground surface (i.e., the earth itself ). An actualground can be an artificial ground plane, such asthat provided in some antenna structures. Actualground can also be modified by nearby rooftops,buildings, guy wiring, and utility wiring. actual height The highest altitude where radiowave refraction actually occurs. actual power Also called active or AVERAGEPOWER. Symbol, Pavg. In a resistive circuit undersine-wave conditions, average power is the prod-uct of the rms voltage and the rms current. It isalso equal to half the product of the maximumcurrent and maximum voltage. actuating device A device or component that oper-ates electrical contacts to affect signal transmis-sion. active satellite See ACTIVE COMMUNICATIONSactuating system 1. An automatic or manuallySATELLITE.operated system that starts, modifies, or stops an active sensor In an electronic security system, aoperation. 2. A system that supplies energy fortransducer that generates an electromagneticACTUATION.field or acoustic-wave field, and detects changesactuating time Also called actuation time. Thein the field resulting from the presence or move- time interval between generation of a control sig-ment of objects in the vicinity.nal, or the mechanical operation of a control de- active substrate In an integrated circuit, a sub-vice, and the resulting ACTUATION.strate consisting of single-crystal semiconductoractuation 1. The starting, modification, or termi-material into which the components are formed;nation of an operation or process. 2. Activation ofit acts as some or all of the components. This is ina mechanical or electromechanical switching de-contrast to a substrate consisting of a dielectric, vice.where the components are deposited on the sur- actuator An electromechanical device that usesface. electromagnetism to produce a longitudinal or ro- active system A radio and/or radar system that tary thrust for mechanical work. It is often therequires transmitting equipment to be carried inend (load) device of a servosystem.a vehicle. ACU Abbreviation of automatic calling unit. active tracking system A system in which aac voltage A voltage, the average value of which istransponder or responder on board a vehicle re- zero, that periodically changes its polarity. In onetransmits information to tracking equipment cycle, an ac voltage starts at zero, rises to a max-(e.g., azusa, secor). imum positive value, returns to zero, rises to a active transducer 1. A transducer that containsmaximum negative value, and finally returns toan active device, such as a transistor or inte- zero. The number of such cycles per second isgrated circuit, for immediate amplification of thetermed the ac frequency.sensed quantity. 2. A transducer that is itself an ac voltmeter See AC METER.active device. acyclic machine Also called ACYCLIC GENERA- active wire In the armature of a generator, a wire TOR. A dc generator in which voltage induced inexperiencing induction and, therefore, is deliver-the active wires of the armature is always of theing voltage.same polarity. activity 1. Intensity of, as well as readiness for, os- A/D Abbreviation for ANALOG-TO-DIGITAL. Seecillation in a piezoelectric crystal. 2. RadioactiveANALOG-TO-DIGITAL CONVERSION.intensity. 3. Intensity of thermal agitation. 4. Ada A microcomputer language designed primarilyThermionic emission of electrons. for use in multi-computer systems, where each activity ratio The ratio of active to inactive records small computer communicates with the others,in a computer file. providing some of the advantages of a larger com- ac transducer A transducer that either requires an puter.ac supply voltage or delivers an ac output sig-Adam A communications code word sometimesnaleven when operated from a dc supply.used for phonetic verbalizing of the letter A. More ac transmission The use of an alternating voltagecommonly, ALPHA is used.to transfer power from one point to another, usu-adapter 1. A fitting used to change either the ter-ally from generators to a distribution center, andminal scheme or the size of a jack, plug, or socketgenerally over a considerable distance. to that of another. 2. A fitting used to provide a actual ground The ground as seen by an an- transition from one type or style of conductor totenna. The actual ground surface is not necessar- another (e.g., waveguide to coaxial line). 3. An 28. 14 adapter address generation addend In a calculation, any number to be added to another. Compare AUGEND. addend register In a digital computer, the register that stores the addend. adder 1. In a digital computer, the device or circuit that performs binary addition. A HALF ADDER is a two-input circuit that can produce a sum out- put and a carry output, but it cannot accommo- date a carry signal from another adder. A FULL ADDER can accommodate a carry input, as well as two binary signals to be added. Also see ANA- LOG ADDER. 2. A circuit in a color TV receiver auxiliary system or unit used to extend the oper- that amplifies the receiver primary matrix signal. ation of another system (e.g., a citizens-bandadditive 1. The character or characters added to a adapter for a broadcast receiver).code to encipher it. 2. In a calculation, an item adaptive communication A method of communi- that is to be added. 3. An ingredient, usually in a cation that adjusts itself according to the particu-small quantity, added to another material to im- lar requirements of a given time. prove the latter in quality or performance. adaptive suspension vehicle Abbreviation, ASV.additive color A color formed by combining the A specialized robot that moves on mechanicalrays from two or three primary-colored lights legs, rather than on wheels. It generally has six onto a single neutral surface. For example, by legs and resembles an insect. It is designed to projecting a red and a green beam onto a neutral move over extremely irregular or rocky terrain, screen, a yellow additive color results. and to carry a human passenger. additive primaries Primary colors that form other adaptivity The ability of a system to respond to itscolors in a mixing of light (see ADDITIVE COLOR), environment by changing its performance char- but are not themselves formed by mixing other acteristics.additive primaries. For example, red, green, and adc Abbreviation of ANALOG-TO-DIGITAL CON-blue are the additive primaries used in color tele- VERTER. vision. Through appropriate mixing, these colors Adcock antenna A directional antenna system can be used to generate an unlimited variety of consisting of two vertical antennas, spaced inother colors. Compare SUBTRACTIVE PRI- such a way that the whole array behaves like aMARIES, which form the color spectrum by mix- loop antenna. Its members are connected and po- ing pigments rather than lights. In additive sitioned so that it discriminates against horizon-systems, each superimposed primary color in- tally polarized waves, and delivers output that iscreases the total light output from the reflecting proportional to the vector difference of signal volt- (viewing) surface; in subtractive systems, each su- ages induced in the two vertical arms.perimposed primary decreases the total reflectiv- ity. Thus, equal combination of additive primaries produces gray or white, and equal combination of subtractive primaries produces gray or black. addition record An extra data store created in a computer during processing. address 1. In computer operations, a usually nu- merical expression designating the location of material within the memory or the destination of such material. 2. The accurately stated location of information within a computer; a data point within a grid, matrix, or table; a station within a network. 3. In computer operations, to select the location of stored information. address comparator A device that ensures that Adcock direction finder A radio direction-finding the address being read is correct. system based on the directivity of the ADCOCK address computation In digital computer opera- ANTENNA.tions, the technique of producing or modifying Adcock radio range A radio range system withonly the address part of an instruction. four ADCOCK ANTENNAS situated at the cornersaddress field In a computer, the part of the in- of a square, and a fifth antenna at the center of struction that gives the address of a bit of data (or the square. a word) in the memory. add-and-subtract relay A stepping relay that canaddress generation The programmed generation be switched either uprange (add) or downrange of numbers or symbols used to retrieve records (subtract). from a randomly stored direct-access file. 29. 15address indirect adjusted decibels address indirect An address that specifies a stor-age location that contains another address. address memory The memory sections in a digitalcomputer that contain each individual register. address modification In computer operations,altering only the address portion of an instruc-tion; if the command or instruction routine isthen repeated, the computer will go to the newaddress. address part In a digital computer instruction, thepart of an expression that specifies the location.Also called ADDRESS FIELD. address register In a computer, a register in whichan address is stored. add/subtract time In a computer, the time re-quired to perform addition or subtraction, ex-cluding the time required to get the quantitiesfrom storage and to enter the sum or differenceinto storage.from the picture signal in the next higher chan- add time In computer operations, the time re- nel and the sound signal in the next lowerquired to perform addition, excluding the time re- channel.quired to get the quantities from storage and toadjacent-channel selectivity The extent to whichenter the sum into storage.a receiver or tuned circuit can receive on one a/d converter A device that changes an analog channel and reject signals from the nearest outly-quantity into a digital signal. See ANALOG-TO- ing channels.DIGITAL CONVERSION. adjacent sound channel In television, the radio- ADF Abbreviation of AUTOMATIC DIRECTION frequency (RF) channel containing the soundFINDER.modulation of the next lower channel. ADI Abbreviation of ALTERNATE DIGIT INVER- adjacent video carrier In television, the radio-SION.frequency (RF) carrier containing the picture adiabatic damping In an accelerator (see ACCEL- modulation of the next higher channel.ERATOR, 1), reduction of beam size as beam en-adjustable component Any circuit componentergy is increased. whose main electrical value can be varied at will adiabatic demagnetization A technique using a (e.g., a variable capacitor, inductor, resistor, ormagnetic field to keep a substance at a low tem- load).perature, sometimes within a fraction of a degree adjustable instrument 1. An instrument whoseof absolute zero.sensitivity, range, or response can be varied at adjacency A character-recognition condition inwill (e.g., multirange meter or wideband genera-which the spacing reference lines of two charac- tor). 2. An instrument that requires adjustmentters printed consecutively in line are closer than or manipulation to measure a quantity (e.g.,specified. bridge, potentiometer, or attenuator). adjacent- and alternate-channel selectivity Theadjustable motor tuning An arrangement that al-selectivity of a receiver or radio-frequency (RF)lows the motor tuning of a receiver to be confinedamplifier, with respect to adjacent-channel andto a portion of the frequency spectrum.alternate-channel signals. That is, the extent to adjustable resistor A wirewound resistor in whichwhich a desired signal is passed, and nearby un- the resistance wire is partially exposed to allowwanted signals are rejected. varying the components value. adjacent audio channel See ADJACENT SOUNDadjustable voltage divider A wirewound resistorCHANNEL. with terminals that slide on exposed resistance adjacent channel The channel (frequency band) wire to produce various voltage values.immediately above or below the channel of in- adjusted circuit A circuit in which leads that areterest.normally connected to a circuit breaker are adjacent-channel attenuation The reciprocal ofshunted so that current can be measured underthe selectivity ratio of a radio receiver. The selec-short-circuit conditions without breaker trip-tivity ratio is the ratio of the sensitivity of a re-ping.ceiver (tuned to a given channel) to its sensitivityadjusted decibels Noise level (in decibels) above ain an adjacent channel or on a specified numberreference noise level (designated arbitrarily asof channels removed from the original. zero decibels) measured at any point in a system adjacent-channel interference In television orwith a noise meter that has previously been ad-radio reception, the interference from stationsjusted for zero (at reference), according to specifi-on adjacent channels. A common form arises cations. 30. 16 admittance affirmative admittance Symbol, Y. Unit, siemens (formerlyaeronautical fixed service station A station thatmho). The property denoting the comparativeoperates in the aeronautical fixed service.ease with which an alternating current flowsaeronautical ground station A land station thatthrough a circuit or device. Admittance is the re- provides communication between aircraft andciprocal of impedance (Z ): Y = 1/Z. ground stations. adp 1. Abbreviation of AMMONIUM DIHYDROGEN aeronautical marker-beacon signal A distinctivePHOSPHATE, a piezoelectric compound used for signal that designates a small area above a beaconsonar crystals. 2. Abbreviation of AUTOMATIC transmitting station for aircraft navigation.DATA PROCESSING.aeronautical marker-beacon station A land sta- adsorption Adhesion of a thin layer of molecules of tion that transmits an aeronautical marker-one substance to the surface of another withoutbeacon signal.absorption. An example is adsorption of water toaeronautical mobile service A radio service con-the surface of a dielectric. This term is often con- sisting of communications between aircraft, andfused with ABSORPTION because the spellings of between aircraft and ground stations.the two words are almost identical. Compare AB- aeronautical radio-beacon station An aeronauti-SORPTION.cal radio-navigation land station that transmits adu Abbreviation of automatic dialing unit. signals used by aircraft and other vehicles to de- advanced-class license An amateur-radio license termine their position.conveying all operating privileges, except for a fewaeronautical radionavigation services Servicessmall bands that are allocated to extra-class li-provided by stations transmitting signals used incensees. The second-highest class of amateur li- the navigation of aircraft.cense.aeronautical radio service A service that encom- advance information Data published prior to the passes aircraft-to-aircraft, aircraft-to-ground,actual production or availability of a manufac-and ground-to-aircraft communications impor-tured component, circuit, or system. Advance in- tant to the operation of aircraft.formation is often only an approximate reflection aeronautical station A station on land, and occa-of the expected characteristics of a device. sionally aboard ship, operating in the aeronauti- advance wire A resistance wire used in thermo-cal mobile service.couples and precision applications. It is an alloy of Aeronautical Telecommunication Agency Thecopper and nickel, which has high resistivity andagency that administers the operation of stationsa negligible temperature coefficient of resistance.in the aeronautical radio service. aeolight A glow lamp using a cold cathode and aaeronauticaltelecommunications Collectively,mixture of inert gases. Because its illumination all of the electronic and nonelectronic communi-can be regulated with an applied signal voltage, itcations used in the aeronautical service.is sometimes used as a modulation indicator for aeronautical utility land station A ground sta-motion-picture sound recording.tion in an airport control tower that provides aerial See ANTENNA. communications having to do with the control of aerial cable A wire or cable run through the air, us- aircraft and other vehicles on the ground.ing support structures, such as towers or poles.aeronautical utility mobile station At an airport, aerodiscone antenna A miniature discone an- a mobile station that communicates with aero-tenna designed for use on aircraft.nautical utility land stations and with aircraft aerodynamics The science dealing with forces ex-and other vehicles on the ground.erted by air and other gases in motionespecially aerophare See RADIO BEACON.upon bodies (such as aircraft) moving through aerospace 1. The region encompassing the earthsthese gases. atmosphere and extraterrestrial space. 2. Per- aerogram See RADIOGRAM. taining to transport and travel in the earths at- aeromagnetic Pertaining to terrestrial magnetism, mosphere and in outer space. This includesas surveyed from a flying aircraft.aircraft, orbiting space vessels, and interplane- aeronautical advisory station A civil defense and tary spacecraft.advisory communications station in service forAES Abbreviation for Audio Engineering Society.the use of private aircraft stations. AEW Abbreviation of airborne (or aircraft) early aeronautical broadcasting service The special warning.service that broadcasts information regarding air aF Abbreviation of ATTOFARAD.navigation and meteorological data pertinent to AF Abbreviation of AUDIO FREQUENCY.aircraft operation. AFC 1. Abbreviation of AUTOMATIC FREQUENCY aeronautical broadcast station A station of the CONTROL. 2. Abbreviation of AUDIO-FRE-aeronautical broadcasting service. QUENCY CHOKE. aeronautical fixed service A fixed radio service affirmative In voice communications, a word oftenthat transmits information regarding air naviga- used for yesespecially when interference istion and flight safety.present or signals are weak. 31. 17AFIPS aircraft bonding AFIPS Acronym for American Federation of Infor- airborne intercept radar A type of short-rangemation Processing Societies.radar used aboard fighter and interceptor aircraft afpc Abbreviation of automatic frequency/phase for tracking their targets.control. airborne long-range input Equipment aboard air- AFSK Abbreviation of AUDIO-FREQUENCY-SHIFT craft, for the purpose of facilitating the use ofKEYING. long-range missiles. afterglow The tendency of the phosphor of a cath- airborne noise See ACOUSTIC NOISE.ode-ray-tube screen to glow for a certain time af- airborne radar platform Surveillance and alti-ter the cathode-ray beam has passed. Also see tude-finding radar used aboard aircraft.PERSISTENCE. air capacitor A capacitor in which air is the dielec- afterpulse An extraneous pulse in a multiplier tric between two sets of conductive plates. Alsophototube (photomultiplier), induced by a pre-called air-dielectric capacitor.ceding pulse.aircarrier aircraft station On an aircraft, a radio AF transformer See AUDIO-FREQUENCY TRANS-station that is involved in carrying people for hireFORMER. or in transporting cargo. a/g Abbreviation of AIR-TO-GROUND.air cell A primary electrochemical cell in which the AGC Abbreviation of AUTOMATIC GAIN CONTROL.positive electrode is depolarized by reduced oxy- AGE Abbreviation of AEROSPACE GROUND gen in the air.EQUIPMENT. air cleaner See DUST PRECIPITATOR. agent An active force, condition, mechanism, or air column The open space inside an acousticsubstance that produces or sustains an effect.chamber, pipe, or horn.Thus, a sudden voltage rise is a triggering agentair-cooled component A component, such as ain certain bistable circuits; arsenic is a doping power transistor, that is cooled by circulating air,agent in semiconductor processing; the slow cool- compared with one cooled by a circulating liquid,ing of a heated metal to improve ductility is ansuch as water or oil.ANNEALING AGENT. air-cooled transistor A transistor (particularly a aging 1. An initial run of a component or circuitpower transistor) from which the heat of opera-over a certain period of time shortly after manu- tion is drawn away, through radiation and con-facture to stabilize its characteristics and per- vection, into the surrounding air. The transistorformance. 2. The changing of electrical is usually mounted on a heatsink or fitted withcharacteristics or of chemical properties over afins.protracted period of time. air-cooled tube An electron tube from which heat agonic line An imaginary line connecting points on is drawn away, mainly via convection, into thethe earths surface at which a magnetic needlesurrounding air. A device called a chimney can beshows zero declination (i.e., points to true geo- placed around the tube, through which air isgraphic north). blown by a fan. Cool air enters through the bot- AGREE Acronym for Advisory Group on Reliabilitytom of the assembly, and hot air escapes from theof Electronics Equipment. top. Ah Abbreviation of AMPERE-HOUR. Depending onair-core inductor A coil of wire wound around athe standard used, the abbreviation can be amp- hollow cylindrical form or in a loop, designed tohr, a-h, a-hr, or A-h.introduce inductive reactance into a circuit or aH Abbreviation of ATTOHENRY.system. In practice, the maximum attainable in- aided tracking In radar and fire control, a system ductance is approximately 1 mH. This type of in-in which manual correction of target tracking er- ductor is used in some wireless transmitters,ror automatically corrects the rate of movement receivers, and antenna networks. The componentof the tracking mechanism.can be designed for high current-carrying capac- AIEE Abbreviation for American Institute of Electri- ity by using heavy-gauge wire and a large windingcal Engineers, now consolidated with the IRE, radius. The magnetic lines of flux extend consid-forming the IEEE. erably beyond the interior of the coil, especially AIP Abbreviation for American Institute of Physics.along the winding axis. This increases the likeli- air The mixture of gases that constitutes thehood of mutual inductance between the coil andearths atmosphere and figures prominently in surrounding electrical components, devices, orthe manufacture and operation of numerous circuits.electronic devices. By volume, air contains aboutair-core transformer A transformer without a fer-21 percent oxygen, 78 percent nitrogen, and romagnetic core, so called because air is the onlylesser amounts of argon, carbon dioxide, helium,material at the center of (and immediately sur-hydrogen, krypton, neon, and xenon. It also con-rounding) the transformer coils.tains varying amounts of water vapor, and in aircraft bonding The practice of solidly connect-smoggy areas, carbon monoxide and the oxides of ing, for electrical purposes, the metal parts of ansulfur and nitrogen.aircraft, including the engine. 32. 18 aircraft flutter airwaves aircraft flutter Rapid, repetitive fading and inten-sifying of a received radio or television signal, re-sulting from reflections of the signal by passingaircraft. aircraft station A nonautomatic radio communi-cations station installed on an aircraft. air-dielectric coax A special type of COAXIAL CA-BLE designed to have minimum loss. The spacebetween inner and outer conductors is mostlyempty (i.e., air-filled). Some such cables aresealed and filled with an inert gas. The inner con-ductor is held away from the inner wall of theouter conductor by beads, washers, or a spiral-wound filament of high-grade dielectric material,such as polyethylene.airport beacon A radio or light beacon that marks the location of an airport.airport control station A station that provides communications between an airport control air environment Pertaining to communicationstower and aircraft in the vicinity.equipment aboard aircraft.airport surveillance radar An air-traffic-control airflow The path or movement of air in, through, or radar that scans the airspace within about 60around an electronic device or piece of equip- miles (approximately 100 kilometers) of an air-mentespecially pertaining to an AIR-COOLEDport, and displays in the control tower the loca-COMPONENT. tion of all aircraft below a certain altitude and all air gap 1. A narrow space between two parts of aobstructions in the vicinity.magnetic circuit (e.g., the gap in the core of a fil- air-position indicator An airborne computer sys-ter choke). Often, this gap is filled with a non-tem that, using airspeed, aircraft heading, andmagnetic material, such as plastic, forelapsed time, furnishes a continuous indicationmechanical support. 2. The space between two orof the position of the aircraft. The indication ismore magnetically coupled or electrostatically affected by high-altitude winds. Comparecoupled components. 3. A device that gets itsGROUND-POSITION INDICATOR.name from the narrow gap between two smallair-to-air communication Radio transmissionmetal balls, needle points, or blunt rod tipsfrom one aircraft to another in flight. Com-therein. When an applied voltage is sufficiently pare AIR-TO-GROUND COMMUNICATION andhigh, a spark discharges across the gap. GROUND-TO-AIR COMMUNICATION. air/ground control radio station A station for air-to-ground communication Radio transmis-aeronautical telecommunications related to the sion from an aircraft in flight to a station locatedoperation and control of local aircraft. on the ground. Compare AIR-TO-AIR COMMUNI- air-insulated line 1. An open-wire feeder or trans- CATION and GROUND-TO-AIR COMMUNICA-mission line. Typically, the line consists of twoTION.parallel wires held apart by separators (bars orair-to-ground radio frequency The carrier fre-rods of high-grade dielectric material) situated atquency, or band of such frequencies, allocated forwide intervals. 2. AIR-DIELECTRIC COAX.transmissions from an aircraft to a ground sta- air-moving device A mechanical device, such as ation.specially designed fan or blower, used to facilitateairwaves 1. Radio waves. The term is slang, but isair cooling of electronic components.widely used. It probably came from the publics 33. 19airwaves aliasing noisemistaken notion that radio signals are propa-gated by the air. 2. Skywaves. Al Symbol for ALUMINUM. alabamine See ASTATINE. alacratized switch A mercury switch in which thetendency of the mercury to stick to the parts hasbeen reduced. alarm 1. An electronic security system. 2. A silentand/or audible alert signal transmitted by anelectronic security system when an intrusion oc-curs. 3. A silent and/or audible signal that in-forms personnel of the occurrence of anequipment malfunction. alarm circuit A circuit that alerts personnel to asystem malfunction, a detected condition, or anintruder. alarm condition 1. An intrusion or equipmentmalfunction that triggers an alarm circuit. 2. Theoperation of an alarm circuit that occurs in re-sponse to an intrusion or equipment malfunc-tion. alarm hold A device that keeps an alarm soundingonce it has been actuated. alarm output The signal sent from an alarm cir-cuit to a siren, buzzer, computer, or other exter-nal device to alert personnel to an ALARMCONDITION. alarm relay A relay that is actuated by an alarmdevice. A-law A form of companding law frequently used inEuropean electronics (the mu-law is more oftenused in North America). A nonlinear transferalgebraic adder In computer operations, an addercharacteristic in companding circuits. It can be that provides the algebraic sum, rather than thecontinuous, or can be a piecewise linear approxi-arithmetic sum, of the entered quantities.mation of a continuous function.algebraic operation A form of electronic calculator A-law companded Companding by means of an 8-operation, in which the keystrokes proceed in anbit binary code following the A-LAW, a specificintuitive sequence, following the way in which thecompanding function. calculation is written down. Compare REVERSE albedo For an unpolished surface, the ratio of re-POLISH NOTATION.flected light to incident light. It can vary from 0.0 algebraic sum The sum of two or more quantitiesto 1.0, or from 0 to 100 percent.with consideration of their signs. Compare albedograph An instrument for measuring the ARITHMETIC SUM.albedo of planets.algorithm A step-by-step procedure for solving a ALC Abbreviation of AUTOMATIC LEVEL CON-problem, (e.g., the procedure for finding theTROL.square root of a number). It can be expressed in a alerting device An audible alarm that includes aline-by-line instruction set or as a flowchart.self-contained solid-state audio oscillator. Pow- algorithmic language A computer language usedered from the ac line or a battery, the device pro-to describe a numeral or algebraic process.duces a raucous noise when actuated.alias A label that is an alternate term for items of Alexanderson antenna A very-low-frequency the same type; a label and several aliases can(VLF) and low-frequency (LF) vertically polarizedidentify the same data element in a computerantenna, designed to minimize ground losses in program.structures of manageable height. It usually con-aliasing 1. In analog-to-digital (A/D) conversion, asists of several wires, each quarter-wave reso-false output signal that results from a samplingnant with a loading coil, and all connectedrate that is too slow. Ideally, the sampling rate is attogether at the apex of a tower. The antenna isleast twice the highest input signal frequency. 2.fed between the ground and the base of one ofSawtooth-like irregularities, also called jaggies,the wires. which are sometimes introduced into a bit-mapped Alford antenna A loop antenna, in a square config-computer image when it is changed in size.uration, with the corners bent toward the centeraliasing noise A form of signal distortion causedto lower the impedance at the current nodes. by a signal with an excessive bandwidth. 34. 20 align alloy diode align 1. To adjust (i.e., to preset) the circuits of anAllen wrench A tool used to tighten or loosen an electronic system, such as a receiver, transmit-Allen screw. It is a hexagonal rod and is available ter, or test instrument, for predetermined re-in various sizes. sponse. 2. To arrange elements in a certain precise orientation and spacing, relative to each other, as in a Yagi antenna. 3. To orient antennas so that they are in line of sight, with respect to each other. alignment The process of ensuring that equip- ment, components, or systems are adjusted, both physically and electronically, for the most effi- cient possible performance. alignment chart A line chart for the simple solu- tion of electronic problems. It is so called because its use involves aligning numerical values on var- ious scales, the lines intersecting at the solution on another scale. Also called nomograph. alligator clip A spring-loaded clip with jagged alignment pin A pin or protruding key, usually inteeth, designed to be used for temporary electri- the base of a removable or plug-in component, to cal connections. ensure that the latter will be inserted correctlyallocate 1. To assign (especially through legisla- into a circuit. Often, the pin mates with a keyway,tion) operating frequencies or other facilities or notch, or slot.conditions needed for scientific or technical activ- alignment tool A specialized screwdriver ority; see, for example, ALLOCATION OF FRE- wrench (usually nonmagnetic) used to adjustQUENCIES. 2. In computer practice, to assign padder or trimmer capacitors or inductor cores.locations in the memory or registers for routines alive See LIVE.and subroutines. alkali See BASE, 2.allocated channel A frequency channel assigned alkali metals Metals whose hydroxides are basesto an individual or group. (alkalis). The group includes cesium, francium,allocated-use circuit 1. A circuit in which one or lithium, potassium, rubidium, and sodium.more channels have been authorized for the ex- alkaline battery 1. A battery composed of alkaline clusive use of one or more services. 2. A commu- cells and characterized by a relatively flat dis-nications link assigned to users needing it. charge curve under load. allocation of frequencies See RADIO SPECTRUM. alkaline cell A common non-rechargeable electro- allocator A telephone system distributor associ- chemical cell that employs granular zinc for ated with the finder control group relay assembly. the negative electrode, potassium hydroxide as It reserves an inactive line-finder for another call. the electrolyte, and a device called a polarizer asallophone A variation in the sound of a phoneme, the positive electrode. Produces approximately depending on what comes before and/or after the 1.5 volts under no-load conditions. The geometry phoneme in the course of speech. Important in of construction is similar to that of the zincspeech recognition and synthesis. There are 128 carbon cell, but it can deliver current effectivelydifferent phoneme variations in the English lan- at lower temperatures. Cells of this type have guage. See PHONEME. shelf lives longer than zinccarbon cells; they also alloter relay A telephone system line-finder relay have greater energy-storage capacity per unitthat reserves an inactive line-finder for the next volume, but they are more expensive than zinc incoming call from the line. carbon cells. They are used in calculators, tran-all