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The Illustrated Dictionary of Electronics—8th Edition has been revised, clarified, and up-
dated, reflecting technological advances of recent years. New definitions have been added in
the fields of wireless technology, robotics, and artificial intelligence. Every effort has been
made to be concise and accurate, without “talking down” to the reader.
Many definitions contain cross references (indicated in ALL CAPITALS); these provide
recommended additional information or allow comparison with related terms. Expressions of
special 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 the
following data tables:
1. Conversion between electrical systems
2. Greek alphabet
3. Mathematical functions and operations
4. Prefix multipliers
5. Resistor color code
Suggestions for future editions are welcome.
Illustrations in this book were generated with CorelDRAW. Some clip art is courtesy of Corel
Corporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7.
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
A Symbol for negative terminal of filament-voltage power. 2. A similar focusing device in an electro-
source in a vacuum-tube circuit. magnetic antenna.
A Symbol for positive terminal of filament-voltage abbreviated dialing In telephone systems, special
source 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 of
tion of cgs prefix AB-. bass sounds at low amplifier gain. 2. Abbrevi-
aA 1. Abbreviation of attoampere. 2. Obsolete for ation of AUTOMATIC BIAS CONTROL. 3. Abbrevi-
ABAMPERE. ation of AUTOMATIC BRIGHTNESS CONTROL.
AAAS Abbreviation for American Association for the 4. Abbreviation of AUTOMATIC BRIGHTNESS
Advancement of Science. COMPENSATION.
AAC Abbreviation of automatic aperture control abcoulomb The unit of electrical quantity in the
(NASA). cgs electromagnetic system. One abcoulomb
AAS Abbreviation of advanced antenna system equals 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 comparison small error in the determination of the direction
of two sources of sound by alternately turning on of a source of electromagnetic energy, on account
one 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 on
magnetic cgs unit (e.g., ABAMPERE, ABOHM, account of the earth’s orbital motion.
ABVOLT). See individual entries of such cgs ABETS Acronym for airborne beacon electronic test
units. 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 farads
problems. Also see ALIGNMENT CHART.
abampere The unit of current in the cgs electro- and is the capacitance across which a charge of
magnetic 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 10–9 henry
2 abhenry • absolute error
and is the inductance across which a current
that changes at the rate of 1 abampere per sec-
ond induces a potential of 1 abvolt.
ABL Abbreviation of Automated Biology Laboratory
abmho The obsolete unit of conductance and of
conductivity in the cgs electromagnetic system.
Replaced with ABSIEMENS.
abnormal dissipation Power dissipation higher or
lower than the customary level, usually an over-
abnormal oscillation 1. Oscillation where none is
desired or expected, as in an amplifier. 2. Oscilla-
tion at two or more frequencies simultaneously
when single-frequency operation is expected.
3. Oscillation at an incorrect frequency. 4. Parasitic
abnormal propagation 1. The chance shifting of absence-of-ground searching selector A rotary
the normal path of a radio wave, as by displace- switch that searches for an ungrounded contact
ments in the ionosphere, so that reception is de- in a dial telephone system.
graded. 2. Unintentional radiation of energy from absiemens The unit of conductance or conductiv-
some point other than the transmitting antenna. ity in the cgs electromagnetic system. One
absiemens equals 109 siemens and is the
3. Propagation over a path or in a direction not
expected. 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 of absolute 1. A temperature scale in which zero repre-
the ionosphere’s 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 Fahrenheit
computer program or other process. Caused by scales. See ABSOLUTE SCALE. 2. Independent of
the detection of an error by the associated hard- any arbitrarily assigned units of measure or value.
ware that indicates that some ongoing series of absolute 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 to
some 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 exact
mal 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 abohm absolute coding In computer practice, coding that
equals 10–9 ohms and is the resistance across uses absolute addresses.
which a steady current of 1 abampere produces a absolute constant A mathematical constant that
potential 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 the
periment, process, or project before it has run its transmission of two synchronized signals from
normal 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 one terval between two such signals from any source,
package. 2. An ac-operated unit in one package as 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 a the output of a given device, and Xs is the output
wire or wire covering to resist mechanical dam- of an ideal device of the same kind under the
age. same operating conditions.
ABS A basic programming abbreviation for the ab- absolute encoder system A system that permits
solute 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
absolute error • absolute tolerance
value. This difference is positive when the ap-
proximate value is higher than the exact value,
and it is negative when the approximate value is
lower than the exact value. Compare RELATIVE
absolute gain Antenna gain for a given orientation
when the reference antenna is isolated in space
and has no main axis of propagation.
absolute humidity The mass of water vapor per
unit volume of air. Compare RELATIVE HUMID-
absolute instruction A computer instruction that absolute Peltier coefficient The product of the
states explicitly and causes the execution of a absolute 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 of dent of other tones in the range of pitch.
the squares of those components). Also see AB- absolute pressure Pressure (force per unit area) of
SOLUTE 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 damage absolute-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 circuit portional to the difference between the two ap-
without permanently altering its characteristics. plied pressures.
absolute measurement of current Measurement absolute scale 1. A scale in which the zero value
of a current directly in terms of defining quan- indicates the lowest physically possible value that
tities. 1. TANGENT GALVANOMETER method: a parameter can attain. 2. A standard scale
Current is proportional to the tangent of the an- for measurement of a quantity. 3. A universally
gle 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 horizontal absolute Seebeck coefficient The quotient, as an
component of the earth’s magnetic field. integral from absolute zero to the given tempera-
2. ELECTRODYNAMOMETER method: With this ture, of the Thomson coefficient of a material di-
2-coil instrument, current is determined from vided by its absolute temperature.
the observed deflection, the torque of the sus- absolute spectral response The frequency output
pension fiber of the movable coil, and the coil di- or response of a device in absolute power units
mensions. (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 in
tities. 1. CALORIMETRIC method: A current- which the fundamental (ABSOLUTE) units are
carrying coil immersed in water raises the those expressing length (l), mass (m), charge (q),
temperature of the water. The difference of and time (t). All other physical units, including
potential 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 this absolute temperature Temperature measured on
setup, a metal disk attached to one end of a either the Kelvin or Rankine scales, where zero
balance beam is attracted by a stationary disk represents the total absence of heat energy.
mounted below it, the voltage being applied to the absolute temperature scale 1. The Kelvin temper-
two disks. The other end of the beam carries a ature scale, in which the divisions are equal in
pan into which accurate weights are placed. At size to 1° Celsius, and the zero point is absolute
balance, 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 it
terminal as physically possible. All potentiome- deviates from the specified or nominal value. It is
ters have two such specifications, one for each usually expressed as a percentage of the specified
end terminal. value.
4 absolute units • A-B test
absolute units Fundamental physical units (see into heat or other forms of energy. 2. Loss of all or
ABSOLUTE SYSTEM OF UNITS) from which all part of a skywave because of absorption by the
others are derived. See, for example, AMPERE, ionosphere. Also called ionospheric absorption or
OHM, VOLT, and WATT. atmospheric absorption.
absolute value The magnitude of a quantity with- absorption marker A small blip introduced onto
out regard to sign or direction. The absolute value an oscilloscope trace to indicate a frequency
of a is written |a|. The absolute value of a posi- point. It is so called because it is produced by the
tive 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 a
equals 10. transmitter or oscillator by means of an audio-
absolute-value circuit A circuit that produces a frequency-actuated absorber circuit. In its simplest
unipolar signal in response to a bipolar input and form, the modulator consists of a few turns of wire
in 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 varying
data is processed in its absolute form; i.e., every rate as the microphone changes its resistance in
variable maintains its full value. (Compare to accordance with the sound waves it receives.
absolute-value device In computer practice, a de-
vice that delivers a constant-polarity output
signal equal in amplitude to that of the input
signal. Thus, the output signal always has the
absolute zero The temperature –273.16°C
( 459.7°F and 0 Kelvin). The coldest possible
temperature, representing the complete absence
of heat energy.
absorbed wave A radio wave that dissipates in the
ionosphere as a result of molecular agitation.
This effect is most pronounced at low and
absorptance The amount of radiant energy ab-
absorption spectrum For electromagnetic waves, a
sorbed in a material; equal to 1 minus the trans-
plot of absorption coefficient (of the medium of
propagation) versus frequency. Also called EMIS-
absorption The taking up of one material or me-
dium by another into itself, as by sucking or
absorption trap See WAVETRAP.
soaking up. Also, the retention of one medium (or
absorption wavemeter A resonant-frequency indi-
a part of it) by another medium, through which
cating instrument that is inductively coupled to
the first one attempts to pass. See, for example,
the device under test.
ABSORBED WAVE, ABSORPTION COEFFI-
CIENT, DIELECTRIC ABSORPTION. Compare
absorption band See ABSORPTION SPECTRUM.
absorption circuit A circuit that absorbs energy
from another circuit or from a signal source—es-
pecially a resonant circuit, such as a wavemeter
absorption current In a capacitor, the current re-
sulting from absorption of energy by the dielectric
absorption dynamometer A power-measuring in-
strument in which a brake absorbs energy from a
revolving shaft or wheel.
absorption fading Fading of a radio wave, result-
ing from (usually) slow changes in the absorption
of 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 it ing them in alternating succession.
abvolt • accentuation
abvolt The unit of potential difference in the cgs acceleration at stall The angular acceleration of a
electromagnetic system. One abvolt equals 10–8 V servomotor at stall, determined from the stall
and is the difference of potential between any two torque and the moment of inertia of the motor’s
points when 1 erg of work is required to move 1 rotor.
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 the spect to time (t): a equals d 2s/dt 2.
power corresponding to 1 erg of work per second. acceleration potential 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 to
fix meaning AUTOMATIC CALCULATOR or which it is attached exceeds a predetermined rate
AUTOMATIC 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 torque
base 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 component erating elements in a vacuum tube, the value of
of base voltage in a bipolar transistor. It is the ac which determines average electron velocity.
input signal voltage in a common-emitter ampli- accelerometer A transducer whose output voltage
fier 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 to accentuation The emphasis of a desired band of
linearize 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. Abbreviation
ac cathode current Symbol, IK(ac). The ac compo-
nent of cathode current in an electron tube.
ac cathode resistance Symbol, RK(ac). The dynamic
cathode 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 is
the ac output signal voltage in cathode-follower
and 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 in
which equipment or a circuit is subjected to an
extreme condition in an attempt to simulate the
effects of average use over a long time.
accelerating conductor or relay A conductor or
relay that prompts the operation of a succeeding
device in a starting mode according to established
accelerating electrode In a cathode-ray tube or
klystron, the electrode to which the accelerating
voltage is applied.
accelerating time The elapsed time that starts
when voltage is applied to a motor, and ends
when the motor shaft reaches maximum speed.
accelerating voltage A positive high voltage applied
to the accelerating electrode of a cathode-ray tube
to increase the velocity of electrons in the beam.
6 accentuator • accuracy rating
accentuator A circuit or device, such as a filter, RC(ac) equals dVC/dIC for a constant value of base
tone 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 to nent of collector voltage in a bipolar transistor.
disclose the environmental conditions that equip- The ac output signal voltage in a common-emitter
ment can endure while maintaining at least the or 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 Cochannnel
centage that represents an acceptable average of sound 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 to taining both ac and dc), the alternating, fluctu-
regularly present for acceptance. ating, or pulsating part of the combination.
acceptance sampling plan A probabilistic method Compare DC COMPONENT.
of sampling a quantity of units from a lot, and de- accordion A printed-circuit connector contact with
termining from the sample whether to accept the a Z-shaped spring that allows high deflection
lot, reject the lot, or perform another sampling. with low fatigue.
acceptance test A test performed on incoming ac-coupled flip-flop A flip-flop that is operated by
equipment or on submitted samples to determine the rise or fall of a clock pulse.
if they meet tester’s or supplier’s specifications. ac coupling Transformer coupling or capacitive
acceptor 1. Any device or circuit, such as a series- coupling, which transmit ac, but not dc. Compare
resonant circuit, that provides relatively easy DIRECT COUPLING.
transmission of a signal, in effect accepting the
signal. 2. A hole-rich impurity added to a semi-
conductor to make the latter p-type. It is so called
because its holes can accept electrons. Compare
acceptor circuit See ACCEPTOR, 1.
acceptor impurity See ACCEPTOR, 2.
access 1. To gain entrance to something, such as
the 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 data
retrieval. 3. A port or opening into a piece of
equipment, placed there to make the equipment
easy to maintain and repair.
access arm A mechanical device that positions the
read/write mechanism in a computer storage unit.
access control register A register that is part of a
computer 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-
access right The access status given to computer
system users that indicates the method of access
permitted (e.g., read a file only or write to a file).
access time The time required by a computer to
begin delivering information after the memory or accumulator 1. In a digital computer, a circuit or
storage 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 and accuracy 1. Precision in the measurement of
recording 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 the
caused by a noise pulse or other extraneous sig- specified value (e.g., 10 V plus or minus 1%), as a
nal. 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-scale
namic collector resistance of a bipolar transistor. value.
accw • ac magnetic bias
ac generator 1. A rotating electromagnetic ma-
accw Abbreviation of ALTERNATING-CURRENT
chine that produces alternating current (e.g., a
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 that
will operate from either ac utility power or a dc
ac grid voltage Symbol, VG(ac). The ac component
power source. A notebook computer is a good ex-
of control grid voltage in an electron tube. The ac
input signal voltage in a common-cathode ampli-
ac directional overcurrent relay A relay that
fier or cathode follower.
works on a specific value of alternating overcur-
A channel The left channel of a two-channel stereo
rent that is rectified for a desired polarity.
ac drain current Symbol, ID(ac). The ac component
achieved reliability A statement of reliability based
of drain current in a field-effect transistor.
on the performance of mass-produced parts or
ac drain resistance Symbol, RD(ac). The dynamic
systems 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, the
tones from black through gray to white. The term
ac drain voltage Symbol, VD(ac). The ac component
occasionally refers to black-and-white television,
of drain voltage in a field-effect transistor. The ac
although MONOCHROMATIC is more often used
output signal voltage in a common-source FET
in this sense.
achromatic locus Also called achromatic region.
ac dump The removal of all ac power from a system
An area on a chromaticity diagram that contains
all points, representing acceptable reference
ac emitter current Symbol, IE(ac). The ac compo-
nent of emitter current in a bipolar transistor.
achromatic scale A musical scale without acci-
ac emitter resistance Symbol, RE(ac). The dynamic
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 solution
ac 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.
acid depolarizer Also called acidic depolarizer.
ac equipment An apparatus designed for opera-
An acid, in addition to the electrolyte, used in
tion from an ac power source only. Compare DC
some primary cells to slow the process of polar-
EQUIPMENT and AC/DC.
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 material
already recorded on the tape.
ac line filter A filter designed to remove extrane-
ac erasing head Also called ac erase head. In tape
ous signals or electrical noise from an ac power
and wire recording, a head that carries alternat-
line, while causing virtually no reduction of the
ing current to erase material already recorded on
power-line voltage or power.
the tape or wire. Also see AC ERASING.
ac line voltage The voltage commonly delivered
acetate Cellulose acetate, a tough thermoplastic
by the commercial power line to consumers. In
material that is an acetic acid ester of cellulose. It
the United States, the two standards are 117 V
is used as a dielectric and in the manufacture of
and 234 V (~ about 5 percent). The lower voltage
is used by most appliances; the higher voltage is
acetate base 1. The cellulose acetate film that
intended for appliances and equipment that
served as the base for the magnetic oxide coating
draws high power, such as electric ovens, cook-
in early recording tape. Most such tapes today
ing ranges, clothes dryers, and amateur-radio
are of polyester base. 2. The cellulose acetate
amplifiers. In Europe, 220 V is the common
substrate onto which certain photosensitive ma-
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 component
of gate voltage in a field-effect transistor. The ac
ac magnetic bias See AC BIAS.
input signal voltage.
8 ac meter • acoustic feedback
ac meter A meter that is intended to work only on quencies. If one fork is struck and then brought
alternating 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 in
rapidly 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; the
ity 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 length
bances, usually in air (versus audio-frequency
of the crystal bar.
currents or voltages).
acoustic absorption The assimilation of energy
from sound waves passing through or reflected by
a given medium.
acoustic absorption loss That portion of sound
energy lost (as by dissipation in the form of heat)
because of ACOUSTIC ABSORPTION.
acoustic absorptivity The ratio of sound energy
absorbed by a material to sound energy striking
the surface of the material.
acoustic attenuation constant The real-number
component of the complex acoustical propagation
constant, expressed in nepers per unit distance.
acoustic burglar alarm An alarm that receives the
acoustic depth finder A direct-reading device for
noise made by an intruder. The alarm device re-
determining the depth of a body of water, or for
sponds to the impulses from concealed micro-
locating underwater objects via sonic or ultra-
sonic waves transmitted downward and reflected
acoustic capacitance The acoustic equivalent of
back to the instrument.
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 absorb
acoustic 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 sound
atmosphere, or it can be through solids or liq-
uids, such as a taut wire, a body of water, or the
acoustic electric transducer A transducer, such
as a microphone or hydrophone, that converts
acoustic compliance COMPLIANCE in acoustic
sound energy into electrical energy. Compare
transducers, especially loudspeakers. It is equiv-
ELECTRICAL/ACOUSTIC TRANSDUCER. Also
alent to electrical capacitive reactance.
see ACOUSTIC TRANSDUCER.
acoustic consonance An effect that occurs when
acoustic feedback A usually undesirable effect
two 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 microphone
related resonant frequencies. An example is shown
(or other input transducer) in the same system.
by two tuning forks with identical fundamental fre-
acoustic feedback • acoustic radiator
This 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, that
transmits sound waves of desired frequency while
attenuating or eliminating others.
acoustic frequency response The sound-
frequency range as a function of sound intensity.
A means of describing the performance of an
acoustic generator A device that produces sound
waves of a desired frequency and/or intensity.
Examples are electrical devices (headphones or acoustic line Baffles or other such structures
loudspeakers operated from a suitable oscillator, within a speaker that act as the mechanical equiv-
buzzer, bell, or flame) and mechanical devices alent 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 simultaneously
allel to one another and arranged a fixed distance as the output load of an amplifier and as a trans-
apart so that an interference pattern forms as ducer of electrical energy into acoustic energy
sound 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 the
ance method in which a missile homes in on transmission 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 two
lar, but generally funnel-shaped) that directs sound sources when there is only one. The phe-
sound and, to some extent, amplifies it. So called nomenon 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 (an acoustic mode Crystal-lattice vibration without
acoustics technician). 2. An AUDIOLOGIST. producing an oscillating dipole.
acoustic impedance Unit, ACOUSTIC OHM. The acoustic noise Interferential (usually disagreeable)
acoustic equivalent of electrical impedance. Like sounds carried by the air (or other propagation
the 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 has sists of extraneous current or voltage impulses
resistive 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 equals
acoustic 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 propagation
uates 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 frequency acoustic phase inverter A bass reflex loudspeaker
or transducer-to-reflector distance varies. enclosure.
acoustic labyrinth A loudspeaker enclosure acoustic pressure 1. The acoustic equivalent of
whose internal partitions form a maze-like path electromotive force, expressed in dynes per
or “tube” lined with sound-absorbing material. square centimeter; also called acoustical pres-
The tube effectively runs from the back of the sure. 2. Sound pressure level.
speaker down to where it terminates in a MOUTH acoustic propagation The transmission of sound
or PORT that opens at the front of the enclosure. waves, or subaudible or ultrasonic waves, as a
The 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 vibrating
with light waves. reed of a buzzer.
10 acoustic radiometer • ac plate resistance
acoustic radiometer An instrument for measuring acoustic scattering The spreading of a sound
the 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 result acoustic suspension A loudspeaker design that
of absorption or reflection of the wave. allows exceptional low-frequency reproduction
acoustic reactance Unit, ACOUSTIC OHM. The for a fairly small physical size. An airtight enclo-
imaginary-number component of ACOUSTIC sure is used to increase the tension on the
IMPEDANCE. It can take the form of ACOUSTIC speaker cone.
CAPACITANCE or ACOUSTIC INDUCTANCE. acoustic system 1. A coordinated array of acous-
acoustic reflectivity The ratio Fr/Fi, where Fr is tic components (e.g., acoustic filters, resonators,
the rate of flow of sound energy reflected from a etc.) 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 in
incident to the surface. which sound energy is converted into electrical
acoustic refraction The deflection of sound waves energy, processed, and then reconverted into
being 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 converting
through 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 of
walls that reflect sound waves, resonance that oc- sound energy without the intermediary of electric
curs 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 when acoustic transmissivity Also called acoustic
it is necessary to get good bass (low-frequency) transmitivity. The ratio et/ei, where et is the
response 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 of
cylinder, or pipe, in which an air column resonates the 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 by ing materials to the interior of an enclosure or
the mechanical dimensions of the body when an room 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
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 dynamic
applications of acoustic phenomena. 2. The qual- plate resistance of an electron tube. RP(ac) equals
ities of an enclosure or sound chamber (room, dEP/dIP, where EP is the plate voltage and IP is the
auditorium, or box) that describe how sound plate current, for a constant value for grid volt-
waves behave in it. age EG.
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-follower
fier. (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, where ac time overcurrent relay A device with a certain
E is in volts, I in amperes, and q is the phase an- time characteristic, which breaks a circuit when
gle. 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 that
cillator, or inverter). Compare DC POWER give 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 an causes 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 or electrical conductivity during exposure to light.
ground radar, which locks in on a strong signal actinoelectric 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 sun’s rays or the actinic
acr 1. Abbreviation of AUDIO CASSETTE RE- power of a light source.
CORDER. 2. Abbreviation of AUDIO CASSETTE action current A small transient current that
RECORDING SYSTEM. flows in a nerve in the human body as a result of
ac reclosing relay The controlling component in stimulation.
an alternating-current circuit breaker. It causes activate To start an operation, usually by applying
the breaker to reset after a specified period of an appropriate enabling signal.
time. activation 1. Supplying electrolyte to a battery cell
ac relay A relay designed to operate on alternating to prepare the cell for operation. 2. Causing the
current 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 cell
like 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 cell
sistance introduces no phase shift. voltage.
acronym A word formed from letters or syllables activator A substance added to an accelerator (see
taken from other applicable words of a multiword ACCELERATOR, 3) to speed the action of the ac-
term. Acronyms are convenient for naming new celerator.
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, which
cepted and popularized, it is written as a conven- operates with no external source of power.
tional word and is no longer thought of as an active antenna An antenna that uses a small
acronym. For example, LASER was once an whip, loop, or ferrite loopstick with a high-gain
acronym 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 kHz
cess, the acronym became a conventional word to 30 MHz).
from which other terms (such as the verb “lase”) active area The forward-current-carrying portion
were derived. of the rectifying junction of a metallic rectifier.
acrylic resin A synthetic resin used as a dielectric active arm See ACTIVE LEG.
and in electronic encapsulations. It is made from active balance In telephone repeater operation, the
acrylic 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 component active chord mechanism Abbreviation, ACM. In
of 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 structure
source resistance in a field-effect transistor; RS(ac) similar to the human spine, with numerous
equals dVS/dIS for a constant value of VG. small, rigid links connected by hinges.
12 active communications satellite • active repair time
active communications satellite A satellite con- active file A computer file in use (i.e., one that is
taining receivers (which pick up beamed electro- being updated or referred to).
magnetic signals from a ground point and amplify active filter A bandpass, bandstop, highpass or
them) and transmitters (which send signals back lowpass 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 infrared
namic function (such as amplification, oscilla- rays reflected from a target to which they were
tion, or signal control) that usually requires a beamed.
power supply for its operation. Examples include active jamming Transmission or retransmission
bipolar 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 semiconductor
tains 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 that
RENT. changes one or more of its electrical characteris-
active computer A computer in an installation or tics in response to the input signal of the trans-
network that is processing data. ducer. Also called active arm.
active comsat See ACTIVE COMMUNICATIONS active lines In a U.S. television picture, the lines
SATELLITE. (approximately 488) that make up the picture.
active control system A device or circuit that The remaining 37 of the 525 available lines are
compensates for irregularities in the operating blanked 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 electrical
nent 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 phase porting material of the plates themselves. 2. A ra-
with the voltage, and is “inactive,” with respect to dioactive substance. 3. The phosphor coating of a
power in the circuit. The active current is equal to cathode-ray tube screen. 4. The material used to
the 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 of tive 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 high
transistor that needs a power supply, and/or that input 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 one grated circuits. An active circuit provides gain,
or more active devices or components, usually input-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 element active 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
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-
active repair time The time during which mainte-
nance is done on a system and the system is out
active satellite • adapter
ily in the same physical location as the true
ground surface (i.e., the earth itself ). An actual
ground can be an artificial ground plane, such as
that provided in some antenna structures. Actual
ground can also be modified by nearby rooftops,
buildings, guy wiring, and utility wiring.
actual height The highest altitude where radio
wave refraction actually occurs.
actual power Also called active or AVERAGE
POWER. Symbol, Pavg. In a resistive circuit under
sine-wave conditions, average power is the prod-
uct of the rms voltage and the rms current. It is
also equal to half the product of the maximum
current and maximum voltage.
actuating device A device or component that oper-
ates electrical contacts to affect signal transmis-
active satellite See ACTIVE COMMUNICATIONS actuating system 1. An automatic or manually
SATELLITE. operated system that starts, modifies, or stops an
active sensor In an electronic security system, a operation. 2. A system that supplies energy for
transducer that generates an electromagnetic ACTUATION.
field or acoustic-wave field, and detects changes actuating time Also called actuation time. The
in 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 semiconductor actuation 1. The starting, modification, or termi-
material into which the components are formed; nation of an operation or process. 2. Activation of
it acts as some or all of the components. This is in a 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 uses
face. electromagnetism to produce a longitudinal or ro-
active system A radio and/or radar system that tary thrust for mechanical work. It is often the
requires transmitting equipment to be carried in end (load) device of a servosystem.
a vehicle. ACU Abbreviation of automatic calling unit.
active tracking system A system in which a ac voltage A voltage, the average value of which is
transponder or responder on board a vehicle re- zero, that periodically changes its polarity. In one
transmits 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 contains maximum negative value, and finally returns to
an active device, such as a transistor or inte- zero. The number of such cycles per second is
grated circuit, for immediate amplification of the termed 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 in
experiencing induction and, therefore, is deliver- the active wires of the armature is always of the
ing voltage. same polarity.
activity 1. Intensity of, as well as readiness for, os- A/D Abbreviation for ANALOG-TO-DIGITAL. See
cillation in a piezoelectric crystal. 2. Radioactive ANALOG-TO-DIGITAL CONVERSION.
intensity. 3. Intensity of thermal agitation. 4. Ada A microcomputer language designed primarily
Thermionic 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 sometimes
nal—even when operated from a dc supply. used for phonetic verbalizing of the letter A. More
ac transmission The use of an alternating voltage commonly, 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, and minal scheme or the size of a jack, plug, or socket
generally 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 to
tenna. The actual ground surface is not necessar- another (e.g., waveguide to coaxial line). 3. An
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-band additive 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 mechanical rays 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 its colors 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 in other colors. Compare SUBTRACTIVE PRI-
such a way that the whole array behaves like a MARIES, 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 is creases 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 with only the address part of an instruction.
four ADCOCK ANTENNAS situated at the corners address 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 can address 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.
address indirect • adjusted decibels
address indirect An address that specifies a stor-
age location that contains another address.
address memory The memory sections in a digital
computer 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 is
then repeated, the computer will go to the new
address part In a digital computer instruction, the
part of an expression that specifies the location.
Also called ADDRESS FIELD.
address register In a computer, a register in which
an 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 quantities
from storage and to enter the sum or difference
into 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 lower
quired to perform addition, excluding the time re- channel.
quired to get the quantities from storage and to adjacent-channel selectivity The extent to which
enter 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 sound
FINDER. 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 component
ergy is increased. whose main electrical value can be varied at will
adiabatic demagnetization A technique using a (e.g., a variable capacitor, inductor, resistor, or
magnetic field to keep a substance at a low tem- load).
perature, sometimes within a fraction of a degree adjustable instrument 1. An instrument whose
of absolute zero. sensitivity, range, or response can be varied at
adjacency A character-recognition condition in will (e.g., multirange meter or wideband genera-
which the spacing reference lines of two charac- tor). 2. An instrument that requires adjustment
ters 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 The adjustable motor tuning An arrangement that al-
selectivity of a receiver or radio-frequency (RF) lows the motor tuning of a receiver to be confined
amplifier, with respect to adjacent-channel and to a portion of the frequency spectrum.
alternate-channel signals. That is, the extent to adjustable resistor A wirewound resistor in which
which a desired signal is passed, and nearby un- the resistance wire is partially exposed to allow
wanted signals are rejected. varying the component’s value.
adjacent audio channel See ADJACENT SOUND adjustable voltage divider A wirewound resistor
CHANNEL. 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 are
terest. normally connected to a circuit breaker are
adjacent-channel attenuation The reciprocal of shunted so that current can be measured under
the 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 sensitivity adjusted decibels Noise level (in decibels) above a
in an adjacent channel or on a specified number reference noise level (designated arbitrarily as
of channels removed from the original. zero decibels) measured at any point in a system
adjacent-channel interference In television or with a noise meter that has previously been ad-
radio reception, the interference from stations justed for zero (at reference), according to specifi-
on adjacent channels. A common form arises cations.
16 admittance • affirmative
admittance Symbol, Y. Unit, siemens (formerly aeronautical fixed service station A station that
mho). The property denoting the comparative operates in the aeronautical fixed service.
ease with which an alternating current flows aeronautical ground station A land station that
through a circuit or device. Admittance is the re- provides communication between aircraft and
ciprocal of impedance (Z ): Y = 1/Z. ground stations.
adp 1. Abbreviation of AMMONIUM DIHYDROGEN aeronautical marker-beacon signal A distinctive
PHOSPHATE, a piezoelectric compound used for signal that designates a small area above a beacon
sonar 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 without beacon signal.
absorption. An example is adsorption of water to aeronautical mobile service A radio service con-
the surface of a dielectric. This term is often con- sisting of communications between aircraft, and
fused 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 few aeronautical radionavigation services Services
small bands that are allocated to extra-class li- provided by stations transmitting signals used in
censees. 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 The
copper and nickel, which has high resistivity and agency that administers the operation of stations
a negligible temperature coefficient of resistance. in the aeronautical radio service.
aeolight A glow lamp using a cold cathode and a aeronautical telecommunications Collectively,
mixture of inert gases. Because its illumination all of the electronic and nonelectronic communi-
can be regulated with an applied signal voltage, it cations 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 motion—especially aerophare See RADIO BEACON.
upon bodies (such as aircraft) moving through aerospace 1. The region encompassing the earth’s
these gases. atmosphere and extraterrestrial space. 2. Per-
aerogram See RADIOGRAM. taining to transport and travel in the earth’s at-
aeromagnetic Pertaining to terrestrial magnetism, mosphere and in outer space. This includes
as 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 for AES 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 often
that transmits information regarding air naviga- used for “yes”—especially when interference is
tion and flight safety. present or signals are weak.
AFIPS • aircraft bonding
AFIPS Acronym for American Federation of Infor- airborne intercept radar A type of short-range
mation 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 of
KEYING. 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. Also
phototube (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 hire
FORMER. 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 acoustic
substance that produces or sustains an effect. chamber, pipe, or horn.
Thus, a sudden voltage rise is a triggering agent air-cooled component A component, such as a
in 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 an such as water or oil.
ANNEALING AGENT. air-cooled transistor A transistor (particularly a
aging 1. An initial run of a component or circuit power 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 transistor
formance. 2. The changing of electrical is usually mounted on a heatsink or fitted with
characteristics or of chemical properties over a fins.
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 the
the earth’s surface at which a magnetic needle surrounding air. A device called a chimney can be
shows zero declination (i.e., points to true geo- placed around the tube, through which air is
graphic north). blown by a fan. Cool air enters through the bot-
AGREE Acronym for Advisory Group on Reliability tom of the assembly, and hot air escapes from the
of Electronics Equipment. top.
Ah Abbreviation of AMPERE-HOUR. Depending on air-core inductor A coil of wire wound around a
the standard used, the abbreviation can be amp- hollow cylindrical form or in a loop, designed to
hr, 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 component
of 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 winding
cal 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 the hood of mutual inductance between the coil and
earth’s atmosphere and figures prominently in surrounding electrical components, devices, or
the manufacture and operation of numerous circuits.
electronic devices. By volume, air contains about air-core transformer A transformer without a fer-
21 percent oxygen, 78 percent nitrogen, and romagnetic core, so called because air is the only
lesser 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 an
sulfur and nitrogen. aircraft, including the engine.
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 passing
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 space
between inner and outer conductors is mostly
empty (i.e., air-filled). Some such cables are
sealed and filled with an inert gas. The inner con-
ductor is held away from the inner wall of the
outer 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 communications tower 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 60
around an electronic device or piece of equip- miles (approximately 100 kilometers) of an air-
ment—especially pertaining to an AIR-COOLED port, 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 a obstructions 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, and
magnetic material, such as plastic, for elapsed time, furnishes a continuous indication
mechanical support. 2. The space between two or of the position of the aircraft. The indication is
more magnetically coupled or electrostatically affected by high-altitude winds. Compare
coupled components. 3. A device that gets its GROUND-POSITION INDICATOR.
name from the narrow gap between two small air-to-air communication Radio transmission
metal balls, needle points, or blunt rod tips from one aircraft to another in flight. Com-
therein. When an applied voltage is sufficiently pare AIR-TO-GROUND COMMUNICATION and
high, 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 located
operation 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 two TION.
parallel wires held apart by separators (bars or air-to-ground radio frequency The carrier fre-
rods of high-grade dielectric material) situated at quency, or band of such frequencies, allocated for
wide intervals. 2. AIR-DIELECTRIC COAX. transmissions from an aircraft to a ground sta-
air-moving device A mechanical device, such as a tion.
specially designed fan or blower, used to facilitate airwaves 1. Radio waves. The term is slang, but is
air cooling of electronic components. widely used. It probably came from the public’s
airwaves • aliasing noise
mistaken 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 the
tendency of the mercury to stick to the parts has
alarm 1. An electronic security system. 2. A silent
and/or audible alert signal transmitted by an
electronic security system when an intrusion oc-
curs. 3. A silent and/or audible signal that in-
forms personnel of the occurrence of an
alarm circuit A circuit that alerts personnel to a
system malfunction, a detected condition, or an
alarm condition 1. An intrusion or equipment
malfunction that triggers an alarm circuit. 2. The
operation of an alarm circuit that occurs in re-
sponse to an intrusion or equipment malfunc-
alarm hold A device that keeps an alarm sounding
once 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 ALARM
alarm relay A relay that is actuated by an alarm
A-law A form of companding law frequently used in
European electronics (the mu-law is more often
used in North America). A nonlinear transfer algebraic adder In computer operations, an adder
characteristic in companding circuits. It can be that provides the algebraic sum, rather than the
continuous, 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 an
bit binary code following the A-LAW, a specific intuitive sequence, following the way in which the
companding 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 quantities
to 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 the
TROL. square root of a number). It can be expressed in a
alerting device An audible alarm that includes a line-by-line instruction set or as a flowchart.
self-contained solid-state audio oscillator. Pow- algorithmic language A computer language used
ered 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 polarized identify the same data element in a computer
antenna, designed to minimize ground losses in program.
structures of manageable height. It usually con- aliasing 1. In analog-to-digital (A/D) conversion, a
sists of several wires, each quarter-wave reso- false output signal that results from a sampling
nant with a loading coil, and all connected rate that is too slow. Ideally, the sampling rate is at
together at the apex of a tower. The antenna is least twice the highest input signal frequency. 2.
fed between the ground and the base of one of Sawtooth-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 center aliasing noise A form of signal distortion caused
to lower the impedance at the current nodes. by a signal with an excessive bandwidth.
20 align • alloy diode
align 1. To adjust (i.e., to preset) the circuits of an Allen 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
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 in teeth, 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 correctly allocate 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 or ity; see, for example, ALLOCATION OF FRE-
wrench (usually nonmagnetic) used to adjust QUENCIES. 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 bases to 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 as allophone 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 zinc– speech recognition and synthesis. There are 128
carbon cell, but it can deliver current effectively different phoneme variations in the English lan-
at lower temperatures. Cells of this type have guage. See PHONEME.
shelf lives longer than zinc–carbon cells; they also alloter relay A telephone system line-finder relay
have greater energy-storage capacity per unit that 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- allotropic Pertaining to a substance existing in
sistor radios, and cassette tape and compact-disc two forms.
players. Compare ZINC–CARBON CELL. alloy A metal that is a mixture of several other met-
alkaline-earth metals The elemental metals bar- als (e.g., brass from copper and zinc), or of a
ium, calcium, strontium, and sometimes beryl- metal and a nonmetal.
lium, magnesium, and radium, some of which are alloy deposition In semiconductor manufacture,
used in vacuum tubes. depositing an alloy on a substrate.
alkaline earths Substances that are oxides of the alloy-diffused transistor A transistor in which the
alkaline-earth metals. Some of these materials base is diffused and the emitter is alloyed. The
are used in vacuum tubes. collector is provided by the semiconductor sub-
all-diffused A type of INTEGRATED CIRCUIT in strate into which alloying and diffusion are
which both active and passive elements have affected. Compare ALLOY TRANSISTOR and
been fabricated by diffusion and related pro- DIFFUSE TRANSISTOR.
cesses. alloy diode A junction-type semiconductor diode
Allen screw A screw fitted with a six-sided (hexag- in which a suitable substance (such as p-type) is
onal) hole. alloyed into a chip of the opposite type (such as
alloy diode • alternating-charge characteristic
n-type) to form the junction. Also called alloy- alphabetic-numeric Also called alphabetical-
junction diode. numerical and alphanumeric. In computer opera-
alloy junction In a semiconductor device, a posi- tions, pertaining to letters of the alphabet and
tive/negative (pn) junction formed by alloying a special characters, and to numerical digits.
suitable material (such as indium) with the semi- alpha cutoff frequency Also called alpha cutoff. In
conductor (silicon or germanium). a bipolar transistor circuit, the frequency at
alloy transistor A transistor whose junctions are which the alpha (current gain) becomes 0.707
created by alloying. Also see ALLOY JUNCTION. (70.7 percent) of its value at 1 kHz. A bipolar
transistor can have considerable gain at its alpha
cutoff. This specification denotes how rapidly a
transistor loses gain as the frequency increases,
an important consideration in the design of radio-
frequency (RF) amplifiers. See ALPHA. Compare
GAIN BANDWIDTH PRODUCT.
alpha decay The decay of a substance in which the
nuclei of the atoms emit alpha particles, resulting
in a change of the atomic number and atomic
weight of the substance over a period of time.
alphanumeric See ALPHABETIC-NUMERIC.
all-pass filter Also called all-pass network. A filter alphanumeric code In computer operations or in
that (ideally) introduces a desired phase shift or communications, a code composed of, or using,
time delay, but has zero attenuation at all fre- both letters and numbers.
quencies. alphanumeric readout A type of digital readout
all-relay central office In telephone service, an that displays both letters and numerals.
automatic central-office switchboard that uses alpha particle A nuclear particle bearing a positive
relay circuits to make line interconnections. charge. Consisting of two protons and two neu-
all-wave Pertaining to a wide operating-frequency trons, it is given off by certain radioactive sub-
range. Few systems are literally all-wave. For ex- stances. Compare BETA RAYS and GAMMA RAYS.
ample, a so-called “all-wave radio receiver” might alpha system An alphabetic code-signaling sys-
cover 500 kHz to 30 MHz only. tem.
all-wave antenna An antenna that can be operated alphatron An ionizing device in which the radia-
over a wide frequency range with reasonable effi- tion source is an emitter of alpha particles.
ciency and preferably without needing readjust- alteration An inclusive-OR operation.
ment. Examples are the DISCONE ANTENNA and alternate channel In communications, a channel
the LOG-PERIODIC ANTENNA. situated two channels higher or lower than a
all-wave generator A signal generator that will given channel. Compare ADJACENT CHANNEL.
supply output over a wide range of frequencies. alternate-channel interference Interference
all-wave receiver A radio receiver that can be caused by a transmitter operating in the chan-
tuned over a very wide range of frequencies, such nel beyond an adjacent channel. Compare
as 10 kHz to 70 MHz. ADJACENT-CHANNEL INTERFERENCE.
allyl plastics Plastics, sometimes used as dielectrics alternate digit inversion In multiplex equipment,
or for other purposes in electronics, based on a method of switching the binary signals to the
resins made by polymerization of monomers (such opposite state, in accordance with A-law com-
as diallyl phthalate) that contain allyl groups. panding.
alnico Coined from the words aluminum, nickel, alternate frequency A frequency allocated as an
and cobalt. An alloy used in strong permanent alternative to a main assigned frequency and
magnets, it contains the constituents noted plus used under certain specified conditions.
(sometimes) copper or titanium. alternate-mark inversion signal A signal that
alpha 1. Symbol, α. The current gain of a common- conveys bits in which the successive signals are
base-connected bipolar transistor. It is the ratio of of opposite polarity (positive, then negative, then
the differential of collector current to the differen- positive, etc.). They are equal in absolute value
tial of emitter current; α = dIC/dIE. For a junction amplitude.
transistor, alpha is always less than unity, but alternate mode The technique of displaying sev-
very close to it. 2. In voice communications, the eral signals on an oscilloscope screen by rapidly
phonetic representation of the letter A. switching the signals in sequence at the end of
alphabet The set of all characters in a natural lan- each sweep.
guage. alternate routing A secondary, or backup, com-
alphabetic coding In computer practice, an abbre- munications path, used when primary (normal)
viation system for coding information to be fed routing is impossible.
into the computer. The coding contains letters, alternating-charge characteristic In a nonlinear
words, and numbers. capacitor, the relationship between the instanta-
22 alternating-charge characteristic • amateur extra-class license
neous charge and the instantaneous value of an above the earth’s surface. 3. The angle, measured
alternating voltage. in degrees, with respect to the horizon, at which a
alternating current Abbreviation, ac. A current that highly directional antenna is pointed.
periodically reverses its direction of flow. In one cy- altitude delay In a plan-position-indicating type of
cle, an alternation starts at zero, rises to a maxi- radar, the sync delay introduced between trans-
mum positive level, returns to zero, rises to a mission of the pulse and start of the trace on the
maximum negative level, and again returns to zero. indicator screen to eliminate the altitude circle in
The number of such cycles completed per second is the display.
termed the ac frequency. Also see CURRENT. ALU Abbreviation of ARITHMETIC AND LOGIC
alternating-current continuous wave An ampli- UNIT.
tude-modulated signal resulting from the opera- alumel An alloy used in the construction of one
tion of an oscillator or RF amplifier with raw ac type of THERMOCOUPLE. It is composed of
voltage. nickel (three parts) and aluminum (one part).
alternating current/direct current See AC/DC. alumina An aluminum-oxide ceramic used in elec-
alternating-current erasing head See AC ERAS- tron tube insulators and as a substrate in the
ING HEAD. fabrication of thin-film circuits.
alternating-current pulse A short-duration ac aluminum Symbol, Al. An elemental metal. Atomic
wave. number, 13. Atomic weight, 26.98. Aluminum is
alternating-current transmission 1. The propa- widely used in electronics, familiar instances be-
gation of alternating currents along a length of ing chassis, wire, shields, semiconductor doping,
conductor—especially for power-transfer pur- and electrolytic-capacitor plates.
poses. 2. A means of picture transmission in aluminum antimonide Formula, AlSb. A crystalline
which a given signal strength produces a con- compound useful as a semiconductor dopant.
stant value of brightness for a very short time. aluminized screen A television picture-tube
alternating voltage Also called alternating-current screen with a thin layer of aluminum deposited
voltage. See AC VOLTAGE. on its back to brighten the image and reduce ion-
alternation In ac practice, a half cycle. In a complete spot formation.
cycle, there are two alternations, one in the positive Am Symbol for AMERICIUM.
direction and one in the negative direction. A/m Abbreviation of ampere per meter: the SI unit
of magnetic field strength.
AM 1. Abbreviation of amplitude modulator. 2. Ab-
breviation of AMPLITUDE MODULATION.
amalgam An alloy of a metal and mercury. Loosely,
any combination of metals.
amateur 1. A nonprofessional, usually noncom-
mercial devotee of any technology (i.e., a hobby-
ist). 2. A licensed radio operator legally
authorized to operate a station in the AMATEUR
amateur band Any band of radio frequencies as-
signed for noncommercial use by licensed radio
amateurs (see AMATEUR, 2). In the United
States, numerous such bands are above 1.8 MHz
(160 meters). Also see AMATEUR SERVICE and
amateur call letters Call letters assigned by a gov-
ernment licensing authority—especially to ama-
teur stations. Call-letter combinations consist of
a letter prefix denoting the country in which the
station is situated, plus a number designating
alternative denial A NOT-AND operation. the location within the country, and two or more
alternator Any mechanically driven machine for letters identifying the particular station. For ex-
generating ac power. Sometimes specifically one ample: W6ABC: W (or K) = United States, 6 = Cal-
having a permanent-magnet rotor, such as a ifornia, and ABC = identification of individual
magneto. licensee (issued alphabetically, except under spe-
altimeter station An airborne transmitter whose cial circumstances).
signals are used to determine the altitude of air- amateur callsign See AMATEUR CALL LETTERS.
craft. amateur extra-class license The highest class of
altitude 1. The vertical distance of an object above amateur-radio operator license in the United
sea level. 2. The vertical distance of an object States. It conveys all operating privileges.
amateur radio • AM/FM tuner
amateur radio 1. A general term, referring to the will cause no malfunction of, or damage to, a cir-
practice of operation, experimentation, and other cuit or device.
work in and related to the amateur service. 2. The ambiguity 1. Any unclear, illogical, or incorrect in-
hardware that comprises an amateur radio sta- dication or result. 2. The seeking of a false null by
tion. 3. A radio receiver, transmitter, or transceiver a servo. 3. In digital computer operations, an er-
that is specifically designed for operation in the ror resulting from improper design of logic.
amateur bands. ambiguous count In digital counters, a clearly in-
amateur radio operator Also called radio ham or correct count. See ACCIDENTAL TRIGGERING.
ham radio operator. An individual licensed to ambisonic reproduction A close approximation of
transmit radio signals in the amateur service. the actual directional characteristics of a sound in
amateur service A two-way radio service, existing a given environment. The reproduced sound al-
purely for hobby purposes (i.e., without pecu- most exactly duplicates the sound in the actual
niary interest). environment in which it was recorded.
amateur station A radio station licensed in the American Morse code (Samuel F. B. Morse, 1791–
AMATEUR SERVICE. 1872). Also called Railroad Morse. A telegraph
amauroscope An electronic aid to the blind, in code, at one time used on wire telegraph lines in
which photocells in a pair of goggles receive light the United States. It differs from the Continental
images. Electric pulses proportional to the light code, also called the International Morse Code,
are impressed upon the visual receptors of the which is used in radiotelegraphy. Compare CON-
brain through electrodes in contact with nerves TINENTAL CODE.
above each eye. American National Standards Institute Ac-
amber A yellow or brown fossil resin that is histor- ronym, ANSI. An industrial group in the United
ically important in electronics. It is the first mate- States that encourages companies to manufac-
rial reported to be capable of electrification by ture devices and equipment in accordance with
rubbing (Thales, 600 BC). Also, the words elec- certain standards. The objective is to minimize
tricity, electron, and electronics are derived from hardware incompatibility problems.
the Greek name for amber, elektron. American Radio Relay League A worldwide orga-
ambience The acoustic characteristic of a room, in nization of amateur radio operators, headquar-
terms of the total amount of sound reaching a lis- tered in Newington, Connecticut. The official
tener from all directions. publications are the monthly magazines, QST
ambient An adjective meaning “surrounding.” Often and QEX. They also publish numerous books and
used as a noun in place of the adjective-noun com- other educational materials.
bination (thus, “10 degrees above ambient,” in- American Standards Association Abbreviation,
stead of “10 degrees above ambient temperature”). ASA. At one time, the name of the national associ-
ambient humidity The amount of moisture in the ation in the U.S. devoted to the formation and dis-
air at the time of measurement or operations in semination of voluntary standards of dimensions,
which dampness must be accounted for. performance, terminology, etc. See ANSI.
ambient level The amplitude of all interference American wire gauge Abbreviation, AWG. Also
(acoustic noise, electrical noise, illumination, called Brown and Sharpe gauge or B & S gauge.
etc.) emitted from sources other than that of a The standard American method of designating
signal of interest. wire sizes. Wire is listed according to gauge num-
ambient light Also called ambient illumination. ber from 0000 (460 mils diameter) to 40 (3.145
Room light or outdoor light incident to a location mils diameter).
at the time of measurement or operations. americium Symbol, Am. A radioactive elemental
ambient-light filter In a television receiver, a filter metal first produced artificially in the 1940s.
mounted in front of a picture-tube screen to min- Atomic number, 95. Atomic weight, 243.
imize the amount of ambient light reaching the AM/FM receiver A radio set that can receive either
screen. amplitude-modulated or frequency-modulated
ambient noise 1. In electrical measurements and signals. Usually, a band switch incorporates the
operation, background electrical noise. 2. In demodulation-selection circuitry so that as the
acoustical measurements and operations, audi- frequency range is changed, the appropriate de-
ble background noise. tector is accessed.
ambient pressure Surrounding atmospheric pres- AM/FM transmitter A radio transmitter whose
sure. output signal can be frequency- or amplitude-
ambient temperature The temperature surround- modulated by a panel selector switch.
ing apparatus and equipment (e.g., room temper- AM/FM tuner A compact radio receiver unit that
ature). can handle either amplitude- or frequency-
ambient-temperature range 1. The range over modulated signals, and delivers low-amplitude
which ambient temperature varies at a given lo- output to a high-fidelity audio power amplifier.
cation. 2. The range of ambient temperature that Compare AM TUNER and FM TUNER.
24 AMI • Amperian whirl
ammeter-voltmeter method The determination of
Character Symbol Character Symbol
resistance or power values from the measure-
A .— U ..—
ment of voltage (E) and current (I ). For resistance,
B —... V ...—
R = E/I; for power, P = EI.
C .. . W .——
ammonium chloride Formula, NH4Cl. The elec-
D —.. X .—..
trolyte in the carbon-zinc type of primary cell.
E . Y .. ..
Also called SAL AMMONIAC.
F .—. Z ... .
AMNL Abbreviation of AMPLITUDE-MODULATION
G ——. 1 .——.
H . ... 2 ..—..
amortisseur winding 1. A winding that acts
I .. 3 ...—.
against pulsation of the magnetic field in an elec-
J —.—. 4 ....—
tric motor. 2. A winding that acts to prevent os-
K —.— 5 ——— cillation in a synchronous motor.
L 6 ......
—— amorphous substance A noncrystalline material.
M 7 ——..
—— amp 1. Slang for AMPERE. 2. Slang for AMPLIFIER—
N —. 8 —.... especially in audio high-fidelity applications.
O .. 9 —..— ampacity Current-carrying capacity expressed in
P ..... 0 amperes.
Q ..—. period ..——.. amperage The strength of an electric current (i.e.,
the number of amperes).
R . .. comma .—.—
ampere (Andre Marie Ampere, 1775-1836). Abbrevi-
S ... question —..—.
ations, A (preferred), a, amp. The SI base unit of
current intensity (I ). The ampere is the constant
current that, if maintained in two straight parallel
conductors of infinite length and of negligible cir-
cular cross section and placed 1 meter apart in a
American Wire Gauge (AWG) Diameters vacuum, would produce between the conductors a
force of 2 × 10 –7 newton per meter. One ampere
AWG Millimeters Inches
AWG Millimeters Inches
flows through a 1-ohm resistance when a potential
21 0.723 0.0285
1 7.35 0.289 of 1 volt is applied; thus I = E/R. Also see MI-
CROAMPERE, MILLIAMPERE, NANOAMPERE,
22 0.644 0.0254
2 6.54 0.257
23 0.573 0.0226
3 5.83 0.230
ampere balance A device consisting of two con-
24 0.511 0.0201
4 5.19 0.204
ductors in which the force between them (caused
25 0.455 0.0179
5 4.62 0.182
by current) is balanced against the gravitational
26 0.405 0.0159
6 4.12 0.163
force exerted on an object in the gravitational
27 0.361 0.0142
7 3.67 0.144 field of the earth. Used for the precise determina-
28 0.321 0.0126
8 3.26 0.128 tion of current of large dimension, or of the size of
29 0.286 0.0113
9 2.91 0.115
ampere-hour Abbreviations: Ah, amp-hr. The
30 0.255 0.0100
10 2.59 0.102
quantity of electricity that passes through a cir-
31 0.227 0.00894
11 2.31 0.0909
cuit in one hour when the rate of flow is one am-
32 0.202 0.00795
12 2.05 0.0807
pere. Also see BATTERY CAPACITY.
33 0.180 0.00709
13 1.83 0.0720
ampere-hour meter An instrument for measuring
34 0.160 0.00630
14 1.63 0.0642 ampere-hours. It contains a small motor driven by
35 0.143 0.00563
15 1.45 0.0571 the current being measured and which moves a
36 0.127 0.00500
16 1.29 0.0508 point on an ampere-hour scale. The motor speed is
proportional to the current. The position of the
37 0.113 0.00445
17 1.15 0.0453
pointer is proportional to current and elapsed time.
38 0.101 0.00398
18 1.02 0.0402
Ampere’s law Current flowing in a wire generates
39 0.090 0.00354
19 0.912 0.0359
a magnetic flux that encircles the wire in the
40 0.080 0.00315
20 0.812 0.0320
clockwise direction when the current is moving
away from the observer.
AMI See ALTERNATE-MARK INVERSION SIGNAL.
ampere-turn Symbol, NI. A unit of magnetomotive
A-minus Also, A-. The negative terminal of an A
force equal to 1 ampere flowing in a single-turn
battery, or pertaining to the part of a circuit con-
coil. The ampere-turns value for any coil is ob-
nected to that terminal.
tained by multiplying the current (in amperes) by
ammeter An instrument used to measure the
the number of turns in the coil.
amount of current (in amperes) flowing in a circuit.
Amperian whirl The stream of electrons in a
ammeter shunt A resistor connected in parallel with
single-turn, current-conducting wire loop acting
an ammeter to increase its current range. Also see
as an elementary electromagnet.
AYRTON-MATHER GALVANOMETER SHUNT.
amp-hr • amplify
tical. 2. The number of decibels by which an AM-
PLIFIER circuit increases the amplitude of a sig-
nal. For voltage or current, this figure has
meaning only when the input and output
impedances are identical. See DECIBEL. 3. The
ALPHA or BETA of a bipolar transistor. 4. In
the operation of an electron tube, the ratio of
the derivative (instantaneous rate of change) of
the plate voltage to the derivative of the grid volt-
age, for zero change in plate current.
amplified ALC Abbreviation, AALC. An automatic-
level-control (ALC) system that uses the amplifi-
cation of the fed-back control signal. It is used in
RF power amplifiers, particularly single-sideband
Direction (SSB) linear amplifiers, to prevent overmodula-
of current tion and nonlinearity.
amplified back bias A declining voltage developed
across a fast-time-constant circuit in an amplifier
stage and fed back into a preceding stage.
amplifier Any device that increases the magni-
tude of an applied signal. It receives an input
signal and delivers a larger output signal that, in
amp-hr One style of abbreviating AMPERE-HOUR. addition to its increased amplitude, is a replica
Also, Ah. of the input signal. Also see CURRENT AMPLI-
amplidyne A dynamo-like rotating dc machine FIER, POWER AMPLIFIER, and VOLTAGE AM-
that can act as a power amplifier because the re- PLIFIER.
sponse of the output voltage to changes in field amplifier diode Any semiconductor that can pro-
excitation is quite rapid. Used in servo systems. vide amplification in a suitable circuit or mi-
crowave system. See DIODE AMPLIFIER.
amplifier distortion A change in the waveform of a
signal, arising within an amplifier that is oper-
ated in compliance with specified conditions.
amplifier input 1. The terminals and section of an
amplifier that receive the signal to be amplified.
2. The signal to be amplified.
amplifier noise Collectively, all extraneous signals
present in the output of an amplifier when no
working signal is applied to the amplifier input
amplifier nonlinearity A condition in which the
amplifier output signal does not exhibit a linear
relationship to the corresponding input signal.
Some amplifiers are designed to operate in a lin-
ear manner at all times, but many amplifier types
need not function in this manner to be effective.
amplification 1. The process of increasing the
Also see AMPLIFIER DISTORTION and LINEAR
magnitude of a signal. This entails an input sig-
nal controlling a local power supply to produce a
amplifier output 1. The terminals and section of
larger output signal. Depending on the kind of in-
an amplifier that deliver the amplified signal for
put and output signals, amplification can be cat-
external use. 2. The amplified signal.
egorized as CURRENT, VOLTAGE, POWER, or
amplifier power The power level of the output sig-
some combination of these. 2. The qualitative sig-
nal delivered by an amplifier (also called OUTPUT
nal increase resulting from the process in 1. 3.
POWER), or the extent to which the amplifier in-
The quantitative signal increase (resulting from
creases the power of the input signal (also called
the process in 1), expressed as a factor (such as
100) or in terms of decibels (dB). See AMPLIFICA-
amplifier response The performance of an ampli-
TION FACTOR and DECIBEL.
fier throughout a specified frequency band. Fac-
amplification factor 1. The ratio of the output
tors usually included are gain, distortion,
voltage, current, or power to the input voltage,
amplitude versus frequency, and power output.
current, or power of an AMPLIFIER circuit. For
amplify To perform the functions of amplification
voltage or current, this ratio has meaning only
(see AMPLIFICATION, 1).
when the input and output impedances are iden-
26 amplifying delay line • amplitude selection
amplifying delay line A delay line that causes am- munications and broadcasting. The modulating-
plification of signals in a circuit intended for signal energy appears at sideband frequencies
pulse compression. above and below, and very close to, the carrier
amplistat A self-saturating magnetic amplifier. frequency. These sideband signals carry all the
amplitron A backward-wave amplifier used in mi- information. The extent of modulation is ex-
crowave circuits. pressed as a percentage, from 0, which represents
amplitude The extent to which an alternating or an unmodulated carrier, to 100, which repre-
pulsating current or voltage swings, positively sents full modulation. In a signal modulated 100
and negatively, from zero or from a mean value. percent, one-third of the power is used to convey
amplitude-controlled rectifier A thyratron- or the data; the other two-thirds is consumed by the
thyristor-based rectifier circuit. carrier. This form of modulation is essentially
amplitude density distribution A mathematical outmoded, although it is still used in the stan-
function giving the probability that, at a given in- dard broadcast band from 535 to 1605 kHz. See
stant in time, a fluctuating voltage has a certain FREQUENCY MODULATION, PHASE MODU-
value. LATION, SINGLE SIDEBAND.
amplitude distortion In an amplifier or network,
the condition in which the output-signal ampli-
tude exhibits a nonlinear relationship to the in-
amplitude error 1. The error in measuring the am-
plitude of a signal, normally expressed as a per-
centage of signal amplitude or as a percentage of
full scale. 2. The frequency at which the output
amplitude of a signal is in error by 1% with am-
plitude at 10% of full scale.
amplitude factor For an ac wave, the ratio of the
peak value to the rms value. The amplitude factor
of a sine wave is equal to the square root of 2 =
amplitude fading In the propagation of electro-
magnetic waves, a condition in which the ampli-
tudes of all components of the signal (i.e., carrier
and sidebands) increase and decrease uniformly.
Compare SELECTIVE FADING.
amplitude/frequency response Performance of
an amplifier throughout a specified range, as ex-
hibited by a plot of output-signal amplitude ver-
sus frequency for a constant-amplitude input
amplitude gate A transducer that transmits only
those portions of an input wave that lie within
two close-spaced amplitude boundaries; also
called slicer. amplitude-modulation noise Spurious amplitude
amplitude limiter A circuit, usually with auto- modulation of a carrier wave by extraneous sig-
matic gain control (AGC), that keeps an amplifier nals and random impulses, rather than by the in-
output signal from exceeding a certain level, de- tended data-containing signal.
spite large variations in input-signal amplitude. A amplitude noise In radar, amplitude fluctuations
dc-biased diode performs passive limiting action of an echo returned by a target. This noise limits
via clipping. the precision of the system.
amplitude-modulated generator A signal genera- amplitude of noise The level of random noise in a
tor whose output is amplitude modulated. Usu- system. The amplitude of noise is measured in
ally, this instrument is an RF generator that is the same way that signal amplitude is measured.
modulated at an audio frequency. amplitude range The maximum-to-minimum am-
amplitude-modulated transmitter A radio- plitude variation of a signal. It can be expressed
frequency transmitter whose carrier is varied in as a direct numerical ratio or in decibels.
amplitude, according to the rate of change of amplitude response The maximum output obtain-
some data-containing signal (such as voice, mu- able at various frequencies over the range of an
sic, facsimile, television pictures, control signals, instrument operating under rated conditions.
or instrument readings). amplitude selection The selection of a signal, ac-
amplitude modulation Abbreviation, AM. A cording to its correspondence to a predetermined
method of conveying intelligence in wireless com- amplitude or amplitude range.
amplitude separator • analog integrator
an output equal to their sum or difference (in any
amplitude separator In a television receiver, a cir-
combination), as desired.
cuit that separates the control pulses from the
analog channel In an ANALOG COMPUTER, an in-
composite video signal.
formation channel in which the extreme limits of
amplitude suppression ratio The ratio of an un-
data magnitude are fixed, and the data can have
desired output of a frequency-modulated (FM) re-
any value between the limits.
ceiver to the desired output, when the test signal
analog communications Any form of communica-
is amplitude modulated and frequency modu-
tions in which a carrier, generally an electromag-
netic wave or high-frequency current, is varied in
amplitude-versus-frequency distortion Distortion
a continuous and controlled way by a data-
resulting from varying gain or attenuation of an
containing signal. See ANALOG, 2.
amplifier or network, with respect to signal fre-
analog computer A computer in which input and
output quantities are represented as points on
AMTOR A form of amateur-radio data communica-
continuous (or small-increment) scales. To repre-
tions, in which the accuracy of a group of charac-
sent these quantities, the computer uses voltages
ters in a message is checked periodically by the
or resistances that are proportional to the num-
receiving station. If an error appears likely, then
bers to be worked on. When the quantities are
the receiving station sends an instruction to the
nonelectrical (such as pressure or velocity), they
transmitting station to retransmit that particular
are made analogous by proportional voltages or
group of characters. Characters are sent in
bunches with pauses for possible inquiries from
analog data 1. Data represented in a quantita-
the receiving station.
tively analogous way. Examples are the deflection
AM tuner A compact radio receiver unit that han-
of a movable-coil meter, the positioning of a slider
dles amplitude-modulated signals and delivers
on a slide rule, and the setting of a variable resis-
low-amplitude audio output to a high-fidelity am-
tor to represent the value of a nonelectrical quan-
plifier. Compare AM/FM TUNER and FM TUNER.
tity. Also see ANALOG. 2. Data displayed along a
amu Abbreviation of atomic mass unit.
smooth scale of continuous values (as by a
amusement robot An electromechanical robot, of-
movable-coil meter), rather than in discrete steps
ten computer-controlled, that is intended for use
(as by a digital meter).
as a toy.
analog differentiator An analog circuit or device
AN- A prefix designator used by American military
whose output waveform is the derivative of the
services to indicate commonality.
input-signal waveform, with respect to time.
anacoustic Pertaining to the lack of sound or ab-
sence of reverberation or transmission of sonic
analog 1. A quantity that corresponds, point for
point or value for value, to an otherwise unrelated
quantity. Thus, voltage is the analog of water
pressure, and current is the analog of water flow.
2. Varying over a continuous range and, there-
fore, capable of attaining an infinite number of
values or levels. Compare DIGITAL.
analog adder An analog circuit or device that re-
ceives two or more inputs and delivers an output
equal to their sum.
analog adder/subtracter An analog circuit or de-
vice that receives two or more inputs and delivers
analog divider An analog circuit or device that re-
ceives two inputs and delivers an output equal to
analog electronics Electronic techniques and
equipment that is based on uniformly changing
signals, such as sine waves, and often having
continuous-scale indicators, such as D’Arsonval
meters. Compare DIGITAL ELECTRONICS.
analog information Approximate numerical infor-
mation, as opposed to digital information, which
is assumed to be exact.
analog integrator An analog circuit or device
whose output waveform is the integral of the in-
put signal waveform, with respect to time.
28 analog inverting adder • AND circuit
that produces an analog record. The counterpart
is a digital recorder, which produces a readout in
discrete numbers (printed or visually displayed).
analog representation Representation of informa-
tion within a smooth, continuous range, rather
than as separate (discrete) steps or points.
analog signal A signal that attains an infinite
number of different amplitude levels, as opposed
to one that can attain only a finite number of lev-
els as a function of time.
analog subtracter An analog circuit or device that
receives two inputs and delivers an output equal
to their difference.
analog summer See ANALOG ADDER.
analog switch A switching device that will only
analog inverting adder An analog adder that de-
pass signals that are faithful analogs of trans-
livers a sum with the opposite sign to that of the
analog-to-digital conversion 1. A process in
analog meter An indicating instrument that uses
which an analog signal (such as a voice wave-
a movable-coil arrangement or the equivalent,
form) is changed into a digital or binary signal
causing a rotating pointer to indicate a particular
that conveys the same information. This process
value on a graduated printed scale. Compare
is commonly used in digital computers to encode
sounds and images. It is also used in communi-
cations systems to improve efficiency, minimize
the necessary bandwidth, and optimize the sig-
nal-to-noise ratio. 2. A process in which continu-
ous mechanical motion is encoded into a digital
or binary electronic signal.
analog-to-digital converter Any circuit or device
that performs ANALOG-TO-DIGITAL CONVER-
analysis 1. The rigorous determination of the con-
stants and modes of operation for electronic
equipment. Compare SYNTHESIS. 2. A branch of
mathematics dealing with point sets, relations,
analytical engine A primitive mechanical calculat-
ing machine, invented in 1833 by Charles Bab-
analog multiplexer 1. A multiplexer used with
analyzer 1. Any instrument that permits analysis
analog signals (see MULTIPLEXER). 2. An analog
through close measurements and tests (e.g., dis-
tortion analyzer, WAVE ANALYZER, or gas ana-
analog multiplier An analog circuit or device that
lyzer). 2. A computer program used for debugging
receives two or more inputs and delivers an out-
purposes; it analyzes other programs and sum-
put equal to their product.
marizes references to storage locations. 3. An
analog network A circuit that permits mathemati-
analysis interface to an oscilloscope.
cal relationships to be shown directly by electric
anastigmatic yoke Also called full-focus yoke. In a
or electronic means.
television (TV) receiver, a deflection yoke with a
analogous pole In a PYROELECTRIC MATERIAL,
cosine winding for better focus at the edges of the
the end or face having the positive electric charge.
analog output An output quantity that varies
anchorage In plastic recording tape, the adhesion
smoothly over a continuous range of values,
of the magnetic oxide coating to the surface of the
rather than in discrete steps.
analog record Also called analog recording. A
ancillary equipment Equipment that does not di-
record or recording method in which some prop-
rectly enter into the operation of a central system.
erty of the recorded material, such as displace-
Examples are input/output components of a com-
ment or magnetization, varies over a continuous
puter and test instruments attached to a system.
range that is relative to time and/or physical po-
AND circuit In digital systems and other switching
circuits, a logic gate whose output is high (logic 1)
analog recorder Any recorder, such as a recording
only when all input signals are high. Otherwise
oscillograph, potentiometric recorder, electroen-
the output is low (logic 0). Compare OR CIRCUIT.
cephalograph, electrocardiograph, or lie detector,
Anderson bridge • angle of beam
anechoic chamber An enclosure that does not re-
Anderson bridge An ac bridge circuit with six flect sound waves that approach its walls. Such a
impedances, permitting the value of an unknown chamber is used to test certain audio devices.
inductance to be determined in terms of a stan- anemograph An electromechanical device that
dard capacitance. produces a recording of wind speed versus time.
Generally, it consists of an ANEMOMETER con-
nected to a PEN-AND-INK RECORDER via a suit-
able electronic interface.
anemometer An instrument that measures or
indicates wind speed, or speed and direction (ve-
angel 1. An extraneous image, usually of short du-
ration, on a cathode-ray-tube (CRT) display. The
term applies particularly to anomalies in a radar
image caused by low-atmospheric reflection,
birds, or other mobile objects. 2. Air-deployed
metallic debris, also known as chaff, designed to
create radar echoes as a decoy or diversion tactic.
angle jamming A radar jamming technique in
which the return echo is jammed with a signal
containing improper azimuth or elevation angle
angle modulation Variation of the angle of a sine-
wave carrier in response to the modulating
source, as in FREQUENCY MODULATION and
angle noise In radar reception, the interference re-
sulting from variations in the angle at which an
AND gate 1. AND circuit. 2. In a TV receiver, an
echo arrives from the target.
AND circuit that holds the keyed-AGC signal off
angle of arrival The angle which the line of propa-
until a positive horizontal flyback pulse and a
gation of an incoming radio wave makes with the
horizontal sync pulse appear simultaneously at
surface of the earth. Compare ANGLE OF DE-
android A sophisticated robot built in humanoid
angle of azimuth The horizontal angle between
form. Usually, it propels itself by rolling on
the viewer and object or target, usually measured
wheels or on a track drive. A rotatable head con-
clockwise from north.
tains position sensors, a machine vision system,
angle of beam The angle enclosing most of the
and/or a machine hearing system. Mechanical
transmitted energy in the radiation from a direc-
arms are equipped with end effectors to perform
tional antenna. It is usually measured between
various tasks. The most advanced androids have
the half-power points in the main lobe of the di-
self-contained computer control systems.
rectional pattern. This angle can be measured in
anechoic Pertaining to the absence of echoes. Ex-
the horizontal (azimuth) plane or in the vertical
amples: ANECHOIC CHAMBER, anechoic enclo-
sure, or anechoic room.
30 angle of conduction • anhysteresis
angle of conduction 1. Also called angle of flow. frequency. Compare ANGLE OF LAG. Also see
The number of degrees of an excitation-signal cy- PHASE ANGLE.
cle during which output (drain, collector or plate) angle of radiation 1. The angle, measured with re-
current flows in an amplifier circuit. 2. The num- spect to the horizon, at which the principal lobe of
ber of degrees of any sine wave at which conduc- an electromagnetic wave leaves a transmitting
tion of a device (e.g., a diode) begins. antenna. 2. The angle, measured relative to the
angle of convergence 1. In any graphical repre- horizon, of a receiving or transmitting antenna’s
sentation, the angle formed by any two lines or optimum sensitivity.
plots that come together at a point. 2. The angle angle of reflection The angle, measured relative to
formed by the light paths of two photocells fo- the perpendicular (orthogonal) to a surface, sub-
cused on the same object. tended by a ray leaving the surface after having
angle of declination The angle between the hori- been reflected from it. Compare ANGLE OF INCI-
zon and a descending line. Compare ANGLE OF DENCE.
ELEVATION. angle of refraction The angle, measured relative
angle of deflection In a cathode-ray tube, the an- to the perpendicular (orthogonal) to a boundary
gle between the electron beam at rest and a new between two different media, subtended by a ray
position resulting from deflection. leaving the boundary after having been refracted
angle of departure The angle, relative to the thereat. Compare ANGLE OF INCIDENCE.
horizon, made by the line of propagation of a angle tracking noise Noise in a servo system that
transmitted radio wave. Compare ANGLE OF results in a tracking error.
ARRIVAL. angstrom (Anders J. Angstrom, 1814 –1874). A
unit of length used to describe certain extremely
short waves and microscopic dimensions; 1
angstrom equals 10–4 microns (10–10 meters).
angular deviation loss The ratio of microphone or
loudspeaker response on the principal axis of re-
sponse to the response at a designated angle from
that axis. Expressed in decibels.
angular difference See PHASE ANGLE.
angular displacement In an ac circuit, the separa-
tion, in degrees, between two waves. See PHASE
angular frequency The frequency of an ac signal,
expressed in radians per second (rad/sec) and ap-
proximately equal to 6.28f, where f is the fre-
quency in Hertz.
angular length Length, as along the horizontal
axis of an ac wave or along the standing-wave
angle of depression See ANGLE OF DECLINA- pattern on an antenna, expressed as the product
TION. of radians and wavelength.
angle of divergence In a cathode-ray tube, the an- angular-mode keys On a calculator or computer,
gle formed by the spreading of an undeflected the DEG, RAD, and GRAD keys for expressing or
electron beam as it extends from the gun to the converting angles in DEGREES, RADIANS, and
screen. GRADS, respectively.
angle of elevation The angle that an ascending angular phase difference For two sinusoidal
line subtends, with respect to the horizon. Com- waves, the phase difference, expressed in degrees
pare ANGLE OF DECLINATION. or radians.
angle of flow See ANGLE OF CONDUCTION. angular rate In navigation, the rate of bearing
angle of incidence The angle, measured relative to change, expressed in degrees or radians.
the perpendicular (orthogonal) to a surface or angular resolution The ability of a radar to distin-
boundary, subtended by an approaching ray. guish between two targets by angular measure-
Compare ANGLE OF REFLECTION and ANGLE ment.
OF REFRACTION. angus pen recorder An instrument that makes a
angle of lag The phase difference (in degrees or ra- permanent record of the time whenever a channel
dians) whereby one component follows another in is used.
time, both components being of the same fre- anharmonic oscillator An oscillating device in
quency. Compare ANGLE OF LEAD. Also see which the force toward the balance point is not
PHASE ANGLE. linear, with respect to displacement.
angle of lead The phase difference (in degrees or anhysteresis The magnetization of a material by a
radians) whereby one component precedes an- unidirectional field containing an alternating field
other in time, both components being of the same component of gradually decreasing amplitude.
anhysteretic state • anomalous propagation
anhysteretic state The condition of a substance anode efficiency Also called plate efficiency. In a
after it has been subjected to a strong magnetic power amplifier using an electron tube, the ratio
field, the intensity of which alternates in direction Po/Pi, where Po is the output power in watts and Pi
and diminishes gradually to zero. is the dc anode power input in volt-amperes.
animism A belief or philosophy, held especially in anode power input Symbol, PA(input). The product of
Eastern civilizations, such as Japan, that all anode current and anode voltage.
things contain an essence of life. This theory ren- anode power supply The ac or positive dc power
ders irrelevant the question of whether or not ma- supply unit that delivers current and voltage to
chines, such as computers and robots can be the anode of a device.
“alive.” anode saturation The point beyond which a fur-
anion A negative ion. Also see ION. ther increase in anode voltage does not produce
anisotropic Pertaining to the tendency of some an increase in anode current.
materials to display different magnetic and other
physical properties along different axes.
ANL Abbreviation of AUTOMATIC NOISE LIMITER.
anneal To heat a metal to a predetermined temper-
ature and let it cool slowly. The operation pre-
vents brittleness and often stabilizes electrical
annealed laminations Core laminations for trans-
formers or choke coils that have been annealed.
annealed shield A magnetic shield for cathode-ray
tubes, that has been processed by annealing.
annealed wire Soft-drawn wire that has been sub-
jected to annealing.
annotations 1. Marking on copies of original engi-
neering-installation documents to show changes
made during the installation. 2. Any set of com-
ments or notes accompanying a program, an
equipment or system, or a process.
annular 1. Pertaining to the region between two
concentric circles that lie in the same plane; ring-
shaped. 2. Pertaining to two or more concentric
circles that lie in a common plane.
annular conductor A number of wires stranded in
three concentric layers of alternating twists
around a hemp core.
annular transistor A mesa transistor in which the
base and collector take the form of concentric anode strap In a multicavity magnetron, a metal
rings around a central emitter. strap connecting the anodes.
annulling network A subcircuit that shunts a fil- anode terminal 1. In a diode, the terminal to
ter to cancel reactive impedance at the extreme which a positive dc voltage must be applied for
ends of the pass band of the filter. forward bias. Compare CATHODE TERMINAL. 2.
annunciation relay A relay that indicates whether In a diode, the terminal at which a negative dc
or not a circuit is carrying current. voltage appears when the device is used as an ac
annunciator A device that produces loud sound rectifier. Compare CATHODE TERMINAL. 3. The
and/or conspicuous light to attract attention terminal that is connected internally to the an-
(e.g., the electronic siren in an automotive secu- odic element of any device.
rity system). anode voltage Symbol, EA or VA. The difference in po-
anode 1. The positive electrode of a vacuum tube tential between the anode and cathode of a device.
or solid-state device (i.e., the electrode toward anodic Pertaining to the anode of a device, or to
which electrons move during current flow). 2. In anode-like effects.
an electrochemical cell, the electrode that loses anodizing An electrolytic process in which a pro-
electrons by oxidation. This is usually the nega- tective oxide film is deposited on the surface of a
tive electrode. metallic body acting temporarily as the anode of
anode balancing coil Mutually coupled windings the electrolytic cell.
used to maintain equal currents in parallel an- anomalous dispersion Dispersion of electromag-
odes operating from a common transformer ter- netic radiation that is characterized by a decrease
minal. in refractive index with increase in frequency.
anode current Current flowing in the anode circuit anomalous propagation 1. The low-attenuation
of a device. propagation of UHF or microwave signals through
32 anomalous propagation • antenna current
atmospheric layers. 2. Unusual, bizarre, or unex- antenna amplifier 1. A radio-frequency amplifier,
plainable electromagnetic-wave propagation (e.g., often installed at the antenna, used to boost sig-
apparent F-layer ionospheric effects in the FM nals before they reach a receiver (also called an
broadcast band). 3. Rapid fluctuation of a sonar RF preamplifier). 2. Occasionally, the first RF am-
echo because of variations in propagation. plifier stage of a receiver, also known as the front
anoxemia toximeter An electronic instrument for end.
measuring or alerting against the onset of anox- antenna array See ARRAY.
emia (deficiency of oxygen in the blood)—espe- antenna bandwidth The frequency range through-
cially in airplane pilots. out which an antenna will operate at a specified
AN radio range A navigational facility entailing four efficiency without needing alteration or adjust-
zones of equal signal strength. When the aircraft ment.
deviates from course, an aural Morse-code signal, antenna beamwidth A measure of the extent to
A (DIT DAH) or N (DAH DIT) is heard; but when the which a directional antenna focuses a transmit-
aircraft is on course, a continuous tone is heard. ted electromagnetic field, or focuses its response
ANSI Acronym for American National Standards In- to incoming electromagnetic fields. Expressed as
stitute. the angle in degrees between opposite half-power
AN signal The signal provided by an AN radio range points in the main lobe of the directional pattern.
to apprise aircraft pilots of course deviation. Usually determined in the horizontal plane, but
answerback The automatic response of a terminal occasionally in the vertical plane.
station to a remote-control signal. antenna coil The primary coil of the input RF
answer cord In a telephone system, the cord used transformer of a receiver, or the secondary coil of
for answering subscribers’ calls and incoming the output RF transformer of a transmitter.
answering machine A device that automatically
answers a telephone and records an audio mes-
sage from the caller.
answer lamp A telephone switchboard lamp that
lights when an answer cord is plugged into a line
jack; it switches off when the telephone answers
and lights when the call is completed.
ant Abbreviation of ANTENNA.
antenna In a communications system, a special-
ized transducer that converts incoming electro-
magnetic fields into alternating electric currents
having the same frequencies (receiving antenna),
or converts an alternating current at a specific
frequency into an outgoing electromagnetic field
at the same frequency (transmitting antenna). An antenna coincidence The condition in which two
antenna can be a simple wire or rod, or a compli- directional antennas are pointed directly toward
cated structure. Thousands of geometries and each other.
specifications are possible. The optimum antenna antenna-conducted interference Extraneous sig-
type for a given situation depends on the commu- nals generated in a transmitter or receiver and
nications frequency, the distance to be covered, presented to the antenna, from which they are ra-
and various other factors. diated.
antenna ammeter An RF ammeter, usually of the antenna core A ferrite rod or slab around which a
thermocouple type, employed to measure current coil of wire is wound to act as a self-contained an-
flowing to a transmitting antenna. tenna, usually in a miniature receiver.
antenna coupler A device consisting of an induc-
tor, RF transformer, or a combination of induc-
tor(s) and capacitor(s), used to match the
impedance of an antenna to that of a transmitter
or receiver. Also known as a transmatch or an-
antenna coupling Inductive and/or capacitive
coupling used to optimize the transfer of energy
from an antenna to a receiver, or from a trans-
mitter to an antenna.
antenna current 1. Radio-frequency current flow-
ing from a transmitter into an antenna. 2. Radio-
frequency current flowing from a receiving
antenna into a receiver.
antenna detector • antenna pattern
antenna detector A circuit that warns aircraft jects in the vicinity of an antenna which, taken
personnel that they are being observed by radar. together, form the radio-frequency (RF) ground
It picks up the radar pulses and actuates a warn- system against which the antenna operates.
ing light or other device. Some antennas require an extensive ground sys-
antenna diplexer A coupling device that permits tem to function efficiently; others need no ground
several transmitters to share one antenna with- system.
out troublesome interaction. Compare ANTENNA antenna/ground system An arrangement em-
DUPLEXER. bodying both an antenna and a low-resistance
antenna directivity The directional characteris- connection to the earth, as opposed to an an-
tics of a transmitting or receiving antenna, usu- tenna system that involves no connection to
ally expressed qualitatively (e.g., omnidirectional, earth.
bidirectional, or unidirectional ). A more precise antenna height 1. The height of an antenna above
expression is ANTENNA BEAMWIDTH. the surface of the earth immediately beneath the
antenna director In a directional antenna, a PAR- driven element(s). 2. The height of an antenna
ASITIC ELEMENT situated in front of the radiator above the effective radio-frequency (RF) ground
and separated from it by an appropriate fraction immediately beneath the driven element(s). 3.
of a wavelength. Its function is to intensify radia- The height of an antenna above average terrain,
tion in the direction of transmission. Compare determined against the mean altitude of a num-
ANTENNA RADIATOR and ANTENNA REFLEC- ber of points on the earth’s surface that lie within
TOR. a certain radius of the antenna structure. Also
antenna duplexer A circuit or device permitting called height above average terrain (HAAT).
one antenna to be shared by two transmitters antenna impedance The complex-number im-
without undesirable interaction. pedance that an antenna presents to a transmis-
antenna effect The tendency of wires or metallic sion line. It can vary over a tremendous range,
bodies to act as antennas (i.e., to radiate or re- and depends on the antenna type, antenna size,
ceive radio waves). antenna height, operating frequency, and various
antenna efficiency The ratio of radio-frequency other factors.
energy supplied to a wireless transmitting an- antenna-induced potential Also called antenna-
tenna, to the energy radiated into space. Electri- induced microvolts. The voltage across the open-
cally, the radiation resistance of the antenna (RR) circuited terminals of an antenna.
appears in series with loss resistance (RL). The ef- antenna lens Also called lens antenna. A radiator
ficiency Eff of the antenna can be determined by designed to focus microwave energy in much the
the following formula: same manner that an optical lens focuses light
rays. Lens antennas are made from dielectric ma-
Eff = RR/(RR + RL)
terials and/or metals.
As a percentage,
antenna loading 1. The insertion of inductance in
Eff % = 100 (RR/(RR + RL) antenna elements to lower the resonant fre-
quency of the system without necessarily making
The efficiency is always less than 1 (100 percent)
the system physically larger or the elements
because, in practice, the loss resistance can
longer. 2. The insertion of capacitance in antenna
never be reduced to zero.
elements to raise the resonant frequency of the
antenna factor A factor (in decibels) added to an
system without necessarily making the system
RF voltmeter reading to find the true open-circuit
physically smaller or the elements shorter.
voltage induced in an antenna.
antenna lobe A well-defined region in the radiation
antenna field The electromagnetic field immedi-
pattern of an antenna in which radiation is most
ately surrounding an antenna.
intense, or in which reception is strongest. Also
antennafier Low-profile antenna/amplifier device,
see ANTENNA PATTERN.
sometimes used with portable communications
antenna matching The technique of establishing a
systems. Also called an active antenna.
satisfactory relationship between the antenna
antenna front-to-back ratio For a directional an-
impedance and the transmission-line or trans-
tenna, the ratio of field strength in front of the an-
mitter-output impedance, for maximum transfer
tenna (i.e., directly forward in the line of
of power into the antenna. Also, the matching
maximum directivity) to field strength in back of
of antenna impedance to receiver-input im-
the antenna (i.e., 180 degrees from the front), as
pedance, for delivery of maximum energy to the
measured at a fixed distance from the radiator. It
is usually specified in decibels.
antennamitter An antenna/oscillator combina-
antenna gain For a given antenna, the ratio of sig-
tion that serves as a low-power transmitter.
nal strength (received or transmitted) to that ob-
antenna pattern A polar plot of antenna perfor-
tained with a comparison antenna, such as a
mance that shows field strength versus angle of
simple dipole. Generally specified in decibels.
azimuth, with the antenna at the center. It is
antenna ground system The earth, counterpoise,
usually specified in the horizontal plane.
guy wires, radials, and/or various conducting ob-
34 antenna polarization • anthropomorphism
antenna range 1. The frequency band, communi-
cation distance characteristically covered, or
other continuum of values that specify the oper-
ating limits of an antenna. 2. The region immedi-
ately surrounding an antenna in which tests and
measurements usually are made. Sometimes
called ANTENNA FIELD.
antenna reflector In a directional antenna, a PAR-
ASITIC ELEMENT situated behind the radiator
and separated from the latter by an appropriate
fraction of a wavelength. Its function is to inten-
sify radiation in the direction of transmission.
Compare ANTENNA DIRECTOR and ANTENNA
antenna relay In a radio station, a low-loss, heavy-
duty relay that enables the antenna to be
switched between transmitter and receiver.
antenna polarization The orientation of electric antenna resistance The resistive component of
lines of flux, with respect to the surface of the ANTENNA IMPEDANCE.
earth, for which an antenna is most efficient. A antenna resonant frequency The frequency, or
vertical antenna radiates and receives vertically narrow band of frequencies, at which an an-
polarized waves. A horizontal antenna radiates tenna’s impedance appears resistive.
and receives horizontally polarized waves broad- antenna stage 1. The first RF amplifier stage of a
side to itself, and vertically polarized waves at receiver. 2. Occasionally, the final RF amplifier of
high elevation angles off its ends. In other direc- a transmitter.
tions, the polarization is slanted at various an- antenna switch In a radio station, a low-loss,
gles. heavy-duty switch that enables the antenna to be
antenna power Symbol, Pant. The RF power devel- connected to transmitter, receiver, or safety
oped in an antenna by a transmitter; Pant equals ground.
I 2R, where I is the antenna current and R is the
antenna resistance at point I is measured.
antenna power gain The ratio of the maximum ef-
fective radiated power (ERP) from a wireless
transmitting antenna to the ERP from a reference
antenna, expressed in decibels (dB). If the ERP
from an antenna under test is PT watts and the
ERP from the reference antenna is PR watts, then
the gain GdB is:
GdB = 10 log10 (PT/PR)
Power gain is always measured in the direction in
which the test antenna performs the best. The
antenna system Collectively, an antenna and all of
reference antenna, usually a dipole, is chosen
the auxiliary electrical and mechanical devices
with a gain assumed to be unity, or 0 dB. Gain
needed for its efficient operation, including cou-
relative to a dipole is expressed in dBd (decibels
plers, tuners, transmission lines, supports, insu-
relative to a dipole). Alternatively, the reference
lators, and rotator.
antenna can be an isotropic radiator, in which
antenna terminals 1. The points at which a trans-
case the gain is expressed in dBi (decibels relative
mission line is attached to an antenna. 2. The sig-
to an isotropic radiator). Gain figures in dBd and
nal input terminals of a receiver. 3. The signal
dBi differ by a constant amount as follows:
output terminals of a transmitter.
GdBi = 2.15 + GdBd antennaverter An antenna and converter com-
bined into a single circuit, intended for connec-
antenna preamplifier A highly sensitive amplifier
tion to the antenna terminals of a receiver to
used to enhance the gain of a receiver. It is usu-
allow operation on frequencies outside the band
ally used at the very high frequencies and above.
for which the receiver has been designed.
antenna radiation The propagation of radio waves
antenna wire 1. The radiator element of a wire-
by a transmitting antenna.
type antenna. 2. A strong solid or stranded wire
antenna radiator The element of an antenna that
(e.g., hard-drawn copper, copper-clad steel, or
receives RF energy from the transmitter and radi-
phosphor-bronze) used for antennas.
ates waves into space. Also known as the driven
anthropomorphism The perception, by people, of
element. Compare ANTENNA DIRECTOR and AN-
machines as having human qualities. This can
anthropomorphism • antiparticle
example, log 10,000 = log 104 = 4, and thus an-
lead to emotional attachment to hardware, such
tilog 4 = 104 = 10,000.
as computers and robots. The more sophisticated
the apparatus, in general, the more powerful this antilogous pole In a PYROELECTRIC MATERIAL,
perception can become. the end that becomes negatively charged as the
antialiasing filter A low-pass or bandpass filter temperature rises.
that limits the bandwidth of an input signal to antimagnetic Pertaining to materials having ex-
prevent aliasing and its effects. See ALIASING, 1. tremely low RETENTIVITY.
anticapacitance switch A switch whose members antimatter Pertaining to particles that are the
are thin blades and stiff wires widely separated to counterparts of conventional particles (i.e.,
minimize capacitance between them. positrons instead of electrons, antineutrons in-
anticathode The target electrode of an X-ray tube. stead of neutrons, and antiprotons instead of
Anticipatory Sciences A group of futurists, people protons). When a particle meets its antiparticle,
who attempt to predict the course of technology. the two annihilate, releasing energy. Also see AN-
Some futurists believe that progress will continue TIPARTICLE.
until, for example, homes become fully automated antimicrophonic See NONMICROPHONIC.
and artificial intelligence reaches a level compara- antimony Symbol, Sb. A metalloidal element.
ble to human intelligence. Other futurists believe Atomic number, 51. Atomic weight, 121.76. Often
that such things are highly improbable. used as n-type dopant in semiconductor manu-
anticlutter circuit A supplementary circuit in a facture.
radar receiver that minimizes the effect of extra- antineutrino The antiparticle of the NEUTRINO,
neous reflections that would obscure the image of emitted as a result of radioactive decay.
the target. antineutron An uncharged particle with a mass
anticlutter gain control In a radar receiver, a cir- equal to that of the neutron, but with a magnetic
cuit that automatically raises the gain of the re- moment in the direction opposite that of the neu-
ceiver slowly to maximum after each transmitter tron.
pulse to reduce the effect of clutter-producing antinode A point of maximum amplitude in a
echoes. standing wave.
anticoincidence Noncoincidental occurrence of
two or more signals. Compare COINCIDENCE.
anticoincidence circuit In computers and control
systems, a circuit that delivers an output signal
only when two or more input signals are not re-
ceived simultaneously. Compare COINCIDENCE
CIRCUIT. Also see NAND CIRCUIT.
anticoincidence operation An exclusive-OR oper-
anticollision radar A vehicular radar system that
is used to minimize the probability of a collision
with another vehicle, whether or not that other
vehicle has a similar system. antinoise carrier-operated circuit A circuit that
antiferroelectric 1. Pertaining to the property cuts off the audio output of a receiver while the
wherein the polarization curve of certain crys- station transmitter is in use. This can be accom-
talline materials shows two regions of symmetry. plished in the automatic-gain-control (AGC) cir-
2. A material that exhibits the aforementioned cuit of the receiver, or in the speaker or audio
property. line. The circuit is actuated by energy from the
antiferromagnetic Pertaining to the behavior of transmitted signal.
materials in which, at low temperatures, the antinoise microphone Any microphone that dis-
magnetic moments of adjacent atoms point in op- criminates against acoustic noise (e.g., a lip mi-
posite directions. crophone or throat microphone).
antihunt The condition in which hunting is coun- antinucleon A particle with the mass of a nucleon,
teracted, usually by removing overcorrection in but with the opposite electrical charge and direc-
automatic control or compensation systems. tion of magnetic moment. Compare NUCLEON.
antihunt circuit 1. A circuit that minimizes or antioxidant A material, such as a lacquer coat or
eliminates hunting. Also see ANTIHUNT. 2. In a an inactive oxide layer, that prevents or slows ox-
television (TV) receiver, a circuit that stabilizes an idation of a material exposed to air.
automatic frequency control (afc) system. antiparticle A subatomic particle opposite in char-
antijamming Pertaining to communications sys- acter to conventional particles, such as electrons,
tems that are resistant to, or that counteract, the neutrons, protons. Antiparticles constitute
effects of jamming. antimatter. Also see ANTINEUTRINO, ANTI-
antilogarithm Abbreviated, antilog or log–1. The NEUTRON, ANTINUCLEON, ANTIPROTON, and
number corresponding to a given logarithm. For POSITRON.
36 antiphase • A plus
antiphase The property of being in phase opposi- aperture 1. The larger, normally open end of a
tion (180 degrees out of phase). horn antenna or horn loudspeaker. 2. An opening
antipincushioning magnets In some television in an opaque disk or mask that passes a prede-
(TV) receivers, a pair of corrective magnets in the termined amount of light or other radiant energy.
deflection assembly on the picture tube that elim- 3. The portion of a directional antenna through
inate pincushion distortion (disfigurement of the which most of the radiated energy passes.
raster so that it resembles a pincushion—a rect- aperture angle For an antenna or telescope or mi-
angle with its sides bowed in). croscope, the half angle formed by the radius of
antiproton A subatomic particle with a mass equal the detecting instrument, as viewed from the
to that of the proton, but with opposite electrical source.
antiquark An ANTIPARTICLE of a QUARK.
antirad substance A material that protects against
damage caused by atomic radiation.
antiresonance 1. Parallel resonance. 2. The con-
dition of being detuned from a resonant fre-
antiresonant circuit See PARALLEL-RESONANT
antiresonant frequency 1. The resonant fre-
quency of a parallel-resonant circuit. 2. In a
piezoelectric crystal, the frequency at which
impedance is maximum (as in a parallel-resonant aperture antenna An antenna whose beamwidth
circuit). depends on the size of a horn, reflector, or lens.
antisidetone Pertaining to the elimination in tele- aperture compensation In a television (TV) cam-
phone circuits of interference between the micro- era, the minimizing of APERTURE DISTORTION
phone and earphone of the same telephone. by widening the video-amplifier passband.
antistickoff voltage The low voltage applied to the aperture distortion In a television (TV) camera
coarse synchro control transformer rotor winding tube, a form of distortion that occurs when the
in a dual-speed servo system to eliminate am- scanning beam covers several mosaic elements
biguous behavior in the system. simultaneously. This condition, caused by exces-
antitransmit/receive switch Abbreviated ATR. In sive beam thickness, results in poor image reso-
a radar installation, an automatic device to pre- lution.
vent interaction between transmitter and re- aperture mask In a three-gun color picture tube, a
ceiver. thin, perforated sheet mounted behind the view-
antivirus program A computer program or utility ing screen to ensure that a particular color phos-
designed to detect and eliminate viruses and Tro- phor will be excited only by the beam for that
jan horses in a computer system. color. Also called shadow mask.
antivoice-operated transmission Radio commu- aperture synthesis In telescopes, a method of ob-
nications that use a voice-activated circuit as a taining high resolution using several small anten-
transmitter interlock during reception on the nas separated by great distances. The small
companion receiver. antennas are moved around to simulate the re-
apc 1. Abbreviation of automatic picture control. 2. solving power of a much larger antenna that
Abbreviation of AUTOMATIC PHASE CONTROL. would, in practice, be impossible or impractical to
aperiodic Characterized by a lack of predictable construct.
repetitive behavior. For example, the sferics or aphelion 1. The point at which a solar-orbiting
“static” electromagnetic interference caused by satellite attains its highest altitude. It occurs
lightning. once for every complete orbit. At this point, the
aperiodic current The unidirectional current that satellite travels slower than at any other point in
follows an electromagnetic disturbance in an LCR the orbit. 2. The altitude, measured from the
circuit, in which R is equal to or higher than the sun’s surface or the sun’s center, of a solar-
critical circuit resistance. orbiting satellite at its most distant point.
aperiodic damping Damping of such a high degree APL Abbreviation for A Programming Language. A
that the damped system, after disturbance, high-level computer language designed for ease of
comes to rest without oscillation or hunting. use, and characterized by the requirement for a
aperiodic discharge A discharge in which current special character set.
flowing in an LCR circuit is unidirectional, rather apl 1. Abbreviation of average picture level. 2. Ab-
than oscillatory. For this condition, 1/LC is less breviation of automatic phase lock.
than or equal to R2/4L2. A plus Also, A+. The positive terminal of an A bat-
aperiodic function A nonrepetitive function (e.g., tery. Also, pertaining to the part of a circuit con-
a hyperbolic trigonometric function). nected to that terminal.
apogee • arc cosecant
apogee 1. The point at which an earth-orbiting appliance Electrical equipment in general. This
satellite attains its highest altitude. It occurs might include any home-operated device.
once for every complete orbit. At this point, the application A task or job for which an electronic
satellite travels slower than at any other point in device or system is used. It especially pertains to
the orbit. 2. The altitude, measured from the personal-computer software that has practical
earth’s surface or the earth’s center, of an earth- usefulness.
orbiting satellite at its most distant point. application factor A factor involved in determin-
A power supply A term sometimes used to denote ing the failure rate of a circuit or system affected
the unit that supplies energy to a vacuum-tube by unusual operating conditions.
filament. Compare B POWER SUPPLY. application schematic diagram A diagram of pic-
apparent bearing In radio-direction finding, the torial symbols and lines that illustrate the inter-
uncorrected direction from which a signal ap- relationship of functional circuit blocks in a
pears to arrive. specific program mode.
apparent power In an ac circuit, the power value applicators 1. In dielectric heating, the electrodes
obtained by multiplying the current by voltage (P between which the dielectric body is placed and
equals IE), with no consideration of the effects of the electrostatic field developed. 2. In medical
phase angle. Compare TRUE POWER. electronics, the electrodes applied to a patient
apparent power loss The loss in an ammeter or undergoing diathermy or ultrasonic therapy.
voltmeter, caused by the imperfection of the in- applied voltage The voltage presented to a circuit
strument. At full scale, the ammeter has a certain point or system input, as opposed to the voltage
voltage across its terminals; the apparent power drop resulting from current flow through an ele-
loss is the current multiplied by this voltage. A ment.
voltmeter carries a small current; the apparent applique circuit A circuit for adapting equipment
power loss is the product of the current and the to a specialized job.
indicated voltage. approach-control radar A radar installation serv-
appearance potential The potential through ing a ground-controlled approach (GCA) system.
which an electron must move to produce a cer- approximate data 1. Data obtained through phys-
tain ion from the atom with which it is associated. ical measurements. Such data can never be ex-
applause meter An instrument consisting essen- act; all measurements are subject to error. 2.
tially of a microphone, audio amplifier, and indi- Loosely estimated data or imprecise calculations.
cating meter (reading directly in sound level). It is AQL Abbreviation of ACCEPTABLE QUALITY
so called because of its familiar use in measuring LEVEL. A statistically defined quality level, de-
audience response, as indicated by loudness of fined in terms of percent defective, accepted on
applause. an average of 95 percent of the time.
Aquadag A tradename for a material that consists
of a slurry of fine particles of graphite. Aquadag
forms a conductive coating on the inside and out-
side walls of some cathode-ray tubes.
aqua pura Pure water; in most instances, distilled
water. Formula, H2O. Pure water is a nonconduc-
tor with a dielectric constant of about 81.
Ar Symbol for ARGON.
arbitrary function fitter A circuit or device, such
as a potentiometer, curve changer, or analog
computer element, providing an output current
or voltage that is some preselected function of the
input current or voltage.
arc 1. A luminous sustained discharge between
two electrodes. Because it is sustained, rather
than intermittent, an arc is distinguished from a
spark discharge, the latter being a series of dis-
charges (sparks)—even when it appears continu-
ous. 2. In graphical presentations, a section of
Applegate diagram For a velocity-modulated tube,
curved line, as of a circle.
a plot of the positions of electron bunches in the
arc angle The angle in degrees traced out by a cir-
drift space versus time.
cular arc if the center point of the circle is con-
Appleton layer Collectively, the F1 and F2 layers
sidered to be the vertex of an angle formed by
of the ionosphere, at a height between 150 and
two rays intersecting the arc at designated
400 kilometers above the surface of the earth.
apple tube A color picture tube, used in television,
arc cosecant Abbreviated arc csc or csc–1. 1. The
with the red, blue, and green phosphor in vertical
inverse of the cosecant function. 2. The angle, in
38 arc cosecant • area code
radians or degrees, corresponding to a given
arc cosine Abbreviated arc cos or cos–1. 1. The in- arc length The length along a given arc, usually a
part of the circumference of a circle. If the circle
verse of the cosine function. 2. The angle, in radi-
has circumference C and the arc measures x de-
ans or degrees, corresponding to a given cosine.
arc cotangent Abbreviated arc cot or cot–1. 1. The grees, then the arc length is Cx/360 units.
arc minute See MINUTE.
inverse of the cotangent function. 2. The angle, in
arc oscillation Oscillations that can occur when
radians or degrees, corresponding to a given
opening relay contacts arc.
arcover The occurrence of an electrical ARC be-
arc failure 1. Damage to, and/or failure of, insula-
tween electrodes, contacts, or capacitive plates.
tion or a dielectric as a result of ARCOVER. 2.
arcover voltage The voltage at which disruptive
Failure of make-and-break contacts through
discharge occurs, typically accompanied by an
damage caused by arcover.
arc function An inverse trigonometric function. See
arc resistance The ability of a material, usually a
ARC COSECANT, ARC COSINE, ARC COTAN-
dielectric, to resist damage from arcing. This
GENT, ARC SECANT, ARC SINE, and ARC TAN-
property is commonly expressed as the length of
time between the start of the arc and the estab-
arc furnace A high-temperature electric furnace in
lishment of a conductive path through the mate-
which heat is produced by one or more electrical
arc secant Abbreviated arc sec or sec–1. 1. The in-
architecture The functional design elements of a
verse of the secant function. 2. The angle, in ra-
computer—especially the components of the cen-
dians or degrees, that corresponds to a given
tral processing unit (CPU) and the manner in
which these elements interact.
arc second See SECOND.
archived file A computer file stored on some
arc sensor A device for detecting visible arcs and
backup medium, such as magnetic tape, disk-
excessive reflected power in microwave systems.
ette, or CD-ROM (compact disk, read-only mem-
arc sine Abbreviated arc sin or sin–1. 1. The inverse
ory), rather than being held on the hard disk.
of the sine function. 2. The angle, in radians or
Such a file will be apart from the operating sys-
degrees, that corresponds to a given sine.
tem’s catalog of current files, but can be reconsti-
arc suppression Extinguishing an arc discharge.
tuted as needed.
Disruptive arcs in electronic circuits are sup-
archives A complete, periodically updated set of
pressed by means of auxiliary diodes or resistor-
arcing See ARCOVER.
arc-suppressor diode A semiconductor diode used
arcing contacts Make-and-break contacts be-
to prevent arcing between make-and-break con-
tween which an arc occurs when they are sepa-
arc tangent Abbreviated arc tan or tan–1. 1. The
arcing ring A metal ring placed around an insula-
inverse of the tangent function. 2. The angle, in
tor in a high-voltage electrical system. This keeps
radians or degrees, corresponding to a given tan-
an arc from charring or breaking the insulator.
arcing time The elapsed time between the break-
arcthrough The puncturing of a material by an
ing of contacts and the end of the arc between the
area code In the United States, a three-digit
arc lamp An electric lamp in which a brilliant arc
number that indicates the location, according to
jumps between the tips of two rods (originally car-
specified assigned districts, of a telephone sub-
area code • arithmetic symmetry
scriber. When making a lon