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( 42)


(main unit only) pull the detector oscillator into phase with itself,
detector blocking • diagnosis

thereby causing the detector to oscillate at the
signal frequency.
detector circuit A demodulator circuit (i.e., one

Instantaneous deviation (kHz)
used to recover the intelligence from a modulated
detector probe See DEMODULATOR PROBE.
= + 5 kHz

detector pull-in See DETECTOR BLOCKING.
detector stage In a receiver or instrument, the
separate stage that contains the detector circuit. Time
Some systems, such as a superheterodyne re-
ceiver, have more than one detector. Also see
detent A mechanical stop used on a rotary switch
to hold the switch pole securely in each selected
detune 1. To adjust a circuit to some frequency
other than its resonant frequency. 2. To set the
frequency of a receiver or transmitter to some
point other than the frequency normally used. 3.
To stagger-tune a receiver intermediate-fre-
duce a specified audio output power. Expressed
quency system.
in kilohertz, or as a percentage of rated deviation
detuning Tuning to a point above or below the fre-
of the receiver, measured with the receiver set for
quency to which a device or system is normally
maximum gain.
(or initially) adjusted (usually the resonant fre-
device 1. A simple or complex discrete electronic
quency of the device).
component. 2. A subsystem used as a unit, and
detuning stub A device used for the purpose of
regarded as a single component.
coupling a feed line to an antenna, while choking
device complexity The number of components in
off currents induced on the feed line as a result of
an integrated circuit.
the near-field radiation of the antenna.
device independence A characteristic of a com-
deupdating Producing an earlier form of a com-
puter, that allows operation independent of the
puter file by substituting older records for cur-
types of input/output devices used.
rent ones.
deuterium Symbol, D, d, H2, or 2H. Also called dew point For a gas containing water vapor
(typically air), the highest temperature at which
heavy hydrogen. The hydrogen isotope having a
the vapor condenses as the gas is cooled. The dew
nucleus consisting of one proton and one neu-
point depends on the amount of vapor in the gas.
dew-point recorder An instrument for determin-
deuterium oxide Symbol, D2O. Also called heavy
ing and recording the temperature at which water
water. This compound has wide use in nuclear
vapor in the air condenses to a liquid.
DF Abbreviation of DIRECTION FINDER.
deuteron The nucleus of a deuterium atom.
DF antenna An antenna that is mechanically ro-
deuton See DEUTERON.
tatable or has an electrically rotatable response
deutron See DEUTERON.
pattern for use with a direction finder.
deviation 1. In a frequency-modulated (FM) radio
DF antenna system Two or more DF antennas ar-
signal, the instantaneous amount of carrier fre-
ranged for maximum directivity and maneuver-
quency shift away from the unmodulated fre-
ability, together with associated feeders and
quency. It is usually expressed in kilohertz;
directly proportional to the amplitude of the mod-
D flip-flop A delayed flip-flop. The state of the in-
ulating signal, up to a certain maximum that de-
put determines the state of the output during the
pends on the bandwidth allowed. 2. The
following pulse, rather than during the current
maximum instantaneous carrier frequency shift
in a FM signal. 3. The extent or amount by which
dg Abbreviation of decigram.
a quantity drifts from its proper value.
dia Abbreviation of diameter.
deviation distortion In a frequency-modulation
diac A two-terminal, bilateral, three-layer semicon-
(FM) receiver, distortion resulting chiefly from
ductor device that exhibits negative resistance.
discriminator nonlinearity and restricted band-
When the applied voltage exceeds a critical value,
the device conducts.
deviation ratio In a frequency-modulated (FM)
diagnosis 1. Determination of the cause and loca-
signal, the ratio between the highest modulating
tion of a hardware malfunction. 2. In computer
frequency and the maximum carrier deviation.
operations, determination of the cause of a sys-
deviation sensitivity For a frequency-modulation
tem operation error.
(FM) receiver, the smallest deviation that will pro-
182 diagnostic routine • diamond lattice

diagnostic routine 1. An efficient sequence of di- dial jack In a telephone system, a set of jacks that
agnostic tests for rapid, foolproof trouble-shoot- facilitates interconnections between dial cords
ing of electronic hardware. 2. A computer and external lines.
software package intended for debugging dial light A lamp or light-emitting diode placed in
programs, or for finding the cause of a hardware the dial mechanism of a radio receiver, transmit-
or operating-system malfunction. Also called ter, or transceiver. Allows the dial to be read in
diagnostic, diagnostic program, or diagnostic dim light or in darkness.
utility. dialog equalizer In sound transmission and re-
diagnostic test 1. A test made primarily to cording, a high-pass filter that reduces low-
ascertain the cause of dysfunction in electronic frequency response during dialog and extreme
equipment. Compare PERFORMANCE TEST. 2. closeups.
To apply a diagnostic routine to hardware faults, dial pulse An interruption of the direct current in a
or to implement one to prevent such a fault. telephone system when the dial contacts of the
diagnotor In digital computer operations, a trou- calling telephone open. The number of such in-
bleshooting routine combining both diagnosis terruptions corresponds to the digit dialed.
and editing. dial scale The graduated portion of a dial.
diagram A (usually line) drawing depicting a cir- dial system 1. See DIAL TELEPHONE SYSTEM.
cuit, assembly, or organization. See, for example, 2. The arrangement of dials and knobs that facil-
BLOCK DIAGRAM and CIRCUIT DIAGRAM. itates adjustment of electronic equipment.
dial 1. A graduated scale, arranged horizontally, dial telephone A telephone set in which a num-
vertically, in a circle, or over an arc. Used to show bered rotatable disk is used to produce the switch
the distance through which a variable component interruptions that cause generation of the trans-
(such as a potentiometer, variable capacitor, or mitted multidigit telephone numbers.
switch) has been adjusted. A pointer can move dial telephone system The complete automatic
over the scale, or the scale can be moved past a circuit, including central-office facilities, for dial
stationary pointer. 2. The graduated face of a me- telephone operation.
ter. 3. In a telephone system, to press the keys or dial tone In a telephone system, a constant hum or
actuate the tones that establish contact with an- whine heard before dialing, indicating that the
other subscriber. system is operational.
dial cable A flexible cable or belt conveying motion dial-up In a telephone system, the calling of one
on the shaft of an adjustable component (such as subscriber by another, using a dial system.
a potentiometer or variable capacitor) to a dial. diam Abbreviation of diameter.
dial-calibrated attenuator A variable attenuator diamagnetic Pertaining to a material having mag-
with a dial reading directly in decibels. netic permeability less than unity.
dial-calibrated capacitor A variable capacitor diamagnetism The state of having magnetic perme-
with a dial reading directly in picofarads. ability less than unity. A material with this prop-
dial-calibrated inductor A variable inductor with erty reduces the flux density of a magnetic field,
a dial reading directly in microhenrys. relative to the flux density in air or in free space.
dial-calibrated potentiometer A potentiometer diamond antenna Also called rhombic antenna.
with a dial reading directly in output volts, A nonresonant wideband directional antenna
percentage of input voltage, number of turns whose horizontal wire elements are arranged in
(when resistance is a linear function), or other the shape of a diamond (rhombus). The arrange-
quantity. ment is fed at one corner, the opposite corner be-
dial-calibrated resistor A variable resistor with a ing terminated with a noninductive resistor.
dial reading directly in ohms, kilohms, or diamond lattice The orderly internal arrangement
megohms. of atoms in a redundant pattern in crystalline
dial-calibrated rheostat See DIAL-CALIBRATED materials, such as germanium or silicon.
dial cord A form of dial cable. Cord usually desig-
nates a fabric string, whereas a cable is a flexible, x x
braided wire.
dial knob The knob used to turn a dial under a Feed
pointer, or to turn a pointer over a dial scale. ≈ 600 „¦
dial lamp See DIAL LIGHT.
dial light A small lamp sometimes used to illumi-
x x
nate a dial. Can also serve as a pilot light.
dial lock A small mechanism used to lock a dial at Maximum
a particular setting to prevent further turning. All sides x are equal radiation
dialing key In a telephone system, a dial that uses
diamond antenna
keys, rather than a rotary dial.
diamond stylus • dielectric constant

diamond stylus A phonograph “needle” having as dichromate cell An electrolytic cell consisting of
its point a small, ground diamond. electrodes of carbon and zinc. The zinc electrode
diapason 1. Either of the two principal stops (open is immersed in a diluted solution of sulfuric acid,
and closed) of an electronic organ that cover the and the carbon electrode in a solution of potas-
entire range of the instrument. When one is used, sium dichromate.
a note played is automatically sounded in several dicing The cutting of a semiconductor melt, crystal
octaves. 2. Tuning fork. wafer, or other material into dice (see DIE).
diaphony See DISSONANCE. dictionary A table of specifications for the size and
diaphragm A usually thin metal or dielectric disk format of computer file operands, and data
used as the vibrating member in headphones, names for field and file types.
loudspeakers, and microphones, and as the pres- die 1. A small wafer of useful electrical material,
sure-sensitive element in some sensors and such as a semiconductor or a precision resistor
barometers. chip. 2. A casting designed to mold molten metal
diaphragm gauge A sensitive gas pressure gauge into a specific configuration until the metal hard-
using a thin metal diaphragm stretched flat. In- ens. 3. Any small object of roughly cubical pro-
crements of pressure move the diaphragm, portions. 4. To lose power or energy completely,
relative to a nearby electrode, varying the usually unintentionally. 5. In a computer pro-
capacitance between the two. gram, to produce unpredicted and useless results
diathermic Pertaining to a substance that effi- following an initial run.
ciently transfers heat or infrared energy. die bonding The bonding of dice or chips to a sub-
diathermotherapy The use of diathermy in the strate.
treatment of various physiological disorders. die casting Making a casting by forcing molten
diathermy 1. In medicine and physical therapy, metal (such as an aluminum alloy, lead, tin, or
the production of heat in subcutaneous (below zinc) under high pressure into a die or mold.
the skin) tissues by means of high-frequency ra- dielectric A material that is a nonconductor of
dio waves. 2. A radio-frequency (RF) power oscil- electricity; especially, a substance that facilitates
lator and associated equipment used to produce the storage of energy in the form of an electric
heat in subcutaneous tissues. field. Such materials are commonly used in ca-
diathermy interference Radio-frequency inter- pacitors and transmission lines.
ference (RFI) resulting from the operation of dielectric absorption The ability of certain dielec-
unshielded and/or unfiltered diathermy equip- tric materials to retain some of their electric
ment. charge”even after being momentarily short-
diathermy machine See DIATHERMY, 2. circuited. Capacitors with this property must be
diatomic Having two atoms (e.g., a DIATOMIC shorted out continuously for a certain length of
MOLECULE). time before the dielectric has completely dis-
diatomic molecule A molecule (such as that of charged.
oxygen) composed of two atoms. Compare MON- dielectric amplifier A voltage amplifier circuit in
ATOMIC MOLECULE. which the active component is a capacitor having
dibble A mathematical function in which a number a nonlinear dielectric. A signal voltage applied to
(usually an integer) is doubled, and then one is the capacitor varies the capacitance, thus vary-
added to the result. Thus, dibble n = 2n + 1. ing the current. The modulated current flows
dibit A combination of two binary digits (bits). The through a load resistor, developing an output-
four possible dibits are 00, 01, 10, and 11. signal voltage higher than the input-signal voltage.
dice Plural of DIE, 1, 3. dielectric antenna An antenna in which some or
dichotomizing search Also called binary search. all of the radiating element is made of a dielectric
In digital computer operations, locating an item material, such as polystyrene. Primarily used at
in a table of items that are arranged by key values microwave frequencies.
in serial order. The required key is compared with dielectric breakdown Sudden, destructive con-
a key halfway through the table; according to this duction through a dielectric when the applied
relational test, half of the table is accepted and voltage exceeds a critical value.
again divided for comparison, etc. until the keys dielectric breakdown voltage The voltage at
match and the item is found. which DIELECTRIC BREAKDOWN occurs in an
dichotomy Characterized by the usually repetitive insulating material. Varies, depending on the
branching into two sets, groups, or factions. particular dielectric substance.
dichroism Also called dichromatism. 1. The pro- dielectric capacity See DIELECTRIC CONSTANT.
perty of a crystal showing different colors, dielectric constant Symbol, k. For a dielectric ma-
depending on which axis corresponds to the line terial, the ratio of the capacitance of a two-plate
of sight. 2. The property of a solid taking on dif- capacitor using the dielectric material, to the ca-
ferent colors as the thickness of the transmitting pacitance of the equivalent capacitor with dry air
layer changes. 3. The property of a liquid chang- as a dielectric. Also called inductivity and specific
ing color, according to solution concentration. inductive capacity.
184 dielectric current • dielectric wire

dielectric current 1. Current flowing over the sur- dielectric matching plate A dielectric plate used
face of a dielectric material in response to a vary- in some waveguides for impedance matching.
ing electric field. 2. Current flowing through a dielectric mirror A reflector containing a number
dielectric as a result of its finite insulation resis- of layers of dielectric material. Its action depends
tance. on electromagnetic energy being partially re-
dielectric dissipation For a dielectric material in flected from the interfaces between materials
which an electric field exists, the ratio of the lost having unequal indexes of refraction.
(dissipated) electrical energy to the recoverable dielectric phase angle For a dielectric material,
electrical energy. the angular phase difference between a sinu-
dielectric dissipation factor The cotangent of the soidal voltage applied to the material and the
dielectric phase angle, also equal to the reciprocal component of the resultant current having the
of the Q factor. same period as that of the voltage.
dielectric fatigue In some dielectric materials dielectric phase difference See DIELECTRIC
subjected to a constant voltage, the deterioration LOSS ANGLE.
of dielectric properties with time. dielectric polarization The effect characterized by
dielectric guide A waveguide made from a solid di- the slight displacement of the positive charge in
electric, such as polystyrene. each atom of a dielectric material, with respect to
dielectric heater A high-frequency power genera- the negative charge, under the influence of an
tor used for DIELECTRIC HEATING. electric field.
dielectric heating The heating and forming of a dielectric power factor The cosine of the dielectric
dielectric material, such as a plastic, by tem- phase angle, or the sine of the dielectric loss an-
porarily making the material the dielectric of a gle.
two-plate capacitor. This capacitor is connected dielectric puncture voltage See DIELECTRIC
to the output of a high-power radio-frequency BREAKDOWN VOLTAGE.
(RF) generator. Losses in the dielectric cause its dielectric rating The breakdown voltage, and
heating. Compare INDUCTION HEATING. sometimes the power factor, of the dielectric ma-
dielectric hysteresis See DIELECTRIC ABSORP- terial used in a device, such as a relay, motor, or
TION. switch.
dielectric isolation In a monolithic integrated cir- dielectric ratings Electrical characteristics of a di-
cuit (IC), the isolation of circuit elements from electric material: breakdown voltage, power fac-
each other by a dielectric film, as opposed to iso- tor, dielectric constant, etc.
lation by reverse-biased pn junctions. dielectric resistance See INSULATION RESIS-
dielectric lens A molded piece of dielectric mate- TANCE.
rial used to focus microwaves. Its operation is dielectric rigidity See DIELECTRIC STRENGTH.
analogous to that of an optical lens. dielectric-rod antenna A unidirectional antenna
that uses a dielectric substance to obtain power
dielectric soak See DIELECTRIC ABSORPTION.
dielectric strain The distorted internal state of a
dielectric, caused by the influence of an electric
field. Also called DIELECTRIC STRESS.
dielectric strength The highest voltage a dielectric
can withstand before DIELECTRIC BREAKDOWN
occurs. Usually expressed in volts or kilovolts per
mil of material thickness.
dielectric stress The distortion of electron orbits
in the atoms of a dielectric material subjected to
an electric field.
dielectric susceptibility For a polarized dielectric,
dielectric lens the ratio of polarization to electric intensity.
dielectric tests Laboratory experiments perform-
ed to determine the dielectric characteristics of a
dielectric loss For a dielectric material subjected
substance”especially the dielectric constant and
to a changing electric field, the rate of transfor-
the dielectric breakdown voltage.
mation of electric energy into heat.
dielectric waveguide See DIELECTRIC GUIDE.
dielectric loss angle Ninety degrees minus the DI-
dielectric wedge A wedge-shaped dielectric slug
placed inside a waveguide for impedance match-
dielectric loss factor For a dielectric material, the
product of the dielectric constant and the tangent
dielectric wire A small dielectric waveguide that
of the dielectric loss angle.
acts as a wire to carry signals between points in a
dielectric loss index See DIELECTRIC LOSS FAC-
Dietzhold network • differential input

Dietzhold network A four-terminal, shunt m-de- End view
rived circuit used in some wideband amplifiers.
Stator A
Dietzhold peaking In some wideband amplifiers,
frequency compensation obtained with a shunt
m-derived network (see DIETZHOLD NETWORK).
difference amplifier See DIFFERENTIAL AMPLI-
Stator B
difference channel In a stereophonic amplifier, an
audio channel that handles the difference be-
tween signals in the right channel and those in
the left channel.
difference detector A detector whose output is the
difference between two simultaneous input sig-
differential capacitor
difference frequency A signal frequency produced
by mixing or heterodyning of signals at two other tomotive force of the series field opposes that of
frequencies. If the lower input signal frequency is the shunt (main) field.
f1 and the higher input signal frequency is f2, differential compound dc motor A compound-
then the difference frequency fd is equal to f2 “ f1. wound dc motor in which the magnetomotive
difference of potential The absolute value of the force of the series field coil opposes that of the
algebraic difference of voltages at two points of shunt (main) field coil.
different electrical potential. Thus, the difference differential cooling Reducing temperature at dif-
of potential between a +5-V point and a “5-V ferent points on a surface at different rates.
point is +5 “ (“5) V = 10 V. Also see POTENTIAL differential delay The difference dmax “ dmin across
DIFFERENCE. a frequency band, where dmax is the maximum
difference quantity See INCREMENT. frequency delay and dmin is the minimum fre-
difference signal 1. The resultant signal obtained quency delay.
by subtracting, at every instant for at least one differential discriminator A device that passes
full cycle, the amplitudes of two signals. 2. The pulses, whose amplitudes are between two prede-
difference of the left- and right-channel outputs termined values above or below zero.
in a stereo system. differential distortion In an automatic-gain-
differential 1. A device, consisting of a gear sys- control circuit, distortion from effects that cause
tem, that adds or subtracts angular motions and shunting of the diode load resistor.
delivers the result. 2. A gear system in which the differential flutter Fluctuations in the speed of a
motion of a shaft is transferred to two other magnetic tape that are nonuniform in different
shafts aligned with each other and perpendicular parts of the tape.
to the first shaft. 3. One of two coils arranged to differential gain In a differential amplifier, the av-
produce opposite polarities at a point in a circuit. erage gain of the two sections of the amplifier.
4. Pertaining to a difference between two signals Compare DIFFERENTIAL UNBALANCE.
or quantities. differential gain control A circuit or device for
differential amplifier A circuit, usually an opera- setting the gain of a radio receiver in terms of an
tional amplifier, that amplifies the voltage dif- anticipated change in signal strength, to reduce
ference between two input signals. The the receiver output signal differential.
instantaneous output voltage is equal to some differential galvanometer A galvanometer in
constant multiple of the difference between the which currents in two similar coils neutralize
instantaneous input voltages. each other; thus, there is zero deflection when the
differential analyzer An analog computer that currents are equal.
solves differential equations using integrators. differential gap The smallest range of values that
differential angle For a mercury switch, the angle a controlled variable must take to change a three-
between operation and release positions. position controller™s output from on to off, or vice
differential capacitor A dual variable capacitor versa.
with two identical stator sections, and a single ro- differential heating Increase of temperature at
tor section that turns into one stator section and different points on a surface at different rates.
out of the other. The capacitance of one section differential impedance See DIFFERENTIAL-
decreases while that of the other increases. INPUT IMPEDANCE.
differential coil See DIFFERENTIAL, 3. differential induction coil An induction coil hav-
differential comparator A linear integrated circuit ing two differentially wound primary coils.
(IC) that delivers an output proportional to the differential input In a differential amplifier, the
difference between two input signals. circuit between input terminals 1 and 2, as op-
differential compound dc generator A com- posed to the circuit between input 1 or input 2
pound-wound dc generator in which the magne- and ground.
186 differential-input amplifier • differential-wound field

differential-input amplifier A differential ampli- (f1) superimposed on a low-frequency, sine-wave
fier whose output is proportional to the difference signal (f2), the difference in phase shift of f1
between two input signals”each applied between throughout the system for two specified levels of
an input terminal and common ground. f2.
differential-input capacitance In a differential differential phase-shift keying Keying of a carrier
amplifier, the capacitance between the input ter- by varying the carrier phase.
minals. differential pressure The difference in pressure
differential-input impedance In a differential am- between two points.
plifier, the impedance between the input terminals. differential-pressure transducer A transducer
differential-input measurement For a differential that delivers an output proportional to the differ-
amplifier, a floating measurement made between ence between two sensed actuating pressures.
the input terminals. differential protective relay A differential relay
differential-input rating In an operational ampli- that operates to protect equipment or personnel
fier, the greatest difference signal that can be when the difference between the two actuating
placed between the inputs while allowing proper quantities reaches a prescribed level.
operation. differential receiver A synchro differential that re-
differential-input resistance In a differential am- ceives the electrical output of two synchro trans-
plifier, the resistance between the input termi- mitters. The receiver can subtract one input

nals. voltage from the other.
differential-input voltage In a differential ampli- differential relay A relay actuated by the differ-

fier, the signal voltage presented to the floating ence between two currents or voltages.
input terminals. differential selsyn A selsyn in which the position
differential-input voltage range In a differential assumed by the rotor is proportional to the sum
amplifier, the range of signal voltages that can be of rotor and stator field values.
applied between the differential input terminals differential stage See DIFFERENTIAL AMPLIFIER.
without overdriving the amplifier. differential synchro See DIFFERENTIAL RE-
differential input-voltage rating The maximum CEIVER and DIFFERENTIAL TRANSMITTER.
differential-input voltage that can be applied differential transducer A dual-input, single-out-
safely to a differential amplifier. put sensor, such as a pressure transducer, that

differential instrument A galvanometer or other is actuated by two sensed quantities and delivers
meter in which deflection results from the differ- an output proportional to their difference.
ential effect of currents flowing in opposite direc- differential transformer A variable inductance
tions through two identical coils. Also see transformer having a (usually cylindrical) core
DIFFERENTIAL GALVANOMETER. that is moved in and out to provide adjustable
differential keying A system of break-in keying, in coupling between the interwound primary and
which the oscillator stage of a transmitter con- secondary windings. This permits adjustment of
taining a keyed amplifier is disabled when the key the amplitude and phase of the transformer out-
is open to prevent interference with the receiver put voltage, with respect to the input voltage.
at the keying station, and is enabled when the differential transmitter A synchro differential
key is closed. connected to a synchro transmitter. In a synchro
differential-mode gain In an operational ampli- receiver supplied by this combination, the change
fier, the ratio, in decibels, between the output in rotor position is the algebraic difference be-
voltage and the differential input voltage. tween the transmitter-rotor position and the dif-
differential-mode input In an operational ampli- ferential-rotor position.
fier in differential mode, the difference between differential unbalance For a differential amplifier,
the two input signal voltages. the average difference in gain between the two
differential-mode signal In a balanced three- amplifier sections. Compare DIFFERENTIAL
terminal circuit, such as the input of a differen- GAIN.
tial amplifier, a signal applied between the differential voltage 1. The voltage difference be-
floating (ungrounded) input terminals. tween the input signals to a differential device. 2.
differential multiplexer An analog multiplexer The breakdown voltage minus the operating volt-
that selects both the high and low portion of the age for a lamp.
input signal. differential voltage gain 1. The ratio, in decibels,
differential nonlinearity Incremental error from between the differential output and differential in-
an ideal analog output difference when the input put voltages of an amplifier. 2. The instantaneous
is changed by a certain value. Generally ex- ratio, in decibels, between the rate of change of
pressed as a fraction of full-scale output. the output signal voltage and the rate of change of
differential permeability The derivative of normal the input signal voltage in an amplifier.
induction, with respect to magnetizing force. differential-wound field In a motor or generator, a
differential phase In a television system tested field winding having series and shunt coils whose
with a low-level, high-frequency sine-wave signal fields are opposing.

differentiate • diffused sound

differentiate 1. To produce an output signal, the tribution of energy at various frequencies, pro-
instantaneous amplitude of which is proportional duced by diffraction of electromagnetic waves. 3.
to the instantaneous rate of change of the input The distribution of energy at various frequencies,
amplitude. 2. To determine the derivative of a produced by diffraction of acoustic waves.
mathematical function. diffractometer An instrument for measuring the
differentiating circuit See DIFFERENTIATING diffraction of radiation, such as light or X-rays.
NETWORK. diffuse 1. To produce or cause DIFFUSION. 2. En-
differentiating network A four-terminal resis- ergy that is diffused.
tance-capacitance (RC) network whose output diffused-alloy transistor See DRIFT-FIELD TRAN-
voltage is the derivative of the input voltage, with SISTOR.
respect to time. Compare INTEGRATING NET- diffused-base transistor A bipolar transistor in
WORK. which the base region has been diffused into the
differentiation 1. The processing of an input sig- semiconductor wafer. Also see DIFFUSED JUNC-
nal to create an output signal whose voltage TION.
waveform represents the derivative, with respect diffused device A semiconductor device in which
to time, of the input voltage waveform. 2. The pro- the junction is produced by diffusion (see DIFFU-
cess of computing a mathematical derivative. SION, 1). Examples: DIFFUSED-BASE TRANSIS-
WORK. 2. An operational amplifier whose output RECTIFIER, and DIFFUSED-MESA TRANSIS-
waveform is the mathematical derivative of the TOR.
input waveform. diffused diode A semiconductor diode having a
diffused junction.
diffused-emitter-and-base transistor A transistor
R in which n and p materials both have been dif-
fused into the semiconductor wafer to provide
emitter and base junctions. Also see DIFFUSION,
Eo = ’RC (dEi/dt)
Ei AV diffused junction In a semiconductor device, a pn
junction formed by diffusing a gas into a semi-
conductor at a high temperature that is below the
melting point of the semiconductor. Typically, a
gas containing an n-type impurity is diffused into
differentiator, 2
p-type semiconductor material. Compare ALLOY
diffused-junction rectifier A semiconductor recti-
diffracted wave A wave or ray of energy undergo-
fier using a diffused junction.
diffused-junction transistor See DIFFUSED-
diffraction 1. Interference of one part of an energy
beam with another part when the beam is de-
flected along two or more paths having different
diffused-layer resistor In an integrated circuit, a
lengths. When this happens with visible light,
resistor produced by diffusing a suitable material
dark and light bands or colored bands appear.
into the substrate.
This effect is responsible for the rainbow-like ap-
diffused-mesa transistor A transistor whose base
pearance of light reflected from the surface of a
is a n-type layer diffused into a p-type wafer (the
compact disc. 2. The bending of electromagnetic
remaining p-type material serving as the collec-
waves around an object. This effect explains why
tor); its emitter is a small p-type area diffused
radio signals can propagate around large ob-
into or alloyed with the n-layer. Unwanted dif-
structions, such as buildings and hills. The effect
fused portions are etched away, leaving the tran-
becomes more pronounced as the wavelength in-
sistor in a mesa shape.
creases (the frequency decreases). 3. The bending
diffused planar transistor A diffused transistor in
of acoustic waves around an object. This effect
which emitter, base, and collector electrodes are
explains why sound propagates around large ob-
exposed at the face of the wafer, which has an ox-
structions, such as buildings. The effect becomes
ide layer to forestall leakage between surface elec-
more pronounced as the wavelength increases
(the frequency decreases).
diffused resistor See DIFFUSED-LAYER RESIS-
diffraction grating A transparent plate containing
thousands of parallel lines or grooves spaced ex-
diffused sound 1. Sound distributed so that its
tremely close together. Light passing through the
energy flux is the same at all points. 2. Sound
slits between the lines produces a rainbow spec-
whose source is difficult to locate or seems to
trum as a result of DIFFRACTION.
shift, as that heard from out-of-phase stereo
diffraction spectrum 1. The spectrum produced
in visible light by a diffraction grating. 2. The dis-
188 diffused transistor • digital comparator

diffused transistor A transistor in which one or SION, 1). 2. Producing a high vacuum by means
both electrodes are created by diffusion. See DIF- of diffusion (see DIFFUSION PUMP).
FUSED JUNCTION. diffusion pump A pump for fast, efficient creation
diffused-junction transistor See DIFFUSED- of a high vacuum in electron tubes and similar
BASE TRANSISTOR, DIFFUSED-MESA TRAN- devices. In one form, the pump, in conjunction
SISTOR, and DIFFUSED TRANSISTOR. with a force pump, uses mercury vapor as the
diffusion 1. In the fabrication of semiconductor pumped medium. Gas molecules evacuated from
devices, the slow, controlled introduction of a ma- the device diffuse into a chamber, where con-
terial into the semiconductor, for example, the densing mercury vapor traps and carries them
high-temperature diffusion of a n-type impurity off.
(from a gas containing it) into a p-type wafer to diffusion theory The notion that, in a homoge-
form a diode. 2. The random velocity and move- neous medium, current density is directly
ment of current carriers in a semiconductor, re- proportional to the gradient of particle flux
sulting from a high-density gradient. 3. The density.
characteristic spreading of light reflected from a diffusion transistor A transistor whose operation
rough surface or transmitted through a translu- is based principally on the diffusion of current
cent material. 4. The spreading-out of sound carriers (see DIFFUSION, 2).
waves, for example when reflected from acoustic diffusor In acoustics, a device or structure deliber-
baffles. 5. The migration of atoms from one sub- ately installed to spread sound waves throughout
stance to another, as in the spreading of one gas a region.
throughout another. dig-in angle A stylus angle of 90 degrees, relative
to the surface of a phonograph disc. Compare
Translucent DIGIRALT Acronym for digital radar altimetry. A
material system that utilizes digital techniques to enhance
the accuracy of an altimeter using radar.
digit A single symbol in a numbering system (e.g.,
0 through 9 in the decimal system, or 0 or 1 in
the binary system), whose value depends on its
position in a group and on the radix of the partic-
ular system used.
digital 1. Pertaining to components, circuits, or
Incident systems that use signals having an integral num-
ber of discrete levels or values, rather than sig-
nals, whose levels or values vary over a
continuous range. 2. Pertaining to a numeric
readout or display. 3. See BINARY, 1.
digital annunciator An annunciator that gives an
alphanumeric digital display of information, as
well as sounding an alarm.
digital audio tape Abbreviation, DAT. A magnetic
tape intended for recording digitally encoded au-
dio data. Used in some high-fidelity applications,
diffusion, 3
and also for computer data storage.
digital barometer An electronic barometer provid-
ing a digital readout.
diffusion bonding A method of joining different
digital capacitance meter Abbreviation DCM. A
substances by diffusing atoms of one into the
meter with a digital readout for measuring capac-
other. This technique is employed in the manu-
itance values.
facture of certain semiconductor diodes, transis-
digital cellular See PERSONAL COMMUNICA-
tors, and other devices.
diffusion capacitance The current-dependent ca-
digital circuit A circuit affording a dual-state
pacitance of a forward-biased semiconductor
switching operation (i.e., on or off, high or low,
etc.). Also called binary circuit.
diffusion current Current resulting from the diffu-
digital communications Radio or wire communi-
sion of carriers within a substance (see DIFFU-
cations using a dual-state mechanism (on/off,
SION, 2).
positive/negative, or modulated/unmodulated)
diffusion length In a semiconductor junction, the
to represent information.
distance a current carrier travels to the junction
digital comparator A comparator that presents
during carrier life.
two digital values, one for each of the quantities
diffusion process 1. The technique of processing
being compared.
semiconductor devices by diffusion (see DIFFU-
digital computer • digital representation

digital computer A high-speed, electronic ma- digital integrator A device that can perform inte-
chine for performing mathematical operations, gration, in which increments in input variables,
file management, machine control, or other “in- and an output variable, are represented by digital
telligent” functions, and whose basic internal signals.
operations (data storage, comparing, and compu- digital logic A form of Boolean algebra, consisting
tation) are based on semiconductor devices as- of negation, conjunction, and disjunction, in
suming one of two states (on or off, high or low). which the binary digit 1 has the value “true” and
Compare ANALOG COMPUTER. 0 the value “false” (in positive logic) or vice versa
digital data Information represented and pro- (in negative logic). Digital logic is the basis by
cessed in the form of combinations of digits (0 which all digital devices function.
and 1, in the binary system). digital-logic module 1. A circuit that performs
digital-data cable A cable designed to conduct digital operations. 2. A logic gate.
high-speed digital pulses with minimal distortion digital meter A meter that produces a readout in
and loss. discrete blocks or directly as numerals. The first,
digital data-handling system A system that ac- more primitive and less precise type, is known as a
cepts, sorts, modifies, classifies, or records digital BAR METER. The second, more sophisticated type
data, displaying the final result or passing the can resolve to several significant digits and often
data to a computer. includes a fixed or floating radix point. This
digital delay circuit A device that stores digitized scheme eliminates the need for personnel to inter-
audio data, and releases it after a specified delay. polate the reading on a scale. There is little chance
digital device 1. A digital integrated circuit (IC). 2. for error on the part of the technician or engineer,
Any circuit or system that operates by digital because the readout is straightforward. Another
means. advantage is the fact that there are no moving
digital differential analyzer Abbreviation, DDA. A parts to wear out or be damaged by physical shock.
digital computer that can perform integration us- Compare ANALOG METER.
ing specialized circuitry. digital multimeter Abbreviation, DMM. A
digital display A presentation of information (such voltohm-milliammeter producing a digital read-
as the answer to a problem) in the form of actual out of measured values.
digits, as opposed to one in the form of, for exam- digital multiplex 1. The combination of several or
ple, a meter deflection. See, for example, DIGI- many digital signals into a single digital signal. 2.
TAL-TYPE METER. Also called digital demultiplex. The reverse pro-
digital divider In a computer, a device that can di- cess from that defined in 1, in which the original
vide (i.e., provide a quotient and remainder using signals are obtained from the combination signal.
dividend and divisor signals). 3. Communication using the techniques defined
digital electrometer An electrometer that has a in 1 and 2.
digital current or voltage indicator. digital multiplex equipment Equipment that ac-
digital electronics The branch of electronics con- complishes digital multiplexing or the reverse
cerned with components, circuits, and systems process, digital demultiplexing.
that use signals having an integral number of dis- digital multiplier In a digital computer, a device
crete levels or values, as opposed to signals that produces a product signal from multiplier
whose levels or values vary over a continuous and multiplicand signals.
range. Compare ANALOG ELECTRONICS. digital output An output signal of digital pulses
digital frequency meter A direct-reading fre- representing a number equal or proportional to
quency meter using high-speed electronic switch- the value of a corresponding input signal.
ing circuits and a digital readout. Such digital panel meter A numeric-readout meter whose
instruments read frequency from less than 1 Hz relatively small size allows mounting on a panel.
to many gigahertz. digital phase shifter A phase shifter actuated by a
digital HIC A hybrid integrated circuit (HIC) de- digital control signal.
signed for digital applications. Also see DIGITAL digital photometer An electronic photometer pro-
INTEGRATED CIRCUIT. viding a digital readout of illumination values.
digital IC See DIGITAL INTEGRATED CIRCUIT. digital power meter An electronic wattmeter pro-
digital incremental plotter A device that can viding a digital readout of measured power.
draw, according to signals received from a com- digital readout An indicating device that displays
puter, graphs depicting solutions to problems. a sequence of numerals that represent a mea-
digital information See DIGITAL DATA. sured value.
digital information display See DIGITAL DIS- digital recording A system for tape-recording
PLAY. high-fidelity sound. The audio is converted from
digital integrated circuit An integrated circuit analog to binary digital form, and the binary dig-
(IC) intended for binary operations, such as its (bits) are recorded on magnetic tape.
switching, gating, etc. Compare LINEAR INTE- digital representation The use of digital signals to
GRATED CIRCUIT. represent information as characters or numbers.
190 digital rotary transducer • digit delay element

digital rotary transducer A device that delivers a
digital output signal proportional to the rotation
of a shaft.
Digital Satellite System Abbreviation, DSS. Trade
name for a satellite television (TV) system devel-
oped by RCA. The analog signal is changed into
digital pulses at the transmitting station via
analog-to-digital (A/D) conversion. The digital
signal is amplified and uplinked to a geostation-
ary satellite. The satellite has a transponder that
receives the signal, converts it to a different fre-
quency, and downlinks it back to the earth. The
downlink is picked up by a portable dish that can
be placed on a balcony or patio, on a rooftop, or
in a window. A tuner selects the channel that the
subscriber wants to watch. The digital signal is
amplified. If necessary, digital signal processing
(DSP) can be used to improve the quality of re-
ception under marginal conditions. The digital
signal is changed back into analog form, suitable
for viewing on a conventional TV set, via digital-
to-analog (D/A) conversion.
digital signal A signal having an integral number
of discrete levels or values, as opposed to a signal digital television 1. A television system in which
whose levels or values vary over a continuous the picture information is encoded into digital
range. form at the transmitter, and decoded at the re-
ceiver. 2. A form of television picture transmis-
sion that functions according to picture motion,
rather than absolute brightness.
digital temperature indicator See DIGITAL
digital thermometer An electronic thermometer
Time that provides a digital readout of temperature.
digital-to-analog conversion The conversion of a
digital signal digital quantity into an analog representation,
such as shown by a performance curve. Compare
digital signal processing Abbreviation, DSP. A
digital-to-analog converter A circuit or device
method of signal enhancement that operates by
eliminating confusion between digital states. This
improves dynamic range and frequency response,
digital transmission 1. A method of signal
reduces the number of errors, and virtually elim-
transmission in which the modulation occurs
inates noise. It is used extensively in digital com-
in defined increments, rather than over a con-
munication and recording, often in conjunction
tinuous range. 2. A message that is sent in dig-
with analog-to-digital (A/D) and digital-to-analog
ital form.
(D/A) conversion to enhance the quality of analog
digital-type meter An indicating instrument in
signals and recordings.
which a row of numeral indicators displays a
digital sound Sound recording and reproduction
value. Compare ANALOG-TYPE METER.
accomplished with digital, rather than analog,
digital voltmeter Abbreviation, DVM. An elec-
signals. Advantages include wideband frequency
tronic voltmeter having a direct numerical read-
response, superior dynamic range, and relative
out, rather than an analog display.
immunity to noise.
digital wattmeter See DIGITAL POWER METER.
digital speech communications A system of voice
digital compression In digital computer opera-
communications, in which the analog voice signal
tion, the process of representing data with an
is encoded into digital pulses at the transmitter,
economy of characters to reduce file size.
and decoded at the receiver.
digit current In digital computer operations, the
digital subtractor In a computer, a device that pro-
current associated with writing or reading a digit
duces an output signal whose value is equal to the
into or out of a memory cell.
difference of the values of two input signals.
digit delay element A logic element (gate) whose
digital switching Routing operations carried out
output signal lags the input signal by one digit
on digital signals to establish communications
links between specified system users.
digit filter • diode-capacitor memory cell

digit filter A device for detecting designations. See dimensionless quantity A quantity that is merely
DESIGNATION. a real number. Example: logarithm, exponent,
digitize 1. To express the results of an analog numerical ratio, etc. In contrast are physical
measurement in digital units. 2. To convert an quantities: 3 volts, 5000 hertz, 10 amperes, etc.
analog signal into corresponding digital pulses. diminished radix complement See COMPLE-
digit period In a digital circuit or system, the time dimmer An electronic device used for controlling
interval between the start of one digital pulse and the brightness of incandescent lamps. Using am-
the start of the next pulse. plified control, the device enables high-wattage
digit place See DIGIT POSITION. lamp loads to be smoothly adjusted via a small
digit plane In a matrix-type computer memory, the rheostat or potentiometer. A photoelectric-type
plane within a three-dimensional array of mem- dimmer automatically controls lamps in accor-
ory storage elements representing a DIGIT POSI- dance with the amount of daylight.
TION. dimmer curve The function of a light-dimmer volt-
digit position The ordinal position of a digit in a age output as a function of setting on a linear
numeral, the first position being occupied by the scale.
least-significant digit (e.g., 7 is in the third posi- DIN Abbreviation for Deutsche Industrie Norme-
tion in the numeral 756). nausschuss. A German association that sets
digit pulse A pulse that energizes magnetic core standards for the manufacture and performance
memory elements representing a digit position in of electrical and electronic equipment, as well as
several words. other devices.
digitron A display in which all of the characters lie D indicator In radar operations, an indicator com-
in a single, flat plane. bining type B and C indicators (see B DISPLAY
digit time The duration of a digit signal in a series and C DISPLAY).
of signals. Dingley induction-type landing system An air-
digit time slot In digital communications, the in- craft landing system that provides lateral and
terval of time assigned to one bit or one digit. vertical guidance; instead of radio, it uses the
digit-transfer bus In a digital computer, a main magnetic field surrounding two horizontal cables
line (of conductors) that transfers information laid on or under either side of the runway.
among various registers; it does not handle con- diode A two-element device containing an anode
trol signals. and a cathode, and providing unidirectional con-
diheptal CRT base The 14-pin base of a cathode- duction. The many types are used in such devices
ray tube. Also see BIDECAL, DUODECAL, and as rectifiers, detectors, peak clippers, mixers,
MAGNAL. modulators, amplifiers, oscillators, and test in-
DIIC Abbreviation for dielectric-isolated integrated struments.
circuit. Several separate integrated-circuit wafers diode action 1. The characteristic behavior of a
are contained in a single package, and kept elec- diode (i.e., rectification and unidirectional con-
trically insulated by layers of dielectric. duction). 2. Two-electrode rectification or unidi-
dilatometer An instrument used to measure ex- rectional conductivity in any device other than a
pansion. diode (e.g., asymmetrical conductivity between
dimension 1. Any measurable quantity, such as the collector and base of a transistor).
distance, time, temperature, humidity, etc. 2. An diode amplifier 1. A parametric amplifier employ-
axis in the three-dimensional Cartesian coordi- ing a varactor. 2. An amplifier utilizing hole-
nate system. 3. An independent variable in a storage effects in a semiconductor diode. 3. A
function of one or more variables. negative-resistance amplifier using a tunnel diode.
dimensional analysis A mathematical procedure diode array A combination of several diodes in a
whereby an equation involving quantities with single housing.
different units is verified as being dimensionally diode assembly See DIODE ARRAY.
correct. The original variables are replaced with diode bias A steady direct-current (dc) voltage ap-
fundamental quantities, such as resistance (R), plied to a diode to establish its operating point.
current (I ), length or displacement (d ), and time diode capacitance The capacitance existing at the
(t), applicable to electrical systems. The equation p-n junction of a semiconductor diode when the
is dimensionally correct if it can be shown that junction is reverse-biased. The capacitance gen-
the left and right sides of the equation are identi- erally varies, depending on the reverse-bias volt-
cal. age.
dimensional ratio In magnetism, the ratio of the diode capacitor 1. A capacitor normally operated
longest diameter of an elongated ellipsoid of revo- with a diode. 2. A voltage-variable capacitor uti-
lution to the shortest. lizing the junction capacitance of a semiconduc-
dimensional stability Nonvariance or little vari- tor diode (e.g., a varactor).
ance in the shape and size of a medium (such as diode-capacitor memory cell A high-value capac-
film) during the processing of that material. itor in series with a high-back-resistance semi-
192 diode-capacitor memory cell • diode peak detector

conductor diode. A data pulse forward-biases the (RF) electromagnetic field. It consists of a short
diode and charges the capacitor, which remains whip antenna, an inductance-capacitance (LC)
charged, thus holding the data bit, because of the tuned circuit, a diode detector, and a direct-
long time constant of the high capacitance and current (dc) microammeter. The deflection of the
the high back resistance of the diode. meter is roughly proportional to the RF signal
diode characteristic The current-versus-voltage voltage.
curve for a diode. diode gate A passive switching circuit of biased
diode checker An instrument for testing semicon- diodes. Also see AND CIRCUIT and OR CIRCUIT.
ductor diodes. There are two forms: A static diode impedance The vector sum (resultant) of the
checker, which measures forward and reverse resistive and reactive components of a diode. In a
current; and a dynamic checker (see DYNAMIC semiconductor diode, the inductive component of
DIODE TESTER), which displays the entire diode reactance is almost entirely the inductance of
response curve on an oscilloscope screen. leads and electrodes, whereas the capacitive com-
diode chopper A chopper using an alternately bi- ponent of reactance is the shunting capacitance
ased diode as the switching element. between leads and electrodes, plus the voltage-
diode clipper A clipper using one or more diodes. variable capacitance of the pn junction. The
A single biased diode will limit the positive or neg- resistive component is almost entirely the volt-
ative peak of an applied alternating-current (ac) age-variable resistance of the pn junction.
voltage, depending on diode polarity and bias. diode isolation A means of insulating an inte-
Two biased diodes with opposing polarity will clip grated-circuit chip from its substrate. The chip is
both peaks. Also see LIMITER. surrounded by a pn junction that is reverse-
biased. This prevents conduction between the
chip and the substrate.
diode lamp See LASER DIODE.
diode laser See LASER DIODE.
Input Output
diode light source See LASER DIODE.
diode limiter See DIODE CLIPPER.
diode load 1. The current drawn from a diode act-
diode clipper ing as a rectifier or demodulator. 2. The output
(load) resistor into which a diode operates.
diode load resistance The required value for a
diode converter See DIODE MIXER.
diode load resistor.
diode current The forward or reverse current flow-
diode load resistor A resistor usually connected to
ing through a diode.
the output of a diode rectifier or diode detector.
diode current meter A direct-current (dc) mil-
diode logic Digital circuitry, such as AND and OR
liammeter or microammeter with a semiconduc-
circuits, using diodes as the principal compo-
tor-diode rectifier that allows the measurement of
alternating current (ac).
diode matrix In some digital devices, a grid of
diode curve changer A diode or network of diodes
wires, the intersections of some being intercon-
used to make a linear current-voltage curve ac-
nected through diodes, whose polarities deter-
quire some nonlinear shape.
mine circuit operation. A series of AND circuits is
diode demodulator See DEMODULATOR PROBE
provided by this arrangement, which acts as a
high-speed rotary switch when it is supplied with
diode detector A detector circuit in which a diode
input pulses.
demodulates a signal. The diode, a simple device,
diode mixer A frequency converter that operates
provides linear response at high signal ampli-
via the nonlinearity of semiconductor diodes.
tudes, but affords no amplification.
diode noise limiter A noise limiter circuit having
diode feedback rectifier 1. In a rectified-carrier,
one or more biased diodes.
negative-feedback system for an amplitude-
diode oscillator An oscillator based on the nega-
modulated (AM) transmitter, the diode that
tive resistance or breakdown characteristics of
rectifies the modulated carrier and provides the
certain diodes, such as high-reverse-biased ger-
audio envelope for use as negative-feedback
manium diodes, tunnel diodes, Gunn diodes, and
voltage. This voltage is applied to the speech
four-layer diodes. It is generally used at mi-
amplifier/modulator channel to reduce distortion,
crowave frequencies.
noise, and hum, at the same time providing
diode pack A device containing more than one
automatic modulation control. 2. The diode that
diode. An example is the full-wave bridge-rectifier
rectifies a part of the signal at the output of an
integrated circuit.
audio amplifier and provides a proportional
diode peak detector A diode detector whose load
direct-current (dc) voltage for use as bias in an
resistance is high at modulation frequencies; the
automatic-gain-control (AGC) circuit.
voltage across the resistance is proportional to
diode field-strength meter A simple meter for
the peak amplitude of the modulated signal.
measuring the intensity of a radio-frequency
diode peak voltmeter • diplex reception

Resonant diode tester See DIODE CHECKER.
cavity diode transistor 1. See UNIJUNCTION TRANSIS-
TOR. 2. A semiconductor diode whose operation
simulates that of a transistor by means of pulsed
operation that alternately makes the single junc-
Regulated tion an emitter or collector. 3. A transistor con-
nected to operate solely as a diode.
diode-transistor logic Abbreviation, DTL. Logic
circuitry in which a diode is the logic element and
a transistor acts as an inverting amplifier.
diode-type meter A rectifier-type alternating-
current (ac) meter consisting of a semiconductor
diode(s) and a direct-current (dc) milliammeter or
microammeter. The diode rectifies the ac input,
the resulting dc deflecting the meter.
diode varactor A conventional semiconductor
diode or rectifier used as a makeshift varactor
(voltage-variable capacitor).
diode oscillator, 1
diode variable resistor See DIODE VARISTOR.
diode varistor A conventional diode used as a
makeshift varistor (voltage-variable resistor).
diode peak voltmeter A diode-type alternating-
diode voltage reference See ZENER VOLTAGE
current (ac) voltmeter, in which the deflection of
the direct-current (dc) milliammeter or microam-
diode voltage regulator See ZENER VOLTAGE
meter is proportional to the peak value of the ap-
plied ac voltage.
diode probe A test probe containing a diode used
dip 1. A distinct decrease in the value of a varying
as either a rectifier or demodulator.
quantity, followed by an increase [e.g., the sud-
diode recovery time The interval during which rel-
den drop, followed by a rise, in collector current
atively high current continues to flow after the
when a bipolar-transistor radio-frequency (RF)
voltage across a semiconductor junction has been
power amplifier is tuned through resonance]. 2.
abruptly switched from forward to reverse. Recov-
Also called magnetic inclination. The slanting of a
ery time is attributable to DIODE STORAGE.
compass needle, resulting from the orientation of
diode rectification Conversion of alternating cur-
the geomagnetic lines of flux, with respect to the
rent (ac) to pulsating direct current (dc) by diode
earth™s surface. It varies, depending on magnetic
diode rectifier 1. A diode device that converts al-
dip adapter An external accessory that allows a ra-
ternating current (ac) to pulsating direct current
dio-frequency (RF) signal generator to be used as
(dc) in a power supply. 2. A small-signal diode de-
vice that converts ac to dc in the automatic-gain-
dip coating 1. Applying a protective coat of insu-
control (AGC) circuit of a superheterodyne
lating material to a conductor or component by
receiver. Also called AGC rectifier.
dipping it into the liquid material, then draining
diode resistor 1. A resistor usually operated with
and drying it. Compare SPRAY COATING. 2. The
a diode. 2. A voltage-variable resistor utilizing the
coat applied in this way.
(usually forward) resistance of a semiconductor
dip encapsulation Embedding a component or cir-
cuit in a protective block of insulating material
diode storage The charge carriers (electrons and
(such as a plastic) while the material is in a liquid
holes) remaining within a pn junction for a short
state, and then allowing the material to harden in
time after forward bias has been either removed
ambient air or in an oven.
or switched to reverse polarity.
dip impregnation Saturating a component or ma-
diode storage time See DIODE RECOVERY TIME.
terial (such as absorbent film) with a substance
diode switch See DIODE GATE.
(such as oil or wax) by dipping or vacuum forcing.
diode sync separator A diode used in a television
diplexer A coupler that permits two or more trans-
receiver circuit to separate and deliver the sync
mitters to operate simultaneously into a single
pulses from the composite video signal.
diode temperature stabilization 1. Keeping the
diplex operation 1. Simultaneous transmission or
temperature of a diode at a constant level. 2. Us-
reception of two signals using a single antenna.
ing the temperature-resistance characteristic of a
2. Simultaneous transmission or reception of two
forward-biased semiconductor diode to stabilize a
signals on a single carrier.
circuit (such as a transistor amplifier stage) (i.e.,
diplex reception The reception of signals while
to prevent variations caused by temperature
transmitting with the same antenna.
194 diplex transmission • direct-conversion receiver

diplex transmission The transmission of signals dipole. The dipole is directly fed by the transmis-
while receiving with the same antenna. sion line, and the dipole radiates energy to the
dip meter A tunable radio-frequency (RF) instru- rest of the system.
ment that, by means of a sharp dip of an indicat- dip oscillator The oscillator that provides the sig-
ing meter, indicates resonance with an external nal for a DIP METER.
circuit under test. Specific names are derived dipotassium tartrate Abbreviation, DKT. An or-
from the active component used: grid-dip meter, ganic piezoelectric material.
gate-dip meter, etc. dipped component A discrete electronic compo-
dip needle See INCLINOMETER. nent that has been given a protective coating by
dipolar Also, bipolar. Possessing two poles (us- dipping into a suitable material (such as oil, var-
ually electric or magnetic). nish, or wax) and draining off the surplus.
dipolarization See DEPOLARIZATION. dipper Collective term for resonance-type instru-
dipole 1. A pair of electrically opposite charge ments, such as a DIP METER or DIP ADAPTER.
poles separated by a specific distance. 2. A pair of dipper interrupter A cyclic switching device in
magnetically opposite poles separated by a spe- which a contact pin is part of a revolving wheel
cific distance. 3. See DIPOLE ANTENNA. 4. See partially immersed in mercury.
FOLDED DIPOLE. dipping 1. The application of a protective coating
dipole antenna Also called dipole and doublet. A or impregnant to a component by immersing it in
half-wavelength radiator fed at the center with a a suitable material. Also see DIP COATING, DIP
two-wire or coaxial transmission line. Each “leg” ENCAPSULATION, and DIP IMPREGNATION. 2.
of the antenna is one-quarter wavelength long. In a resonant (tuned) amplifier circuit, the ad-
Such an antenna can be oriented horizontally or justment of the resonant circuit for minimum
vertically, or at a slant. The radiating element is current through the amplifying device.
usually straight. For a straight wire radiator, dipping needle See INCLINOMETER.
properly insulated at the ends and placed well dip soldering 1. Soldering leads or terminals by
away from obstructions, the length L ft (in feet) at dipping them into molten solder and then remov-
a design frequency f (in megahertz) is approxi- ing excess solder. 2. Tinning printed-circuit pat-
mately terns by dipping the boards into molten solder or
placing them in contact with the surface of a sol-
L ft = 467/f
der bath. 3. Soldering leads in printed circuits by
The length Lm (in meters) is close to the methods defined in (2).
DIP switch A switch (or group of miniature
L m = 143/f
switches) mounted in a dual-inline package (DIP)
Because of its simplicity, this antenna is popular for easy insertion into an integrated-circuit
among shortwave listeners and radio amateurs, socket or printed-circuit board.
especially at frequencies below 10 MHz. A full- direct-access storage device A computer memory
size antenna of this type has a feed-point in which data access time is unaffected by the
impedance of approximately 73 ohms, purely re- data location. Also called random-access memory
sistive. Compare FOLDED DIPOLE. device.
direct-acting recorder See GRAPHIC RECORDER.
direct-acting recording instrument See
»/4 »/4
direct address The actual address of a computer
storage location (i.e., the one designated by ma-
chine code 0. Also called absolute address or real
direct capacitance The capacitance between two
points in a circuit, as opposed to the capacitance
between either point and other objects (including
Feed direct allocation In digital computer operations,
line to specify the necessary memory locations and
peripherals for a particular program when it is
dipole antenna written.
direct coding Computer programming in machine
dipole disk feed A method of coupling radio-fre-
direct control Control of one machine by another,
quency energy to a disk-shaped antenna. The en-
for example, the control of a computerized mobile
ergy is applied to a dipole located adjacent to the
robot by a central computer system.
direct-conversion receiver A heterodyne receiver
dipole feed A method of coupling radio-frequency
in which the incoming radio-frequency (RF) signal
energy to an antenna by means of a half-wave
direct-conversion receiver • direct ground

direct-current bar See DC BAR.
direct-current beta See DC BETA.
direct-current block See DC BLOCK.
direct-current bus See DC BUS.
direct-current circuit breaker See DC CIRCUIT
direct-current component See DC COMPONENT.
direct-current converter See DC CONVERTER.
direct-current coupling See DC COUPLING.
AF amp.
RF amp. Mixer
direct-current dump See DC DUMP.
direct-current equipment See DC EQUIPMENT.
direct-current erase head See DC ERASE HEAD.
direct-current generator See DC GENERATOR.
direct-current inverter See DC INVERTER.
Speaker or direct-current leakage See DC LEAKAGE.
Local direct-current motor See DC MOTOR.
osc. direct-current noise See DC NOISE.
direct-current power See DC POWER.
direct-current relay See DC RELAY.
direct-current resistance See DC RESISTANCE.
direct-conversion receiver
direct-current shift See DC SHIFT.
is amplified, then mixed with the RF output of a direct-current short See DC SHORT.
tunable local oscillator, producing an audio- direct-current signaling See DC SIGNALING.
frequency (AF) beat note. The AF is amplified; direct-current source See DC SOURCE.
audio filtering can be added. Although the direct- direct-current transducer See DC TRANSDUCER.
conversion receiver somewhat resembles the direct-current transformer See DC TRANS-
superheterodyne type, it has no intermediate- FORMER.
frequency (IF) chain, and does not normally direct-current transmission See DC TRANSMIS-
provide single-signal reception. Also see ZERO- SION.
BEAT RECEPTION. direct digital control In a digital computer, multi-
direct-coupled amplifier An amplifier in which plexing or time sharing among a number of con-
the output circuit of one stage is wired directly to trolled loops.
the input circuit of the following stage (i.e., there direct display unit A cathode-ray-tube (CRT) pe-
is no intervening capacitor or transformer). Such ripheral that displays data recalled from memory.
an amplifier can handle alternating-current (ac) direct-distance dialing A form of telephone ser-
or direct-current (dc) signals, and has wide fre- vice that allows dialing of long-distance numbers
quency response. without involving a human operator.
direct-coupled transistor logic Abbreviation, direct drive 1. Pertaining to electromechanical ac-
DCTL. In digital computer and switching circuits, cessories for electronic equipment. 2. The trans-
a logic system using only direct-coupled transis- mission of power directly from a source (such as
tor stages. a motor) to a driven device without intermediate
direct coupling Direct connection of one circuit gears, belts, or clutches.
point to another for signal transmission (i.e., direct-drive robot A robot that uses the minimum
without intermediate capacitors or transformers). possible number of gears and other drive sys-
Because coupling devices aren™t used, direct cou- tems.
pling provides transmission of direct current (dc), direct-drive torque motor In a positioning or
as well as alternating current (ac). speed-control system, a servoactuator connected
direct current 1. Abbreviation, dc. A current that directly to the driven load.
always flows in the same direction (i.e., the po- direct-drive tuning A tuning or adjusting mecha-
larity never reverses). The current might be con- nism in which the shaft of the variable compo-
stant, as from a battery or a regulated power nent (such as a potentiometer or variable
supply; it might be pulsating, as from an unfil- capacitor) is turned directly by a knob (i.e., with-
tered rectifier. 2. Pertaining to current that al- out gearing, dial cable, or similar linkage).
ways flows in the same direction. 3. Descriptive directed number A number having direction as
of a voltage, resistance, or other parameter un- well as magnitude; a vector quantity.
der conditions in which there is a usually con- direct electromotive force A direct-current (dc)
stant current that always flows in the same voltage that does not fluctuate or pulsate.
direction. direct emf See DIRECT ELECTROMOTIVE FORCE.
direct-current amplifier An amplifier for boosting direct ground 1. A ground connection made by the
direct-current (dc) signals, as opposed to dc volt- shortest practicable route. Compare INDIRECT
age signals. GROUND. 2. An earth ground.
196 direct induced current • directional wattmeter

jx directional coupler A microwave device that cou-
ples an external system to waves traveling
+j4 4 + j4 through the coupler in one direction.
directional diode A high-back-resistance semi-
conductor diode inserted into a direct-current
+j2 (dc) signal circuit or control circuit. Permits uni-
directional current flow.
directional filter In carrier-current transmission,
a filter that halves the frequency band, one half
j0 R
being for transmission in one direction, and the
other half being for transmission in the opposite
’j2 direction.
5 ’ j2
directional gain Symbol, kS. The ratio of the power
that would be radiated by a loudspeaker if the
’j4 free-space axial sound pressure were constant
over a sphere, to the actual radiated power. Usu-
ally expressed in decibels.
directional homing A scheme for locating the
directed number

source of a radio signal. An effort is made to keep
the bearing of the target or guiding station con-

direct induced current A transient current in- stant. Therefore, the search path is as direct (as
duced in the same direction as the induction cur- nearly a straight line) as practicable.
rent when it is interrupted. directional horn See DIRECTIVE HORN.
directing antenna See DIRECTIONAL ANTENNA. directional hydrophone A hydrophone whose re-
direct-input circuit A circuit, especially an ampli- sponse pattern strongly favors one direction.
fier, whose input is wired directly to the input directional lobe In the spatial response pattern of
electrode of the active device (i.e., without a cou- a device, such as an antenna or loudspeaker, a
pling capacitor or transformer). portion showing emphasized response in a given
direct-insert subroutine In digital computer oper- direction.

ations, a subroutine directly inserted into a larger directional microphone A microphone that
instruction sequence. It must be rewritten at ev- strongly favors sound emanating from in front of
ery point it is needed. it.
direct instruction A computer program instruc- directional pattern See DIRECTIVITY PATTERN.
tion that indicates the location of an operand in directional phase shifter A phase-shifting circuit
memory. in which the characteristics are different in one
directional 1. Depending on direction or orienta- direction, as compared with the other direction.
tion. 2. Having a concentration in an identifiable directional power relay A relay that is actuated
direction. 3. Pertaining to a transducer in which when the monitored power reaches a prescribed
radiation, or sensitivity, is concentrated in cer- level in a given direction.
tain directions at the expense of radiation or sen- directional relay See POLARIZED RELAY.
sitivity in other directions. directional response For any form of transducer,
directional antenna An antenna that transmits a radiation or sensitivity pattern that is concen-
and receives signals more effectively in some di- trated in certain directions.
rections than in others. Also called beam, beam directional separation filter See DIRECTIONAL
antenna, and directive antenna. FILTER.
directional array 1. A directional antenna having directional transducer A device that senses or
a set of elements assembled in such a way that emits some effect to an extent that depends on
their combined action shapes the radiation into a the direction from which the effect comes. Direc-
unidirectional pattern. 2. A group of antennas tional effects are often, but not always, accom-
spaced and phased to produce unidirectional ra- panied by gain in the favored direction(s).
diation and reception patterns. Examples: directional microphone, directional
directional beam 1. An antenna whose radiation speaker, and directional antenna.
or reception pattern strongly favors a specific di- directional variation of radio waves Changes in
rection. 2. The radiation or reception pattern of the field strength of radio waves, depending on
such an antenna. the direction. There are various causes, including
directional characteristic The precise directional antenna directivity, ground characteristics, iono-
properties of an antenna or transducer. spheric factors, weather conditions, and the pres-
directional CQ In amateur radio, a transmission ence of obstructing objects.
that invites replies only from stations in a cer- directional wattmeter A device that can measure
tain direction or in a particular city, state, or radio transmitter output power and can also give
country. an indication of how well an antenna is matched

directional wattmeter • directivity index

to a transmission line. Such meters fall into two left-hand lay or right-hand lay. If the cable is
categories. One type has a single scale, calibrated viewed from either end, left-hand lay is equivalent
in watts, and sometimes also in milliwatts or kilo- to conductors that rotate clockwise as they re-
watts (switch selectable). The meter reads either cede from the viewer; right-hand lay is equivalent
forward power or reflected power, depending on to conductors that rotate counterclockwise as
the position of a switch or rotatable internal ele- they recede from the viewer.
ment. Another type has two needles in a single direction of polarization The direction of the elec-
enclosure, with a different calibrated scale for trostatic field in a linearly polarized wave.
each needle. Both of these scales are graduated direction of propagation The direction in which
in watts, and sometimes also in milliwatts or kilo- energy moves from a transmitter, or between
watts. One needle/scale indicates forward power equivalent points in a sector of space under con-
and the other needle/scale indicates reflected sideration.
power. There is a third scale, calibrated for the direction rectifier In a control system, a rectifier
point where the two needles cross. This scale in- whose direct-current (dc) output voltage has a
dicates the standing-wave ratio (SWR). See also magnitude and polarity dependent on the magni-
CROSSED-POINTER INDICATOR. tude and phase of an alternating-current (ac) sel-
direction angle In radar operations, the angle be- syn error voltage.
tween the center of the antenna baseline and a direction resolution 1. The smallest difference in
line going to the target. azimuth that a direction-finding device can de-
direction finder A receiver specially adapted to tect. 2. The smallest angular separation between
show the direction from which a signal is re- two targets that allows a radar set to show two
ceived, thus revealing the direction of the receiver separate echoes rather than a single echo.
with respect to the transmitting station, and vice directive In a computer source program, a state-
versa. In its simplest form, it is a receiver with a ment directing the compiler in translating the
loop antenna that is rotatable over a map or com- program into machine language without being
pass card. For increased accuracy, checks are translated itself. Also called control statement.
made with signals from two transmitting sta- directive antenna An antenna designed for best
tions; the exact location of the receiver is pin- propagation or reception in one (often steerable)
pointed by triangulation. horizontal direction. Also called beam antenna
direction finding The taking of bearings by means and directional antenna.
of a direction finder. directive gain For a directional antenna, a rating
direction of lay In a multiconductor cable, the lat- equal to 12.566(Pr/Pt), where Pr is the radiated
eral direction of winding of the topmost conduc- power per steradian in a given direction and Pt is
tors as they recede from the observer; called the total radiated power.
directive horn A microwave antenna having the
shape of a (usually rectangular) horn.
directivity 1. In an antenna, a directional re-
sponse. 2. The degree to which the radiation or
sensitivity of a transducer is concentrated in cer-
tain directions. 3. The angle between the half-
power points of a directive antenna in the
x Rcvr azimuth plane. 4. In an antenna system, the ra-
y tio, in decibels, between the power in the favored
direction and the power in the exact opposite di-
rection; also called front-to-back ratio. 5. The for-
ward power gain of an antenna, with respect to a
dipole in free space. 6. The forward power gain of
an antenna, with respect to an isotropic radiator
in free space.
directivity diagram A graph of the radiation/
Position of response pattern of a beam antenna or other
vessel sending directional device, usually in a horizontal or
distress signal vertical plane. Also see DIRECTIVITY PATTERN.
directivity factor 1. A measure of the directivity of
an antenna or transducer. 2. In acoustics, the ra-
tio, in decibels, between the gain in the maximum
direction and the gain in the minimum direction,
for a transducer, such as a speaker or micro-
directivity index 1. For an acoustic-emitting
transducer, the ratio, in decibels, of E1 to E2,
direction finding
198 directivity index • directrix

where E1 is the average intensity over an entire tions in conjunction with the reflector element,
sphere surrounding the transducer, and E2 is the which is usually mounted behind the radiator.
intensity on the acoustic axis. 2. For an acoustic directory See DICTIONARY.
pickup transducer, the ratio, in decibels, of E1 to direct pickup The broadcasting, especially in tele-
E2, where E1 is the average response over an en- vision, of events at the same time as they occur


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