. 10
( 42)


dark current The usually tiny current flowing
Time through a darkened photoconductive cell, photo-
transistor, or glow-discharge device.
dark discharge The occurrence of a discharge in a
gas, without the production of visible light.
dark-spot signal A spurious signal generated by
some camera tubes, arising from secondary-
emission effects.
dark-trace tube An oscilloscope tube on whose
white screen a long-persistence magenta image is
damped wave traced by the electron beam. Illuminating the
screen with bright light intensifies the image.
Darlington amplifier A high-gain amplifier that
damper winding A special short-circuited motor
uses a COMPOUND CONNECTION of two bipolar
winding that opposes pulsation or rotation of the
magnetic field.
Darlington pair See COMPOUND CONNECTION.
damping 1. See DAMPING ACTION. 2. In a loud-
D™Arsonval current A large, low-voltage, high-
speaker, sound-absorbent material used to mini-
frequency current at one time thought to be
mize resonant effects within the enclosure.
damping action 1. Quenching action. 2. The pre-
D™Arsonval meter A electromechanical analog me-
vention of overswing, dither, or flutter in a meter
ter, in which a coil turns on jeweled pivots be-
or loudspeaker (see DAMPED GALVANOMETER,
tween the poles of a strong magnet and against
the force of spiral springs. A pointer is attached to
The prevention of oscillation or ringing in a cir-
the coil. The pointer moves over a calibrated scale.
cuit. 4. Inhibition of the vibration of an acoustic
D™Arsonval movement The mechanism of a
transducer to prevent ringing and other un-
D™Arsonval meter.
wanted effects.
DART Abbreviation of data analysis recording tape.
damping coefficient A figure expressing the ratio
dart leader A flow of electrons along a path trav-
of the damping in a system to critical damping.
eled by a lightning stroke, preceding a second
damping diode A diode used to prevent oscillation
stroke. The dart leader, if any, occurs a few mil-
in an electric circuit (e.g., the diode that prevents
liseconds after the first stroke. Several strokes
ringing in the power supply of a television re-
could occur, each preceded by a dart leader,
ceiver). Also called damper.
within less than 1 second.
damping factor 1. Symbol, a. For a coil of induc-
dash The longer of the two characters (DOT and
tance L and RF resistance R in a damped-wave
DASH) of the telegraph code. The duration of the
circuit, the value R/2L, where L is in henrys and
dash is three times longer than that of a dot.
R in ohms. 2. Abbreviation, Fo. For a torque mo-
dashpot A delayed-action device in which the
tor, the ratio of the stall torque to the no-load ro-
movement of a piston is slowed by air or a liquid
tational speed.
in a closed cylinder.
damping magnet A permanent magnet so situ-
dashpot relay A time-delay relay assembly in
ated, with respect to a moving conductor, disk, or
which the delay is obtained with a DASHPOT.
plate, that the resulting field opposes the move-
DAT 1. Abbreviation of DIGITAL AUDIO TAPE. 2.
Abbreviation of diffused-alloy transistor.
damping ratio See DAMPING COEFFICIENT.
data 1. A collection of digital bits (binary digits)
damping resistance 1. The value of shunt resis-
with informational content (e.g., a computer file,
tance required to prevent ringing in a coil. 2. The
a digital image, or a digital sound recording). 2.
value of resistance required for critical damping
General expression for information, especially in
of a galvanometer.
encoded or written form.
damping resistor 1. A shunt across a coil to pre-
data acquisition The reception and gathering of
vent ringing. 2. A resistor used to provide critical
damping of a galvanometer.
TEM, 1).
Daniell cell A nonpolarizing primary wet cell with
data-acquisition system A computer or dumb ter-
zinc (negative) and copper (positive) electrodes.
minal used to gather data from one or more ex-
The zinc plate is in a porous cup containing a
ternal points.
weak zinc-sulfate solution with a little sulfuric
data analysis display unit • data processor

data analysis display unit A video display periph- or processing data. 3. A unit of data (e.g., a field
eral for online data analysis. in a file).
data area A computer memory area that holds data data-flow diagram A block diagram showing the
only (i.e., one that does not contain program in- movement of data through a data-processing sys-
structions). tem.
data bank A data file stored in a direct-access stor- data format The form of data in a record or file
age device, which can be drawn from by many (e.g., character format or numerical format).
system users through remote terminals. data gathering See DATA COLLECTION.
database 1. A computer file containing often-used data-handling capacity 1. The amount of data
information (e.g., names and addresses, or elec- that can be stored in a memory circuit. 2. The
tronic part numbers). 2. A popular form of com- amount of data that can be transmitted over a
puter software that allows users to create, certain medium. 3. The rate at which data can be
maintain, and modify information. transferred under certain conditions.
data block A set of data bits, comprising an identi- data-handling system A system that gathers,
fiable item. routes, transmits, or receives data, but does not
data bus A conductor or medium over which digital necessarily process it.
data is transmitted from one place to another data item A logical element (character, byte, or bit)
within a computer. describing a characteristic of a record used by a
data carrier storage A medium of data storage system for which there is a specific application.
outside of a computer (e.g., a magnetic disk). data level Descriptive, through a programming
data code A set of abbreviations or codes for data language, of the relative weight of logical ele-
characters or words. ments (data items) in a computer record. Also
data collection The pickup of signals representing called data hierarchy.
test data and their transmission to a computer, data link The portion of a computer system that
data processor, or recorder. Also see DATA SYS- gathers data and, if necessary, converts it to a
TEM, 1. form acceptable by a computer.
datacom Acronym for DATA COMMUNICATION. data matrix Variables and their possible values
data communication The transmission and re- stored as a series of columns and rows of values
ception of data signals between or among points in a computer memory.
in a system. data name An operand specified in a computer
data communication terminal A computer pe- source program.
ripheral providing an input and output link to a data pickup 1. A transducer that collects data sig-
central computer system, and that can be used nals from a source; it converts nonelectrical data
offline for other functions. into corresponding electrical signals and delivers
data compression 1. The process of reducing the its output to a data processing system. 2. Data
size of a data file by eliminating redundancies. 2. acquisition.
The process of minimizing the length of a data data playback The reproduction of data signals
transmission by eliminating redundancies. 3. stored by some method of data recording.
The process of reducing the bandwidth of a data data plotter See X-Y PLOTTER.
transmission. 4. The process of reducing the dy- data printout 1. A device that prints a record of
namic amplitude range of a data transmission. data or the results of a computation. 2. A perma-
data control The automatic control of incoming nent printed record, usually of a calculation or
and outgoing data in a data processing system. computation”especially the printed output of a
data conversion The process of changing data computer peripheral device.
from one form to another, e.g., from analog to dig- data processing Work performed on acquired
ital (A/D), digital to analog (D/A), parallel to se- data, as in solving problems, making compar-
rial, or serial to parallel. isons, classifying material, organizing files. Usu-
data converter 1. A circuit or device for perform- ally done by a computer.
ing DATA CONVERSION. 2. An analog-to-digital data-processing equipment A digital computer
(A/D) converter. 3. A digital-to-analog (D/A) con- and the peripheral equipment needed to collate,
verter. 4. A parallel-to-serial converter. 5. A store, analyze, and reduce data.
serial-to-parallel converter. data-processing machine A computer or system
data description The description of a unit of data, used to collate, store, analyze, and reduce data,
as included in a computer source program. as opposed to a computer or system used primar-
data display A device, such as a cathode-ray tube ily to solve problems or perform routine tasks.
(CRT) or liquid-crystal display (LCD), that pre- Also called data processor.
sents data for visual examination. Compare data-processing system An electronic system for
DATA PRINTOUT. automatic data processing. It can be based on
data element 1. A component of a data signal (e.g., analog and/or digital techniques.
a number, letter, symbol, or the equivalent elec- data processor See DATA-PROCESSING MA-
trical pulses). 2. A device or circuit for acquiring CHINE.
166 data receiver • daylight lamp

data storage The preservation of data, particularly
telephone computer files, for long periods of time in non-
Monitor volatile form (no source of power is required to
ensure that the data remains intact).
data storage media Hardware that preserves data,
particularly computer files, for long periods of
time in nonvolatile form (no source of power is re-
Modem Computer Printer
quired to ensure that the data remains intact).
Common media include magnetic disks, mag-
netic tape, and optical disks.
data synchronizer A device used to synchronize
Software data transmission within a computing or pro-
cessing system.
data system 1. An arrangement for collecting,
recording, and routing data in the form of electri-
cal signals. 2. An arrangement for processing
data-processing system
data (i.e., for correlating, computing, routing,
storing, etc.).

data terminal A remote input/output device con-
nected to a central computer.
data receiver At a particular point in a data-

data throughput In a computer system, the
processing system, a circuit or device for
amount of data per unit time (bytes, kilobytes,
receiving data from a data transmitter.
megabytes, gigabytes, or terabytes per second or
data reception Receiving data signals from some
minute) that can be transferred from one place to
point within or outside a data-processing system.
data-reception system A data receiver and its as-
data transducer In tests and measurements, a
sociated equipment.
transducer that converts a monitored phe-
data record A computer-processed record contain-
nomenon into electrical quantities that can be
ing a data unit.
used for computer analysis or calculations.
data recorder A machine for storing data acquired

data transmission Sending data signals from a
in the form of electrical signals (see DATA
pickup point or processing stage to another point
within a data-processing system; also, sending
data recording 1. The preservation of data signals
such signals to points outside the system.
by some process, such as magnetic-disk encod-
data-transmission system A data transmitter and
ing, optical-disk encoding, or tape recording, for
its associated equipment.
future use or as a backup. 2. A record of data sig-
data transmission utilization measure The ratio
nals, as on magnetic tape.
of the useful data output of a data-transmission
data reduction The summarization of a mass of
system to the total data input.
electronically gathered data.
data transmitter A circuit or device for sending
data-reduction system A system used to minimize
data from point to point within or outside of a
the amount of data necessary to convey given in-
data-processing system.
data unit Characters in a group that are related in
data representation Values and data as described
a way that makes them a meaningful whole (e.g.,
by numerals, symbols, and letters (e.g., computer
a text word, or an object such as a circle in vector
program instructions).
data segment As related to a particular computer
data value A measure of the amount of informa-
process, a subunit of allocated storage containing
tion contained in a certain number of data bits.
data only.
The greater the ratio of the actual information to
data selector/multiplexer A digital circuit that
the number of bits, the higher the data value.
has several or many input signals, and feeds one
data words In digital computer operations, words
of them onto a common line.
(bit groups) representing data, rather than pro-
data set A device that connects a data processor to
gram instructions.
a telegraph or telephone line.
data signal 1. A signal (such as one of binary bit
combinations) that can represent data as num-
David Phonetic alphabet code word for letter D.
bers, letters, or symbols. 2. A signal current or
daylight effect The modification of transmission
voltage proportional to some sampled quantity,
paths during the day because of ionization of the
and that can be used to actuate indicating in-
upper atmosphere by solar radiation.
struments during tests or measurements.
daylight lamp An incandescent lamp whose fila-
data statement A computer source program state-
ment is housed in a blue glass bulb, which ab-
ment identifying a data item and specifying its
sorbs some red radiation and transmits most of

daylight lamp • dc converter

the green, blue, and violet. So called because the dc-ac converter A circuit that converts a dc input
spectral output resembles that of typical daylight. voltage into an ac output voltage, with or without
daylight range The distance over which signals step-up or step-down. Also called INVERTER.
from a given transmitter are consistently received dc alpha The current amplification factor (ALPHA)
during the day. of a common-base transistor stage for a dc input
DB 1. Abbreviation of DIFFUSED BASE of a tran- (emitter) signal. Compare DC BETA.
sistor. 2. Abbreviation of DOUBLE BREAK (relay). dc amplifier 1. A direct-coupled amplifier. 2. An
dB 1. Abbreviation of DECIBEL or decibels. 2. amplifier for boosting direct-current signals.
Symbol for differential of susceptance. dc balance 1. Adjustment of a circuit or device for
dBa Abbreviation of ADJUSTED DECIBELS. dc stability or dc null. 2. Adjustment of a circuit
dBc Abbreviation of decibels referred to the carrier. for dc stability during gain changes. 3. A poten-
DBD Abbreviation of double-base diode. tiometer or other variable component used to sta-
dBd The power gain of an antenna in the direction bilize or null a dc circuit.
of maximum radiation, compared to the radiation dc bar See DC BUS.
in the favored direction of a half-wave dipole in dc base current Symbol, IB(dc). The static direct
free space receiving the same amount of power. current in the base element of a bipolar transis-
Expressed in decibels. tor.
dBi The power gain of an antenna in the direction dc base resistance Symbol, RB(dc). The static dc re-
of maximum radiation, compared to the radiation sistance of a bipolar transistor™s base element;
from a theoretical isotropic antenna in free space RB(dc) = VB/IB.
receiving the same amount of power. Expressed dc base voltage Symbol, VB(dc). The static dc volt-
in decibels. age at the base element of a bipolar transistor.
dBj The level of an RF signal, in decibels, relative to dc beta The current amplification factor (BETA) of
1 millivolt. a common-emitter-connected transistor for a dc
dBk Abbreviation of DECIBELS REFERRED TO 1 input (base) signal. Compare DC ALPHA.
KILOWATT. dc block A coaxial section that has a capacitance
DBM Abbreviation of database management. in series with the inner or outer conductor, or
dBm Abbreviation of DECIBELS REFERRED TO 1 both, to block dc while passing RF. Compare DC
dBm0 Signal level in dBm, referred to a zero-trans- dc bus A supply conductor carrying direct current
mission level. only.
dBm0p Noise in dBm0, measured with set phos- dcc Abbreviation of double cotton covered (wire).
phometric weighting. dc cathode current Symbol, IK(dc). The static direct
dB meter A usually high-impedance ac voltmeter current in the cathode element of an electron
with a scale reading directly in decibels. tube.
dBmp The level in dBm, measured with phospho- dc cathode resistance Symbol, RK(dc). The static dc
metric weighting. Generally equal to dBm “2.5, resistance of the cathode path of an electron
for a noise level that is flat within the communi- tube.
cations audio range. dc cathode voltage Symbol, VK(dc). The static dc
dBmr Decibels measured with respect to zero voltage at the cathode of an electron tube.
transmission level. dc circuit breaker A circuit breaker operated by
dBmV Abbreviation of DECIBELS REFERRED TO direct-current overload or underload, depending
1 MILLIVOLT. on its design and application.
dBrap Abbreviation of DECIBELS ABOVE REFER- dc collector current Symbol, IC(dc). The static di-
ENCE ACOUSTIC POWER (10“6 W). rect current in the collector element of a bipolar
dBrn Abbreviation for decibels above reference transistor.
noise. A level of 0 dBrn is defined as noise power dc collector resistance Symbol, RC(dc). The static
of 10“9 W (1 nanowatt). dc resistance of a bipolar transistor™s collector el-
dBrnc Noise power in dBrn for a circuit with mes- ement; RC(dc) = VC/IC.
sage weighting c. dc collector voltage Symbol, VC(dc). The static dc
dBrnc0 Noise in dBrnc measured with respect to voltage at the collector element of a bipolar tran-
zero transmission level. sistor.
dBV Abbreviation of DECIBELS REFERRED TO 1 dc component In a complex wave (i.e., one con-
VOLT. taining both ac and dc), the current component
dBW Abbreviation of DECIBELS REFERRED TO 1 having an unchanging polarity. The dc compo-
WATT. nent constitutes the mean (average) value around
dBx Abbreviation of DECIBELS ABOVE REFER- which the ac component alternates, pulsates, or
ENCE COUPLING. fluctuates.
dC Symbol for differential of capacitance. dc converter A dynamoelectric machine for con-
dc 1. Abbreviation of DIRECT CURRENT. 2. Abbre- verting low-voltage dc into higher-voltage dc. It is
viation of direct-coupled. essentially a low-voltage dc motor coupled me-
168 dc converter • dc plate resistance

+ nal energizes the field winding of a constant-
speed machine; because the output voltage is
proportional to field flux and armature speed, a
high output voltage is obtained. Also see AMPLI-
dc component dc grid bias Steady dc control-grid voltage used to
set the operating point of an electron tube.
dc grid current Symbol, IG(dc). The static direct cur-
’ rent in the control-grid element of an electron tube.
dc grid resistance Symbol, RG(dc). The static dc re-
dc component sistance in the control-grid element of an electron
tube; RG(dc) = VG/IG.
dc grid voltage Symbol, VG(dc). The static dc voltage
at the control grid of an electron tube.
chanically to a higher-voltage dc generator. Com-
dc inserter In a television transmitter, a stage that
adds the dc pedestal (blanking) level to the video
dc coupling See DIRECT COUPLING.
dc drain current Symbol, ID(dc). The static direct
dc inverter An electrical, electronic, or mechanical
current in the drain element of a field-effect tran-
device that converts dc to ac. Also called IN-
dc drain resistance Symbol, RD(dc). The static dc
dcl Abbreviation of dynamic load characteristic.
resistance of an FET™s drain element; RD(dc) =
dc leakage The unintended flow of direct current.
dc leakage current 1. The direct current that nor-
dc drain voltage Symbol, VD(dc). The static dc volt-
mally passes through a correctly polarized elec-
age at the drain element of a field-effect transis-
trolytic capacitor operated at its rated dc working
voltage. 2. The zero-signal reverse current in a
dc dump In digital computer operation, removing
semiconductor pn junction.
dc power from a computer, which would eradicate
material stored in a volatile memory.
dc emitter current Symbol, IE(dc). The static direct
D/CMOS Combination of DMOS and CMOS on a
current in the emitter element of a bipolar tran-
monolithic chip.
dc motor A motor that operates from direct cur-
dc emitter resistance Symbol, RE(dc). The static dc
rent only.
resistance of a bipolar transistor™s emitter ele-
dc noise Noise heard during the playback of mag-
ment; RE(dc) = VE/IE.
netic tape that was recorded while direct current
dc emitter voltage Symbol, VE(dc). The static dc
was in the record head.
voltage at the emitter element of a bipolar tran-
dc noise margin In a digital or switching circuit,
the difference Vo “ Vi , where Vo is the output-
dc equipment Apparatus designed expressly for
voltage level of a driver gate and Vi is the input
operation from a dc power supply. Compare AC
threshold voltage of a driven gate.
dc operating point For a bipolar transistor, field-
dc erase head In a magnetic recorder, a head sup-
effect transistor, or vacuum tube, the static, zero-
plied with a dc current for the purpose of remov-
signal dc voltage and current levels.
ing data.
dc overcurrent relay A relay or relay circuit actu-
dc error voltage In a television receiver, the dc
ated by dc coil current rising above a specified
output of the phase detector, which is used to
control the frequency of the horizontal oscillator.
dc overvoltage relay A relay or relay circuit actu-
dc gate current Symbol, IG(dc). The very small static
ated as a result of the dc coil voltage rising above
direct current in the gate element of a field-effect
a specified level. Compare DC UNDERVOLTAGE
dc gate resistance Symbol, RG(dc). The very high,
dc patch bay A patch bay in which the dc circuits
static dc resistance of an FET™s gate element;
of a system are terminated.
RG(dc) = VG/IG.
dc picture transmission In television, transmis-
dc gate voltage Symbol, VG(dc). The static dc volt-
sion of the dc component of the video signal; this
age at the gate element of a field-effect transistor.
component corresponds to the average illumina-
dc generator 1. A rotating machine (dynamo) for
tion of the scene.
producing direct current. Also see DYNAMO-
dc plate current Symbol, IP(dc). The static direct
ELECTRIC MACHINERY. 2. Generically, a device
current in the plate element of an electron tube.
that produces direct current: batteries, photo-
dc plate resistance Symbol, RP(dc). The static dc re-
cells, thermocouples, etc.
sistance of the internal plate-cathode path of an
dc generator amplifier A special type of generator
electron tube; RP(dc) = VP/IP.
that provides power amplification. The input sig-
dc plate voltage • dead band

dc plate voltage Symbol, VP(dc). The static dc volt- dc transformer A dc-to-dc converter providing
age at the plate electrode of an electron tube. voltage step-up. The applied dc is usually first
dc positioning Alignment of the spot on the screen converted to ac, which is then stepped up by a
of an oscilloscope tube, by means of adjustable dc transformer. The higher-voltage ac is then recti-
voltages applied to the horizontal and vertical de- fied to produce a high dc output voltage.
flecting plates.
dc power Symbol, Pdc. Unit, watt. The power in a
+ +
dc circuit; Pdc = EI, where E is in volts and I is in
Chopper Rectifier Filter
In Out
amperes. Compare AC POWER. Also see POWER. ’ ’
dc power supply A power unit that supplies direct
current only. Examples: battery, transformer/
dc transformer
rectifier/filter circuit, dc generator, and photovoltaic
cell. Compare AC POWER SUPPLY.
dc relay A relay having a simple coil and core sys- dc transmission 1. Sending dc power from a gen-
tem for closure by direct current, which can be erating point to a point of use. 2. In television
rectified ac. transmission, the retention of the dc component
dc resistance Resistance offered to direct current, in the video signal.
as opposed to in-phase ac resistance. dc tuning voltage The capacitance-varying dc
dc resistivity The resistivity of a sample of mate- voltage applied to a varactor in an inductance-
rial measured using a pure dc voltage under capacitance (LC) tuned circuit.
specified conditions (physical dimensions, tem- dcu Abbreviation of decimal counting unit.
perature, etc.). dc undercurrent relay A relay or relay circuit that
dc restoration The reinsertion of the dc compo- is actuated as a result of the dc coil current drop-
nent into a signal from which the component has ping below a specified level. Compare DC OVER-
been extracted through a capacitor or trans- CURRENT RELAY.
former. dc undervoltage relay A relay or relay circuit that
dc restorer A circuit that reinserts the average dc is actuated as a result of the dc voltage dropping
component of a signal after the component has below a specified level. Compare DC OVERVOLT-
been lost because the signal passed through a ca- AGE RELAY.
pacitor or transformer. dcv Abbreviation of DC VOLTS or DC VOLTAGE.
DCS Abbreviation of DORSAL COLUMN STIMULA- dc voltage Abbreviation, dcv. A voltage that does
TOR. not change in polarity, an example being the volt-
dc shift A shift in the DC OPERATING POINT. age delivered by a battery or dc generator. Also
dc short A coaxial fitting providing a dc path be- see VOLTAGE.
tween the center and outer conductors, while dc working voltage Abbreviation, dcwv. The rated
permitting radio-frequency (RF) current to flow dc voltage at which a component can be operated
easily through the coaxial section. Compare DC continuously with safety and reliability.
BLOCK. dc working volts Abbreviation, dcwv. The actual
dc signaling A signaling procedure that uses direct value, expressed in volts, of a DC WORKING
current as the medium (e.g., simple wire telegra- VOLTAGE.
phy or telephony). dcwv Abbreviation of DC WORKING VOLTAGE.
dc source 1. DC GENERATOR. 2. A live circuit dD Symbol for differential of electric displacement.
point from which one or more direct currents can DDA Abbreviation of digital differential analyzer.
be taken. DDD Abbreviation of DIRECT DISTANCE DIALING
dc source current Symbol, IS(dc). The static direct (telephone).
current in the source element of a field-effect D display See D SCOPE.
transistor. DE Abbreviation of decision element.
dc source resistance Symbol, RS(dc). The static dc dE Symbol for differential of voltage.
resistance of an FET™s source element. deac In frequency-modulation (FM) receivers, a de-
dc source voltage Symbol, VS(dc). The static dc vice used for deemphasis. The name is short for
voltage at the source element of a field-effect deaccentuator.
transistor. deactuating pressure For an electrical contact,
DCTL Abbreviation of DIRECT-COUPLED TRAN- the pressure at which contact is made or broken
SISTOR LOGIC. as the pressure reaches the level of activation.
dc-to-dc inverter See DC INVERTER. dead 1. Unelectrified. 2. Lacking electromagnetic
dc transducer 1. A transducer that depends on di- signals or fields. 3. Electrically or mechanically
rect current for its operation (i.e., it has a dc inoperative.
power supply whose output is modulated by the dead band 1. A radio-frequency band on which no
sensed phenomenon). 2. A transducer that con- signals are heard. 2. A range of values for which
verts a direct current into some other form of en- an applied control quantity (e.g., current or volt-
ergy, such as heat, pressure, or sound. age) has no effect on the response of a circuit.
170 deadbeat • decade capacitor

deadbeat The state wherein a moving body (such grams. 2. To optimize the design and construc-
as the pointer of a meter or the voice coil of a tion of electronic equipment.
loudspeaker) comes to rest without overswing or debugging A process by which engineers eliminate
oscillation. the flaws in a circuit, machine, or computer pro-
deadbeat galvanometer See DEADBEAT INSTRU- gram.
MENT. debugging aid routine A computer program used
deadbeat instrument A meter or recorder that is to test other programs.
highly damped to ensure that overswing or oscil- debugging period The time interval following com-
lation does not occur. pletion of a software design, a hardware inter-
deadbeat meter See DEADBEAT INSTRUMENT. connection, or the manufacture of a piece of
dead break An unreliable contact of a relay, electronic equipment, during which errors and
caused by insufficient pressure. imperfections are sought and corrected.
dead circuit A circuit that is electrically disabled. debunching In a velocity-modulated tube, such as
dead end The unused end of a tapped coil (i.e., the a Klystron, a beamspreading space-charge effect
turns between the end of the coil and the last that destroys electron bunching.
turn used). Debye length The maximum distance between an
dead-end tower A supporting tower for an antenna electron and a positive ion over which the elec-
or transmission line that can withstand stresses tron is influenced by the field of the ion.
caused by loading or pulling. Debye shielding distance See DEBYE LENGTH.
dead file A computer file that is not in use, but is deca- A prefix that indicates multiplication by 10.
being kept in a record. decade 1. A frequency band whose upper limit is 10
dead front panel A metal panel that, for safety and times the lower limit. Example: 20 Hz to 200 Hz. 2.
desensitization, is completely insulated from volt- A set of 10 switched or selectable components in
age-bearing components mounted on it; it is often which the total value is 10 times that of individual
grounded. values. Example: a decade capacitor. Also called
dead interval See DEAD TIME. DECADE BOX. 3. A group, sometimes a unit of ac-
dead line A deenergized line or conductor. cess, of 10 computer storage locations.
dead period See DEAD TIME. decade amplifier An amplifier or preamplifier
dead room An anechoic room in which acoustic whose gain can be adjusted in increments of 10
(—1, —10, —100, etc.).
tests and studies are made.
dead short A short circuit with extremely low (vir- decade box A group of components that provides
tually no) resistance from dc into the radio- values in 10 equal steps selected by a switch or
frequency spectrum. jacks. For compactness, the components and the
dead space See DEAD BAND. associated hardware are enclosed in a box or can.
dead spot 1. An area in which radio waves from a See, for example, DECADE CAPACITOR.
particular station are not received. 2. On a decade capacitor A composite capacitor whose
vacuum-tube cathode (directly or indirectly value is variable in 10 equal steps. For example,
heated), a spot from which no electrons are the values might be set at 100 picofarads (pF),
emitted. 200 pF, 300 pF, etc., up to 1000 pF. Compare
dead stretch The tendency of insulating materials DECADE INDUCTOR and DECADE RESISTOR.
to permanently retain their approximate dimen-
sions after having been stretched.
dead time 1. DOWN TIME. 2. An interval during 0 1 2 3 4 5 6 7 8 9
which there is no response to an actuating signal.
3. In a computer system, an interval between re-
lated events that is allocated to prevent interfer-
ence between the events.
dead volume In a pressure transducer, the zero-
4 5
stimulus volume of the pressure port cavity.
3 6
dead zone See ZONE OF SILENCE.
debatable time Computer time that cannot be 7
placed in any other category.
debounced switch A switch in sensitive computer 1 8
or control systems that has circuitry for eliminat-
ing the electrical effects of bounce (see BOUNCE, 9
de Broglie waves Electromagnetic waves that are
believed to be associated with moving particles
(such as electrons, protons, and neutrons).
debug 1. To eliminate errors in, and maximize the
efficiency of, a computer program or group of pro- decade box
decade counter • decimal code

decade counter A counter (see COUNTER, 1, 2) in Gain (dB) = 10 log10(Pout/Pin ),
which the numeric display is divided into
sections, each having a value 10 times that of the where Pout is the output power and Pin is the input
next and displaying a digit from zero to nine. power. For voltage, if the input and output
decade inductor An inductor whose value is vari- impedances are the same, the gain in decibels is
able in 10 equal steps. Compare DECADE CA- given by:
Gain (dB) = 20 log10(Vout/Vin ),
decade resistor A resistor whose value is variable
in 10 equal increments. Compare DECADE CA- where Vout is the output voltage and Vin is the in-
PACITOR and DECADE INDUCTOR. put voltage. For current, if the input and output
decade scaler A scale-of-10 electronic counter impedances are the same, the gain in decibels is
(i.e., a circuit delivering one output pulse for each given by:
group of 10 input pulses).
Gain (dB) = 20 log10(Iout/Iin),
decametric waves Waves in the 10- to 100-meter
band (30 to 3 MHz). where Iout is the output current and Iin is the input
decay 1. The decrease in the value of a quantity, current. Losses are indicated by negative dB gain
e.g., current decay in a resistance-capacitance values.
circuit. 2. The gradual, natural loss of radioactiv- decibels above reference acoustic power Abbre-
ity by a substance. viation, dBrap. The ratio of a given acoustic
decay characteristics 1. The decay of a parame- power level to a lower reference acoustic power
ter; usually an exponential function. 2. The per- level, specified in decibels.
sistence time in a storage oscilloscope. decibels above reference noise Abbreviation,
decay curve A curve, usually logarithmic, repre- dBrn. The ratio of the noise level at a selected
senting the function of quantity versus time for a point in a circuit to a lower reference noise level,
signal decrement, the decrement of radioactivity, in decibels.
or other natural process. decibels referred to 1 millivolt Abbreviation,
decay rate A quantitative expression for the rapid- dBmV. The relative voltage level of a signal when
ity with which a quantity decreases. Generally compared with a 1-mV signal measured at the
listed in decibels per second (dB/s) or decibels same terminals.
per millisecond (dB/ms). decibels referred to 1 milliwatt Abbreviation,
decay time The time required for pulse amplitude dBm. The ratio, in decibels, of an applied power
to fall from 90% to 10% of the peak value. Also level to the power level of 1 mW.
called FALL TIME. decibels referred to 1 volt Abbreviation, dBV. The
Decca A 70- to 130-kHz CW radio navigation sys- ratio, in decibels, of a given voltage to 1 V, ex-
tem (British). pressed in decibels.
decelerated electron A high-speed electron that is decibels referred to 1 watt Abbreviation, dBW.
abruptly decelerated upon striking a target, caus- The ratio of a given power level to the power level
ing X-rays to be emitted. of 1 W, expressed in decibels.
decelerating electrode A charged electrode that decider See DECISION ELEMENT.
slows the electrons in an electron beam. decigram A unit of mass equal to 0.1 gram.
deciliter A unit of volume equal to 0.1 liter, or 10“4
deceleration Acceleration that results in a de-
crease in speed. cubic meter.
deceleration time 1. The time taken by magnetic decilog A unit equal to 0.1 times the common log-
tape to stop moving after the last recording or arithm of a ratio.
playback has finished. 2. The time taken by a decimal 1. Pertaining to the base-10 number sys-
mechanical data storage medium, such as tem (see DECIMAL NUMBER SYSTEM). 2. A
a hard disk, to come to rest after completion base-10 numerical fraction, represented by fig-
of a read or write operation, or on powering- ures to the right of the radix point (decimal point),
down. and arranged serially according to negative
powers of 10. Examples: 0.12 = 1.2 — 10“1,
decentralized data processing Data processing in
0.00135 = 1.35 — 10“3.
which the computing equipment is distributed
among managerial subgroups. decimal attenuator An attenuator circuit whose
deception A method of producing misleading resistances are chosen for attenuation in deci-
echoes in enemy radar. mal steps. Thus, one section provides attenua-
deception device A radar device, or radar-associ- tion in steps of 0.1 times the applied voltage,
ated device, for deception. another in steps of 0.01 times the applied volt-
deci- Abbreviation, d. A prefix meaning one-tenth age, another in steps of 0.001 times the applied
(10“1). Examples: DECIBEL, DECIMETER. voltage, etc.
decibel Abbreviation, dB. A practical unit of rela- decimal code A method of defining numbers, in
tive gain. In terms of power, the relative gain in which each place has a value of ten times that im-
decibels is equal to: mediately to the right.
172 decimal-coded digit • decommutation

decimal-coded digit 1. A numeral from 0 to 9. 2. declarative macroinstruction As part of an as-
A numeral in the DECIMAL NUMBER SYSTEM. sembly language, instructions to the compiler to
3. A binary representation of a decimal value do something or record a condition without af-
from 0 to 9. fecting the object program.
decimal digit A numeral from 0 to 9. declarative statement A computer source pro-
decimal equivalent The decimal number equal to gram instruction specifying the size, format, and
a given fraction (e.g., the decimal equivalent of kind of data elements and variables in a program
64 is 0.3281). for a compiler.
decimal fraction See DECIMAL, 2. declination 1. The angle representing the devia-
decimal notation See DECIMAL NUMBER SYS- tion of magnetic north from true north; it is the
TEM. angle subtended by a freely turning magnetic
decimal number system The familiar base-10 or needle and the meridian. Compare INCLINATION.
radix-10 number system, in which the digits 0 2. Celestial latitude.
through 9 represent values according to their po-
sition, relative to the decimal point (also called
the radix point). Positions to the left of the point
represent successive positive powers of 10, and
those to the right represent successive negative
θ = Declination
powers of 10.
decimal point The radix point in a decimal num-
ber. It serves to separate the integral part from
the fractional part of the number.
decimeter waves See MICROWAVES.
Compass needle
decimetric waves Electromagnetic waves having
lengths ranging from 0.1 meter to 1 meter (3000
MHz to 300 MHz). Also known as ultrahigh fre-
quency (UHF).
decineper A natural-logarithmic unit equal to 0.1
neper. declination, 1
decipher See DECODING, 3.
decision 1. A choice based on the evaluation and
comparison of data, and the identification of a declinometer An instrument for measuring decli-
specified objective. 2. In digital computer opera- nation.
tions, the automatic selection of the next step in decode 1. To unscramble a coded message. 2. In
a sequence, on the basis of data being compared digital computer operations, to deliver a specific
by a relational test. output from character-coded inputs. 3. In a mul-
decision box A block on a computer flowchart in- tiplex system, the separation of the subcarrier
dicating the point at which a decision (see DECI- from the main carrier.
SION, 2) must be made as to which of several decoder A circuit or device for performing DECOD-
branches the program will take. ING.
decision elements See LOGIC CIRCUITS. decoder/demultiplexer A circuit that places an
decision instruction A computer program input signal on a selected output line.
instruction to compare the values of operands decoder/driver An integrated circuit containing a
and take an appropriate action, as per the BASIC decoder and driver.
instruction “IF A = B THEN GO TO (line num- decoding 1. In computer and data-processing op-
decision procedure In decision theory, a series of 2. The conversion to English of a message re-
calculations made to optimize the speed or effi- ceived in a code. 3. Translating a message from a
ciency of a process, or to minimize risk, failure, secret code (i.e., deciphering a message). 4. The
cost, etc. automatic conversion of a signal into the appro-
decision theory A statistical discipline concerned priate switching action (as the enabling of a
with identifying and evaluating choices and alter- transmitter or receiver by a tone in a selective
natives, and determining the best sequence of calling system).
steps to take in reaching an objective. decoding circuit A circuit intended for the pur-
decision tree In decision theory, a diagram show- pose of translating a code into ordinary language.
ing alternative choices, so called from its resem- decollator An offline computer device for separat-
blance to a tree with branches. ing the parts of output continuous stationery
decision value A value that defines the boundary sets. Also see CONTINUOUS STATIONERY.
between two intervals in the encoding process. decommutation The extraction of a signal compo-
deck 1. See TAPE DECK. 2. A pack of punched nent from the composite signal, resulting from
cards in a computer file. commutation.
decommutator • definite-purpose component

decommutator A circuit or device for performing dee In a cyclotron, one of the D-shaped chambers
decommutation, including demodulators, demul- in and between which particles accelerate in a
tiplexers, and signal separators. spiral path to high velocity.
decoupler A device that isolates two circuits so dee line In a cyclotron, a support for the dee, with
that a minimal amount of coupling exists be- which it forms a resonant circuit.
tween them. deemphasis In frequency modulation, the intro-
decoupling The elimination or effective minimiza- duction of a low-pass characteristic (response
tion of coupling effects, as in decoupling amplifier falls as modulating frequency increases) to com-
stages to prevent interaction through a common plement the rising response of preemphasis. Also
power-supply lead. called postemphasis or postequalization. Com-
decoupling capacitor 1. A capacitor that provides pare PREEMPHASIS.
a low-impedance path to ground to prevent deemphasis amplifier An amplifier used to re-
undesired stray coupling among the circuits in a move the high-frequency preemphasis applied to
system. 2. The capacitive member of a resistance- signals prior to broadcasting, multiplexing, tape
capacitance (RC) decoupling filter. recording, or telemetering. Also see DEEMPHA-
decoupling filter A resistance-capacitance (RC) fil- SIS and PREEMPHASIS.
ter, usually inserted into a common dc line in a deemphasis circuit A low-pass filter that provides
multistage amplifier to prevent interstage feed- deemphasis in an FM receiver.
back coupling through the common impedance of deemphasis network See DEEMPHASIS CIRCUIT.
the line. deenergize To take a circuit or device out of opera-
decoupling network One or more decoupling fil- tion (i.e., to remove its power or signal excitation).
ters. deep cycle Pertaining to a rechargeable cell or bat-
decoupling resistor The resistive member of a re- tery that can operate until it is almost completely
sistance-capacitance (RC) decoupling filter. discharged. It generally has a high ampere-hour
decoy In radar, an object that provides misleading capacity.
reflections. Also see CHAFF. deep-diffused junction A pn junction made by dif-
decreasing function A function whose curve has a fusing the impurity material deep in the semicon-
negative slope at all points in the domain. ductor wafer. Compare SHALLOW-DIFFUSED
decrement 1. Also called logarithmic decrement. JUNCTION.
The rate at which a damped wave dies down. The deep discharge The nearly complete discharge of a
decrement value is the natural (base-e) logarithm cell or battery; usually done prior to recharging.
of the ratio of two successive peaks of the same deep-space net A radar system intended for con-
polarity. 2. A quantity used to lessen the value of stant monitoring of spacecraft.
a variable. 3. To lower the value (of a register, for defeating 1. The disabling or circumvention of an
example) by a single increment. alarm or security system, leaving the protected
decremeter An instrument for measuring the de- property vulnerable to intrusion. 2. The danger-
crement of a radio wave. ous, and potentially lethal, disabling of a safety
decremeter capacitor A variable capacitor for use device in an electrical or electronic system.
in a decremeter. The rotor plates are shaped so defect 1. Absence of an electron (hence, presence
that equal angular rotations correspond to the of a hole) in the lattice of a semiconductor crystal.
same decrement at all settings. Thus, the percent- 2. An abnormality of design, construction, or per-
age of capacitance change for a given angle of rota- formance of an electronic circuit or device. 3. In a
tion is constant throughout the capacitance range. computer system, a hardware or software fault
decryption The conversion of an encrypted signal that could be the eventual cause of a failure. 4. A
from a cipher into plain text, graphics, or other flaw in a crystalline substance.
commonly recognizable form. Also see CIPHER. defect conduction In a semiconductor material,
Compare ENCRYPTION. conduction via holes.
decryption key An algorithm, or a set of algorithms, deferred addressing Indirect addressing in which
that converts an encrypted signal from a cipher a preset counter makes several references to find
into plain text, graphics, or other commonly rec- a desired address.
ognizable form. Each cipher has its own unique deferred entry An entry into a computer subrou-
algorithm or set of algorithms for this purpose. tine, delayed because of a delay in the exit from a
The signal cannot be decrypted unless all the control program.
components of the key are present. deferred exit An exit from a computer subroutine,
dedicated Assigned exclusively to a certain pur- delayed because of a particular command.
pose [e.g., a dedicated facsimile (fax) line]. defibrillation Use of a CARDIAC STIMULATOR to
deductive logic A form of symbolic logic used to halt fibrillation of the heart, as caused by electric
demonstrate that a certain conclusion will always shock.
follow, given a certain set of circumstances. The defibrillator See CARDIAC STIMULATOR.
logic of digital circuits is deductive. Compare IN- definite-purpose component A component de-
DUCTIVE LOGIC. signed for a specific use, rather than for a wide
174 definite-purpose component • degenerate parametric amplifier

range of possible applications (e.g., a video detec- an electrostatic cathode-ray tube. Expressed in
tor diode, as opposed to a general-purpose diode). volts per centimeter (V/cm) or volts per inch
definition 1. Clarity of a video image (i.e., one hav- deflection voltage The potential difference be-
ing good contrast and faithful tones). 2. Good in- tween the deflection plates of an electrostatic
telligibility of reproduced sounds. cathode-ray tube. It is used to control the direc-
deflecting coil One of a set of external coils carry- tion of the electron beam striking the phosphor
ing sawtooth currents, which provide electromag- screen.
netic deflection of the cathode-ray beam in deflection yoke An assembly of deflection coils in
picture tubes, camera tubes, radar display tubes, picture and camera tubes, and in some magneti-
sonar display tubes, and some oscilloscopes. Also cally deflected oscilloscope tubes. The usual com-
called deflection coil. bination is two series-connected horizontal
deflecting electrode An electrode, such as a de- deflection coils and two series-connected vertical
flecting plate, used to alter the direction an elec- deflection coils.
tron beam. Also called deflection electrode. deflector 1. A beam-forming plate in a beam-
deflecting plate In a cathode-ray tube, a plate that power tube. 2. A deflection plate in a cathode-ray
attracts or repels the electron beam, causing the tube. 3. A deflection coil or yoke in a picture tube,
spot to move horizontally or vertically on the camera tube, or magnetic-deflection oscilloscope
screen. Also called deflection plate. tube. 4. A mechanical attachment for improving
the angle of radiation of a loudspeaker by spread-
ing the higher-frequency waves.
+ defocusing Blurring of the image on the screen of
plates a cathode-ray tube, caused by spreading of the
electron beam.
deformation potential The voltage generated
when a crystal lattice is subjected to pressure. An
example is the voltage produced by a crystal mi-
Path of crophone when acoustic waves strike the crystal.
electron defruiting The elimination of non-synchronized
echoes in a radar system.
deg Abbreviation of DEGREE.
’ degassing During the evacuation of a vacuum tube
or similar device, the removal of gas, including
deflecting plate that which has bonded to the glass and metal
degauss See DEMAGNETIZE.
deflecting torque The torque required to move the
degausser 1. A circuit that performs DEGAUSS-
pointer of a meter, or the pen or mirror of a
ING. 2. A device for bulk erasing magnetic tape;
also called a bulk tape eraser.
deflection 1. In a cathode-ray tube, movement of
degaussing 1. The demagnetization of an object; in
the electron beam by electric or magnetic fields.
particular, the removal of all residual magnetism.
2. Movement of the pointer of a meter or the pen
2. The erasure of data from a magnetic or
or mirror of a recorder by an applied current or
magneto-optical data-storage medium.
degaussing circuit In a color television receiver, a
deflection factor Symbol, G. The reciprocal of DE-
circuit including a thermistor, voltage-dependent
resistor, and coil for automatically demagnetizing
deflection plane In a cathode-ray tube, the plane
the picture tube when the receiver is switched on.
perpendicular to the axis of the tube. This plane
degaussing coil A coil carrying an alternating cur-
contains the electromagnetic and/or electrostatic
rent; the resulting magnetic field demagnetizes
lines of flux that result in deflection of the elec-
objects that have become accidentally magne-
tron beam.
deflection coil See DEFLECTING COIL.
degeneracy In microwave practice, the appearance
deflection electrode See DEFLECTING ELEC-
of a single resonant frequency for two or more
modes in a resonator.
deflection plate See DEFLECTING PLATE.
degenerate modes In microwave operations, a set
deflection polarity In a cathode-ray tube, the po-
of modes with the same resonant frequency or
larity of the voltage applied to a particular de-
propagation constant.
flecting plate to move the electron beam in a
degenerate parametric amplifier An inverting
particular direction.
parametric amplifier, in which the two signals are
deflection sensitivity Symbol, S. A quantitative
of the same frequency, which is half the pump
measure of the extent to which the input voltage
will displace the electron beam on the screen of
degenerate semiconductor • deka-

degenerate semiconductor A semiconductor that degree absolute Symbol, K. The unit of tempera-
behaves like a metal over a wide range of temper- ture on the absolute scale. Also see ABSOLUTE
atures. SCALE.
degeneration In an amplifier, the technique of degree Celsius Symbol, °C. The unit of tempera-
feeding a portion of the output back to the input ture on the CELSIUS SCALE.
out of phase with the input signal, to improve fi- degree centigrade Symbol, °C. The unit of temper-
delity at the expense of gain. Also called negative ature on the centigrade scale (now called CEL-
feedback or inverse feedback. Compare REGEN- SIUS SCALE).
ERATION. degree Fahrenheit Symbol, °F. The unit of tem-
degenerative resistor An unbypassed emitter re- perature on the FAHRENHEIT SCALE.
sistor in a common-emitter bipolar-transistor degree of current rectification For a rectifier, the
circuit, or an unbypassed source resistor in a ratio of the average direct output current to the
common-source field-effect transistor circuit. root-mean-square (rms) alternating input cur-
Signal current flowing through the resistor rent.
produces negative feedback current (degenera- degree of voltage rectification For a rectifier, the
tion), which reduces the gain of the stage, but ratio of the average direct-current (dc) output
increases the linearity of the transfer character- voltage to the root-mean-square (rms) alternat-
istic. ing-current (ac) input voltage.
degree Reaumur Symbol, °R. The unit of tempera-
ture on the REAUMUR SCALE.
+ degrees of freedom 1. The ways in which a point
can move or a system can change. In three-
dimensional space, a rigid body has six degrees of
freedom: motion in three linear directions, and
rotation around three linear axes extending
through its center. 2. The ways in which a robot
arm can move, including linear motion and rota-
tional motion.
degrees of rotation A measure of the extent to
which a robot joint, or a set of robot joints, can be
turned. Some reference axis is always used; an-
gles are specified in degrees, relative to that axis.
In degrees-to-radians conversion The conversion of
angles in degrees to angles in radians. To change
degrees to radians, multiply degrees by 0.01745.
deion circuit breaker A circuit breaker in which
the arc occurring when the contacts open is
quickly extinguished by an external magnetic de-
Degenerative vice.
resistor deionization The conversion of an ionized sub-
stance, such as a gas, to a neutral (non-ionized)
state. The process changes the ions into un-
degenerative resistor
charged atoms.
deionization potential The voltage at which an
ionized substance becomes deionized; for exam-
degradation 1. Gradual deterioration in the condi-
ple, the voltage at which a glow discharge is ex-
tion or performance of a circuit or device. 2. In a
tinguished when the gas ions become neutral
computer system, compromised performance
atoms at that voltage. Also called extinction poten-
caused by component failure.
degradation failure Failure occurring at the termi-
deionization time The time required for an ionized
nal point of degradation.
gas to become neutral after the removal of the
degraded operation See DEGRADATION.
ionizing voltage.
deionization voltage See DEIONIZATION POTEN-
degree 1. A unit of circular angular measurement
equal to 1 360 of the circumference of a circle. Also
deionize To restore to an electrically neutral condi-
called GEOMETRIC DEGREE. 2. A unit of
tion (i.e., to convert ions to neutral atoms, as in
temperature measurement. See DEGREE
the deionization of the gas when the discharge in
a glow tube is extinguished).
deka- A prefix meaning ten(s) (e.g., DEKAMETER).
176 dekahexadecimal number system • delay time

dekahexadecimal number system See HEXA- delayed repeater A repeater that receives and
DECIMAL NUMBER SYSTEM. stores information, and retransmits the informa-
delamination The splitting apart, in layers, of an tion later, in response to a switching or interroga-
insulating material, such as mica or bonded plas- tion signal.
tic film. delayed repeater satellite An active communica-
delay 1. The interval between the instant at which tions satellite that acts as a delayed repeater (i.e.,
a signal or force is applied or removed and the in- it receives and records information at one time
stant at which a circuit or device subsequently and retransmits it at a later time).
responds in a specified manner. 2. The time re- delayed sweep 1. In an oscilloscope or radar, a
quired for a signal to traverse a given medium, sweep that starts at a selected instant after the
such as air, mercury, or quartz. signal under observation has started. 2. The
delay action Response occurring some time after a (usually calibrated) circuit for producing a sweep,
stimulus has been applied or removed (e.g., the as defined in (1).
retarded opening of a delayed-dropout relay). delayed updating Updating a computer record or
delay circuit 1. A circuit, such as a resistance-ca- record set so that the record fields are left un-
pacitance (RC) or resistance-inductance (RL) changed until all other changes attendant to the
combination, that introduces a time delay. 2. See pertinent event are processed.
DELAY LINE. delay equalizer A network that corrects DELAY

delay coincidence circuit A coincidence circuit DISTORTION.
(see AND CIRCUIT) triggered by two pulses, one of delay-frequency distortion Distortion caused by

which lags behind the other. variation of envelope delay within a frequency
delay counter In a digital computer, a device that band.
halts a program run long enough for an operation delay line A device (not always a line) that intro-
to be completed. duces a time lag in a signal. The lag is the time re-
delay distortion 1. Distortion resulting from vari- quired for the signal to pass through the device,
ations in the phase delay of a circuit or device at minus the time necessary for the signal to tra-
different points in its frequency range. 2. In a fac- verse the same distance through a wire, cable,
simile (fax) signal, variations in the delay of dif- optical fiber, or free space.
ferent frequency components of the signal. delay-line memory In a digital computer, a mem-

delayed AGC See DELAYED AUTOMATIC GAIN ory that uses a delay line, associated input- and
CONTROL. output-coupling devices, and an external regen-
delayed automatic gain control An automatic erative-feedback path. Information is kept stored
gain control circuit that operates only when by causing it to recirculate in the line by regener-
the signal amplitude exceeds a predetermined ation.
threshold level, thus providing maximum amplifi- delay-line register In a digital computer, a register
cation of weaker signals. that operates in the manner of a DELAY-LINE
delayed automatic volume control See DE- MEMORY and has a register length (capacity) of
LAYED AUTOMATIC GAIN CONTROL. an integral number of words.
delayed break In relay or switch operation, con- delay-line storage See DELAY-LINE MEMORY and
tacts separating some time after the switch has DELAY-LINE REGISTER.
been thrown or the relay deenergized. Compare delay multivibrator See MONOSTABLE MULTIVI-
delayed close See DELAYED MAKE. delay-power product Unit, watt-second. The fig-
delayed closure See DELAYED MAKE. ure of merit for an integrated circuit (IC) gate. In-
delayed contacts Contacts that open or close at a creasing gate power reduces propagation delay.
predetermined instant after their activating sig- Also called PROPAGATION DELAY-POWER
nal is applied or removed. PRODUCT.
delayed drop-in See DELAYED MAKE. delay relay A relay that opens or closes at the end
delayed dropout See DELAYED BREAK. of a predetermined time interval.
delayed loop In security applications, a circuit or delay switch A switch having delayed make, de-
system that registers an alarm some time after layed break, or both.
intrusion is first detected. The delay can usually delay time 1. The interval between the instant a
be selected or preadjusted. voltage or current is applied and the instant a
delayed make In relay or switch operation, con- circuit or device operates. 2. In an output pulse,
tacts closing some time after the switch has been the interval between the instant an ideal pulse
thrown or the relay has been energized. Compare is applied to the input of a system and the in-
DELAYED BREAK. stant the output pulse reaches 10% of its maxi-
delayed open See DELAYED BREAK. mum amplitude. 3. The time elapsed between
delayed PPI Plan-position indicating radar having the presentation of a pulse to the input of a de-
a delayed time base. lay line and the appearance of the pulse at the
delayed pull-in See DELAYED MAKE. output.

delay timer • demodulator

delay timer 1. A timer that starts or stops an op- delta quantity An increment (i.e., the difference
eration after a prescribed length of time. 2. A de- between two values of a variable).
lay relay or switch. delta rays The emission of secondary electrons as
delay unit In a radar system, a circuit for delaying a result of radioactivity.
pulses. delta-sigma modulation A method of analog-to-
delete 1. To erase or blank out a signal. 2. The digital conversion. The output is a pulse density
elimination from a computer file of a record or function of the input. The input can be obtained
record group. 3. To remove a computer program by low-pass filtering of the output.
from memory or storage. delta tune Also called receiver incremental tuning
deletion record In the master file of a digital com- (RIT). In high-frequency (HF) communications
puter, a new record that causes existing ones to transceivers, a control that allows the receiver
be deleted. frequency to be adjusted up to several kilohertz
delimiter In digital computer operations, a charac- higher or lower than the transmitter frequency.
ter limiting a sequence of characters of which it is delta waves Brain waves having a frequency less
not itself a member. than 9 Hz. Also see ELECTROENCEPHALO-
Dellinger effect The sudden disappearance of a GRAPH and ELECTROENCEPHALOGRAM.
radio signal as a result of an abrupt increase in Deluc™s pile See DRY PILE.
atmospheric ionization caused by a solar erup- dem Abbreviation of DEMODULATOR.
tion. demagnetization curve The portion of a magnetic
deliquescent material A material that absorbs hysteresis curve, showing reduction of demagne-
enough moisture from the air to get wet. For ex- tization.
ample; calcium chloride, a deliquescent material, demagnetization effect The phenomenon in
is often used to keep electronic equipment dry. which uncompensated magnetic poles at the sur-
Compare HYGROSCOPIC MATERIAL. face cause a reduction of the magnetic field inside
delta circuit A three-phase electrical circuit with a sample of a material.
no common ground. demagnetize To remove magnetism from an ob-
delta connection A triangular connection of coils ject, either temporarily or permanently.
or load devices in a three-phase system, so called demagnetizer See DEGAUSSER.
from its resemblance to the Greek letter delta. demagnetizing current The half-cycle of an alter-
Compare WYE-CONNECTION. nating current (or polarity of a direct current)
delta-matched antenna See WYE-MATCHED IM- flowing through a coil wound on a permanent
PEDANCE ANTENNA. magnet (as in a headphone, permanent-magnet
delta-matched impedance antenna See WYE- loudspeaker, or polarized relay), that reduces the
delta matching transformer In a WYE-MATCHED demagnetizing force 1. A magnetic force whose
IMPEDANCE ANTENNA, the fanned-out (roughly direction reduces the residual induction of a
delta-shaped) portion of the two-wire feeder at its magnetized material. 2. An effect that reduces the
point of connection to the radiator. It matches the magnetism of a permanent magnet, such as high
impedance of the feeder to that of the radiator. temperature or a physical blow.
demand factor In the use of electric power, the ra-
tio of the consumer™s maximum demand to the
Antenna actual power consumed.
demand processing Descriptive of a system that
processes data as it is available, without storing
demarcation strip An interface between a termi-
nal unit and a carrier line.
Dember effect The appearance of a voltage be-
tween regions in a semiconductor when one of
the regions is illuminated.
feed line
demodulation The process of retrieving the infor-
mation (modulation) from a modulated carrier. In
delta-matching transformer
receivers and certain test instruments, this pro-
cess is called DETECTION.
delta modulation The conversion of an analog sig- demodulator 1. A circuit that recovers the infor-
nal into a digital pulse train that can be decoded mation from a modulated analog or digital signal.
to yield the original analog signal. In radio communications, such a device is
delta network See DELTA CONNECTION. usually called a DETECTOR. 2. In computer
delta pulse-code modulation In wire or radio communications, a device that performs
communications, the conversion of an audio sig- ANALOG-TO-DIGITAL CONVERSION of incoming
nal into a digital pulse train. online signals.
178 demand read (write) • depth of discharge

demand read (write) Inputting or outputting data dependent equations Equations that are alike
blocks to or from a central processor, as needed and have an infinite number of solutions. Com-
for processing. pare INDEPENDENT EQUATIONS and INCON-
demodulator probe A diode probe that removes SISTENT EQUATIONS.
the modulation envelope from an applied ampli- dependent linearity Linearity (especially in its de-
tude-modulated signal, and presents the enve- viation from an ideal slope) as a dependent vari-
lope to a voltmeter or oscilloscope. able.
demonstrator A device used to show and teach the dependent variable A changing quantity whose
way in which a component, circuit, or system op- value at any instant is governed by the value at
erates. that instant of another changing quantity (the in-
DeMorgan™s theorem A rule of sequential or digi- dependent variable). Compare INDEPENDENT
tal logic. It states that the negation of (A AND B), VARIABLE.
for any two statements A AND B, is equivalent to depletion-enhancement-mode MOSFET A metal-
NOT A OR NOT B. Also, the negation of (A OR B) oxide-semiconductor field-effect transistor (MOS-
is equivalent, logically, to NOT A AND NOT B. FET) designed for zero gate-bias voltage. An ac
demultiplexer A circuit or device that separates gate signal voltage drives the MOSFET alternately
the components of a multiplexed signal transmit- into the depletion mode (negative signal half-
ted over a channel. cycle) and enhancement mode (positive signal
demultiplexing circuit See DEMULTIPLEXER. half-cycle). Compare DEPLETION-TYPE MOSFET
denary band A band in which the highest fre- and ENHANCEMENT-TYPE MOSFET.
quency is 10 times the lowest frequency. depletion field-effect transistor A field-effect
dendrite 1. The branching (tree-like) structure transistor whose operation is based on the con-
formed by some materials, such as semiconduc- trol of depletion layer width.
tors, as they crystallize. 2. The branching portion depletion layer See BARRIER, 1.
of a nerve cell; hence, the corresponding circuit depletion-layer capacitance See JUNCTION CA-
element in the electronic model of such a cell. PACITANCE.
dendritic growth 1. Dendrite (see DENDRITE, 1). depletion-layer rectification Rectification pro-
2. The process of growing long, flat semiconduc- vided by a semiconductor junction.
tor crystals. depletion-layer transistor A transistor whose ac-
dendron See DENDRITE, 2. tion depends on modulation of current carriers in
dens Abbreviation of DENSITY. a space-charge region (depletion layer).
dense binary code A binary representation sys- depletion mode Operation characteristic of the
tem, in which any possible combination of char- DEPLETION-TYPE MOSFET.
acters is assigned some correspondent. depletion region See BARRIER, 1.
densitometer An instrument for measuring the depletion-type MOSFET A metal-oxide-semicon-
density of a body. ductor field-effect transistor (MOSFET) in which
density 1. Mass per unit volume of a material. 2. the channel directly under the gate electrode is
Concentration of charge carriers or of lines of narrowed by a negative gate voltage (in an n-
flux. 3. The number of items per unit volume, channel device) or by a positive gate voltage (in a
area, distance, or time. p-channel device).
density modulation Modulation of the density, depolarization 1. In a primary cell, the removal of
with respect to time, of electrons in an electron the agents that have caused polarization. 2. The
beam. addition of a polarization-inhibiting substance to
the electrolyte of a primary cell.
depolarizer A substance that retards polarization
Electron beam in an electrochemical cell. An example is the
manganese dioxide used in dry cells.
depolarizing agent See DEPOLARIZER.
deposition The application of a layer of one sub-
stance (usually a metal) to the surface of another
(the substrate), as in evaporation, sputtering,
(Least) (Most) (Least) (Most) (Least)
electroplating, silk-screening, etc.
density modulation
depth indicator 1. A sounding instrument for de-
termining the depth of a body of water. 2. On an
density of electrons The concentration of elec- ACOUSTIC DEPTH FINDER, the meter that indi-
trons (i.e., the number per unit volume, area, dis- cates the depth of water.
tance, or time). depth of cut On a phonograph disk, the depth of
density packing A figure indicating the quantity of the recorded groove.
bits per inch or per centimeter, stored on a mag- depth of discharge Abbreviation, DOD. In a re-
netic tape. chargeable cell or battery, a measure of the extent
depth of discharge • designation

rate of change (derivative) of the controlled
to which discharging has occurred. It is generally
specified as a percentage. For example, if the
derivative control A method of automatic control,
DOD of a 10-ampere-hour (10-AH) battery is 80
actuated according to the number of errors per
percent, then 8 AH have been used up, and 2 AH
remain before recharging will be necessary.
derivative function For a mathematical function
depth of heating In dielectric heating, the depth of
f (x), the function f '(x) = df (x)/dx, over the domain
heat penetration in the sample when both elec-
of f. For any specific point x0 in the domain of f,
trodes are applied to one of its faces.
the value of f '(x0) is equal to the slope of a line
depth of modulation The degree to which a carrier
tangent to f at the point (x0, f (x0)).
wave is modulated.
derived center channel The sum or difference of
depth of penetration The extent to which a skin-
the left and right channels in a stereophonic sys-
effect current penetrates the surface of a conduc-
Dershem electrometer A variation of the quadrant
depth sounder See ACOUSTIC DEPTH FINDER.
electrometer. In the Dershem instrument, the
de-Q 1. To reduce the Q of a component or tuned
needle (to which a small mirror is attached) ro-
circuit. 2. To inhibit laser action during an
tates within slots cut in the quadrant plates and,
interval when an ion population excess is
therefore, can never accidentally touch the
pumped up.
derating To reduce an operating parameter (e.g.,
descending node For a satellite orbiting the earth
current, voltage, power) as another factor (such
or another planet, any point at which the ground-
as temperature) increases, to ensure efficient, re-
track crosses the equator as it moves from the
liable, and safe operation.
northern hemisphere into the southern hemi-
derating curve A graph that shows the extent to
sphere. This node generally changes for each suc-
which a quantity (such as allowable power dissi-
ceeding orbit, because the earth or planet rotates
pation) must be reduced as another quantity
underneath the orbit of the satellite. Compare
(such as temperature) increases.
derating factor The amount by which a current,
descending pass For a specific point on the earth™s
power, or voltage must be decreased to ensure
surface, the time during which an artificial com-
safe and efficient operation of a circuit or device
munications satellite is accessible when its lati-
in a given environment (temperature, altitude,
tude is moving southward. The duration of
humidity, etc.). Also see DERATING and DERAT-
accessibility depends on the altitude of the satel-
lite and on how close its groundtrack comes to
derivative 1. A mathematical expression indicat-
the earth-based point. Compare ASCENDING
ing the rate at which a function changes, with
respect to the independent variable. See
description A data element that is part of a record
DERIVATIVE FUNCTION. 2. The slope of a line
and is used to identify it.
tangent to a curve at a given point. 3. The output
desensitization 1. The process of making a circuit
signal of a DIFFERENTIATOR, relative to the
or device less responsive to small values of a
input signal.
quantity. 2. Also called desensing. In a communi-
derivative action In a control system, an action
cations receiver, an unwanted, often intermittent
producing a corrective signal proportional to the
reduction in front-end gain, caused by an ex-
tremely strong local signal.
desensitize 1. To reduce the sensitivity of a re-
y ceiver. 2. To reduce the gain of an amplifier. 3. To
reduce the small-quantity response of an instru-
dy ment.
dx desiccant A compound, such as cobalt chloride,
used for the purpose of keeping enclosed items
design 1. A unique, planned arrangement of elec-
tronic components in a circuit, in accordance
with good engineering practice, to achieve a de-
dy sired end result. 2. A unique layout of compo-
dx = (Positive) nents or controls, in accordance with good
engineering practice, esthetics, and (often) er-
dx = (Negative) gonomics. 3. Invention. 4. Plan. 5. To produce a
design, as defined in 1, 2, 3, or 4.
designation Within a computer record, coded in-
formation identifying the record so that it can be
handled accordingly.
180 design-center rating • detector blocking

design-center rating A specified parameter that, if destination 1. The point in a system to which a
not exceeded, should provide acceptable average signal of any sort is directed. 2. In communica-
performance for the greatest number of the com- tions, a receiving station.
ponents so rated. destination file A computer file that receives data
design compatibility The degree to which a trans- output during a specific program run.
mitter and receiver are designed for the rejection destination register In a digital computer, a regis-
of unwanted electromagnetic noise. ter into which data is entered.
design engineer An engineer who is skilled in the Destriau effect Light emission resulting from the
creation of new designs and in the comparative action of an alternating electric field on phos-
analysis of designs. phors embedded in a dielectric.
design-maximum rating See MAXIMUM RATING. destructive addition A computer logic operation
design-proof test A performance test made on a in which the sum of two operands appears in
newly completed circuit or device to determine the memory location occupied by one of the
the suitability of the design. operands.
Desk-Fax A facsimile transceiver that can be destructive breakdown A breakdown in which the
placed on a desktop, used for wire or radio trans- effects are irreversible (e.g., permanent damage to
mission and reception of still images. a dielectric by excessive applied voltage).
desk microphone A microphone equipped with a destructive interference Interference resulting
stand that sits on a table or desktop. It allows the from the addition of two waves that have the
operator to use both hands for equipment adjust- same frequency, but opposite phase.
ment, taking notes, etc. destructive read In a computer or calculator, the
desktop computer A personal computer designed condition in which reading the answer erases the
for nonportable use, usually equipped with a data (as from a location) used in the calculation.
built-in hard disk, one or more diskette drives, a destructive test A test that unavoidably destroys
CD-ROM drive, and a fax/modem. It generally the test sample. Compare NONDESTRUCTIVE
uses an external cathode-ray-tube display, TEST.
printer, and keyboard. The power supply is in- DETAB A COBOL-based computer programming
tended for use with 117-volt utility circuits. language permitting the programmer to present
desolder To unsolder joints, usually with a special problems as decision tables.
tool that protects delicate parts and removes detail constant Pertaining to a video signal, the
melted solder by suction. ratio VH/VL, where VH is the amplitude of high-
destaticization A chemical process used to mini- frequency components, and VL is the amplitude of
mize the retention of electrostatic charges by cer- the low-frequency reference component.
tain substances. detected error In a computer system, an error
that is identified, but remains uncorrected until
final output is available.
detection 1. See DEMODULATION. 2. The sensing
of a change in the operating parameters of a cir-
phone line
cuit or system.
detection range In security applications, the ra-
dius within which transducers or sensors can be
expected to reliably operate. This radius varies,
depending on the environment, the sensitivity of
the receiving circuits and transducers, and the
Hard Fax/
strength of the transmitted signal (if any).
disk Modem
detectophone A device for eavesdropping on a
conversation. The device can use a tape recorder
or a tiny radio transmitter.
detector 1. In radio communications, a device or
Microprocessor circuit that extracts the information from a mod-
ulated carrier. Also sometimes called a demodula-
tor. 2. A device that senses a signal or condition
and indicates its presence.
detector balanced bias In a radar system, bias ob-
tained from a controlling circuit and used to re-
Diskette duce or eliminate clutter.
To drive #2
drive #1 detector bias Steady dc voltage applied to a detec-
tor to set its operating point.
detector blocking In a regenerative receiver, a
phenomenon in which a strong signal tends to
desktop computer


. 10
( 42)