DAMPED WAVE - A sinusoidal wave in which the amplitude steadily decreases with time.
Often associated with energy loss .
DAMPING - (1) The process of smoothing out oscillations. (2) In a meter, this process
is used to keep the pointer of the meter from overshooting the correct reading . (3) A
mechanical or electrical technique used in synchro receivers to prevent the rotor from
oscillating or spinning. Damping is also used in servosystems to minimize overshoot of the
load .
D'ARSONVAL METER MOVEMENT - The permanent-magnet moving-coil movement used in most
meters .
DATA - Facts represented by numbers, letters, or symbols to which meaning is or can be
assigned.
DATA BASE - A structured collection of data that can be extracted, organized, and
manipulated by a program.
DATA COMMUNICATIONS - The means by which data is transmitted electronically from one
location to another over a communications channel.
DATA ELEMENT - One item of information; the smallest unit of data that can be
referenced.
DATA FLOWCHART - See flowchart.
DATA PROCESSING - The execution of a systematic sequence of operations performed upon
data. Synonymous with information processing .
DATA, REFERENCE - The source document identification.
DATA REPRESENTATION - The symbols and codes used by computers to represent letters,
numbers, and special characters
DATA TRANSMISSION - The transfer of information from one place to another or from one
part of a system to another .
dBm - An abbreviation used to represent power levels above or below a 1-milliwatt
reference .
DEAD SHORT - A short circuit having minimum resistance .
DEBUGGING - The process of finding errors (bugs) in a program or system and correcting
them so that the program or system runs correctly.
DECIMAL - Pertaining to the number representation system with a radix of ten .
DECIMAL DIGIT - In decimal notation, one of the characters 0 through 9 .
DECIMAL NOTATION - A fixed radix notation where the radix is ten .
DECIMAL NUMERAL - A decimal representation of a number .
DECIMAL POINT - The radix point in decimal representation .
DECOUPLING CAPACITOR - A capacitor used to transfer unwanted signals out of a circuit;
for example, coupling an unwanted signal to ground. Also called a BYPASS CAPACITOR .
DEFECT - (1) An imperfection in the tape leading to a variation in output or a dropout.
(2) The most common defects are surface projections of oxide agglomerates, embedded
foreign matter, and redeposited wear products.
DEFLECTION COILS - In a cathode-ray tube, coils used to bend an electron beam a desired
amount .
DEFLECTION PLATES - Two pairs of parallel electrodes, one pair set forward of the other
and at right angles to each other, parallel to the axis of the electron stream within an
electrostatic cathode-ray tube .
DEGAUSSER - See bulk eraser.
DEGENERATION - The process whereby a part of the output signal of an amplifying device
is returned to its input circuit in such a manner that it tends to cancel part of the
input .
DEGENERATIVE FEEDBACK - Feedback in which the feedback signal is out of phase with the
input signal; also called NEGATIVE FEEDBACK .
DEGREE-OF-FREEDOM - The number of axes about which a gyro is free to precess .
DEIONIZATION POTENTIAL - The potential at which ionization of the gas within a
gas-filled tube ceases and conduction stops; also referred to as extinction potential .
DEIONIZATION TIME - In a spark gap, the time required for ionized gas to return to its
neutral state after the spark is removed .
DELAY MODULATION - (See modified frequency modulation.)
DELTA - A three-phase connection in which windings are connected end-to-end, forming a
closed loop that resembles the Greek letter delta. A separate phase wire is then connected
to each of the three junctions .
DEMODULATION - The removal of intelligence from a transmission medium .
DEMODULATOR - A circuit used in servosystems to convert an ac signal to a dc signal.
The magnitude of the dc output is determined by the magnitude of the ac input signal, and
its polarity is determined by whether the ac input signal is in or out of phase with the
ac reference voltage .
DeMORGAN'S THEOREM - A theorem which states that the inversion of a series of AND
applications is equal to the same series of inverted OR applications, or the inversion of
a series of OR applications is equal to the same series of inverted AND applications. In
symbols, AB = A + B or A + B = A · B .
DENSITY - (1) The compactness of a substance. (2) Mass per unit volume .
DEPLETION REGION - The region in a semiconductor where essentially all free electrons
and holes have been swept out by the electrostatic field which exists there .
DEPOT-LEVEL MAINTENANCE (SM&R CODE D) - Supports SM&R Code I and SM&R Code
O activities through extensive shop facilities and equipment and highly skilled personnel
.
DESIGNATION - Operational phase of a fire-control or track radar during which the radar
is directed to the general direction of a desired target .
DETECTION - The separation of low-frequency (audio) intelligence from the
high-frequency carrier .
DETECTOR - A mixer or converter in a superheterodyne receiver .
DICE - Uncased chips .
DIE BONDING - Process of mounting a chip to a package .
DIELECTRIC - An insulator; a term applied to the insulating material between the plates
of a capacitor .
DIELECTRIC CONSTANT - The ratio of a given dielectric to the dielectric value of air .
DIELECTRIC FIELD - The space between and around charged bodies in which their influence
is felt. Also called ELECTRIC FIELD OF FORCE or an ELECTROSTATIC FIELD .
DIELECTRIC HEATING - The heating of an insulating material by a high-frequency electric
field .
DIELECTRIC HYSTERESIS LOSS - Power loss of a capacitor because of the changes in
orientation of electron orbits in the dielectric; the changes in orientation are caused by
rapid reversal in polarity of line voltage. The higher the frequency, the greater the loss
.
DIELECTRIC LEAKAGE - Power loss of a capacitor because of the leakage of current
through the dielectric. Also relates to leakage resistance; the higher the leakage
resistance, the lower the dielectric leakage .
DIELECTRIC LOSSES - The losses resulting from the heating effect on the dielectric
material between conductors .
DIELECTRIC STRENGTH - The ability of an insulator to withstand a potential difference
without breaking down (usually expressed in terms of voltage) .
DIFFERENCE FREQUENCY - See BEAT FREQUENCY .
DIFFERENCE OF POTENTIAL - A voltage between two points .
DIFFERENTIAL AMPLIFIER - A circuit that amplifies the difference between two input
signals .
DIFFERENTIAL VOLTMETER - A precision voltmeter that measures an unknown voltage by
comparing it to a precision internal-reference voltage supply.
DIFFRACTION - The bending of waves (as light or rf) when the waves are met with some
form of obstruction .
DIFFUSION - (1) The scattering of reflected light waves from an object, such as white
paper . (2) Controlled application of impurity atoms to a semiconductor substrate .
DIGIT - A symbol that represents one of the nonnegative integers smaller than the
radix. For example, in decimal notation a digit is one of the characters from 0 through 9
.
DIGITAL COMPUTER - (1) A computer in which discrete representation of data is used. (2)
A computer that operates on discrete data by performing arithmetic and logic processes on
these data .
DIGITAL RECORDING - (1) A method of recording in which the information is first coded
in a digital form. (2) Usually, a binary code is used, with recording taking place in two
discrete values/polarities of residual flux.
DIODE - An electron tube containing two electrodes: a cathode and a plate . (2) A two
element, solid-state device made of either germanium or silicon; it is primarily used as a
switching device .
DIODE DETECTOR - A demodulator that uses one or more diodes to provide a rectified
output with an average value that is proportional to the original modulation .
DIPOLE - A common type of half-wave antenna made from a straight piece of wire cut in
half. Each half operates at a quarter wavelength of the output .
DIRECT ACCESS - A storage method that allows the computer to locate and read a
particular record without having to search through an entire file. The computer is able to
access data independent of its location. Magnetic disks, diskettes, and drums are
considered direct access devices.
DIRECT CURRENT - An electric current that flows in one direction only .
DIRECT RECORDING - An analog recording that records and reproduces data in the
electrical form of its source.
DIRECTIONAL ANTENNA - An antenna that radiates most effectively in only one direction .
DIRECTIONAL COUPLER - A device that samples the energy traveling in a waveguide in one
direction only .
DIRECTIVITY - The ability of an antenna to radiate or receive more energy in some
directions than in others. The degree of sharpness of the antenna beam .
DIRECTLY HEATED CATHODE - A wire, or filament, designed to emit the electrons that flow
from cathode to plate. The filament is designed so that a current is passed through it;
the current heats the filament to the point where electrons are emitted .
DIRECTOR - The parasitic element of an array that reinforces energy coming from the
driver element .
DIRECT SHORT - Same as SHORT CIRCUIT .
DISCRETE COMPONENTS - Individual transistors, diodes, resistors, capacitors, and
inductors .
DISCRIMINATOR - A circuit in which amplitude variations are derived in response to
phase or frequency variations .
DISK - (1) A disk-drive storage device on which information is magnetically recorded
and retrieved. (2) Can be either hard (rigid) or floppy (flexible).
DISK DRIVE - A direct-access storage device for recording and retrieving data on hard
(rigid) disk or floppy disks (diskettes).
DISK PACK - A mass storage device in which information is stored on one or both sides
of a rigid disk that can be magnetized. The disk is rotated by a disk drive and
information is stored and retrieved by one or more magnetically sensitive read/write
heads.
DISKETTE - A mass storage device in which information is stored on one or both sides of
a flexible disk that can be magnetized. The diskette is rotated by a diskette drive and
information is stored and retrieved by one or more magnetically sensitive read/write
heads. Diskettes are also called floppy disks because the disk bends easily.
DISPERSION - The refraction of light waves that causes the different frequencies to
bend at slightly different angles .
DISPLACEMENT CURRENT - The current that appears to flow through a capacitor .
DISTILLED WATER - Water that has been purified through a process of evaporation and
condensation .
DISTORTION - Any unwanted change between an input signal and output signal .
DISTRIBUTED CONSTANTS - The constants of inductance, capacitance, and resistance in a
transmission line. They are spread along the entire length of the line and cannot be
distinguished separately .
DISTRIBUTIVE LAW - In Boolean algebra the law which states that if a group of terms
connected by like operators contains the same variable, the variable may be removed from
the terms and associated with them by the appropriate sign of operation (for example, A(B
+ C) = AB + AC) .
DOMAIN THEORY - A theory of magnetism based upon the electron-spin principle. Spinning
electrons have a magnetic field. If more electrons spin in one direction than another, the
atom is magnetized .
DOMINANT MODE - The easiest mode to produce in a waveguide, and the most efficient mode
in terms of energy transfer .
DONOR - An impurity that can make a semiconductor material an N-type by donating extra
"free" electrons to the conduction band .
DONOR IMPURITY - See PENTAVALENT IMPURITY .
DOORKNOB TUBE - An electron tube that is similar to the acorn tube but larger. The
doorknob tube is designed to operate, at high power, in the uhf frequencies .
DOPING - The process of adding impurities to semiconductor crystals to increase the
number of free charges that can be moved by an external, applied voltage. Doping produces
N-type or P-type material .
DOPPLER EFFECT - (1) The apparent change in frequency or pitch when a sound source
moves either toward or away from a listener . (2) In radar, the change in frequency of a
received signal caused by the relative motion between the radar and the target .
DOPPLER FREQUENCY - The difference between transmitted and reflected frequencies;
caused by the Doppler effect .
DOUBLE-MODING - In a transmitter output tube, the abrupt and random change from one
frequency to another .
DOUBLE NEGATIVE LAW - In Boolean algebra, the law which states that the complement of a
complement is the equivalent of the original term .
DOUBLE RECEIVER - A fine and coarse synchro receiver enclosed in a common housing with
a two-shaft output (one shaft inside the other) .
DOUBLET - Another name for the dipole antenna .
DOUBLING UP - This is a type of two-equipment installation where one unit can be
substituted for another in the event of failure .
DOWN LINK - The frequency used to transmit an amplified signal from a satellite or
other craft back to earth .
DOWNTIME - The length of time the computer is not operating, either because of
preventive maintenance (scheduled downtime) or a malfunction (nonscheduled downtime).
DRAG - The fractional tension differential across the contact area caused when the tape
contacts some element in the tape path (such as the head, tape guides, tape bearings, or
column walls).
DRIFT SPACE - In an electron, a region free of external fields in which relative
electron position depends on velocity .
DRIVEN ARRAY - An array in which all of the elements are driven .
DRIVEN ELEMENT - The element of an antenna connected directly to the transmission fine
.
DRIVER - The final stage of amplification .
DROPOUT - (1) A temporary reduction in the output of a magnetic tape of more than a
certain predetermined amount. (2) Expressed in terms of the percentage reduction or
decibel loss.
DROPOUT COUNT - The number of dropouts detected in a given length of magnetic tape.
DRUM-TYPE ARMATURE - An efficient, popular type of armature designed so that the entire
length of the winding is cutting the field at all times. Most wound armatures are of this
type .
DRY-AIR SYSTEM - Provides dehumidified air for electronic equipment that is moisture
critical .
DRY CELL - An electrical cell in which the electrolyte is not a liquid. In most dry
cells the electrolyte is in the form of a paste .
DUAL-GATE MOSFET - A two-gate MOSFET in which either gate can control the conductor
independently, a fact which makes this MOSFET very versatile .
DUAL IN-LINE PACKAGE (DIP) - IC package having two parallel rows of preformed leads .
DUCTILE - Easily drawn out (as to form filaments or wires) .
DUCTING - Trapping of an rf wave between two layers of the earth's atmosphere or
between an atmospheric layer and the earth .
DUMMY ANTENNA - See DUMMY LOAD .
DUMMY LOAD - A dissipative but nonradiating device that has the impedance
characteristics of an antenna or transmission line. Also called ARTIFICIAL LOAD .
DUPLEXER - A radar device that switches the antenna from the transmitter to the
receiver and vice versa .
DURABILITY - The number of passes that can be made before a significant degradation of
output occurs, divided by the corresponding number that can be made using a reference
tape.
DUTY CYCLE - In a transmitter, ratio of time on to time off .
DYNAMIC - (See tape skew.)
DYNAMIC MICROPHONE - A device in which sound waves move a coil of fine wire that is
mounted on the back of a diaphragm and located in the magnetic field of a permanent magnet
.
DYNAMIC RANGE - (1) The bandwidth within which a satisfactory signal-to-noise ratio is
obtained. (2) See also resolution.
DYNAMIC SKEW - The change in skew caused by tape motion.
DYNAMIC TAPE SKEW - (See tapDECADE RESISTOR (DECADE RESISTANCE BOX) - It typically has
two or more sections, each containing 10 precision resistors wired to selector switches. A
piece of test equipment that provides a ready source of various resistances for
engineering and measurement applications.
