18WuD2x

206 DNS • donut pattern
DNS Abbreviation of Doppler navigation system.
doctor To use unconventional (sometimes substandard)
methods in fixing a circuit or device or
in correcting a bad design.
document 1. In digital computer operations, especially
in file maintenance, a form that provides information
pertinent to a transaction. Also see
TRANSACTION. 2. To perform documentation (see
DOCUMENTATION, 2). 3. A computer text file.
documentation 1. Paperwork explaining the scope
of programs and how they can be optimized. 2. Annotating
a computer program at critical points during
its writing (e.g., so that the purpose of various
segments are understood). A measure of good programming,
documentation becomes especially
valuable for program modification or debugging.
document reader An electronic device that reads
printed cards, usually for data entry into a computer.
dog 1. A malfunctioning circuit or device. 2. The
cause of a circuit or device malfunction.
doghouse An enclosure for antenna loading inductors
and other resonating components, placed at
the base of a vertical broadcasting tower.
dog whistle See ULTRASONIC WHISTLE.
Doherty amplifier A highly efficient linear radiofrequency
(RF) amplifier in which a carrier tube and
a peak tube operate jointly, both receiving amplitude-modulated
RF excitation. During unmodulated
intervals, the carrier tube supplies carrier
power to the load, while the peak tube, biased to
cutoff, idles. On positive modulation peaks, the
peak tube supplies output power that combines
with that of the carrier tube, the increase in power
corresponding to the condition of full modulation of
the carrier. On negative modulation peaks, the
peak tube does not supply power, and the output
of the carrier tube is reduced to zero.
Dolby An electronic method of improving the audio
reproduction quality of magnetic-tape systems.
The gain is increased for low-level sounds during
the recording process. During playback, the gain
of the low-level sounds is reduced back to its original
level.
Dolby A A Dolby system with four frequency
ranges, operated independently. It is used mostly
by recording professionals.
Dolby B A modified form of Dolby A, with only one
band of noise-reducing circuitry. It is used primarily
by hobbyists.
Dolezalek electrometer See QUADRANT ELEC-
TROMETER.
dolly 1. A low, wheeled frame or platform for transporting
electronic equipment. 2. A tool with
which one end of a rivet is held while the head is
hammered out of the other end.
DOM Abbreviation of DIGITAL OHMMETER.
domain 1. A region of unidirectional magnetization
in a magnetic material. 2. A region of unidirectional
polarization in a ferroelectric material. 3. A
region in which a variable is confined.
domestic electronics Also called consumer electronics.
The branch of electronics concerned with
appliances, automatic controls, protective devices,
entertainment systems, communications
devices, and other equipment for the home.
domestic induction heater A household cooking
utensil heated by currents induced in it. A primary
coil (connected to the power line) is imbedded
in the utensil, which acts as a short-circuited
secondary coil.
dome tweeter A speaker designed for highfrequency
(treble), high-fidelity audio, and often
functional at frequencies considerably above the
limit of the human hearing. Characterized by a
convex diaphragm. Usually part of an assembly
including a woofer and midrange speaker.
dominant In statistical analysis, the nature of any
quantity that imposes its effects even in the presence
of other quantities.
dominant mode In a waveguide, the propagation
mode exhibiting the lowest cutoff frequency.
dominant wave In a waveguide, the wave having
the lowest cutoff frequency.
dominant wavelength For visible light of a given
hue, the wavelength at which the emitted energy
is the greatest.
donor An electron-rich impurity added to a semiconductor
to make it into an n-type material. So
called because it donates its excess electrons.
Compare ACCEPTOR.
donor atom An atom having an excess electron.
When a substance having such atoms is added to
an intrinsic semiconductor, the extra electron is
donated, making the semiconductor into an n-
type material.
donor impurity A substance whose atoms have
excess electrons, and that donates electrons to
the atomic structure of the semiconductor crystal
to which it is added. Donor elements make semiconductors
into n-type materials. Also see
DONOR ATOM. Compare ACCEPTOR IMPURITY.
do-nothing instruction A computer program instruction
that causes no action to be taken. Can be
used to provide space for future program updating,
or to fill out a block of instructions, as needed by a
compiler. Also called dummy instruction.
don’t-care state In a logic function or gate, an input
digit whose state (high or low) does not affect
the output.
donut capacitor A flat, ring-shaped capacitor.
donut coil See TOROIDAL COIL.
donut crystal A relatively large, zero-temperaturecoefficient
piezoelectric quartz crystal cut in the
form of a torus with the y-axis passing through
the center of rotation.
donut magnet See RING MAGNET.
donut pattern The three-dimensional radiofrequency
(RF) radiation/response pattern of a
free-space straight antenna element measuring
1 ⁄2 wavelength, neglecting the effects of ground
and nearby objects.