18WuD2x

delay timer • demodulator 177
delay timer 1. A timer that starts or stops an operation
after a prescribed length of time. 2. A delay
relay or switch.
delay unit In a radar system, a circuit for delaying
pulses.
delete 1. To erase or blank out a signal. 2. The
elimination from a computer file of a record or
record group. 3. To remove a computer program
from memory or storage.
deletion record In the master file of a digital computer,
a new record that causes existing ones to
be deleted.
delimiter In digital computer operations, a character
limiting a sequence of characters of which it is
not itself a member.
Dellinger effect The sudden disappearance of a
radio signal as a result of an abrupt increase in
atmospheric ionization caused by a solar eruption.
deliquescent material A material that absorbs
enough moisture from the air to get wet. For example;
calcium chloride, a deliquescent material,
is often used to keep electronic equipment dry.
Compare HYGROSCOPIC MATERIAL.
delta circuit A three-phase electrical circuit with
no common ground.
delta connection A triangular connection of coils
or load devices in a three-phase system, so called
from its resemblance to the Greek letter delta.
Compare WYE-CONNECTION.
delta-matched antenna See WYE-MATCHED IM-
PEDANCE ANTENNA.
delta-matched impedance antenna See WYE-
MATCHED IMPEDANCE ANTENNA.
delta matching transformer In a WYE-MATCHED
IMPEDANCE ANTENNA, the fanned-out (roughly
delta-shaped) portion of the two-wire feeder at its
point of connection to the radiator. It matches the
impedance of the feeder to that of the radiator.
Antenna
radiator
Matching
transformer
Parallel-wire
feed line
delta-matching transformer
delta modulation The conversion of an analog signal
into a digital pulse train that can be decoded
to yield the original analog signal.
delta network See DELTA CONNECTION.
delta pulse-code modulation In wire or radio
communications, the conversion of an audio signal
into a digital pulse train.
delta quantity An increment (i.e., the difference
between two values of a variable).
delta rays The emission of secondary electrons as
a result of radioactivity.
delta-sigma modulation A method of analog-todigital
conversion. The output is a pulse density
function of the input. The input can be obtained
by low-pass filtering of the output.
delta tune Also called receiver incremental tuning
(RIT). In high-frequency (HF) communications
transceivers, a control that allows the receiver
frequency to be adjusted up to several kilohertz
higher or lower than the transmitter frequency.
delta waves Brain waves having a frequency less
than 9 Hz. Also see ELECTROENCEPHALO-
GRAPH and ELECTROENCEPHALOGRAM.
Deluc’s pile See DRY PILE.
dem Abbreviation of DEMODULATOR.
demagnetization curve The portion of a magnetic
hysteresis curve, showing reduction of demagnetization.
demagnetization effect The phenomenon in
which uncompensated magnetic poles at the surface
cause a reduction of the magnetic field inside
a sample of a material.
demagnetize To remove magnetism from an object,
either temporarily or permanently.
demagnetizer See DEGAUSSER.
demagnetizing current The half-cycle of an alternating
current (or polarity of a direct current)
flowing through a coil wound on a permanent
magnet (as in a headphone, permanent-magnet
loudspeaker, or polarized relay), that reduces the
magnetic field.
demagnetizing force 1. A magnetic force whose
direction reduces the residual induction of a
magnetized material. 2. An effect that reduces the
magnetism of a permanent magnet, such as high
temperature or a physical blow.
demand factor In the use of electric power, the ratio
of the consumer’s maximum demand to the
actual power consumed.
demand processing Descriptive of a system that
processes data as it is available, without storing
it.
demarcation strip An interface between a terminal
unit and a carrier line.
Dember effect The appearance of a voltage between
regions in a semiconductor when one of
the regions is illuminated.
demodulation The process of retrieving the information
(modulation) from a modulated carrier. In
receivers and certain test instruments, this process
is called DETECTION.
demodulator 1. A circuit that recovers the information
from a modulated analog or digital signal.
In radio communications, such a device is
usually called a DETECTOR. 2. In computer
communications, a device that performs
ANALOG-TO-DIGITAL CONVERSION of incoming
online signals.