18WuD2x

212 double Zepp antenna • dress
Also called two half waves in phase. Its name was
derived because it is, in fact, two Zepp antennas
forming a collinear array.
doubling 1. Producing the second harmonic of a
signal. 2. In communication, unintentional simultaneous
transmission by both operators, resulting
in missed information. 3. In a speaker,
distortion resulting in large amounts of secondharmonic
output.
doubly balanced modulator See BALANCED
MODULATOR.
doughnut capacitor See DONUT CAPACITOR.
doughnut coil See TOROIDAL COIL.
doughnut crystal See DONUT CRYSTAL.
doughnut magnet See RING MAGNET.
down convert In superheterodyne conversion, to
heterodyne a signal to an intermediate frequency
lower than the signal frequency. Compare UP
CONVERT.
down lead See LEAD-IN.
downlink The signal sent down from an active
communications satellite to the earth, usually on
a different frequency than the signal sent up. See
UPLINK.
downlink beamwidth The angle subtended between
the half-power points of the downlink signal
from an active communications satellite.
downlink frequency The frequency of the downlink
signal from an active communications satellite.
Usually, the downlink signals occupy a
certain band of frequencies, anywhere from several
kilohertz to several megahertz wide.
downlink power 1. The output power of the downlink
transmitter in an active communications
satellite. 2. The effective radiated power (ERP) of
the downlink signal from an active communications
satellite.
down time A period of time during which electronic
equipment is completely inoperative (for
any reason).
downturn A usually sudden dip in a performance
curve. Compare UPTURN.
downward modulation Modulation in which the
average carrier component decreases during
modulation. Example: amplitude modulation of a
transmitter in which the antenna current decreases
during modulation. Compare UPWARD
MODULATION.
DP Abbreviation of DATA PROCESSING.
DPDT Abbreviation of double-pole, double-throw
(switch or relay).
DPM 1. Abbreviation of digital power meter. 2. Abbreviation
of DIGITAL PANEL METER. 3. Abbreviation
of disintegrations per minute.
DPS Abbreviaton of disintegrations per second.
DPST Abbreviation of double-pole, single-throw
(switch or relay).
dr Abbreviation of dram.
drag 1. A retarding force, caused by friction, acting
on a moving body in contact with another moving
or stationary body or medium. 2. A retarding
force introduced by an applied magnetic or electric
field.
drag angle In disk recording, an angle of less than
90° between the stylus and the disk. The acute
angle causes the stylus to drag instead of digging
in.
drag cup
A cup of nonmagnetic metal (usually copper
or aluminum) that, when rotated in a magnetic
field, acquires a voltage proportional to the
speed of rotation. The device is often used as a
brake.
drag-cup motor A servomotor whose shaft has a
copper or aluminum drag cup that rotates in the
field of a two-phase stator. Eddy currents set up
in the cup by the field winding produce torque;
braking action, direction control, and speed control
are obtainable by means of associated electronics.
drag magnet In a motor-type meter, a braking
magnet (i.e., one used to reduce speed through
eddy-current effects). Also called retarding magnet.
drain
1. The current or power drawn from a signal
or power source. 2. A load that absorbs current
or power. 3. The electrode in a field-effect transistor
(FET) from which the output is usually taken;
equivalent to the collector of a bipolar transistor.
drainage equipment Devices and systems for protecting
circuits against transients generated by
circuit breakers and similar safety devices.
drain-coupled multivibrator An oscillator that
uses two field-effect transistors (FETs) in the circuit
equivalent of a collector-coupled bipolartransistor
multivibrator. The drain of one stage is
capacitance-coupled to the gate of the other
stage.
R1
C1
Q1
R2
+ dc
R3
C2
R4
Q2
drain-coupled multivibrator
C3
Out
D-region A low region of the ionosphere beneath
the E-region, whose ionization varies with the inclination
of the sun. The greatest ionization is at
midday; the layer disappears at night.
dress The (usually experimental) arrangement of
leads for optimum circuit operation (minimum