18WuD2x

double-coil direction finder A radio direction
finder (RDF) using an antenna that consists of
two identical, perpendicular coils. The directivity
of the antenna is the resultant of the directivity of
the individual coils.
double conversion 1. Two complete frequency
conversions in a superheterodyne system. For example,
the incoming signal might be converted to
a 9-MHz first intermediate frequency (first IF); at
a later stage, this signal might be converted to a
455-kHz second IF. The high first IF widely sepadouble-button
microphone • double-extended Zepp antenna 209
double-button microphone A carbon microphone
having two buttons mounted on each side of the
center of a stretched diaphragm, and connected
in push-pull. Also see BUTTON MICROPHONE.
double-channel duplex Two-way communication
over two independent channels. One station
transmits on one channel, and the other station
transmits on the other channel. The result is conversation-mode
communications, in which one
operator can interrupt the other at any time; both
receivers are always operational.
double-channel simplex A system of communication
in which two channels are used. One station
transmits on one channel, and the other station
transmits on the other channel. Interruption is
not possible because whenever either operator
transmits, the station receiver is muted.
double-checkerboard pattern In a magnetic core
memory, the maximum noise that appears when
half of the half-selected cores are in the one state
and the others are in the zero state. Also called
worst-case noise pattern.
double circuit tuning A circuit whose output and
input are tuned separately. Such tuning provides
increased selectivity when the input and output
are resonant at the same frequency, and decreased
selectivity when they are tuned to different frequencies.
Also see DOUBLE-TUNED AMPLIFIER.
double clocking A phenomenon that occurs in
some digital circuits when the input pulse is
nonuniform, and appears as two pulses to the device.
The device is thus actuated at twice the desired
frequency.
In
1st
mix.
1st
IF
Amp.
2nd
mix.
2nd
IF
Out
rates the signal from the image; the low second IF
allows superior selectivity to be achieved at a reasonable
cost. Also called dual conversion. 2. Pertaining
to a superheterodyne receiver with two
intermediate frequencies.
double-conversion receiver Also called doubleconversion
superheterodyne. A superheterodyne
receiver using DOUBLE CONVERSION to achieve
optimum selectivity and image rejection.
double-current generator 1. A dynamo-type generator
supplying both alternating current (ac) and direct
current (dc) from one armature winding. 2. A
rotary converter operating on dc and delivering ac.
double-diamond antenna A broadband antenna
consisting of two rhomboid plates, one attached
to each side of the feeder.
double-diffused epitaxial mesa transistor A transistor
in which a thin mesa crystal is overlaid on
another mesa crystal. Also called epitaxial-growth
mesa transistor.
double-diffused transistor See DIFFUSED-
EMITTER-AND-BASE TRANSISTOR.
double diode See DUODIODE.
double-diode limiter A limiter in which two diodes
are connected back to back in parallel, to limit
both peaks of an alternating-current (ac) signal.
double-doped transistor See GROWN-JUNCTION
TRANSISTOR.
double edit In audio tape recording, to make two
changes in a given span of the tape. For example,
a producer might dislike the wording of a certain
sentence, and re-record the sentence. Then,
changing his or her mind, the producer might
record the original sentence back over the rerecorded
sentence. These changes increase the
risk of audible irregularities appearing in the final
recording.
double emitter follower See COMPOUND CON-
NECTION.
double-ended amplifier See PUSH-PULL AMPLI-
FIER and DOUBLE-ENDED CIRCUIT.
double-ended circuit A symmetrical circuit (i.e.,
one having identical halves, each operating on a
half-cycle of the input signal). Example: a pushpull
amplifier.
double-extended Zepp antenna A horizontal,
collinear, center-fed antenna, in which each section
measures 0.65 wavelength. This antenna
gives increased gain over that of the Zepp and
double Zepp (see DOUBLE ZEPP ANTENNA).
0.65λ/2
Radiator
0.65λ/2
Osc.
Osc.
Feeder
double conversion
double-extended Zepp antenna