18WuD2x

diversity reception • DNL 205
diversity reception Also called dual-diversity reception.
A method of minimizing the effects of fading
in ionospheric communication at high
frequencies (HF). Accomplished using two receivers
whose antennas are 5 to 10 wavelengths
apart. Each receiver, tuned to the same signal,
feeds a common audio amplifier. The timing of
the fading is different at the two antennas because
of phasing effects. The composite signal,
therefore, fades less than either of the component
signals. Some diversity systems use three or more
antennas and receivers to reduce the effects of
fading even further; this is sometimes called
multiple-diversity reception.
RF
stages
Mixer and
local
oscillator
IF
stages
Second
detector
5 to 10
wavelengths
Audio
amplifier
Output
diversity reception
Second
detector
RF
stages
Mixer and
local
oscillator
IF
stages
diversity transmission Also called dual-diversity
transmission or multiple-diversity transmission. A
scheme similar to DIVERSITY RECEPTION, except
applied at the transmitting end of a communication
circuit. The signals from two or more
transmitters, at identical frequencies, are fed to
antennas spaced several wavelengths apart.
diverter-pole generator A well-regulated directcurrent
(dc) generator, whose shunt winding is on
the main field pole, the series winding being on a
diverter pole whose flux opposes that of the main
pole.
divide-by-seven circuit A three-stage binary circuit
having feedback from stage three to stage
one. Stage three is switched on by the fourth input
pulse; at that time, the feedback pulse
switches on stage one, simulating one input
pulse and reducing the usual counting capacity
from eight to seven.
divide-by-two circuit A circuit that delivers one
output pulse for each two successive input pulses
(i.e., a flip-flop).
Input
4 7 7
C
5 5
divide-by-seven circuit
divided-carrier modulation Modulation obtained
by adding two identical frequency carriers that
are 90 degrees out of phase.
divided circuit A parallel circuit.
divided equipment A system of modular electronic
components interconnected with cables. A
simple example is a radio receiver having an external
power supply and external loudspeaker.
divider 1. See VOLTAGE DIVIDER. 2. See FRE-
QUENCY DIVIDER. 3. See PULSE-COUNT DI-
VIDER. 4. A computing circuit or device for
performing mathematical division.
divider probe A test probe that divides an applied
signal voltage by some factor (such as 2, 5, or 10)
to place it within the range of the instrument with
which the probe is used.
dividing network See CROSSOVER NETWORK.
division 1. Separating a quantity into a number of
equal parts, as indicated by the divisor. 2. Voltage
division (see VOLTAGE DIVIDER). 3. Frequency
division (see FREQUENCY DIVIDER). 4.
Pulse-count division (see PULSE-COUNT DI-
VIDER).
division of vectors 1. The quotient of two rectangular
vectors determined by the principle of rationalization
in algebra (i.e., by multiplying the
numerator and denominator of the indicated division
by the conjugate of the denominator, simplifying,
and performing the division). 2. To find the
quotient of two polar vectors: the quotient of their
moduli and the difference of their arguments.
dj Abbreviation of diffused junction.
DKT Abbreviation of dipotassium tartrate.
D layer A layer of the ionosphere that is below the
E layer; its altitude is approximately 60 kilometers.
dm Abbreviation of decimeter.
DMA Abbreviation of DIRECT MEMORY ACCESS
and direct memory addressing.
DME Abbreviation of DISTANCE-MEASURING
EQUIPMENT.
DMM Abbreviation of DIGITAL MULTIMETER.
DMOS Abbreviation for double-diffused metal-oxide
semiconductor, a type of field-effect transistor
that exhibits extremely low capacitance and low
source-drain resistance when conducting.
DNL See DIFFERENTIAL NONLINEARITY.
R
6
7
Output