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TM 1 1-5820-509-35
is again turned off so that the discriminator may again
envelope at the collector of these transistors is similar to
assume control of the error-correction circuits of the hf
the center waveforms in figure 2-15.  {It should be
recalled that the waveforms can be reversed depending
upon whether the upper channel leads the lower
channel, or vice versa.} The integrator circuit at the
2-15. Electrical Equipment Chassis CH-474/PRC-47
output of Q11 (C93-R104) and at Q13 (C92-R103)
(A8A4) (fig. 7-8)
change the output waveshape into dc levels known as
error voltage A and error voltage B respectively. (The
a. When a dc power source is connected to the
mnemonic used has no real significance except to
receiver-transmitter, and dc power control relay K1 is
differentiate between the respective channels and their
operated, +26.5 volts dc is applied to capacitor C1 and
outputs.) In the phase control mode, the envelope
diodes CR1 and CR2 of the power oscillator circuit. As
frequency will approach zero and the bistable switching
the push-to-talk relay (A5K1) is energized, the +26.5
of transistors Q10 and Q13 will stop. The error voltages
volts dc is routed through its contacts and the primary
at the output of the discriminator will be equal to the dc
winding of high-voltage transformer A5T1 to the emitter
envelope values, and will vary as the phase-difference
circuits of Q1 and Q2. Any difference in the operating
between the two channels varies.  The phase control
characteristics of these two transistors will cause a slight
mode continues until the phase-difference between the
potential difference to exist between their emitters. This
hf oscillator and the reference oscillator is constant. At
difference is coupled to their respective base circuits by
this time, the phase-difference is equal to the fixed
the windings of saturable reactor T1, and causes one
phase-shift introduced by network C21-R34 at the input
transistor to conduct more heavily than the other. For
to transistor Q8, and the voltages at the error A and
example, suppose that the emitter of Q2 is initially a
error B outputs are approximately 1.5 volts dc as
little more positive than the emitter of Q1. This voltage
indicated in the lower waveform of figure 2-15. (The
is coupled through reactor T1, and causes the base of
waveforms used to illustrate the operation of the
Q2 to become more positive and its conduction is
discriminator circuits are not continuously available for
reduced. At the same time, the transformer-action of T1
measurement at signal test points, but are only present
places a slightly less positive charge on the base of Q1
during brief intervals immediately following a channel
and the conduction of this transistor is increased. The
selection.)
regenerative action continues until the core of reactor
f. A portion of the signal applied to the base of
T1 is saturated, and then the flux-change ceases. At
transistor amplifier Q27 is developed across emitter
this point, the bias is removed from the base of each
resistor R142. This signal is rectified by voltage-doubler
transistor, the magnetic flux in the core collapses, and
CR12-CR13 in the automatic capture circuit and is
the regenerative cycle begins in the reverse direction.
applied to the base of dc amplifier Q28. The resulting
The period required for a complete cycle is dependent
positive voltage causes conduction of Q28 whose output
upon the core properties of the reactor and the dynamic
clamps the base of transistor switch Q29 at a positive
characteristics of the two transistors. The squarewave
level just below that required for its conduction. If no
generated in the primary winding of high-voltage
signal is present at the emitter of Q27, dc amplifier Q28
transformer A5T1 is approximately 400-Hz. Diodes CR1
is turned off and the positive voltage at the base of
and CR2 limit the voltage swing of each emitter land
transistor switch Q29 rises causing this transistor to
hence the peak voltage applied to the primary winding
conduct.  The ground supplied through the collector-
of A5T1) to about 26.5 volts peak.
emitter junction of Q29 is applied to antilock relay K6 on
b. During the transmit cycle, the rf output of driver
the main chassis of the receiver-transmitter and this
A3V3 is applied to the grid circuit of power amplifier V
relay is operated. As K6 contacts close, a voltage of
101 This single-sideband signal is amplified by V101
approximately 1 0 volts dc is applied to the error A and
and routed through the power amplifier LOAD-TUNE
the error B inputs to the varicap control circuit in signal
circuit and the t/r relay to the connected load. The grid
data translator A3. Since this fixed voltage condition is
bias for the power amplifier is derived from the-110-volt
also the calibrating condition for the hf oscillator, the
dc output of bias rectifier CR1 through CR4 in power
output error is reduced and capture is once again
supply A5. The level of the rf input signal at the power
obtained. After capture, a voltage-drop again appears
amplifier grid circuit is controlled so that maximum drive
across the emitter resistor (Rl42) of Q27 and transistor
can be used without introducing
Q29
2-31


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