Electrical Equipment Chassis CH-474/PRC-47 (A8A4)

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

oscillator.

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