Amplifier-Modulator AM 3507/PRC-47 (A8A2)

TM 11-5820-509-35

Figure 2-7. Receiver Amplifier, AGC Circuit, and Sidetone Gate, Schematic Diagram.

and off in parts by the symetrically-fed transmit 500-kHz

2-10. Amplifier-Modulator AM 3507/PRC-47 (A8A2)

standard signal. The output, therefore, consists of a

{fig. 2-8 through 2-10)

alternate positive and negative 500kHz pulses that

constitute the double-sideband, suppressed carrier

a. During transmit periods, vox relay A1 K1 is

signal.

This double sideband is routed through

operated and 500-kHz relay K4 (on the main chassis) is

transformer T2 to alc amplifier Q1. The gain of alc

also energized. The transmit 500-kHz standard signal

amplifier Q1 is controlled by the +alc and-alc bias

from radio frequency oscillator A6 is routed through K4

voltages that are returned to it from the power amplifier

to the balanced modulator where it is mixed with the

and this assures that the sideband power level at the

transmit audio output of amplifier A1Q4. The output of

transmitter output is maintained within the capabilities of

balanced modulator CR1 through CR4 is a series of

the power amplifier tube. alc amplifier Q1 is connected

pulses whose polarity and repetition rate are determined

in a common-base configuration and operates normally

by the phase and frequency of the 500-kHz standard

with only self bias. The +alc bias is a-100-volt dc

signal and whose amplitude is proportional to the

reference voltage that is applied to the emitter circuit of

instantaneous amplitude of the audio input signal. In

Q1. The-alc bias is applied to the base of Q1 and is

terms of frequency analysis, the balanced modulator

also-110 volts dc except when the power amplifier stage

output contains both upper- and lower-sideband signals

draws grid current (class AB2).When this occurs, the -

displaced from the 500-kHz intermediate frequency by

alc bias becomes more negative and the circuit

the instantaneous audio modulation frequency. The

gain of Q1 is reduced causing a corresponding reduction

balanced modulator has the familiar diode ring

in the power amplifier driving signal.

configuration and provides a push-pull output. The

diodes of the ring are alternately switched on

2-18