General Description

TM 11-5820-509-35

26.5-volt dc source is desired, Storage Battery BB-

operation is desired, Telegraph Key J-45 is connected to

451/U or a suitable dc generator set may be used. The

the AUDIO connector of RT-671/PRC-47. This device

power supply circuits of the RT-671/PRC-47 provide

keys an oscillator in the receiver-transmitter circuits that

high-power dc voltages for the transmitter circuits, and

produces an audio tone. This modulating signal, or the

low-power potentials for the receiver circuits and for

voice input signal from the handset microphone or the

control purposes.

fsk unit, is amplified in the AM-3506/PRC-47 A1), and is

mixed in the AM-3507/PRC-47 (A2) with a 500-kHz

2-4. General Description

standard signal to produce a double-sideband,

a The transmit signal path through the receiver-

suppressed carrier signal. With the undesired sideband

transmitter circuits of the radio set is shown by the solid

and the carrier signals greatly attenuated, the remaining

lines of figure 2-2. The transmit audio signal is applied

singlesideband signal is heterodyned to the desired hf

to the input of the microphone amplifier where it is

radio channel in the CV-1377A/PRC-47 (A3} by mixing it

amplified and compressed before application to other

with the hf oscillator signal from the frequency control

circuits in the AN/PRC-47. When continuous wave (cw)

circuits. This rf signal is then amplified by the driver

telegraphy is required, the telegraph key is connected to

stage and the power amplifier and then applied to the

an 800-Hz audio oscillator. The output of this circuit is a

antenna system. A portion of the transmitter audio is

single audio tone that is present when the telegraph key

returned to the connected audio output device as a

is closed. This signal is amplified by circuits in the

sidetone signal to permit monitoring during these

microphone amplifier. The amplified voice audio (or

transmit periods.

tone) from the microphone amplifier circuit is routed to

the vox circuit, the audio output amplifier, and to the

balanced modulator. The vox (voice-operated-transmit}

b. During receive periods the receiver transmitter

circuit generates a control voltage that switches the

circuits process the incoming signal using some of the

radio set from the receive mode to the transmit mode

identical circuits just mentioned in connection with the

when audio signals are present in the microphone

transmit function. This receive signal is heterodyned to

amplifier output. The audio output amplifier receives a

an intermediate frequency near 500 kHz and then it is

sidetone signal when the transmit mode is enabled.

demodulated to recover the desired audio component.

This sidetone is amplified and routed to the earphone

The audio signal is then applied to the connected audio

(or other audio output device) and permits monitoring

output device. The receiver output is controlled by the

the transmitted signal. The transmit audio is mixed in

VOLUME control on the front panel of RT-671/PRC-47.

the balanced modulator with a 500-kHz standard signal

This control permits adjustment of the receiver output

from the frequency control circuits. The out-put of the

for a comfortable listening level with the earphone of

balanced modulator is a double-sideband signal with the

Handset H-33G/PT, with Headset H-233, or with

amplitude of the 500-kHz standard signal greatly

loudspeaker LS-166/U. It also permits adjustment of

reduced. This intermediate (if.) frequency signal is

the input level to the external fsk unit, if connected.

amplified and then applied to a bandpass filter where

the upper sideband and the carrier are further

c. The frequency control circuits provide two highly

attenuated but the lower sideband is permitted to pass

stable signals that are used in the receiver transmitter

on the remaining if. amplifier stages. The amplified

circuits to generate hf singlesideband transmit signals

lower-sideband signal is applied to the transmit mixer

and to demodulate these signals to obtain audio output

where it is combine with a 2.5 to 12.499-MHz hf

in the receive mode. The 500-kHz standard signal is

oscillator signal from the frequency control circuits.

fixed-tuned and applied to the balanced modulator

The difference frequency (2.0to 11.999-MHz) present in

circuit of the transmitter and to the product detector

the output of the transmit mixer is amplified by the rf

circuit of the receiver. The 2.5 to 12.499-MHz hf

amplifier and driver stages and by the power amplifier

oscillator signal is tunable in 1-kHz steps to provide

and is applied to the antenna system through the t/r

transmitter output in the hf range between 2.0-11.999-

relay.

MfHz.

b. The receive signal path through the receiver-

d. The power supply circuits provide all operating

transmitter circuits of the AN/PRC-47 is shown by the

voltages required by the AN/PRC-47.

dashed lines in figure 2-2. The

These potentials are derived from either a 26.5 volt dc

or a 115-volt, 400-Hz ac primary power source. If the

2-3