TRANSMITTER OPERATION.

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

output audio level that will not overmodulate the

to the headset output and audio (or data) output of the

transmitter. The output of the compression amplifier is

receiver-transmitter. Impulse type noise is blanked from

passed through a low-pass and high-pass filter that

the audio output by a noise channel blanking circuit in

together shape the audio response of the transmit audio

the 30-MHz if circuit. Receive squelch is provided by a

signal. The input data signal to be transmitted is fed

squelch circuit in the audio circuit. Receiver selectivity is

around the compression amplifier and applied to a

determined by a crystal filter in the 10.7-MHz if circuit.

second high-pass filter. This filter in conjunction with the

Audio (or data) response is determined by active filters in

low-pass filter following the percent modulation (% MOD)

the audio circuit. The crystal filter (36-kHz bandwidth)

control shapes the frequency response of the transmit

supplied with the radio set provides for 50-kHz channel

data signal. The output of the high- pass filter is applied

spacing. An optional narrow bandwidth (20-kHz) or wide

to the % MOD control located on the front panel of the

bandwidth data (60-kHz) filter can be installed for 25-kHz

receiver-transmitter. The % MOD control is adjusted to

channel spacing or 100-kHz channel spacing

set the audio level to give the desired percent of

respectively. Noise channel blanking is disabled when

modulation of the transmit rf signal. The audio signal

the wide bandwidth filter is installed.

from the % MOD control is passed through the

clipper/low-pass filter of audio module A4 to the

4-9. The transmitter section of the receiver- transmitter

modulator of power amplifier module A8. The clipper

contains a broadband rf amplifier that amplifies the

removes audio peaks that could overmodulate the

transmit rf signal from the frequency synthesizer to

transmitter.

provide 16- to 24-watt (nominal 20- watt) carrier power at

the antenna. An automatic load control (ALC) circuit

4-14

To key the transmitter, push-to-talk (ptt) keying

receives forward and reflected power signals to maintain

information from the receiver-transmitter front panel

control of the power output level. The transmit rf signal

REMOTE/LOCAL switch is applied to the keying con- trol

is amplitude modulated by input audio (or data) that is

circuit of audio module A4. The keying control circuit

amplified, filtered, and applied to the modulator of the

provides two transmitter key lines, one a fast attack-slow

power amplifier. Harmonics in the transmit rf signal are

release key line (key 1) and the other a slow attack-fast

attenuated by the rf filter.

release key line (key 2). For remote operation, keying

from five separate inputs can key the transmitter. They

4-10. A meter circuit in the receiver-transmitter allows

are the audio loop, current loop, and voltage loop keying

measurement (from the front panel) of power supply

inputs, the remote ptt key-line input, and the keying

voltages, antenna forward and reflected powers, the

information supplied on the audio inputs (CT 1 and CT 2)

percent modulation of the transmit rf signal, and the

to the receiver-transmitter. The audio loop, current loop,

relative heat-sink temperature of the power amplifier.

and voltage keying signals are applied through the emi

filter to the keyer circuit of keyer module A9. The remote

4-11.

TRANSMITTER OPERATION.

key output of the keyer is applied to the remote side of

the REMOTE/LOCAL switch. The remote pit key line is

4-12. Refer to the transmit signal flow diagram of

applied directly to the remote side of the

figure FO-16. The transmit section of the receiver-

REMOTE/LOCAL switch. Keying information sup- plied

transmitter consists of power amplifier module A8,

on the audio input lines is applied to the remote ptt keyer

transmit audio circuits of audio module A4, and the

of audio module A4. The remote ptt output of the remote

common rf signal path through rf filter module A7.

ptt keyer is applied to the remote side of the

Transmitter keying circuits are contained in audio module

REMOTE/LOCAL switch. For local operation, the ptt

A4 and keyer module A9. Tuning for the rf filter of rf filter

lines from the MIC jacks and from the PTT/ CARRIER

module A7 is provided by d/a servo amplifier Al.

TEST switch on the front panel of the receiver-

transmitter are connected to the local side of the

4-13. For remote operation, three audio inputs can be

REMOTE/LOCAL switch.

applied to the transmitter. They are the micro- phone

input, audio input, and data input. All three inputs are

4-15. Refer to figure FO-16, sheet 2. The rf signal to

applied to audio module A4 through the electromagnetic

be transmitted is generated by the phase-locked loop

interference (emi) filter on chassis A10 of the receiver-

(p11) of frequency synthesizer module A2. The fre-

transmitter. For local operation, microphone audio is

quency of the rf signal is determined by bcd frequency

applied to audio module A4 from jacks located on the

select information applied to the phase-locked loop from

front panel (chassis A10) of the receiver-transmitter.

the radio control. During transmit mode, the output of

The input audio is coupled through transformer T1 to the

the phase-locked loop is applied to power amplifier

compression amplifier. The microphone audio is applied

module A8 through the frequency synthesizer

directly to the compression amplifier. The compression

transmit/receive switch (actually a diode switch) that is

amplifier amplifies the audio signal and maintains a

closed by the slow attack-fast release transmitter key line

constant

(key 2).

4-16. The transmit rf signal (carrier signal) from

frequency synthesizer module A2 is applied to the

4-2