TRANSMITTER SIGNAL FLOW.

TM 11-5820-670-30

1-32. RECEIVER SQUELCH AMPLIFIER MODULE A5200 AND SQUELCH FILTER MODULE

A5300 (RECEIVE MODE). (CONT)

DIS (SQUELCH MODE)

When the squelch switch is set to DIS position, receiver squelch amplifier A5200 is bypassed since a

squelch disable ground signal is applied through A3 and A2 of relay K5501 to relay K5502. A ground

signal at K5502 causes + 16 vdc to flow through A1 and A2 to audio amplifier A5400 causing

unsquelching.

For a discussion of the squelch amplifier module A5200 and squelch filter operating in transmit mode,

1-33. TRANSMITTER SIGNAL FLOW.

A system block diagram showing transmitter signal flow can be found on FO-5 in the back of this

manual. See the foldout while reading the text in this paragraph.

Voice signals from microphone (1) are applied through interphone amplifier (2) and control unit (3)

to K9606 dummy relay (4). Squelch amplifier A5200 (29) and squelch filter A5300 (30) generate a

150 Hz tone signal which is applied through K9606 to audio mixer A8600 (5). The 150 Hz tone signal is

always generated when the radio is in the transmit mode. The audio signal from K9606 is filtered in

3 kHz low-pass filter FL8701 and combined with the 150 Hz tone signal in audio mixer A8600 (5).

The combined 150 Hz tone and audio signal is used to frequency modulate transmitter 11.5 MHz

modulator A8100 (6). The output of the transmitter 11.5 MHz modulator is fed to transmitter phase

discriminator A8200 (7) which also receives the 11.5 MHz if. signal from mixer A1400 (19) through

transmitter first and second if. amplifiers A8300 (20).

Transmitter phase discriminator A8200 compares the two incoming signals and outputs an audio

signal and a dc correction voltage. The audio signal is coupled through transmitter hunt generator

A8400 (8) to frequency modulate the frequency of master oscillator A6300 (9). The frequency of the

master oscillator is determined by setting the tuning dials at the control unit.

The dc correction voltage from the phase discriminator is applied through the hunt generator to the

master oscillator. If the master oscillator changes frequency (drifts), a dc correction voltage will

bring the frequency to that of the frequency settings on the tuning dials. The dc correction voltage acts

as a fine tuning control for the master oscillator.

When the master oscillator frequency is beyond the correcting range of the phase discriminator,

transmitter hunt generator (8) will apply a signal to the oscillator and reduce the change in frequency

to within the correcting range of the phase discriminator. The hunt generator acts as a coarse tuning

control for the master oscillator. The audio modulated output of master oscillator A6300 is amplified by

buffer amplifier A6400 (10) and applied to rf drivers A6500 (11). The buffer amplifier isolates the

master oscillator from loading effects of the rf drivers. For a detailed discussion of the master

oscillator frequency control, see paragraph 1-34.

1-31