RECEIVER SQUELCH AMPLIFIER MODULE A5200 AND SQUELCH FILTER MODULE A5300 (RECEIVE MODE).

TM 11-5820-670-30

1-31. AUDIO AMPLIFIER MODULE A5400 (RECEIVE MODE). (CONT)

The 150 Hz signal from output of amplifier Q5401 (1) operates relay K5501, which in turn, operates A2

and A1 of relay K5502, sending + 16 vdc to amplifier Q5403 (4). The 16 vdc from relay K5502 biases

amplifiers Q5403 (4), Q5404 (5), and Q5405 (6), which will allow amplified audio intelligence to flow

to transformer T5401 (7).

Amplified audio signals are coupled from transformer T5401 to the interphone amplifier to be heard in

the headset.

800 HZ TONE OSCILLATOR Q5402

The audio amplifier provides an 800 Hz tone signal heard in the headset when the radio set is tuning.

Selection of an operating frequency at the control unit causes the radio set to tune, which, in turn,

causes gearbox assembly A9700 (8) to supply a ground signal to relay K9605 (9). When relay K9605

energizes, + 16 vdc is applied to 800 Hz tone oscillator Q5402 (10) and the audio amplifier. This

causes the audio amp to unsquelch (bias the amplifiers) and allows the oscillator to oscillate.

The output of the 800 Hz oscillator is applied to amplifier Q5403 (4). The signal then flows through

Q5404 (5), Q5405 (6), and transformer T5401 (7) to be heard in the headset.

1-32. RECEIVER SQUELCH AMPLIFIER MODULE A5200 AND SQUELCH FILTER MODULE A5300

(RECEIVE MODE).

To follow the signal path through the squelch amplifier and filter, see FO-4 while reading the text in this

paragraph.

The receiver-squelch amplifier passes or blocks the output audio signal of the audio amplifier by

allowing or not allowing + 16 vdc to enter the audio amplifiers. See the following table.

RECEIVER

AUDIO HEARD OR

+16VDC

Q5403 (4), Q5404 (5)

SQUELCHED OR

NOT HEARD IN

FROM RELAY

Q5405 (6), BIASED

UNSQUELCHED

HEADSET

ON OR OFF

K5502

HEARD

ENTERS AUDIO

UNSQUELCHED

AMP A5400

SQUELCHED

NOT HEARD

DOES NOT ENTER

OFF

AUDIO AMP

Receiver-squelch amplifier A5200 controls the application of +16 vdc to audio amp A5400 in either one

of two modes: TONE OR CARR. When the squelch switch is set to DIS, the squelch amplifier is

bypassed and +16 vdc is applied to the audio amp for the duration of the DIS mode setting.

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