AUDIO AND SQUELCH PREAMPLIFIER MODULE A4300.

TM 11-5820-670-30

1-30. AUDIO AND SQUELCH PREAMPLIFIER MODULE A4300.

The discriminator in module A4200 demodulates both the audio intelligence and the 150 Hz squelch

tone signal. The 150 Hz squelch tone signal will be present in the receiver circuits only if the operator

of a nearby transmitter is transmitting rf. Audio and squelch preamplifier A4300 subjects both these

frequencies to preliminary stages of amplification, then applies the signal(s) to audio amp A5400.

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

To follow the signal path through audio amplifier module A5400, see FO-4 while reading the text in this

paragraph.

The audio signal and 150 Hz tone signal from the audio and squelch preamplifier are applied to

amplifier Q5401 (1) in audio amplifier module A5400. See the following table.

NEARBY TRANSMllTER

SIGNALS APPLIED

TO AUDIO AMP

SQUELCH SWITCH SET TO

TONE

audio intelligence and 150 Hz

audio intelligence and noise components

CARR

DIS (disable)

audio intelligence and noise

The amplified output from Q5401 (1) is applied through:

B3 and B2 of relay K5501

Low-pass filter FL5501 (2)

Signals flowing through B3 and B2 of relay K5501 will be used to unsquelch the audio amplifier. The

same signals are also applied to low-pass filter FL5501 (2) in order to filter out noise above 3000 Hz.

The audio intelligence is applied from the filter through potentiometer R5405 (3) to amplifier Q5403

(4) for amplification. Potentiometer R5405 provides adjustment of the standard audio output level of

2.8 volts.

1-28