TONE (SQUELCH MODE)

TM 11-5820-670-30

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

A5300 (RECEIVE MODE). (CONT)

TONE (SQUELCH MODE)

The received 150 Hz signal at the output of amplifier Q5401 (1) in the audio amplifier is applied

through B3 and B2 of relay K5501 to amplifier Q5201 (11) in the squelch amplifier. The signal is

amplified and applied to amplifiers Q5203 (12) and Q5204 (13) for further amplification.

The 150 Hz signal at the output of amplifier Q5204 is applied through B2 and B1 of tone mode relay

K5503 to tone frequency adjust and capacitor coupling (14) in squelch filter module A5300. In the

TONE mode of squelch operation, the signal is applied through parallel twin T-circuit (15), which

attenuates the 150 Hz tone. Potentiometer R5301 (14) is adjusted to provide maximum attenuation of

the 150 Hz squelch tone signal. All other frequencies are fed back to amplifier Q5202 (16), which

completes the feedback loop. The ac amplifiers are completely degenerative for all frequencies except

150 Hz, and provide maximum gain at 150 Hz.

The 150 Hz signal at maximum gain from Q5204 (13) and from squelch filter (15) is applied to tone

rectifier CR5202 (17) for rectification. The rectified signal from CR5202 causes the current in Q5206

(18) to increase. Increased current flowing through B2 and B1 of energized relay K5505 is amplified in

amplifier Q5207 (19).

The output of amplifier Q5207 is applied through A3 and A2 of relay K5501, which energizes relay

K5502. Energizing K5502 causes A1 and A2 to make contact, sending +16 vdc to the audio amplifier to

cause unsquelching.

CARR (SQUELCH MODE)

In carrier squelch mode, audio signals and noise components at the output of Q5401 (1) in the audio

amplifier are applied through B3 and B2 of relay K5501 to ac amplifier Q5201 (11) in squelch

amplifier. Q5201 (11), Q5203 (12), and Q5204 (13) provide amplification of the signals. Once

amplified, the signals are applied from Q5204 through B2 and B3 of deenergized relay K5503 to

squelch filter (14). In the CARR mode of squelch operation, the signal is applied through the twin T-

circuit (20) which attenuates noise components centered around 7300 Hz. Potentiometer R5301 (14)

is adjusted to provide maximum attenuation of 7300 Hz signals. All other frequencies are fed back to

amplifier Q5202 (16) which completes the feedback loop. The ac amplifiers are completely degen-

erative for all frequencies except 7300 Hz, and provide maximum gain at 7300 Hz.

The 7300 Hz noise component at maximum gain and an audio signal enter carrier rectifier CR5201

(21) from amplifier Q5204 (13) and squelch filter (20). When an audio signal is present, the carrier

rectifier rectifies the noise component which causes current in Q5205 (22) to reduce. The reduced

current level through B3 and B2 of deenergized relay K5505 causes amplifier Q5207 (19) to conduct.

The output of amplifier Q5207 (19) is applied through A3 and A2 of relay K5501, which energizes relay

K5502. Energizing K5502 causes A1 and A2 to make contact, sending +16 vdc to the audio amplifier

causing unsquelching.

When an audio signal is not present, receiver noise alone is present in the receiver. The rectified

noise from carrier rectifier CR5201 (21) causes the voltage in Q5205 (22) to increase. Increased

voltage is applied through B3 and B2 of deenergized relay K5505 to amplifier Q5207 (19) which causes

it to turn off. When Q5207 is turned off, relay K5502 does not become energized and + 16 vdc does not

enter the audio amplifier, causing squelching.

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