Squelch Filter

TM 11-5820-401-34-3/0967-LP-432-3060

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RECEIVER SQUELCH FUNCTION. (CONT)

Squelch Filter

The squelch filter contains circuitry to filter out 150-Hz signals. These signals are applied to the

Squelch Amplifier A5200. A feedback loop applies the 150-Hz signals to the squelch filter. Since the

150-Hz signals come from the Audio and Squelch Preamplifier A4300, audio frequencies and some

noise are also applied to the squelch filter along with the 150-Hz tone.

However, the squelch filter attenuates 150-Hz signals and feeds back all other frequencies degen-

eratively to the ac amplifier. Therefore, the ac amplifier responds well to 150 Hz, but degenerates

sharply for any other frequencies.

The degenerative feedback is important to insure that the receiver remains squelched until 150 Hz is

received with the rf carrier. Without degenerative feedback, frequencies other than 150 Hz could

unsquelch the radio.

The ac amplifier increases the signal amplitude of the 150-Hz sine wave. The sine wave is then

rectified and applied to the NEW ON DC amp. Application of the rectified signal to the dc amplifier

results in a ground path being made available at one of the amplifier's transistors.

The ground path is the enable circuit for the squelch relay. When grounded, the relay energizes,

providing 16-vdc power to the audio amplifier. Therefore, when a 150-Hz tone is received, the audio

amplifier turns on, thus unsquelching the radio.

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