This squelch circuit is placed at the input of the single receiver audio amplifier stage. Its purpose is to silence background noise. The circuit is from an 80's documentation.
We found this circuit at Modern Electronics in January 1991. The magazine no longer exists, but...
The integrated circuit used in this filter is not very common today, but the reader can use...
Found in Linear Technology documentation from the 90s, this circuit uses an operational amplifier...