This circuit works with the previous two by demodulating the signals received modulated in FM. The circuit is from the Radio Electronics magazine of December 1992.
Found in a 1967 Electronic Design, this transistorized circuit compresses and then expands a pulse....
This squelch is activated by its own noise, acting automatically. It is used in communications...
This is the battery-powered version of the previous circuit. The circuit is from the same Radio...