This simple sensitive circuit was suggested in a July 1992 Radio Electronics issue. The relay is a double-contact changeover relay. Sensitivity adjustment is made at R2.
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...