This PLL with operational amplifiers was found in 1969 documentation. The configuration can be adapted to use modern components. The circuit has a gain of 15 V / V and can operate with 10 kHz signals.
This circuit was obtained from an English magazine from 1979, but can be easily assembled today...
This squelch circuit used in transmitters was found in a magazine for radio amateurs 73 in the...
With this circuit, obtained from an American publication for radio amateurs in 1976, it is...