Found in an old American documentation this FM modulator makes use of a varactor diode. The circuit can be easily implemented given the small number of components used.
This sequential circuit appears in other versions on this site. This is from American...
Found in a 303 Circuits from the 90s, this circuit converts signals from the 10 kHz to 150 kHz...
This beat frequency oscillator or BFO was found in an American 1980s documentation. The circuit is...