This 1970 Electronic Design circuit uses a varactor or varicap. The circuit divides the frequency of a 150 MHz signal by 2. Similar versions appear on this site.
This frequency modulated light transmitter is from a 1990s documentation. The circuit may use...
This amplifier is from the 80s integrated circuit manual itself. Equivalent configurations can be adopted for...
Found in a 1968 Mullard manual, this circuit can function as an infrared audio link. The...