This circuit is from an old Signetics documentation. It can be implemented with modern operational amplifiers. The power supply must be symmetrical.
This circuit is indicated for the PX or 11-meter band, having been found in a 2003 documentation. The...
This configuration from a 1976 technical documentation shows how to use a varicap in a direct...
Other operational amplifiers can be used in this circuit obtained from the manufacturer's own...