Varactor diodes are our varicaps of today. This circuit for switching signals in an RF circuit was found in a Radio Electronics magazine from July 1982.
We found this circuit in a 1990 documentation. The operational amplifiers are type 741 and the LED is...
We found this circuit on an Elektor from the 90s. The frequency is given by capacitor C1. The...
Found in National Semiconductor publication from the 1980s. This gain-100 circuit can be...