Using the name of varactor this circuit was found in the Radio Electronics magazine of July 1982. Varicaps of any type can be used and the components selected according to the component.
The circuit shown in the figure is suggested by Allegro Micro (www.allegromicro.com) and consists of...
This circuit is a variation of the common grid dip meter, having been found in a 1975 publication on FETs....
The time obtained in this circuit, from a 1978 publication, depends on R3 and C. R3 can have...