This circuit is from a 1967 documentation. It makes use of varicap and diode tunnel in addition to currently uncommon FET. It serves as a reference.
This circuit was found in an old documentation, being able to generate signals of frequencies in...
Found in a Popular Electronics from the 90's, this circuit is used to recognize the frequency of a...
Found in a 1990s American documentation, this circuit provides an output voltage approximately 4 times...