This circuit was found in an ancient American documentation. With it is possible to double the frequency of a transmitter For the range of 6 meters obtaining 8 W. The circuit makes use of varicap.
Two inverters, of the 6 available in a Low-power Schottky 74LS04, are used in this anti-ring...
Found in Radio Electronics from the 90's, this circuit can be implemented with other operational...
Taken from a 1956 Raytheon transistor manual, this circuit uses varistors to obtain modulation of a signal...