This circuit was described in an article in the February 1993 Radio Electronics magazine. The frequency depends on the crystal and L1 is optional.
Found in American documentation from the 90s, this circuit can use a BC548 instead of the original...
This circuit acts on the dynamic range of an audio signal, which can be useful for recording,...
This circuit doubles the frequency of a signal using a varicap. In this case, the input is 28 MHz,...