This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics magazine. The source must be symmetrical. The capacitors can be changed for other frequencies.
This oscillator has its frequency controlled by crystal and its frequency can be between 100 kHz...
This small crystal microphone transmitter was indicated in an 80s spy book. The range depends on...
The circuit shown is from the 1994 Linear Applications Handbook by National Semiconductor. The...