This circuit was found in a publication in the 1980s. Modern equivalent components can be used. The source must be isolated. The circuit includes an oscillator.
This small crystal microphone transmitter was indicated in an 80s spy book. The range depends on...
The figure shows how to use an operational amplifier with a low impedance head. The gain is...
Voltage comparators, such as those in the LM139/239/339 series, consist of devices that can be...