Found in American documentation from the 1980s, this circuit can be designed with equivalent components. The microphone can be of the piezoelectric type.
This zero-crossing detector circuit produces an output pulse every time the input sinusoidal...
This circuit for the 3.5 MHz band (80 meters) was found in an old radio amateur documentation. The circuit...
This circuit was found in a 1980s documentation. Similar configurations appear in the section, but from...