This circuit that uses a loop antenna was found in a 1924 publication. The circuit has several supply voltages and sets of audio and RF coils.
This circuit uses high voltage transistors to provide direct power from the 110 V power grid or a...
This circuit was designed to work with the previous one in triggering a relay by the sounds picked up...
This circuit was suggested by Signetics in 1980s documentation. The circuit makes use of the...