This simple circuit found in a 1968 EEE was intended for data transmission over the telephone line. The components are from that time, some are uncommon today.
This circuit for a 455 kHz ceramic filter was found in the October 1952 Radio Electronics...
This circuit was found in a Poptronics of the 90's. It can be powered by voltages between 6 and 15...
The microphone of this short-range MW transmitter should be low impedance magnetic (a small...