It actually consists of a tunable field strength meter. The circuit is of an old documentation and the circuit must be tuned to the frequency to be monitored. The circuit offers the option to use a headset.
Found in a 1960 Sylvania manual, this circuit is intended to measure audio signals frequency....
We found this circuit for vocal effects in the September 1990 issue of Radio Electronics magazine. The...
Depending on the output transistor used, this transmitter can provide power from 1 to 3 W. The...