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.
This oscillator, which can be used as a signal injector, was found in a Popular Electronics from the 90s....
We found this circuit in a publication from the 1980s. The circuit drives a triac with isolation...
This circuit was found in an American publication from 1969. Transistors are from the time and can be...