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 simple circuit for a high impedance magnetic phone (500 ohms or more) has been found in a...
This configuration enables the use of low current switches or sensors to control high power loads...
We found this circuit in the 1993 Motorola Linear Interface ICs. The operational is unusual today, but...