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 is a configuration much explored by assemblers, being found on this site in dozens of similar...
This simple circuit was found in an English magazine that no longer exists, January 1970 issue. It is...
Texas Instruments Type D flipflops N74LVC1G79 and SN74LVC1G179-Q1 for operation from 1.65 to 5.5V...