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.
We find this current meter circuit from 0 nA to 200 nA in a Linear Technology application manual....
One pulse in the output is produce at each 5 pulses applied to the input. The circuit uses CMOS...
The circuit presented was found in a European publication of the 1980s. Used transistors are not...