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 found this test circuit in a March 1967 Radio Electronics. The circuit uses a zener-regulated supply and...
This amplifier for small cassette tape players was found in an English documentation from 1969. The...
We found this circuit in a 2005 Linear Technology manual. The resistor is calculated for the...