This is a field strength meter found in an 80's Hands On. The circuit operates at frequencies up to 500 MHz and has a buzzer as its indicator. Can be used as a detector for spy transmitters.
This circuit was found in an American documentation from the 90's. The operational amplifier is the...
This detector circuit was found in documentation from the 1980s. The diode is a high frequency detector...
For those who like electronic games, have good experience in the design of printed circuit boards...