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 alarm, found in a 2002 documentation, uses several sensors and has a 12 V supply, not...
This circuit uses a special 1950's RCA strobe tube. It can be built with equivalent components for the rest...
This circuit, which can act as a shield, was found in a 1970s American documentation. The...