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 produces the hum of a mosquito, scaring the female of the species that are the ones...
This circuit is from an American publication from 1974. The circuit can be designed with PNP BC558...
This circuit was found in the Spanish magazine No longer in existence, Mundo Electrónico, in a...