Suggested by a 90s Popular Electronics this circuit is intended to receive volleys or whistles from thunderstorms in the wave range below 20 kHz. The coil consists of 300 turns of wire 26 in a ferrite rod.
This experimental AM microphone was found in an Argentine publication from 1973. The recommended...
The integrated circuit is the 4093 and one of its four gates is used. The frequency is given by...
This TTL circuit was obtained in a 1985 Italian magazine, but it can be easily implemented, as the...