This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and was found in an English publication. The sensor is semiconductor type.
This circuit was found in a Popular Electronics from the 90's. The circuit has gained 10 to 20 dB...
This simple circuit uses a car ignition coil. The circuit appeared in the 1983 Radio Electronics Annual...
The modified Hartley oscillator seen in the figure can generate signals ranging from 3 MHz to 10...