This detector uses an unusual sensor today. The circuit is from an 80s documentation. Its sensitivity is 10 ppm. The transformer has two secondary voltages.
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...