We found this circuit in a spy book from the 90s. Transistors admit equivalents and the coil can be designed as in the CB19425E project. Power is provided by cells or 9 V battery.
In this circuit of a 1975 publication, a silicon transistor is used as a sensor. We can employ a...
This circuit was found in a 1978 publication. Equivalent operational amplifiers can be used. The...
The great advantage of the circuit shown in the figure is the fact that its frequency is...