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.
This stage with polarization of only one resistor can use any general-purpose transistor. The...
This voltage-controlled potentiometer using an LDR was found in an English documentation. LDR is...
This interesting sensor for RF signals was found in an article in the June 1989 Radio Electronics...