We found this circuit in an Australian publication from 1991. It is a kit of the time with input for a guitar pickup. The range is a few tens of meters.
We found this circuit in a 1976 documentation. The FET can be BF245 or MPF102 and the power supply...
This circuit was obtained in a transistors manufacturer's manual from the 90s. The circuit uses an...
The instrument of this field strength meter, from a 1970s publication, can be a 200 uA...