We found this circuit in a documentation from the 90's. The coil has its characteristics given next to the diagram. Power is provided by a 9 V battery and a range of a few tens of meters.
This circuit was found in a Radio Electronics of July 1984. It consists of the traditional 1 A...
This circuit is from a 90's Radio Electronics. The circuit operates accurately up to about 15 kHz...
I found this circuit in an old British magazine from 1976. It is possible to test operational...