This circuit was found in old American documentation. Transistor is general purpose and coil rated is for 1.5 MHz. Wind 50 + 50 turns of wire 28 onto ferrite rod for 1 MHz.
This practical idea from a 1992 documentation shows how to count the turns of a winder using a...
It is an electronic capacitor where the capacitance "seen" by an external circuit connected to...
This project from a 1983 publication can be assembled using more modern transistors. We can use...