The Romer-Lewin ring with inductors (part 2) - Raising the frequency and calibrating the voltmeter

Raising the frequency of the changing magnetic flux by using an ad hoc winding driven by a signal generator, and calibrating my slow multimeter to work out of specs so that I can use it together with the faster one to give two simultaneous readings at 4 kHz.
The frequency of 4 kHz is a sweet spot in that it gives appreciable values for the reactances, and is within the operating range of one of multimeters. It is also slow enough to give an EMF of about 100 mV per turn (I. using a toroidal core designed for 50 Hz operation).
The role of the series resistance will be explored in a subsequent video.