Joule Thief: Supplement: Determining Resonant Frequency Using Scope and FG
Here I show briefly how to use a Function Generator and the Oscilloscope to determine the resonant frequency of a small JT inductor removed from an old TV chassis. The FG is connected to the drive coil (primary) thru an approx. 50 ohm resistor. The output from the driven (secondary) coil is monitored using a 10x attenuated probe. The FG output is swept across frequencies and the amplitude of the secondary’s output is monitored on the scope. The resonance is obvious when it is encountered.