This is all kind of Schrodinger’s cat, but it turns out not all 6uH is made equally. 6uH can be 6uH, 6uH can be 12uH and 6uH can be a capacitor and the only thing different between all these 6uH’s is the frequency they have been measured at.

So tonight i got well and truly schooled on inductance and why my bandpass filter was looking rather bonkers. I built it with the right capacitors, i wound inductors with the right number of turns for the required inductance i assembled a really nice looking filter. But when it came to measuring the bandpass it was orders of magnitude wrong.

This is how my filter should have looked, well, at least something like that.

This was the bonkers mess I was measuring in the Bode Analyser.

So after much discussion with a much smarter man than me, and working out everything i was doing wrong, I ended up with this testy jig, 200R in series with the inductor, feeding one side with the signal generator while measuring both the input voltage and the voltage across the inductor. Changing frequency until my output voltage is 50% of the input and then using this following formula to calculate the inductance. L= R*sqrt(3)/(2*pi*f) that at least gets me in the ball park, and it turns out I was orders of magnitude off with the inductors i wound and were most likely acting like capacitors at 20mhz where my filter was peaking.