Measured C and calculated L of thick and thin insulated coil winding wires ... questions

[green]

I have measured two different coils @20 windings each.
One has "normal" insulation the other a very thick insulation.

I am somewhat puzzled by the results.
The measurements were made via resonant frequency.


Thin insulation:
650kHz with 150pF capacitor in measuring circuit.
1150kHz with no capacitor in measuring circuit.
The calculated distributed capacitance is 70pF
The calculated inductance is 272uH.

Thick insulation:
878kHz with 150pF cap.
1815kHz no cap.
The calculated distributed capacitance is 45pF
The calculated inductance is 168uH.

Maybe I've done something very wrong here. My interpretation is that to get back up to the "nominal"
inductance of 272uH I would have to put on MORE windings of the thick insulated wire, which in
turn would raise the self capacitance again ... this appears futile ...
Having read a lot here about winding spacing being the bee's knees for faster coils, this has me scratching my head.

So, what am I not getting here? Thanks!

Good to see someone try the method to get coil inductance, coil capacitance and SRF. I use a 10nf cog ceramic or 100nf polypropylene instead of 150pf across coil to calculate inductance. Minimize the effect of distributed capacitance. Do you have an inductance meter to compare with calculations? I don't so I have been using the calculations. The inductance calculation for the 10nf and 100nf capacitor are within 1% using capacitance measurements with my multimeter. Have been told I should be using an inductance meter instead of this method. Interested if we can prove the method good or bad.

What is the diameter of your coils?

[Polymer]

I have measured two different coils @20 windings each.
One has "normal" insulation the other a very thick insulation.

I am somewhat puzzled by the results.
The measurements were made via resonant frequency.


Thin insulation:
650kHz with 150pF capacitor in measuring circuit.
1150kHz with no capacitor in measuring circuit.
The calculated distributed capacitance is 70pF
The calculated inductance is 272uH.

Thick insulation:
878kHz with 150pF cap.
1815kHz no cap.
The calculated distributed capacitance is 45pF
The calculated inductance is 168uH.

Maybe I've done something very wrong here. My interpretation is that to get back up to the "nominal"
inductance of 272uH I would have to put on MORE windings of the thick insulated wire, which in
turn would raise the self capacitance again ... this appears futile ...
Having read a lot here about winding spacing being the bee's knees for faster coils, this has me scratching my head.

So, what am I not getting here? Thanks!