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On Sun, Jun 25, 2023 at 02:27 PM, Mike wrote:

Thank you Roger. The coil is 95 turns of 0.9mm enamelled copper wire close
wound on a 36mm PVC former.

Mike,

Attached is an analysis of your coil using Coil64. The numbers are close to
what you measured. For an air wound coil the actual L will not vary much in
the frequency range of up to 12 MHz. Note the following:

--> ESR is increasing with frequency and simulation shows .299 ohms at DC,
.422 at 1 MHz. and 9.233 ohms at 5 MHz.
--> Self capacitance is calculated at 1.61 pF which is very small. You
estimated 2 pF based on your SRF measurement. Any stray capacitance in your
test setup will significantly affect your self resonant frequency so you need
a good test jig if this is an area of concern.

Note: For air wound coils assuming that apparent inductance at low frequencies
is equal to actual inductance L at higher frequencies is a reasonable
approximation. Therefore the method of calculating parasitic capacitance
based on using this value of L and the SRF to calculate parasitic capacitance
gives a decent estimate. BUT this method does not work if the inductor is a
ferrite core design.

Roger