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As a hobby I've decided to pick up EE and I've been reading quite a bit and I'm interested in building some basic circuits and determining the SRF in some coils that Ive wound.

I have found that you can calculate SRF using this formula:

..........................(1/5)

.........29.85 x (H/D)

F = -------------------

...............N x D

I dunno if this will post right, it should be (H/D) to the power of (1/5)

where:

F= self resonant frequency in Mhz of an 'isolated' coil

H= coil height in meters

D= coil diameter in meters

N= total number of turns

I'm confused about this formula though, what is "coil height"?

Its obviously not the diameter since that is covered with another variable - If it is the "Length of the coil", is that the unwound length of the wire? or the physical length of the actual coil itself?

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This formula will give you 1 value as a function of the properties of your coil. So obviously there is only 1 SRF for a given coil.

So why arnt the harmonics of that SRF also in resonance? I ask this because these harmonic frequencies are sort of in the same phase as the SRF. Obviously I've missed something though.

Can anyone point me in the right direction?

Thanks in advance!