[Elecraft] RE: OT: Effect of Compression and Expansiononthe Inductance of Toroids?

[Ron D'Eau Claire]

Jim wrote:
So the apparent change in L as the turns are expanded or compressed is 
simply the CIRCUIT resonance moving as the stray capacitance changes. 
For all practical purposes, L does NOT change. C changes. 

--------------------------------

The inductance measurement method I used does not rely upon a resonant
frequency of any sort. It measures the inductance by differentiating a
square wave. 

The frequencies involved do span the RF spectrum, of course, since the
waveform used to test the inductance is a square wave. A square wave is made
up of the fundamental and a very large number of harmonics, all added
together.

The validity of the inductance measurement using this method is borne out by
noting that the inductance value reported is that at which the inductor can
be used to form a resonant circuit at the desired operating frequency within
the normal range for the core material. That is, for a core designed for HF,
a measured 3.1 uH resonates properly at HF (e.g. 3.1 uh in parallel with 47
pf resonates at about 13 MHz). 

Ron AC7AC