Ilya, I've see that too, it's the formula used for skin depth returning a depth that is deeper than the conductive radius of the wire. I put a conditional guard in there:
http://www.mediafire.com/download/p8gcc02tarjxpbm/Theremin_simulation_v9_2015-02-28.xls
Thank Dewster for your efforts. Lets make the sim better!
But there is still (IMO) a fundamental issue in your simulating. That is the coil's self capacitance. I know you used the David Knight' formula (5.3). And you didnt beer in mind that the formula corresponds the hypotetical case of "isolated" (or "flying") coil.
But coils in theremins are never "flying". For example, the EQ coil is a "grounded on the one side" (or "powered from the low impedance source", in pacticy).
According the LTL (long transmition line) theory of coil's self capacitance we have the 1/4 resonance system instead of 1/2 resonance. The different mode means the different resonace frequency and the different self capacitance value, as result.
Ilya, I believe you're talking about "Integer multiples of a quarter-wavelength - the ground mirror effect" which is shown graphically in Knight's experiments here (~1/2 way down the page):
http://g3ynh.info/zdocs/magnetics/appendix/self_res/gallery.html
I am absolutely in awe of the visualization aspect of old style experiments (something that was almost completely missing in my formal EE education). The importance of crude means to gain insight into what is physically going on cannot be overestimated. You know all the formulas in the world came out of trying to explain these sorts of experiments.
Anyway, I'll look into it.
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