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Re: Isotropic Capacitance
Hi everyone,
I've been interested to read this, and thought I'd
mention coil self-C as it is a parameter I rely on heavily in design.
Bert wrote....
<snip>
> It is interesting to note that tesla spent a lot of time and work
> making an exhaustive study of elevated capcitances, it therefore
> was of great importance to him. You would think that the higher
> the sphere was above the earth, the lower the capacitance, but if
> you plot the values Tesla got, then you see this is not the case.
> There is a trend toward lower capacitances, but only at the maximum
> altitudes.
This is mirrored in Medhurst's self-C formula for single layer
solenoids. I have come to the conclusion that his formula is measuring
nett capacitance, probably of a cylinder. His formula ignores both
turns spacing and wire size. I have found this in conjunction with
Wheeler to give a quite reasonable accuracy for design a resonator
for a particular frequency. Throws the rules for helical resonator
design out the window but works very well and I've yet to find a case
where it doesn't. I should stress that as a recipe it's fine, but it
is certainly not a description of how a 1/4 wave resonator works.
Malcolm