Re: PVC secondaries - environmental effects on coil performance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

R. Scott Coppersmith wrote:

> My own observations lead me to believe that a change in humidity
> changes topload-C due to change in the permittivity of air -
> which requires a tuning change.

Yes.

The effect of humidity on permittivity of air depends on the
prevailing temperature.  At 20 degC, the Kr varies from around
1.00045 at 0% humidity to 1.00067 at 100% humidity - a change
in Kr of +0.02%, and a consequent shift in Fres of -0.01%.

This order of frequency shift is observed in Terry's recent
Q variation experiments.

At higher temperatures the air holds more water for a given
percentage humidity, and the frequency shift is greater, eg
at 50 degC:

   0% humidity, Kr = 1.00043;
 100% humidity, Kr = 1.00140;

A much bigger effect, giving a change in Kr of almost +0.1%,
thus -0.05% for Fres.

For dry air at 20 degC, the temperature coefficient of
permittivity is -3.41e-3, which derives from the reducing volume
density of particles.
--
Paul Nicholson
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