Re: Ungrounded Secondary

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

Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 

Tesla list wrote:

 > Original poster: "Gavin Dingley" <gdingley-at-ukf-dot-net>
 >
 > if you connect a "top-load" to either end of a secondary coil, then you will
 > find it will resonate at half the usual frequency, i.e. at half-wave
 > resonance rather than quarter-wave, providing the coil is positioned
 > horizontally (parallel to the ground).

Humm...
You have the same coil with inductance L, with two terminals. Let's
assume that the terminals account for the greater part of the load
capacitance C. So we have the same coil, and two capacitances C in
series (assuming not much changed due to the different position).
This would resonate at:
f=1/(2*pi*sqrt(L*C/2)).
The frequency would be -greater- than the "1/4" wave frequency by a
factor of sqrt(2)=1.4142.

 > This is only if all things are equal,
 > which they will not be due to dramatic changes in the capacities involved,

Not dramatic, and the capacitance affects the frequency with a -1/2
exponent, what reduces its effect (10% increase -> -5% change).

 > so resonance will be at an entirely, almost unrelated, frequency (usually
 > much higher).

It's difficult to tell what happens with the "self-capacitance" of
the coil in this configuration, but it's expected to decrease in each
of the half-coils, what would increase the frequency a bit above the
1.4142 factor.

 > If you mount this arrangement vertically, the bottom "top-load" will arc and
 > make its own connection to ground, resonating somewhere around quarter-wave.

Yes, if something grounded is close to the bottom terminal.

Antonio Carlos M. de Queiroz