Re: eddy current with secondary coil

["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: Bart Anderson <classi6-at-classictesla-dot-com>

 > I set up a counterpoise under the coil. I leave the coil completely set up
 > and short the gap. I use the planewave for the Fres measurement to the
 > scope. I drive the coil with the generator with the low-z amp (which has
 > just become my typical drive approach).

 >From the base of the secondary?

 > The generator is adjusted for Fres.
 > C is measured between topload or top of coil and counterpoise.

With the secondary coil removed, or disconnected?

 > C will
 > measure 1/2 the capacitance.

Why? Which capacitance? The "self-capacitance" of the secondary can't
be directly measured with a normal capacitance meter.
(But a measurement of the capacitance between a coil, suspended high
above the ground and the ground (counterpoise) measures about twice
the Medhurst capacitance, what makes sense.)
A measurement of the capacitance between the coil connected to the
topload but insulated from the counterpoise and the counterpoise
would result in a higher capacitance.

L is solved from Fres and C. There is some
 > loading due to the direct C measurement, but the results match the model
 > well and show the affect on L and C.

Ok, but it's not clear how did you measure the effective capacitance
of the coil+topload.

 > Since Javatc can model the change in L and C, I'll show measured and
 > modeled numbers.
 >
 > The coil driven at Fres unloaded w/counterpoise in place:
 > Measured:                   Modeled:
 > 418 kHz                     419.8 kHz
 > 5.3 x 2 = 10.6 pF            9.87 pF

This x 2 is strange.

Antonio Carlos M. de Queiroz