Re: A new Tesla coil and k measurements

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

 > Original poster: "Barton B. Anderson by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

 > If you are measuring at a high frequency, you may want to compare against a
 > low frequency measurement to confirm a change of Lm at low and high 
frequency.

I am measuring at the conditions where the coil works, measuring
primary inductance by resonating the primary coil with the measured
primary capacitor, and obtaining the coupling coefficient directly
from the primary voltage waveform, when I excite the system with
a low-impedance square wave generator across the spark gap.
The geometry of my primary coil is not very perfect, but I didn't notice
any difference when trying to rearrange the coil more precisely.
I even noticed a curious effect: If I move the secondary coil to
a side, the waveforms continue practically unchanged even for a
movement of several cm. Vertical movements cause evident changes,
even at 1 mm, but I have to move the coils apart by ~1 cm to have a
coupling coefficient that agrees with the calculations.
I am imagining that, since the secondary current is higher at the
bottom, the coupling shall be higher than what an uniform current
predicts (or the opposite?). I will make a test, varying the top load.
If I am right, a smaller top load shall result in higher coupling,
and a larger top load in a smaller coupling.
I didn't try a low-frequency measurement of the coupling coefficient,
but if it disagrees with the effective coupling at operating
conditions, I think that the method shall be revised.

Antonio Carlos M. de Queiroz