Re: Ground system for outside operation: Counterpoise?

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

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

Tesla list wrote:
> 
> Original poster: "Dave Hartwick by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>

> The larger question may be: What constitutes an adequate tesla coil ground,
> an optimum tesla ground, and what are the characteristics of both? Then, for
> the selected proposed physical ground arrangement--ground rod(s),
> counterpoise, etc.--how must that ground be constructed to meet the
> conditions demanded by the answer to the first question.

I think that the answer for this, in what concerns the operation of the
system, is that the ground connection shall have an impedance to the
effective ground significantly smaller than the impedance from the
secondary terminal to the ground, at the operating frequencies.
This is not much. Consider the load capacitance of a small coil as
being 20 pF, at 300 kHz. The load impedance is then:
Z = 1/(2*pi*f*C) = 27 kOhms.
Any kind of ground connection, resistive (ground rod) or capacitive 
(counterpoise) with less than a few kOhms of impedance would be
adequate.
This is easy to verify by operating the coil at low-power, with a
low-impedance square-wave generator across the primary gap, and
observing the primary waveforms in an oscilloscope. With a small
coil as described above, there is little difference between a solid
ground connection and a finger touching the disconnected ground
connection (of course, in the low-power test only!).

Antonio Carlos M. de Queiroz