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Re: [TCML] Counterpoise

Hi Jim,

Just a few comments/questions.

> bear in mind that tesla coils run at very low frequencies compared to HF
> radio.  Folks who come into this from the ham radio side get all excited
> about "that long ground wire", because of their experience with HF antennas
> .. but that long wire is a tiny fraction of a wavelength at 100kHz (lambda
> = 3km).

Most experiences with EMI and TCs (at least for solid-state driven types)
suggests that the fundamental frequency is not where the trouble is.  That
is, when the TC is just sparking into free air there usually isnt a
problem, but when the sparks find a large charge-accepting body (not even
necessarily ground, could be a large isolated object) then higher
frequencies are generated.  I measure big spikes in the 5-10MHZ range, but
also the entire spectrum above that is elevated, so 10s of MHz easily...
Any ideas on dealing with that?

> And what you really don't want to do is have your coil inside, and ONLY
> grounded to a stake in the ground outside.  Now the RF path *is* going
> through the building.

I believe that anything near a TC becomes part of its "RF" circuit just
because of mutual capacitance with the TC itself.  So being near the very
high dv/dt of a ground-sparking TC can induce currents in un-intended
paths, and your grounding system may not make enough difference to avoid
this problem.  An electrostatic shield (not truly a faraday cage) often
fixed this problem.  Sometimes your ground plane should go vertical so as
to capture more of the TCs field.

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