Re: [TCML] Alternate RF Ground

[Jason Johnson <jasonmsusolar@xxxxxxxxx>]

Grant,

Last year I had to run my coil indoors at a bar that was full of expensive
A/V equipment. Of course no good ground was available, but we were on the
first floor so I made a simple wire counterpoise (just 4 wires, each about 8
feet long) spread out and taped to the concrete floor in a cross pattern.
The center connection of this counterpoise went to both the secondary coil
base and to a cold water line about 25 feet away. All wire was 20 gauge
tinned copper with PVC insulation, except the base connection to my
secondary which is two 18 gauge wires in parallel (speaker wire pair just
twisted together at both ends).

The idea was that the counterpoise couples the RF energy into the ground and
the otherwise feeble ground connection (to the water line) is just there to
keep the couterpoise from floating at some arbitrarily high voltage. The
counterpoise wires, BTW were routed about 1 foot away from all of the audio
connections at the closest point (but generally as far away as possible,
also run off a separate 120V circuit). Also, I checked that the water line
was in fact grounded with a multimeter and a nearby 120 volt outlet.

Sparks were about 4 foot long (~1600 watts input, 2 MOT powered with "Terry
filter" on HV side), ground targets were a couple of fluorescent tubes. RFI
was worse when the coil was allowed to spark directly to the grounded bulbs,
but was still not bad in either case (i.e. I didn't fry anything or reboot
any computers). I believe that this is the case in general though, that when
you get low impedance ground sparks the interference is worse than with free
air streamers.

>From personal experience I would say that you are better off covering a
large area with low percentage filled (i.e. a few fine wires spread on the
floor) than a small area with a high percentage filled (i.e. a sheet of Al
foil). Wires are also much easier to wind up when you are done, and are
literally flexible enough to be used in many situations, as compared to
chicken wire or the like.

As always however, YMMV.

- Jason


On Mon, Apr 11, 2011 at 4:42 AM, Grant Visser <freeekyg@xxxxxxxxx> wrote:

> Hi all,
>
> I have a 2KW SSG coil which I need to run in a conference centre
> environment where I will have no access to a solid dedicated RF ground
> point.
>
> I could of course connect it to the nearest fire extinguisher outlet
> or even the 3phase ground but I would be VERY concerned about inducing
> spikes and RF noise into sensitive equipment elsewhere in the
> building.
>
> Thus I am looking for alternate solutions and am hoping someone on the
> list may be able to help.
>
> I read somwhere that it is possible to use a spare secondary coil as a
> dummy load on the RF earth???
>
> Any suggestions or ideas would be greatly appreciated!
>
> PS. I also need to keep all RF and EM emissions to an absolute minimum
> as there will be a lot of sensitive equipment being used in the same
> area like video projectors, amps, UHF wireless microphones, computers,
> DMX controlled lighting, etc.
>
> Keep em sparks flying
> Grant
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