On 9/25/12 3:58 AM, Colin Heath wrote:
Your best bet Is to sink a plate in the ground or to drive 6 or 8 shorter posts into ground then parallel then up.
I think if you do the calculations, you'll find that even with fairly conductive soil, it's not nearly as good as laying out wires/mesh on the surface.
that is, even if you drive a bunch of rods spaced out, the wire leading to the rods would be a better RF "ground" than the soil and rods.
tesla coils are not antennas, nor are they lightning rods. Dissipating energy (lightning ground) or radiating energy (antenna ground) aren't what you're looking for.
What you want is a big conductive plane *close* to the coil, where the field from the top load can interact with it. I am amused by folks running a 50 foot ground wire outside to a rod for their 4 foot high TC. Whether the ground wire is connected to anything at the far end has very little effect on the performance of the coil.
There are plenty of large TCs in spaces without a good connection to "earth" ground: on the upper floors of museums, hanging from the rafters, etc.
Yes, you need to connect the RF counterpoise (to use a better word) to earth ground for safety reasons, but that connection can have a pretty high RF impedance (and, in fact, probably should.. to reduce carrying EMI into the building's grounding system)
those who cite the example of Wardenclyffe and the huge pit should be aware that our knowledge of electromagnetic theory and it's practical application has greatly improved since then; and, NT was actually deliberately trying to get a good "earth" connection (that is, he was building an antenna, not a display coil).
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