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Re: Ground ground ground
Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
Folks.. we're not trying to dissipate hundreds of kilojoules from a
lightning strike or trying to broadcast a radio signal. We're, to a first
order, trying to create the "other plate" for the capacitor formed by the
topload. Low resistance, in the neighborhood of the coil, where the RF
currents are, is important. Run ETesla and see where the field is
strongest...that's where you need a good low resistance/low inductance ground
Reasonably low resistance to earth is good, but you're not building an
antenna (I hope), so you don't need a good connection to the ground (via
the ground) hundreds of feet away.
Reasonably low resistance to earth is also useful for safety reasons and to
provide a path for the RF current from the base of the secondary that
doesn't share the "green wire" or power lines.
I would think that a suitable counterpoise of mesh (comparable in
resistance/impedance to the earth) under the coil that extends several
topload heights (above ground, not secondary length) in radius would serve
as well as almost anything else. That big counterpoise would be
capacitively coupled to the earth quite effectively.
Let's say you've got a coil where the topload sits 2 meters off the ground,
so you've built a 4 meter square counterpoise (i.e. about 13 feet on a
side). Lets further assume that the counterpoise is 15 cm from the "true
ground" (allowing for limited conductivity, rugs, etc.). If we assume that
the "true ground" is a perfect conductor, as is the counter poise, then
we've just built a big capacitor. Worst case would be if the dielectric
constant is 1.
C= 8.85E-12 * 16 /0.15 = 944 pF
compare that to the 100 pF or so "topload capacitance"
Consider the circuit like this...
TopLoad - C1 - counterpoise - C3 - ground
Topload - Lsec - counterpoise
Topload - C2 - ground (not covered by counterpoise)
Most of the RF current flows through the circuit Topload-Lsec-Counterpoise-C1
Some will flow through the path Topload - C2 - ground - C3 - counterpoise,
I'd venture to say, without actually calculating it, that C1 is about 1000
times as big as C2 (most of the field is in close), this is a MUCH smaller
The reason to drive the stake deep is to get low resistance to "the mass of
earth", especially since the surface tends to dry out and it's resistance
increases. If you live in the desert on sand, driving the stake
arbitrarily deep probably isn't going to do you a bunch of good (other than
it forms a capacitor...)
Tesla list wrote:
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi Matt,
> 6-8" into moist soil? First of all moist soil doesn't stay moist for long
> and second when I read your 6-8" meaurement I first thought it was FEET
> then I saw the ".
> I have been told that the ground rod should be 4 FEET or more into the
> ground. That's what I did for my satellite dish anyway.
> So when I get around to testing my TC I will no doubt add a ground rod DEEP
> into the ground by where I'm going to operate it. Here in South Florida the
> ground is solid coral rock so I'm lucky to get 4 feet into the ground.
> Hope this helps.
> Getting closer...........
> Ft. Lauderdale