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On 12/6/13 6:50 AM, jhowson4@xxxxxxxxxxx wrote:
Question about a counterpoise,
Does one want to ground it to the greenwire ground or not? found an
article on earthlink (
http://home.earthlink.net/~jimlux/hv/tcground.htm ) which says yes
connect a counterpoise to safety ground and then in the next section
says but don't let any rf travel through safety ground, which at
least seems partially contradictory to me. Would someone care to
clarify this for me?
ANything that you might "touch" needs to be "green wire" grounded, in
case you get a short from, e.g., your power transformer secondary to
the counterpoise (not uncommon when a spark jumps to the primary.. the
spark is a low impedance connection).
However, you don't really want to feed RF (which is what the
counterpoise is for) back into your building grounding system. So, it
would be ok to put an RF choke in the connection between the
counterpoise and building safety ground.
The idea, really, is to not make the building and surroundings part of
the RF circuit, which can only cause problems (killing appliances and
the like). So you give the RF a good place to go: a nice low impedance
plane under the coil (or a cage around the coil), and keep that RF from
going other places.
The other reason to ground the counterpoise to the building ground is so
that you don't get sparks from the counterpoise to ground.
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).
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.
Is it the case that the counterpoise actually absorbs the rf energy
(absorbs in a sense that its no longer traveling to the ground), and
the ground just serves as to hold the counterpoise at ground level,
as well as existing for purely safety purposes?
yes. so you don't spark from counterpoise to ground.
Thanks, John "Jay" Howson IV
"Why thank you, I will be happy to take those electrons off your
hands."
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