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ground problems
From: Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: bert.hickman-at-aquila-dot-com
Sent: Tuesday, September 23, 1997 9:08 AM
To: Tesla List
Subject: Re: ground problems
Tesla List wrote:
>
> From: Geoff Schecht[SMTP:geoffs-at-onr-dot-com]
> Sent: Wednesday, September 17, 1997 3:24 PM
> To: Tesla List
> Subject: Re: ground problems
<SNIP>
> > >
> > > Hello All:
> > >
> > > I've used soldered-together sections of "chicken wire" as a form of
> radial
> > > system (counterpoise) for my vertical ham antennas from time to time.
> It
> > > works fairly well in that application and is quite cheap. Any
> > > opinions/experience from other list members about how this might work
> with
> > > a TC that needs a grounding system? It's an RF ground, though, not a
> safety
> > > (green-wire, in the US) ground.
> > >
> > > Geoff (NQ7A)
> >
> > Geoff,
> >
> > Good point, Geoff. I considered suggesting a counterpoise, but it wasn't
> > clear if Mad Coiler's apartment was wood/frame construction or steel
> > beam/concrete. A counterpoise could work very well, especially if Mad
> > Coiler lived on the first floor. Since Mad Coiler lives on the second
> > floor, an elevated counterpoise would still work very well if he was in
> > a steel/concrete building, and less so if he lived in a wood/frame
> > environment.
> >
> > -- Bert --
> >
> Hi Bert:
>
> I suppose that any counterpoise is better than nothing but at the
> frequencies a TC operates at, it's hard to imagine a 1/4 wave radial
> grounding system being installed in a 2nd story apartment! I've read about
> tuned radial systems for limited-space applications....I wonder if
> something like that would be applicable to a small counterpoise system like
> a "chickenwire carpet"? Tuned radials probably only make sense when you're
> dealing with a coherent oscillator due to their relatively high Q (and a
> coherent oscillator is something that a TC is _far_ from :) ).
>
> A chicken wire counterpoise should at least provide an efficiency-enhancing
> current node point for the cold end of the TC and it gives the arcs
> something to strike other than the TV, sofa, cat, etc.
>
> Geoff
Geoff,
A relatively small counterpoise will work with a small coil (see my
earlier post to Randy). Unfortunately, the cold end of the coil, unless
tied to low impedance RF ground, tends to be quite "hot" electrically.
The counterpoise on a small coil will easily develop thousands or even
tens of thousands of volts RF, with relatively large amounts (amperes)
of current available if it should arc to ground. Fortunately, for TC
use, a counterpoise doesn't need to be anywhere as large as a 1/4 wave
radial grounding system. A few times the diameter of the toroid or the
height of the coil (whichever is greater) should suffice for relatively
good electrostatic coupling to the resonator/toroid.
Safe counterpoisein' to you!
-- Bert --