On Fri, 20 Apr 2007 07:44:52 +0100, "Richard"
wrote:

Before you dig up the earth, you might try a quickie fix, a 1/4 wave
elevated counterpoise, run from your tuner ground nut, out the window,
hung from the side of the house or whatever. That's all it took to
provide a 1:1 swr for my last "long wire," a 3/4 wave wire for 20
meters.

bob
k5qwg


"Jim Lux" wrote in message
...
Richard wrote:
I want to put up a "long wire" with the feedpoint at one of the back end
corners of the garden. I need a good RF ground.

If I got a length of 6 foot wide copper sheet and made out of it a
cylinder,
say 6 feet in diameter, and then placed that cylinder in an upwards
position
in the ground, the top level with the surface, would that be a good idea
for
trying to acheive a decent RF ground? Also, is there anything I could
place
around the cylinder to better the conduction between the cyinder and the
earth around it? Should I drill holes in the cylinder so I can pour water
into the cylinder to keep the ground around it moist?

Would I still benefit from some radials in the ground?

My garden's about 33 foot long, 21 foot wide. Ground gets rather rocky
and a bit sandyish at about 9 inches or so from the surface.TIA.

That might be overkill.. Why not spend the money on a spool of copper
wire and lay radials. For RF purposes, large area of coverage is more
important than low impedance at a particular point. You want to improve
the apparent conductivity of the soil over as much volume as you can.
Think of your grounding system as (partially) a big leaky capacitor to
"the earth".. you want to spread the RF current out over as large an area
as possible, and radials are probably the easiest way to do it. There's
nothing special about how you lay the radials or their length (they're in
dirt, so they're not tuned or resonant.. just wires).

Maybe a 3 foot wde cylinder would be adequate.

One thing: Why are radials so effective? They are not resonant
counterpoises, and from the aspect of surface area in contact with ground,
radials have hardly any surface area that "connects" with "the earth". I can
understand if I put in a 20 foot by 20 foot copper plate flat in the earth
that would "connect" to earth quite well, I mean the measured ohmic
resistance to "the earth" could be quite low. But also capacitive coupling
would be low too. But radials have no real capacitive coupling to "the
earth" neither much surface area in contact with "the earth". So it confuses
me as to why they are so effective.

BTW, since it looks like many wires in the earth are as good as a plate,
perhaps I could put in a wire mesh grid about 1 foot under the soil over the
whole garden . I'm digging up the garden anyway. Perhaps with some ground
stakes here and there connected to the grid, although maybe not necessary.