From: Chris Trayner <C.Trayner@leeds.ac.uk>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Date: Tue, 2 Jun 2009 09:49:01 +0100
Thread-Topic: 136k/500k Grounding experiments (long!)
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Dear James and others,

Thanks for your very interesting post. A couple of comments.


> Since the wire mesh would be quite a convenient earth system to use for an
antenna over a paved area, or on rocky ground, I tried laying it on the
concrete driveway:

The mesh might not be as good on a rocky hilltop. There is probably conducti=
ve soil under only 10cm or so of concrete drive, whereas a mountain may be i=
nsulating rock all the way down to Old Nick.



> For portable antennas, it is often difficult to drive long ground rods int=
o
the earth. It seems that short ground spikes, like the tent pegs, or
metallic conductors laid on the surface of the ground, do not make a very
good ground connection.=20

Have you tried arrays of tent pegs? We meet the same problem with cave radio=
 - it's normally done on limestone, with very shallow soil, and driving long=
 spikes in is virtually impossible. What does work well is (say) half a doze=
n tent pegs connected together. It doesn't seem to matter much whether they=20=
are in a straight line, a circle or whatever, as long as they are far enough=
 apart. There are recommendations for the minimum separation, which I forget=
, but keeping them a couple of peg lengths apart should be adequate.



For mountain top experiments, there is one comparison which might be worth t=
rying. One of our cave radio people noticed years ago that Loran reception w=
as far weaker on peat than on bare limestone. Since she said this, I've ofte=
n noticed that it's far weaker on deep soil than on the thin soil over limes=
tone. Cave radio aerials are completely different from yours, so I'm not sug=
gesting the difference would be in the same direction. My guess is that you'=
d get a better aerial on (ideally wet) peat than on bare rock.


73,
Chris G4OKW