From: John Rabson <john.rabson@numeo.fr>
Date: Tue, 3 Jan 2012 21:51:27 +0100
Message-Id: <50CB5299-C570-4ECC-9419-0D01FC708876@numeo.fr>
Cc: Robin Gape <robingape@ukfsn.org>,
 Chris Trayner <C.Trayner@leeds.ac.uk>
To: rsgb_lf_group@blacksheep.org
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Subject: LF: Improving Earth Resistance
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LF, Robin, Chris,

I am trying to reduce the resistance of the earth connection I use with =
my LF antenna. =20

The antenna consists of two wires each 16 m long, connected in parallel =
and with a height of about 6 m (it was 8 m but the structure has =
suffered recently in the severe gales).

The earth system consists of three wires radiating from the shack with =
angular spacings of about 60=B0. They run underground through plastic =
conduit for a distance of about 10 m and the remote ends are terminated =
in metal rods of the type used here to provide safety earth connections =
for mains installations.  The three wires are connected together at the =
transmitter to provide the earth.

The local geology is a mixture of granite and limestone with intrusions =
of calcite.

At present the resistance at 137 kHz at the feed point is about 150 ohms =
(plus of course some reactance which it is not difficult to cancel).  At =
a frequency of 980 Hz, I get a resistance of about 25 ohms, depending on =
whether there has been recent recent rain.

Reasoning that the much higher resistance at 137 kHz might result from =
the return current flowing through the ground rather than through the =
earth spikes,  I tried strapping the remote ends of the earth wires. The =
additional wire ran almost below and effectively parallel to the antenna =
wires.

This strapping made practically no difference to the 137 kHz resistance, =
so I had further thoughts:

1) laying down an earth mat or something like chicken netting, or the =
kind of metal mesh which is used for fencing.  Unfortunately, such =
things are expensive here (I estimate the cost would run into three =
figures in Euros), or

2) making the mat out of hookup wire or something similar. I have plenty =
of such wire. Would I need to join the wires at each crossing, and what =
spacing should I use?

Any suggestions, please?

John F5VLF