References: <50CB5299-C570-4ECC-9419-0D01FC708876@numeo.fr>
From: Roger Lapthorn <rogerlapthorn@gmail.com>
In-Reply-To: <50CB5299-C570-4ECC-9419-0D01FC708876@numeo.fr>
Message-Id: <384312BC-AEB6-4F18-BA5C-683F1DF80B5C@gmail.com>
Date: Tue, 3 Jan 2012 21:51:22 +0000
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
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Subject: Re: LF: Improving Earth Resistance
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You might want to consider a large vertical loop antenna? Then the earth res=
istance is far less important.=20

73s
Roger G3XBM

-- Via my iPod Touch 4g --

On 3 Jan 2012, at 20:51, John Rabson <john.rabson@numeo.fr> wrote:

> LF, Robin, Chris,
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> I am trying to reduce the resistance of the earth connection I use with my=
 LF antenna. =20
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> The antenna consists of two wires each 16 m long, connected in parallel an=
d with a height of about 6 m (it was 8 m but the structure has suffered rece=
ntly in the severe gales).
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> The earth system consists of three wires radiating from the shack with ang=
ular spacings of about 60=C2=B0. They run underground through plastic condui=
t for a distance of about 10 m and the remote ends are terminated in metal r=
ods of the type used here to provide safety earth connections for mains inst=
allations.  The three wires are connected together at the transmitter to pro=
vide the earth.
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> The local geology is a mixture of granite and limestone with intrusions of=
 calcite.
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> 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 fr=
equency of 980 Hz, I get a resistance of about 25 ohms, depending on whether=
 there has been recent recent rain.
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> Reasoning that the much higher resistance at 137 kHz might result from the=
 return current flowing through the ground rather than through the earth spi=
kes,  I tried strapping the remote ends of the earth wires. The additional w=
ire ran almost below and effectively parallel to the antenna wires.
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> This strapping made practically no difference to the 137 kHz resistance, s=
o I had further thoughts:
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> 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 ex=
pensive here (I estimate the cost would run into three figures in Euros), or=

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> 2) making the mat out of hookup wire or something similar. I have plenty o=
f such wire. Would I need to join the wires at each crossing, and what spaci=
ng should I use?
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> Any suggestions, please?
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> John F5VLF
>=20
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