You might want to consider a large vertical loop antenna? Then the earth
resistance is far less important.
73s
Roger G3XBM
-- Via my iPod Touch 4g --
On 3 Jan 2012, at 20:51, John Rabson <[email protected]> wrote:
> LF, Robin, Chris,
>
> I am trying to reduce the resistance of the earth connection I use with my LF
> antenna.
>
> 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°. 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
>
>
>
>
>
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