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LF: Re: Ground

To: <[email protected]>
Subject: LF: Re: Ground
From: "Alan Melia" <[email protected]>
Date: Sat, 19 Sep 2015 11:24:24 +0100
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Sadly Marcin there is probably no answer to your question. Over the early years of LF activity I tried to make sense of the various "recipes" that were floating around. I found that in general they don't necessarily work for you. The reason being that the local ground condition varies widely at different locations and in various weather patterns. The commercial site designs bear little relation to amateur dimensions.
Eventually I came to the conclusion that the only way to proceed was to do
measurements at your site and see what strategy is the best. The "best"
solution will depend very much on the type of antenna you intend to erect
above it. The idea that quantities radials are necessary by comparision with
160m and commercial systems is a myth. To be reasonably effective radials
need to me of the order of 1/8th wavelength long at least. This is way
beyond practical amateur site dimensions. Running one conductor along the
ground under a top-wire (of say an inv L) has a positive effect, but often
running out more can be a waste of effort and money. Again it depens on your
local conditions. These measurements proved that after you reach the
diminishing returns point of ground stakes and counterpoises, then
increasing the antenna capacity has most effect. It seems counter-intuitive
but putting more horizonal wire in the air reduces the "ground loss" !! In
my case doubling the capacity halved the "ground loss".
At LF in amateur situations the loss resistance is very often not due to
grounding but to the effect of the surrounding environment. Commercial
station chose open land and do not try to install antenna in the middle of a
forest. Amateurs have to deal with building and foliage with the near field
range of the radiator. There is no advice in the manuals about this and the
condition is not modelled well (or at all !) in simulator packages.
Alan
G3NYK


----- Original Message ----- From: "Marcin" <[email protected]>
To: <[email protected]>
Sent: Saturday, September 19, 2015 8:44 AM
Subject: LF: Ground


Hello,

I'd like to design a ground for 136kHz/472kHz. I have a few hundred metres
of steel tape at my disposal for this. I'd like to find out how deep into
ground 136kHz and 472kHz respectively can go?
How deep do I have to dig the tape for 136kHz and for 472kHz, or what would
suit both frequencies?

Thanks in advance.
73! Marcin SQ2BXI



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