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Re: LF: Re: Ground

To: [email protected]
Subject: Re: LF: Re: Ground
From: pat <[email protected]>
Date: Sat, 19 Sep 2015 21:36:54 +0100
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I would tend to agree with Alan. My limited experience has tended to suggest that treating the 'sky-borne' wires of an antenna system as one 'plate' of a capacitor of which the other 'plate' is the Earth and the rest of the universe has made a certain amount of sense.

73

On 19/09/15 12:26, Graham wrote:
In saying that , I have the idea capacity to ground, may be more important than 'resonant' length , besides , in the ground , the effective length must be longer , as the Vfactor of the ground , is not the same as free space ?

There are some , huge signals rolling Down under , where the stations are located in the outback, 100's of miles from water , with nothing but 'dry land' A circular perimeter fence some miles long seems to do the trick

Bob over in NY State , uses wire mesh to cover his front lawn , granted bigger than the average , but again , capacity as opposed to resonance ?

May be , just make a large ground 'mat' and tune against that ? loop couple the ATU as the tuner earth and the equipment will not be the same

Or -If there is the height , use a  Loop  ?

73-Graham
G0NBD


NB  -   Steel tape  ?

--------------------------------------------------
From: "Alan Melia" <[email protected]>
Sent: Saturday, September 19, 2015 11:24 AM
To: <[email protected]>
Subject: LF: Re: Ground

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






--
73 de Pat G4GVW
QTH Nr. FELIXSTOWE
EAST COAST UK


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