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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