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
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