Hello Marcin,
My experience on 2200m seems to agree with Alan's suggestion.
I buried 6 sections of 30cm wide copper mesh at about 20cm deep,
10 to 15m long, totaling about 70m.
My first experiment was with a radiator 20m long hung from 22m tower,
at at least 4m horizontally spaced from the tower.
When I connected each section, and their combinations,
I found that some section worked better than others.
i.e. lower feed point resistance (measured with Antenna Analyzers, AA-54,
AA-600).
The tendency I found was;
Those directly visible from the radiator were good.
Those hardly visible from the radiator were rather useless,
i.e. did not lower the feed point resistance when connected.
Those with the house or heavy trees in between made it worse,
i.e. INCREASED the feed point resistance when connected.
I have to say also, that the tower as a ground-rod was
as good as the buried copper mesh ground.
The loss resistance at 136kHz (coil resistance removed) went
from 20.45ohm with tower-ground only
to 13.21ohm with best combination (tower and copper mesh).
The loss did not halve, after 5 days of exhausting hard work.
Obviously, the tower-ground was directly visible from the
entire length of the radiator.
The earth-resistance meter measurement said (at 820Hz, the standard)
15.7ohm with the tower-ground only,
5.6ohm with all connected (the more the lower, of course).
I had soil ground.
The resistivity was measured to be 98 ohm-meter at 136kHz,
using Open-Wire-Line method by N6LF.
The earth-resistance meter values and the
actual feed point resistance measurement did not correlate.
Later, I mounted my radiator on top of my house.
The effectiveness of each segment changed, but the tendency
remained the same.
Based on the above, I support Alan's suggestion :
"measure and see", or "try and select".
BTW, I do not have much knowledge on the depth of the buried wire,
except that the skin depth of the soil at 136kHz is usually 10m or more.
I rather thought my copper mesh should be in good contact with the soil,
and that they will not come up uncovered to trap someone's feet,
after rain for example, and choose 20cm (which varied greatly in reality).
Maybe, little "resistive-soil" between the radiator and the buried-wire
is suggested.
Hideho YAMAMURA / JF1DMQ
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of pat
> Sent: Sunday, September 20, 2015 5:37 AM
> To: [email protected]
> Subject: Re: LF: Re: Ground
>
> 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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