[DX] K9AY ja maadoitus

["T & M Ritola" <ritola@xxxxxxxxxx>]

Ehkäpä jotakuta kiinnostaa ao. Don Nelsonin erittäin hyvin asiaa kuvaileva teksti K9AY:n maadoituksesta (lainaus kyseiseltä listalta). Alkuperäisessä artikkelissaanhan antennin suunnittelija Gary Breed kirjoitti, että maadoituksen ei tarvitse olla mitenkään erikoinen, muutama maatasolanka riittää. Kuitenkin viimeaikaiset kokemukset, sekä omat että muiden, osoittavat aivan päinvastaista: maadoituksen on oltava erittäin hyvä (tai sitten kyseinen maaperä huippuhyvää antennin maadoitukseen):

Having used EWEs for several years, I noted the need for constant surface
watering during the dry months to maintain an adequate ground. I was hopeful
that the new K9AY, with the closed loop construction would be advantageous
(I'd already tried the flag; only recently the pennant). My experiences with
ground plane requirements differ from your statements, but I am will point
out one difference in the sites at the end of this message....

The units owned by John Bryant, Guy Atkins and myself are the commercially
available units from Andy Ikin.

The results we've seen out here on the West Coast, with the K9AYs installed
on former Sand Dunes a thousand feet back from the shoreline, gave variable
results over the past year using just the 4-wire counterpoise suggested by
Andy Ikin (Tests were made using Andy's units that three of us have,
including one 4-loop model)  in December, March, May, June, July, September,
and most recently, November.

 While some installation sites varied by a few yards over this timeframe,
most were sited identically within a foot. The K9AY worked well when the
sandy soil underfoot  was extremely saturated (including one installation in
a foot of standing water  December 1999, and performing better than the
onsite beverages) in the wettest of months(Dec,March,May) but in the drier
months of June, July and September the reception was marginal, never beating
the beverages onsite. At the site this past weekend, the K9AY performed
poorly so that John Bryant abandoned using it, and Guy Atkins and I did not
even bother to put each of ours up. (John noted only one reception where the
K9AY made a difference, and here it was not F/B but the apparent lower noise
floor in spite of lower signal strength, when compared to one of the
beverages ).

Since the K9AY antennas have the same mast height and installation wires,
identical heads and controls, constant lengths of cable , and identical
sites, this leaves only the ground as a variable. Since the material
underfoot  is packed sand (former dunes, about 350 meters from the high tide
line) over rock, the only variable is ground water saturation at the surface
(notably lacking in the past 6 months as we've had a dry summer and no rains
to speak of this winter).

In May, I installed my K9AY at the edge of the surf with approximately 900
feet of control wire/900 feet of RG8X, and compared it to a K9AY sited
within 100 feet of the building using 75ohm hardline. There were no
discernible differences in signal strength or F/B... we don't bother putting
out that much cable anymore. Proximity to the Ocean is a key ingredient to
successful TP MW dxing...we had hoped that signal strengths would be better
the closer you were but this proved to make no difference.

Down the coast in Oregon, Patrick Martin permanently installed his K9AY
about a mile from the Pacific Ocean. He's been doing some extensive testing
using TP signals to determine how well his F/B and side lobes are
controlled.  He's noted that an extensive set of driven ground rods (he uses
copper pipe as it does not rust away in the salt environment) rather than
the simple counterpoise makes a substantial difference. His record of TP DX
requiring nulling of US MW stations off the backsite(and down the coast such
as the station at Coquelle, Oregon)  is evidence of his ability. His initial
results with the K9AY, as shared with the rest of us at a recent DXpedition,
were said to  no better than his existing EWE. Further he was not getting
F/B nulling that was controllable. Improvement in grounds made a difference.
I trust Patrick's results and controlled experiments of adding a ground rod
at a time and making comparisions ("just how many ground rods are required?
Wish I knew when to stop" (he mentioned he was at 11 at this time), Patrick
speculated)

So, why do you get different results? I'll  hazard to make the following
speculation...

Its been years since I drove down Asoteaque(sp?)/Chincoteague Islands. Sure
was obvious you're on a coastal salt marsh with a lense of saltwater
floating on the freshwater water under the hard spots(plenty of
wells)...this is different than our Pacific Coast which is sand over rock.

I am betting that you'd have an exceptionally stable, excellent ground even
if you failed to put out the counterpoise.....  Wish we had this at the site
in Washington state<g> .. but then we'd have too many mosquitos.


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