I like your definite answer: It Depends! Truly!
It unfortunately seems a bit complex to make a rule other than build it and
see! Your
experiences match what I would expect, but there seems to be more at work than
just
distance to seawater. I built several unsuccessful beverages in Yangon next to
water-
they worked but not all that usefully - and parts of the spans were unavoidably
over
water.
Ducie island is only a few feet above sea level at the highest places, and the
lagoon has
obvious flows from the outside sea to the lagoon. No point could reasonably be
expected
to be more than 10 feet above sea water under the lava and coral We built an
array of
classic 2 wire beverages from ladder line- 500 to 1000 ft, and one phased array
of two 2
wire beverages.
I have used stations with REALLY good classic delectable beverage systems -
selecting
beverages is like turning a 10 element beam on 20 meters, if you aren't pointed
at it, you
don't hear it.
The Ducie beverages worked fantastically well - easily 20+ dB directivity,
repeatedly -
with a local noise floor of zero zero, listening on the beverages was truly
amazing. we
have recordings- you hear a weak weak unreadable signal in the low noise,
change beverages
and the signal shoves the S meter to 9+ - that's more than 20 dB by a lot, but
it is on
record, and without that directivity to reduce the gargantuan static crashes,
we would not
have done anywhere as well as we did. I will not forget the sight of Dietmar
stumbling
out of the topband tent at dawn with blood running out of his ears muttering,
No
Beverages, No contacts!
You build a beverage as well as you possibly can, get the terminations done and
right and
match it correctly, and the strong majority of the time you will be rewarded
with a
listening treat on topband, but there is no guarantee. BUT, at worst you have
a low noise
Omni antenna, not useful for sorting things out, but can help if there is
locally
propagated noise
Build it and see! Unfortunately, its the only certain answer. Dry sand,
Coral, Lava,
even moist loam, all seem to be suitable for changing the surface velocity
factor, and
that's what makes a beverage work- it can be best labeled as a differential
traveling
wave antenna.
Robin Critchell, WA6CDR
----- Original Message -----
From: "GEORGE WALLNER" <aa7jv@atlanticbb.net>
To: <topband@contesting.com>
Sent: Friday, April 22, 2011 06:01
Subject: Re: Topband: Beverages near the ocean
> On Thu, 21 Apr 2011 09:36:33 -0600
> Mike Fatchett W0MU <w0mu@w0mu.com> wrote:
>> I was reading ON4UN's Low Band DXing Book beverages not >working near the
>> ocean...
>
> Mike,
>
> Here is the definite answer: it depends.
>
> I have built a number of Beverages near the sea, with
> varying results. On VK9WWI (Willis Islets) the Beverage
> ran parallel about 100 yards from the shore and 2 meters
> above the high tide line. It worked. On Mellish Reef
> (VK9GMW), we tried three Beverages that were close to the
> water. Two did not work at all. The third one was 120 m
> long, ran across the narrow island and had its ends about
> 10 meters from the water's edge. It was near useless on
> 160, but OK on 80 and great on 40. On TX3A, we built three
> Beverages. Again, two that were close to the water,
> running alongside the beach, did not work. A third, one,
> which was about 180 meters long and ran diagonally across
> the island's rocky spine, with its ends about 20 meters
> from the water's edge and about 6 meters above the high
> tide level, was an excellent performer.
>
> My tentative conclusion is that if the Beverage is away
> from the water by more than .3 wavelength, and there is no
> salt-water in the soil under the Beverage wire (!), it
> will most likely work, even if the ends are close to the
> water's edge. Keep in mind, however, that many coastal
> areas and low islands have a salt-water table as little a
> foot under the soil. A Beverage there will most likely not
> work no matter how far from the sea.
>
> 73,
>
> George, AA7JV
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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