I have two close-spaced (30 km) QTHs
One is inland, 30 km from the coast, city location, HF horizontal
antennas 40m high (top of building)
The other is just 200m from sea line, sub-urban location, similar
antennas 30m high on tower
I can simultaneously monitor signals from each receiver at any of those
2 locations.
Seaside QTH is always better in every direction, specially towards the
sea, but not just in those directions.
Rather than higher level signals on the beach QTH (which is certainly
the case, but just a few dB), main difference is lower noise, and it is
S/N that makes the difference.
I attribute difference between QTHs to:
- Slightly higher signal levels specially towards the sea (no
obstructions, efficient reflections) more evident when band is opening
or closing
- Far lower noise levels (less QRN from less populated area), specially
when beaming towards the sea (no man-made noise sources there!)
As for verticaly polarized antennas, that lower Brewster angle really
helps. I had a friend of mine last CQWW CW at the seaside QTH work 113
countries on 80m with a simple inverted V, when hitting 80 was a big
success in the past from inland locations.
FWIW
Juan EA5RS
-----Mensaje original-----
De: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] En nombre de Jim Lux
Enviado el: martes, 18 de enero de 2005 20:41
Para: towertalk@contesting.com; Pete Smith
Asunto: Re: [TowerTalk] horizontally polarized antennas and salt water
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: "Jim Lux" <jimlux@earthlink.net>; "Stephen Reichlyn"
<Stephen.Reichlyn@ryansci.com>; <towertalk@contesting.com>
Sent: Tuesday, January 18, 2005 11:00 AM
Subject: Re: [TowerTalk] horizontally polarized antennas and salt water
> At 11:21 AM 1/18/2005, Jim Lux wrote:
>
> >Pete Smith wrote:
> > >
> > > It does, but not a bunch.
> > >
> > > I quickly modeled a 40m yagi at 104 feet over average ground
> > > versus
salt
> > > water. Forward gain went from 11.86 dBi (avg) at 18 degrees to
> > > 12.45
dBi
> > > (salt). Takeoff angle, interestingly, went up one degree for the
better
> > > ground plane. Moving the antenna down 6 feet over salt water
> > > moved
the
> > > takeoff angle up 1 more degree, from 19 to 20 degrees.
> > >
> >
> >Just as an idle question.. I wonder if the gain change is due to a
pattern
> >shape change (narrower main lobe), or due to a reduction in losses.
> >The average gain number would tell you, since it's integrated over
> >all look angles.
>
> It appears to be reduced losses. The average gain over salt water
is -0.06
> dB; over average ground it is -0.96 dB, per NEC-2.
Very interesting...In fact, the directivity is less with the salt
water... The difference in foward gain is about 0.5 dB, but the
difference in loss is 0.9 dB, so the "extra" 0.4dB must be going into
making the main lobe "fatter".
All in all, though, such a small difference that you'd never see it in
real life.
Jim, W6RMK
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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