You really need to be no more than 1/4 wave IN THE DIRECTION of interest to
see any benefit. Even at 1/4 WL back, at 90 degrees perpendicular from the
water, it's all land. 180 degrees from the water its all land. The
farther you move the antenna back, the greater the land-water distance is
at the azimuth not pointed at the water.
Team Vertical has done empirical tests with verticals, and the work in NCJ
was a modelling exercise loosely based on our work. One
specific empirical test involved 2 full length 10m vertical dipoles. One
1/4 from the water, another 100' from the water. The one 100' back was on
average 2-7 S units weaker in directions over the water. I seem to recall
a delta of about 9 S units in once case.
We also did testing moving an antenna away from the water and found peaks
and nulls based on distance. 1/4 WL had about a +3 dB peak compared to
right at the waters edge. 1/2 WL back was about -2 dB, and 3/4 WL was
about +2 dB peak. The water/land reference was a sea wall, so it was a
very steady boundary (vs a beach with tides), and the testing was across 17
miles of the San Francisco Bay, with a take off angle of fractions of a
degree (in the Pseudo Brewster angle). While those gains/losses are real,
chasing them in your design is pointless since any change in tide will
change the distance. And remember, the gain/loss is based on distance to
antenna, which changes on the azimuth and tide. So that gain/loss is only
effective in a very small azimuth. After installing a few hundred
verticals by the ocean, we put them as close to the water as possible
to maximize overall benefits in maximum directions.
Hundreds of feet back will have no advantage to verticals, especially over
lossy ground.
N6BV once did some modeling for a site where we couldnt get 1/4 WL from the
water (maybe 100-150' from the average tide distance??), but the site was
elevated about 25'. We were surprised that his modeling of this site
showed the high angles being suppressed but not the low angles. So there
may be some merit to an elevated QTH somewhat farther from the water.
73, Kenny K2KW
Team Vertical
> Hi All..not sure if this is better suited for TOWERTALK or CQ-CONTEST, but
> since my interest is primarily contesting, I'll post here first.
>
>
>
> Wife and I are looking at waterfront properties in VE1/9/VY2/VO1/2.
Ideally
> I would like to locate my antennas inland (in the trees)
>
> a little ways to (hopefully?) minimize salt water corrosion and/or
> 'potential' problems from neighbours.
>
>
>
> If I was to locate a yagi up 40' of tower, (or say a Butternut vertical
10'
> agl) or even a 6m yagi on a short tower inland does it matter?
>
>
>
> Let's say the rocky land itself was 20' ASL and 400-500' away from shore,
is
> there any benefit seen in being "close" to salt water or is all the
benefit
> (whatever that may be) seen only if the salt water is nearly underneath
the
> antenna?
>
>
>
> Thanks much,
>
>
>
> Mike VE9AA
>
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