Topband: Salt-Water Qth!

[Kenneth Silverman]

Below, KK9A took a snip from my web page.  When I wrote that, I missed one
very important point: simple trigonometry.

Let's imagine a perfectly straight coastline, and we place a 160 vertical
1/2 WL back(520' for this discussion) to try and get that potential of 3 dB
of gain.  That "gain" is only seen for the point directly in front of the
vertical - i.e. 520' away.  Let's call this azimuth 0 (zero)

If your target destination is 45 degrees off zero azimuth, the distance
over land is 735'.  Based on or tests, that could be in the -3 dB zone! If
the destination is 75 degrees off zero, the distance over land is +2000'.

One quickly realizes that the distance over land varies, meaning the first
reflection point over water is farther away at any azimuth other than
zero.  And the enhancement of the salt water reflecting plane is quickly
diminished.

In hindsight, having the vertical as close to the water as possible (or
over it), will give you better overall performance in multiple directions.
And that's been the secret to our success.

One time in Jamaica I ran a test between two 10m verticals:  one right on
the sea wall, and another 100' back and spaced about 200' apart (enough
that they shouldn't have much interaction at 10m).  The vertical on the sea
wall was at least 2 S-units better than the one 100' back, and often much
more.

Going back to W3LPL';s comments, he was right on.  When placing a vertical
near the water, the goal is to minimize the near field loss (maximize
current return), while maximizing the far field reflecting surface in
multiple directions.

Going to an elevated site 1 mile from the shore line will have unknown
benefits.  But the vertical is likely to work better than a horizontal
antenna regardless.

73, Kenny K2KW
Team Vertical


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I did not recall seeing tests for verticals a wavelength or more way from
the sea so I checked the team vertical website and found the following:

John KK9A

While field testing the verticals this past summer, we decided to test the
effect of the land-water boundary on the pseudo Brewster angle. Since our
receive site was elevated less than 1 degree across the bay, we could see
any change in the low angle energy. To our knowledge, there has not been
any published tests of this kind. The goal was to see how far from the
water the vertical would loose the benefit of the salt water on the pseudo
Brewster angle. The tests were done with a 20m ZR vertical, and we moved
the antenna away from the water in 5' steps. The water's edge was
considered the reference point. As the vertical was moved back from the
water, there was little change until we came close to 1/4 wavelength from
the water. At that point there was a 3 dB increase in signal level! Moving
farther, the received signal level dropped, indicating a loss of low angle
energy. This was most significant at 1/2 wavelength from the boundary,
being down about 3dB from the waters edge. Moving farther back to 3/4
wavelength, the signal picked up again, to more than 2dB enhancement from
the water's edge. We could not move the antenna farther due to
obstructions. During the tests, we did not believe the data, and reran the
test. We also observed the same results on the second test. At the time we
only had 20m antennas, so we could not confirm that enhancement was truly
frequency dependent. But based on these results, more testing is
warranted.