The problem John, with that experiment is it does not tell you what is happening just above the very lowest angle. By modelling you can see that the last lobe to reduce is that contained down near the horizon. We are also interested in the content between 2 degrees up to 20+ degrees. By moving the antenna away from the sea the energy contained in that sector reduces. For example on HF the content between 3-10 degrees is all important. 73 Clive GM3POI
-----Original Message----- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of j...@kk9a.com Sent: 02 April 2015 15:00 To: topband@contesting.com Subject: Re: Topband: Salt-Water Qth! 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. To: <topband@contesting.com> Subject: Re: Topband: Salt-Water Qth! From: "Ed Sawyer" <sawye...@earthlink.net> Reply-to: sawye...@earthlink.net Date: Wed, 1 Apr 2015 13:13:17 -0400 The best write up and data I have seen on this subject was the "team vertical" report on test done in Jamaica back about 10 or more years ago. As I recall, the vertical signal strength to low angle DX went up "dramatically" within 2 or less wavelengths of the edge of the high water mark and maybe leveled off as "fantastic" from within 0.5 wavelength. But further and further away past 2 wavelengths, the signal strengths dropped away and had very diminishing effects. I don't recall how far back before the benefits were disappointing but that article has the answers you need. Just scale it for 160 or 80M vs their 40 - 10M data. By the way, I used a vertical as 9M6/N1UR at Layang Layang island in the Spratlys in 1998. 40 and 30M performance was "amazing" but 20 - 10 was good but not great. The vertical was placed about 100 feet from the edge of the water. So it would have been just under a wavelength on 40, just over on 30, and 2 - 3 wavelengths on 20 - 10. Ed N1UR _________________ Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband