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 ----------------------------------------------------------------------------------- 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. _________________ Topband Reflector Archives - http://www.contesting.com/_topband
