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## Re: [TowerTalk] Terrain Effects

 To: "Michael Tope" ,"TowerTalk" Re: [TowerTalk] Terrain Effects "Jim Lux" Fri, 3 Dec 2004 07:06:27 -0800
 ```To my recollection, HFTA does geometric theory of diffraction, in a 2D plane. So there is a big difference between a flat 3 degree slope and a 1000 ft high ridge 4 miles away. The key here is the size of the features in terms of wavelengths: knife edges vs rounded mountain tops. It's also 2D, so a conical needle sticking up would model the same as a circular ridge would model the same as a straight ridge, even though in real life the propagation would be different. I don't think it works as far out as 30 miles, either (although, perhaps the limit is on the number of points defining the terrain). I don't know if it takes into account the curvature of the earth (which would be important at 30 mi kinds of distances). ----- Original Message ----- From: "Michael Tope" To: "TowerTalk" Sent: Thursday, December 02, 2004 11:37 PM Subject: [TowerTalk] Terrain Effects > Using tools like TA has anyone compared the effects of > very close-in terrain to distant horizon clutter. Specifically > which would be more detrimental to take-off angle, an HF > antenna mounted directly over a gentle 3 degree upward > slope for a mile or two, or that same antenna mounted over > flat terrain which looks at a range of +3 degree high mountains > say 30 miles off in the distance? Simplistically, it seems > that these two cases would be about equal in terms of their > impact on TOA, but the high mountains might provide > some interesting diffraction effects, whereas the flat local > slope would probably just skew the antenna elevation > pattern up +3 degrees. > > I was looking at a site (rural setting with a very low noise > floor) that I was considering for portable operation that > exhibits a gentle upward slope toward the SW with a > nearby visual horizon (+0.5 miles away) that is approximately > concident with the mountains that are ~30 miles away. Both > the close-in and far distance visual horizons sit at about 2.5 > degrees elevation (e.g. you can see the mountain ridges > peaking just slightly above the close-in visual horizon). In > other directions the terrain is very favorable. Any thoughts > on this? > > Thanks, > > Mike, W4EF.......................................... > > > _______________________________________________ > > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Terrain Effects, Michael Tope Re: [TowerTalk] Terrain Effects, Jim Lux <= [TowerTalk] Terrain Effects, William Barney Stacy Re: [TowerTalk] Terrain Effects, Michael Harris