[TowerTalk] Terrain Effects

[Michael Tope]

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..........................................