> At one point I had read a number for figuring out the gain you get by > increasing the height. Of course at the moment I'm unable to > locate that. > > ie: If I move the same antenna (VHF 2m) up a hill and gain 100' of > elevation, but it costs me the line loss (300'), did I really gain > anything.
It's not as simple as that. If the receiver and transmitter are line-of-sight with full Freslen clearance, going any higher buys you nothing, you just have more line loss. If the transmitter and receiver aren't LOS, going higher may help clear intervening terrain obstructions, but how much improvement is realized will vary depending on the obstruction. If going up an extra 100' helps you clear a near-by obstruction, the improvement can be significant. Coverage models that take terrain into an account can give a much better indication as to how much improvement might be realized in raising the antenna height. Field testing is even better, but obviously expensive if you have to install a new antenna to test with. Anything short of those is a guess at best. For those of you that haven't already seen it, there's kind of a neat site that can help give you some idea of what kind of terrain obstructions you're dealing with http://www.heywhatsthat.com . It will do a "panorama" where you give it all of the details for your site (location and elevations) and it will give you a panoramic view of the terrain. It will also do the equivalent of a point-to-point path profile, showing you the terrain along the path. It doesn't do any actual propgation analysis; it's aimed more toward outdoorsmen than engineers. It takes a little time to figure out how to use it - don't get discouraged if it seems confusing at first. To get an idea of what it does, go to the site and pick "K1WHS" (as an example) from the list of previously-saved paranoramas. Click somewhere on the panorama and the path will show up on the topo map. Click on "View Profile" over on the right side, then click again on the panorama and you'll see the point-to-point path profile between your site and the location you clicked. You'll also see there are markers (little triangles) for recognized landmarks, and elevation/lat/lon for those is also displayed. Poke around and you'll find more features. The site runs slow sometimes, so be patient. --- Jeff WN3A
