Another reason to consider the terrain is that if you raise it up more, will you be "overshooting" some of the users close in "under" (in the cone) of the antenna (ie: needing downtilt). my $.02 worth, Mike KB5FLX ----- Original Message ----- From: Eric Lemmon To: [email protected] Sent: Saturday, August 09, 2008 12:17 PM Subject: RE: [Repeater-Builder] Height Gain figure
Chuck, It's just not that simple. If the earth were completely flat, you would get some increase in range- but there are many other factors to consider besides transmission line loss. Most propagation calculation programs consider free-space loss, diffraction loss, and Fresnel loss separately. This is because one must consider the topography for the latter two factors, including the type of ground cover such as trees or shrubs, and if there are buildings in the way. That's one reason why the HAAT (Height Above Average Terrain) is more important than HAGL or HAMSL. Although high-end propagation programs like ComStudy can be a great help in evaluating candidate sites, nothing can replace a drive test with a Coyote or similar signal-survey instrument. Obviously, the higher your antenna is, the further away is the horizon and the greater is the line-of-sight distance. Here's a good reference on this topic: <www.repeater-builder.com/ge/datafile-bulletin/df-10003-01.pdf> 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Chuck Kimball Sent: Saturday, August 09, 2008 9:58 AM To: [email protected] Subject: [Repeater-Builder] Height Gain figure 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. I'll figure in the line loss, and adjust the hardline to minimize the loss, but I'm looking for the number to compare how much gain (in db) did I get with the increased height. So... Anyone know what number is for gain as a function of height? or know a reference I can look up. Thanks Chuck n0nhj
