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Re: [TowerTalk] Trees, Mountains, 15 degrees...

To: "Michael Tope" <>,"Pat Barthelow" <>, <>,<>, "Pete Smith" <>
Subject: Re: [TowerTalk] Trees, Mountains, 15 degrees...
From: Jim Lux <>
Date: Mon, 24 Jan 2005 17:49:58 -0800
List-post: <>
At 05:36 PM 1/24/2005, Michael Tope wrote:
> However, Jim did say "a few miles" away.  HFTA, N6BV's terrain analysis
> software for the ARRL, only includes terrain out to about 3 miles in its
> calculations.  The shape of the terrain obstruction can also make a
> substantial difference in how much impact it will have.
> All that being said, 15 degrees... wow.
> 73, Pete N4ZR

Pete are you sure that is correct? I thought HFTA would do 149 terrain
points at whatever spacing provided, the tradeoff being fine structure
detail versus distance covered.

I believe it is the latter...
In fact, the bottom of page 24 and the top of page 25 of hfta.pdf (Version 1.0) describes manually editing a .pro file to add a big mountain a long way away.

I don't know if HFTA takes into account curvature of the earth and atmospheric refraction, though. While for short distances (a mile or so) the error's only a few feet, when you get out to 10s of miles, the error starts to get bigger. Ignoring refractive effects you're looking at about 30m difference at a distance of 20km... a pretty small angle, though, perhaps a tenth of a degree.


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