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

[Jim Lux <jimlux@earthlink.net>]

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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