Scott -
Yes, I think you can go too high.
Why do I say this? First, I believe in the basic method used in the HFTA
program, having produced a similar computer program for my personal use in
about 1980. See http://www.w3yy.com/reflection_point_migration.htm,
http://www.w3yy.com/the_math.htm, and http://www.w3yy.com/grand_canyon.htm.
Secondly, my personal experience seems to back up the program's predictions.
For example, my 4-El SteppIR at 100ft is much too high for EU over my
sloping terrain in that direction. Sure enough, I get nice results, but not
great, in that direction. (If so, why did I do that? - simply to clear the
trees!). Guys with similar antennas at lower heights over flat terrain do
much better.
Another example was when I purposely lowered a 30-meter antenna to increase
its radiation at a desired vertical angle. I swear it worked better
afterwords, although that might just be because I want to believe it, HI.
I'm about to put up some 20-10 meter yagis at a relatively very low height
that is predicted to be a killer into EU. We'll see what happens!
73, Bob - W3YY
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Scott McClements
Sent: Wednesday, March 18, 2009 5:23 PM
To: towertalk reflector
Subject: [TowerTalk] HFTA Accuracy / Usefulness
Hi All,
I've been in several discussions with some local contesters/DXers over the
High Frequency Terrain Assessment (HFTA) software included with the ARRL
antenna book. I have used the program myself several times. I was a bit
surprised when a local had chosen his new tower height solely based on the
HTFA assessment. He had purposefully chosen 78 feet over even higher heights
because HFTA showed that higher heights actually raised his angle of
radiation towards Europe. There would have been a limit to his tower height
at some point, for aesthetic and neighbor relation reasons, but I don't
think momentary reasons.
This brings me to my main point. I went back and read the HFTA documentation
looking for statements about its accuracy. The author doesn't try to
oversell it accuracy (+/-3dB), but its clear not much has done to validate
its results. So the question - Is there any real value to this tool?
My opinion was that I would go as high as I could despite what HFTA said
(esp. since it will include a 40m yagi). Perhaps I am wrong - I was curious
what the consensus was. I am asking this with all due respect - I know there
was much effort put into this tool and it uses the technology and
information we have available to us today to the fullest.
-Scott, WU2X
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