[TowerTalk] HFTA Accuracy / Usefulness

[W0MU Mike Fatchett]

They way I understand the data is this:

Data was collected that shows the angles of the incoming signals for the
desired area over the opening.  Yes you can go too high for the highbands if
you want to keep your antenna in the desired incoming angles.  If your
antenna has a angle of say 10 degrees and the incoming signal is coming in
at 20 degrees there could be a reduction in signal.  Is it enough to make a
difference who knows.  I would think it would.

What I have seen is the higher towers will get the band opened sooner and
close later but during the main opening the high antennas could very well be
too high.  This is why so many people are using stacks.  Yes you get
increased gain but you also gain flexibility.  K0RF will be working stations
on his high antennas that I might just hear or can't hear at all, early on a
band or late.

In my case I decided on a 70ft tower for budget and family considerations.
I have some terrain issues that adding in a second lower antenna really
helps to solve at least on paper.

KH7XS/K4XS has done extensive modeling with this on his hillside location.
Maybe he will jump in here and tell us if he is seeing what the model was
predicting.

With a single tower it will be all about compromise.  A very high tower may
work great on 40m but could turn out to be way too high for 10m or 15m.  

So higher is not always better.  You want your main antenna to have the same
or close to the same angle as the inbound signals for as long as possible.

That is how I understand the program to work.


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-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Scott McClements
Sent: Wednesday, March 18, 2009 11:23 AM
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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