Without passing judgment on the usefulness of HFTA, let me tell you my story...
I live on a hilltop, with a net dropoff of 400 feet in the first quarter mile,
in every direction except west. The dropoff is not smooth and regular - lots of
bumps in that quarter mile. When I showed Dean, N6BV, the terrain profile I
for HFTA, he commented "you have a very complex terrain profile".
When I first moved here, 5 years ago, I spent hours doing analysis with HFTA.
Then, something interesting happened. I was looking at the output of HFTA on 20
meters using the same antenna and antenna height, with two nearly identical
terrain profiles. And, I do mean nearly identical - no single data point on one
terrain profile differed by more than 6 inches in elevation from the other
terrain profile. Most of the differences were 1 to 3 inches. Certainly within
the range of uncertainty of any map, or most surveying techniques. Now, you
would expect that with nearly identical terrain profiles, you would get nearly
identical results with HFTA. Here's the shocker - the HFTA results were vastly
different - up to 8 dB difference at some vertical takeoff angles.
Now, I am an engineer. When you make trivial changes to the model input, and
non-trivial changes in the model output, you have to be very careful, even
suspicious, of your interpretation of the model output.
I no longer use HFTA.
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