On Sat,1/3/2015 12:03 PM, Steve London wrote:
If you are playing with HFTA, I strongly urge you to do a sensitivity
analysis by changing your datapoints, randomly, by 1 to 3 feet. Do
this on each band of interest. If the results change significantly,
then HFTA is not a valid model at your QTH.
I believe that's an incorrect conclusion, Steve. N6BV, HFTA's author,
recommends making multiple runs to rule out the granularity issue that
you noted. That is, he suggests modeling not at single heights or
azimuths, but at multiples of both. He advises that it IS possible to
have a condition that yields bogus results, but by doing those multiple
calcs, it's easy to weed them out.
For my QTH, which is far more irregular than yours, I modeled in 5
degree steps from 0 to 45 degrees, at 5 ft height increments. Knowing my
terrain, he also recommended going out something like 10 miles or more.
Many of us out here in the Bay area have used HFTA extensively, and
swear by it. I know that K6XX has, and so have I. My on-the-air
experience with a SteppIR at 120 ft and monobanders in the range of
30-45 ft is in great agreement with the models.
73, Jim K9YC
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