On 01/03/2015 04:18 PM, Jim Brown wrote:
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.
I did not see the granularity by changing heights in small increments,
only changing the terrain profile by insignificant amounts.
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,
That's quite a sweeping statement coming from someone who has never been
to my QTH. Nor have I been to your QTH.
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 bet very, very few have put up a reference antenna to compare against.
They run HFTA. Put up antennas. Guys tell them they have a good signal.
That HFTA must be great !
73,
Steve, N2IC
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