HK1A wrote: Testing with HFTA at different heights and stack separation,
we found that the best heights are 18/21/24 meters, in order to cover
with the best gain and angles the wave angle of arrival stats.
You violated the close stacking rule of HFTA. Anything closer than 0.28
wavelength stacking does not give the correct answer. That's about 10 ft
spacing on 10 meters.
Quote from HFTA help file:
The internal Yagi model in HFTA is a simple mathematical model. It does
not compute interactions between individual Yagis in a stack—HFTA
assumes that each antenna is a “point source.” For antennas stacked more
than about a half wavelength apart this is not a problem. For example,
you should be cautious specifying spacings less than about 20 feet on 20
meters (and proportionately scaled on other bands) because of
mutual-coupling effects between real antennas.
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