Testing with HFTA at different heights and stack separation, we found that
best heights are 18/21/24 meters, in order to cover with the best gain and
angles the wave angle of arrival stats.
Obviously, that is quite a short separation compared with the range of
separations that is normally used.
There is one warning about HFTA that everyone who uses it should know.
N6BV says that it can give false gain readings if the antennas are to close
to each other (less than 1/2 wavelength). Obviously, the 3 meter separation
is way less than 1/2 wavelength.
I went through the same stuff when I modeled my three high stack of
KT36XAs. I got all kinds of great gain with only 1/4 wave spacing, but it was
all make believe.
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