Chad, I am NOT familiar with your antenna. BUT I just tuned and adjusted
two new 15 meter antennas and learned quite a bit. I wanted to share this
and think it might help.
First, everyone says pointing them upward is as good as as anyway to match
them. I can not substantiate this with my monoband antennas, but it
should be verified with your tribander before you put any strong value on
the readings.
Second, I DO know that ground interaction affects the feedpoint impedance.
This is regardless of the antenna. Some antennas have the impedance go up
and others have it go down as height increases. You have a meter that
measures R and X. I suggest you use it. You should know this usefull
fact: at a height beyond 40 feet or so, the ground interaction is minimal
and the feed impedance will change only slightly. Try to get that high in
your measurements.
Third, my antenna shifted its VSWR curve DOWNWARD in frequency as the
antenna was raised up the tower. This contradicts other postings I saw on
this list. You need to verify with your particular antenna what its curve
will do. All antennas change. Some go up and some go down. It is
impossible to predict how your curve will change without measuring it at
different heights.
I do not know how high your tower is, or what the physical limitations you
have on you location. Personally, I suggest doing as much of this
measuring and adjusting on the tower at an intermediate height rather than
the end up method. This might minimize surprises. For now, you could
verify your measurements with the end up before scrapping all your hard
work and making the original settings again.
Sometimes a new baseline is needed when we get into uncharted ground.
Good luck.
David J. Rodman, MD
Assistant Clinical Professor
Department of Ophthalmology
State University of New York at Buffalo
FAX 716-859-4565
Office 716-854-1137
e-mail: rodman@acsu.buffalo.edu
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