[TowerTalk] End mounting of boom on 10 meter beam vs mount @ CG

[L. B. Cebik]

Since my name was mentioned, I shall suggest a response, but certainly not
the only one that can be made.

Boom-end mounting a 10 meter beam with decent spacing from anything above
or below is not likely to cause any significant pattern problems.  The
vertical orientation of the tower ordinarily creates minimal problem for
the horizontal antenna.  So the chief problem is mechanical--hanging 20
lbs (but not LBs) can create a significant lever moment.

However, with a fixed beam to EU, perhaps one might consider a second
fixed beam in the opposite direction.  Remember that the 1/2 power (-3 dB
down) points are many degrees left and right of the center line.  Hence,
one might do a minor compromise and line up EU with VK-ZL in many parts of
the country.  Then a. you have a balanced load for the tower and b. a
back-to-back situation that should show little interaction.  I suspect the
degree of antenna tuning difference between "independent" hanging and
back-to-back would be similar to initially tuning the antenna by pointing
it straight up with the reflector about 10' off the ground at 10 meters.

I have not modeled this particular problem, but I have run some Moxon
rectangles through a similar exercise for both same band and adjacent band
tests, and they showed no pattern problems, despite the sensitivity of the
Moxon to dimension disturbances.

One other mechanical note:  be sure your boom can handle end-mounting.
Most are designed to handle mid-point mounting and may not be strong
enough for end mounting without strengthening.  VHF beams, on the other
hand, are often designed for end mounting the boom.

At about 60 degree beamwidths, an array of 6 10 meter beams around the
compass would permit automated strongest signal selection by a
computerized receiver and thus avoid all problems associated with
rotators.  (Actually, this system becomes more feasible at UHF/VHF.)

This is not so much of an answer as further food for thought on the
problem-challenge.

-73-

LB, W4RNL



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