[TowerTalk] Rohn BX/HBX/HDBX and Boom Length

[Floyd Soo, W8RO]

Here is more info to cloud this issue.  I have all 8 sections of the BX
Series tower.  This tower is 10 years old and show no signs of rust or
corrosion.  I am located in southern Michigan.  I suppose it may be a
different situation near the ocean.

I am presently using the largest 7 sections (HBX-56 configuration) and
the tower has been fine.  At one time, I had the largest 6 sections
(HDBX-48) up with the same antennas (TA-33 & A270-10S); and again, it
was fine, even thru the winter gales around here.

With regard to the structural integrity of the tower itself, I agree
with Steve.  This ONE time I planned on bending the Rohn specs a bit. 
Any other time following the manufacturer's recommendations is the
prudent thing to do.  This tower was originally intended for large TV
arrays and small ham arrays.  I talked to a Rohn engineer directly
before installing the tower.  I asked him specifically about the boom
length issue as I planned on putting a TA-33 or TA-33 Jr. on the tower. 
After taking off his Rohn cap and making it VERY CLEAR that this was
UNOFFICIAL, he said that if he had one of these towers, he wouldn't
hesitate for a second, in installing a small tribander on it.  The 10
foot rule was their very conservative engineering and legal practice in
case of problems with lawsuits.  He then proceeded to run through some
numbers as to forces, strengths, moments, etc; and showed me that they
are very conservative with their ratings.

Do I recommend that you exceed the ratings that Rohn gives; no! 
However, with a good understanding of exactly what is involved, even
good engineering practice can allow a certain amount of "bending" of the
rules.  Speaking of bending, I agree with the comments that the real
weak link with this tower is the thin sheet metal rotor shelf.  With my
TA-33, it seems to be fine, but if anyone is considering beefing up this
combo, this would be one place to pay attention to!  BTW, just remember
that if you do beef up the rotor shelf, you are just shifting the forces
involved to the next weak link in the chain...be careful!
-- 
73,
Floyd Soo, W8RO
President, HI-RES Communications, Inc.
Net Manager and Board Member, Collins Collectors Association (#002)
QRP-L #392
hires@rust.net
http://www.rust.net/~hires

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