There have been a number of comments regarding the HDBX series of
towers, especiallyt the HDBX-48 which I used to own and just sold.
Many of the comments relate to the lack of any specifications from Rohn
except (and I quote) from Rohn:
"Antenna types for HDBX should be limited to those having a maximum
boom length of 10 feet. No engineering data relating to the use of
boom lengths in excess of 10 feet is available and the use of such boom
lengths is not recommended."
They go further to say: "All towers are recommended to be bracketed
for extra safety and to withstand gusty wind conditions."
The HDBX is also specified to have an 18 sq. ft. capacity.
I installed a CDR rotator and KLM KT-34XA (30 foot boom) about 2 feet
above the top of the tower and the thrust bearing using the top plate
and rotor plate supplied by Rohn. The thickness (or maybe I should say
thin-ness) of these two plates made me somewhat concerned at the time
but I put it out of my mind. Also, the fact that the attachement
points on both plates were bent down did not cause me any concern.
All in all, the tower was fantastic. I have been up on it in some
pretty strong winds and, although I regretfully present a rather
large windload ( due to too many cold 807's), the tower with me at the
top did not budge that I could tell. There has been twice when my
finger has slipped off the rotator control unit thus bringing the
antenna (and rotator) to an unplanned and fatally fast stop, plus the
antenna did swing in an arc of about 5 to 10 degrees in the wind
(rotator slop).
All of this is leading up to the fact that when I sold my tower, the
gentleman who bought it called me up a couple weeks later and advised
me that two of the tabs that secured the rotor plate to the tower legs
had sheared in half and there was only 1 tab holding the rotor plate to
the tower (along with the upper tower plate where the thrust bearing
was mounted). I think you all can fill in the rest of the scenario,
i.e., plate fails, antenna windmills, coax wraps around tower, etc.
6 May 98
Well, I just saw Steve's (K7LXC) comments regarding stress failure of
the rotor plate and top plate. Also of note is David Bunte, K9FN's
thread from 2 May 98, subject HDBX towers relating to same problem.
These cheap, crummy, #$@*&&# plates are less than 1/16 th. inch thick
. I should have had my head examined for not replacing them from the
start, but then I am new to towers. Maybe that is why Rohn won't
specify anything but the minimum for the tower. It is hard to believe
that a company with Rohn's reputation would allow something this poorly
designed to be put on the market. I don't care if you use even their
10 foot boom, the looseness in the rotor itself will let the antenna
swing back and forth and fatigue th metal. Even if you only have up a
TV antenna, if you should accidentally let your fingers slip off the
rotator switch and let everything come to a screeching halt (which I
have done) you will eventually stresss the plates.
Steve: Wish I had seen a thread something like this 5 years ago!!!
Bill Haselmire - WX8S
bg@tir.com
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