In a message dated 98-02-03 08:40:26 EST, firstname.lastname@example.org writes:
> So what kind questions am I talking about that Rohn does not address in
> their catalog? Here are a few examples.
> 1. Ham wants to install a guyed Rohn tower and can't put the guys exactly
> 120 degrees apart. In what ways and by how much must he "derate" the load
> on the tower to compensate for this deviation from the pictures in the Rohn
Get a PE (Professional Engineer) to do the calculations. The ARRL also has
a list of VCE's (Volunteer Civil Engineers) on their web page.
> 2. Ham wants to install a guyed Rohn tower and can't put one or more of
> guys out quite as far as the diagram in the Rohn catalog says he should.
> How does he "derate" the tower in this case?
See question #1 - get an engineer involved.
> 3. Ham wants to install a guyed Rohn tower but he wants to stack antennas
> on a mast that puts some of the load well above the "2 foot" point where
> loads are shown in the Rohn catalog diagrams. How does he compensate for
I don't know if anyone has the answer to that or what Rohn's position is.
All of Rohn's specs are for commercial applications. I suspect that as long as
the load meets the round or square load figures on their catalog drawings that
they don't care how it's configured (IMO).
> 4. Other than the BX tower, I know of no data that suggests how much
> a Rohn tower will safely take. How do you know if you can safely use a 60
> foot long 20 meter Yagi on Rohn 25? On BX tower, they simply say you can't
> use any antenna with a boom length longer than 10 feet. I am not aware
> they address boom length at all on their other models.
First of all, the antenna exceeds the windload rating of the 25G. And we
know that a TowerTalkian stays within the manufacturer's specs. Second, you
can use a double-guy bracket (Torque Arm Stabilizer or star bracket). This
essentially locks the tower down and prevents almost all twisting.
> 5. Speaking of BX tower, almost ALL installations I have seen use longer
> than 10 foot booms. How does this affect the area of antenna that can be
> safely installed on them? Rohn would tell you that you can't do it but
> thousands of installed towers would say you can. So thousands continue to
> do it, in spite of Rohn's warnings.
See my previous post on BX, HBX and HDBX.
> 6. Rohn's current information regarding bracketed towers always require
> brackets. I don't know of a single tower installed that way. Rohn MUST
> know that nobody installs bracketed towers according to their instructions.
> So what is the proper way to install a bracketed tower with a single
> bracket? How much can you put on it? I have seen lots of people guess at
> this but I find no help in the current Rohn catalogs.
The best article I've seen is by Tony, K1KR which goes through the whole
exercise including engineering calcs. It's available for a buck from TOWER
I think the 2-bracket spec was due to one of the recent TIA-222 revisions
(either E or F).
Why would somebody do something contrary to the manufacturer's specs?
Personally for 40 feet of 25G next to a one-story house, I think that one is
plenty. The Rohn housebracketed specs go all the way up to 100 feet so these
aren't necessarily a typical amateur installation.
Regardless of what happens to installations in the field, the
manufacturer provides (at least in the case of Rohn) specs for various
configurations that they would like followed. If you're not sure, get a
> I could go on with other examples involving elevated guy posts, side-
> antennas, and many other things but there is no point in it. My point is
> that the Rohn catalog information leaves A LOT of unanswered questions for
> the user to guess at. Rohn's answer is to pay them big bucks for an
> engineering evaluation of your specific system. I have never known any ham
> to ever take advantage of that service. Who could afford it?
Mostly true. I think that Rohn goes out of its way to provide the
plethora of information that's in their catalog. But you're right - it doesn't
cover EVERYTHING. As the buyer, user, installer, it's YOUR job to make the
final decisions in regard to your project. And those decisions should be made
only after taking everything into consideration. You and the manufacturer both
have liability exposure with your installation so it's in everyone's best
interest to do the best job you can. Did I mention getting an engineer
The specs for the civil work (bases, anchors) also assume 'normal' soil.
What do you do if it's rocky or sandy? There are lots of things that they
> So when we have questions, we get on this reflector and we get some pretty
> good empirical data from experienced users who have seen a few tragic
> failures and have taken the time to understand the failure modes. I have
> never seen Rohn help out in this area. What they must have seen over the
> years could have a very devastating effect of their business, if they chose
> to share the information. At the same time, it could save some lives.
> do they risk in NOT sharing failure data? Apparently nothing . . .
> What you don't know can not only hurt you, it can kill you . . .
They have legitimate reasons to play things close to the vest. It has to
do with risk, insurance, lawyers and ultimately - costs. If you call Rohn, you
CANNOT talk to an engineer directly - they won't let you.
I guess that's why TowerTalk is such a valuable forum for these topics. We
CAN talk about them.
73, Steve K7LXC
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