On 12/26/2013 3:17 PM, Tim Duffy wrote:
Hello Patrick:
I would not suggest you do either of these choices. The Rohn 25 tower is
heavy and the base insulator has to be able to support the tower and the
aluminum stinger down force and wind loads. I suggest you consult with Rohn
and follow their advice 100%.
At less than 30# per section, I'd not consider 25G to be heavy. I
consider 45 G to be moderately heavy. Having said that, the Insulators
are important. If not following a manufacturers recommendation, which
would be normal for a quadrature array, it's already into experimental
territory.
The Hy-Tower reminds me of a short tower made of HBX tower sections. Not
HDBX, but HBX
You could call one cage loaded, but there are cross sections and it
appears as a large element.I don't see it any different than using a
tower or pipe.
3 of the old pop bottles would "Probably support considerably more than
100# if guyed.
I'd not be afraid to experiment, but anyone doing so needs to take into
consideration the strength of the insulators, any side force, and guy
the tower with insulated guys. Years ago, when on the farm I put up a 40
meter 1/4 wave on pop bottles. Two tower sections and a pipe guyed with
insulted cord. If the antenna went down it could do little damage.
With the winters/winds we had back in the 70's it stood just fine.
We always need to take into account what damage the system could do
(worst case) even when putting up a well engineered system and that goes
more than double for a home brewed system.
I've received many calls over the years about a problem raising this or
that. Almost invariably my advise was "don't do it" as they were unsafe
in one respect or another. It's amazing how many variables and ratings
are often neglected.
Many of us have just thrown together what we had. Normally we put it
wher and damage from a worst case would be minimal, but we wer working
with 40 foot towers and rarely above 50. Many fail to realize how fast
forces and risks multiply with height and size. I have little worry
about specs with normal materials (That I'm familiar with) up to 40
feet. With the spec sheets and a bit of math I'm willing to go to a 100
feet and neat a ton of weight "for my own projects", but I'd not tackle
that for someone else. Think about what a 100' 45G with a large array on
it could do if it came down across a house. It most likely would cleave
it clear through to the floor. Those are not the sort of things we
think of with a 40 or 50 footer. Damaged shingles and roof, or maybe
broken windows, but not the kind of damage a more massive installation
could inflict.
OTOH the Quadrature array on another thread, is not tall or massive by
these standards. 40 feet out from any structures and any failure would
most likely do little more than bend up the antennas. Expensive, but
unlikely to be dangerous. ("It all depends!")
This is not a recommendation!
I'd probably make my own insulators out of fiberglass or other materials
and guy it. OTOH I have hundreds of hours working with fiberglass and
resins, I'm not an engineer, but have had most of the classes and can do
the math. I'm not a certified welder, but can do all the requirements
except welding inverted. I used a lot of material just to learn how to
weld vertically. Now with fine motor control in only one hand, my
welds look like crap, but they are strong. Still, I try not to venture
beyond my abilities and knowledge.
73
Roger (K8RI)
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