Howdy folks,
Something about antenna square feet, tower ratings, etc, has been
bothering me ever since I started planning my little antenna farm. And
the queasy just won't go away.
Not so much about the following, I can read the manufacturer's book, &
do the math, can't argue with the calculator, etc. Can't argue with the
conclusions if I accept the givens. Got no argument with the
tower-talkians.
>
> Hi Roger & All,
> I agree with all of what Roger said, with one exception. Note 4 on the 45G
> guying diagrams says the designs include 8.0 SqFt for side arms. If we aren't
> using them, we get to add 8.0 SqFt. to the value in the oval outline. That
> would allow the TH7DX at 11.5 SqFt go to 110 Mph basic speed.
> The 25G doesn't get to take advantage of this.
I just want to get this stuff into my country boy terms, and maybe
you'll understand what bothers me. Maybe someone will explain it...
I have a golf umbrella. It has more square feet than what Rohn 25g is
rated by the manufacturer at 90 mph. What is the point of paying over a
thousand dollars for a tower that isn't rated to even handle a golf
umbrella's worth of square feet. It seems ludicrous.
Further, I can name five different guyed 25g towers around here that
carry at least twice 25g's rated load and went through Hurricane Fran
(75-80 mph for over an hour), which took down enough trees around here
that it took an army of trucks and chain saws four months to cut it all
up and haul it away.
Three cynical thoughts roll around in my gut. I don't spend any time
cultivating them. They just keep popping up by themselves as I watch the
impressive lack of precision and consistency in matters square feet.
1) The state of tower ratings is law suit insurance -- rate towers so
excessively conservatively that the chances of being taken to court on a
fallen tower approach the microscopic.
2) Ratings have been made conservative just to run up sales by making
the thicker stuff seem more attractive, despite the much higher price.
3) The science used to rate them hasn't really been up to the task,
computer tools just now coming into their own. The published ratings are
just to protect their flank.
I am struck also about what *has* taken down guyed towers. Scratching
back through the archives... big trees down across the guy wires, that's
number one. There's nothing in second place. Maybe nothing in third
place. Next comes directly due to huge amounts of ice. One story about a
self supporting tower, two inches of radial ice, 50 mph winds. I have
zero problem understanding why those take down any tower. Only really
massive stuff survives that. Other stuff about improper base, improper
guy construction, weakening by corrosion. The solution to these is in
proper practices, not in jacking the ratings.
Are we really to believe that 25g is too weak to handle a TH11 on top?
Has anybody tested this stuff in a wind tunnel?
I understand "do what the manufacturer says and stay out of trouble".
Indeed! I *could* use Sitka Spruce 8x8's as wall studs. No need to worry
about it holding up the sheet rock. I could also use 3" marble instead
of the sheet rock and the 8x8's would carry the weight just fine.
Where is the independent rating and analysis on towers? Anyone ever do
it? Maybe they did and won't let it out for fear of being sued?
Somethin's rotten in Denmark.
73, y'all. Guy.
--
Guy L. Olinger K2AV
k2av@qsl.net
Apex, NC, USA
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