>
> With due respect, I think it is necessary to make a fundamental
> Observation on this topic.
>
> Rohn's catalog...and mine is missing so I can't verify the numbers...
> But as I recall, it specified a 2 sq. ft. windload 30' above a house
> bracket, for 25G. That's considerably less than a 3 el tribander will
> present.
The older catalogs can be a bit confusing. Self supporting the 25G is only
rated to 1.8 sq ft at 40 feet and 70 mph BUT (unless I misread) drawing
A871302 (No 25 Bracketed tower, no ice) shows a 40 foot 25 G bracketed at 15
feet as being rated fo 15.3 sq ft @ 70 mph or 7.7 sq ft @ 90 mph. However
the supporting structure at the bracket must be able to withstand a
horizontal force of nearly one half ton.
>
> N4ZKF, Dave, has 40' 25g housebracketed @ 10'. Windloads are more like 12
> sq ft, 30' above the bracket, and he reports surviving some harsh weather.
>
> I had 60' of 45G, house bracketed at 6' & 16'...with an lpda and vertical
> on
> top. It survived some harsh weather.
45g bracketed Drawing A880496R1 (45G Bracketed Towers - No Ice) shows a 60
footer bracketed at 23 feet as being rated for 33.3 sq ft @ 70 mph and 19
sq ft at 90 mph. Self supporting 45G is rated for 2.3 sq ft at 45 feet and
70 mph.
NOTE the self supporting information ( drawing A871266 ) is only a couple
pages from the back of the book while the bracketed tower information is at
the beginning of the appropriate section of the catalog for each model of
tower (IE 25G and 45G)
BTW bracketed towers are bracketed on TWO legs rather than one. IOW the two
legs are on the house side and not away from the house. The bracket is
*substantial* and nothing like the little stand off we see for one leg on TV
towers.
Considering how low they rate the towers when self supporting I find these
numbers more than a little surprising.
Roger (K8RI)
>
> Neither of those are relevant.
>
> What IS relevant, is that the structure is not RATED for what's proposed.
> If the tower fell and nothing would be hit, then the risk is low...and who
> cares? But if it would hit a populated house? I would not personally
> risk
> an installation which would make you liable for serious results.
>
> It IS true that Rohn's specs were highly conservative, and were influenced
> by anticipated litigation. Hams have been overloading the stuff and
> getting
> away with it for years. But risking life and limb for the sake of a
> hobby,
> or a few dollars...does that make sense? Doesn't to me.
>
> Having said that....I personally believe that 25g is stronger than hbdx,
> and
> with a proper foundation, would serve reasonably in the 40-50' vicinity.
> Just don't ask me to climb it. I've built 100+' 25g...and being 30' above
> a
> guy is a puckering experience. It's THAT flexible.
>
> Jim/N2EA
>
>
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>
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>
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