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Contesting Online Forums : Tips : Free standing towers Forums Help

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Free standing towers Reply
by N5XZ on October 3, 2001 Mail this to a friend!
How much antenna will 45-50 ft of 45G or 55G support if non-guyed but house bracketed at, say, 25-30 ft?
RE: Free standing towers Reply
by N6VI on October 5, 2001 Mail this to a friend!
First, I am not an expert or an engineer. I've put up a lot of stuff that has all stayed up, and I study the manufacturer's literature. Your question is addressed, in part, by Rohn drawing # B-691119, which apears in an older Rohn catalog I have. Using a wind load of 50 pounds per square foot (corresponding to around 112 mi / hr windspeed) and assuming no ice, the unbracketed ( freestanding) height of 15' (best case you gave) to 25' (worst case you gave) results in 10 sq. ft. to 4 sq. ft. using Rohn 45. and (unspecified at 15') to 10 sq. ft. using Rohn 55.

If you consider 1/2" of ice, then 25' of unbracketed Rohn 45 has an allowable antenna load of zero! Reducing the unbracketed height to your best case of 15' gets you about 7 square feet of antenna. Using Rohn 55 in the same icy conditions allows about 5 sq. ft. if you have 25' unbracketed; the 15' case is not presented.

All this presumes your bracketing is sufficiently strong, doesn't consider loading of transmission lines, rotators, etc.and assumes the antenna right at the apex of the tower (not up another 5 or 10 feet on a mast). If this thing could crash through a bedroom or something, I'd sure consult a local engineer before loading the thing up.

Hope this helps, and good luck.

Marty Woll N6VI

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