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Ralph Mowery wrote: If the ladder is very long and a beam is mounted to the top of it, when the wind blows it will tend to twist the ladder. The narrow sections of that H form are not designed for much twisting. A 3 element beam can cause a lot of twist in a 40 or more MPH wind . The twisting torque could also stress or break the junctions between the ladder uprights and the steps. Once that starts to happen, the ladder's structural integrity is going to go to hell... it could twist more easily, or want to "rack". For small light-weight beams with a very modest wind surface area, the old-style telescoping "push-up" antenna masts aren't bad - they do need to be guyed. You can get 'em with two, three, four, or (I think) even more sections (about 10' each). A friend of mine swears by the use of threaded electrical conduit... not the light-weight "EMT" stuff, but the heavier pre-threaded type (about three times the weight and three times the cost of same-diameter EMT). Rohn tower certainly has a lot going for it... and if I could figure out a place to mount one at my house that wouldn't put the antenna too close to the power lines or reaching over the property line into my neighbors' airspace, my friend would gladly hand me two or three sections of Rohn 25 for the asking. Sure would be nice... and it's a lot more robust than any aluminum ladder would be. |
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