In a message dated 11/30/2007 9:05:18 A.M. Pacific Standard Time,
towertalk-request@contesting.com writes:
> I have a question about star guying.
> This fall I erected 170 feet of Rohn 55. The tower is mounted on a pier
pin with a tapered base section. I have another 20 feet to go, but due
to weather, that will have to wait until next spring. The only antenna
on the tower at this point is my full size 3-el 30 meter beam at 100 ft.
After completing the tower, I plan to put long boom (50') yagis for
other bands at 160 and 190 ft.
> Even with just the 30 m beam on the tower, the tower exhibits a modest
amount of twisting at the 100 ft. level. when the wind blows (which is
most of the time here on the Great Plains). I'm thinking that star
guying at one or more levels would help reduce the torque. However,
since I haven't used star guying before, I don't know if I should just
do this at the 100' level, the 190' level, or both.
While I agree with Frank, W3LPL, about the stress issues on the legs due
to increased guy tension, 55G is good to at least 300 feet so the additional
stresses introduced by the 6-way guying at 190' should be well within the
design limits. (I'm not an engineer but I've worked on several towers.)
Using a star bracket will certainly lock down the tower and prevent it
from twisting but I've never heard of a properly installed Rohn tower failing
because of too much wind induced torque. They'll take a fair amount of abuse
even when overstressed so either way I'd say you're okay.
One thing you can do is to have the guy wires mounted as close to the
rotator plate as possible. That way the torque is transmitted directly to the
guy wires without as much influence on the tower itself.
Cheers & GL,
Steve K7LXC
TOWER TECH
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