For smaller antennas it would not be an issue. I never expereienced that
with my 6 el 10s. However on my Rohn 55 had a 5 el 40+ ft boom (10 ft2
wind load) and the antenna mast was about 2 feet from the tower on the arm.
That created lots of torque on the tower (and the rotor).
Even though the tower was guyed every 40 feet with torque bars and 1/4 inch
EHS. You could definitely feel the sway...especially so if someone turned
the antenna and then hit the brake the instant they stopped rotating.
K4XS
In a message dated 5/30/2013 2:31:26 A.M. Coordinated Universal Time,
K8RI-on-TowerTalk@tm.net writes:
On 5/29/2013 7:57 PM, Steve Maki wrote:
> On 5/29/2013 3:52 PM, Cqtestk4xs@aol.com wrote:
>
>> Been doing swinging arms for years...
>>
>> Make sure the tower face is set in such a way as to allow the rotation
in
>> the direction you want. You can make a model of this on a piece of
>> acetate
>> over a drawing. It makes it easier to visualize.
>>
>> Make an effort to place the mount just above a set of guys as
sidemounts
>> really tend to torque a tower. Ask anyone who has ever been on a tower
>> with a large beam sidemounted, and then had someone in the shack
>> rotate the
>> beam. Even without hitting the brake on the rotor it can be
>> uh...exciting.
>
> Which is why I always chuckle when someone, apparently thinking of their
> tower as some sort of rigid rod (sorry about that :-)), agonizes over
> their rotator brake.
Now mine never did that. You could just feel it in the tower when it
started or stopped and it was a big antenna...as far as UHF, TV antennas
go<:-))
On a 45G the gate will likely be 2 feet long. If that's the case,
multiply the weight of the antenna by two for the off center leverage in
foot pounds. How fast it decelerates, or accelerates will give the force
in Gs. So you then multiply the leverage in ft lbs by Gs to get the
twisting force on the tower. Ever get an antenna rotating on a shaft
and then try to stop the rotation by gripping the shaft, or just hold
one against the wind. Be careful, you can lose a lot of hide doing this
experiment.
73
Roger (K8RI)
>
> -Steve K8LX
>
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