[TowerTalk] Swinging gate antenna mounts

[Cqtestk4xs at aol.com]

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 at tm.net writes:

On  5/29/2013 7:57 PM, Steve Maki wrote:
> On 5/29/2013 3:52 PM,  Cqtestk4xs at 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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