[TowerTalk] Sidemount yagis

[K7LXC@aol.com]

In a message dated 04/04/2000 7:31:57 AM Pacific Daylight Time, 
ke3q@erols.com writes:

> Yeah, but that square foot rating is at the top, right?  I've never seen
>  figures on how sidemounting yagis decreases the allowable "at the top," and
>  how much sidemounted at various spots on the tower, and depending on the
>  guying of course, is possible, IN ADDITION TO what's at the top.
>  
>  To take an extreme, something sidemounted a foot, or 5' or 10' above the
>  ground wouldn't add much wind loading at all to the tower, I wouldn't 
think.
>  
      Well, everytime I've talked to an engineer at a tower manufacturer 
they've said that the capacity figure is over the whole tower. Obviously a 
big headload creates the biggest overturning moment and other forces. The 
poster's tower was 25G so there's not a lot of engineering overhead left to 
take care of additional antennas and also the forces from the sidemount. With 
a 3-foot sidemount the side torque is increased by a factor of 3 so that can 
create some big stresses down the tower.

      There are several nuances involved here, i.e. windspeeds are higher up 
the tower than near the ground, etc. And you still need to observe the LXC 
Prime Directive to "DO what the manufacturer says" so that you end up with a 
reliable installation.

Cheers,    Steve   K7LXC
Tower Tech

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