[TowerTalk] Sidemount yagis

[DavidC]

> Rich,
> Not quite correct. The square foot rating is total, wherever antennas 
> are mounted. Kurt, K7NV, has the calculations on his Web site 
> proving this for guyed towers, though it intuitively doesn't seem 
> correct.
> 
> Side mounts create a lot more turning moment (aka torque) on the 
> tower when the wind blows. As an example, the Rohn HDBX 
> towers have a sq ft rating, but then they go on to say don't use any 
> antenna with a boom longer than 12 (?) ft.  This is due to torque. I 
> believe is the total sq foot rating would need to be derated when 
> using a side mount. Maybe one of the PEs can explain in more 
> detail...
> 
> 73 Barry

So, we should see this as a rather complex calculation?

Where the sidemount is attached (height)?  The torque load of the 
antenna?  The nature of the surrounding area (whether cleared for a 
distance or nearby trees and/or buildings that limit the wind stress on 
the tower via the antenna?  The way the tower has been constructed
(pier pin versus section-in-concrete, guying methodology)?  And etc.?

Sure sounds as though a PE is necessary if one gets even a little 
close to the recommended limits.  Sure appreciate reading this before 
I risk carelessly over-loading my tower!  (They are forecasting a
rough season of Summer-Fall storms here on the Gulf side of Florida.)

- Thanks! & 73, DavidC  K1YP in Hudson, FL

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