[TowerTalk] Is there a decent way to fit a prop pitch in Rohn 25 tow

[Rob Frohne]

Thanks Steve,

That explains a thing that was really bothering me on the 45G specs.  I
saw so many people putting much more than the specs allowed, and getting
away with it for decades.  It seems intuitively It just didn't add up.
It makes me want another seven sections of 45G even more.  Thanks for
the tip!

Another thing that doesn't completely make sense to me is that as the
towers grow, the wind loading falls very slowly (less than a square foot
per ten foot section).  If you look at the wind loading of another
section that has been added, it is significant (around three square feet
per section).  The explanation I guess is that the guy wires move up.
This makes me wonder what the allowable wind loading is if you move the
guys up to the top of the top section instead of five feet down.  It
should improve it seems to me, and maybe fairly significantly.  Does
anyone have a good explanation of this?

Thanks,

Rob, KL7NA

On Wed, 2008-02-06 at 11:44 -0500, K7LXC at aol.com wrote:
> In a message dated 2/5/2008 4:51:47 P.M. Pacific Standard Time,
> towertalk-request at contesting.com writes:
>         >  I am having difficulty finding 100 feet of Rohn 45 or
>         larger tower in
>         the neighborhood of Walla Walla, Washington, but I can find
>         heaps of
>         Rohn 25 tower.  I am considering putting a shorty 40 and a 4
>         element
>         Steppir on top.  The wind loading specs of 25G and 45G are not
>         that
>         different if you believe Rohn.  The big thing is that I would
>         like to
>         use my prop pitch to turn the antennas, and I'm afraid I can't
>         fit it.
>         There are three top sections available for Rohn 25G. 
>          
>             Actually you need to read the General Notes to see a
>         difference in the windload rating. For 45G and up, there is 8
>         sq. ft. already taken out of the loading for what Rohn calls a
>         "symmetrical mount" which is pretty common in commercial
>         installations. So add the 8 sq.ft. back into the 45G windload
>         rating and you'll be in business. 
>          
>             As far as the PP in 25G, I'm not sure it'll fit. If it
>         will, you'll need to cut out a brace to get it in. The other
>         problem with 25G is that the rotator shelf only goes in a
>         taper top section or at the junction of two sections. 
>          
>         Cheers,
>         Steve      K7LXC
>         TOWER TECH -
>         Professional tower services for hams
> 
>  
> 
> 
> 
> 
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