At 05:37 AM 10/13/02 -0500, Kelly Taylor wrote:
>...
>I hesitate to disparage your idea, but it appears you may be making
>assumptions about windloading and the transfer of forces that may not be
>quite accurate. Five square feet at the top of a 30-foot mast will transmit
>one heck of a lot more force to the tower than five square feet at the top
>of the tower. Add the five square feet you estimate for the mast and I would
>guess you would exceed the ability of the Rohn in very short order.
I think Kelly's got a pretty good point. I have a ~3 square foot short 40m
yagi 9 feet above a 25AG2 top section, on 2" mast with a .250" wall. The
amount that mast twists and wiggles in the wind is "impressive" (read
scarey). All of that torque and/or overturning force would be transmitted
through the few small welds at the top of a tower section that is really
not designed for that sort of thing.
Rather than the Hexbeam or the A3S, to go with your crankup I'd suggest you
look at the Force 12 C3-SS. It's a little bigger than the Hexbeam and
significantly smaller than the A-3S, and will outperform either one, with
only 4.4 square feet of wind area. If you can deal with the extra cost,
you might also look at the Force 12 low profile tower that nests to 12 feet
and extends to 42. It costs about $1400 plus freight but is a clean design
that is likely to grab hold of neighbors' and your XYL's eyeballs less than
the crankup. See www.force12inc.com for details.
Please note I have no connection with F12 other than as a happy customer
and volunteer manager of the F12 web site, force12talk@qth/com.
73, Pete N4ZR
Sometimes a tower is just a tower
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