For some free software to make these calculations go to
http://www.arrl.org/qexfiles/
and download the file labled TRANVITY.ZIP. Also download the following
pdf file.
http://www.arrl.org/qex/1123.pdf
To give you a feeling as to what this load does, I have the same
antennas you are planning. I have an HDX555 with a 4 element SteppIR 2
ft above the top of the tower, and an XM240 9 feet above that, and a 20
ft mast. That's total of 16.4 sq ft (of antenna plus mast) on a tower
rated for 29.5 sq ft at 70 mph. This load max'es out my tower at 74 mph
average with gusts to 95 mph. So this is good for a 70 mph area, but if
you're in a 90 mph area, this tower is underrated.
Jerry, K4SAV
Jeff Kinzli wrote:
>So I know that wind load at the top of the tower is much different
>than wind load 10 feet up from the top of the tower, and that towers
>are wind load rated at the top of the tower.
>
>I'm trying to understand how this fits together in terms of stacking
>yagis. My plan is to use a 4el Steppir and a 2 el Cushcraft 40M about
>10 feet above that. With the roughly 10sqft for the Steppir, and 6
>sqft for the Cushcraft, that's 16 sqft total, but I'm sure it's quite
>a bit more than that given the stack, and ratings for towers looking
>at the wind load at the top of the tower rather than 10' above the
>tower.
>
>Are there calculations that I can do to figure out how much tower I
>need to support this? Or would that be something a civil engineer
>would do (or my architect) before I get the permit for the tower (and
>buy the tower).
>
>Thanks for any ideas...
>
>-J
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