[TowerTalk] wind load revisited

[brunet@us.ibm.com]

I looked through my notes from a discussion on this reflector a while back and
want to rediscuss it just to be sure our plans are OK.  Let's assume 70' of 45G
at 70mph.  The flat spec is 9.5 sq ft.  Since our tower will not have the side
arms mentioned in the notes we can add 8 sq ft for a total of 17.5 sq feet.  We
are only going to have 3 or 4 runs of RG213 and the specs include 2 transmission
lines per face, so I will add the wind load for the 1/2" and 7/8" transmission
lines on one face or (1/2 + 7/8) / 12 * 70 * .67 = 5.4 for a total allowable
flat spec of 22.9.

I was told on this reflector that the specs for ham antennas are numbers that
can be directly related to the flat spec numbers.  A C-31XR has a rating of 10.7
and a XM240 has a rating of 5.5.  A 2" x 20' mast will have a flat spec of 2 /
12 * 20 * .67 = 2.2 so the total is 18.4 which is within spec by 4.5 sq feet.
Are there any errors in any of my assumptions, especially the 5.4 added in for
the unused coax lines?

Thanks, Pete



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