Hi Gerald,
Also be sure to include the wind area of your feedlines--they add up
quickly! For example, for RG-8/LMR-400 (diameter 0.405"), 87 ft along the
tower leg gives you another 87 ft x 0.405 in x 1 ft/12 in = 2.94 ft^2. Two
of these lengths gives you 5.87 ft^2, etc. (These numbers don't include the
factor for round members, but Rohn specs include this factor in their "round
member" ratings.)
73, Chris KA8WFC
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Gerald Boutin
Sent: Friday, April 06, 2007 11:12 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Stacking Antennas and Windloads
Thanks for all of the responses to my "dilemma" that I am having to endure
in moving to the East Coast.
I have an additional question. (Won't be the last time I say that.)
I would like to put up a C31XR tribander with a Mag240N 2 element 40 meter
yagi above it. The total tower windload is:
C31XR: 10.7 SF
Mag240N: 6.8 SF
16 ft Mast: 1.6 SF for 2 inch or 2.4 SF for 3 inch
Rotator: 1 SF (approx)
Total load: 20 to 21 SF
Still deciding on height, but the desire is for either 80/87 feet or 90/97
feet. In either case in a 100 MPH environment, this load exceeds the
capacity of 45G and 55G.
A light just lit up in my head. What if I rotate the 240N by 90 degrees? Now
the cross section in parallel with the tribander elements is that of the
boom rather than 6.8 SF. ie) Assume average 3 inch boom by 24 feet =
3/12*24*0.67 = 4 SF.
I don't know the actual boom diameter, so it may be slightly smaller. Since
I am right on the edge, the reduction in 2.8 SF is a big deal to me. Is this
really legit, or am I tempting the wind gods?
--
Gerald Boutin, VE6WA
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