In a message dated 98-03-19 18:52:48 EST, brunet@us.ibm.com writes:
> Chad, Thanks for all the info. Based on what you said my '81 Rohn book
shows
> that a 70' Rohn 45 guyed at two spots can handle 9.5 sq. feet of wind load
> at
> 70 mph. On the chart just before that one it says the allowable antenna
> area
> (sq ft) at 70 mph is 32. Can you explain the difference?
Pete - you need a current Rohn catalog. There have been 2 or 3 revisions
to the EIA/TIA-222 since then. They're five bucks from TOWER TECH.
Please cite which drawing you are looking at so that we're literally on
the same page.
>
> I did not find the info you mentioned on how to determine the impact of the
> torque associated with a 40m antenna at the top of a mast. Does anyone
know
> if
> there is a concern with the torque associated with the force of the wind
> resistance of the top antenna (eg F12 Magnum 340) applied at a distance of
> 10'
> to 15' from the top of the tower?
>
Torque is the same regardless of where the antenna is on the mast.
(Minus the torque absorbed by the mast which will act like a torsion rod
spring.) The torque goes through the rotator, the rotator shelf to the tower
legs, guy brackets and then the guy wires. Mounting the rotator shelf close to
the guy bracket does an excellent job of transferring the torque to the guy
wires to minimize the effects on the tower.
Bending moment on the mast is another matter.
73, Steve K7LXC
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