Using 25G for a rotating mast gets you a lot of strength for a low cost. As
Steve mentioned, you need to allow a wind load for the 25G itself which is on
the order of 7 pounds per lineal foot at 70mph. This is roughly equivalent to
3.5 sq ft per 10 ft section. 25G is supposed to be good for about 7500 foot
pounds safe moment of restraint so deducting the 140 pounds in 20 ft
multiplied by half length of 10 feet= 1400 foot pounds to be deducted, leaving
about 6000 foot pounds for antenas. A single 15 square foot antenna at the
top= 15 X 20= 300 pound load X 20 feet=6000 foot pounds of force at the bottom
of the mast. These approximations are based on 70mph wind speeds which may not
be enough where you are and at the height you want to install the mast.
FYI, Tnx/73 de K5GW
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search
|