Kelly Johnson Wrote:
> Who can tell me how to calculate the reduction in windload capacity
> of a tower that occurs when you add a reasonably long mast to the tower
> to hold stacked yagi's? How do things change as you change the height
> of the yagis above the top of the tower?
As the antenna(s) are raised above the tower top, the allowable antenna
projected area is reduced below the area allowed at the tower top.
W9JCC Wrote:
> See the article I wrote in QEX July/August 2001 re Tower Wind Loading. If
> you have a free standing tower and can verify from the engineering specs
> that the worst case moment is at the base, you should be able to use the
> spread sheet (Written in Excel) that is available on the ARRL QEX web
> site.
It's also covered in the 19th edition of the ARRL Antenna Handbook, pages 22-19
thru 22-22, including mast stress calc's.
Remember, that all such calculations assume that you are using the correct
antenna area values, which is also covered in the same chapter of the Handbook.
--
73, Kurt, K7NV
http://yagistress.freeyellow.com
|