I found a really good mast pipe load calculator on the DX Engineering web site.
www.dxengineering.com
They advertise a 22 ft X 2 inch pipe (also stock a 3" one) which seems about
perfect for my next upgrade. I made up a situation based on antennas that I
have around just to see how it worked. I put the mast 18 ft above the TB3
bearing, and 4 ft below so the rotor could be down a bit from the top. Then I
placed a 205CA (9 sq ft) half a foot above the bearing. Then I placed a 155CA
(5.2 sq ft) 6 feet above the bearing. Then I put a 105CA (3.9 sq ft) 12ft
above the bearing. Finally I put a 6M7JHV (2.5 sq ft) at the very top just to
see what would happen. For me, these are pretty realistic antennas.
The program has a good diagram and lets you fill in the names of the antennas
and spacing so you can actually visualize your plan. Then you hit "Calculate"
and get the result. In my example, the configuration passed 60 mph, and 80
mph, but failed at 100 mph. This is a great starting point! So I have to
downsize a bit. We get fierce winds and the antennas get covered in ice a
couple times in the winter. I really don't like stacking so many antennas
because it's nearly impossible to do any maintenance without taking everything
down. This is so much more scientific that getting a Rohn mast and welding
some water pipe inside to beef it up a bit. It's fun to play with, but it took
me a while because I just had to browse throug all the towers and associated
hardware.
RalphK9ZO
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