[TowerTalk] Sources for mast material
K7LXC at aol.com
K7LXC at aol.com
Tue Aug 5 18:59:17 EDT 2008
In a message dated 8/5/2008 6:23:13 A.M. Pacific Daylight Time,
towertalk-request at contesting.com writes:
> I used Champion Radio's WinMARC tool to calculate the recommended masts
my planned VHF/UHF stack. If I enter an extra safe wind speed of 100 mph
(my county is 70 mph basic speed), the tool suggests the following masts:
Wall Yield Strength Description
---- -------------- ------------------------------------------
0.120 40,000 6063-T835 Drawn aluminum tube
0.120 42,000 2024-T3 Drawn aluminum tube
0.120 46,000 A 500 Grade B Structural steel pipe
0.120 50,000 1010 Carbon steel CDBW
What was the bending moment figure you're working with? 40,000 psi or
This is much simpler IMO. Your 100 MPH safety factor has skewed the
whole thing. That's 2-3 times the wind pressure as your REAL windspeed rating.
I'll never discourage anyone from over-engineering something but you should
back up a step or two.
Your vhf/uhf stack is pretty small. If you lower the windspeed to 90 or
even 80 - it'll change what's required - resulting in you saving a bunch of
money and hassle. (I don't discourage anyone from spending money either.)
All you really need is - dare I say it - some galvanized pipe; e.g.
Schedule 40 water pipe, conduit, EMT, etc. It's rated around 35,000 psi yield
strength which should be fine for your proposed installation. And you can drive
down to your big box hardware store and get what you need. Cheap. Maybe you
have some in your boneyard.
While the galvanized pipe is 1.9" OD, your yagis won't know the
difference. That's what I'd do.
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