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Re: [TowerTalk] Sources for mast material

Subject: Re: [TowerTalk] Sources for mast material
Date: Tue, 5 Aug 2008 18:59:17 EDT
List-post: <">>
In a message dated 8/5/2008 6:23:13 A.M. Pacific Daylight Time, 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 

Howdy --
    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 
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. 
Steve     K7LXC


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