[TowerTalk] Mast

[K7LXC@aol.com]

In a message dated 04/19/2000 11:12:16 AM Pacific Daylight Time, 
wa9pam@arrl.net writes:

> Since you all brought up masting.....I have a ssvn tower, my center mast is 
>  a 2.4210 OD
>  schedule-80 with a 2" ID, x 21' , five feet in the tower.  here is my 
>  problem.  I have a TH6DXX
>  antenna at the 100' level, 2-440 ant's, then 2-2Meters ant's.  I want to 
>  put a 5 element M2
>  6 meter antenna at about a foot from the top.  Then there is a 6/2/440 
>  antenna on the end of the mast.
>  
>  Should I change the mast to something different or should I drop another 
>  mast inside and bolt it in?  
   
      First of all, Chippewa County is an 80 MPH windspeed zone so you need 
to take that into consideration. (All US TIA-222 county windspeeds are listed 
at http://www.championradio.com under "Tech Notes".)

      You didn't say how far above the tower the TH6 is. If it's right at the 
top of the tower at the bottom of the mast, then it doesn't really exert any 
bending moment to your mast. 

      A typical Schedule 80 pipe can be as much as 35,000 psi yield strength. 
According to my MARC (Mast, Antenna and Rotator Calculator) Program your 
proposed installation will exert 34,479 in-lbs of bending moment and needs a 
mast with 65,000 psi yield strength and 1/4" wall so you need to replace your 
mast. Then you can sleep nights when those BIG storms blow through. (MARC is 
available at the same website.) Something like an SAE 1027 is around this 
strength. 

Cheers,   Steve    K7LXC
Champion Radio Products 

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