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Re: [TowerTalk] aluminum mast again

To: stetrekve@yahoo.com, towertalk@contesting.com
Subject: Re: [TowerTalk] aluminum mast again
From: K7LXC@aol.com
Date: Tue, 2 Sep 2003 17:23:17 EDT
List-post: <mailto:towertalk@contesting.com>
In a message dated 9/2/03 1:53:54 PM Pacific Daylight Time, 
stetrekve@yahoo.com writes:

> This topic has probably come up countless times before
>  but I am on the verge of making a decison this week
>  for my installation.  I will have a M2 2M5WL 2 meter
>  beam (17 element, 33' boom, 13 lb), the M2 6M7JHV 6
>  meter beam (7 element, 33' boom, 17 lb), and a Force
>  12 C31XR on one mast out of Rohn 25 at 85 feet.  The
>  tower is guyed per the Rohn book for the next wind
>  area above my location (which is the lowest wind
>  rating of 70+ MPH).  I made the tower fulfill the
>  specifications for the next higher wind loading.
>  
>  The mast will be into the top section about 6-7 feet
>  with a M2 2800 rotator and and TB3 thrust bearing at
>  the top.  The total mast length will be 24 feet long
>  to extend 16" or so out of the tower to separate the
>  three beams from each other.  The C31 will be one foot
>  above the top of the tower so only the two lighter
>  weight beams will on the unsupported mast.
>  
>  I have this 24 foot steel mast of 2" OD and about 0.2
>  wall thickness of unknown origin (type, specifications
>  unknown). It weighs 98 lb.  To lower the total weight,
>  I am serious thinking of the following.
>  
>  Does anyone have a problem with me using a 24 foot
>  mast of 6061T6 aluminum, 2" OD, 0.25" thick wall?  The
>  less weight will mean an easier time of shoving up the
>  mast with each antenna being put on and less weight at
>  the top of the tower.  Both VHF antennas have a dacron
>  rope to make the ends even with the center.

    The antennas up on the mast are relatively small so the bending moment 
they exert on the mast vis-a-vis your low windspeed rating is also relatively 
small. The aforementioned aluminum has a yield strength of 35,000 psi. 

    Give me the square footage and spacing of the VHF antennas and I'll run 
my MARC (Mast, Antenna, and Rotator Calculator) Program. My educated guess is 
that you'll be okay.

Cheers,
Steve    K7LXC
TOWER TECH 
_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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