Subj: Re: [TowerTalk] A Question about Mast Tubeing (sic)
To: <towertalk@contesting.com>
Date: 07/01/98
To: hglent@ix.netcom.com
In a message dated 98-07-01 13:07:41 EDT, you write:
<< I am putting up a new M2 Rotor on a Rohn 25 tower to swing a Sommers
XP708 antenna. I am using the Rohn bearing plate on top of the standard
25G section. I intend on mounting the rotor at the bottom of the first
tower section down from the top. I plan on running a 2" OD mast from
the rotor through the bearing and approximately 10 feet above the XP708
which I intend on placing on right above the bearing. I will be placing
a Cushcraft AR270B at the very top of the mast above the beam.
>>Here is the question: I have been trying to decide what kind of
material I should use for the 2"OD mast. I have gotten prices for 4130
material 2"OD with a 1/8" wall thickness, and a carbon steel tubing 2"OD
with a 7/32" wall thickness. The 4130 will cost about $7.95 per foot
and the Carbon Steel will cost about $6.50 per foot.
>>What is the strongest and best type of material of the 2 possibilities?
Are these prices about right for these products? >>
First things first. If you're in Larimer County, CO, your windspeed
rating is 85 MPH with local areas of higher windspeeds.
When you've got loads on an exposed mast, your questions become pretty
important. (I wouldn't classify an AR270B as much of a load.) Nonetheless, the
best tool for mast selection is the MARC Program (Mast, Antenna and Rotator
Calculator). You put in the parameters such as windspeed, stacking distance,
antenna specs, etc. and MARC will calculate the bending moment and make
recommendations about yield strength and wall thickness required. It's
available at www.championradio.com for $9.95 + s/h.
Then you can go shopping for the right piece of metal.
Cheers, Steve K7LXC
Champion Radio Products
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