In a message dated 99-01-05 15:52:23 EST, G3ZEM@btinternet.com writes:
> I have a TH11 mounted on the mast about a foot above the tower top. I am
> now planning to stack a CC XM240 about 10 ft above the TH11. I don't think
> the 2 inch aluminium mast that supports the TH11 is adequate but don't know
> what spec of mast or type of material it is sensible to replace it with.
> (Both yagis and my rotator will handle up to 2.5 inch mast)
You're right about the aluminum mast.
First off, do you know what your local windspeed zone exposure is? The
lowest value in the States is 70 MPH with higher windspeeds as you get closer
to the coasts (115 MPH in parts of Florida!). Contact your local building
department or airport for more information on this important factor. USA hams
can look up their county windspeed at http://www.championradio.com; the
TIA-222 windspeeds are listed there.
BTW, a couple of minutes spent in the TowerTalk archives
(http://www.contesting.com) will yield the information that you're looking for
also.
>
> I know a lot has been written on this reflector about mast materials and
I'm
> sure if I read it all and study for a degree in mechanical and structural
> engineering I'd be able to figure this out for myself....but life's short
> and there's dx to be worked.
The easiest way to find out what you need is to use the MARC (Mast,
Antenna and Rotator Calculator) Program from Champion Radio Products. Put in
the windspeed, antennas and spacing and it'll tell you what the bending moment
and recommended mast material and wall thickness is. It's only $9.95 from the
aforementioned Champion Radio Products.
BTW, the manufacturer probably recommends 10 foot spacing but I've had
success with spacing as close as 7 feet.
Cheers and GL, Steve K7LXC
Champion Radio Products
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