Ok, What to use for a Mast?

[K7LXC@aol.com]

In a message dated 96-12-03 15:29:13 EST, you write:

>My plan is to place 2" mast into the tower, lower the rotor to the bottom of
>the first section and place a thrust bearing where the rotor would mount at
>the top.  I plan to place a slightly larger antenna on the tower in the
>fall...like a TH7 or .... something!  I don't know yet.
>
>If schedule 80 iron or steel pipe is not recommended...then what is?  Where
>do you get it?  What is the cost?
>
>I live in Southcentral Kansas, near Wichita, which is known for a tornado or
>twoand strong straight line winds from time to time.  What kills towers out
>here is four or five days of 30 to 40 MPH winds.
>
Hi, Lee --

     First of all, if you're in Harvey County, it is an 80 MPH wind zone.  A
little more than the minimum of 70 that the TIA-222 gives but not a bad spot.
 Just watch out for those tornados.

    Secondly, all of the pithy and largely scathing comments regarding pipe's
usefulness in antenna mast applications is directed to having stacked
antennas UP the mast.  If you 're just going to have one antenna on the mast
and it's at the top of the tower (or within inches), go ahead and use
Schedule whatever.  There isn't enough moment of force to worry about.  It's
when you start putting big loads up the mast and creating reasonably large
moments that the problems arise.  That's what'll separate the men from the
boys and the tubing from the pipe.

     In other words, the TH7 is fine by itself at the top of the tower but
you'll need something more substantial if you want to add a 2L 40M or
something like that.  And you'll probably want to sometime.  Additional
information on specific mast calculations and applications can be found in
Dave Lesson's, W6QHS, book on "Physical Design of Yagi Antennas".

    Last, how does 4 or 5 days of 30 to 40 mph winds topple a tower?  Were
these too small or underengineered to begin with?   I think they'd have to
be.  

73,  Steve  K7LXC

    TOWER TECH -- professional tower supplies and services for amateurs

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