> I like Dave's idea of using a regular Rohn 45 section as the top section
> rather than a "top section." My other tower has a regular one. The Rohn
> "top section" lacks the diagonals for the top several feet, I guess for
> ease of rotator installation there...many of us with longer masts are
> putting our rotator further down anyway. So the top several feet of
> tower must be weaker than the rest of the tower that has diagonals.
>
> 73 - Rich Boyd, KE3Q
Rich and all, I have 100" of 45. I use four sets of guys at approx
99', 89', 59' and 29'. I have a 4" mast that sits in two bearings
at the 99' and 89' level. However the rotor is at the 59' level.
My experience is that it is almost impossible to set the rotor at
the bottom of a two bearing mast configuration because the rotor is
extremely difficult to get aligned with the two bearings without
binding.
The mast from the 89' bearing to the Rotor at 59' is a 2" [nothing
fancy] tubing that will allow you to disreguard any small alignment
problems to the rotor. As a benefit, because of the twisting action
of the long mast, it acts like a shock absorber to the rotor. Be
sure to install some guides along the 2" mast between the rotor and
the bottom bearing.
This configuration allows me to put a TH6DXX at 100' and a 2 el 40
15' above it. The mast above the 45 is set inside Rohn 35 ( Motorola
comercial stuff) so it's easy to climb.
Using the mast, bearings and guys in this method, it removes almost
all the moment from the top tower sections.
This has been up for quite a few years, and the tower/mast setup has
survived winds in excess of 90 mph that literally damaged or
destroyed every antenna up there. Not to mention the dreaded ice
storms.
GL
------------------------
James Wolf, KR9U
jbwolf@cris.com (home)
jbwolf@most.fw.hac.com (work)
jbwolf@compuserve.com (alt)
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