Gary, W5FI wrote:
> The problems that I have had coming up through the center are with
>excessive binding of the raising rope or line going through to thrust
>bearing or through the tower. Either way, there will be problems with being
>other than totally vertical coming through the thrust bearing and there is a
>tendency to want to scrape all the galvanizing or anti-rust outer surface
>due to lifting torque producing a bind. I have found that the over the top
>process seems to be a little less destructive to my mast. I have found less
>binding and scraping when I am using the over the top system than the pull
>it up through the center system... I have found the pulling it up through
>the center from the bottom system to be incredibly tedious to get the mast
>worked up through the thrust bearing and then raised with the antennas on it
>using only a bottom raising point. That was tough. I wonder how the ops
>coming up from the bottom find that they get leverage and stability to move
>the mast up through the bearing with no rotor or bottom stabilitization
>point as the mast plus one or two big yagis are slowly elevated. Piece of
>cake from the top.
K6NA writes:
I have no problem bringing it up inside the tower, or continuing to raise
the mast once the first beam is on it. The difference I see is that you
have a bearing at the top, as expected, but you do not have another
intermediate, "centering plate" down about 4 feet from the tower top. I
always have this intermediate plate, with sleeve, in place about 4 feet
above my rotator plate. That way, when the rotator and its plate are
removed, the mast is still held vertically in place. The antenna load can't
cause the mast to move out of line, even when the mast is very top-heavy,
and so with a come-along or winch the mast is easy to run up and down.
The intermediate plate is very necessary also to keep sideload off the
rotator, once the installation is in operation. Just a bearing at the top
won't do it. There was a post here a few months ago about the freak
windstorm in Phoenix which killed some towers. At one location, the tower
worker reported that a Tailtwister housing inside a Rohn tower had simply
fractured from sideload on the mast. You can bet there was no intermediate
plate in that tower!
I recently built and installed a prop pitch system at W6EEN for his big 40m
beam.This was a retrofit on an existing system where the Japanese rotator
had vaporized. Don had a 3-inch mast extending down about 9 feet in the
Rohn 45, but no intermediate plate. We designed some centering brackets and
installed them halfway down. With a come-along, it was easy to jack the
mast up or down to complete the installation and mate the mast to the prop
pitch (mast plus beam weigh 600 pounds). Without the intermediate, slip-fit
brackets, Don will tell you this would have been nearly impossible, at best
dangerous. And, now there is no side load whatsoever on the prop pitch.
I use Tri-Ex tower and they make movable intermediate mast plates for their
towers. Rohn does not make one apparently. Since most of you guys out
there seem to be using Rohn guyed tower, you should consider making your own
plate. One way is to have a metal-fab shop modify a Rohn rotator plate to
act as an intermediate mast plate. The ideal intermediate plate has a
slip-fit sleeve about 3 inches long welded on the underside of the plate,
carefully centered, and another thrust bearing on the top of the plate, just
like on the tower top. This may be overkill but do it if you can afford it.
Gary, your oversize gin pole method is perfectly fine for insertion of the
long mast. I did it that way when I built the 9Y4H Rohn 55 tower, and we
had to build our own long gin pole to make it all happen!
73! Glenn K6NA
rattmann@cts.com
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