In a message dated 5/15/2010 12:01:22 P.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:
> For various reasons (some inherent in bearing manufacturing tolerances)
three spaced bearings are almost never done in machinery - it's just too
hard to get them/keep them aligned.
And this is in more precision machinery than you'll ever find in tower
components. The purpose of the middle "bearing" is to capture the mast so that
you can do a rotator swap on a top-heavy mast and antenna array. A simple
plate with a hole in the middle (e.g. AS25G, 45G, Trylon, etc.) is PLENTY.
It's not going to go anywhere. Lacking a middle plate, you can still
capture the mast with some angle iron and U-bolts. It's not difficult to
fabricate and use.
And I still think that top mounted thrust bearings are a ham radio old
wive's tale and not necessary. All you want to do is hold the mast against
horizontal wind forces - the vertical forces can go to the rotator in most
cases with no problem.
Cheers,
Steve K7LXC
TOWER TECH -
Professional tower services for hams
and author of UP THE TOWER - The Complete Guide To Tower Construction
available from _www.championradio.com_ (http://www.championradio.com)
Cell: 206-890--4188
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