[ADXA] rotator mast pinning

[Dennis Schaefer]

After my comment about pinning the mast, I thought I should research the
issue again since I’m getting ready to swap out a rotator.   I have to say
right up front that in the last 35 years or so, I have never gone up the
tower to correct an aiming error.   With rotator repairs and several
antenna change-outs during that time, making  sure the mast clamps were
properly tightened every few years did the job.

I read lots of comments, many in the old tower talk forum, where the big
dogs hung out.  The word most often associated with NOT pinning the mast
was “nuisance” or “inconvenience”.  The words most often associated with
pinning the mast was “catastrophic failure”.    A reason often given for
pinning the mast was “Yaesu said to do it”.

I understand that catastrophic failure caused by pinning  is rare and
unlikely, but brake wedge failure and bell housing damage were often
mentioned.  This would probably only occur with a very large and/or
unbalanced antenna.   The problem is that big antennas  exert more torque
and are more likely to cause slippage.  Pinning the mast might be
 necessary for those really big antennas.  You’re going to spend time and
money maintaining a large antenna system anyway.

My antennas have usually been relatively small tribanders, except for the
Mosley PRO-57, which was a little larger.  My C-3 has been trouble free and
slippage free for over 20 years and I don’t expect any problems.  If I had
a 30 foot boom, I would anticipate problems, such as more rotator failure,
weather damage, sheared mast pin bolts, etc.  That’s one reason I stick
with smaller antennas.

This article seems sensible:
https://ve3vn.blogspot.com/2022/02/hy-gain-rotator-mast-slippage.html

I just remembered something - At our club station, we had a KLM KT-34XA,
which was a pretty big tribander.  (about a 36 foot boom and very
unbalanced).  We found a bunch of ball bearings on the ground from its
Ham-4 after some wind.  I don’t remember if the mast was pinned, or just
good and tight, but it did not slip, and there was catastrophic damage to
the rotator.  Would it have helped if the mast had slipped?  Maybe, maybe
not.

I’m not trying to change anyone’s mind, or soliciting comments or arguments
- it’s like politics, everyone has their minds made up.  By all means, do
what you are comfortable with.   I just did this research to refresh my
knowledge and wanted to share my thoughts.   I learn a lot from ADXA
members and seldom have anything technical to contribute.

73,
Dennis/RZ
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