KG5U wrote, in part:
>A. What is the best way to secure the mast segment within
>the tower so that it (1) doesn't drop down putting the 204BA
>boom-mast clamp plate on the thrust bearing; and (2) doesn't
>allow the array to tilt?
Dale, your proposed method will work. When you say "crowbar" it up, do you
mean wedge a crowbar under the 204BA clamp, loosen the rotator clamps, and
lever the antenna/mast combo up a couple inches? If so, while holding it up
you can insert a muffler clamp on the mast just above your bearing and
quickly tighten it up ( use a ratchet with DEEP SOCKET for speed)... it will
hold that stuff fine. If you are conservative, add a second muffler clamp
above the first one. Then do the in-line tie-off as you mentioned, and
remove the rotator. The above is most safely done with two people-- one to
hold the crowbar up and the other to put on the clamp, but one CAN do it.
One of my pet peeves about Rohn is their assumption that people should put
rotators "close" to the top of the tower. Their construction method
precludes hanging a come-along in the tower for moving and holding a mast
because there is not enough vertical dimension available (you need several
feet). With 1.)a come-along, 2.)a removable clamp to attach the bottom hook
to just above the rotator, and 3.)several feet of exposed mast there, one
man can move ANY CONCEIVABLE AMATEUR MAST AND STACK OF ANTENNAS up and down
with ease and total safety. In addition, extra space in there allows you to
put in an intermediate "centering plate" (Rohn doesn't make one, of course,
but Tri-Ex does!), which also takes care of the mast-tilt problem when the
rotator is removed.
Since I'm on the soapbox, here's another related bit of heresy: The
so-called "locking collar", usually with sockethead screws which comes with
some two-part thrust bearings is essentially worthless in our application.
Those slightly eccentric collars/bearings are intended for use in factories
and such with one-way shaft rotations. So they don't really lock properly
in our application. Today's free advice: The bearing itself is fine; throw
the collar away. Make your own dead-weight support collar to ride on top of
the bearing. Muffler clamps do work, if a bit inelegant. My personal
solution is the Hy-Gain aluminum block clamshells (redrilled for 3/8 bolts).
Whatever your personal method is, make it FAST TO USE with a deep-socket
ratchet.
73, Glenn K6NA
p.s. for Dale... Tnx to NASA gang for the great Mars show!
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