Press --
I suppose it would be correct to say that I am using too much coax around
the rotator, but that is because I have a base-rotated tubular crankup
tower! The rotator is located at the very bottom of the tower, underneath
the rotating tubular mast. The typical short loop that you describe is what
I have when the tower is extended to its full height of 72 feet. In fact,
this loop is positioned several feet above the rotator, and behaves just as
you describe when the tower is fully extended.
However, whenever I retract the tower to less than its full height
(necessary under high-wind conditions and for XYL-pleasing cosmetic
reasons), as much as 50 feet of extra coax will be lying in a pile on the
ground near the rotator. As I described in my original post, there are four
coax standoff arms on the tower, one at the top of each tubular section.
They are positioned in a straight line so that the coax drops through them
into a pile on the ground when the tower is retracted. As this happens,
stiff coax tends to form large loops that wrap themselves around the tower
and get into bad places like the nooks and crannies around the rotator and
the raising motor housing (which is about 10 feet up and quite large.) When
the tower is extended again, these loops can get snagged and cause
significant damage (as happened to me a few days ago.)
Note also that the tower can be rotated when it is not fully extended, and
that this is a highly desirable feature because it allows me to operate
during higher wind conditions and keeps the peace with the XYL (at less than
60 feet, it's below a set of trees that screen it from the house.) When the
tower is rotated in this fashion, theres a whole bunch of extra coax lying
in the ground around the rotator.
Before anyone goes and suggests fixing the coax to each standoff arm so it
forms a series of loops, I should mention that experiments with this were
not very encouraging. As the tower was raised, the loops twisted and gyrated
enough that it was almost certain that they would catch on one or both of
the limit switches mounted at the top of the first section. It looks like
that possibility could be reduced by using a somewhat more flexible coax,
like RG/213, and staggering the coax arms (although there is somewhat less
that 180 degrees of tower in which to do so, and the arms have to be
staggered around a series of four narrow tubes that range from 3 to 8 inches
in diameter.) However, I still think it's unlikely that this will work and
I'm not too excited about risking damage to those limit switches. Of course,
I am open to suggestion from anyone who has successfully dressed the coax
into loops on a U.S. Tower 72' motorized base-rotating tubular tower
(results on other tower configurations may not be relevant.)
So far, my plan is to add another standoff just above or below the motor (or
both). This should keep the coax from snaking around the tower and getting
hung up in the motor housing. Also, I plan to build a tubular shield around
the base of the tower to keep the coax away from the rotator and the sharp
angles and bolts near it. Finally, on the excellent advice of Stan, N3KK, I
plan to try a low amperage fast-blow fuse for the raising motor. This should
add another level of protection in case the coax snags.
Any other ideas would be much appreciated.
73, Dick, WC1M
-----Original Message-----
From: Press W Jones <n8ug@juno.com>
To: dick.green@valley.net <dick.green@valley.net>; towertalk@contesting.com
<towertalk@contesting.com>
Cc: cqwire@juno.com <cqwire@juno.com>
To: <towertalk@contesting.com>
Date: Monday, October 13, 1997 8:54 PM
Subject: Re: [TowerTalk] Coax Mishap on Rotating Crankup
>Dick, it would seem that you are using too much coax around the rotor.
>The ideal set up on a simple tower/rotor installation is a 45 degree
>departure from the vertical below the rotor and a 45 degree return to the
>mast above it, while the rotor is at 180 degrees of rotation. The
>rotation to zero or 360 then displays the coax wrapped 1/2 of the way
>around the mast, with the two previous departures to 45 degrees reduced
>to 5 to 10 degrees, more or less. There is nothing to snag, by chance,
>wind, ice, or design this way, and at no time is the ideal bend radius(15
>X OD) of the coax exceeded.
>LMR400UF should work perfectly well, as will several other coaxes with
>lower loss. The stiffness of the coax for whatever reason is not the
>significant criteria - it is the stranded center conductor, making
>rotation possible without harm to the coax when properly installed. How
>it feels to you is not relevant -- the rotator doesn't know the
>difference in one correct cable from the other.
>73
>Press Jones, N8UG
>The Wireman, Inc., Landrum, SC 29356
>use n8ug@juno.com or (864) 895-4195 for tech help
>orders only use 800-727-WIRE(9473) or cqwire@juno.com
>http://www.thewireman.com
>
>On Sat, 11 Oct 1997 21:47:23 -0400 "\"Dick
>Green\"."<dick.green@valley.net> writes:
>>Hi, folks. I need some help again
><SNIP>
>>73, Dick, WC1M
>>
>>
>>
>
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