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Re: [TowerTalk] Rotator loops was: Re: Feedline for a new tower

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rotator loops was: Re: Feedline for a new tower
From: Grant Saviers <grants2@pacbell.net>
Date: Sun, 11 Nov 2018 07:40:08 -0800
List-post: <mailto:towertalk@contesting.com>
For me the "best" alternative is a slack vertical coax from a point on the boom about 18" out from the mast to a point on the tower top.  The boom needs to be 2' or more above the tower top. Then there is no chance for coax to catch an edge of the tower or possibility of getting frozen in place.     For north centered rotation the fixed points are on the north side of boom and tower, so the "twist" put in the coax is +/- 1/2 turn.  This was done for a SteppIR DB36 with an upsized 16 conductor motor cable plus coax for it and another antenna with control cable above.  I've used the 2 or 3 turn laying on the solid top plate but there remained a chance of catching the tower edge or getting frozen as Joe mentions.

A swing arm follower is another way to keep cables away from the tower.  I have 30" long arms about 18" below my Rohn 65 ring rotators to a stub on the ring and they allow coax and motor leads to follow and not touch tower or ring.  The actual flex point is then at the hinge of the follower, and this works for the 270+ deg rotation of the seven rings.  With a follower mounted just above a tower top the follower rotation limit would only be the mast diameter so with some coax slack some over-travel would likely work.  The jumpers from the Heliax inside my R65 to the coax choke at the feedpoint are Buryflex.  The choke is in a plastic j-box and coax in and 10ga feedpoint out leads out go thru waterproof cable glands.  The TFE coax wound chokes are soldered so there are no coax connectors out on the boom.  Fewer outdoor coax connectors = more reliability and its been 100%.

I replaced all the cables on a re-purposed live truck Will-Burt mast a while ago.  The new ones went into new coiled nylon carrier  ($1k).  A task I never want to do again.

Grant KZ1W

On 11/11/2018 6:13 AM, Joe Subich, W4TV wrote:

On 2018-11-11 8:44 AM, N4ZR wrote:
> I've never understood typical ham practice of a hanging loop.

Two or three turns laying on the top plate works where one has a
top plate, the turns are supported so they can't shift and catch
on a "corner" of the plate, and there is no snow or ice to freeze
the loops.

Where one has no top plate (a "pointy top" tower, or mast mounted
rotator) or there is snow/ice, the chance of tearing the cables
(or cutting the jacket) is much higher in the "two or three turn"
approach.

In broadcast we do it all the time with Heliax on live trucks.

In every live truck I ever built (several hundred), the *entire*
feedline up the mast was part of the "rotator loop" - that was a
dozen or more three to four foot diameter turns all the way down
a 40 to 60 foot mast.  It also resulted in the feedline being
almost twice as long as would have been needed to if it went
straight up the side of the mast.

73,

   ... Joe, W4TV


On 2018-11-11 8:44 AM, N4ZR wrote:
I've never understood typical ham practice of a hanging loop.  What Chuck describes is mechanically much superior.

73, Pete N4ZR
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

On 11/11/2018 8:24 AM, Chuck Tifft via TowerTalk wrote:
No need to transition. I just use about 2 to 3 turns of the LMR in about a 12" diameter coil basically laying on the top of the tower. That leaves plenty to absorb 360 degrees of rotation. In broadcast we do it all the time with Heliax on live trucks.

Chuck W6RD


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