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

[Grant Saviers]

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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