HansLG@aol.com wrote:
> Hi Michael,
>
> Dave, K1TTT, gave me the advice to tape the coax to the tower legs. Just
> plain, good, electric tape. You should, of course, us some flexible coax at
> the
> point when you need the flexibility for the rotation of the antenna and that
> has to be movable, but the rest can just be taped in place. No, I wouldn't
> recommend you to have the coax hanging along the boom but tape it there to.
> Naturally, you should keep the tape tension "just right" so you don't make
> indentations in the coax.
>
> A story has it that when they installed the coax for a TV transmitter in
> Gothenburg, Sweden, they managed to put the cable clamps at just the right
> (or
> wrong) distance that the combined reflections from all the clamps came back
> in
> phase with a catastrophic result on the SWR. I don't know if the story is
> right but I am sure if you clamp or tape the coax you will not manage to see
> a
> noticeable result on the SWR.
>
> Good luck with your tower and antennas.
>
> Hans, N2JFS
>
>
>
> ____________________________________
> From: k5mef@mefox.org
> To: towertalk@contesting.com
> Sent: 8/24/2008 10:03:00 P.M. Eastern Daylight Time
> Subj: [TowerTalk] Strain releif for vertical coax
>
>
> I'm putting up my first antennas on a rotator and roof-top tower and I could
> really use some help.
>
>
>
> Sorry if these questions are simplistic for those of you who have put up at
> least one mast. But being this is my first, tower, first experience with a
> rotator, etc., I need some help regarding the routing and securing of the
> coax for several VHF/UHF antennas sharing the same mast. I'm planning to
> use LMR 400 Ultraflex (plain LMR 400 seems too stiff).
>
>
>
> The coax will be connected to the antenna connector and then taped to the
> antenna boom to strain relieve the connector.
>
>
>
> 1) Should the coax be taped to the boom all the way back to the mast and
> then down the mast? Or should it be allowed to fall vertically somewhere
> before it gets to the mast in order to make the rotating loop easier? (Bear
> in mind there are 4 antennas on the mast.)
>
>
>
> 1a) Just in case your answer is to not tape it all of the way back to the
> mast, it seems like letting the coax simply hang from the antenna boom would
> put stress on the boom and also, eventually, pull the tape free. These are
> VHF/UHF antennas which means they are light weight and probably would not do
> well with coaxing pulling down on them. Suggestions?
>
>
>
> The lowest antenna is planned to be 2 feet above the thrust bearing in order
> to have some room for a cable loop for the rotator. It's feed point is
> close to the mast. So that cable will probably be taped to the mast for
> strain relief. So now I've got to make a loop to allow for the rotator to
> turn.
>
>
>
> Simply letting the coax hang doesn't seem right. As the rotator turns, it
> will have to haul the coax up as it reaches full rotation in either
> direction and the coax will be rubbing against the mast and guy wires.
> Plus, there are four cables so that's some added strain for the rotator. So
> I presume I need to hold the coax up so that there is a strain-relieved loop
> of free cable to allow the rotator to turn easily.
>
>
>
> 2) How do you hold the coax up to make the rotator loop? Just tape it to
> the tower leg? Seems like if the tape is in the sun and becomes soft, the
> coax would eventually slip down.
>
>
>
> 3) How do you make certain that the twisting applied to the coax doesn't
> get translated into twisting at the antenna? Just plenty of tape to
> strain-relieve the antenna connector?
>
>
>
> Thank much in advance.
>
>
>
> 73,
>
> Michael - K5MEF
>
>
>
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>
Regarding the fixing of feeder- our company installed a UHF TV antenna
on a tower in Thailand about 400 feet high using 5 inch feeder. The
local riggers overtensioned the cable clamps on the cable runway up the
tower and the indentations in the feeder caused significant problems
with return loss. We loosened of the cable clamps - rotated the feeder
90 degrees and retensioned the clamps. The rotation and retensioning was
enough to restore the feeder to its normal shape and the return loss to
an acceptable figure. The moral of the story is- dont use unskilled and
unsupervised labour to run your feeders.
Rod (VK5UV)
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