When I installed my 72' rotating tubular motorized crankup back in 1997, I
used LMR400UF. Big mistake. IMHO, that stuff is so stiff it shouldn't be
called "flexible". There were a number of issues with dressing the coax on
the tower that were due to total lack of instructions from U.S. Tower, but
the long and short of it is that the LMR400UF was so stiff that a big loop
of it "crept" around the tower while it was being lowered and got caught in
the motor mounting brackets. Next time I raised the tower, the coax snagged
on the brackets just before the tower reached full up. The tower proceeded
to lurch violently back and forth in a sickening manner in the second or so
before I realized what was happening and hit the power switch (I was in the
shack at the time, 265' away, watching through a window.) I ran to the tower
and found, much to my relief, that the plastic balun housing on the TH-7 had
exploded, which freed the SO-239 and the coax before the raising cables
snapped or the pulleys or the motor were destroyed.
I reconfigured the standoffs and bought an extra one to put below the motor
so the coax couldn't possible get snagged again. I also put a hardware cloth
cage around the base to keep the coax away from the rotor. Most important, I
replaced the LMR400UF with RG-213. I have had no snags since. I'm completely
confident in raising and lowering the tower remotely without seeing it.
Some years later, I ran some flexibility tests between Buryflex, LMR400UF,
Belden 9913 and RG-213. It was no surprise that the 9913 was too stiff for
the crankup or rotor loops, nor was it a surprise that the LMR400UF came in
a distant 3rd. What did surprise me was that the Buryflex was almost as
flexible as the RG-213, and the jacket was much more slippery -- perfect for
gliding through the coax standoffs on the crankup (I don't attach the coax
to the standoffs because it results in all sorts of twisting and snagging.)
Anyway, I replaced the RG-213 with Buryflex and it has performed perfectly
ever since. I can't recall how long it's been, but I'm sure it's at least 10
years. Maybe more like 15.
Incidentally, I used LMR400UF for a number of runs on the ground, like the
feedline to my 40m 4-square. That was problematic, too, because it seems
that the critters on my property love to munch on the jacket material. I had
to replace that particular 100' run, and several others, countless times.
Then I replaced the runs with Buryflex and haven't had a critter problem
since.
YMMV
73, Dick WC1M
> -----Original Message-----
> From: Marv Shelton [mailto:marvs@att.net]
> Sent: Tuesday, May 14, 2013 8:10 AM
> To: K8RI
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Attaching "flex" cable to crank-up standoffs
>
> So, what do you think is best? RG-213???
> I think getting 5 years out of low loss coax is acceptable. I can help
> force at least that interval of mainten ance on one's amtennas.
>
>
> Best 73's
> de Marv WA2BFW/7
> (from my iPad)
> >
> > LMR 400 is not recommended for repeated bending. It has a Copper
> plated solid Aluminum center conductor. OTOH LMR-400UF is very
> flexible but does not normally stand up well to out door use. The jacket
> is a rubber like material that is easily abraded, catches on most any
> thing and has a short advertised life of 10 years. Best I've gotten out
> of using it in normal situations has been around 6 years. It works very
> well, but not for long.
> >
> > 73
> >
> > Roger (K8RI)
> >
> >
> >>
> >> 73's from Marv
> >> wa2bfw@att.net
> >>
> >>
> >>
> >> _______________________________________________
> >>
> >>
> >>
> >> _______________________________________________
> >> TowerTalk mailing list
> >> TowerTalk@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> >
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