Securing Coax to a tower.
Since hams tend to be experimenters it is nice to select a method
that can be reused if more cables are added in the future -- which
gives an advantage to using TW wire for the cable ties. TW ties
can be reused if they are installed without a lot of twisting. You can
fold a short length of wire in half, wrap the doubled wire around the
tower leg and cables, and then feed the tails of the TW through the
loop in the middle of the TW and pull that tight. This is actually easier
than twisting the wire. But it is not very tight and may not provide
much vertical support, so you will need periodic ties like Kellems grips.
(Correct spelling = Kellems grip from the Kellems Cable Grip's Company
founded by a woman, Vivien Kellems (who was a withholding-tax protester),
based on a patent granted to her brother.)
http://en.wikipedia.org/wiki/Vivien_Kellems
Tape works well but only use good stuff like Scotch 33+ or Scotch 88,
which are specified as all-weather tapes and their adhesive will not
seriously degrade in freezing temperatures. (Scotch 33+ is 7 mil and
Scotch 88 is 8.5 mil thick, BTW.) But there are two precautions to take
with tape. 1) If you pull it very tight by stretching it for every wrap AND
you put on a lot of wraps it can crush the cable with the cumulative force
of many wraps, as the tape tries to regain its original shape. But it
takes a lot of layers and if you use good tape, which is expensive,
you are less likely to use that much of it. 2) On the last turn or two
of tape you do not want to pull it very tight so that it won't "flag" on
you, a problem which is exacerbated by pulling the tape to break the
roll loose from the wrap. You always want to CUT the tape when you
stop the wrap. Good scissors are best because even using a knife
can add some stretch to the tape as you tension the tape enough to
cut it. Tape does provide a bit of vertical support if enough layers are
used, but it is difficult to reuse the tape again if you want to add cables
in the future.
Plastic cable ties are a possible choice but there are THREE types.
Ones that are not UV resistant and that will promptly degrade in a
season or two of sunshine. There are ones (usually black) that are
UV resistant and that will last many seasons in the sunshine, but probably
not "forever". And then there are ones that CLAIM to be UV resistant
but are not very good and will fail in a couple of seasons. It is difficult
to tell the second group from the third group and about all you can do is
to use QUALITY UV-resistant nylon ties -- the bargain ones that are
1,000 for $8 (or whatever) are probably NOT UV resistant even if they say
they are. Some cable ties can be reused because the latch is accessible
enough to be released in the future. But that can be a pain while on the
tower, so I consider them expendable and never reuse them.
The classical method, provided by cable and antenna suppliers is the
cable tie made of thin stainless steel. These can be reused in some latch
designs, but I am not sure of the Harbor Freight ones since I have never
used them. But now that I am aware of them I think I will give them a
try. They are a lot cheaper than the ones from the antenna and cable
companies.
Running a LONG span of cable with only a single support for the weight
of the cable at the top will result in the cable stretching with time, so it is
best to provide some sort of vertical clamping every 50 ft or so. And cable
ties need to be placed close enough together so that the cable does not
beat against the tower leg in the wind. There is nothing more annoying
(especially to the neighbors) to have the cable slapping the tower like
a flag pole rope clanging against the flag pole.
For my own ham projects which change occasionally I tend to use three
or four decent tape wraps at the top of an RG-213 run for the vertical support
and then an occasional tape tie every tower section or two, and then fill
in the gaps with TW wire ties. But with the explosion in prices of copper
wire in the past year or two I may have to rethink the use of TW and just
use gold chains from the jewelry store! ;-)
One thing to think about is planning multiple cable runs, especially if they
are added one at a time over a long period. It is most convenient and safest
to run all cables on one leg of a tower, leaving the other two legs
cable-free for
ease of climbing the tower. But there is nothing more frustrating than wanting
to remove a cable that is under a bundle of other cables that have been
added on top of it. That bottom cable has countless wraps from added cables
and is almost impossible to get to without disrupting all of the cable runs.
This is not much of a problem for a smaller tower with a couple of antennas,
a rotator cable, and/or an antenna switch cable. But when it is a big tower
with a lot of antennas, lots of switching cables, plus some side-mount rotator
cables, as well as the top rotator, it is worth the effort to put some thought
into the cable routing. This is especially important if there is some sort of
failure during a contest that requires a quick repair.
And they call this hobby WIRELESS!
--John W0UN
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