John,
If you're referring to "attaching" the cable to the tower leg, it's fine to
use vinyl tape, just don't pull it hard and stretch it while you're wrapping
it around the cable and tower leg.
The "lineman's" method, which works well, is to pull, stretch and wrap the
tape a couple of layers on ONLY THE TOWER LEG, without the coax be wrapped
inside the tape, just to make the tape grab the tower well at that point;
then, place the cable over the area just wrapped and continue wrapping the
tape, but not pulling the tape tightly while doing so. A few wraps of tape,
spread over an area of 2"-3" of tower leg, works just fine, then go on to
the next point.
By applying tape at several locations, no single location is stressed much,
so the tape needn't be particularly strong.
Likewise, even nylon tie-wraps may be used, but not pulled tightly.
Unfortunately, the common 8" nylon tie-wrap is only 3/16" wide and can be
pulled by hand to 100 lbs per square inch...and can be pulled tighter than
that if you have a good grip, or use pliers. That's a ridiculous amount of
force to be applying to coaxial cable, unless the cable is rigid (hardline,
Heliax). If you just pull them "snug," it's more than sufficient and won't
damage the cable. Problem is, it's very easy to pull them too tight.
LMR400 is soft cable, easily damaged, and not just by cable ties. You also
shouldn't walk on it, pull it over the edge of your roof, or do anything to
it that you wouldn't do to your cat. And it's not just LMR400 that has such
frailties, it's all the soft, cellular foam dielectric cables, as well as
the spiral-wound dielectric cables like 9913.
RG213/U, 214/U, 217/U, etc. don't have such frailties -- they are very
strong and rugged by comparison; of all the small-diameter cables, only the
PTFE dielectric types (RG142, RG400, etc) have any mechanical strength --
the rest should be handled with care.
WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: KB2HUK@aol.com [SMTP:KB2HUK@aol.com]
> Sent: Monday, October 07, 2002 6:24 PM
> To: Towertalk@contesting.com
> Subject: [Towertalk] attaching coax to the tower legs
>
> <PRE>In what fashion should coax coming down the tower be attached to the
> legs of
> the tower , I am using LMR 400 Coaxial cable ? thanks John KB2HUK
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