"Dick Green" <dick.green@valley.net>: [TowerTalk] Yum, yum!
That LMR400UF sure is tasty!
n8ug@juno.com
n8ug@juno.com
Tue, 31 Mar 1998 21:14:30 -0600
Interesting post, Dick - we don't often hear of the level of damage you
and the other respondents report from burying coax.
We welcome the stories, however, since they emphasize the problems
inherent with direct burial of communication cables. None of the cited
cables were designed for direct burial, though all of them can be if one
is willing to accept the risk or possible
annual or more frequent replacement.
Cable designed for direct burial usually has, to one degree or another,
an armor of corrosion resistant metal under or over an impermeable
plastic such as high density polyethylene. A moisture block or "flooding
compound " follows, to prevent longitudinal moisture migration in the
metal "armor" if it is not impregnated by the plastic. The flavor of
these agents is a deterrent to animal damage as well. A second jacket can
follow, with either no void or flooded void, based on the need for
protection and for flexibility. The shield, be it solid metal or braid is
also water proofed either by its definition or moisture block. A foil
shield over the dielectric must be bonded or flooded, and the center
conductor needs to be impregnated if stranded to complete the buriable
package, self sealing and vile tasting. Depending on the installation, a
first thin covering of earth is followed by a plastic or other brightly
colored and insect, animal repellent material that shows up just before
later digging, warning of cable below. After complete back fill, the
warning signs are placed to complete the job. High power or super
critical jobs utilize conduit encased in concrete.
The above is a bare outline of what can be involved in a cable designed
for direct burial - more would be a bore. The point is that we can bury
darn near any cable, but we must alter the expectations and live with the
results. If 10 cables cost $500 and last 2 years and 10 cables designed
to last 20 years while doing the same job cost $5000, which would you
choose?
If it were me, I'd look for a middle path: use conduit or pipe laid
correctly where possible. Select cable that has a good chance of making
it, if given a bit of help.
Knowing what can occur makes an excellent set of guidelines.
Using the same material again is to accept the replacement schedule and
its cost, in which case it is not a mistake but a protocol. If it doesn't
fail in the middle of a contest
or an emergency, great - good planning!
Hope this is of some interest - meantime note the great comments: Salt
and human scent on the cable, something other that rotting sticks in the
warm sun popping through the snow, nice resilient teething material,
tasty metallic salt from a saliva/braid combo, a dab of grease or other
lubricant from a connector to round out a critter diet --- gotta go for
my midnite snack---
CUL
Press Jones, N8UG, The Wireman, Inc., Landrum, SC, 29356
Sales(800)727-WIRE(9473) or cqwire@juno.com.
Tech help (864)895-4195 or n8ug@juno.com
www.thewireman.com
Our 21st year!
--------- Begin forwarded message ----------
From: "Dick Green" <dick.green@valley.net>
To: "Tower" <towertalk@contesting.com>
Subject: [TowerTalk] Yum, yum! That LMR400UF sure is tasty!
Date: Mon, 30 Mar 1998 23:27:24 -0500
Message-ID: <016201bd5c5d$6a3f7720$04f421ce@dns1.tpk.net>
Well, that's what the critters on my property seem to think...
After five months (yes *five* months) of continuous snow cover, El Nino
has
graced the Upper Connecticut River Valley of New Hampshire with record
warm
temperatures. In 27 years of living here, I've never seen it get up to 80
degrees in March! A week ago we had more than a foot of snow on the
ground;
today it's almost all gone.
A casual trip down to the antenna farm during CQ WPX on Saturday revealed
that the animals went to town as soon as the snow pulled back from the
three
100' lengths of Times Microwave LMR400UF coax running along the ground
between the antenna switch and the 40M vertical, 80M inverted vee, and
old
GAP Titan. I found tiny teeth marks wherever the snow had melted, and in
several spots the coax jacket had been either flattened or bitten through
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to
expose the shield braid. Hard to say what kind of animals did it -- the
tooth marks were small enough to be from mice, but the flattened sections
must have been done by something bigger (maybe deer, which are plentiful
around here.) They even managed to gnaw on the coax and connector bootie
at
the base of the GAP vertical, which is almost three feet off the ground.
It's kind of odd because they didn't touch the 20-50 feet of RG/213 that
was
often coiled up on the ground at the base of the crankup tower and fully
exposed all winter long. I did see tooth marks on a small section of the
#16
three-wire outdoor AC (!) line running between the pedestal and the tower
motor. It's almost four feet off the ground.
I got to wondering about the composition of the cable jackets and how
much
that may be contributing to the problem. For several years, the GAP Titan
had a section of yellow-jacketed mini coax laying on the ground. Once or
twice a year, the amp protection circuits would trip (always during a
contest) and I would go down to the antenna and find that the critters
had
chewed through the mini coax again. I got so sick of fixing it (usually
in
the rain or snow), that I finally added a flush-mounted SO-239 jack to
the
antenna. What's strange is that there was at least six feet of exposed
Belden 9913 connected to the mini-coax and they never touched it. In
fact,
last year when I installed a 250' conduit run between the house and
antenna
farm, I pulled up 250 feet of 9913 from where I'd buried it six inches
under
the grass three years earlier and found absolutely no external damage
whatsoever.
The jacket of the 9913 is hard and shiny. The jacket of the RG/213 is
softer, but it's kinda shiny too. Both the LMR400UF and the #16 AC wire
have
soft, matte-finish jackets. I've also noticed that a fine white powder
has
formed on the LMR400UF jacket (UV damage?) Does anybody know the
composition
of these cable jackets? Any idea why the animals seem to prefer one over
the
other? Are there any substances I can put on the coax to keep the
critters
off? (Yes, I'm willing to relieve myself on the cables, but I'm afraid it
will take quite a few beers to cover 300'...) Conduit is not an option
(not
after installing three expensive 250' runs last year). Direct burial is
possible but very difficult (all three runs pass through thick woods with
lots of exposed or shallow tree roots, and one run passes over a radial
field.)
73, Dick, WC1M
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Or call Juno at (800) 654-JUNO [654-5866]
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