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[TowerTalk] Coax

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Subject: [TowerTalk] Coax
From: (W0UN--Signal Hill Ranch)
Date: Sat, 28 Apr 2001 09:26:53 -0600
At 08:19 AM 2001-04-28, you wrote:
>I am sure what you say is true for some areas of the US.  However,
>Pipes with holes GUARANTEE submerged coax around here during certain
>times of year.  Water table rises quite high.  I would say the same
>for most coastal areas.   Also the other problem in areas with clay.
>Water goes down and hits clay area and builds up much above the water
>table.  This is the case here.  In the spring one can dig a hole down
>1' and have it fill up immediately.
>As you say, solid pipe isn't a solution either.
>Some people just have to realize that local conditions require
>suspending coax above the ground.
>73 de Brian/K3KO

Brian, I couldn't agree more--that is why I said "if you MUST"
bury the cable.  My point is that even in dry climates the pipe
fills up with water.  If your water table is high or you have very
marshy soils it will fill up with water from condensation as well as
with the rise of the water table in the case of the pipe with
holes.  But with holes at least the water can drain back out
when the water table goes back down.

I have worked on many thousands of feet of coax buried in
many different environments (although more dry climates than
wet) and I always see problems with moisture collecting in
low places in the pipe--even when attempts are made to seal
the ends.

Same goes for any equipment boxes -- below or above ground.
They fill with water unless holes are made for draining it out.
Even when attempts are made to hermetically seal an enclosure--
in the case of an array of UHF coaxial collinear antennas that
were installed in fiberglass tubing.  The matching networks were
build into sealed boxes and everything was sealed with a special
epoxy.  It all looked like it could handle 50 psi of water pressure.
But the boxes filled up with water and temperature cycling forced
moisture through the N connectors into the closed-cell foam of some
Andrews hard line.  Something that Andrews claimed was not
possible--but with enough pressure (built up during sunny periods)
the water was forced back into the coax for up to 18 inches.
Not good when the cables are phase matched.

Anything you put into the environment will collect moisture (unless
you go to mil-spec lengths to hermetically seal the equipment.  The
only solutions are 1) use something that isn't affected by moisture
such as hardline or direct burial cable  or 2) LET THE MOISTURE
GET OUT with drain holes.

John  W0UN

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