[TowerTalk] Conduit, Coax, and Water: The Answer from Davis RF

[Jeff Stevens]

Thanks again to everyone who sent me info on-list and off.  I called up
Davis RF to get their take on coaxial cable in standing water.  I
explained the situation as cable buried in a conduit with standing water
-- the situation I expect here at my location.

For what it's worth:

The individual at Davis said that if water infiltration is a concern,
their experience suggests a polyethylene jacket to be superior to PVC.
There is apparently the possibility of wicking some moisture through the
PVC.  Coaxial cable with a poly jacket in standing water should have a
normal life span.

That's their take on it.

I find this somewhat interesting as we've all heard stories of PVC
electrical tape alone keeping a coax termination apparently dry for
years.  At the same time, some of my research in college was complicated
by the permeability of polyethylene.  I was mixing  and storing gases in
polyethylene bags (argon, ethylene, nitrogen, oxygen and carbon
dioxide).  After 24-48 hours, the gas mixtures were measurably different
(due to leakage)  so I would have to make up a new batch.  The poly
proved quite gas permeable.  I can't recall if it was just the ethylene
gas that was able to migrate through the bag (which would make sense --
small non-polar molecule) or if other gases could too.  Could, for
example, water vapor migrate through polyethylene?

Just a thought.  Anyway, Davis says a poly jacket is the way to go in
standing water.  Davis RF BuryFlex, of course, has a poly jacket.

-Jeff
KE7FRJ


> On Tue, 2008-04-29 at 00:00 -0700, Jeff Stevens wrote:
> > Currently I'm running coax right on the ground between my station and
> > antennas.  I'm looking to install some conduit so I can bury multiple
> > runs.  When installing conduit I've seen suggestions to put a drain hole
> > in at the lowest point so the water can drain out.
> > 
> > I'm located on property with heavy clay soil in the Pacific Northwest --
> > it's wet most of the year.  The soil is saturated.  I understand the
> > need to protect coax from rocks and other object in the soil, does it
> > *really* need to be protected from water?
> > 
> > Conduit or no conduit, any coax buried here will be sitting in water for
> > all but a few months of the year.  If a cable lays in conduit filled
> > with water for years on end, what happens?
> > 
> > -Jeff
> > KE7FRJ