When I investigated this about 5 years ago, I found at that time only =
two 50 ohm coaxial cables rated for direct burial. The "key" for direct =
burial rating seemed to be the high density polyethylene jacket, which =
is impervious to moisture. Most other cables use a polyvinylchloride =
jacket. Many of these are rated "non-contaminating", which is quite =
different than direct burial as moisture can and does penetrate PVC =
jacketed cables.=20
The two direct burial cables were "Davis Buryflex" and "Times LMR400DB" =
with the "DB" suffix indicating direct burial. The Times direct burial =
cable is flooded with a moisture resistant goo between the jacket and =
the shield and there is a foil shield in addition protecting the foam =
dielectric from contamination of the flooding material. The flooding goo =
must be thoroughly cleaned of the shield with a solvent like alcohol =
prior to soldering and does require a bit of extra effort to install =
connectors to it due to its flowing back into the area being heated. =
Once you get the hang of it, its not really a big deal. The Davis direct =
burial cable costs a bit less and does not incorporate this flooding =
agent and it will likely provide ample service when buried but should =
anything cause an invasion of the jacket, it will likely become quickly =
contaminated. This can happen from insects and rodents chewing on it, =
gardeners hitting it with a spade, etc., abrasion by rocks, or even tree =
roots growing into it, etc. It should be OK if buried in a PVC pipe but =
that isn't "direct burial" in my opinion.=20
I chose and used Times LMR400DB for all my underground direct burial =
needs in hopes of not needing to replace it for as long as I will care =
about it.=20
My real purpose of this posting is to make it general knowledge that if =
a coaxial cable jacket is rated non-contaminating, it does NOT, by any =
means, indicate that it will provide ample service life in a buried in =
the ground environment. Non-contaminating is not direct burial! It only =
means that the jacket chemical composition will not degrade or =
contaminate the inner foam dielectric insulating the center conductor to =
the shield. When the foam becomes contaminated, losses are increased and =
the cable becomes more of a dummy load than a feedline. Beware that even =
when protected in a conduit or PVC pipe underground, direct burial cable =
should be used for maximum service life. This would be a perfect =
situation to use the Davis Buryflex. All the PVC jacketed cables, =
including LMR400 and LMR400UF allow for moisture penetration through the =
jacket when submerged, accelerating contamination and losses. Direct =
burial cables have high density polyethylene jacket material. Check the =
specs if in doubt. 73, -=3DRog-K9RB=3D-
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