Thanks Roger - I have always wondered what they were hinting at - bottom
line appears to be if the jacket is water tight it truly is direct
burial - and just because it is plastic do not think it won't pass
water! Interesting.....
73,
Jim, K4OJ
Roger Borowski wrote:
>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.
>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.
>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.
>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, -=Rog-K9RB=-
>
>
>
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