[TowerTalk] burying cable

DavisRFinc@aol.com DavisRFinc@aol.com
Sun, 8 Feb 1998 04:33:05 EST

In a message dated 98-02-08 00:45:10 EST, you write:

<< Why bother to hose your coax?   If it doesn't need armor, get direct burial
 and be done with it!  Unless you provide drainage, air, or desiccant it
 will get wet.
  Jim Bradshaw, ac6tk >>

I have to agree with Jim.  The original inquirer mentioned RG213 and I believe
one other PVC jacketed cable he wanted to bury.  There is a great
misconception among many hams (and I suspect only few of them might be  on TT)
that a PVC IIA "non-contaminating" (vis a vis non migrating) jacket is direct
burial.  In fact I see it claimed in ads.  PVC of any type compound is NOT
direct bury.  Now, if you put it in a garden hose, I'm not saying that in all
cases you will have problems as some earth conditions, drainage, etc. would be
better ambients than others.  However, I will say that there is a good chance
that the hose will enhance production of moisture inside and also many hoses
would chemically deteriorate over time.  PVC is not necessarily a problem on a
SHORT time basis inside any conduit that creates moisture; however the safest
approach, I believe, is a polyethylene jacket of high polymeer density in the
area of .951.  This is the type Polyethylene ("PE") that a conscientious
supplier such as Wireman or DAVIS RF stocks.   A "flooded" PE is expensive and
in my opinion is not needed, particularly if you put a non-flooded PE in a
conduit as the "flooded" aspect is primarily to seal accidental piercing of
the outer jacket by errant shovels, etc. (and by the way, as of recent TT
postings I should add chain saws as they now seem to have a new ham
application - McCullock, etc. will want the ham marketing lists HI).  Press
Jones of the Wireman gave excellent input on TT a few weeks ago as to the
proper installation of conduit.  If you are not concerned about accidental
damage by errant shoveling, you do not need a conduit with quality PE
jacketing.   A quality formula Polyethylene does not have a plasticide
ingredient (phthalate filler added to enhance molding/extrusion) which is the
prime cause of migrating contamination of the dielectric.  It is also a real
tough, abrasive and cut resistant jacket (use a real sharp razor when doing
connectors).  In some cases you can obtain a 50 ohm cable with PE jacket that
has all the other spec's of a 213 or RG8 at only about 20 cents more per foot
(vs. the cost of  an outer PVC conduit).  Wireman and DAVIS RF and our dealers
carry "Bury-FLEX" Tm designed by DAVIS RF which gives you the PE outer jacket
and lower loss at VHF and UHF (and obviously HF), as compared to RG8 or 213
and very close to LMR 400, along with flexibility better than LMR or 9913.
This item is highly appreciated by many, and serves some otherwise unserved
needs, including its economic price.  Lastly, if you want to just lay BURY-
FLEX Tm on the ground, in the woods, etc. it has proven undesirable to rodents
based on my testing, at least in New England with squirrels, woodchucks,
beavers, etc.  If you live in Florida, no guarantess about alligators. HI !!
73, Steve Davis, K1PEK,   DAVIS RF Co., commercial wire/cable, custom design,
discounts to hams, "FLEX-WEAVE" Tm.  

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