-=> Quoting Mraz@maverick.aud.alcatel to All <=-
Mr> Subject: Non-Contaminating Coax
Mr> Quoth The Wireman:
Mr> "Class IIA is also PVC but is referred to as "non-contaminating".
Mr> ..."Non-contaminating" does not mean direct-buriable...
Mr> ...Wirebook II, Press Jones, N8UG
Hams have been directly burying their coax far longer than N8UG has been
peddling it! Since PVC is plastic and is not porous, the only way water
can get in is if the jacket is breeched due to insect or rodent damage or
the like, or through improperly sealed joints. If rodents are a problem
you can protect it with some old water hose or PVC pipe, or use "flooded"
cable which is self-sealing (I run flooded RG-6 on the ground through the
woods to my beverage). I obtained my flooded cable from RadioKit (KM1H)
who believes that the animals also hate the taste and smell of the stuff!
The "contamination" of the center conductor insulation and resultant increased
loss due to migration of the jacket PVC seems to be strongly influenced by
the amount of UV exposure the cable receives. I have some Superex RG-8
Class I coax that is well over 15 years old that still meets the original
attenuation specs at HF, even though it was directly buried for about 5 years!
N8UG may be correct when he writes that coax starts to degrade the day it is
made but I would not throw out my coax unless the MEASURED loss at the
frequency of use exceeds the original specs by a significant amount. Old coax
that is no longer useable at VHF may still be quite adequate for HF work.
Surplus hardline and Heliax is readily available and doesn't seem to degrade
over time. I have hundreds of feet of the stuff and it has very low loss
even through some of it looks pretty beat up. I suppose it lasts because of
the solid outer conductor. I wonder if 9914-type cables with 100% foil
shields really degrade to any degree as long as water is kept out?
73 de Bill, N6CQ/3 (n6cq@paonline) Lewisberry, PA
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