[TowerTalk] Blackened Sheild on Belden Coax?

[K7LXC@aol.com]

In a message dated 9/19/00 10:27:20 AM Pacific Daylight Time, 
alsopb@gloryroad.net writes:

> Could it be
>  that the blackened stuff will choke off reflected outer shield
>  currents and actually help more than it hurts?  I thought that certain
>  coax cables did not do this.  My understanding was that weathering
>  causes the migration of the rubber onto the shield.  Are we talking
>  about two separate mechanisms here?

    Good question. I've heard good logical explainations that the chlorine in 
the PVC (polyvinyl choride remember) reacts with UV and causes the jacket 
material migration through the coax shield thus blackening it. That's why 
RG-213 with a non-contaminating jacket is preferred for outdoor applications.

    OTOH someone a couple of years ago mentioned an engineer that worked for 
Belden or other cable manufacturer that claimed it was ENTIRELY due to water 
migration. I tried tracking the guy down for clarification but was never able 
to get ahold of him. Maybe someone will do the research and let us know. 

Cheers,    Steve   K7LXC
Tower Tech 

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