[TowerTalk] Blackened Sheild on Belden Coax?

[alsopb]

This brings up two questions.  It should be that the inside of the
shield carries all the current for coax. Thus if only the outside of
the shield is blackened there should be no effect. However braded
shields where the little wires weave in and out seems to confound
things. As pointed out, IF the wires have perfect contact with those
next to it, then crud on the outside won't matter a bit. 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?

The next question regards the copper oxide coating that all antenna
wires get.  How thick is it relative to the skin depth?  Does it have
any practical negative effect?


Tom K Osborne wrote:
> 
> On Tue, 19 Sep 2000 04:52:30 -0400 "Tom Rauch" <w8ji@contesting.com>
> writes:
> 
> > Any time I've had "blackened braid", it has been from water. It
> > doesn't matter if the cable is one month old, if I get water in the
> > cable the braid turns black and loss goes way up.
> > I wonder what other people's experiences are?
> 
> Hi Tom
> 
> I have some antennas here that have the black coating on the coax.  I
> have been going to change it for a long time but just haven't gotten
> around to it.  As far as performance and SWR, the antennas haven't
> changed since I put them up.  The antennas are 3 phased 40 meter
> verticals.  Last year I redid the radial connections and noticed the
> blackened coax.  I cut a couple of feet off and it was still black so I
> just scraped the coating off and soldered the radials to the shield.  I
> would like to see some measurements made somehow to actually see what is
> happening.  I know it sure looks ugly but so far hasn't impeded the
> performance of the array.  At least as far as I can tell.  73.
> Tom W7WHY
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