Moisture reacts with trace contamination in the plastic or there are
other trace compounds that oxidize the copper. There are so many
variables in off-brand coax, who knows what it is.
On the other hand, a mil-spec spool of RG213 I have that is 20 years old
measures just fine. I measured with the same power meter at both ends
(reel has a stub at the inside) to a dummy load and the loss is "just
like new". A TDR is nice, but not in most shacks, so if you can get to
both ends this is an easy measurement. You can vary the frequency of
the test, and get accurate results even with the not so calibrated power
meter in most SWR meters since only the db/watts difference matters.
Tom Osborne wrote:
> Hi Don
> What makes coax turn black anyway??
> I was checking some feedlines here and some off-brand RG8X I have and the
> center conductor and the sheild turned both black. It was not just at the
> ends but a long way back from the end.
> It doesn't look like it was wet.
> Looks like I'll have to get rid of a bunch of it. 73
> Tom W7WHY
> Beg, borrow, buy a TDR and look at it that way.
> Most coax will last many more years than people believe.
> Problems occur from moisture ingress, but, if trimmed when necessary,
> will do just fine.
TowerTalk mailing list