[CQ-Contest] oxidized inner conductor when coax carries DC power

ac0w at charter.net ac0w at charter.net
Tue Nov 1 21:46:00 EDT 2016

The green mush is probably due to the DC power and other affects.
Don't have a solution on this.
The black center conductor, have you checked any other coaxes to
verify whether their center conductors or copper or black? I've seen
copper buses in electrical distribution gear turned black from gases
released into the air from some type of manufacturing process and
animal handling processes. Generally the gas is hydrogen sulfide or a
gas produced by decaying products. This gas can be found in sewer
gases, released from drywall and tends to smell like rotten eggs.
Gases can travel a long way in the coaxed compared to moisture. Also a
coax seal that is effective against moisture may easily pass the gas.
Usually copper turned black by this process is very hard to clean and
make usable again.
Don't have a solution to prevent, we just learn how to live with it.

 Message: 2
 Date: Mon, 31 Oct 2016 11:51:10 +0100
 From: Franki ON5ZO 
 To: cq-contest at contesting.com
 Subject: [CQ-Contest] oxidized inner conductor when coax carries DC
 Content-Type: text/plain; charset=utf-8; format=flowed

 A few weeks ago I was doing some relocating and rerouting of the
coaxes outside. One RG-213 is used for my active RX loop. It needed a
different plug on the antenna switching side 
 so I cut the existing one off and prepared the cable for a new one.
Much to my surprise I found the inner conductor black from corrosion.
I cut off a few centimeters at a time, but 
 after having cut off two meters, it still was black. I have been
working with these things for ages and I can tell you: it is NOT water
ingress. Everything is sealed properly. I 
 was a pain to solder the new plug to the center conductor. I had to
sand the black film off and even then the tin wouldn?t flow.

 Last week I took the loop down and cut away the layers of tape that
kept the feed point coax dry. And dry it was. However I noticed the N
male-female junction had a green mush 
 developed around the mating pins of the inner conductors.

 I didn?t pay attention in chemistry class, but I?d label this as
corrosion. Right?
 Since I have never seen this before, and this is the only coax that
ever carried DC around here, I assume the DC voltage is the culprit

 * Can I avoid this?
 * Does it hurt? I seem to remember something about DC and polarity
that can eat your copper away?
 * My coax shields are tied to a dedicated earth system. Does this
relate to the corrosion in a good or bad way?

 I?m thinking of ways to improve my 80/160 RX situation, and several
scenarios involve DC over the coax. So I better know what I?m up
 Thanks and 73
 Franki ON5ZO / OQ5M

More information about the CQ-Contest mailing list