[CQ-Contest] oxidized inner conductor when coax carries DC power
w5prchuck at gmail.com
Tue Nov 8 17:56:55 EST 2016
I think the 12 V would only be relevant when there is a dissimilar metals problem. In other words copper against aluminum.
Sent from my iPad
> On Nov 7, 2016, at 4:16 AM, Franki ON5ZO <on5zo at telenet.be> wrote:
> A lot of useful replies about the black inner conductor and the green mush inside the connector. Many of which sent directly to me.
> Some people think that it water ingress even though I'm pretty sure it isn't. But if you ask advice, you must be open to views that don't match yours. So I looked for evidence.
> I took a one meter stretch that I cut off before soldering a new plug a while ago. It's only the inner conductor that got black. The braid (shield) is pristine: gold-yellow, not a sign of contamination. Even the inside of the braid that touches the dielectric.
> This end of the cable was never exposed to the elements. It sat in an outdoor cabinet. Although the inner conductor turned back, there was no green on the N-plug's pin.
> I only found the green 'powder' (like you sometimes find on battery terminals) on the other side of the cable, where it mated an N-style jumper that goes to the RX loop's feedpoint. I inspected both connectors (male and female). The green was only around both center pins, where they mated. There is no sign of green on the shield side of the plugs. I also can't find any sign of real water sipping through. Moisture can be the case though. With lots of oxygen because there is plenty of air space inside an N-plug, especially the female type.
> I unwrapped the sealing tape one of the jumper's N-plugs. No sign of water in any form. I took apart the plug (nut and grommet type). The plug is only green inside the shell, where it is exposed to air. By this I mean the air in the void between pin and shell inside the N-connectors when M+F get screwed together. The lower part of the pin (part that slides over the coax inner conductor and is soldered), where the white 'dielectric extension' spacer cap slides over the pin, was not green. This part of the pin is covered by this spacer and is not exposed to air.
> The sleeve says 'RG 213 / UBX' made in Germany'. I can't find a manufacturer. I bought this 50m run at a hamfest. I seem to remember it was pretty cheap. I bought it with 'RX only' in mind so I didn't actually think of losses and power handling.
> FWIW a sweep with the dummy from 1.5 MHz to 50 MHz shows a flat SWR graph.
> The main question however, remains unanswered: is there a link with the fact that this coax carried +12V DC, or not?
> Franki ON5ZO
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