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Re: [TowerTalk] Old Coax and cable questions

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Old Coax and cable questions
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 29 Sep 2025 03:00:13 -0700
List-post: <mailto:towertalk@contesting.com>
On 9/28/2025 1:19 PM, kq2m@kq2m.com wrote:
In the process I have been discovering old coax, some of it in possibly re-useable and some of it ready for the landfill.

About 15 years ago, I helped the widow of a neighbor ham with a fine station he'd built himself get rid of his stuff. In doing so, I coordinated the extensive help from his friends and other local hams.

There was a lot of coax of varying vintage, some indoors, some outdoors. Nearly all of it was pretty good stuff, so I took most of it to an NCCC meeting. Everyone turned their noses up at it, so I brought it home and made a lot of stubs from it. Virtually all of the stubs measured as good (looking at depth of their nulls) as if they had been brand new. The sole exceptions were a few that had obvious water intrusion and extreme corrosion of the braid.

There is no question that a LOT of perfectly good coax ends up in the dumpster out of stupidity and ignorance. If in doubt, open a connector and look at it. I strongly suggest that if you find no visual signs of corrosion that you consider it good as new, and donate it to another ham if you don't need it yourself.

I had the experience of finding water intrusion in some RG11 that was feedling my high dipoles. I discovered it when I pulled a cable off my grounding panel and water leaked out. The coax was less than a year old, and the intrusion occurred due to insufficient moisture sealing of a very nice and very sophisticated center insulator that a friend, and first rate engineer, had built for us.

I measured the two cables involved with a well-calibrated, high quality VNA, and found a fractional dB increase in loss in these cables, which were on the order of 160 ft long, in less than a year. There was obvious corrosion, but not a lot, and the moisture was still present.

This is, of course, separate from any other issues involved with UV exposure to certain vulnerable cable components.

73, Jim K9YC

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