What is coax "Black Death"

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#1
Read this in another post where a member was discussing a J pole he built and was having issuess. He said his coax had some "black death"

Tried googling but of course google thinks I'm interested in music.

Can someone tell me what this means?

I've been wondering about some coax I have laying around myself. Its a Columbia RG8 /U (.405 diameter) and when I strip it back, the copper shield isn't brightly colored.

My copper shield is a dingy darker color although the center conductor looks fine. The shield is copper and you can see the copper color, but there's a dark oxidation taking place.

Is that what black death is? Is my coax going bad?
 

ipfd320

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#2
Thats the Black Death--The Shielding Starts Oxidizing Until its Black--Sometimes the Center Conductors can Get the Oxy--Usually happens when cable is old and outer casing is pourus or the casing has a chunk opened up on it---this will let moisture into the shielding and if there is foam around the center conductor then the death will occur there also acts like a sponge
 
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#3
Black Death; I like that term.... :)
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I have seen it often in older coax's, but the phenomenon isn't limited to water issues- I seen it in cables put away in their orginal rolls, in dry warehouses, after years of storage. I think it may have something to do with heat, the chemical interactions between the copper and the plastics of the inner and outer materials,..... maybe other stuff.
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It looks ghastly, irregardless.
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But to tell the truth, the only time it has ever been an issue is when we discover'd it inadvertently. Usually this discovery occurred when taking down some long term project and reusing a cable;- it was cut into and that Black Stained copper braid was seen. But before that there had not been a deterioration of the equipment's preformance. And these were often in cables used at UHF+ frequencies.
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Except for being a bear to solder, I have no qualms about using Black Death cables- provided its not otherwise physically damaged and there wasn't water intrusion. Good coax isn't cheap...It **should** be good for general use.... but don't tell anyone I said that.... ;)
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Lauri :)
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PS- You can run some test to see if there is a resistance between the inner conductor and the shield, run an SWR test to a known load etc. and see what it does...if its not so hot, what is copper selling for per pound today?... :)
 
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#6
I think the "black death" being talked about is actually the black outer jacket contaminating the shield. It's why some cables are rated as "non-contaminating". It has nothing to do with the environment around the coax.
 
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#7
What kind of performance issues are we looking at? I'm assuming the part that says "death" is a hint, but mine is dark and seems to work fine so far as I can tell.
 
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#11
Could be the jacket becoming porous due to UV thus allowing moisture to cause corrosion of the braid. The process is so gradual so as to probably escape notice especially if baseline measurements were not taken when the coax was first put in service. If the coax jacket has become porous and the braid is black or green it is time to replace it.

For hobby use it may still "work" but why spend $$$ on rigs and antennas and then connect them with crappy coax ?.
 

DJ11DLN

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#12
I have tried to get a certain VFD to replace the co-ax at their firehouse on and off for years. It's Belden RG-8 that was installed in 1959. The antenna has been replaced once when the original started falling apart about 1977. Alleged to be "too much trouble and $$$." It still works fairly well. I just shake my head and keep my mouth shut now.
 
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#14
Any mission-critical coax over ten years old is suspect, and should be replaced after fifteen. Halve that is there is regular lighting.

Period.
If you will, please elaborate on your technical justification(s) for that statement. In other words, what happens after 10 (or 5) years that justifies replacement of cable which otherwise shows no apparent indicators of degradation? Assume that "because I say so" and similar reasons will be summarily rejected.
 
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#15
I was once working to diagnose a cell site....in Port Moresby, Papua New Guinea of all places....for its traffic having dropped off to almost nothing.

Started checking the antennas for each sector and my trusty Sitemaster told me that a certain one was pretty much not there at all.

Probably a moisture issue. Cut off the lower connector and check the heliax condition.

About a gallon of green water poured out.

OK, that cable goes to the scrap bin. Take it down, put a new one in, cut the old one into six foot sections for scrapping.

The hollow copper center conductor was green on the inside surface all the way to the top. It was about a 110 foot run according to my notes.

The cable was well sealed at the upper connector as far as the eye could tell. Until the tower worker actually started cutting and removing the sealing tape. It was squishy like a wet sponge.

Connector sealing is very important and has to be done right. If you have exposed connectors on antennas and you're not in the dry desert, you're doing it wrong.
 
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#16
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"Any mission-critical coax over ten years old is suspect, and should be replaced after fifteen."
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"Halve that is there is regular lighting."
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I think that is quite a blanket statement; I mean, are we talking indoor or out door runs? A cable run indoors, protected from the elements and physical abuse should last forever. I have seen runs of RG11 that are much older than I am (guess :) ) that date to the 1960's used in installations that is just as good as when it came from the factory. We didn't routinely cut into them to look for rot or anything, but if these cables were reused and new connectors were placed, the copper was usually shiny bright. These cables were over 50 years old, and I'd take home a hundred foot roll of it (if the government wouldn't come after me) anytime.
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We used Belden 8214 Coax all the time in the tropical Pacific. I can just hear one my Tech's should I have dared suggest they climb a tower and replace such cables because they were "old."
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"Get out of the sun, Lauri, its doing something to your brain"
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"Halve that is there is regular lighting." --
I've tried to decipher this--- but I think whenever I have looked at Black Death I hope'd I had enough regular lighting.
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Lauri :)
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#17
It would be interesting to run some tests on a length of such cable comparing it to new cable of same type.

I would be concerned that severe oxidation would lead to;

1) Increased PIM,
2) Increased cable loss at higher frequencies.

In a new cable the layers of copper braid are in intimate electrical contact, as they corrode, there will be resistance between layers and thus possibly increased loss and overall inductance of the shield.

Very expensive military grade coax has silver plated braid. You won't see much of that in ham shacks beyond expensive jumpers and inside duplexer cable harnesses.

Now I am worried about those rolls in my garage! Especially my 400 feet of bespoke Belden TEFLON insulated and TEFLON jacketed double shielded 50 Ohm RG8 style LAN cable, I bought for pennies because nobody knew what it could be used for. It has a wild part number. Belden kindly sent me specs for it.
 
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#18
Although I recall Dr. Fever, I prefer to reminisce about Bailey Quarters myself..
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Oh, damn, don't get me started on Bailey. The Bailey vs. Jennifer thing was never even an argument for me

As for replacing cable, that would be an interesting call.
I've reused 200 foot runs of 1-5/8" Heliax that swept just fine after 20 years of use. That was mostly indoors, with the last 40 feet or so exposed to the sun, fog, rain, and salt air near the ocean. The reason why it was still good was because of proper connector installation AND proper waterproofing.

Installers/hobbyists failing to properly seal the connections is going to cause a lot of issues. Using proper cable for the job is important, too. Cheap coax may not have the proper jacket compound to really stand up to UV or chemicals it may come in contact with. A good reason to stick with known name brands and avoid the cheap Chinese crap.

With the right tools, it's pretty easy to check a cable to see if it's still good. If it's a mission critical application and the cable has been installed for a long time, and there is any reason to doubt it, then it would be safe to assuming replacing the cable is good insurance. When looking at expensive radio systems, replacing coax or older antennas might be considered good insurance.
 

W9BU

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#19
I used to have some jumpers made from an RG-8X that used a clear PVC jacket. Over time, the copper braid in the shield oxidized and turned green...which you could clearly see through the jacket. I threw those jumpers in the trash. They may have still been good, but they sure looked ugly. Not exactly a black death, but a green sickness that proved terminal.

Bailey Quarters was played by Jan Smithers. I think I would have married her, given the opportunity. For a time, she was married to James Brolin who made a name for himself as Dr. Steven Kiley, M.D., on the Marcus Welby. M.D., TV program. He was a bit of a stud in his day, so I'm sure Ms. Smithers would have been more interested in him than me. :(
 
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#20
Bailey Quarters was played by Jan Smithers. I think I would have married her, given the opportunity. For a time, she was married to James Brolin who made a name for himself as Dr. Steven Kiley, M.D., on the Marcus Welby. M.D., TV program. He was a bit of a stud in his day, so I'm sure Ms. Smithers would have been more interested in him than me. :(
Alas I'm probably in the same category.

While Jan Smithers has stayed out of the spotlight, I did see a recent photo of her, still great looking. But then again Loni Anderson isn't looking bad, either for 70 some odd years old.


Unsealed coaxial cable connections are often the cause, although jackets can certainly get damaged.
Good reason some stuff is run with a slight positive pressure with dried compressed air or nitrogen.
One of my sites has a dual compressor/dry air system for pressurizing AT&T copper cables. Some of that cable has been underground and for the most part, submerged, since the mid 1960's. Still running.
 
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