[TowerTalk] Coax Life Expectancy

[Grant Saviers]

 From an SK estate I was given a NOS 100ft never unspooled roll of what 
by markings was on the order of 50 years old.  I swept it for loss and 
it was good as new RG8 specs to 30MHz.  Then it started misbehaving with 
some high loss around 50MHz.  I don't have an explanation for what 
deterioration might have caused that, but have seen what appears to be 
cover to core plasticizer migration in other old coax causing the 
translucent core insulation to turn grey/brown.

OTOH, some white cover RG8 made for the marine market (ANCOR), measures 
ok after 30+ years of occasional use.

Best to measure is old coax is what I learned.

Grant KZ1W



On 2/14/2023 21:22, Jim Brown wrote:
> On 2/14/2023 4:30 PM, Jim W7RY wrote:
>> Ultraviolet from the sun is what degrades PVC I believe... ?
> 
> That's my understanding as well, but I don't know it to be a fact.
> 
> I do, however, have additional experience with vintage coax from several 
> manufacturers that I, along with many of N6RZ's neighbors, helped his 
> widow remove from his station (indeed, to break down all of his station, 
> including several towers). I also helped her catalog his "stuff" and 
> dispose of it.
> 
> Much of his stuff was sold, but I took a lot of the coax to a meeting 
> the large contesting club of which we were both members, and offered for 
> the taking. Nearly all of it looked to be in good shape, nearly all of 
> it being pretty good quality stuff, but I'm guessing much of it was 20 
> years old. Everyone turned their noses up at it, so I took it home, made 
> stubs out of it, and measured them, plotting attenuation vs. frequency. 
> Out of several dozen stubs, only one showed any significant degradation, 
> the coax from which it was made came from a shed and the shield showed 
> significant oxidation from water intrusion. I think a lot of folks throw 
> away a lot of good coax for no good reason.
> 
> My conclusion was, and remains, that unless coax has suffered either 
> that sort of damage, or is of quality that is damaged by UV, it's going 
> to last a long time. I experienced significant water intrusion due to 
> construction of a dipole center insulator that allowed leakage into the 
> coax -- water flowed through more than 150 ft of coax to the entry 
> panel! Visual inspection showed oxidation of the shield had begun, and 
> loss measured with a VNWA had increased a bit in the 6-8 months since it 
> had been installed. This was RG11, either Belden 8213 or an equivalent 
> from Davis RF that measured like 8213.
> 
> 73, Jim K9YC
> 
> 
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