26 Jul 2001 11:29:40 -0700
On Thu, 26 July 2001, "Bill Hohnstein" wrote:
> I've generally use flooded cables for my Beverages. While an occasional
> critter may take a quick bite, I haven't seen one continue for a meal. The
> cable flooding prevents water from future rains from significantly wicking
> in and the ruining the cable via causing high attention. Plus, it "prevents water
> migration by using a customized polymer adhesive over the center conductor."
> "Protection against moisture ingress and other underground contaminants is
> assured by using a unique highly flexible polyethylene jacket on all
> underground products."
Let me describe a problem I encountered which I think is related to water migration. I feed my Beverages with RG-6. Over a period of time one of my Beverages started to exhibit extremely high noise levels, not related to atmospheric noise. I found the noise persisted even after I disconnected the feedline from the Beverage itself. Eventually I traced the problem to a section of feedline which was essentially lying on semi-swampy ground. I replaced that section and all was fine.
I examined the bad section I took out but couldn't find any obvious signs of jacket damage or water ingress. However, when I connected a voltmeter across the center conductor and shield, I measured 0.7 VDC with the far end open-circuited! I verified this with another meter, too. If I shorted the far end, the voltage went away, but returned as soon as I removed the short! My coax had apparently become a dielectric battery which produced a lot of RF noise. The swamp water migrating into the coax had to be the cause.
A few weeks later--guess what? The new feedline became noisy again and it was the same problem! I replaced it but this time I elevated the feedline off the ground and everything has been fine since.
I don't know the make of this RG-6 because there is no brand name on the jacket. I can only guess it's some cheap junk.
Moral of the story: use good quality feedline, even for Beverages or avoid laying feedlines in swamps!
73, John W1FV
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