Towertalk
[Top] [All Lists]

[Towertalk] coax losses over time

To: <towertalk@contesting.com>
Subject: [Towertalk] coax losses over time
From: stevek@jmr.com (Steve Katz)
Date: Mon, 2 Dec 2002 08:10:48 -0800


> I've seen lots of printed references to the fact that coax losses increase
> over time but have never seen any "hard" data.   Are there any real
> studies of coax deterioration?     Makes sense that it would deteriorate
> more quickly outside, in the sun, or buried, than inside, for example.
> 
> //While some (like Pres, W8UG) do claim that coax degrades in dry/dark
> storage, if that's the case, it must take an awfully long time.  I've
> measured every characteristic that's measurable on very old cables like
> RG8/U (original MIL-C-17 product manufactured in 1959 and still carrying
> its DoD contract tags) that were stored (dry/dark) for 40+ years and they
> were the same as what we'd expect of newly manufactured cable of the same
> type.  Possibly some of the newer chemistry used in low-loss cellular
> dielectric cables deteriorates faster.
> 
> 
> I assume that the primary cause of deterioration is the dielectric
> material, correct?   How does CATV hardline compare to something like RG-8
> foam, for example?
> 
> //In my experience, which I think it quite a lot, CATV hardline lasts
> forever, or until it takes in water, whichever occurs first.  I've never
> seen hardline go "bad" just by age alone.  But the cellular dielectric can
> absorb water, and when it does, the cable degrades quickly  -- to the
> extent that the signals carried are sufficiently attenuated to draw the
> attention of users and the concern of the service providers, and the
> cable's replaced.  I've seen this happen in just a couple of years, with
> buried cables having the distribution amp literally immersed in water
> after heavy rainfall.
> 
> Or, is it all so variable that it makes more sense just to measure the
> loss on each one.  (i.e., no rules of thumb apply)
> 
> //The only "experiment" I've ever done is accelerated life testing using
> 150W U.V. lamps shining directly on cables.  We monitored illumination
> (similar to direct sunlight in the tropics, but 24 hours a day and not
> reduced by humidity) and thermal rise (negligible) vs. attenuation at 10
> MHz, 100 MHz and 1000 MHz.  The Type IIA and Type IIIA cables fared best,
> with small change after 1000 hours.  The Type I cables, and almost
> anything having a soft jacket and cellular dielectric, mostly drifted to
> >+100% change in attenuation over 1000 hours, but only negligible change
> in impedance, so a standard "SWR" measurement would not reveal any
> problem.  In fact, due to the higher cable loss, "SWR" would likely
> measure *better* with age, rather than worse, if the measurement is made
> at the generator end of the line.  1000 hours of tropical intensity
> sunlight would be only about three months at the equator, but might be
> years at 40 degrees latitude.  -WB2WIK/6
> 
> 
> =====
> e-mail: frenaye@pcnet.com
> Tom Frenaye, K1KI, P O Box J, West Suffield CT 06093 Phone: 860-668-5444
> 
> 
> _______________________________________________
> AN Wireless Self Supporting Towers at discounted prices, 
> See http://www.mscomputer.com 
> 
> Wireless Weather Stations now $349.95. Call Toll Free, 
> 888-333-9041 for additional information.
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>