[50mhz] [VHF] Replacing coax

[Stan]

Hello John,

I replace coax when I can not live with the increase in insertion loss.

Coaxial cables can experience an increase in insertion loss with normal 
degradation due to aging.
Pin hole openings in the outer dielectric can leak acid rain which 
increases the insertion loss.
Other human induced problems include not sealing connectors from the 
weather,
abrading the outer dielectric either actively with the lawn mower (weed 
wacker) or
passively by allowing the cable to slap in the wind and create a worn spot.
Excess flexing around a rotator will also increase insertion loss.

The insertion loss only goes up with time, sometimes more, sometimes less.

Buying used coaxial cable:
Open up the ends and look at the outer shield, either braid or
solid aluminum or copper,as in hard line.
If the outer shield is not new and shiny, it has probably been exposed 
to water at one time or another.
Avoid anything that does not look new.
Or run insertion loss tests to characterize the degradation/performance.
If you can live with the performance, use it.

What is insidious is that any coax cable insertion loss only makes your
actual antenna VSWR look better than it actually is, when measured in 
the shack.
One reason to only look at antenna VSWR  "AT" the antenna.

Hopefully, when you installed your coaxial cable, you benchmarked its' 
performance for insertion loss.
Any retesting, however infrequent, would show any possible degradation.

Bottom line: if you can live with what you got, continue to live with it.

Stan, W1LE     Cape Cop    FN41sr






O

n 3/1/2011 11:39 AM, John Geiger wrote:
> I went out this morning and did a visual inspection on my coax runs, and they
> all look in very good condition. No cracking on the jacket at all, and the
> jacket still looks as good as when new.  One run of RG-11 I have is 12 years
> old, but still looks great.  I don't recognize any signal degradation on the
> coax runs either, nor changes in SWR.  Now I don't have any complex test
> equipment to test the coax runs with, just a SWR/power meter built into my
> antenna tuner.
>
> Given that the jacket on the coax looks ok, and I haven't noticed any change
> in antenna performance, is it safe to assume that the coax is still good, or
> is there an age limit for coax after which it starts to deteriorate from the
> inside?  Is there a rule of thumb on how often coax should be replaced?
>
> 73s John AA5JG
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