"Frank Gilliland" wrote in message
...
In , jim wrote:

I have been using Belden 9913 RG-8U solid core for the past 7 years.
Its used with a Jogunn 5+5 beam and Yaesu rotor. Will this stand up for
another 10+ years or ditch it for some low loss, stranded, foam or
non-contaminating coax?


Used coax can be tested on the bench for characteristic impedance,
dielectric
integrity, DC resistance, and even for pinholes in the outer insulation.
But
unless you measured these factors when new, you can't make a good
determination
of its quality after several years of use. The problem is that your
average coax
isn't hermetically sealed, so moisture will eventually seep in and slowly
corrode the conductors. Weaknesses in the outer insulation (due to age,
oil
contamination, mechanical stresses and manufacturing imperfections) cause
microscopic pinholes that make the corrosion process go faster. It's best
to
replace your coax periodically. I would say that seven years is plenty
long
enough for an outside line.

Now I can't stress this enough: -=DON'T USE FOAM=-!!! There are several
reasons
not to use foam. First, foam coax is very porous and is intended for
controlled
environments where there is little variation in temperature and humidity,
the
factors primarily responsible for moisture seeping into the coax. Second,
the
dielectric softens with just mild heat, and the line could be ruined by
nothing
more than a hot sunny day. Also, the foam doesn't have the mechanical
strength
to handle the stresses of being clamped to an antenna and hung from any
decent
height, not to mention the repeated movements caused by wind, or the
expansion
and contraction caused by wide temperature changes. For antenna
installations,
foam coax is -BAD NEWS-!

As far as solid vs. stranded is concerned, the only real advantage of
solid is a
higher usable frequency (we're talking GHz here). Stranded conductors
offer more
flexibility, which is important when the coax is constantly under the
mechanical
stresses of an antenna installation.

The only other thing you may want to know about any type of coax is how
flexible
it will be when the weather turns cold. In that respect, I have yet to
find any
coax that fills the bill.







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Excellent answer! My only addition is (and correct me if I'm wrong)
electrons follow the surface of the wire and stranded wire offers more
surface area than solid wire.

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