> In climates like the midwest where there can be significant
> temperature contraction and expansion of the connector components over
> the years, even pressurized hardline commonly develops leakage around
> the seals and "O" rings. It generally manifests after the first
> cold-snap of the season.
Anyone who has worked with CATV or BC air dielectric cables
KNOWS how well the connectors are constructed. They have "O"
ring seals, carefully mated and machined surfaces, and solid metal
outer walls covered with a good coating.
Contrast that to a hunk of stuff like 9913. Take its thin cheap jacket
and air seal, stuff it into an ill-fitting PL-259, and hang it outside
around a rotor loop, down a tower leg and goop and tape the ends
to not only water seal it, but to air seal it.
Then think how CATV systems abandoned air cables as soon as
they could, and think back at all those nitrogen tanks along the
cables! A broadcaster would never dream of using airline without
pressure, and they have good connectors that usually can hold a
few pound of pressure for weeks or months!
> I suspect that 9913 was intended only for controlled, indoor
> environments. I would be somewhat surprised if Belden rates this cable
> in an outdoor environment, regardless of the weatherproofing method.
To top this all off, there is virtually no difference in performance
using a foam dielectric. The vast majority of loss is conductor
resistance related, and has nothing to do with what dielectric is
used in a coaxial cable except as that dielectric affects the size of
conductor you can use for a given outside diameter to have a given
impedance.
If you use a closed cell foamed dielectric with large air cells it
allows the same conductors to be used, and loss is the same
without the headaches. The main reason that cable has low loss is
the center conductor is smooth and solid, and the shield area
carrying current is a smooth foil.
Of course seeing the air core makes us "feel better" about the
cable. Like using a Rhombic even though a yagi has more gain.
73, Tom W8JI
W8JI@contesting.com
AN Wireless Self Supporting Towers are now available! Windloading tables,
foundation diagrams and charts, along with full details are now at the
AN Wireless Web site: http://www.ANWireless.com
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