> Think of all those people at broadcast and CATV installations who
> pressurize their air core cables, when all they need to do is seal
> them!
Tom, W8JI is right here. All air dielectric cables require pressurization.
I cannot imagine any broadcast installation relying on the quality of the
connector installation in order to keep moisture from entering the line.
And, the quality of connectors, cables and installation methods for
broadcast Heliax and hardline are far superior to that of 9913 and PL-259
connectors. The use of Scotch-Kote and heat-shrink tubing certainly helps,
but it's no substitute for pressurization.
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.
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.
Finally, the last thing I want nagging in the back of my mind every time the
SWR jumps a bit is to consider moisture in the line. There's enough to rule
out in the antenna and connectors alone...especially in complex
installations where maintenance and servicing of the line is troublesome.
Believe me, it's no fun purging and drying out an air-dielectric
transmission line on a 100-foot tower.
For new cable purchases, the latest genre of coaxial cable choices like
LMR-400 should be a "no-brainer."
-Paul, W9AC
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