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[TowerTalk] 9913 Reliability

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Subject: [TowerTalk] 9913 Reliability
From: W8JI@contesting.com (Tom Rauch)
Date: Thu, 20 Dec 2001 09:19:41 -0500
> 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 

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