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RE: [BULK] - Re: [TowerTalk] Replacing coax question

To: "'Tom Rauch'" <>
Subject: RE: [BULK] - Re: [TowerTalk] Replacing coax question
From: "Daron J. Wilson" <>
Date: Tue, 12 Oct 2004 16:54:12 -0700
List-post: <>
> > An advantage of LMR-400 or any similarly constructed cable
> is that it's
> > double shielded, and literally 100% shielded by the inner
> foil shield.
> Why is that important?

I'm sure I'll take some heat on this, but oh well.

First, I would consider LMR-400 to have a dual shield, not to be double
shielded.  It has a foil shield which likely provides 100% shield
covered with a braided shield.  Personally I believe this provides a
very good shield for a reasonable cost.  Double shielded coax such as
RG-214 and RG-142 have two braided shields over the dielectric, my hunch
is that no braid is tight enough to ensure 100% shielded so one over the
other pretty much gives you that while still maintaining the

Second, the importance of the shield has to do with the use of the
product.  I hope we can agree that the shield around the dielectric and
center conductor is a necessary component to the coax, it is apparently
there for a reason.  I also hope that we can agree that the amount of
shielding can change the characteristics of the coax.  To the extreme, a
5% braid around the dielectric is going to produce a different product
than a 95% braid.  These products will produce different results at
varying frequencies and power levels.  There are reasons that higher
power (lower loss) feedlines go to a solid shield.

I think Tom's point is that you don't need to have dual shield or 100%
shield for many applications, and frankly spending the extra money for
it may be a waste.  I've had electrical engineers spec quad shield RG6
coax inside a grounded metallic raceway to 'reduce interference'.  I'm
no PE, but what will that 5th shield catch that the first 4 don't?

Third, I kind of like the idea of as much shielding as practical on the
outer jacket.  My experience with CATV and other services taught me that
a dual shield was considerably better at keeping signal in the wire than
was a 90% shield, so it makes sense to me for some installations.


Daron J. Wilson, RCDD          ) )
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