> > 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 ) )
Telecom Manager ( (
LH Morris Electric, Inc. ) )
(541) 265-8067 office _|****| mmm!
(541) 265-7652 fax ( | | coffee!
(541) 270-5886 cellular \| |
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list