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Re: [TowerTalk] Shields

Subject: Re: [TowerTalk] Shields
From: VR2BrettGraham <>
Date: Wed, 13 Oct 2004 23:33:51 +0000
List-post: <>
WB2WIK/6 added:

Actually, in my experience using hardline or 100% (or at least very good
double) shielded cables in VHF-UHF repeater systems and cavity interconnects
in duplexers does make a difference, not necessarily in notch depth but in
generated noise that can bother receivers.  I also see this "noise" issue
when using many antenna designs that are perfect for simplex operation and
stink in duplex operation with any power applied.  It seems the oxidation
between shield strands, which is always there even with brand new cable and
worsens with age, creates minute noise-generating interfaces (or something).
I've put up repeaters using brand new mil-spec RG213/U and running 100W
output power with a very good duplexer had desense problems resulting in
poor receiver performance.  Replacing absolutely nothing in the system
except the transmission line, going from 213 to 9913 or hardline or some
other 100% shielded cable, completely eliminates the noise -- it's gone.
This has happened to me so many times it cannot be coincidence.

<snip bit on clamped vs welded antenna construction>

With all the energy floating around hilltops, any diode action anywhere is
bound to bring grief.  Certainly sounds like the mechanism here & going
to better shielded cable might have simply gotten rid of a bunch of diodes
& not really improved things because of the greater amount of shielding.

Ditto for the antennas.  I can just imagine what sort of nasty joints there
are on some of our repeater antennas here, as it has been hard to spend
the money on the better ones & everything lives in a very moist, salty &
dirty atmosphere that eats into just about anything in short order.

73, VR2BrettGraham


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