Hi Frank,
Thanks for saving me from a 'terrible practice'. I hadn't considered the
potential for noise/signal injection via bundled cable screens, other than
K9YC's fine work on keeping common mode currents out.
The first 80m/250ft of my coax runs from the shack are in 4 inch conduit. I
have laid 4 runs of conduit a couple of feet underground. I'm planning to put
RX coax runs in one of the conduits, TX runs (Heliax) in two of the others and
control cable in the 4th run. So RX runs will at best be 4-20 RG6 cable
diameters from the Heliax. Does that sound like enough separation from your
experience?
73, David G3WGN M6O WJ6O
-----Original Message-----
From: donovanf@starpower.net [mailto:donovanf@starpower.net]
Sent: 14 March 2019 22:54
To: cq-contest@contesting.com
Subject: Re: [CQ-Contest] Station Re-Build - Coax
Hi Alan,
Your quotation from the Navy study omitted the important details described in
the next few paragraphs.
The context was multiple single shielded coaxial cables bundled
with cables radiating interfering signals into the victim cables.
Double shielding greatly reduces this problem but its also very
effective if coaxial cables feeding microvolt signals to receivers are
not bundled with cables carrying high level signals, a terrible
practice.
73
Frank
W3LPL
----- Original Message -----
From: "Alan Higbie" <alan.higbie@gmail.com>
To: cq-contest@contesting.com
Sent: Thursday, March 14, 2019 2:59:07 PM
Subject: [CQ-Contest] Station Re-Build - Coax
Relevant to this discussion is an extensive study conducted by US Navy:
THE MITIGATION OF RADIO NOISE AND INTERFERENCE FROM ON-SITE SOURCES
at RADIO RECEIVING SITES (November 2009) by Wilbur R. Vincent, George F.
Munsch, Richard W. Adler, Andrew A. Parker. (By the way, each of the
study's authors is a ham.)
The authors surveyed noise floor problems at 40 Navy receiving sites around
the world. They drew on data from thee Navy's
Signal-to-Noise-Enhancement-Project.
They had many recommendations and conclusions. But the most relevant to
the original question of this thread is this one:
*"5.3 Cable Leakage*
*Leakage of noise and other spectral components into RF cables running from
antennas to receivers has been noted at all receiving sites that use
single-shielded coaxial cables. Receiving sites using high-quality
double-shielded coaxial cable and properly-assembled coaxial connectors
seldom encounter cable-leakage problems." *
I am currently in the midst of replacing my "single-shielded coax" with
"high-quality double-shielded" RG400.
I recently purchased 200 feet of Harbour Industries RG400 from Electro
Enterprises, Inc. for $1.43 per foot. It came with certification as
factory new MFG certificate.
A link to the US Navy study can be found at:
http://www.arrl.org/radio-frequency-interference-rfi
(scroll down to bottom of page under heading Naval Postgraduate School RFI
Handbooks)
73, Alan K0AV
alan.higbie@gmail.com
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