[CQ-Contest] Station Re-Build - Coax

[Alan Higbie]

Frank ~

Agreed.  Bundling cables (especially single-shielded coax) is a terrible
practice.

The original question in this thread was whether to use single-shielded or
double-shielded coax.

My set-up is for SO2R - - and I have recently realized that my RADIO 1 and
RADIO 2 output cables run "bundled" for about 25 feet.  A terrible practice
(I admit).
So obviously I have an opportunity to mitigate leakage between these
cables.
And, upon reinstall I will also separate the cables from each other (and
from a parallel AC line!!).

Additional context from the US Navy study:

"7. MITIGATION TECHNIQUES
. . .

7.5 Cable Leakage

Examples of signal and noise leakage into coaxial cables are provided in
Section 5.3, and Figure 11 in that section provides measured values of
cable-to-cable isolation for typical flexible coaxial cables. Note that a
0-dBm signal in a single-shielded cable with only 80 dB of isolation to
another similar nearby cable will result in a -80 dBm signal in the second
cable. If a receiver connected to the second cable has a noise floor of
-130 dBm for a 3-kHz bandwidth, the leakage signal will be 50-dB above the
noise floor of the receiver.

The following procedures will eliminate emission leakage problems in RF
paths.

· For long coaxial cable runs, use low-loss and solid-shielded coaxial
cable such as Times LMR series or Andrew Corporation Heliax cable.
Carefully check the total attenuation for the length needed from the
manufacturer‚s literature, and use an appropriate size cable.

***· Never use single-shielded coaxial cable for any application in a
receiving site, even for very short coaxial cables.***

***· Always use double-shielded coaxial cable. ***
Where flexible cable is needed for short 50-Ohm runs, use a cable such as
MI7/84-RG-223/U or one with equivalent shielding."

73, Alan K0AV




On Thu, Mar 14, 2019 at 4:53 PM <donovanf at starpower.net> wrote:

> 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
>
> ------------------------------
> *From: *"Alan Higbie" <alan.higbie at gmail.com>
> *To: *cq-contest at 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 at gmail.com
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