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Re: [RFI] just what everyone needs!

To: rfi@contesting.com
Subject: Re: [RFI] just what everyone needs!
From: Cortland Richmond <ka5s@earthlink.net>
Reply-to: ka5s@earthlink.net
Date: Mon, 10 Sep 2012 11:51:52 -0400
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
There was a (German?) firm some 10 or 125 years ago selling cable and coax whose jacket was loaded with ferrite powder. However, over a relatively short time, years, not decades, and maybe less than that, the binder failed and pieces started falling-off. This happened in some other rubber-plastic/ferrite sheet and tubing materials of the time, too. I forgot the company name -- and I don't need it!

Before retiring from GE I once used some newer absorbing sheet material to trouble shoot a GHz range immunity problem in a less than adequately shielded cabinet. But I wouldn't trust it to stay put in an airplane.

And WRT to ferrite on coax, I once found a lab problem where conducted emissions on the OATS table power got onto the coax shield and then (via LPDA imbalance) back to the EMI receiver. That was fun. Instead of putting ferrites on the antenna coax, they rerouted power through a different conduit. Some will know the lab, up Silverado Canyon.

Cortland Richmond
KA5S



On 9/10/2012 1107, Dale Svetanoff wrote:
... On a related note, back in the 1990s, I was Chair of an IEEE standards
writing working group making major revisions to IEEE Std-299, which deals
with measuring the RF shielding effectiveness of shielded enclosures.  Some
of the working group members noted that coax cable with ferrite-loaded
jacket was a (then) new item available from at least one manufacturer, in
Europe, I believe.  We ran some actual tests using ferrite loaded coax (in
the outer jacket) to see if the ferrites affected readings being taken when
making measurements (the coax was being used to carry signal from a sense
antenna to a spectrum analyzer or EMI receiver).  Yes, it did, so we had to
specify use of cable that had continuous (or multiple load areas) on the
coax, as opposed to single point loading, because the ferrites caused
either suck-outs or reflections (depending upon frequency) when used within
an enclosure being measured.  Continuous jacket loading minimized these
effects.  Note that loaded jacket coax does not affect the signal within
the cable itself.

73, Dale
WA9ENA



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