[RFI] just what everyone needs!

[Cortland Richmond]

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
>
>
>