[Antennas] ferrite bead source

Sat, 07 Sep 2002 19:20:08 -0700

Patrick,

I don't recall the ferrite compound number.  If you don't have a sprectrum
analyzer to characterize the spurious emissions from your computer, you could
use an HF receiver along with a scanner to pinpoint the spur frequencies.  It
might help to remove all modems, sound cards, etc., to verify that the RFI is
the fault of the motherboard CPU and not one of the plug-in cards- which may
also have a CPU.  In the ideal installation, the computer and all peripheral
devices should be plugged into a dedicated branch circuit that is properly
grounded.  This will minimize the possibility of EMI being conducted through the
house wiring or grounding impedance.

Once you have a handle on what the interfering frequencies are, contact one of
the ferrite manufacturers for application assistance.  It may turn out that what
ferrite composition is best for your RFI problem is different from the one that
worked for my computer.  Moreover, there is no "one ferrite fits all" as other
posters have noted.  Good luck!

73, Eric Lemmon WB6FLY

"Patrick A. Thompson Sr." wrote:

> I've got an Athlon running at 1300MHz that puts a lot of RF trash out on 20
> through 6 meters and some still audible on 2 meters.  Even the small standby
> (wake on LAN) power supply radiates some trash.
>
> Snap-on square ferrites from MFJ didn't help.  I suspect they are similar to
> the RS ferrites.
>
> I found the Fair-Rite web page.   http://www.fair-rite.com/
>
> Which devices seem to help best?
>
> Patrick Thompson
> wa4tuk
>
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]]On Behalf Of Eric Lemmon
> > Sent: Saturday, September 07, 2002 11:37 AM
> > To: Ed
> > Cc: [email protected]
> > Subject: Re: [Antennas] ferrite bead source
> >
> >
> > Ed,
> >
> > I started looking for clamp-on ferrite filters after I discovered
> > that  my then-new 950 MHz Athlon computer was radiating a pure
> > carrier in the 152 MHz business band, locking open a repeater I
> > was trying to tune.  All of the covers were tightly screwed in
> > place, so I believed that the RF was being conducted out of the
> > computer case on one or more connecting cables.
> >
> > My first fix, using snap-on ferrite filters from Radio Shack,
> > failed miserably.  The filters had almost no effect at all.  Even
> > looping the wires through several times had no effect.
> >
> > I then rang up Fair-Rite, a leading manufacturer of ferrite
> > filters.  I learned that "all ferrites are Not the same."  Indeed,
> > the cheaper ferrites often don't begin to filter until very high
> > frequencies.  Based upon my description of the problem, the
> > applications engineer suggested using a ferrite compound that was
> > formulated especially for the frequency range that was giving
> > me a problem.  He even sent me some free samples to test.
> >
> > When the samples arrived, I quickly snapped them onto the cables
> > right at the connector plate on the back of the computer.  They
> > worked perfectly.  As a result of this experience, I convinced my
> > employer to purchase a large quantity of the same filters to
> > solve some similar EMI problems at work.  Needless to say, the
> > problems were solved.
> >
> > I should make it clear that I have no financial interest in
> > Fair-Rite.  I believe that other manufacturers of ferrite filters can
> > provide similar products and technical support.  Since there are
> > dozens of different ferrite compositions, each with well-defined
> > frequency cutoff and attenuation characteristics, a ferrite
> > filter should be carefully selected to optimize its effect on the
> > unwanted signals and minimize its effect on the desired signals.
> > Choose wisely!
> >
> > 73, Eric Lemmon WB6FLY
> >
> > Ed wrote:
> >
> > > Speaking of ferrite beads what is the best source for the snap
> > on variety? I have a difficult time finding them at ham fests.
> > > ED YEARY W4TEY
> > > 325 CUMBERLAND DRIVE
> > > HARROGATE, TN. 37752-6942
> > >
>
> - - -
>
> Your moderator for this list is:
> Larry Wilson KE1HZ [email protected]
> _______________________________________________
> Antennas mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/antennas