[Antennas] ferrite bead source

[Eric Lemmon]

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
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