At work we bought some giant Ferrishield snap-on "beads" for >200$US each.
They'r e really only useful for troubleshooting and we got them because we
need to go over 5cm diameter cables. 5cm ID, and 115mm OD. VERY heavy. But
even with their size and weight, teh material provided would be ineffective at
the frequencies used in this application. How about SMPS cores? Or possibly
high end audio transformers?
Cortland
KA5S
----- Original Message -----
From: Gert Gremmen <mailto:g.grem...@cetest.nl>
To: Ken Javor <mailto:ken.ja...@emccompliance.com> ;Untitled
<mailto:emc-p...@ieee.org>
Sent: 8/12/2008 7:23:49 AM
Subject: RE: Ferrite snap-on rfi suppression for cable in AM BCB
I do not think so.
Unless you are ready for huge volumes of ferrite.
Normal snap-on ferrites (large ones) are effective only
from 50 MHz off, and the effect may be improved at the cost of it’s
effectiveness in the 100’s of MHz range
by winding the cable 2 -3 times through the ferrite.
So I expect that you will need at least 100 time s the volume
of an ordinary ferrite clamp to get some effect.
And it will be partially inductive too….
A solution may be using a high mu ring ferrite of suitable dimensions
as used
in transformers
and creating a secondary winding (current transformer) with a suitable
secondary circuit to absorb the frequencies you search to suppress.
( I was thinking of a parallel resonance LCR circuit)
Outside resonance the LC has a low impedance, so has the primary
When in resonance the R transforms to the primary with the ratio of the
windings squared.
Anyway, the effect is limited to the impedance the ferrite has without
secondary, and the transformed R may not suit your requirements.
Gert Gremmen
Van: emc-p...@ieee.org [mailto:emc-p...@ieee.org] Namens Ken Javor
Verzonden: Tuesday, August 12, 2008 6:59 AM
Aan: Untitled
Onderwerp: Ferrite snap-on rfi suppression for cable in AM BCB
Does anyone out there know of a product or material that could be
clamped or
formed around an installed cable and be absorptive, not inductive, in the low
end of the AM BCB (around 500 - 800 kHz)?
Thank you,
Ken Javor
Phone: (256) 650-5261
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