[RFI] Ferrite Beads

Ford Peterson ford at cmgate.com
Wed Oct 20 20:35:46 EDT 2004

Jim wrote:

> The moral of the story is that you have to watch that air gap.  When you 
> split your toroids, if a bunch of the material crumbles away you will 
> have an air gap.

I use a machinist vice to do the dirty deed.  By separating two blocks to the approximate diameter of the toroids, and using a drill bit on the opposite side of the core, in the middle between the blocks, the vice will split them in two nearly perfect every time.  As long as you keep the halves matched up in pairs, they can be placed back together with an almost imperceptible crack between them.  I think the coupling in this manner is actually much better than the traditional split cores could ever be.

I'm getting lots of conflicting information regarding this stunt (some through this list and some direct).  Some feel that the cores with one turn through them will not create enough resistance to make much, if any, difference in the noise.  I still have not decided what to try next.  Buying 48 to 96 cores at $1.20 to $1.70 each, and snapping them in two, seems like a waste of money, energy, and otherwise perfectly good toroids if it is not going to work.  How much RF resistance would be required to make a noticable difference?  I'm not smart enough to know.  Perhaps others on this list could provide some guidance for me.  Is 20 ohms on each COP enough?  Is 50 ohms enough?  How about 300 ohms?  I have no experience with this type of problem and therefore I'm truly clueless.

ford at cmgate.com

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