[RFI] Ferrite Beads

[Ford Peterson]

Jim wrote:

> And finally, to clarify what Tom was saying, it is VERY important that you 
> operate the ferrite choke in the range where it is hardly a choke at all, but is 
> primarily resistive. Why?  Simple -- any inductance will increase the current 
> by resonating with the capacitance of the short antenna.  
> 
> I'm currently at an EMC workshop in CA lectured by Henry Ott, so don't 
> have time to say a lot more. 
> 
> Jim Brown  K9YC

I appreciate the help everybody is trying to provide me.  But frankly, I know less now than I did before I started this query...

My application is somewhat unique.  I have ignition noise eminating from the 8 COPs on my Toyota.  This is the same engine (4.7L V8) used in the Lexus, 4 Runner, Tundra, and possibly others.  Toyota did not give me much wire to work with on the engine harness.  The connector is about 1" wide with 4 conductors in-line.  They've taken great strides to weather pack the connector to seal out the elements.  There are 4 ~ #18 or #16 wires going to the connector.  There is NO male/female connector available from Toyota, and the connector on the COP is integrated into the injection molded assembly.  I have no options available to fabricate 8 little EMI suppressors out of available connectors.  So I am stuck attempting to wrap the existing 4 conductors into the bead/toroid or whatever.  A split bead (~ $5 each) of #43 (all I can find available) seems easy enough to incorporate, but I have doubts about the effectiveness of the #43 material in this application.

I have enough excess wire on the harness to allow me to slip up to several toroids over each of the 8 wire assemblies without ripping this $30K vehicle all apart, effectively voiding the 6 year/70,000 mile warranty.  That means one turn through each core.  I would prefer to use a toroid and need to select an appropriate mix.  I will split them by hand and slip them over the wires, using tape to secure them.

The question remains, what is the best material (among those available) and how many single turn toroid forms should I plan to incorporate to effectively suppress this noise?  Maybe there is a better way?  I'm all ears...

Ford-N0FP
ford at cmgate.com