[RFI] Ferrite Beads

[Ford Peterson]

I'm confused about selecting the appropriate mix for beads for RFI suppression.

The application is the COPs (coil on plug) on my Toyota Tundra pickup.  These COPs are the source of considerable RFI (See last month's QST article in The Doctor is In).  The peak noise appears to be on 40M, although it is quite evident on 80M and to a lesser extent on 20M and still a problem on 17M.

I have some type #43 ferrites and have been playing with the Autek VA1 and find that they don't respond well to relatively low frequencies.  I have two types here.  Both are beads.  The first style is 1-1/8" long x 1/4" ID.  The second is about 0.8" long and 1/2" ID.  Both are known to be type #43 mix.  I just happen to have some beads mounted on short lengths of coax and thought I would measure and describe my findings...

A 9 stack of the 1-1/8" long x 1/4" ID style #43 produces the following response on a length of RG8X:

MHz  Ohms
   1         15
   2         47
   4       234
   8       515
 16       812
 21       >1K

A 12 stack of the 0.8" long x 1/2" ID style produces the following response on a length of RG8:

MHz  Ohms
   1         38
   2         89
   4       208
   8       442
 16       816
 21       >1K

Looking at the Palomar website http://www.palomar-engineers.com/Ferrite_Cores/ferrite_cores.html
I am confused about the suggested frequency ranges for optimum results.  The type 43 are suggested for 1-1000 MHz for RFI, 0.2-1 MHz for Coils, and .01-10 MHz for transformers.

Ocean State also sells ferrites http://www.oselectronics.com/ose_p88.htm
Here the type 43 are suggesting 0.01 - 1 MHz and type 61s for 0.2-10 MHz.

My gut is telling me (based on the above measurements) that the 43 mix is not the best.  Rumor states that the #61 is the way to go for 3-18 MHz response.  I only have a few inches of leads on each COP to play with (only room for a couple of toroids on each COP) and need to select the optimum mix for the greatest suppression of noise.

Any and all informated observations on the subject would be appreciated.

Ford-N0FP
ford at cmgate.com