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@cmgate.com
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