I'm confused about selecting the appropriate mix for beads
for RFI suppression.>>
I'm confused about most things in life.
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.>>>
I agree Ford, 43 is a crappy mix. As a matter of fact the
manufacturer suggests 43 and 44 for 20 MHz and higher.
Whoever wispered 61 in your ear is seriously mistaken. 61
will be worse than 43 by a factor of ten at HF. Now if we
were talking 300-1800MHz, 61 would be perfect.
What you want is a bead with high loss tangent and high
impedance. When the impedance is primarily reactance adding
the bead can actually make the problem worse.
The recommended beads are 31 or 73. The problem is in a
large size 31 and 73 have internal resonances when the
diameter and thickness is large, so you will be stuck with
something like a 33 material in large beads. It's only a bit
better than 44, but at least it's better.
73 Tom
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