Tom wrote:
> 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
Unfortunately, I can find NO beads or toroids for sale that are 33 or 73. A
figure in the new 2005 handbook (Figure 13.9) describes the impedance (in ohms)
of a "101" size ferrite bead.
5MHz 10MHz Perm
Type Ohms Ohms u
64 4 8 N/A (not available)
43 11 16 850
73 20 25 N/A (not available)
75/77 28 28 75=5000 77=1800
I can see that the availability of cores is going to be a problem. You cannot
buy what is not available. Perhaps these companies have had the various mixes
in the past and simply do not produce them today. It is the initial
permeability that I'm looking for? It appears that the high 'u' or high AL
numbers will work the best. Is this true?
In this application, I will have to take a toroid and snap it in two to make a
bead to encase the wires coming from the COP. The #43 split beads are
expensive. Snapping them and keeping them in pairs will be much more
economical and effective if I select the correct mix. Based on this, I would
guess that the #75 mix would be the way to go. Does this sound correct?
Ford-N0FP
ford@cmgate.com
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