> I am going to order some used components from Surplus
Sales of Nebraska. I
> thought I might order some beads to use to help me with
some RFI problems I
> am experiencing. For example, the A/D for in computer
assisted rotator
> controller has some RFI problems on the higher HF bands.
Bypassing and grounding is generally much more effective
than throwing a bead at a problem.
> Can someone recommend which type of beads I should have
handy to assist with
> RFI problems as they arise.
You generally want the highest possible **resistance** and a
core that allows multiple turns. Impedance goes up nearly by
the SQUARE of the turns increase. Two turns through one bead
is generally about twice the impedance of one turn through
two of the same beads.
Look carefully at the impedance vs frequency, and IGNORE the
"frequency range" in descriptions. Pick the highest
impedance in the operating frequency range where you have
the problem. Once again, bypassing with capacitors is often
much more effective than slapping a bead on the problem
(unless the equipment already has good bypasses). A bead is
useless when the common mode impedance is significantly
higher than the bead impedance.
> Here is the URL to the web page with the information on
the beads and
> sleeves that Surplus Sales of Nebraska sells.
> http://www.surplussales.com/FerBeaSle/FerBeaSle-1.html
Why not go to a regular suppression core vendor? At least be
sure you look at the real data for the cores. You generally
want hundreds or more ohms of impedance, and you want that
impedance to be largely resistive. That precludes using 43
and similar materials in suppression applications. You want
something with a well-defined broad peak at HF for HF
suppression, not a material who's impedance keeps climbing
with frequency well up into VHF.
73 Tom
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