[RFI] Choosing Snap-On Toroid for 6M?

Jim Brown jim at audiosystemsgroup.com
Mon Feb 19 16:48:37 EST 2007

On Mon, 19 Feb 2007 15:08:33 -0500, Morse, Earl (E.A.) wrote:

>Since these beads are common they are also very cheap.  Especially when
>you get them off of junk box computer cables.  At 50 MHz you won't
>notice a whole lot of difference in impedance between the #31 and #43
>for the same size bead.  


>In selecting sizes of bead you may want to use a larger bead and use
>multiple turns or fit the bead to the size of the cable.  I prefer the
>solid beads but realize the issues of getting them on cables that can't
>be disconnected.  There is some loss of impedance due to using a split
>material vs a solid material but I can't remember how large it is.

If you study the data, the small air gap of the clamp-ons is mostly a 
factor at lower frequencies, but no big deal at higher frequencies. But 
the clamp-ons are about twice the cost for equivalent suppression, so 
you'll get more bang for your buck with solids (assuming you're buying 

Higher Z = more suppression, and at 50 MHz, Z is proportional to length, 
so go for a longer bead (and the Z of beads in series adds). 

>Try what beads you have around the junk box as they are probably #43 mix
>and see how they work.  Then see if you can improve by ordering other

Yes. This is one of those relatively few applications where almost any 
hamfest clamp-on or cylinder will work fine, because as Earl notes, most 
of them are #43. I'm a huge fan of Fair-Rite's #31 mix for HF, but above 
10 MHz, #43 is just as good, much cheaper, and much easier to find. 


Jim Brown K9YC

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