any update on GSM interference issue

Al Johnson openmoko at
Tue Aug 5 16:09:03 CEST 2008

On Tuesday 05 August 2008, arne anka wrote:
> >
> > Maybe that could provide a less invasive means to getting rid of the
> > problem?
> jOERG proposed using a ferrite bead on the wired headset a while ago in a
> german forum ( or so).
> i am still trying to find one which is capable to be put on the included
> headset non-destructive (both the bead and the headset).
> ps: i was still under impression, the bead has to fit _around_ the cable
> -- the page says, it can be attached simple with tape as well.
> has someone a link explaining exactly what kind of voodoo that thing does?
> has it to have a hole?

The ferrite is increasing the common mode inductance of the cable because the 
ferrite has a better magnetic permeability than air. Taping the ferrite to 
the cable is a bit like a half turn on a ferrite rod. It will still affect 
the inductance, but not as much as if it went through a ferrite ring.

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