Buzzing on GSM audio

Joerg Reisenweber joerg at
Sat Jul 26 07:24:05 CEST 2008

Am Sa  26. Juli 2008 schrieb christopher bradski:
> Just curious if there is a gsm "saw filter" somewhere in the audio path (or
> another filter by the amp)?
Not quite sure what you mean by saw-filter, but i guess the answer is "No".

> Also, I haven't popped open my freerunner yet 
> but could another fix be that a small capacitor could be strategically
> placed to filter out the noise (like the sd card issue (worked in my car
> audio....))?
That's our big hope, but so for all investigations/reworks (there were quite a 
few) didn't yield the results we needed.

> Sorry for so many questions/possibilities... Is the Vcc path to 
> the gsm transmitter to close to an audio path 
Yes it is (near bat-con), but we seem to have made clear it's not the source 
of the problem. The problem can be triggered by introducing external RF 
(second cellphne e.g.), so internal VCC-issues are off he list.

> or could it just be something 
> is tied down to an incorrect ground location?
See above

> I'm sure the Openmoko team is 
> already on top of this though.
Bet we are ;-)

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