GSM-noise "buzz" issue / ways forward
wiederling at googlemail.com
Mon Sep 22 17:13:18 CEST 2008
On 9/22/08, Andy Green <andy at openmoko.com> wrote:
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> Somebody in the thread at some point said:
> | Is there any way to switch the audio path to some file output?
> | i.e. can I (potentially) record "buzz" without an active GSM connection
> | ( while irradiating the phone from an external HF source )
> | would be cheaper and easier to set up that way.
> Werner pointed out yesterday to a guy asking the same thing that
I'le look into that.
> should be the thing.
> As far as I know, nobody yet tested this with buzz and so confirmed that
> the effective buzz problem actually comes at the MIC inputs to WM8753.
> | <someone>
> |> Well maybe luckily we *might* eventually find a magic place for a
> (33pF) C
> |> somewhere near Wolfson chip, to rework GTA02 out in the field this way.
> |> Anyway I'd rather expect this magic fix to be found by try and
> error, rather
> |> than probing on a setup that's completely changed by mere applying a
> probe to
> |> it.
> | Could someone with the device open place 100Ohm resistor in series with
> | 3/4pF from the mic line to GND and test it? ( instead of the ferrite
> | Is the trace in the top layer of the pcb or is it burried?
> I don't have gerber layer data, but the bead was placed in series with
> headphone jack p4, it should be possible to try.
> But I don't have 3.. 4 pF caps lying around, I order some for tomorrow.
4pF @1.8GHz ~= 22Rx, anything in the range of 2..20pF will be OK I guess.
we can experiment a bit further when you are here.
i have a stash of 0805 parts and should be able to badger some 0204
size stuff from the regulars here.
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