Buzzing on GSM audio
joerg at openmoko.org
Sat Jul 26 06:02:39 CEST 2008
Am Sa 26. Juli 2008 schrieb Dave Clark:
> Jim Morris wrote:
> > Dave Clark wrote:
> >> Can you correlate the buzzing to your signal level? IIRC, most phones
> >> will increase transmit power as needed to overcome noise. If the noise
> >> is caused by RFI from the GSM radio, increased power would tend to
> >> increase the interference.
> > I have a very low signal here one bar at most, I haven't tried it where
there is good reception, as
> > I can't really use it as a phone yet. However with that clue I'll try it
ASAP in an area where I get
> > better reception.
> > FWIW my other Cell phones also get very low reception here, but don't have
> > I hope if this is a H/W problem we can get it fixed even after the
warranty expires as it definitely
> > makes the phone a brick otherwise.
> I know GSM transmissions can present significant interference on audio
> equipment - if my phone (any GSM phone) is on my desk, I can hear
> periodic static in my computer speakers as the phone "checks in" with
> the cell tower - it sounds like three quick, buzzes in about 1 second.
> This happens a couple times an hour.
> When it receives a call, I get a steady buzz starting 1 to 3 seconds
> before the phone rings, and continuing until I hang up.
> I would imagine that ALL cell phone hardware would have to deal with
> this audio interference, and since I don't hear it in many other phones,
> I'm pretty sure it can be filtered out with some sort of audio processing.
Nope, it has to be stopped on RF-side, before even entering audio-path. For
this we have to spot the exact way RF is entering back to the device. That's
what we're about to do.
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