GSM-noise "buzz" issue
openmoko at torsten-sievers.de
Thu Oct 9 09:26:04 CEST 2008
is there any further progress on this issue?
How can we help to solve this issue?
On Wednesday 01 October 2008 05:34:24 Joerg Reisenweber wrote:
> Am So 21. September 2008 schrieb Uwe Klein:
> > On 9/21/08, Werner Almesberger <werner at openmoko.org> wrote:
> > > Andy Green wrote:
> > > > One interesting thing would be stick a tracking generator on the GSM
> > > > antenna, put it near the headphone socket in a repeatable way, stick
> > > > spectrum analyzer probe on the victim net, and sweep them to get a
> > > > display of coupling efficiency vs frequency.
> > >
> > > Do you think this will work ? I thought of using a tracking generator
> > > when I wrote that mail lamenting that Joerg didn't have a signal
> > > source, but then I realized that almost all tracking generators have
> > > their maximum output at about 0dBm, while our troublemaker should be
> > > more like 30dBm.
> > I had thought about using the FR as an energy sink.
> > Using a 4pole networkanalyzer and a pair of antenna
> > in a grid dip meter style arrangement.
> > This should indicate all absorbtive elements.
> A very cute test setup.
> Anyway I don't exactly see what we have learnt once we know all dips by
> name, err frequency and dB. I'd guess we get a lot of dips, and we can't
> tell what element caused them, and especially we don't learn anything about
> audio contamination path. Even less we learn something *new*.
> Werner's original proposal seems somewhat more result oriented, alas all
> this fails when attaching probe to the "victim net", due to total change of
> RF-properties (probe has some pF! need to open can, etc). So probably the
> most helpful test would be to use a +36dBm generator at 850/900/.... and
> "record" buzz by arecord piped to ssh-stdout to external PC, so you can
> level up generator and see what dBm you need at different frequencies to
> start buzz. Basically exactly the tests I already did in TPE, though I had
> to use a second phone for generator purpose, and this was rather clumsy and
> not very reproduceable.
> Also direct coupling of RF to JK4401:4 at a moderate level might be a way
> to go, then check with scope/spectralizer all the pins and pads inside can,
> and get an idea of where RF jumps to from primary path (if any). Again we
> won't learn anything about how we could improve things, other than KEEP RF
> OUT of CAN, i.e. away from non-linear audio-circuits.
> Anyway, I'm looking forward to read your report on test results.
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