steve at openmoko.com
Mon Jun 1 20:37:33 CEST 2009
Yes. Since I'm marketing I'll give the only description I can which
is considerably dumbed down.
RF ( from GSM) gets coupled onto the lines leading INTO the audio mixer.
the mixer cannot filter this signal. The RF remains on the line coming
out of the mixer. The only way to remove it before it gets on the
microphone is to apply a filter: the CAP in the buzz fix.
It's unclear whether this buzz can be removed by processing done
by carriers or receiving handsets once the infected signal leaves the
FR. Clearly in some cases it is not removed. Since the buzz signal is
obviously in the hearable range I would imagine that any post processing
would be a hit on S/N or audio quality.
[To remove the ROOT cause ( RF from GSM getting on the lines) you apply
ferrite beads ( or other EE contraptions that I won't pretend to
comprehend) on the input side of the Mixer. ]
Now, to the question of how the RF gets on the lines going into the
mixer. I believe there is a frequency dependency. That is, some
frequencies ( say 900 for example) will couple more readily than others
( say 1900) and obviously harmonics of 900 might couple more readily as
well. EMI is black magic as far as I'm concerned so I'll shut up and not
beclown myself any further.
arne anka wrote:
>>> Aother note to all who read this: the Buzz rework is only required if
>>> you have the Buzz problem.
>> Hmm, wasn't there an environmental component as well, i.e., band and
>> signal strength ? So changes in the network, e.g., traveling, moving,
>> or the provider messing with things, might bring buzz to phones that
>> still lacked that experience.
> as far as i understood the issue, the buzz is there by design and not to
> be solved by tewaking a state file.
> thus, while actually experiencing that buzz is subject to several factors,
> otoh nobody can be said to be sure not to be bitten by it.
> conclusion: everyone having access to the buzz fix should take hold of it.
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