GSM-noise "buzz" issue

[Werner Almesberger]

Andy Green wrote:
> Yeah, waving hands about RF in cans is not understanding: pretty sure
> about it.

I think we all would be much more comfortable about our understanding
of the situation if someone could identify the actual contamination
path.

It's one thing to identify violations of good design practice (and to
avoid them in the future), but to debug an actual problem, we can only
be sure the true root cause has been found if we have the complete
story, or at least a plausible theory for every step.

This, by the way, also applies to the SD vs. GPS interaction. We now
have what I believe is a thorough understanding of what gets emitted
and how to silence it, but we never identified where this gets picked
up and causes trouble.

If this is an over-the-air path, we'll know that we'll have to expect
similar issues in the future, and that we have to provide appropriate
countermeasures. But if it's just a poorly routed trace, then
hardening future designs against over-the-air contamination would be
of limited use and might draw attention from more deserving areas.

Now, I'm not suggesting to reopen the GPS noise investigation, but I
would very much like to see an explanation for how and where the RF
noise "received" by the audio jack jumps into the mic signal even
after all components actually connecting the traces have been removed.

- Werner