GSM-noise "buzz" issue

[Andy Green]

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Somebody in the thread at some point said:

| But if it's something more complex, such as the GSM module contaminating
| GND itself, then you'll have to be able to do proper GSM signaling in
| order to be able to reliably reproduce the problem.

I don't think so, I could just make a call and "reliably reproduce the
problem" for the duration of the call when I force it to transmit.  It
seems the customers are the same in not needing expensive gear to make
the problem come.

This seems to be a pure frequency-dependent coupling issue, especially
since Joerg tells us he can force coupling to this net by external GSM
phone transmission nearby.

| (BTW, I also don't get the buzz in Argentina, where GSM uses the
| 1900MHz band.)

You would think it also depends on output power from our RF section; it
might be worth trying with "piece of wire" antenna to force it to use
highest transmit power if otherwise your base station is close.

If it isn't that you are using low power, that's pretty interesting, it
couples at 1.7GHz but not 1.8 - 1.9GHz then.  It seems something we are
missing is frequency response of the radiated coupling to the victim net.

- -Andy
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