I'm working with a client who has his own board design that includes an embedded SIM340 GSM modem. The modem interfaces to the client's board via the modem's 60-pin SMT connector (ENTERY 1008-G60N-01R / Molex 53729-0608).

We're having problems that when the modem engages in GSM/GPRS traffic, we see a lot of noise on the client's board's power supply--to the extent that it causes the TI MSC1210 microcontroller to reset (or possibly causes the supervisor IC to trigger a reset, I'm trying to investigate that possibility now). This only happens with the modem's antenna and patch cable attached. If the patch cable/antenna are removed then no noise whatsoever is detectable--even though the modem usually still seems to be able to communicate with the cellular network (albeit with extremely poor signal strength).

I know this is very vague information--and I will be severely limited in how much information I can provide in terms of board layout, etc. since the design belongs to my client--but I was wondering if anyone has had similar problems with GSM embedded modems in the past and what solutions you may have implemented to solve them?

Regards,
Craig Steiner