reset gsm modem
This could be an antenna related problem or power supply related problem, or both. If the antenna is mismatched and/or it has high VSWR, will cause high currents being consumed from the power supply, during TX pulses. If your power supply is not powerfull enough, this pulses will cause voltage drops below minimum operating value, and this can dazzle the logic part, causing strange behaviour. The power supply connection is also important (this is valid for almost all GSM modems). You should place decoupling capacitors nearby the module. The caps must have the value as indicated in the module's datasheet. The traces between the caps and power pins must be as short and as thick as possible. Use the maximum width you can afford, and avoid stub connection between the caps and power nets. Use low ESR capacitors. If the power supply is not ok, the same phenomena will happen, during transmission (when the module can surge usually up to 2A in low signal strenght conditions), the main voltage can temporarely drop below minimum operating voltage and can cause strange behaviour.
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