UART noise on A6 GSM module

I’m using the A6 GSM module to send data from my sensors board to a server via GPRS.

The problem is that most of times, usually when the module attaches to the network or connects to the server, noise appears on the UART A6 TX line and the microcontroller reads garbage. After this noise appears, the next command sent to the module gets a CME error response. I suspect the noise it generated by the chip, maybe caused by the RF transmitter.

Sometimes it works, but most of the times it fails. I’ve tried placing 100pF capacitors to GND on the UART lines and lowering the baud rate to 2400 baud, but with the same results.

If it has anything to do with this problem, I mention that I am applying 3.3V level on the UART line (the A6 supports 2.8V), since I did not have a voltage translator available when I made the board.

Has anyone encountered this problem? Is there a solution or should I use a different GSM module?

I am feeling its a power supply issue. When it connects to network it draws more current and the power source is not able to deliver the 2A pulse current. Change to a stable power supply and try once.

Thanks for the reply. I found out, by accident, that the problem is in fact a design issue related to incorrect grounding of the antenna.

See here more details: