Hi, i bought the sparkfun electronics GM862 GSM module v2.4 with usb.
Pins 10-12 (earphone out) are connected to vias located right under the antenna (not very smart). When my earphone-out is connected to my computer and listen to received signal, it is very noisy. There is some sort of burst interference on line which sounds like a telegram transmission.
When i connect my speaker-out from pc to mic-in of GM862 and listen to the received signal on a home telephone, i dont have any interference of the sort, at all. (Note: mic-in pins are 14-16 and are just a bit further from the antenna connection.)
Do i have a bad GM862 setting or a bad connection on the module??? The speaker out is meant to be connected directly to earphones and so, no extra filters or shielding should be needed.