I have designed a board with SIM808 which is connected to the 32-bit microcontroller. There is some extra power circuitry on board – MPPT switching converter. Distance from switching controller to GPS_antenna SIM808 trace is about 30mm.
My SIM808 GSM and GPRS communication works perfect. It connects to cellular network in matter of seconds and everything works. But GPS… can't get it work. Below you can see my board design(both layers "transparent", top layer, bottom layer). On bottom layer, below GPS copper trace and antenna connector, there is plain solid ground copper pour. Surrounding vias are grounds. PCB is 2-layer. Trace width is 0.61mm.
Using standard passive GPS antenna: https://e-radionica.com/en/ceramic-gps-antenna-1575-42mhz-with-ipx-connector.html
System is powered from battery and there are enough capacitors around which should cover current peaks(up to 2A for SIM808).
Tried going outside with it, leaving it for some time, once even whole night :), tried bigger passive antenna – no movement. I have tested if I have got a fix using both LED from 1PPS pin and using AT+CGNSINF command.
I even got so far that I googled bunch of different breakboards with SIM808 and, oddly(or not?), all of them had trace for GPS antenna routed not directly from my pin, but at 90 degrees angle. Don't know if that could be the key.
I am really confused about this one. Before designing this board, I read few online articles regarding antenna and traces and tried to apply those rules as close as possible. It worked for GSM, but for GPS can't not find solution.
Best Answer
Ground should be removed from top layer right below the connector main trace. See the remark in the data sheet for the recommended connector Pcb footprint.