Connecting NMEA Stream to UART using virtual tty's


I would like to add a simulated GPS to SITL runing on my ubuntu machine. I created a virtual pair of com-ports using the socat command:

sudo socat -d -d pty,link=/dev/myttySim,raw,echo=0 pty,link=/dev/myttyGPS,raw,echo=0

i start the sim with: -A “–uartB=uart:/dev/myttySim” – console --map

i can see some stuff being written to this port doing a cat on /dev/ttyGPS. But somehow i do not manage to make my sim accept the NMEA stream i write on this interface.

Does this port require some special protocol or should it accept plain NMEA?

Any suggestions?