Please note that you need a separate GPS Antenna for the Class B transceiver.The antenna which is on board, does not work probably. The normal GPS antenna are „active“ antenna, which are already sending a coded telegram (NMEA 0183). These telegrams are perfect adapted for PC programs and cardplotter. Most telegrams are only closely for 1 second or 1/10 second. That is to incorrect for a class B AIS transmitter. The timebasis for AIS radio communication must be closely 1ms also a/1000 second. This accuracy will be reached when the GPS antenna is sending the raw data to the Class B AIS tranceiver also easyTRX. The raw data are transmitted from easyTRX into the correctly time base.
Thats why you need an separate GPS mushroom-type antenna, which send the raw data to the easyTRX.