All class B transceiver have in common, that they need an own GPS.
This is necessary because the normally existing GPS antennas deliver NMEA GPS data. This NMEA datas are generally not exactly enough in reference to their time-base. A typical class B AIS telegram takes 25ms. Within 1 ms the class B transceiver has to deliver his „beam“. In order that the sent telegrams are not overlapping, every sender has to keep an exact for sending. The date for sending has to be more accurate as the telegram. The date of sending is determined at ca. 100µs by the class B sender. This is only possible, when the sender gets the raw data from the GPS antenna and not NMEA data, which are only accurate to 1/10 s. This is the reason. For a reliable operation GPS datas on a µs base are needed. With the explanation above you need 2 GPS antennas. One with NMEA data for your chartplotter and one for the easyTRX.