Em-Trak B921 - 3.2 Antennas; 3.2.1 VHF antenna:; 3.2.2 GPS Antenna:

About your AIS class B transceiver
Page 13
2.8 Mobile app
An em-trak mobile app CONNECT-AIS is available for Apple and Android
devices from the App store and Google play.
2.9 Transceiver overview
Figure 2 AIS transceiver overview
NMEA 2000NMEA 2000Power and data
B921, B922, B951 and B952
NMEA 2000Power and data
B923, B924, B953 and B954
VHF antennaGNSS antenna
VHF radio
GNSS antenna
VHF antenna
indicator lights
Mounting bracket
indicator lights
Mounting bracket