Class B transceivers were pioneered to offer AIS benefits to smaller vessels. Class B devices offer lower power, fewer receivers and different display options to a Class A transceivers. Coupled with cost savings, Class B devices are ideal for mariners with small pleasure craft or fishing boats.
Class B transceivers offer small vessels all the AIS features of Class A devices, but without some of the requirements needed for larger vessels. Class B devices offer:
- Lower power, 2W, transmission output
- Multiple outputs to different displays
- Same number of transmitters and receivers as Class A, but used differently
- One transmitter must be multiplexed to the VHF DSC radio
- Active GPS antenna incorporated in the device
- Not interfaced to a compass, so heading information rarely transmitted
Class B units are designed for smaller vessels with fewer power options, less space and fewer antennas than a large commercial vessel. The lower transmission power means their range is significantly less than a Class A device, but this is compensated by the anticipated stopping distance in an emergency situation of the vessel compared to a large commercial vessel. Also, the devices are a lot smaller than a Class A device, ensuring they can be installed quickly and integrated easily to many different displays. As smaller vessels rarely include a second antenna, most Class B devices need to use an antenna splitter to regulate use of the VHF antenna between the VHF radio and AIS device.