AIS CTRX GRAPHENE Class B AIS Transponder Manual
1.9E
33
CTRX GRAPHENE Manual
APPENDIX B
ANTENNAS AND ANTENNA MOUNTING
GPS Antenna
The GPS antenna used must be of the active type (i.e. it should incorporate an LNA) and
must be suitable for marine shipboard applications (index of protection, ruggedness, means of
mounting, etc.). An antenna should be selected with a gain (in dB) depending on the length
of cable between the antenna and the AIS unit; after subtraction of cable and connector
losses a minimum total gain of 25 dB should be available at the AIS CTRX GRAPHENE unit
GPS antenna connector.
The GPS antenna to be used for AIS use must be a dedicated antenna, i.e. not shared with
any other GPS receiver.
Installation of the GPS antenna is critical for the performance of the built in GPS receiver
which is used for timing of the transmitted time slots and for the supply of navigational
information should the main navigational GPS fail. We strongly recommend that:
1.
The GPS antenna is mounted in an elevated position and free of shadow effect from
the ship’s superstructure
2.
The GPS antenna has a free view through 360 degrees with a vertical angle of 5 to 90
degrees above the horizon.
3.
As the received GPS signal is very sensitive to noise and interference generated by
other on board transmitters, ensure that the GNSS antenna is placed as far away as
possible from radar, Inmarsat and Iridium transmitters and ensure the GPS antenna is
free from direct view of the radar and the Inmarsat antenna beam.
4.
It is also important that the MF/HF and other VHF transmitter antennas are kept as far
away as possible from the GNSS antenna. It is good practice never to install a GNSS
antenna within a radius of 5 Metres from these antennas.
VHF antenna for AIS use
The VHF antenna employed for AIS use:
Must be a dedicated antenna, i.e. not shared with any other VHF transmitter/receiver.
Must be suitable for marine shipboard applications (index of protection, ruggedness,
means of mounting, etc.)
Should be omni-directional and vertically polarised with unity gain (0 dB) and with a
bandwidth sufficient to maintain a VSWR less than 1.5 over the frequency range 156
– 163 MHz. As a minimum the 3dB bandwidth must cover the two AIS channels and
the DSC Channel 70.
Should be mounted with at least a two meter vertical separation distance from any
other VHF antenna used for speech or DSC communication. See EMI warning below.
Should be mounted at least 2-3 metres above sea level for good performance.
