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All outdoor connectors on the coaxial cables should be fitted with preventive isolation, such
as shrink-stocking with silicone to protect the antenna cable against water penetration.
Coaxial cables should be installed in separate signal cable channels/tubes, and at least 10
cm away from any power supply cables. Crossing of cables should take place at right angles
(90°). Coaxial cables should not be exposed to sharp bends, which may lead to changes to
the characteristic impedance of the cable. The minimum bend radius should be 5 times the
cables outside diameter.
Grounding
Coaxial down-leads must be used for all receiving antennas, and the coaxial screen should
be connected to the ground at one end.
3.13.2 GNSS Antenna installation
A Class A AIS must be connected to a GNSS antenna.
Location
The GNSS antenna must be installed where it has a clear view of the sky, so that it accesses
the horizon freely through 360°, with a vertical observation of 5 to 90 degrees above the
horizon. Small diameter obstructions, such as masts and booms, do not seriously impair
signal reception, but such objects must not eclipse more than a few degrees of any given
bearing.
The antenna must be located at least three meters away from, and out of the transmitting
beam of high-power transmitters (S-Band Radar and/or Inmarsat systems). This includes the
ship‟s own AIS VHF antenna, if it is designed and installed separately. See also sample for
antenna layout in Installation Manual Appendix 8.2 (Drawings)
If a DGNSS system is included or connected to the AIS system, the installation of the antenna
should be undertaken in accordance with IEC 61108-4, Edition 1.
Cabling
To achieve optimum performance, the gain of the antenna pre-amplifier should match the
cable attenuation. The resulting installation gain (pre-amplifier gain - cable attenuation)
should be within 0 to 10 dB (RG214 at GPS attenuation per meter of app. 0.35 dB/m (45m =
15.75dB); GPS frequency app. 1.2GHz).
The coaxial cable between the antenna and the AIS ship borne station connector should be
routed directly, in order to reduce electromagnetic interference. The cable should not be
installed close to high-power lines, such as radar or radio-transmitter lines, or near the AIS
VHF antenna cable. A space of one meter or more is recommended in order to avoid
degradation due to RF-coupling. Crossing of antenna cables should take place at 90 degrees,
to minimize magnetic field coupling.
Attenuation
As described above, the resulting installation gain should be between 0 to 10 dB. If the
internal GPS receiver will be overloaded with more than 18 dB, then it could be damaged.
Installation Manual
30
Y1-03-0212 Rev. E
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