2.3 GNSS Antenna installation
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Circulars - Safety of Navigation - Circular SN/Circ.227- Guidelines for the Installation of a Shipborne Automatic Identification System (AIS) – (6 January 2003)Amended by SN/Circ.245 - Annex - Guidelines for the Installation of a Shipborne Automatic Identification System (AIS) - 2 AIS Installation - 2.3 GNSS Antenna installation

2.3 GNSS Antenna installation

 Class A AIS should be connected to a GNSS antenna.

Parent topic: 2 AIS Installation

2.3.1 Location

 The GNSS antenna should be installed where it has a clear view of the sky. The objective is to see the horizon freely through 360° with a vertical observation of 5 to 90° above the horizon. Small diameter obstructions, such as masts and booms, do not seriously degrade signal reception, but such objects should not eclipse more than a few degrees of any given bearing.

Locate the antenna 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.

If a DGNSS system is included or connected to the AIS system, the installation of the antenna should be in accordance with IEC 61108-4, Ed 1, annex D.

2.3.2 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.

The coaxial cable between the antenna and the AIS shipborne station connector should be routed directly in order to reduce electromagnetic interference effects. The cable should not be installed close to high-power lines, such as radar or radio-transmitter lines or the AIS VHF antenna cable. A separation of one meter or more is recommended to avoid degradation due to RF-coupling. Crossing of antenna cables should be done at 90° to minimise magnetic field coupling.

All outdoor installed connectors on the coaxial cables should be waterproof by design to protect against water penetration into the antenna cable.

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