Installation Manual

AIS Installation Manual Issue 1 15
5.4 Antenna units
The AIS Transponder has to be connected to two antennas: a VHF antenna and a GNSS
antenna. The GNSS (GPS) antenna is supplied as standard.
5.4.1 Antenna mounting position
In accordance with IMO guidelines, antennas should be mounted in positions which, as far as
possible, minimise interaction between them. The sketch summarises the recommendations:
5.4.2 VHF antenna
The VHF antenna is an important part of the receiver and transmitter system; the reception
range is heavily dependent on the antenna installation. The VHF antenna must be installed as
high as possible and free of shadow effects from the ship superstructure; effective installation
will maximise the range of the system. The antenna must also be mounted so as to achieve the
safety standards detailed in Section 2.
WARNING: The antenna must have sufficient bandwidth to suit the AIS system, as otherwise
the high VSWR produced may cause the transponder to shut down. It is recommended to use
an omni-directional vertical polarised VHF antenna with unity gain (0 dB), and a bandwidth
sufficient to maintain VSWR <1.5 over the frequency range 156 – 163 MHz. A suitable antenna
is available from McMurdo as an option, part number 89-020-001.
5.4.3 GNSS antenna
The Transponder package contains a GNSS antenna and a mounting bracket. The mounting
bracket is designed for welding to the ship’s superstructure.
Installation of the GNSS antenna is critical for the performance of the GNSS, which is used for
timing of the transmitted time slots and for the supply of navigational information should the
main navigational GNSS fail. We strongly recommend that the supplied antenna is used.
1. The GNSS antenna must be mounted in an elevated position and free of shadow effect
from the ship’s superstructure
Vertical
separation
2m
GNSS antenna
alternative
position
180°
Horizontal
separation
10 m
Vertical
Separation
2 m
360°
GNSS antenna
preferred
position