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3.11 Installation of VHF / GPS Antennas
Interference to the Ship's VHF Radiotelephone
The AIS ship borne equipment, like any other ship borne transceiver operating in the VHF
maritime band, may cause interference to a ship‟s VHF radiotelephone. Because AIS is a
digital system, this interference may occur as a periodic (e.g. every 20 seconds) soft clicking
sound on the ship‟s radiotelephone. This affect may become more noticeable if the VHF
radiotelephone antenna is located close to the AIS VHF antenna, and when the
radiotelephone is operating on channels near the AIS operating channels (e.g. channels 27,
28 and 86).
Attention should be paid to the location and installation of the various antennas, in order to
support the antenna characteristics in the best possible way.
3.11.1 VHF Antenna Installation
Antenna Location
Location of the mandatory AIS VHF-antenna should be carefully considered. Digital
communication is more sensitive than analogue/voice communication to interference created
by reflections caused by obstructions such as masts and booms. It may be necessary to
relocate the VHF radiotelephone antenna to minimize interference effects.
To minimize the interference effects, the following guidelines apply:
The AIS VHF antenna should have omnidirectional vertical polarisation.
The AIS VHF antenna should be placed in an elevated position, as free standing as
possible, with a minimum of 2 meters in horizontal direction from constructions made of
conductive materials. The antenna should not be installed close to any large vertical
obstruction. The AIS VHF antenna should have a visible sky of 360°.
The AIS VHF antenna should be installed at least 3 meters away from interfering high-
power energy sources such as radar and other transmitting radio antennas, and out of the
way of the transmitting beam.
There should not be more than one antenna on each level. The AIS VHF antenna should
be mounted directly above or below the ship‟s primary VHF radiotelephone antenna, with
no horizontal separation and a minimum of 2 meters vertical separation. If it is located on
the same level as other antennas, the distance apart should measure at least 10 meters.
See also sample for antenna layout in the Appendix (Error! Reference source not found.)
Cabling
The cable should be kept as short as possible to minimize attenuation of the signal. Double
shielded coaxial cables equal to or better than RG214 is recommended.
RG214 at VHF attenuation per meter of app. 0,07 dB/m (45m = 3,15db)
VHF AIS frequency app. 162MHz
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
Installation Manual
28
Y1-03-0204 Rev.K
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