5 ANTENNA INSTALLATION
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Statutory Documents - IMO Publications and Documents - Circulars - Radiocommunication and Search and Rescue - COMSAR/Circ.32 - Harmonization of GMDSS Requirements for Radio Installations on Board SOLAS Ships - (16 August 2004) - Annex - Guidelines for the Harmonization of GMDSS Requirements for Radio Installations on Board SOLAS Ships - 5 ANTENNA INSTALLATION

5 ANTENNA INSTALLATION

 5.1 General

Special attention should be paid to the location and installation of the different antennas on a ship in order to ensure effective and efficient communication. Incorrect installed antennas will degrade the performance of the radio equipment and will reduce the range of radiocommunications.

 5.2 Location of VHF antennas

  • .1 VHF antennas should be placed in a position which is as elevated and free as possible, with at least 2 metres horizontal separation from constructions made by conductive materials.

  • .2 VHF antennas should have a vertical polarisation.

  • .3 Ideally there should not be more than one antenna on the same level.

  • .4 The location of mandatory VHF antennas should be given priority compared with mobile telephone antennas. If they are located on the same level, the distance between them should be at least 5 metres.

  • .5 It is recommended to use double screened cable with a maximum loss of 3 dB.

  • .6 All outdoor installed connectors on the coaxial cables should be watertight by design in order to give protection against water penetration into the antenna cable.

  • .7 AIS VHF antenna should be installed safely away from interfering high-power energy sources like radar and other transmitting radio antennas, preferably at least 3 metres away from and out of the transmitting beam.

  • .8 The AIS VHF antenna should be mounted directly above or below the ship’s primary VHF radiotelephone antenna, with no horizontal separation and with minimum 2 metres vertical separation. If it is located on the same level as other antennas, the distance apart should be at least 5 metres.

 5.3 Location and choice of MF/HF antennas

  • .1 The mounting arrangement of the antenna or pedestal should be constructed in order to withstand the strain from swaying and vibration.

    The transmitting whip antenna should be installed as vertical as possible.

  • .2 Wire antennas should be protected against breakage by having a weak link installed.

  • .3 Whip antennas should be installed as vertical as possible and located in an elevated position on the ship at least 1 metre away from conductive structures.

  • .4 Attention should be paid to self-supportive vertical antennas and their swaying radius.

  • .5 The recommended minimum length of the antenna is 8 metres.

  • .6 The down lead from the base of the antenna to the antenna tuner should be insulated and run as vertically as possible and not less than 45° towards the horizontal plane.

  • .7 The transmitting antenna should have an insulation resistance to earth which is recommended to be of more than 50 MΩ in dry weather and of no less than 5 MΩ in humid weather (transmitter to be disconnected when measuring).

 5.4 Location of antenna tuner for MF/HF transceiver

The antenna tuner should normally be located externally (outdoor) and as close to the antenna as possible, and so that the down lead wire/cable from the antenna should be as vertical as possible.

 5.5 Receiving antennas

  • .1 As a general rule, all receivers including watchkeeping receivers should have their own separate antenna.

  • .2 Antennas for watchkeeping receivers should be located as far away as possible from MF/HF transmitting antennas in order to minimise receiver blocking.

 5.6 Satellite communication antennas

5.6.1 General

  • .1 In general, satellite antennas should be located so that they have a 360° free view for the satellite at all times. In practice terms this can be difficult to achieve due to shadow sectors from nearby structures.

  • .2 It is recommended for Inmarsat-A , B and F-77 antennas (stabilized directional antennas) that communication should be maintained with the satellite down to an elevation of minus 5°. For Inmarsat-C (omni-directional antenna) it is recommended that communication should be maintained with the satellite down to an elevation of minus 5° in the fore and aft direction and minus 15° in the port and starboard direction.

 5.6.2 Satellite communication antenna installation

The following guidelines should be observed in order to fulfil the above recommendations:

  • .1 The antenna should be located at the top of the radar mast; or

  • .2 On a pedestal, in the radar mast, or on the top deck so that:

    • - for directive antennae; shadows from constructions, especially within a distance of 10 metres, is maximum 6°;

    • - for omnidirectional antennas; shadows from constructions, especially within a distance of 1 metre, is maximum 2°.

  • .3 Antennae should be installed in a readily accessible location.

  • .4 Satellite antennae should not be located in an area where they can be damaged by heat and smoke.

  • .5 The satellite antenna should not be located on the same plane as the ships' radar antenna.

  • .6 GNSS antennae should not be located close to or on the same plane as the Inmarsat antenna.

  • .7 Consideration should be given to installing the Inmarsat antenna on a suitable pedestal.

(IMO resolutions A.663(16), A.698(17), A.807(19), as amended, A.808(19) and MSC.130 (75) and Inmarsat Design and Installation Guidelines)

Note: - The mast/or pedestal should be constructed so that vibrations are reduced as much as possible.

5.6.3 Safe antenna distances

The following "safe distance" from Inmarsat antennas to other antennas and to the compass are recommended:

  • .1 Distance to the HF antenna should be more than 5 metres.

  • .2 Distance to VHF antennas should be more than 4 metres.

  • .3 Distance to the magnetic compass should be more than 3 metres.

(The installation manual for the equipment and Inmarsat guidelines)

 5.6.4 Inmarsat-C antenna

The antenna should be constructed so as to function up to 15° pitch and roll. In order to obtain this result, the antenna should be located in such position that no objects or constructions down to 15° below the horizon are degrading the performance of the equipment.

Note: - As it may be difficult to fulfil this recommendation in fore-and-aft, the free area in this direction may be reduced to 5° below the horizon.

(IMO resolutions A663(16) and A.807(19), as amended)

5.6.5 Calculation of distance to obstructions:

If obstructions such as i.e. mast, funnel etc. is unavoidable, the following guidelines should apply:

The distance to the obstruction should be so that the obstruction only covers a 2° sector.

Note: - In such case the safe distance will be the following: 20 x the diameter of the obstruction (in metres).

If two Inmarsat-C antennae are installed the vertical distance between them should be at least 1 metre to eliminate interference.

5.6.6 Antenna cable

The manufacturers specifications regarding total attenuation and maximum DC resistance (short-circuit in one end) should be complied with. Only double-screened cable should be used.

5.6.7 Antennas for voluntary radio equipment

Antennas for voluntary radio equipment may be located on deck, provided its use does not interfere with antennas of mandatory radio equipment. When mobile telephone is installed on board ships, special attention should be made to the facts that some types of mobile telephones (especially GSM telephone equipment) may interfere with the ship’s navigational equipment (especially GNSS) and other electronic equipment.

 5.7 Installation of coaxial cables

Coaxial cables should be installed in separate ducting and at least 10 cm away from power supply cables.

Incorrect installation of cables my change their characteristic impedance resulting in power reflections, which will attenuate the RF signal and reduce the efficiency of the radio equipment.

In VHF antennas the reflected power should not be greater than 10% of the measured output power.

The following guidelines should be applied when bending coaxial cables:

  • .1 Cables should be crossed at right angles.

  • .2 Where there is one bend in a permanent fixture the bending radius should be 5 times the cables' outside diameter.

  • .3 Where there are several bends, the bending radius should be 10 times the outside diameter of the cable.

  • .4 When using flexible cable the bending radius should be 20 times the outside diameter of the cable.

Parent topic: Annex - Guidelines for the Harmonization of GMDSS Requirements for Radio Installations on Board SOLAS Ships
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