Satellite communications
Satellite communications are particularly important elements of the GMDSS.
1The Inmarsat system, which employs geostationary satellites and operates in the 1.5 and 1.6 GHz band (Lband),
provides ships fitted with ship earth stations with a means of distress alerting and a capability for two-way
communications using direct-printing telegraphy, data transmission and radiotelephone. L-Band satellite EPIRBs
are also used for distress alerting. The International SafetyNET system is used as a main means to provide MSI to
areas not covered by the International NAVTEX system.
2 A polar-orbiting satellite system, operating in the 406 MHz band using satellite EPIRBs (COSPAS–
SARSAT system), provides one of the main means of distress alerting and determining the identity and position
of the ship in distress or its survivors in the GMDSS.
Terrestrial communications
3 With terrestrial communications, DSC forms the basis of distress alerting and safety communications.
Distress and safety communications following a DSC call can be performed by radiotelephony or direct-printing
telegraphy or both.
Long-range service
4 Use of HF provides a long-range service in both the ship-to-shore and shore-to-ship directions. In areas
covered by Inmarsat it can be used as an alternative to satellite communications and outside these areas it provides
the only long-range communication capability. Frequencies have been designated in the 4, 6, 8, 12 and 16 MHz
bands for this service.
Medium-range service
5 MF radiocommunications provide the medium-range service. In the ship-to-shore, ship-to-ship and
shore-to-ship directions 2187.5 kHz is used for distress alerts and safety calls using DSC, and 2182 kHz is used for distress and safety traffic by radiotelephony, including SAR co-ordinating and on-scene communications. 2174.5 kHz is used for distress and safety traffic by direct-printing telegraphy.
Short-range service
6 VHF provides short-range service on the frequencies:
. 156.525 MHz (channel 70) for distress alerts and safety calls using DSC, and
. 156.8 MHz (channel 16) for distress and safety traffic by radiotelephony, including SAR co-ordinating
and on-scene communications.
There is no short-range direct-printing telegraphy service on VHF.
Satellite communications are particularly important elements of the GMDSS.
1The Inmarsat system, which employs geostationary satellites and operates in the 1.5 and 1.6 GHz band (Lband),
provides ships fitted with ship earth stations with a means of distress alerting and a capability for two-way
communications using direct-printing telegraphy, data transmission and radiotelephone. L-Band satellite EPIRBs
are also used for distress alerting. The International SafetyNET system is used as a main means to provide MSI to
areas not covered by the International NAVTEX system.
2 A polar-orbiting satellite system, operating in the 406 MHz band using satellite EPIRBs (COSPAS–
SARSAT system), provides one of the main means of distress alerting and determining the identity and position
of the ship in distress or its survivors in the GMDSS.
Terrestrial communications
3 With terrestrial communications, DSC forms the basis of distress alerting and safety communications.
Distress and safety communications following a DSC call can be performed by radiotelephony or direct-printing
telegraphy or both.
Long-range service
4 Use of HF provides a long-range service in both the ship-to-shore and shore-to-ship directions. In areas
covered by Inmarsat it can be used as an alternative to satellite communications and outside these areas it provides
the only long-range communication capability. Frequencies have been designated in the 4, 6, 8, 12 and 16 MHz
bands for this service.
Medium-range service
5 MF radiocommunications provide the medium-range service. In the ship-to-shore, ship-to-ship and
shore-to-ship directions 2187.5 kHz is used for distress alerts and safety calls using DSC, and 2182 kHz is used for distress and safety traffic by radiotelephony, including SAR co-ordinating and on-scene communications. 2174.5 kHz is used for distress and safety traffic by direct-printing telegraphy.
Short-range service
6 VHF provides short-range service on the frequencies:
. 156.525 MHz (channel 70) for distress alerts and safety calls using DSC, and
. 156.8 MHz (channel 16) for distress and safety traffic by radiotelephony, including SAR co-ordinating
and on-scene communications.
There is no short-range direct-printing telegraphy service on VHF.
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