Engineering guidance for operators to upgrade shore based facilities to operate the Global Maritime Distress and Safety System in the A1@ A2 and A3/A4 sea areas
Overview In order to establish a new A2@ A3@ or A4 sea area it is necessary to gain some knowledge of how the propagation conditions vary. A2 coverage is by groundwave@ which is stable@ enabling the extent of the service area to be confirmed by measurement before committing capital expenditure@ which is recommended by the IMO. A3 and A4 coverage is by skywave which depends upon the condition of the ionosphere which varies with solar activity. Since this follows an 11-year cycle@ the extent of the service area cannot be confirmed by performing a new measurement study@ and administrations wishing to join the HF shore station network may require methods to verify feasibility and size the equipment required in order to confidently establish a project budget. The extent of the sea areas A2@ A3@ and A4 are specified by the IMO in Annex 3 to their resolution A.801(19)@ and ??.4.1 of this Report provides charts for rapid assessment of the extent of the A2 sea area using this data@ and also guidelines to enable administrations to make their own assessment of potential A3 and A4 coverage using HF prediction software in the context that each shore station is a member of a community of HF stations working together to provide the required grade of service. ?? Section 2 defines the functional requirements@ and describes the equipment required. ?? Section 3 defines single sideband (SSB) carrier oise ratio and useable signal level@ outlines the grades of service@ presents performance criteria@ reviews the software tools available and provides guidance on determination of receive ranges and transmitter power requirements. ?? Section 4 covers site engineering issues: including selection of good receive sites@ isolation between sites@ protection of watch frequencies@ station earthing and lightning protection.