Inmarsat-A/lnmarsat-B Telephone/Telex Procedures
Telephone and telex operating procedures for routine
communications are covered in Chapter 4 while procedures for Distress,
Urgency and Safety communications are covered in Chapter 5. The main
difference between Inmarsat-A and Inmarsat-B telephone procedures is
that Inmarsat-A telephone is a two-stage process. You have to ask for a
line from the Land Earth Station and then provide the number you wish
to call, whereas all Inmarsat-B installations have a preferred LES
programmed into the equipment, and you can make the call using a
single stage process (see also Inmarsat-A/lnmarsat-B Equipment set up
later in this chapter).
Satellite acquisition
Before you use Inmarsat-Allnmarsat-B equipment there is usually
some setting up to do and you have to acquire (point your antenna at) a
satellite. The procedure for aligning your antenna to the satellite will be
covered in your equipment manual and is also explained generically in
ALRS Vol. 5 satellite alignment section. The things you have to do with
most equipment are:
- Plot your ship's position on a map showing the four Inmarsat satellites
(e.g. figure 8.1 or the one in ALRS Vol. 5).
Decide which satellite you want to use, normally, but not necessarily,
the one nearest to your longitude. - Plot your position on the satellite alignment diagram for your chosen
satellite, in ALRS Vol. 5 and calculate the azimuth and elevation
required to hit the satellite (figure 8.6). - Adjust the azimuth reading to account for your ship's head (the tables
in ALRS Vol. 5 assume a ship'S heading ofOOOO), or enter ship's head
in your Inmarsat-A/lnmarsat-B system if your system makes the
calculation automatically. - Enter the azimuth and elevation figures according to the instructions
in your equipment manual. - Sit back and watch as your antenna acquires the satellite.
Once acquired, the antenna will track the satellite automatically,
as long as the satellite remains in Sight of the antenna. You only need to
reacquire the same satellite, or change satellite, if: - Your equipment has suffered cable-wrap - where the cable inside the
antenna has been wrapped-around the pedestal and there is no cable
left, so the antenna has been dragged away from the satellite (more
likely on older Inmarsat-A units).
MARINE COMMUNICATIONS 167