telephone/telex connection and sounds an alarm when a Distress
Priority call/message is received from an MRCC. A less sophisticated
distress button system is available on some Inmarsat-A installations
but may not have the incoming distress call alarm.
6 Facsimile (Fax) Machine: for sending/receiving fax messages.
7 Telephone Exchange: telephone handsets, fax machines and
computers (from cabins, etc.) can be given access to the Inmarsat-A/
B unit through a telephone exchange, rather than connected directly
to the M CV /junction box.8 and9
Computer/Printer for Telex/Data Service: Inmarsat-A and
Inmarsat-B installations that are part of a ship's GMDSS equipment
fit must have telex facilities and a printer (item 9 in the diagram). In
more modern installations, the telex software is run on a computer -
which should not be used for any purpose other than for the telex
service and for the operation of the Inmarsat-A/B installation (e.g.
antenna alignment for satellite acquisition).
If data communications are required from an Inmarsat-AlInmarsat-
B GMDSS installation a separate computer, attached to a special data
port, will be required. Where the Inmarsat-A/Inmarsat-B terminal is
part of the ship'S G MDSS fit for distress and safety purposes and not
installed as additional to the main GMDSS fitting, the computer
attached directly to the Inmarsat-A/Inmarsat-B unit specifically for
TELEX communications must be able to take control of the system
in an emergency - from any other computer (e.g. those installed as
part of a Local Area Network (LAN - item 13 on Fig 8.5) onboard the
vessel) in an emergency.
10 Incoming Message Indicator: audible/visible alarm when telex,
fax and/or data messages received.
11 Gyro Input: once a satellite has been acquired the gyro input allows
the antenna to compensate for your vessel's pitch and roll. Some
installations may use a different method of antenna stabilisation. If
your antenna has no gyro input but appears to be tracking the satellite- despite the vessel pitching, rolling and changing course - you
probably have another method of stabilisation built into the antenna.
12 AC/DC Power Supply: most units will normally function from an
AC (11O/230V) power supply, converted to DC to drive the MCU,
antenna control and RF units. A DC supply (typically 11-34V on a
modern Inmarsat-B GMDSS unit) should be available as a backup.166 THE NAUTICAL INSTITUTE