The radiated power, and the transmitter radio (carrier) frequency.
The distance a person is from the antenna at the time of transmission
(the closer you are, the greater the hazard).
The length of time that a person remains within the hazardous area.
An indication of the potential radiation hazardl safe distance for
your own unit will be included in your equipment manual but, as a guide,
the radiation safe distance for a typical Inmarsat-C antenna is considered
to be about two feet (0·6 metre). As radiation is omnidirectional the hazard
is equal in all directions around the antenna.
Hazard warning labels should be displayed:
At the normal operating position.- On the antenna.
- At locations around the antenna (to warn against entering the
hazardous area).
Inmarsat-A and Inmarsat-B Installations
Inmarsat-A and Inmarsat-B offer the full range of Inmarsat services,
(with the exception, in most cases, of SafetyNET) , normally required for
GMDSS purposes. Both types of equipment are often fitted in addition
to the ship's minimum GMDSS requirement to provide additional,
automatic, telephonelfax/telex/e-mail and/or data communications
facilities.
Inmarsat-A was the original analogue service at the start ofInmarsat
commercial operations in 1982. Inmarsat-B a digital service -
commenced operation in 1993 and is intended to supersede Inmarsat-A
at some stage. Being digital, Inmarsat-B uses less satellite power and
bandwidth than 'N and, because of this, usually attracts lower call charges
from the LES. The range of services provided by A and B is identical,
however, and the equipment and antenna is similar in size and
appearance.
The main components of an Inmarsat-A/lnmarsat-B installation
are (see figure 8.5):
1 The antenna: A dish antenna about 0·9 - 1·2 metre diameter, with
its steering mechanism, enclosed in a protective radome (which also
houses the transceiver radio frequency (RF) unit - some weighing
approximately 200lb (90kg). The operator should point the antenna
at a satellite that, once acquired, will be tracked automatically by the
unit (as long as the satellite remains in sight).
164 THE NAUTICAL INSTITUTE