| 43
AIS menu | RS40/RS40-B User Guide
AIS menu
Warning: Valid GPS data must be entered into this radio
before the AIS functions can be used. The plotter PPI function
will not display targets accurately with incorrect GPS data.
About AIS
The marine Automatic Identification System (AIS) is a location and
vessel information reporting system. It allows vessels equipped with
AIS to automatically and dynamically share and regularly update
their position, speed, course and other information such as vessel
identity with similarly equipped vessels. Position is derived from
the Global Positioning System (GPS) and communication between
vessels is by Very High Frequency (VHF) digital transmissions.
There are a number of types of AIS device as follows:
• Class A
Vessel-mounted AIS transceiver (transmit and receive) which
operates using SOTDMA. Targeted at large commercial vessels,
SOTDMA requires a transceiver to maintain a constantly updated
slot map in its memory such that it has prior knowledge of slots
which are available for it to transmit. SOTDMA transceivers will
then pre-announce their transmission, effectively reserving their
transmit slot. SOTDMA transmissions are therefore prioritised within
the AIS system. This is achieved through 2 receivers in continuous
operation. Class A’s must have an integrated display, transmit at
12.5 W, interface capability with multiple ship systems, and offer a
sophisticated selection of features and functions. Default transmit
rate is every few seconds. AIS Class A type compliant devices receive
all types of AIS
• Class B
Vessel-mounted AIS transceiver (transmit and receive) which
operates using either carrier-sense time-division multiple-access
(CSTDMA) or SOTDMA; there are now 2 separate IMO specifications
for Class B. Aimed at lighter commercial and leisure markets.
CSTDMA transceivers listen to the slot map immediately prior to
transmitting and seek a slot where the ‘noise’ in the slot is the same
or similar to background noise, thereby indicating that the slot
is not being used by another AIS device. Class Bs transmit at 2 W
and are not required to have an integrated display: Class Bs can be
connected to most display systems where the received messages
will be displayed in lists or overlaid on charts. Default transmit rate
is normally every 30 seconds, but this can be varied according to
4
To Next Page
Loading...
Need help?
General
