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services, those intended for the recreational and small vessel market
generally have fewer options. However, all contain the ability to use DSC for
distress alerting, distress and routine call acknowledgment, and all stations
and single station alerting. The ability to transmit position information, either
from a GPS receiver interface or from manual entry, may also be provided.
70.3 Search and rescue authorities strongly recommend connection of a ship
station DSC transceiver to a GPS receiver to ensure that accurate and current
position information is automatically transmitted in the case of a Distress Alert.
70.4 Some MF/HF transceivers may offer the option of sequentially scanning all
MF/HF DSC frequencies for alerts.
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70.5 Whilst DSC operational procedures are not difficult, and in most cases simply
parallel standard radiotelephony procedures, operators of DSC-capable
equipment must ensure that they are entirely familiar with the manufacturer's
instructions concerning controls and programming, particularly those
concerning transmission and reception of priority calls.
70.6 Radiotelephony only MF/HF and VHF transceivers are not capable of
encoding or decoding DSC Alerts.
70.7 DSC should not be confused with the proprietary selective calling systems
(selcall) presently available on some MF/HF marine transceivers. These
systems are not compatible with international DSC signalling standards.
71. DSC Identification
71.1 To use DSC techniques, a MF/HF or VHF transceiver must be permanently
programmed with a unique nine digit identification number known as a
Maritime Mobile Service Identity (MMSI). This can be regarded as the
electronic equivalent of a radiotelephony call sign and uniquely identifies that
maritime communication, limited coast, or ship station.
71.2 The MMSI is automatically included in all DSC transmissions from a station
and electronically identifies that station to the receiving station(s). The MMSI
also acts as an "electronic filter" whilst the transceiver is operating in the
watchkeeping mode to ensure that only routine DSC Alerts intended for that
station are actually decoded and displayed. The filter is deactivated when any
DSC Alert carrying a distress priority indicator is received as these messages
are implicitly addressed to all stations. Similarly, DSC urgency and safety
Alerts which are not specifically addressed to a particular station will be
received by all stations within radio range and keeping a DSC watch.
71.3 Three of the nine digits of a MMSI identify country of origin. In the case of a
maritime communication station or limited coast station these digits indicate
the country of location, and in the case of a ship station, the country of
registration. The remaining six digits uniquely identify the station itself. The
three digits identifying country are known as Maritime Identification Digits or
MIDs. Australia's MID is 503 with these figures forming the first three digits for
ship stations, and third to fifth digits for maritime communication station or
limited coast stations.
71.4 An Australian ship station MMSI will be formed 503xxxxxx where x is any
figure from 0 to 9.
71.5 An Australian limited coast station MMSI will be formed 00503xxxx where the
first two figures are zeros and x is any figure from 0 to 9. The MMSI for both
Australian maritime communication stations is 005030001.
71.6 At present, any person purchasing a VHF or MF/HF transceiver with DSC
capability and wishing to use the option must obtain a MMSI which is issued
by AMSA. This must then be programmed into the transceiver. See the AMSA
website for more information (http://www.amsa.gov.au/AUSSAR/mmsi.htm#form).
71.7 A full international list of MIDs appears in Appendix 43 of the Radio
Regulations published by the International Telecommunication Union.
72. Information Contained in a DSC Alert
72.1 A DSC Alert contains the following information as digitised data:
" the identity of the calling station (MMSI);
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" the priority of the alert - distress, urgency, safety or routine; and
" the station being called (a specific station or all stations)
72.2 The alert may also contain data indicating the frequency or channel on which
subsequent communications are to be conducted. Normally, but not
necessarily, this is the associated radiotelephony frequency/channel (see
paragraph 73.1). However, if frequency/channel information is not contained in
the alert, it is always the associated radiotelephony frequency or channel.
72.3 In the case of DSC distress alerts, the position of a vessel, either directly from
an electronic interface with a GPS receiver, or by manual entry may also be
included.
72.4 The use of priority DSC alerts (distress, urgency and safety) is subject to
exactly the same requirements as outlined in chapter 4 of this handbook.
73. Frequencies for DSC Distress, Urgency and Safety Alerts
73.1 Frequencies have been internationally allocated in the MF/HF and VHF
marine bands for DSC distress, urgency and safety alerts. In each case there
is a radiotelephony frequency directly associated with the DSC frequency for
communications subsequent to the DSC alert. Only the HF DSC frequencies,
indicated with an asterisk (*), are monitored by Australian maritime
communication stations. The other DSC frequencies may not be monitored in
your area. The DSC and associated radiotelephony frequencies are:
DSC freq Associated radiotelephony freq
2187.5 kHz 2182 kHz
4207.5 kHz* 4125 kHz
6312 kHz* 6215 kHz
8414.5 kHz* 8291kHz
12577 kHz* 12290 kHz
16804.5 kHz* 16420 kHz
VHF Ch 70 VHF Ch 16
( VHF channel only)
73.2 The MF/HF DSC frequencies indicated above are reserved exclusively for
DSC alerts associated with distress, urgency and safety messages.
73.3 Marine VHF channel 70 may additionally be used for routine station-to-station
DSC alerts.
73.4 DSC is not used in the 27 MHz marine band, and Australian maritime
communication stations no longer monitor the MF and VHF bands.
73.5 Unless the frequency/channel is specifically indicated in the DSC alert then
radiotelephony communications should follow on the associated
radiotelephony distress and calling frequency. For example, on 2182 kHz after
a DSC alert on 2187.5 kHz, or on VHF channel 16 after a DSC alert on VHF
channel 70. [ Pobierz całość w formacie PDF ]

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