The following procedures were adapted from the International Telecommunications Union, Radiocommunications Study Group Recommendation M.541, Operational Procedures for the use of Digital Selective-Calling (DSC) Equipment in the Maritime Mobile Service.
Operating procedures may vary somewhat among different radios, depending upon how the radio is designed, how the radio's software is configured, and how the DSC processor is connected to the radio transceiver.
Transmission of safety messages
Transmission of safety messages shall be carried out in two steps:
- announcement of the safety message,
- transmission of the safety message.
The announcement is carried out by transmission of a DSC safety call on the DSC distress calling channel (2187.5 kHz on MF, channel 70 on VHF).
The safety message is normally transmitted on the distress and safety traffic channel in the same band in which the DSC call was sent, i.e. 2182 kHz on MF, channel 16 on VHF.
The DSC safety call may be addressed to all ships, all ships in a specific geographical area or to a specific station.
The frequency on which the safety message will be transmitted shall be included in the DSC call.
The transmission of a safety message is thus carried out as follows:
- tune the transmitter to the DSC distress calling channel (2187.5 kHz on MF, channel 70 on VHF);
- select the appropriate calling format on the DSC equipment (all. ships, area call or individual call);
- key in or select on the DSC equipment keyboard:
- specific area or 9-digit identity of specific station, if appropriate,
- the category of the call (safety),
- the frequency or channel on which the safety message will be transmitted,
- the type of communication in which the safety message will be given (e.g. radiotelephony),
in accordance with the DSC equipment manufacturer's instructions;
- transmit the DSC safety call.
Transmission of the safety message:
- tune the transmitter to the frequency or channel indicated in the DSC safety call;
- transmit the safety message as follows:
- "SECURITE", repeated 3 times,
- "ALL STATIONS" or called station, repeated 3 times,
- "this is",
- the 9-digit identity and the call sign or other identification of own ship,
- the text of the safety message.
Reception of a safety message
Ships receiving a DSC safety call announcing a safety message addressed to all ships shall NOT acknowledge the receipt of the DSC safety call, but should tune the radiotelephony receiver to the frequency indicated in the call and listen to the safety message.