Testing the equipment used for distress and safety

Testing on the exclusive DSC distress and safety calling frequency 2 187.5 kHz should be avoided as far as possible by using other methods.

No test transmission should be made on VHF DSC calling channel 70.

Test calls should be transmitted by the ship station and acknowledged by the called coast station. Normally there would be no further communication between the two stations involved.

A test call to a coast station is transmitted as follows:

1. tune the transmitter to the DSC distress and safety calling frequency 2187.5 kHz,

2. key in or select the format for the test call on the DSC equipment in accordance with the DSC equipment manufacturer's instructions,

3. key in the 9-digit identity of the coast station to be called,

4. transmit the DSC call after checking as far as possible that no calls are in progress on the frequency,

5. wait for acknowledgment.

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Special conditions and procedures for dsc communication on hf General

The procedures for DSC communication on HF are - with some additions described below - equal to the corresponding procedures for DSC communications on MF/HF.

Distress

Transmission of DSC distress alert

DSC distress alert should be sent to coast stations - e.g. in A3 and A4 sea areas on HF - and on MF and/or VHF to other ships in the vicinity.

The DSC distress alert should as far as possible include the ship's last known position and the time (in UTC) it was valid. If the position and time is not inserted automatically from the ship's navigational equipment, it should be inserted manually.

Ship-to-shore distress alert

Choice of HF band

Propagation characteristics of HF radio waves for the actual season and time of the day should be taken into account when choosing HF bands for transmission of DSC distress alert.

As a general rule the DSC distress channel in the 8 MHZ maritime band (8414.5 kHz) may in many cases be an appropriate first choice.

Transmission of the DSC distress alert in more than one HF band will normally increase the probability of successful reception of the alert by coast stations.

DSC distress alert may be sent on a number of HF bands in two different ways:

a) either by transmitting the DSC distress alert on one HF band, and waiting a few minutes for receiving acknowledgment by a coast station;

if no acknowledgment is received within 3 min, the process is repeated by transmitting the DSC distress alert on another appropriate HF band etc.;

b) or by transmitting the DSC distress alert at a number of HF bands with no, or only very short, pauses between the calls, without waiting for acknowledgment between the calls.

It is recommended to follow procedure a) in all cases, where time permits to do so; this will make it easier to choose the appropriate HF band for commencement of the subsequent communication with the coast station on the corresponding distress traffic channel.

Transmitting the DSC alert;

6. tune the transmitter to the chosen HF DSC distress channel (4207.5, 6312, 8414.5, 12577, 16804.5 kHz);

7. follow the instructions for keying in or selection of relevant information on the DSC equipment keyboard as described earlier;

8. transmit the DSC distress alert.

NOTE - Ship-to-ship distress alert should normally be made on MF and/or VHF, using the procedures for transmission of DSC distress alert on MF/HF described earlier.

- Some maritime HF transmitters shall be tuned to a frequency 1700 Hz lower than the DSC frequencies given above in order to transmit the DSC alert on the correct frequency.

In special cases, for example in tropical zones, transmission of DSC distress alert on HF may, in addition to ship-to-shore alerting, also be useful for ship-to-ship alerting.

Preparation for the subsequent distress traffic

After having transmitted the DSC distress alert on appropriate DSC distress channels (HF, MF and/or VHF), prepare for the subsequent distress traffic by tuning the radiocommunication set(s) (HF, MF and/or VHF as appropriate) to the corresponding distress traffic channel(s).

If method b) described above has been used for transmission of DSC distress alert on a number of HF bands:

• take into account in which HF band(s) acknowledgment has been successfully received from a coast station;

• if acknowledgments have been received on more than one HF band, commence the transmission of distress traffic on one of these bands, but if no response is received from a coast station then the other bands should be used in turn.

The distress traffic frequencies are:

HF (kHz):

Telephony 4125 6215 8291 12290 16420

Telex 4177.5 6268 8376.5 12520 16695

MF (kHz):

Telephony 2182

Telex 2174.5

VHF: Channel 16 (156.800 MHZ).

Distress traffic

The procedures described earlier are used when the distress traffic on MF/HF is carried out by radiotelephony.

The following procedures shall be used in cases where" the distress traffic on MF/HF is carried out by radiotelex:

1. The forward error correcting (FEC) mode shall be used unless specifically requested to do otherwise;

2. all messages shall be preceded by:

   • at least one carriage return,

   • line feed,

   • one letter shift,

   • the distress signal "MAYDAY";

3. The ship in distress should commence the distress telex traffic on the appropriate distress telex traffic channel as follows:

   • carriage return, line feed, letter shift, the distress signal "MAYDAY",

   • "this is",

   • the 9-digit identity and call sign or other identification of the ship,

   • the ship's position if not included in the DSC distress alert,

   • the nature of distress,

   • any other information which might facilitate the rescue.

Actions on reception of a DSC distress alert on HF from another ship

Ships receiving a DSC distress alert on HF from another ship shall not acknowledge the alert, but should:

4. watch for reception of a DSC distress acknowledgment from a coast station;

5. while waiting for reception of a DSC distress acknowledgment from a coast station:

prepare for reception of the subsequent distress communication by tuning the HF radiocommunication set (transmitter and receiver) to the relevant distress traffic channel in the same HF band in which the DSC distress alert was received, observing the following conditions:

• if radiotelephony mode was indicated in the DSC alert, the HF radiocommunication set should be tuned to the radiotelephony distress traffic channel in the HF band concerned;

• if telex mode was indicated in the DSC alert, the HF radiocommunication set should be tuned to the radiotelex distress traffic channel in the HF band concerned. Ships able to do so should additionally watch the corresponding radiotelephony distress channel;

• if the DSC distress alert was received on more than one HF band, the radiocommunication set should be tuned to the relevant distress traffic channel in the HF band considered to be the best one in the actual case. If the DSC distress alert was received successfully on the 8 MHZ band, this band may in many cases be an appropriate first choice;

if no distress traffic is received on the HF channel within 1 to 2 min, tune the HF radiocommunication set to the relevant distress traffic channel in another HF band deemed appropriate in the actual case;