DIGITAL SELECTIVE CALLING ( DSC )

The DSC ststem employs digital technology and is an important part of the GMDSS System, being used as the primary means of VHF / MF / HF alerting.
DSC is used for calls in the ship to ship , ship to shore and shore to ship directions for distress and routine purposes .
Note ; it is a calling system and not a working system.

In a distress situation, the DSC distress call contains at least the distress vessels MMSI no and position with its time of update.

DSC is used for distress and safety as well as routine communications.

A typical DSC calling sequence consists of ;

• Format specifier - specifies the type of call , ie Distress / all ships / selective
• Address - is used to specify which station is to receive the call , ie all ships / selective / individual
• Category - call priority , ie Distress / Urgency / Safety / Routine
• Self Identification - own ships MMSI 
• Telecommand Information
• Frequency Information- frequency / channel 
• End of sequence- to indicate whether this call requires Ack or is Reply to a call

VHF DSC 

Once the ITU Channel number is entered in the transceiver , it automatically sets the frequency of the Transmitter and Receiver Frequencies can also separately by using the Tx and Rx controls.

Mode is a Transmitter and Receiver Control ;-

J3E also termed SSB , USB
H3E also termed AM
F1B / J2B also termed TLX

• Squelch is a receiver control , used to eliminate noise.
• Tune is a Transmitter Control
• Power is a Transmitter Control
• Dummy Load is a Transmitter Function
• Frequency Selection in a Transmitter & Receiver Control 

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