Question 1

After activating a DSC distress alert on Ch 70, what must the operator do next?

Accepted Answer

Switch to Ch 16 and transmit a voice Mayday call — the DSC alert summons attention, the voice call gives full details DSC distress alert on Ch 70 automatically summons attention. The operator must then move to Ch 16 and transmit the full voice Mayday message (MIPDANIO). Ch 70 is data only and cannot be used for voice. The Coastguard will acknowledge on Ch 16 and may assign a working channel.

Question 2

What is the primary purpose of DSC (Digital Selective Calling) on a VHF radio?

Accepted Answer

To send a digitally coded distress alert containing the vessel's MMSI and position automatically to all DSC-equipped stations and the Coastguard DSC is a digital signalling system that allows a vessel to send a distress alert with MMSI, position, and nature of distress (if programmed) in one button press. The alert is received by the Coastguard and all DSC-equipped vessels in range. Channel 70 is dedicated to DSC; voice distress uses Ch 16.

Question 3

What is an MMSI number and why must it be programmed into a DSC radio before it is used?

Accepted Answer

Maritime Mobile Service Identity — a unique 9-digit number identifying the vessel; without it a DSC distress alert cannot identify the vessel to rescuers MMSI is a unique 9-digit identifier (UK leisure vessels: 235 prefix) that must be programmed into the DSC controller. When a distress alert is sent, the MMSI is transmitted and the Coastguard can immediately look up the vessel's details, including description, contact numbers, and registered position. An unprogrammed or wrongly programmed MMSI delays rescue.