Digital Selective Calling

An automated VHF and MF/HF radio communication system used in maritime environments to send distress alerts, establish contact, and exchange routine messages between vessels and shore stations.

Digital Selective Calling (DSC) is a critical component of the Global Maritime Distress and Safety System (GMDSS), designed to enhance safety and efficiency in maritime communications. It operates on VHF and MF/HF radio frequencies and allows mariners to send pre-formatted digital signals to specific vessels, groups of vessels, or shore stations without requiring continuous voice communication. DSC is particularly valuable in emergencies, as it enables a vessel to send a distress alert containing its identity, position, and nature of distress with the press of a button, significantly reducing response times.

Each DSC-enabled radio is assigned a unique Maritime Mobile Service Identity (MMSI) number, which functions like a telephone number for the vessel. This allows for selective calling, where a signal is directed to a specific MMSI or group, rather than broadcasting to all stations. DSC also supports routine and urgency communications, such as requesting a specific working channel or sending safety warnings. 

The system operates using digital tones, which are less prone to interference than traditional voice transmissions. When a DSC alert is received, the radio emits an audible alarm to ensure the message is noticed. This is particularly useful in distress situations, as it ensures nearby vessels and authorities are promptly alerted. DSC has become a standard feature in modern marine radios, offering a reliable and efficient means of communication for both safety and operational purposes.