DSC controller

A DSC controller is the digital selective calling unit, built into a radio or fitted as a standalone module, that sends and receives the coded calls of the GMDSS. It forms a digital message carrying the calling and called station MMSIs, the call category such as distress, urgency, or routine, and a position and time, then transmits it as a burst on a dedicated DSC frequency: VHF channel 70, MF 2187.5 kHz, or the HF distress frequencies. A distress alert is sent by lifting a guarded button. The receiving controller decodes the call, alarms, and displays the data, so voice then moves to a working channel. SOLAS GMDSS ships keep a continuous DSC watch.