Digital Selective Calling

The DSC system employs digital technology and is an important part of the GMDSS system, being used as the primary alerting system on VHF.

The DSC control unit is able to monitor/keep watch on all DSC frequencies allocated for distress and safety purposes. When a coast ststion or a ship receives a DSC distress alert, a display or printout of the message will be produced including notification that distress communication will follow on the radiotelephony frequency allocated for distress and safety purposes. In addition to the printout of the message, an audible/visual alarm will be activated to attract the attention of the operator.

The Case for DSC
There is no question that GMDSS has a big part to play in improving safety at sea.

Firstly a vessel’s position and the time are automatically included in distress and urgency alerts if a DSC radio set is interfaced with a GPS navigator (if it isn’t, the position can be manually input). Secondly, a digital alert is more certain of reaching a maritime rescue centre than voice transmission, having a 15 per cent greater range and not being prone to misunderstanding. Thirdly the increasing use of the digital broadcasting channel, Ch70, should free up Ch16 for use during an emergency which will still be available for making contact.