Technical Circular No: 009/2023

VHF Marine Radios with Digital Selective Calling (DSC) Capability – Automatic Channel Switching.

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1. VHF marine radios with DSC capability have a function that enables automatic channel switching to VHF channel 16, when a DSC distress alert is received. This design function complies with the International Telecommunications Union (ITU) Recommendation ITU-R M.493-15 (2019).

2. This automatic channel switching feature in VHF DSC radios may impact voice communications during safety critical operations.

3. In this regard, it is to be noted that the above stated automatic channel switching function can be disabled by the user to prevent automatic channel switching. When disabled, transceivers will continue to detect DSC distress alerts. The user can then decide whether to accept the channel switch request.

4. Manufacturers implement above feature (disabling of automatic channel switching function) in different ways and usually include instructions in the user manual. If the user manual or documentation is not clear in this regard, advice from the supplier or service agent should be sought.

5. Owners, managers and masters of vessels fitted with VHF marine radios with DSC capability are advised to be aware of the implications of the automatic channel switching feature in VHF DSC radios and ensure that ships’ bridge procedures include instructions on how and when to disable and re-enable automatic channel switching during safety critical operations. 



This Technical Circular and the material contained in it is provided only for the purpose of supplying current information to the reader and not as an advice to be relied upon by any person. While we have taken utmost care to be as factual as possible, readers/ users are advised to verify the exact text and content of the Regulation from the original source/ issuing Authority. 

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