Question 11B3

The Global Maritime Distress and Safety System (GMDSS) relies on precise frequency control for reliable communication, particularly for digital modes like Digital Selective Calling (DSC). DSC uses specific audio tones and timing, making it highly sensitive to frequency deviations. An allowable frequency tolerance of 10 Hz for GMDSS MF-HF transmitters is mandated by international telecommunication regulations (ITU-R recommendations and Radio Regulations). This stringent requirement ensures that digital signals can be accurately decoded and that voice communications are clear and intelligible across different stations and nationalities. Larger frequency errors (e.g., 15 Hz, 20 Hz, or 30 Hz) would significantly degrade or even prevent the successful reception and decoding of critical distress and safety messages, compromising the integrity of the GMDSS.