Why must all MF-HF Distress, Urgency and Safety communications take place solely on the 6 assigned frequencies and in the simplex operating mode?

Communications related to distress, urgency, and safety in the medium frequency (MF) and high frequency (HF) bands adhere to specific protocols to ensure that these critical messages are effectively relayed and received by other vessels and rescue authorities. The correct answer highlights the importance of utilizing assigned frequencies in simplex mode for both non-GMDSS and GMDSS-equipped ships.

When distress, urgency, and safety communications occur on the designated frequencies, it significantly enhances the likelihood that other vessels monitoring those frequencies will receive the crucial information. This shared use of specific frequencies creates a common channel where multiple vessels are tuned in, allowing for immediate assistance in emergencies. This is especially important in scenarios where time is of the essence, as lives and resources may depend on rapid response.

The simplex operation mode means that only one station transmits at a time, whereas other stations listen. This ensures clarity by preventing overlapping communications that can occur in full-duplex systems, where multiple transmissions can happen simultaneously. By using simplex mode, the message from the vessel in distress can be clearly heard without interference, which is critical in high-stress situations.

The correct answer effectively captures the necessity of these protocols for maximizing communication effectiveness in emergency scenarios, ensuring that all maritime vessels and response authorities have the