The proper sequence of channel spacing from narrow to widest is?

The correct answer demonstrates an understanding of the channel spacing requirements for different modes of communication used in maritime operations.

SITOR (Selective Information and Telex Over Radio), which is primarily a narrowband digital communication system, operates on a smaller bandwidth compared to SSB (Single Sideband) voice communications. SSB voice uses a wider bandwidth to facilitate clear voice transmissions over long distances. On the widest end of the spectrum, VHF-FM voice operates with an even broader bandwidth, the widest of the three options presented.

This sequence from narrow to wider channel spacing (SITOR (NBDP), SSB voice, and then VHF-FM voice) reflects the technical requirements and operational practices associated with each communication mode, highlighting the variation in bandwidth utilization essential for effective maritime communication. Understanding these distinctions is crucial in GMDSS operations to ensure efficient and appropriate communication methods are employed based on the situation at hand.