The proper sequence of channel spacing from narrow to widest is:
Official USCG Answer & Rule Citation
Correct Answer: Option D — NBDP SITOR, SSB-voice, VHF-FM voice.
Narrowband Direct Printing (NBDP/SITOR) requires the least bandwidth, followed by SSB voice, and finally VHF-FM voice, which requires the widest bandwidth due to its frequency modulation characteristics. Channel spacing must increase accordingly to accommodate these varying bandwidths, moving from the narrowest to the widest requirements.
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