🔍 Key Concepts

• ITU channel numbering system for duplex channels • Relationship between the two-digit band identifier and the two-digit channel number (e.g., 16 / 04) • Typical frequency bands (MF vs HF) used for maritime duplex channels

💭 Think About

• What does the first part of the number (the first two digits) usually indicate in an ITU duplex channel like 1604? • What does the second part of the number (the last two digits) usually indicate about the channel itself? • Based on common GMDSS channel groupings, which frequency band is associated with the number 16 in the context of HF bands?

✅ Before You Answer

• Identify whether 16 is referring to a band (MHz range) or a VHF channel number in this notation. • Confirm which bands are considered MF (around 2–3 MHz) versus HF (3–30 MHz) and see which options fit. • Check whether the format "1604" would normally be read as channel 04 in the 16 MHz band or channel 16 in the 4 MHz band, and eliminate options that reverse this logic.