U.S. Coast Guard updates to four-digit VHF channel numbers

The United States Coast Guard has issued a new bulletin (MSIB Number 07-24, dated November 7, 2024) announcing an important update to the VHF marine radio system. The change involves a shift from the older two-digit channel numbers, which ended with the letter "A," to a new four-digit numbering scheme. This change is designed to better align U.S. maritime radio use with international standards set by the International Telecommunications Union (ITU).

Key Points of the Update:

New Four-Digit Channel Numbers:

1. VHF marine radios will now display four-digit channel numbers, replacing the previous two-digit numbers that ended in "A." For example, U.S. channel 22A will now be shown as 1022.
2. The new numbering system involves adding the prefix "10" to the previous two-digit number. This means that what was once channel 22A (for simplex communication) will now be designated as channel 1022.

International Harmonization:

1. The change comes in response to updates to the ITU Radio Regulations made in 2015, which revised the frequency table for the VHF maritime mobile band. These updates allow for the use of simplex (one-way) communication on duplex channels, which had been used for decades by the U.S. but needed alignment with international practices.
2. Duplex channels require two frequencies: one for ship