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

Eda Zenic -

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 station transmissions and another for coast station transmissions. Radios tuned to a duplex channel cannot communicate with radios using simplex communication on that same channel.

Historical Context:

  1. In 1965, the Federal Communications Commission (FCC) added the suffix “A” to U.S. channels to distinguish simplex use over the ship station portion of international duplex channels, preventing confusion between the two. The new prefix "10" now serves the same function of marking channels for simplex communication.

Impact on Coast Guard Communications:

  1. The U.S. Coast Guard uses VHF channel 1022 (formerly 22A) to transmit urgent marine information broadcasts (UMIBs) and to communicate with mariners. A shipboard radio set to channel 1022 in the U.S. mode will transmit and receive on the 157.1 MHz frequency and can receive these important safety warnings.
  2. In contrast, radios set to the international version of channel 22 will transmit on 157.1 MHz but will listen on 161.7 MHz, meaning they cannot receive the Coast Guard’s UMIB safety broadcasts. This distinction is crucial for maritime safety, especially since these broadcasts contain urgent navigational and safety information.

Regulatory Compliance:

  1. According to 33 CFR 26.03(d), which mandates that ships must have a radiotelephone capable of transmitting and receiving on VHF channel 22A (157.1 MHz), this regulation now applies to both U.S. and foreign ships in U.S. waters. The change to the four-digit numbering system ensures that vessels can still comply with this requirement while using the updated channel scheme.

Resources and Further Information:

  1. The Coast Guard has provided additional information and resources about the updated VHF channel system on their website, which can be accessed at https://www.navcen.uscg.gov/us-vhf-channel-information.
  2. For any questions or clarifications, mariners are encouraged to contact the Coast Guard Spectrum Management and Communications Policy Division or the Coast Guard Navigation Center via their "Contact Us" page.