HF Maritime Communications

From The RadioReference Wiki

HF Maritime communications have undergone a radical change over the last several years. Many stations that used to have voice communications have either gone dark or using digital modes, some of which are not readable except to the intended target. Let's take a look at what is out there.


  • US commercial stations have ceased most voice communications. There are some countries that have stations that are still on the air. Ships and stations are allocated in fixed frequency ranges, and you can find those ranges listed here.
  • The Canadians have the Radio Aids to Navigation
  • USCG Voice Marine weather broadcasts can be found here. Click the USCG HF Voice link

Digital (below the AM broadcast band)

  • Navigational aids such as DGPS are slowly dying out. The US discontinued its DGPS support as of the 30th of June 2020.
  • SITOR-B / NAVTEX broadcasts are quite plentiful, and there is a wide range of software that can decode them. The main issue with receiving these broadcasts lie with the typical receiver; sensitivity is generally reduced in this band because of a perceived lack of interest (due to the lack of broadcasts in North America on this band) as well as reducing the possibility of mixing products from the MW band appearing here (which it does anyway). SDRs may need some front end preselection to prevent overload in areas where there are many MW stations (such as those found in urban areas). Active Loops are commonly used as antennas to hear these broadcasts.

Drift Net Buoys and Navigational Aids

  • Like DGPS, the navigational aids found in the 1700-1800 Khz range are also slowly dying out and being replaced with satellite tracking.

Digital (2-30 Mhz)

  • CODAR is used to make ocean measurements such as wave height and current. They have a distinctive swishing sound when listened to in USB mode. It has been found being used as high as the 20 meter amateur band.
  • CW (Morse Code) is frequently found in the lower HF ranges being used by Russian military units, among others. See this PDF document from the UDXF website for a description of different CW alphabets
  • GMDSS / DSC is a digital system on several fixed frequencies. There are numerous packages for decoding
  • Baudot RTTY is all but dead in the maritime service. The only station known to use it regularly is the German Weather service (Deutsche Wetterdienst). See the links in the article for the schedule.
  • There are 4 main types of PACTOR. These are PACTOR I, PACTOR II, PACTOR III and PACTOR IV. It is typically used for communicating with ships at sea; you may see the initial calls in Pactor I or II, but then once the connection is made, the messages may be heavily encrypted and compressed, making the signal unreadable. One such system is the Sailmail system, and this document outlines, among other things, the station locations and frequencies. Although it is a bit old, it gives the reader a rare look into what is needed to run a marine PACTOR station and its operations
  • SITOR-A used to be used by numerous stations but this mode is gradually dying out. Using the UDXF logs and examination over the last year only show Guangzhou, Shanghai, Istanbul Radio (Turkey) and Olympia Radio (SVO) Greece as being active. Note that this mode is not exclusively used in the maritime service; the Egyptian Diplomatic service also uses this, utilizing the ATU-80 alphabet, making this difficult to read with most applications. There are numerous applications that can copy this mode when used in the maritime service. See this PDF article from the UDXF website on reading the MFA Egypt transmissions.
  • SITOR-B / NAVTEX is, like GMDSS, found on a few fixed HF frequencies . There are numerous applications that can copy this mode, but like SITOR-A, you will occasionally find other services using it.
  • STANAG 4285 This mode is used by NATO forces. As a result, it is generally heavily encrypted; however it can be seen in the clear if the station is sending a test tape or sending a CARB broadcast in the clear
  • Weather FAX (WEFAX) was thought to be going dead years ago, but continues to be heavily used. There are even reports of the Japanese news agency (KYODO) sending newspapers (in Japanese) to fishing fleets. It should be noted that FAX use by other press services died out years ago. There are numerous applications that can copy this mode


  • NOTE: The links for the various modes comes from the Signal Identification Wiki
  • When a hurricane (cyclone in the Pacific) is spotted, the Tropical Cyclone Plan of the Day will give you an idea of when the flights to track these storms will take place
  • UDXF Links page See the Beacons, Long Wave and Maritime / NAVTEX sections
  • UDXF Files page See the Aero / Maritime section

William Hepburn's DX Information Center

How to Find Activity?

The spectrum for HF maritime communications is very wide. Unlike VHF/UHF scanning, it's challenging to automatically scan a segment of the band because HF noise will always be present. While some maritime stations are on a fixed schedule, others (such as fishing fleets) are much more difficult to detect due to their transient nature; thus, listening for maritime comms can be a game of patience. The more time passes, the harder it is to hear again. Mailing lists are one of the best ways to keep ahead of what is being heard, as traffic can be passed relatively quickly. See the Utility Related Clubs, Mailing lists and Publications of the Utility_Monitoring article for some suggested resources