Marine Glossary

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SITOR

Acronym for Simplex Teletype Over Radio. A means of communication over HF radio whereby text messages can be sent to and from vessels using the ship's SSB radio. SITOR messages from a vessel are first prepared in a personal computer and then transmitted via modem to the small SITOR unit on board which is in turn connected to the HF radio (SSB).

There are dedicated SITOR frequencies for these transmissions which generally provide more dependable communications than possible with voice transmissions. SITOR charges are 2.85 dollars per minute (1994) with data transmitted at 100 baud. On shore, the communications are received and sent by private marine radio stations, such as WLO (Mobile Marine) on the Gulf Coast. Messages received on land can be forwarded to land addresses via fax, mail, or telephone.

To send a vessel a SITOR message, it must be sent first to the land station by any means, however, direct transfer of the text to the land station by computer modem is the most cost effective. For a vessel to receive a message, it must have its radio tuned to a proper SITOR frequency and have SITOR receiver and computer connected. Otherwise, vessels will only know of pending messages by their appearance in a "traffic list" which is broadcast periodically or upon request. In addition to the regular call sign, a vessel also must apply for a sellcall number from the Federal Communications Commission if they are to use SITOR communications.

For more information on SITOR and other forms of marine communications, see the Source Book.