FLDIGI Users Manual 4.0
NAVTEX (Navigational Telex) is an international automated service for delivery of meteorological and marine safety information to ships. These broadcasts are sent with the SITOR collective B-mode (Also known as AMTOR-B or AMTOR-FEC), using the CCIR 476 character set. SITOR-B is also used in amateur radio, where it is known as AMTOR-B or AMTOR-FEC.
It transmits at 100 baud FSK modulation with a frequency shift of 170 Hz. The frequencies are:
The implementation reflects this structure: The Navtex modem is a specialization of the SITOR-B modem. Fldigi supports both modes. We will specify when their behaviors are different.
Transmitting a text is done with the usual GUI. The only difference between the SITOR-B and Navtex modes, is that data (Whether sent with the GUI or with XML/RPC) are untouched in SITOR-B. In Navtex, on the contrary:
The only difference between the SitorB and Navtex modes, is that messages are processed (Parsed and optionally stored) only in Navtex mode. Here is a typical transmission showing:
The modem has some flexibility when interpreting messages, and is able to deal with missing or incomplete preamble and terminator.
As shown in the reception screen hard-copy, it is possible to tick "AFC". The consequence is that the frequency is continuously monitored.
Navtex messages are delimited with the usual separators ZCZC and NNNN. Their format is:
(message text ...)
These four characters are:
As for any modem, there is a specific configuration tab for Navtex which allows:
Navtex messages can be logged to the ADIF file. This is done with other extra data:
The emitter station is extracted from the Navtex message, and used to extract latitude, longitude, station name and other characteristics from a file containing well-known station, data/NAVTEX_Stations.csv. It is possible to edit this text file, or to choose another one.
Two XML/RPC functions are create:
|navtex.get_message||Returns next Navtex/SitorB message with a max delay in seconds passed as an integer parameter. Empty string if timeout.|
|navtex.send_message||Send a Navtex/SitorB message, passed as a string. Returns an empty string if OK otherwise an error message|