FLDIGI Users Manual  4.0
NAVTEX and SITOR-B

Table of Contents

Navtex-Choosing.png
Op Mode Select

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

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:

Receiving a text

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.

Navtex-Reception.png
Navtex Reception

AFC: Automatic Frequency Control

As shown in the reception screen hard-copy, it is possible to tick "AFC". The consequence is that the frequency is continuously monitored.

Logging Navtex data to ADIF files

Navtex messages are delimited with the usual separators ZCZC and NNNN. Their format is:

ZCZC B1B2B3B4
(message text ...)
NNNN

These four characters are:

Configuration

Navtex-Configuration.png
Navtex Configuration

As for any modem, there is a specific configuration tab for Navtex which allows:

ADIF journal file

Navtex-Logged-Contacts.png
Logging Contacts

Navtex messages can be logged to the ADIF file. This is done with other extra data:


Stations file

Navtex-Choosing-Stations-File.png
Choosing Stations File

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.

XML/RPC functions

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


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