Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1403 – Revised NAVTEX Manual – (23 May 2011) - Annex - Annex 2 – Recommendation ITU-R M.540* - Annex II to Recommendation ITU-R M.540
Annex II to Recommendation ITU-R M.540
Technical Characteristics
1 The signals transmitted should be in conformity with the collective B-mode of the direct-printing system specified in Recommendations 476 and 625.
2 The technical format of the transmission should be as follows:
in which ZCZC defines the end of the phasing period,
the B1 character is a letter (A-Z)footnote identifying the transmitter coverage area,
the B2 character is a letter (A-Z) for each type of message.
2.1 Both the B1 characters identifying the different transmitter coverage areas and the B2 characters identifying the different types of messages are defined by IMO and chosen from Table I of Recommendations 476 and 625, combination numbers 1-26.
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2.1.1 Ship equipment should be capable of automatically rejecting unwanted information using character B1.
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2.1.2 Ship equipment should be capable of disabling print-out of selected types of messages using character B2 with the exception of messages with B2 characters A, B, and Dfootnote (see also § 2.1).
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2.1.3 If any facility is rejected or disabled in § 2.1.1 and 2.1.2 above, the extent of any such limitation must be clearly indicated to the user.
2.2 B3B4 is a two-character serial number for each B2, starting with 01 except in special cases where the serial number 00 is used (see § 6 below).
2.3 The characters ZCZC B1B2B3B4 need not be printed.
3 The printer should only be activated if the preamble B1~B4 is received without errors.
4 Facilities should be provided to avoid printing of the same message several times on the same ship, when such a message has already been satisfactorily received.
5 The necessary information for the measures under § 4 above should be deduced from the sequence B1B2B3B4 and from the message.
6 A message should always be printed if B3B4 = 00.
7 Extra (redundant) letter and figure shifts should be used in the message to reduce garbling.
8 In case a message is repeated by another transmitting station (e.g., for better coverage) the original preamble B1~B4 should be used.
9 The equipment on board ships should be neither unduly complex or expensive.
10 The transmitter frequency tolerance for the mark and the space signals should be better than ± 10 Hz.
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