Annex I to Recommendation ITU-R M.540

  1 Narrow-band direct-printing techniques should be used for an automated telegraph system for promulgation of navigational and meteorological warnings and urgent information to ships. Common frequencies for such transmissions should be internationally agreed upon and the frequency 518 kHz has been designated for world-wide use in the international NAVTEX service (see Radio Regulations Nos. 474, 2971B and N2971B).

• 1.1 For national NAVTEX services Administrations should also utilize the format of this Recommendation on the appropriate frequencies as defined in the Radio Regulations.

  2 The radiated power from the coast station transmitter should only be that sufficient to cover the intended service area of that coast station. The range extension occurring during night hours should also be considered.

  3 The information transmitted should primarily be of the type used for coastal waters preferably using a single frequency (Resolution No. 324 (Mob-87)).

  4 The transmission time allocated to each station should be restricted to that which is adequate for the anticipated messages to be broadcast to the area concerned.

  5 Scheduled broadcasts should take place at intervals not exceeding eight hours and be co-ordinated, to avoid interference with broadcasts from other stations.

  6 Message priorities

• 6.1 Three message priorities are used to dictate the timing of the first broadcast of a new warning in the NAVTEX service. In descending order of urgency they are:

  	VITAL:	for immediate broadcast, subject to avoiding interference to ongoing transmissions;
  	IMPORTANT:	for broadcast at the next available period when the frequency is unused; and
  	ROUTINE:	for broadcast at the next scheduled transmission period.

  Note Both VITAL and IMPORTANT warnings will normally need to be repeated, if still valid, at the next scheduled transmission period.

• 6.2 In order to avoid unnecessary disruption to the service, the priority marking VITAL is to be used only in cases of extreme urgency, such as some distress alerts. In addition, VITAL messages are to be kept as brief as possible.

• 6.3 Periods should be scheduled between the regular transmission periods permitting immediate/early transmission of VITAL messages.

• 6.4 By use of the message serial number 00 in the preamble of a message (see also Annex 11 § 6) it is possible to override any exclusion of coast stations or of message types which might have been made in the receiving equipment.

  7 Initial shore-to-ship distress-related messages should first be broadcast on the appropriate distress frequency by coast stations in whose SAR area distress cases are handled.

  8 Participating transmitting stations should be provided with monitoring facilities to enable them to:

• monitor their own transmissions as to signal quality and transmission format;
• confirm that the channel is not occupied.

  9 In case a message is repeated by more than one transmitting station within the same NAVTEX region (e.g., for better coverage) the original preamble B₁~B₄ (see annex II) should be used.

  10 In order to avoid overloading of the channel it is desirable to use a single language and where a single language is used it shall be English.

  11 Dedicated onboard equipment is recommended.

  12 Other operational characteristics and detailed guidance are given in the NAVTEX Manual developed by the International Maritime Organization.