Part B - Transmitters
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Resolutions - Assembly - IMO Resolution A.804(19) – Performance Standards for Shipborne MF Radio Installations Capable of Voice Communication and Digital Selective Calling – (Adopted on 23 November 1995) - Annex – Recommendation on Performance Standards for Shipborne MF Radio Installations Capable of Voice Communication and Digital Selective Calling - Part B - Transmitters

Part B - Transmitters

  1 Frequencies and Classes of Emission

  1.1 The radiotelephone and DSC transmitter should be capable of transmitting on a number of frequencies in the bands between 1,605 kHz and 4,000 kHz considered by the Administration as adequate for the operation of the ship, but at least on the frequencies 2,182 kHz and 2,187.5 kHz.

  1.2 Radiotelephone frequencies are designated in terms of the carrier frequency; DSC frequencies are designated in terms of the assigned (centre) frequency. When DSC signals are transmitted using a transmitter in J2B mode, the (suppressed) carrier frequency should be adjusted so as to have the DSC signal transmitted on the assigned DSC frequency. The selected transmitter frequency should be clearly identifiable on the control panel of the equipment.

  1.3 The transmitter should be capable of transmitting (upper side band signals, where appropriate) using classes of emission J3E, H3E and either J2B or F1B.

  1.3.1 When switching to the preset distress frequency 2,182 kHz, the appropriate class of emission in accordance with the Radio Regulations should be selected automaticallyfootnote

  1.3.2 When switching to the preset distress frequency 2,187.5 kHz, the class of emission J2B or F1B should be selected automatically.footnote

  1.4 It should be possible to change the transmitter from any class of emission to another for which it is designed to operate by means of not more than one control.

  1.5 It should be possible for the user to select transmission frequencies independent of any receiver setting. This does not preclude the use of transceivers.

  1.6 It should be possible to change the transmitter quickly from operation on any frequency to operation on any other frequency, and in any event within a period not exceeding 15 s. The equipment should not be able to transmit during channel switching operations.

  1.7 Means should be provided to prevent over-modulation automatically.

  2 Frequency Stability And Accuracy

 The transmitter frequency should remain within 10 Hz of the required frequency at all times following the warming-up period.

  3 Output Powerfootnote

  3.1 During normal modulation, the peak envelope power in the case of J3E or H3E emissions, or the mean power in the case of J2B or F1B emissions, should be at least 60 W at any frequency within the specified frequency range.

  3.2 If the rated output power exceeds 400 W, provision should be made for reducing the output to 400 W or less.

  4 Permissible Warming-Up Period

 The equipment should be capable of operating on 2,182 kHz and 2,187.5 kHz within 1 min after switching on.

  5 Continuous Operation

 Continuous operation should be possible when the transmitter is adjusted to its rated power.

  6 Controls and Indicators

  6.1 Provision should be made for indicating the antenna current or power delivered to the antenna. Failure of the indicating system should not interrupt the antenna circuit.

  6.2 Manually tuned equipment should be fitted with a sufficient number of indicators to permit accurate and rapid tuning.

  6.3 Operation of the transmit/receive control should not cause unwanted emissions.

  6.4 All adjustments and controls necessary for switching the transmitter to operate on 2,182 kHz and 2,187.5 kHz should be clearly marked, in order that these operations may be performed readily.

  7 Safety Precautions

 The equipment should be so designed and constructed that, when the transmitter is providing power to the antenna, the transmitter is protected against damage resulting from disconnection of the antenna or short-circuiting of antenna terminals. If this protection is provided by means of a safety device, that device should automatically be reset following removal of the antenna open-circuit or short-circuit conditions.

  8 Power Supply

  8.1 If it is necessary to delay the application of voltage, for example anode voltage, to any part of the transmitter after switching on, this delay should be provided automatically.

  8.2 If the transmitter includes parts which are required to be heated in order to operate correctly, for example crystal ovens, the power supplies to the heating circuits should be so arranged that they can remain operative when other supplies to or within the equipment are switched off. If a special switch for the heating circuits is provided, its function should be clearly indicated; it shall normally be in the "on" position and be protected against inadvertent operation. The correct operating temperature should be reached within a period of 30 min after the application of power.


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