TREATIES 6. The main and emergency (reserve) installations must be capable of transmitting and receiving on the frequencies (wave lengths) and types of waves assigned by the International Radiotelegraph Con- vention in force for the purpose of distress and safety of navigation to ships compulsorily fitted with radiotelegraph installations in accord- ance with the present Convention. 7. The main and emergency (reserve) transmitters shall have a note frequency of at least 100. 8. The main transmitter shall have a normal range of 100 nautical miles, that is to say, it must be capable of transmitting clearly per- ceptible signals from ship to ship over a range of at least 100 nautical miles by day under normal conditions and circumstances, the receiver being assumed to be one employing a rectifier of the crystal type without amplification.* 9. Sufficient power must be available in a ship station at all times to operate the main radiotelegraph installation efficiently under normal conditions over the above range. 10. All parts of the emergency (reserve) installation shall be placed in the upper part of the ship, in a position of the greatest possible safety, as high above the deepest load water line as practicable. The emergency (reserve) installation must be provided with a source of energy independent of the propelling power of the ship and of the main electricity system and must be capable of being put into opera- tion rapidly and of working for at least six continuous hours. For the emergency (reserve) installation, the normal range as defined in paragraph 8 above must be at least 80 nautical miles for ships required to maintain a continuous watch and at least 50 nautical miles for all other ships.* 11. The receiving installation must permit of the reception of such of the waves used for the transmission of time signals and meteoro- logical messages as may be considered necessary by the Administration. 12. The receiver must be so arranged as to be capable of main- taining reception by means of a rectifier of the crystal type.
- Unless a more precise and practical method is available to determine the
range of transmitters it is recommended that, as a guide, the following relations between the range in nautical miles (from ship to ship under normal conditions in daytime) and the power of the ship transmitter in metre amperes for 500 kilocycles per second (600 m) be used:- 100 nautical miles 60MA 80 nautical miles 45MA 50 nautical miles 25MA M being the actual height in metres of the aerial from its highest point to the load line. A being the current in amperes measured at the base of the aerial in case of B, or fully modulated A 2, transmitters. [Footnote in the original.]