INTERNATIONAL RADIO CONVENTION. NOVEMBER 25,1927. §4. All apparatus in mobile stations established for the transmis- sion of Type Al waves between 125 and 150 kc/s (2400-2000 m.) must permit the uae d at least three frequencies chosen from this band, and ~ust permit it rapid change from one to· another of these fre- quenCIes. §5. (1) All stations on ships compulsorily equipped with radio apparatus must be able to receive the wave of 500 kc/s (600 m.) and in addition all the waves necessary for the proper accomplishment of the s<lrvice which they carry on. (2) Beginning January 1, 1932 they must be able to receive easily and efficiently on the same frequencies, waves of Types Al and A2. §6. Transmitting apparatus used in the mobile service must be provided with devices permitting reduction of power. This provision shall not apply to transmittal'S, the input power of which does not exceed 300 watts. , §7. Receiving apparatus must be such that the current which it produces in the antenna shall be as small as possible and shall not disturb neighboring stations. §8. The transmitting and receiving apparatus of all mobile stations must be such as to allow changing of frequency as rapidly as possible. All installations must be such that communications once being estab- lished the time necessary to change from transmission to reception and vice versa shall be as short as practicable. ARTICLE 17 Galling and listening waves §1. (I) In the band between 360 and 515 kc/s (830-580 m.) the only Type B waves permitted shall be the following; 375, 410, 425, 454 and SOO kc/s (800, 730, 705, 660, and 600 m.) . (2) The general calling wave, which must be used by all ships com- pulsorily equipped and by coast statioIlS, shall be 500 kc/s (600 m.) (AI, A2 or B). (3) Besides the wave 500 kc/s (600 m.) the use of waves of all types between 485. and 515 kc/s (620-580 m,) shall be forbidden. (4) The wave of 500 kc/s (600 m.) shall be the international calling and distress wave. It may be used, but with discretion, for other purposes, if it does not interfere with distress, urgent, safety, or call signals. (5) Coast stations must be able to use at least one wave besides that of 500 kc/s (600 m.). This additional wave shall be underlined in the nomenclature to indicate that it is the normal working wave of the station. The additional waves thus chosen may be the same as those of ship stations or may be different. In any case, the work- ing waves of the coast stations must be chosen in such a way as to avoid interference with neighboring stations. (6) Besides the normal working waves underlined in the nomen- clature, coast and ship stations may use in the authorized band additional waves which they deem suitable. These waves shall be given in the nomenclature without being underlined. §2. (1) In order to increase safety of life at sea (ships) and over the sea (aircraft), all stations in tho mobile maritime service must, during their hours of service, take the necessary measures to assure the watch on the distress wave (500 kc/s-600 m.) for three minutes twice per hour, beginning at the 15th minute and at the 45th minute after each hour Greenwich Mean Time. 2867 Calling and listening waves.
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