IMPROVEMENTS IN OR RELATING TO COMMUNICATION SYSTEMS

1,203,909. Stand-by power supplies. ULTRA ELECTRONICS Ltd. 11 April, 1969, No. 18829/69. Heading H2H. An aircraft communication system, in which communication services are provided via radio links outside the aircraft and via electric conductors inside the aircraft, comprises a plurality of control units 8-12 interconnected by way of a ring main 1, a plurality of radio transmitters 2, 3 and a plurality of radio receivers 4, 5 also being connected to the ring main 1, the ring main being supplied from a main power supply 6 and a stand-by supply 7 and each of the control units 8-12 being provided with a battery which functions as a further power supply connected to the ring main 1, the arrangement being such that in the event of the failure of any one or two of the three power supplies the services are maintained by the remaining power supply. Whilst the power supplies 6, 7 are available arrangements may be made so that the battery in the units 8-12 can be trickle-charged therefrom. The transmitters and receivers 2-5 may be either H.F. or V.H.F. and the control units, although similar to one another, may serve different purposes such as for the pilot's use or for a cabin address system. The system is provided with built-in automatic fault protection together with testing devices.