A digital data link for aircraft communication

The main features of a digital data link system for communication with a number of aircraft over a single radio frequency by time division multiplex are described. Part 1 describes a ground-to-ground link for conveying the coded messages from the originating centre to the radio transmitter site. Six telephone lines are used, each line carrying 19 parallel 50-baud voice frequency telegraph channels. The equipment is engineered with transistors and printed circuit boards and some figures of fault incidence and reliability are given. Part 2 describes the airborne decoder. Message recognition and means to extract the digit synchronization are described and the design considerations for filtering and coupling the message from the receiver to the decoder are given. Two digital-toanalogue conversion circuits are outlined, one to provide a 400-c/s voltage proportional to the digital quantity, the second a means to generate an angular quantity as a shaft position within the decoder. Brief mention is made of the engineering methods adopted to give the necessary reliability.