A Survey of Past, Present and Possible Future Systems for the Transmission of Signals from the EMC Viewpoint

The paper surveys the transmission of information by electrical signals in analogue and digital form from the early days of the electric telegraph to the present day and makes observations on possible future developments. Although the scientific discipline of electromagnetic compatibility (EMC) is comparatively new, and comprises a host of familiar engineering practices under one isolated title, the problems of interference have always been the concern of the telecommunications engineer, who by force of necessity, had to seek the co-operation of the electrical power engineer and electrical traction engineer. In many branches of engineering it is often salutary to step back and to study the important factors known to earlier engineers, but left unrecorded in modem engineering literature, and see if they are applicable to the present day. This is particularly the case with the present rate of advance in engineering science where new devices and techniques appear almost daily. The temptation to be 'up-to-date' is fraught with danger from the EMC view point and examples are given of performing a particular function in a new and untried way when a routine answer is available and efficient. As an example of present-day techniques the design philosophy of the digital data transmission system for automatic flight control in a modem aircraft is considered in some detail. The achievement of EMC is intimately affected by the total avionic fit and this in turn determines the optimum transmission network for a particular aircraft. Transmission media other than wire and cable are considered and mention is made of various forms of isolator as they affect both reliability and EMC. A look into the future is made by mention of ultra-sonic transmission utilising the aircraft structure as the transmission medium.