Radio data system links using leaky feeders and E.M.C. problems.

Radio Data System on FM channels should be of prominent use into the near future. As these data transmissions are of relatively low rate, good quality transmissions must be achieved. Starting from this condition and from the fact that RDS tunnel communications have to be maintained, we have studied the performances of RDS transmissions using leaky feeders. In this paper, error rate measurements of RDS FM radio retransmissions using leaky feeders are presented. As the radiation modes in tunnels are quite different from open areas and are also dependent on the tunnel shape and on the leaky feeder used, these performances have been measured on several test sites in France and in Belgium. From electromagnetic field measurements and from a statistical analysis of these results, two complementary approaches are selected: an analogical one which considers the percentage of time where the synchronization of the restored clock is maintained. A second one detects the number of errors in each block of 26 bits. Furthermore, starting from these results, we introduce an open road RDS beacon using a leaky feeder developed in view to transmit very local information without the need of a new equipment on board the cars, nor the need of a specific frequency. In a second step, a leaky feeder can be considered as a very long antenna thus coupling with natural or man-made noise is important. When a system is installed in a tunnel, the most important interfering fields are those from the motor vehicle ignition and from the local oscillator of the car receiver. When the leaky feeder is used on open air roads, other interfacing fields, generated by several different sources (e.g. high voltage power-lines, broadcasting transmitters, industrial equipment) are considered. Therefore, the international CISPR and European Standard on ElectroMagnetic Compatibility are commented on and listed. Then, by starting from the limits in force today and given in the relevant standards, a prediction of disturbance fields on roads is done. Application to the impact of impulsive noise on the RDS signals is presented.