Influence of crosstalk in transmission line on accuracy in inductive radio system for detecting the position of linear motor vehicles

The three-phase three-conductor transmission line can be used in an inductive radio system for detecting the position of a vehicle of a linear synchronous motor car. A quantitative investigation is developed on the relation between the crosstalk between positive and negative-phase-sequence components in a helically wound transmission line and deviations of the line conductors from their normal positions. The authors have derived the required accuracy in a manufacturing process of a line for the desired accuracy in detecting the vehicle position. Cases where line conductors deviate randomly from their normal positions and cases where there exist manufacturing imperfections similar to “asymmetrical twisting,” which occasionally happens in manufacturing “star quads” used in ordinary telephone cables, are analyzed. It is clarified that the position detection error is affected mainly by the near-end crosstalk between positive and negative phase circuits, which is maximized when a vehicle approaches the nearest start terminal of the transmission line. Moreover, it is expected that the fairly satisfactory accuracy in the vehicle position detection is obtained if we can make the layout accuracy of line conductors within a few percent of the helical radius. The obtained results are expected to be applied analogously also to the flat-type three-phase three-conductor line.