Radio interference from extra-high-voltage overhead lines: short-line effects

The radio-interference (r.i.) analysis of multiconductor overhead lines of short length has been carried out by applying the theory of natural modes of transmission and deriving the mathematical expression for the spectral density of the noise voltage at different modes characterising the line. The net effect of the mode signals, in forming the interference field in the vicinity of the line, has been evaluated on the assumption that the corona-generated noise sources are uncorrelated and uniformly distributed over the length of the line, and that the independent modes having different propagation characteristics undergo an infinite number of reflections at the line ends. Long-line r.i. predictions on the basis of short-line measurements reported by previous authors have been analytically verified. Complications arising out of the effect of terminations on high-frequency signals have been pointed out and the importance of the generalised mathematical expression has been brought out. The composition of the noise field for a short-circuited case has been determined. A digital computer has been used in the analysis.