Error reduction in tacan bearing-indication facility

The employment of redundancy coding to reduce bearing indication error is described. The method makes use of a rotating radiation pattern in which the field strength varies in intensity with the sum of the cosine of the bearing angle and its ninth harmonic, the latter component being theoretically redundant. The bearing of the receiver is deduced by examination of the received pattern in time relative to transmitted time signals. The author studies the increase in accuracy achieved by the system's redundancy, in cases where the radiation pattern is disturbed by reflections in the field. A small-reflection analysis is presented in detail. The author concludes that in all cases where the distorting reflections are small and random, the r.m.s. spread of errors in bearing indication is one ninth that which would be obtained if reliance were placed solely on the fundamental sinusoid in the radiation pattern.