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1986 Edition, January 1, 1986

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Improvement of the reception quality in automobiles for frequency modulation sound broadcasts in band 8 (VHF)

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There are major difficulties in achieving high-quality reception of FM sound-broadcasting signals in a moving automobile. Severe signal drop-outs may be experienced by the receiver as the vehicle encounters a continously changing multipath receiving environment. At high vehicle speeds, these drop-outs appear as short staccato-like bursts of noise. At lower speeds, losses of programme are replaced by noise created by two completely different effects. In cases of non-selective fading caused by short-distance multi path propagation, the receiver attempts to compensate for a diminished signal level. In cases of selective fading, caused by long distance mulipath propagation, the distortions appear similar to a strong modulation-dependent noise. The rate of drop-out occurrences is usually random, with the greatest incidence occurring in urban areas where numerous buildings may shadow or reflect the transmitted radio signals. The incidence of the selective fade-out is additionally dependent upon topography.