September 1981 | NTIA Technical Report TR-81-84
Larry G. Hause
Abstract: This report presents the description, analysis and results of a set of measurements made on a 90 km line-of-sight path in Italy. The measurements were made during the late spring of 1980 by the National Telecommunications and Information Administration under the sponsorship of the Defense Communication Engineering Center, Reston, VA. Received signal level and IF spectrum were measured to obtain statistics about the distortion of the frequency spectrum amplitude during periods of multipath fading. Digital format violation and reframe events were monitored to measure the tolerance of the 3-level-partial-response radios (12.6 Mb/s) to this distortion. A number of interesting results were observed from the data analysis. Large values of spectrum amplitude distortion, greater than 1 dB/MHz, were observed during multipath fading events due to nulls in the path frequency response. Diversity reception looks very promising for counteracting these larger magnitude distortion effects. Multipath received-signal-level statistics can be used to predict the frequency and severity of in-band-fading distortion on line-of-sight paths. Frequency selective fading develops and subsides at low rates, often over a period longer than one minute. It was found that the 3-level-partial-response radios were robust in the presence of amplitude distortion suffering insignificant outage time from this cause.
Keywords: diversity; digital radio; microwave radio; multipath distortion; selective fading
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