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View File - University of Engineering and Technology, Taxila

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<strong>and</strong> Lin [5]:whereL ¼L o1 þ L oðr r 6:2Þ2636ð4:27aÞH gL o ¼ H oð4:27bÞsin yy ¼ earth station elevation angle (degree), as defined by (2.20).H g ¼ altitude <strong>of</strong> earth station (km).H o ¼ freezing height (in km), expressed in terms <strong>of</strong> the earth station’slatitude L ET , thus:H o ¼ 4:8; L ET < 30 7:8 0:1L ET ; L ET 30 ð4:27cÞPrecipitation (rain) loss (4.24) will be included as part <strong>of</strong> path losses L u <strong>and</strong>=orL d in (4.17) <strong>and</strong>=or (4.18), respectively, when considering the combinedcarrier-to-noise ratio <strong>of</strong> the communications link.Figures 4.4 <strong>and</strong> 4.5 are borne out <strong>of</strong> Eqs. (4.24) <strong>and</strong> (4.27), respectively.Rain effects become severe at wavelengths approaching the water drop size,which is dependent on the type <strong>of</strong> rainfall. If a satellite link is to be maintainedduring rainfall, it is imperative that enough extra power be transmitted toovercome the maximum additional attenuation induced by the rain: implyingthat an accurate assessment <strong>of</strong> expected loss when evaluating link parametersbe made. This attenuation loss is calculated by multiplying the loss perFIGURE 4.4 Rainfall attenuation vs. frequency <strong>and</strong> rainfall rates, r r .Copyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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