ADTRAN TRACER 4106 Plan A System Manual

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ADTRAN TRACER 4106 Plan A System Manual Manual pdf 22 page image

Section 2 Microwave Path Engineering Basics TRACER 4106/4206 System Manual22 © 2004 ADTRAN, Inc. 612804206L2-1AAntennas are also designed to radiate RF energy efficiently for a specific range of frequencies. Pleaseconsult the data sheet for your particular antenna make and model to ensure that it is specified to operate inthe 2400 MHz to 2483.5 MHz frequency band for TRACER 4106 models, and the 5725 MHz to 5850MHz frequency band for the TRACER 4206 system.Fresnel Zones, Earth Curvature, & Antenna HeightsFresnel zones correspond to regions in the microwave path where reflections of the intended signal occurand combine in both constructive and destructive manners with the main signal, thereby either enhancingor reducing the net power at the receiver.In general, the odd numbered Fresnel zones (1, 3, 5, ...) add constructively at the receiver, while the evennumbered Fresnel zones (2, 4, 6, ...) add destructively at the receiver.The first Fresnel zone corresponds to the main lobe, 60% of which must be free of physical obstructionsfor the path calculations to be valid. Since the main lobe contains the vast majority of the microwaveenergy, this zone is typically used to determine proper antenna heights when placing antennas on towers orbuildings.The curvature of the Earth becomes a legitimate obstruction for path lengths of 7 miles or greater, and mustalso be accounted for when determining minimum antenna heights.The aggregate expression for minimum antenna height that incorporates both the 60% first Fresnel zoneand the Earth’s curvature is given bywhere f is in GHz and d is in miles.Table 5 tabulates minimum antenna heights for given path lengths.Table 5. Minimum Antenna Height for Given Path LengthsPath Length(miles)Min. Antenna Height@ 2.4 GHz(ft)Min. Antenna Height@ 5.8 GHz(ft)2 33 224 48 326 61 418 73 5010 85 6014 111 8116 124 9218 138 10420 153 11722 169 13124 185 14526 202 161h 72.1 d4f----- 0.125d2+= (feet)