04-18-1994 Planning Packet - Laserfiche WebLink

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shion entric field Dy the libels, nter. ms of ih of a jency. tterent s. For length height 7 MHz. Table all the and 5 Hect of itensity ease it 4). the of 30®. ovide a if about pattern 14 MHz t a [he compass direct»ofts. as a solid une The brot^en ime m F*g 6 shcK»$ the pattern o? a halt-wavelength dipole, for comparison Fig 7 shows the elevation plane or vertical- profile pattern This pattern is that seen from the ends of the elements, with the anterma m free space The soitci line again represents the Yagi. and the broken hr>e the dipole, th^ ■■ perfect circle ” which was ment«x>ed earlier Performance of most other Yag»-type arrays with three or four elements will no* be significantly different from the patterns shown here Another often-used type of becm antenna is the quad array Typically, a quad is constructed with two or more wire elements m tho form of a square or a diamofKJ. The conducting wires are usuafly supported by X-shaped frames of wood or fiberglass material For the same number o* elements and soacinq. the pedormance of a quad beam is generally Similar to that of a Yagi beam The vertical patterns of Figs 4 and 5 were calculated by assuming the earth is a perfect refiector an unrea'istic Situation Actual earth does not reflect ail of the radio- frequency energy striking it, some absorption fakes place Over real earth, therefore, the patterns wiH be slightly different, depencing upon the electrical con ductivity and Qieiectnc constant of the soil, and upon the radio frequency Computer programs are available to take these factors mto account, and reliable calculations of patterns over real earth may oe made > agi patterns over real eanh are shown in Figs 8 through f4. These patterns were calculated with an Apple He personal computer ^ “Average ” soil conoitions were used for these plots, that is. a conductivity of 5 nillisiemens per meter and a dielectric constant of 15 ^ These patterns compare the performance of Yagi arrays at heights of 35 and 70 feet In Figs 6 through 12, the broken line is the plot for a 35-toof height, and the solid line for 70 feet. For 24 9 and 28 MHo Figs 13 and 14. it is helpful to present the 35- and 70-foot patterns m separate graphs, for clarity. Otherwise the multiple lobes become indis tinguishable commefcialiy available so*iAare prog'am ANNIE, was used to calculate all oattems presentee in tnis paper ‘Such soil conditions may be considered typical for the central pan of tne United States such as tne Oriio and Mississippi river val'evs «c 1 Fig 8—Vertical-profile pattern of a ;-MHz Yagi beam over average earth at a height of 70 feet (solid line) and at 35 feet (broken line). / \\ -V- V • A, i ! J. Fig 9—Vertical-profile pattern of a lO.f-MHa Yagi beam at 70 feet (solid line) and at 35 feet (broken line). \ ''V >■ X. Fig 10—VeflicaJ-profiic pattern of a 14-MHz Yagi beam at 70 feet (solid tine) and a! 35 feet (broken line). Fig 11—Vertical-profile pattern of an 18.1-MHz Yagi beam at 70 feet (solid line) and at 35 feet (broken line). Fig 12—Vertical-profile pattern of a 21-MHz Yagi beam at 70 feet (solid line) and at 35 feet (broken line). j