01-18-1994 Planning Packet - Laserfiche WebLink

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r compass directions a> a solid line The Sroken line in F g 6 shows the pattern of a haif-wavetength dipole, tor comparison F.g 7 shows the elevation plane or vertical- profile pattern This pattern is that seen from the ends of the elements, with the antenna in tree space Tne soiid line again represents the Yagi. and the brc>en ime the dipoie, that ‘‘perfect circle ” which was mentioned earlier Performance of most other Yagi-type arrays with three or tour elements will not Pe significantly dirfe’’en! from the patterns shown here Another often-used type of oec.m antenna is the quad array. Typically, a quad is constructed with two or more wire elements in the form of a scuare or a diamond The conouctmg wires are usually supported P> X-snaped frames of wood or fioergiass material For tne same number of elements and spacing, the pe'tormance of a quad tjeam is generally similar to that of a Yag' beam The vertical patterns of Figs ana 5 were calculated by assuming the earth is a perfect reflector an unrealistic situation. Actual earth does not 'efiect all of the raoio- frequency energ> strik.ng it; some absorption takes place. Over real earth, therefore, the patterns will be slightly different, cependmg upon the electrical con ductivity and dielectric constant of the soil, ano upon the radio frequency Computer programs are available to take these factors into account, and reliable calculations of patterns over real earth may oe made Yagi patterns over real earth are shown in Figs 8 through 14. These patterns were calculated with an Apple lie personal computer ^ "Average ” so*l conditions were used for these plots, that is. a conductivity of 5 milhsiemens per meter and a dielectric constant of 15 ■* These patterns compare the performance of Yagi arrays at neights of 35 and 70 feet In Figs 6 througn 12. the broken line is the plot for a 35-foot height, and the solid line for 70 feet. For 24.9 and 26 MHz. Figs 13 and 14. if is helpful to present the 35- and 70-foot patterns in separate graphs, for clarity. Otherwise the multiple loPes become indis tinguishable M commerciaiiy available sohAare p'ogi’am AfJNlE. was used to calculate all oatterns oresentea m th s baoer ^Sucn soil conditions may be considered typica' ‘or t.ne central oan of the United States, sucn as tne Onic ana Mississippi river val'evs [ 1 i -W-— -. Fig 8 —Verticai-profile pattern of a 7-MHz Yagi beam over average earth at a height of 70 feet (solid line) and at 35 feet (broken tine). Fig 9 —Vertical-profile pattern ol a 10.1 -MHz Yagi beam at 70 feet (solid Ime) and at 35 feet (broken line). «0 N . X Fig 10 —Vertical-profile pattern of a 14-MHz Yagi beam at 70 feet (solid Ime) and at 35 feet (broken line). Fig 11 -Vertical-profile pattern of an I8.I-MH2 Yagi beam at 70 feet (solid Ime) 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