Mobile VHF Antennas - K0BG

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Did you know that what size car youdrive can and does have a profoundeffect upon how your antenna per-forms? You might be surprised at thevariations in an antenna s pattern andgain depending if it is installed on afull-size or mid-sized passenger alone a pickup truck or had been trying to resolve for my-self the many claims and counter-claims regarding the 3-dB gain attrib-uted to the 5/8-wavelenght monopolewhen used in VHF Mobile applica-tions. In that pursuit, using computermodeling, I soon discovered that de-pending upon what vehicle was usedmade a noticeable difference in per-formance sometimes ModelingThe availability of antenna model-ing software has provided an excel-lent tool for predicting antenna per-formance, however, until recentlymodeling Mobile antenna systemshas been a major pain. Calculatingand entering all the geometric data -without errors - for a wire-grid modelsof vehicles such as those shown inFigure 1 can take many hours of te-dious work.

antenna’s was slightly lower (7º - 70º) with the 5/8-wave the lowest (7º - 60º). In all the elevation plots the lowest significant lobe was about 9º.

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