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"christofire" wrote:
I think there's some confusion there about polarisation. VP requires lowest height to achieve a peak at zero degrees elevation; HP requires a frequency-specific height and low height usually results in an elevated beam. ____________ But a v-pol monopole up to 5/8-wavelength in electrical height, and mounted with its base near the earth _always_ launches its maximum relative field at zero degrees elevation (the horizontal plane) -- regardless of the quality of the r-f ground it uses, its operating frequency, or earth conductivity at the antenna site. Radiation launched at low elevation angles by such a monopole is progressively less than in the horizontal plane. But its h-plane radiation (especially), and its low-angle radiation as launched are nowhere nearly as poor as shown in a NEC-2 analysis for these values over real earth -- which is what leads to the erroneous conclusions of many people. The reason for this is that a NEC-2 analysis over a "real" earth is based on the field surviving at an infinite distance from the monopole, and over over a flat earth, at that ! But if that was the true radiation envelope of the elevation pattern actually launched by that monopole, then daytime AM broadcasting would be impossible (reality check). The real-world, h-plane field intensity measurements made in 1937 from such v-pol monopoles at 3/10 of a mile over real earth of poor conductivity by Brown, Lewis & Epstein of RCA showed peak fields that were within a few percent of the theoretical maximum possible for monopole heights of about 45 through 90 degrees. RF http://rfry.org |
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