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ANTENNAS FOR 100 POUND DXPEDITIONS antenna and its performance. The modeling input data additionally provides a means for the reader to perform these calculations themselves and possibly further alter the simulated environment to learn more. The ARRL Antenna Book is an excellent resource for anything relating to amateur radio antennas. It is also recommended that the reader study the relevant sections of that reference work for any particular antenna type discussed here (vertical monopole, vertical dipole, etc.). Such reading will help set reasonable expectations for each antenna type. For example, this antenna presents about 30 ohms of R, not 50 ohms. This is expected in a vertical monopole with a good radial system. The far-field plots have a great deal of information within them. The general shape of the azimuth plot shows the relative strength of the signals emitted in any given direction. These relative strengths are normalized to the 0 dB outer ring and directions where the signal is less than the maximum appear plotted within the circle intersecting with graphed rings of -5 dB, -10 dB, etc. The elevation plot provides an indication of the angles where most of the radiation is being emitted. This simple vertical monopole has only one lobe but other antennas may have several lobes and deep nulls between them. Those deep nulls would indicate angles where little or no radiation is emitted. The large lobes would represent the antenna’s “take off angle”, the angle from which the most radiation is emitted or received. Though the relative shapes of the plots for good ground and poor ground may appear similar, the magnitude of the radiation represented by the outer ring may be vastly different. In this case, the outer ring for the good ground plot represents 0.33 dBi; the outer ring for the poor ground plot represents -0.2 dBi. In other antenna systems the effects of ground on antenna efficiency are more pronounced. Finally, the effects of ground can also affect the antenna’s take off angle. Generally, better ground lowers the take off angle. This is a problem for two reasons: (1) some of the more interesting and fun places to visit have sandy soil and provide a very poor ground, and (2) these interesting places are typically far away from stations we would like to work so a low take off angle is especially important. There is a discussion about the effects of ground, and things that might be done to manage it, later in the paper. This system of diagrams for SWR and far-field plots provides some visual means of comparing antenna systems to a standard set of antennas and to each other. A significant amount of space is dedicated to these comparisons later in this paper.

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Antennas for 100 Pound DXpeditions - volume 1  

Computer-based antenna modeling and direct experience with lightweight portable antenna systems. Volume 1: Selected high band antennas [20-6...

Antennas for 100 Pound DXpeditions - volume 1  

Computer-based antenna modeling and direct experience with lightweight portable antenna systems. Volume 1: Selected high band antennas [20-6...

Profile for ne1rd
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