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![]() Walter Maxwell wrote: Roy, W7EL wrote: I haven't looked into this carefully, but one person I know who was very involved in NVIS operation (where ground characteristics are important) tried it some years ago. He concluded that it wasn't possible to set the antenna height and make measurements with sufficient accuracy to infer the ground characteristics with any confidence. Roy Lewallen, W7EL Understood, Roy, but was this person saying that with just one height it wouldn't give sufficient accuracy, or is he saying that with impedance knowledge at many different heights there would still be no determination of any of the ground characteristics? I interpreted what he said as meaning that he looked into the method and determined it wasn't practical. Surely he thought of making numerous measurements. He's a very capable engineer, so I took what he said at face value. On the other hand, I don't think he's highly skilled in making precision antenna measurements, so he might have assumed that a level of accuracy wasn't achievable which in fact might be. You might spend a little while with EZNEC looking at how much a change in ground conductivity or permittivity changes the antenna input Z at various heights, and how much the height changes the Z with a given set of ground characteristics. Then consider whether you'd be able to set the height and make the impedance measurements accurately enough to infer the ground characteristics with any degree of confidence. Would you not like to see my data before concluding it couldn't reveal any ground characteristics.? I'd like to see your data, but it wouldn't be enough information to conclude whether the method would be practical or not. Roy Lewallen, W7EL |
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