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On Wed, 26 Nov 2008 14:49:06 -0800 (PST), Richard Fry
wrote: When I use their distance of a mile, I get 188 mV/m, all else identical. Their paper reports by formula that I should see 194.5 mV/m. ... No, the BL&E paper (accurately) stated that 194.5 mV/m is the theoretical maximum field possible at 1 mile for 1 kW radiated by a perfect 1/4-wave monopole over a perfect ground plane. The peak values they measured came very close, but never quite achieved that value. No? No what? Is your rejection rhetorical? a dramatic conceit? Is there some cognitive gap between "by formula" and "theoretical" you are trying to mine? To what purpose? Are you demanding an exact accounting between measured vs. modeled? If so, my model comes within 2mV/m of their graphed data (which, in its own right, does not mean they actually measured that particular cardinal point but as it encompasses their explicitly stated variables is tantalizingly close enough). Expectations of accuracy performed in the field for a continuum of points (verging on 1%) for a fabricated argument of more/less is seeking advantage where there is no salvation to be found. It would appear that with the average of the two distances, my model accords quite closely to BL&E. Mr. Clark - kindly note that in your first quote above you say that, if anything, "modelers" show MORE response than BL&E Then when pressed a bit you say that your model "accords quite closely" with BL&E. There is more than one model involved as described by BL&E. I explicitly selected from one of several available - all of which I have modeled. The model I describe conforms to far more of their variables available than those expressed by you. It also exhibited more response than your 1kM touchstone. Is this touchstone derived from BL&E or some other source unknown to all here, but you? It seems when I followed your offering, you want to challenge its authority. Those two data points I offer exhibit variations of barely a quarter dB about the touchstones you supply (one available from BL&E), and which you fall considerably short of in your own effort. Their average around these touchstones average is an amazingly small difference. The difference between the model I selected, and the one they report (one in the same) is on order of 0.1dB. If this does not constitute an accord, then I would suggest you have more water to carry than myself to turn modeling results into congruency. I am not particularly motivated to improve things when my experience suggests that it is a fool's mission given it implies accuracies that were beyond what was achievable in that cold winter field, 70 odd years ago. Yet the results of my EZNEC near-field model showed considerably LESS ground wave field at 1 km than either the FCC approach or the BL&E data. Clarifications, please? You don't provide enough detail of your model to be able to point to anything in error, but by the multitude of your statements, it doesn't sound like you have spent enough time in the practice of modeling. The rest of my discussion below hardly reveals anything beyond the obvious - for one versed in the craft. My models were arrived at through the simple, but tedious craft of close reading and conforming to expressed facts in the literature. Some art was involved in the selection from a choice of grounds, for which such choice drives a wide variation of results. Does this sound familiar? Even there, calling it art denies the information supplied by photographs revealing a very commonplace description: Pastoral. My choice of ground characteristics, if anything, hardly exhibits a radical departure. In fact I choose no other ground than average for the vast majority of my modeling. Within the confines of the abilities of the model to support buried wire, that was performed by suggestions offered in the help manual (clarity is achieved in reading that too and is generally obtained in the course of considerable exposure to the toolset). Here, the radials hovered less than half an inch above ground instead of buried six inches beneath. Perhaps this explains the remaining 0.1dB variation, but I doubt it. To infer such tight coupling between model and measure is a fantasy only Art would embrace to prove we can't trust established theory. 73's Richard Clark, KB7QHC |
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