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#1
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steveeh131047 wrote:
Tom, Yes I have EZNEC and recognise what a great tool it is. Its predictions were the benchmark against which I tested the various coil models I read about, and no-one has yet suggested that it can't be trusted for modelling a helix. I'm not on some "philosophical quest" - I'm just an old, retired, guy who still likes learning and wants to understand more about how things work; I hope that never leaves me! I stumbled on this discussion quite by chance and tried to understand the various "positions" being taken. Perhaps I'm over-simplifying, but it seemed to me there was a group who favoured the transmission-line model and a group against it. I've tried dispassionately to understand the various arguments and to form my own conclusions. Now here's my problem: * The results I get using a model based on transmission-line analysis are very close to my EZNEC predictions - not perfect, but way better than any lumped-element analysis results * I don't see quantitative, non-empirical, arguments being put forward to support lumped-element analysis * I see numeric arguments being put forward by Cecil to support a transmission-line approach - they look convincing to me and, although I see a lot of unpleasant personal attacks on him, I don't see any scientific challenge to his figures * On the other hand I see folk whose work I rate highly, seemingly willfully to misunderstand some of the points which Cecil puts forward Please don't think I'm trying to defend Cecil - I wouldn't be so presumptuous, and anyway he's old enough to look after himself! I'm just trying to understand why, what seems to me to be such a persuasive argument, generates such opposition. Either there's some glaring technical error here which I haven't yet spotted, or perhaps there's a long "history" between various "personalities" of which I'm ignorant? Still confused, Steve G3TXQ There aren't many people who would support a lumped-element analysis on this newsgroup. Most people know the limitations of using network theory in these circumstances. The technical arguments against Cecil's approach were offered a long time ago. This latest is just a flareup that will soon die down. You shouldn't be confused. The transmission line model of antennas is well accepted and hoary with age, particularly for bi-conical antennas (see Schelkunoff). There are a couple of other types of models with equal validity. If you really want to know the physical score, though, you have to get an electromagnetics text that discusses the integral equations that govern antenna behavior. Pay particular attention to the parts that explain why numerical methods like EZNEC have to be used for solutions rather than the symbolic math most people would expect and want. 73, Tom Donaly, KA6RUH |
#2
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Tom Donaly wrote:
There aren't many people who would support a lumped-element analysis on this newsgroup. Most people know the limitations of using network theory in these circumstances. The technical arguments against Cecil's approach were offered a long time ago. This latest is just a flareup that will soon die down. You shouldn't be confused. The transmission line model of antennas is well accepted and hoary with age, particularly for bi-conical antennas (see Schelkunoff). There are a couple of other types of models with equal validity. If you really want to know the physical score, though, you have to get an electromagnetics text that discusses the integral equations that govern antenna behavior. Pay particular attention to the parts that explain why numerical methods like EZNEC have to be used for solutions rather than the symbolic math most people would expect and want. 73, Tom Donaly, KA6RUH I did and do support lumped element analysis for a very small toroidal loading inductor, and extensively posted the reasons why in this newsgroup about six years ago ("Current in antenna coils controversy", 2003). Cecil and Yuri were arguing that the coil would replace some number of "degrees of antenna" and its current therefore would have a substantial phase difference between input and output ends. I made and posted careful measurements to support my statement, after which Cecil invented his "standing wave current" and went off in various directions. Roy Lewallen, W7EL |
#3
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Roy Lewallen wrote:
I did and do support lumped element analysis for a very small toroidal loading inductor, and extensively posted the reasons why in this newsgroup about six years ago ("Current in antenna coils controversy", 2003). Cecil and Yuri were arguing that the coil would replace some number of "degrees of antenna" and its current therefore would have a substantial phase difference between input and output ends. I made and posted careful measurements to support my statement, after which Cecil invented his "standing wave current" and went off in various directions. I didn't invent "standing wave current". Standing wave current is what EZNEC displays for standing wave antennas. Standing wave current is what Kraus describes graphically on page 464, Figure 14-2, of "Antennas ...", 3rd edition. Standing wave current is what Ramo and Whinnery describe mathematically in "Fields and Waves ...". It has been at least 5 years since I explained why the phase of the current on a standing wave antenna cannot be used to determine the delay in a wire or in a coil. EZNEC, Kraus, Balanis, and Ramo and Whinnery all agree with me and disagree with you. I explained, 5 years ago, how the magnitude of the current can be used to calculate the delay through a coil. All my explanations fell on deaf ears and you called them gobblygook, or some such. Once again, most of the current in a standing wave antenna is of the form, I = Imax*cos(kx)*cos(wt) For any given time = t1, the phase of the current all up and down the antenna does not change with x. The phase is the same at the feedpoint, at the bottom of the coil, at the top of the coil, and at the top of the stinger. The phase of that current cannot be used to calculate delay in a wire or through a coil. You once said you were quick to admit a mistake. It has been 5+ years since you made that conceptual mistake and you have not admitted it yet. -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
#4
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Roy Lewallen wrote:
Tom Donaly wrote: There aren't many people who would support a lumped-element analysis on this newsgroup. Most people know the limitations of using network theory in these circumstances. The technical arguments against Cecil's approach were offered a long time ago. This latest is just a flareup that will soon die down. You shouldn't be confused. The transmission line model of antennas is well accepted and hoary with age, particularly for bi-conical antennas (see Schelkunoff). There are a couple of other types of models with equal validity. If you really want to know the physical score, though, you have to get an electromagnetics text that discusses the integral equations that govern antenna behavior. Pay particular attention to the parts that explain why numerical methods like EZNEC have to be used for solutions rather than the symbolic math most people would expect and want. 73, Tom Donaly, KA6RUH I did and do support lumped element analysis for a very small toroidal loading inductor, and extensively posted the reasons why in this newsgroup about six years ago ("Current in antenna coils controversy", 2003). Cecil and Yuri were arguing that the coil would replace some number of "degrees of antenna" and its current therefore would have a substantial phase difference between input and output ends. I made and posted careful measurements to support my statement, after which Cecil invented his "standing wave current" and went off in various directions. Roy Lewallen, W7EL I should have specified a large, solenoidal loading coil such as Cecil is so fond of using. Cecil has since eschewed his "degrees of antenna" position, but, for some reason, he keeps claiming your tests on the small solenoid were wrong. 73, Tom Donaly, KA6RUH |
#5
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Tom Donaly wrote:
I should have specified a large, solenoidal loading coil such as Cecil is so fond of using. Cecil has since eschewed his "degrees of antenna" position, but, for some reason, he keeps claiming your tests on the small solenoid were wrong. Yes, I have fine-tuned my concepts over the past 5 years. What rational person would not adjust their concepts to match the technical evidence? (It's a rhetorical question. We all know who refuses to do that.) Roy's tests were wrong in the sense that they were meaningless no matter how accurate the readings. Quoting my web page: "All of the reported conclusions based on loading coil measurements using the current on standing-wave antennas are conceptually flawed." -- 73, Cecil, IEEE, OOTC, http://www.w5dxp.com |
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