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#1
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On Apr 23, 4:42*pm, Jim Kelley wrote:
For a more quantitative illustration of how distributed reactance in transmission lines causes delay seehttp://www.rhombus-ind.com/dlcat/app1_pas.pdf 73, ac6xg Jim, thanks for the reference. Perhaps I should have expressed myself more clearly. What I've not seen, for example, is a lumped-element analysis which takes just the coil dimensions as input, and predicts theoretically - without a lot of empirical "tweaking" - the reactance at a particular frequency; particularly a frequency close to self-resonance. There may be one out there, but I've not yet found it! In contrast, the ON4AA calculator - based on Corums' transmission-line analysis - does just that, and produces results which seem to match well the EZNEC modelling results. Regards, Steve G3TXQ |
#2
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On Apr 23, 11:26*am, steveeh131047 wrote:
On Apr 23, 4:42*pm, Jim Kelley wrote: For a more quantitative illustration of how distributed reactance in transmission lines causes delay seehttp://www.rhombus-ind.com/dlcat/app1_pas.pdf 73, ac6xg Jim, thanks for the reference. Perhaps I should have expressed myself more clearly. What I've not seen, for example, is a lumped-element analysis which takes just the coil dimensions as input, and predicts theoretically - without a lot of empirical "tweaking" - the reactance at a particular frequency; particularly a frequency close to self-resonance. There may be one out there, but I've not yet found it! In contrast, the ON4AA calculator - based on Corums' transmission-line analysis - does just that, and produces results which seem to match well the EZNEC modelling results. Regards, Steve G3TXQ That is because the transmission line is considered to be within a arbitrary boundary where all applicable forces equals zero, ie in equilibrium. Eznec is also based on the condition of equilibrium as applied by Maxwell in concert with Newton. This group is using the conditions accounted on this Earth where as scientific laws are based upon a Universe within a boundary and not just the Earth. TRhat is equivalent to saying weight is the same metric as mass ! Art |
#3
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steveeh131047 wrote:
On Apr 23, 4:42 pm, Jim Kelley wrote: For a more quantitative illustration of how distributed reactance in transmission lines causes delay seehttp://www.rhombus-ind.com/dlcat/app1_pas.pdf 73, ac6xg Jim, thanks for the reference. Perhaps I should have expressed myself more clearly. What I've not seen, for example, is a lumped-element analysis which takes just the coil dimensions as input, and predicts theoretically - without a lot of empirical "tweaking" - the reactance at a particular frequency; particularly a frequency close to self-resonance. There may be one out there, but I've not yet found it! In contrast, the ON4AA calculator - based on Corums' transmission-line analysis - does just that, and produces results which seem to match well the EZNEC modelling results. Regards, Steve G3TXQ EZNEC is a mathematical model just as the transmission line model is a model. EZNEC doesn't use a transmission line analog in order to reach its conclusions. If you're really interested in this subject, you have to read Schelkunoff and others who did the research on this years ago. A big, honking loading coil doesn't act much like a lumped component. It makes a pretty shabby transmission line, too. If you want to understand it, you have to study electromagnetics and approach it from that standpoint, which may not be easy. Finally, a modest question: if you have EZNEC, why would you be wasting time with something inferior? The gold standard is the gold standard. Or are you on some philosophical quest, like Cecil? 73, Tom Donaly, KA6RUH |
#4
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On Apr 23, 1:34*pm, "Tom Donaly" wrote:
steveeh131047 wrote: On Apr 23, 4:42 pm, Jim Kelley wrote: For a more quantitative illustration of how distributed reactance in transmission lines causes delay seehttp://www.rhombus-ind.com/dlcat/app1_pas.pdf 73, ac6xg Jim, thanks for the reference. Perhaps I should have expressed myself more clearly. What I've not seen, for example, is a lumped-element analysis which takes just the coil dimensions as input, and predicts theoretically - without a lot of empirical "tweaking" - the reactance at a particular frequency; particularly a frequency close to self-resonance. There may be one out there, but I've not yet found it! In contrast, the ON4AA calculator - based on Corums' transmission-line analysis - does just that, and produces results which seem to match well the EZNEC modelling results. Regards, Steve G3TXQ EZNEC is a mathematical model just as the transmission line model is a model. EZNEC doesn't use a transmission line analog in order to reach its conclusions. If you're really interested in this subject, you have to read Schelkunoff and others who did the research on this years ago. A big, honking loading coil doesn't act much like a lumped component. It makes a pretty shabby transmission line, too. If you want to understand it, you have to study electromagnetics and approach it from that standpoint, which may not be easy. Finally, a modest question: if you have EZNEC, why would you be wasting time with something inferior? The gold standard is the gold standard. Or are you on some philosophical quest, like Cecil? 73, Tom Donaly, KA6RUH Tom,TomTom. Eznec DOES use the transmission line analogy because like Gauss it uses an abitrary border where the contents are in equilibriumn or in a state of balance where all forces are accounted for when a time varying field is applied. The same goes for a transmission line where the radiation factor is also accounted for. The radiation force losses are accounted for by the depreciating impedance with time which is also shown by the deprecating amplitude of occilation where each period loss of amplitude represents radiation energy. If the amplitude showed no change then you have a tank circuit without friction or other losses. No losses means perpetual motion and vica versa. If on Earth friction is always there which is also equal to the energy for an acceleration of a particle. On the reverse side, a deccelerating force on a particle represents kinetic energy as opposed to the potential energy supplied for radiation where the product is seen as light. As with a light bulb radiant heat is what we know as light. Just classical physics no less Art |
#5
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On Apr 23, 7:34*pm, "Tom Donaly" wrote:
Finally, a modest question: if you have EZNEC, why would you be wasting time with something inferior? The gold standard is the gold standard. Or are you on some philosophical quest, like Cecil? 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 |
#6
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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 |
#7
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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 |
#8
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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 |
#9
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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 |
#10
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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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