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Current through coils
Richard and everybody,
Let's try again from scratch, fresh, I will try to go step by step, so there are no ambiguities, twists and turns to each own's la-la land. Cecil is on well deserved break, so I am am on my own, stuck on whatever it might be. I will not continue, unless there is an agreement at each point, I go sloooow, for the benefit of mine and others who duntgetit. The "camp" think is to signify two groups claiming the different behavior of the current in the antenna loading coil. No intent to punish anyone. Please go to the new thread that I started. "Current across the antenna loading coil - from scratch" If needed I will post pictures on my web site, unless there is a way to do it here. Thank you! Yuri, K3BU.us |
Current through coils
Cecil Moore wrote:
But its propagation speed will be slower than it would be if the wire were straight. don't know if that qualifies it for a "slow wave" line or not. A velocity factor of 0.0175 for a 75m bugcatcher seems to qualify. I guess this depends on the official definition if "slow wave". It may already be taken for something specific and limited. It may be something like high frequency has come to mean an arbitrary frequency band. This group is the first place I have come across the term. |
Current through coils
Cecil Moore wrote:
John Popelish wrote: If there is a standing wave on a wire, and you have a tiny current transformer sensor you can slide along the wire, you can measure the instantaneous current (or the RMS) at any point along the wire. If the sensor sits at a single point and sees an AC current, you have no way, from this one measurement, if this current is the result of a standing wave (two oppositely traveling equal waves adding), or a single traveling wave, or any combination of traveling waves of different amplitudes. You know only the net current at that point. But if one it smart enough to slide the sensor up and down the wire and note the phase is fixed and unchanging, one knows he is dealing with a standing wave. Another point, entirely. My point is that current has a point definition, and standing wave current is certainly indistinguishable from traveling wave current, at a point. Current is current. Patterns of current over length is another subject. But you keep saying that there is something different about current in a standing wave. There isn't. It is the pattern of current distribution over time and distance along a conductor that is different with a standing wave. It is a nit, but it is snagging other people in the discussion, too, so I thought it would help to clear it up. |
Current through coils
Cecil Moore wrote:
Ian White GM3SEK wrote: - and yet again Cecil snips the statement he is replying to. For the second time in a day, I have to put back what I actually said: The human observer sees a larger picture of the whole antenna, and can choose many different ways to theorize about it. But a theory cannot be correct if it requires that components behave in different, special ways according to the way a person happens to be thinking about it at the time. If you cannot see that statement as a fundamental principle of scientific logic, then I have run out of ways to tell you. That statement was not innuendo at all. It means nothing more than what it literally says. It applies to any and every observer who attempts to construct a theory about something. Everybody is included; but nobody is exempt. It means the lumped-circuit model works where the distributed- network model fails. That is false. It is just the opposite. the distributed-network model works where the lumped-circuit model fails. No... The difference is that my views join up with the rest of human knowledge about antennas and circuit behaviour. Only up to where the coils are 15 degrees long. Then the distributed network model must be engaged to avoid blunders exactly like you and others are making. You are missing the point still. Yours don't. They fail that crucial test. Distributed network analysis fails the test??? Please provide an example. The IEEE would probably publish a paper on such. Every time I say that you are not applying established concepts and techniques correctly, you twist it to make me say I am denying the validity of the concepts themselves. For the very last time: the basic concepts are valid; but the way that you are applying them is not. Can you really and truly not see the difference? -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
This thread belongs back in the original place, so it flows in context.
Yuri Blanarovich wrote: OK, I have been accused of being wrong, claiming that current across the antenna loading coil is or can be different at its ends. No one said that. I and "my camp" say that we are seeing somewhere 40 to 60 % less current at the top of the coil, than at the bottom, in other words, significant or noticeable drop. Quit trying to make it a gang war. It is antenna theory, not a bar room brawl with a bunch of drunks. W8JI and "his camp" are claiming it can't be so, current through the coil has to be the same or almost the same, with no significant drop across the loading coil. I have no camp. You are lifting what I say out of context and deleting important things. What I say, over and over again, is I can build an inductor in a short mobile antenna that has essentially equal currents at each end. A compact loading coil of good design has this type of performance. The current taper across the inductor is not tied to the number of "electrical degrees" the inductor "replaces". It is tied to the distributed capaciatnce of the coil to the outside world in comparison to the termination impedance at the upper end of the coil. wrote in message Let's focus on one thing at a time. You claim a bug cather coil has "an electrical length at 4MHz of ~60 degrees". That concept is easily proven false, just like the claim a short loaded antenna is "90-degree resonant". Both can be shown to be nonsense pictures of what is happening. Assume I have a 30 degree long antenna. If the loading inductor is 60 electrical degrees long, I could move it anyplace in that antenna and have a 90 degree long antenna. We all know that won't happen, so what is it you are really trying to say? OK lets get me some educating here. I understand that, say quarter wave resonant vertical (say 33 ft at 40m) has 90 electrical degrees. Is that right or wrong? Right. The current distrubution on said (full size) vertical is one quarter of the wave of 360 deg. which would make it 90 degrees. Max current is at the base and then diminishes towards the tip in the cosine function down to zero. Voltage distribution is just opposite, min at the base, feed point and max at the tip. EZNEC modeling shows that to be the case too. Is that right or wrong? Right. Although the distributed capacitance can change the shape. If we stick them end to end and turn horizontal, we get dipole, which then would be 180 deg. "long" or "180 degrees resonant". If not, what is the right way? Right. If I insert the coil, say about 2/3 up (at 5 ft. from the bottom) the shortened vertical, I make the coil size, (inductance, phys. dimensions) such that my vertical will shrink in size to 8 ft tall and will resonate at 7.87 MHz. I learned from the good antenna books that this is still 90 electrical "resonant" degrees. Maximum of current is at the feed point, minimum or zero at the tip. What "good book"? It would help to see the context. None of my engineering books use electrical degrees except to describe overall antenna height or length. They might say "60 degree top loaded resonant radiator" but they don't say "60 degree tall radiator 90 degree resonant". There might be a correct context, but I can't think of one off hand. So I need an example from a textbook. If you stick those verticals (resonant) end to end and horizontal, you get shortened dipole, with current distribution equal to 180 degrees or half wave. Max current at the feed point, minima or zero at the tips. (RESONANT radiator) The current distribution would not be the same as a half wave, becuase the antenna is not 1/2 wave long. Can we describe "pieces" or segments of the radiator as having proportional amount of degrees corresponding to their physical length, when excited with particular frequency? Yes. It works fine for length. It does NOT work for loading inductors, it does not work for short antennas which have anything form a uniform distribution to triangular distribution, or any mix between including curves of various slopes. A 30 degree tall antenna with base loading simply has power factor correction at the base, provided the inductor is not a significant fraction of a wavelength long. It is a 30 degree base loaded radiator, not a 90 degree antenna. And the inductor is not 60 degrees long. 73 Tom |
Current through coils
John Popelish wrote:
. . . Of course, it can't. But a lumped LC network made of perfect, ideal components can be constructed that mimic the terminal conditions of the coil in question to any degree of accuracy desired. The caveat is that you may not explore much of a frequency range if you expect this idealized model to remain a good mimic. At another frequency, you have to rebuild it to copy the effects at that frequency. The broader the frequency range of such a model, the more complexity it must have. Yes, but you can use an arbitrarily large number of sections, each with a small amount of L and C, and mimic a transmission line to any desired degree, over any frequency range you want. And all with zero physical size in the theoretical case, and arbitrarily small physical size in the practical case. In the limit of an infinite number of sections of vanishingly small L and C each, you arrive at the general equations for a transmission line, valid at all frequencies. The point I'm trying to make is that you don't need any particular physical size or any particular length of wire to make something that behaves like a transmission line to any degree of accuracy. Roy Lewallen, W7EL |
Current through coils
Roy Lewallen wrote: The point I'm trying to make is that you don't need any particular physical size or any particular length of wire to make something that behaves like a transmission line to any degree of accuracy. and more important to this discussion, you don't need standing waves or antennas. For any given load impedance, it behaves the same way. It's a shame Cecil misses that point, and thinks it is standing waves that affect the system. 73 Tom |
Current through coils
Roy Lewallen wrote:
John Popelish wrote: . . . Of course, it can't. But a lumped LC network made of perfect, ideal components can be constructed that mimic the terminal conditions of the coil in question to any degree of accuracy desired. The caveat is that you may not explore much of a frequency range if you expect this idealized model to remain a good mimic. At another frequency, you have to rebuild it to copy the effects at that frequency. The broader the frequency range of such a model, the more complexity it must have. Yes, but you can use an arbitrarily large number of sections, each with a small amount of L and C, and mimic a transmission line to any desired degree, over any frequency range you want. And all with zero physical size in the theoretical case, and arbitrarily small physical size in the practical case. In the limit of an infinite number of sections of vanishingly small L and C each, you arrive at the general equations for a transmission line, valid at all frequencies. The point I'm trying to make is that you don't need any particular physical size or any particular length of wire to make something that behaves like a transmission line to any degree of accuracy. Oh. Then never mind. :-) |
Current through coils
John Popelish wrote:
Roy Lewallen wrote: John Popelish wrote: Roy Lewallen wrote: You keep going back to how lumped components can mimic actual distributed ones (over a narrow frequency range). I get it. I have no argument with it. But why do you keep bringing it up? We are talking about a case that is at least a border line distributed device case. I am not interested in how it can be modeled approximately by lumped, ideal components. I am interested in understanding what is actually going on inside the distributed device. I'm sorry I haven't explained this better. If we start with the inductor in, say, the example antenna on Cecil's web page, we see that the magnitude of current at the top of the inductor is less than at the bottom of the inductor. Cecil has promoted various theories about why this happens, mostly involving traveling wave currents and "replacement" of "electrical degrees" of the antenna. He and others have given this as proof that the current at the two ends of an inductor are inherently different, regardless of its physical size. My counter argument goes something like this: 1. If we substitute a lumped component network for the antenna, there are no longer traveling waves -- along the antenna at least -- and no number of "missing electrical length" for the inductor to replace. Or if there is, it's "replacing" the whole antenna of 90 degrees. Yet the currents in and out of the inductor are the same as they were before. I feel this is adequate proof of the invalidity of the "replacement" and traveling wave arguments, since I can reproduce the same results with the same inductor without either an antenna or traveling waves. This is shown in the modified EZNEC file I posted. 2. The argument that currents are inherently different at the ends of an inductor is shown to be false by removing the ground in the model I posted and replacing it with a wire. Doing so makes the currents nearly equal. 3. Arguments have then been raised about the significance of the wire and inductor length, and various theories traveling waves and standing waves within the length of the coil. Let's start with the inductor and no ground, with currents nearly equal at both ends. Now shrink the coil physically by shortening it, changing its diameter, introducing a permeable core, or whatever you want, until you get an inductance that has the same value but is infinitesimal in physical size. For the whole transition from the original to the lumped coil, you won't see any significant(*) change in terminal characteristics, in its behavior in the circuit, or the behavior of the whole circuit. So I conclude there's no significant electrical difference in any respect between the physical inductor we started with and the infinitesimally small lumped inductor we end up with. And from that I conclude that any explanation for how the original inductor worked must also apply to the lumped one. That's why I keep bringing up the lumped equivalents. We can easily analyze the lumped circuit with elementary techniques; the same techniques are completely adequate to fully analyze the circuit with real inductor and capacitance to ground. (*) I'm qualifying with "significant" because the real inductor doesn't act *exactly* like a lumped one. For example, the currents at the ends are slightly different due to several effects, and the current at a point along the coil is greater than at either end due to imperfect coupling among turns. But the agreement is close -- very much closer than the alternative theories predict (to the extent that they predict any quantitative result). The question, I think is whether large, air core coils act like a single inductance (with some stray capacitance) that has essentially the same current throughout, or is a series of inductances with distributed stray capacitance) that is capable of having different current at different points, a la a transmission line. And the answer must be that it depends on the conditions. At some frequencies, it is indistinguishable from a lumped inductance, but at other frequencies, it is clearly distinguishable. You have to be aware of the boundary case. Yes. It's a continuum, going from one extreme to the other. As Ian has pointed out several times, any theory should be able to transition from one to the other. Or start with a less simplified theory that covers all cases, so you don't have to decide when to switch tools. That's fine, too. Will Cecil's theory explain the behavior of a lumped constant circuit? Or everywhere along the transition between the physical inductor and lumped circuit I described above? The example Cecil posted on his web page was one for which the L could be modeled completely adequately as a lumped L, at least so far as its current input and output properties were concerned. (if you add to that model, the appropriate lumped capacitors at the appropriate places) No. The inductor itself can be adequately modeled as a lumped inductor without any capacitors at all. When you add ground to the model, you have to add the equivalent shunt C to the lumped model. The C isn't a property of the inductor itself; it's the capacitance between the inductor and ground. This difference is the source of confusion and misunderstanding about the current -- the current we see at the top of the inductor is the current exiting the inductor minus the current going via the shunt C to ground. It's not due to a property of the inductor itself. We're seeing the *network* current, not the inductor current. Removing the ground lets us see the inductor current by itself. Being a significant fraction of the antenna's total length, it of course does a substantial amount of radiating which a lumped model does not. Another reason to avoid that model, unless you are just looking for the least amount of math to get an approximation. But computation has gotten very cheap. The problem is that it obscures what's happening -- we can no longer easily tell which effects are due to the radiation, which are due to the capacitance, and which are inherent properties of inductance unless we separately analyze separate simplified circuits (as I did with EZNEC). And that's really what the whole disagreement has been about. Effects due to shunt capacitance have been claimed to be inherent properties of all inductors, and elaborately crafted theories developed to attempt to explain it. If all you want is numbers, they're plenty easy to get without the programmer needing to have the slightest understanding of what's happening. And he will have learned nothing he can apply to other situations. Distributed analysis is just fine, but it should predict the same coil currents with the antenna replaced by lumped components. And it should predict nearly equal currents in the inductor ends when ground is removed. And it should predict the same results when the coil and the shunt C to ground are replaced by lumped components. Because that's what really happens. My simplified lumped component analysis does all this. A rigorous solution of the fundamental equations for distributed networks does this also -- EZNEC does its calculations with just such equations and reaches the correct conclusions. But I don't believe that Cecil's theories and methods provide the correct results in all these cases. . . . A lumped inductor has no stray capacitance. Those also have to be added to the model, before the effect would mimic the real coil (neglecting radiation). By removing the ground in the model on my web site, I found that a lumped inductor mimics the real inductor very well without any C. Of course, to model an inductor close to ground requires adding a shunt C. Modeling an inductor connected to a resistor would require adding a resistor to the model. But we shouldn't confuse what the inductor is contributing to the performance of the circuit with what the other components are. And that confusion has been common here. . . . But in the real world, the capacitance is always there. It varies, depending on the location of the coil, but it never approaches zero. It can get insignificantly small, as in the modified model. But that's really beside the point. The point is that the shunt C isn't an inherent property of the inductor, and the current difference between the top and bottom of an electrically short coil is due to the current flowing through the external shunt C, however big or small it is. It's not due to waves bouncing around inside the coil or painstakingly winding their way turn by turn from one end to the other, or by any inherent and fixed property of the inductor or the antenna it's connected to. Roy Lewallen, W7EL |
Current through coils
Cecil,
You can be the master of brevity, at least when it serves your purposes. You might take a look at the entire sentence rather than clip out the portion that sets the context. "Certainly these consolidating functions are useful for a general overview, but how can you learn anything about the details of a complex system by averaging and netting?" By the way, "steady-state analysis" has nothing whatsoever to do with averaging. Steady-state simply means the system does not have a defined starting time. There are no remaining startup transients. It cannot be determined whether operation started one second ago or one year ago. Steady-state does not mean DC, averaged, or RMS. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: ... how can you learn anything about the details of a complex system by averaging and netting? Because the conservation of energy principle is about averaging and netting. Because steady-state analysis is about averaging and netting. Because engineers have 200 years of averaging and netting behind us to prove that it works. When you try to track an individual electron's velocity and position, guess what happens? |
Current through coils
Roy Lewallen wrote:
John Popelish wrote: You keep going back to how lumped components can mimic actual distributed ones (over a narrow frequency range). I get it. I have no argument with it. But why do you keep bringing it up? We are talking about a case that is at least a border line distributed device case. I am not interested in how it can be modeled approximately by lumped, ideal components. I am interested in understanding what is actually going on inside the distributed device. I'm sorry I haven't explained this better. If we start with the inductor in, say, the example antenna on Cecil's web page, we see that the magnitude of current at the top of the inductor is less than at the bottom of the inductor. Cecil has promoted various theories about why this happens, mostly involving traveling wave currents and "replacement" of "electrical degrees" of the antenna. He and others have given this as proof that the current at the two ends of an inductor are inherently different, regardless of its physical size. I agree up till you add, "regardless of physical size". I have seen him talk only about large air core space wound coils. I came to the discussion late, but this is what I have seen. My counter argument goes something like this: 1. If we substitute a lumped component network for the antenna, there are no longer traveling waves -- along the antenna at least -- and no number of "missing electrical length" for the inductor to replace. Or if there is, it's "replacing" the whole antenna of 90 degrees. Yet the currents in and out of the inductor are the same as they were before. I feel this is adequate proof of the invalidity of the "replacement" and traveling wave arguments, since I can reproduce the same results with the same inductor without either an antenna or traveling waves. This is shown in the modified EZNEC file I posted. But what is the need for such an argument? Just to prove that lumped component networks can model real, distributed things? I get that. As I see Cecil's point (and I hate to say this with him absent), it is that real, large coils with all their poor turns coupling and stray capacitance both turn to turn and more important, to ground, take a lot of those lumped components to model, accurately, but only their own self, described by distributed network concepts to model, accurately. 2. The argument that currents are inherently different at the ends of an inductor is shown to be false by removing the ground in the model I posted and replacing it with a wire. Doing so makes the currents nearly equal. But the ground is there, in the application under discussion. All components act differently if you connect them to something else. This coil is connected to ground by its capacitance. 3. Arguments have then been raised about the significance of the wire and inductor length, and various theories traveling waves and standing waves within the length of the coil. Let's start with the inductor and no ground, with currents nearly equal at both ends. Now shrink the coil physically by shortening it, changing its diameter, introducing a permeable core, or whatever you want, until you get an inductance that has the same value but is infinitesimal in physical size. For the whole transition from the original to the lumped coil, you won't see any significant(*) change in terminal characteristics, in its behavior in the circuit, or the behavior of the whole circuit. Sounds reasonable to me. But it is not the application in question. So I conclude there's no significant electrical difference in any respect between the physical inductor we started with and the infinitesimally small lumped inductor we end up with. And from that I conclude that any explanation for how the original inductor worked must also apply to the lumped one. But only if you reduce the capacitance to ground to a low enough value. That's why I keep bringing up the lumped equivalents. We can easily analyze the lumped circuit with elementary techniques; the same techniques are completely adequate to fully analyze the circuit with real inductor and capacitance to ground. (*) I'm qualifying with "significant" because the real inductor doesn't act *exactly* like a lumped one. For example, the currents at the ends are slightly different due to several effects, and the current at a point along the coil is greater than at either end due to imperfect coupling among turns. But the agreement is close -- very much closer than the alternative theories predict (to the extent that they predict any quantitative result). I have no argument with any of that. (snip) Or start with a less simplified theory that covers all cases, so you don't have to decide when to switch tools. That's fine, too. Will Cecil's theory explain the behavior of a lumped constant circuit? Or everywhere along the transition between the physical inductor and lumped circuit I described above? Distributed network theory includes the possibility of lumped components, it is just not limited to them. (snip) (if you add to that model, the appropriate lumped capacitors at the appropriate places) No. The inductor itself can be adequately modeled as a lumped inductor without any capacitors at all. Not if it is located in close proximity to ground, as this coil in question is located. It does not act like any kind of pure inductance, but as a network that contains some inductance and also some other effects. When you add ground to the model, you have to add the equivalent shunt C to the lumped model. The C isn't a property of the inductor itself; it's the capacitance between the inductor and ground. That is a very strange statement to my mind. Stray capacitance is an unavoidable effect that any real inductor in any real application will have as a result of it having non zero size. A thing made of wire that takes up space has inductive character and capacitive character, and transmission line character, and loss, all rolled into one. You can set the situation up that it finds itself in, is that some of those properties not very significant, but that are all part of the effect of a real, physical inductor. I don't understand why you keep pretending that these non ideal effects are the fault of something else. They are a result of the device taking up space and being made of metal. This difference is the source of confusion and misunderstanding about the current -- the current we see at the top of the inductor is the current exiting the inductor minus the current going via the shunt C to ground. It's not due to a property of the inductor itself. We're seeing the *network* current, not the inductor current. I agree. But a large, air core, spaced turn coil is a network, not a pure inductance. This is just reality. Removing the ground lets us see the inductor current by itself. Or, emphasizes that particular aspect of its nature. Another reason to avoid that model, unless you are just looking for the least amount of math to get an approximation. But computation has gotten very cheap. The problem is that it obscures what's happening -- we can no longer easily tell which effects are due to the radiation, which are due to the capacitance, and which are inherent properties of inductance unless we separately analyze separate simplified circuits (as I did with EZNEC). And that's really what the whole disagreement has been about. Effects due to shunt capacitance have been claimed to be inherent properties of all inductors, and elaborately crafted theories developed to attempt to explain it. If all you want is numbers, they're plenty easy to get without the programmer needing to have the slightest understanding of what's happening. And he will have learned nothing he can apply to other situations. Distributed analysis is just fine, but it should predict the same coil currents with the antenna replaced by lumped components. And it should predict nearly equal currents in the inductor ends when ground is removed. And it should predict the same results when the coil and the shunt C to ground are replaced by lumped components. Because that's what really happens. My simplified lumped component analysis does all this. A rigorous solution of the fundamental equations for distributed networks does this also -- EZNEC does its calculations with just such equations and reaches the correct conclusions. But I don't believe that Cecil's theories and methods provide the correct results in all these cases. (snip) Sorry, here is where I have to withdraw. I can't say what Cecil is thinking. |
Current through coils
John Popelish wrote: But what is the need for such an argument? Just to prove that lumped component networks can model real, distributed things? I get that. As I see Cecil's point (and I hate to say this with him absent), it is that real, large coils with all their poor turns coupling and stray capacitance both turn to turn and more important, to ground, take a lot of those lumped components to model, accurately, but only their own self, described by distributed network concepts to model, accurately. Cecil's point is rather obscure, but as I read it Cecil thinks the ONLY way to model a loaded antenna is through reflected wave theory. As I understand what Cecil writes, he seems to be saying if we use a current meter we cannot measure current. If we look at an inductor's properties he seems to say they change in the presence of standing waves. He also seems to be saying a loading inductor replaces a certain number of electrical degrees through some reflection property. What most others seem to be saying is an inductor is an inductor. It behaves the same way and has the same characteristics no matter how it is used, so long as we don't change the displacement currents by varying capacitive coupling to surroundings. That is where the difference is. I can easily build a loading coil that has no appreciable change in current from end-to-end. My measurements of typical loading coils shows it is the ratio of load (termination) impedance to capacitance to the outside world that controls any difference in current, and not the "electrical degrees" the coil replaces. It is also not the reflected waves that cause the unequal currents, but rather the fact the inductor has distributed capacitance to earth or other objects besides the coil. Capacitance from the coil to itself won't cause these problems. The change in phase of current at each end of a coil would depend heavily on stray C of the coil to the outside world as compared to reactance of the coil, and it would also depend on less than perfect flux linkage across the inductor. I measured a typical inductor and found it did have more phase delay in current at each terminal than the actual spatial length of the coil form would indicate. I measured a delay about equal to double the length of the 10 inch coil form length. If the inductor was perfect, the delay would be about equal to light speed across the length of the inductor form. The only thing in all of this I can't find agreement with is what Cecil is saying. I'm not disputing currebnt can be different, and phase can be different. What I am disputing are Cecil's claims that an inductor behaves differently in an antenna than in a lumped system that represents the antenna, and that the cause of inequality in currents or phase delay is caused by reflected waves and cannot be understood without applying reflected wave theory. In my experience, either lumped circuits or reflected waves will work IF applied correctly. This is my take of the disagreement. 73 Tom |
Current through coils
On Fri, 24 Mar 2006 20:13:26 -0500, John Popelish
wrote: He and others have given this as proof that the current at the two ends of an inductor are inherently different, regardless of its physical size. I agree up till you add, "regardless of physical size". I have seen him talk only about large air core space wound coils. I came to the discussion late, but this is what I have seen. Hi John, One of the problems is the thread discussion is freely mixed with practical observations and theoretical arguments - these can clash, especially when mixed indiscriminately to prove one point. First, several years ago, came the shocking observation that the current into a coil is not the same as the current out of it. Somewhere along the debate, this practical measurement was then expressed to be in conflict with Kirchhoff's theories. However, Kirchhoff's current law is for currents into and out of the same point intersection, not component. The association with a point is found in that the "lumped" inductance is a dimensionless load. The association with Kirchhoff was strained to fit the load to then condemn the load instead of simply rejecting that failed model and using the correct one. The problem came from incorrectly specifying the coil in EZNEC which offers a coil generator (inductor) in the wires table as well as a coil specification (inductance) in the loads table. This shocking difference between model and observation would have been easily resolved by simply using the coil generator (inductor) in place of the lumped equivalent (inductance). How do you know when you've made a mistake in application? You do two designs and compare each to what nature provides. You discard the model that does not conform to nature. Want to know what the difference is between the two (the good and the bad design) at the far receiver? ±.32dB Hence the name of my thread "Current through coils - BFD." ....snip But the ground is there, in the application under discussion. All components act differently if you connect them to something else. This coil is connected to ground by its capacitance. Roy's point is that the proposed "theory," as Ian has also pointed out, has to correctly answer all scenarios, not just one. We don't have enough shelf space in libraries that prove the resistance of each resistor constructed - one formula does quite well for 99.999% of them, and a couple more formulas for those that don't (and those new formulas will give the same answer for the first 99.999% as well). When you add ground to the model, you have to add the equivalent shunt C to the lumped model. The C isn't a property of the inductor itself; it's the capacitance between the inductor and ground. That is a very strange statement to my mind. Stray capacitance is an unavoidable effect that any real inductor in any real application will have as a result of it having non zero size. You are mixing an observational fact with a theoretical statement. The lumped model contains ONLY inductance, to make it conform to nature, as Roy is doing here, you have to add in all the nasty bits. OR Build a helix (inductor) in the wires table. A thing made of wire that takes up space has inductive character and capacitive character, and transmission line character, and loss, all rolled into one. These are all properties that reside in a helix (inductor) constructed in the wires table. Some of these properties (like inductance) also reside in the load table, but not the capacitance to earth. If it matters, it is up to you to make the correct choice. ....snip Well, the rest was more conflict between theory and practice that is and has been resolvable for a long time. Even the conflict is separable. For those who persist in making poor choices, they will always have either a problem with a model, or the genesis of a new theory, or rattle on beyond 500 posts - sometimes all three. 73's Richard Clark, KB7QHC |
Current through coils
Thanks, Tom and Richard. I've said what I want to say in just about
every way I can possibly think of, and without a great deal of success in communicating to John what I mean. I hope you'll have better luck -- I've run out of different ways to say it. I hope some of the readers, at least, have understood what I've been saying. Roy Lewallen, W7EL |
Current through coils
Roy Lewallen wrote:
Thanks, Tom and Richard. I've said what I want to say in just about every way I can possibly think of, and without a great deal of success in communicating to John what I mean. I hope you'll have better luck -- I've run out of different ways to say it. I hope some of the readers, at least, have understood what I've been saying. I want to thank you for the efforts and patience with me. I hope my insight into the operation of large air core inductors has improved because of it. Please do not think that I am taking up a defense of everything Cecil thinks (since I am sure I don't know what that is, anyway), but just found this technical discussion stimulating. It isn't often I get to talk with such experienced people without getting dismissed or ignored. It has been useful to me. I can't think of a better compliment to offer. |
Current through coils
Tom, the W8JI one, wrote, among other things,
"Capacitance from the coil to itself won't cause these problems. The change in phase of current at each end of a coil would depend heavily on stray C of the coil to the outside world as compared to reactance of the coil, and it would also depend on less than perfect flux linkage across the inductor." I've lost track of exactly what "these problems" are, but I was wondering about the "and it would also depend on less than perfect flux linkage across the inductor" part. To help resolve that, I did a Spice simulation; I modelled a transmission line with ten "L" sections cascaded. Each was 1uH series, followed by 100pF shunt to ground. I put a 100 ohm load on one end and fed the other end with a 2.5MHz sine wave with 100 ohms source resistance. Sqrt(LC) is 10 nanoseconds per section, so I expect 100 nanoseconds total delay, or 90 degrees at 2.5MHz. That's what I saw. Then I added unity coupling among all the coils, and to keep the same net inductance, I decreased each inductor to 100nH. The result was STILL very close to a 90 degree phase shift, with a small loss in amplitude. In each case, the current in each successive inductor shifts phase by about 1/10 the total. Although the simulation is less than a perfect match to a completely distributed system with perfect flux linkage (and just how you do that I'm not quite sure anyway...), but it's close enough to convince me that perfect flux linkage would not prevent behaviour like a transmission line, given the requisite distributed capacitance. (That was from a "transient" simulation, 10usec after startup so it should be essentially steady-state; but I'll probably play with an AC sweep of both cases as I find time.) Cheers, Tom |
Current through coils
K7ITM wrote: cascaded. Each was 1uH series, followed by 100pF shunt to ground. I put a 100 ohm load on one end and fed the other end with a 2.5MHz sine wave with 100 ohms source resistance. Sqrt(LC) is 10 nanoseconds per section, so I expect 100 nanoseconds total delay, or 90 degrees at 2.5MHz. That's what I saw. Then I added unity coupling among all the coils, and to keep the same net inductance, I decreased each inductor to 100nH. The result was STILL very close to a 90 degree phase shift, with a small loss in amplitude. In each case, the current in each successive inductor shifts phase by about 1/10 the total. Although the simulation is less than a perfect match to a completely distributed system with perfect flux linkage (and just how you do that I'm not quite sure anyway...), but it's close enough to convince me that perfect flux linkage would not prevent behaviour like a transmission line, given the requisite distributed capacitance. Thanks Tom, That's very interesting. My thought is the difference in phase-of-current at each of the inductor would be affected by mutual coupling, with perfect coupling preventing phase differences in current, but maybe that is shortsighted. I'll have to think about that a while and how it might affect what I am saying. 73 Tom |
Current through coils
The phase shift in degrees, along a coil or any other sort of
transmission line, is fixed rigidly by its physical dimensions and test frequency. Phase shift is entirely independent of the way it is used, the circuit it is in and the circuit currents which flow. ---- Reg. G4FGQ |
Current through coils
Of course, that's blatantly false, taken literally. A 2" diameter 10"
long solenoid coil coaxially inside a 2.5" ID grounded conductive tube will not have the same phase shift as the identical coil inside a 5" ID grounded conductive tube, and neither will behave the same as the same coil included as a loading coil in Cecil's mobile antenna. It won't even have the same inductance in each case. Before you say, "Give us a break, Tom. Of course it won't and clearly that's not what was meant," just consider how literally both the posters and the lurkers here take things. AND in fact, as shown in the simulation I just reported on, the coupling between that coil and the magnetic fields of other nearby components does affect the performance of that coil. In general, when the fields, electric and magnetic, around any component interact with their environment, a change in that environment will change the behaviour of the component. Thankfully, we have a lot of components where that effect is minimal at the frequencies of interest, but we do need to take note of cases where the effect is important. I DAILY work with tiny components that DO behave differently, depending on their environment. At several GHz, seemingly small couplings can be very important. Cheers, Tom |
Current through coils
K7ITM wrote:
(snip) To help resolve that, I did a Spice simulation; I modelled a transmission line with ten "L" sections cascaded. Each was 1uH series, followed by 100pF shunt to ground. I put a 100 ohm load on one end and fed the other end with a 2.5MHz sine wave with 100 ohms source resistance. Sqrt(LC) is 10 nanoseconds per section, so I expect 100 nanoseconds total delay, or 90 degrees at 2.5MHz. That's what I saw. Then I added unity coupling among all the coils, and to keep the same net inductance, I decreased each inductor to 100nH. The result was STILL very close to a 90 degree phase shift, with a small loss in amplitude. In each case, the current in each successive inductor shifts phase by about 1/10 the total. Although the simulation is less than a perfect match to a completely distributed system with perfect flux linkage (and just how you do that I'm not quite sure anyway...), but it's close enough to convince me that perfect flux linkage would not prevent behaviour like a transmission line, given the requisite distributed capacitance. (That was from a "transient" simulation, 10usec after startup so it should be essentially steady-state; but I'll probably play with an AC sweep of both cases as I find time.) I look forward to your tests with turn-to-turn capacitance added to the model as well. It will no longer match the 100 ohm source and load over as wide a frequency range, but it will look closer to the real thing above the self resonant frequency. You may be able to measure the phase shift versus frequency up to resonance, and test Cecil's idea that you can measure the self resonant frequency and use that to predict the phase shift at much lower frequencies. |
Current through coils
Richard Clark wrote:
First, several years ago, came the shocking observation that the current into a coil is not the same as the current out of it. Somewhere along the debate, this practical measurement was then expressed to be in conflict with Kirchhoff's theories. However, Kirchhoff's current law is for currents into and out of the same point intersection, not component. The association with a point is found in that the "lumped" inductance is a dimensionless load. The association with Kirchhoff was strained to fit the load to then condemn the load instead of simply rejecting that failed model and using the correct one. So much has been said in this debate - and this is at least the third or fourth re-make of the whole show - that I honestly cannot remember if the exact words that Richard reports were ever used. If they were, then they were excessively condensed, skipping some essential steps in the explanation. Both sides of the debate have often been guilty of skipping details that seemed "obvious" (at least to their way of thinking) in order to get to their main point. So please let me try to respond to Richard's criticism above. Since I don't want to skip anything this time, this is going to take a little longer. If there's anything that someone doesn't agree with, please comment... but please read the whole thing first. Many of the problems with this debate are because people start to throw in comments before finding out where the original poster is heading. This destroys any kind of connected thinking, and reduces the "debate" into a series of disconnected nit-picks. The main electrical property of the thing we call a "coil" or "inductor" is - obviously - inductance. But a real-life coil has many other properties as well, and these complicate the picture. If we're going to understand loading coils at all, we first need to strip away all the complications, and understand what loading by pure inductance would do. Then we can put back the complications and see what difference they make. If we want to understand real-life loading coils, it's absolutely vital to understand which parts of the coil's behaviour are due to its inductance, and which parts are due to other things. Please have patience about this. If we cannot even agree what pure inductance does, then this debate will run forever... From the beginning, then: "Lumped" inductance is another name for the pure electrical property of inductance, applied at a single point in a circuit. It has none of the complications of a real-life coil: no physical size, no distributed self-capacitance, and no external electric or magnetic fields. Its only connections with the antenna are through its two terminals. Lumped inductance is just inductance and nothing else. Unlike capacitance, inductance has NO ability to store charge. If you push an electron into one terminal of a pure inductance, one electron must instantaneously pop out from the other terminal. If there was any delay in this process, it would mean that charge is being stored somewhere... and then we'd no longer be talking about pure inductance [1]. The inability to store charge means there can be no difference between the instantaneous currents at the two terminals of a lumped/pure inductance. Any difference in amplitude or phase at a given instant would mean that charge is being stored or borrowed from some other time in the RF cycle... which inductance cannot do. There is some kind of difference in phase and amplitude in the voltage between its two terminals, but not in the current. Therefore any difference in currents between the two ends of a real-life coil are NOT due to its inductance. They come from those OTHER properties that make a real-life coil more complicated. But let's stay with loading by pure lumped inductance for a little longer, and look at a centre-loaded whip. The loading inductance is responsible for almost all the features of the voltage and current profiles along the antenna. Starting at the bottom (the feedpoint), voltages are low and currents are high, so the feedpoint impedance is low. Going up the lower part of the whip, the magnitudes of the voltage and current remain almost constant until we meet the loading inductance. As we have seen, if the whip is loaded by pure inductance only, there is no change in current between the two terminals of the inductance - but there's a big step increase in voltage. At the upper terminal, the current is the same but the voltage is very high, so we're into a much higher-impedance environment. As we go further up towards the top of the whip, current magnitude has to taper off to zero at the very top. This also means that the voltage magnitude has to increase even more as we approach the top of the whip. Single-point loading by pure inductance has thus created almost all the major features that we see in a practical centre-loaded whip - particularly the big step change in voltage across the loading coil. What we don't see in a practical antenna are exactly equal current magnitudes and zero phase shift between the terminals of a real-life loading coil - but that is ONLY because a real-life coil is not a pure inductance. The harder we try to reach that ideal (by winding the coil on a high-permeability toroidal core which confines the external fields and allows the whole thing to become very small), the closer the currents at the bottom of the coil come to being equal. Solid theory and accurate measurements come together to support each other. The only gap between theory and practice is due to our inability to construct a pure inductance that has no other complicating properties. If we can agree about pure inductive loading, we all have a firm place to stand. Then we can then put back those "other" complicating properties of a real-life loading coil, and see what difference they make. [1] This principle of "conservation of charge" is also the underlying principle of Kirchhoff's current law. If you connect three ordinary wires together, the current flowing into the junction from one wire must be exactly and instantaneously balanced by the currents flowing in or out on the other two wires. If this was not so, there would have to be some means of adding, storing or losing electrons at the junction... which contradicts our initial assumption of three simple wires with no special properties. It is not strictly accurate to say that Kirchhoff's current law applies to pure inductance, but the underlying principle of "conservation of charge" does apply. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Ian White GM3SEK wrote:
(snip everything but context) From the beginning, then: "Lumped" inductance is another name for the pure electrical property of inductance, applied at a single point in a circuit. It has none of the complications of a real-life coil: no physical size, no distributed self-capacitance, and no external electric or magnetic fields. Its only connections with the antenna are through its two terminals. Lumped inductance is just inductance and nothing else. (snip) Single-point loading by pure inductance has thus created almost all the major features that we see in a practical centre-loaded whip - particularly the big step change in voltage across the loading coil. (snip) If we can agree about pure inductive loading, we all have a firm place to stand. Then we can then put back those "other" complicating properties of a real-life loading coil, and see what difference they make. I see nothing to quibble over yet. :-) |
Current through coils
Patterns of current over length is another subject. But you keep saying
that there is something different about current in a standing wave. There isn't. Do you really think that func(kx)*func(wt) is the same thing as func(kx +/- wt)? If so, time to dust off the old math books. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
The point I'm trying to make is that you don't need any particular physical size or any particular length of wire to make something that behaves like a transmission line to any degree of accuracy. Are you admitting that a 75m bugcatcher behaves like a transmission line? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
EVERYTHING has Inductance, Capacitance and Resistance, and therefore
behaves as a transmission line. ---- Reg, G4FGQ |
Current through coils
Cecil Moore wrote:
John Popelish wrote: Cecil Moore wrote: John Popelish wrote: If the sensor sits at a single point and sees an AC current, you have no way, from this one measurement, if this current is the result of a standing wave (two oppositely traveling equal waves adding), or a single traveling wave, or any combination of traveling waves of different amplitudes. You know only the net current at that point. But if one it smart enough to slide the sensor up and down the wire and note the phase is fixed and unchanging, one knows he is dealing with a standing wave. Another point, entirely. My point is that current has a point definition, and standing wave current is certainly indistinguishable from traveling wave current, at a point. Current is current. Patterns of current over length is another subject. But you keep saying that there is something different about current in a standing wave. There isn't. Do you really think that func(kx)*func(wt) is the same thing as func(kx +/- wt)? If so, time to dust off the old math books. ( I restored some context) func(kx)*func(wt) describes the instantaneous current if you pick a point along dimension, x, and a moment in time, t. It is a map of the pattern of current over these two dimensions. func(kx +/- wt) describes a different pattern of the instantaneous current if you pick a point along dimension, x, and a moment in time, t. If you put a tiny current transformer around some point of the conductors in question, (pick an x) and watch the pattern of current through time (without comparing the phase to any reference) you will see a sinusoidal current variation for both the standing and traveling wave cases. The amplitude will vary in a different way, over x, for the traveling and standing wave cases. If you include comparing the phase of sinusoidal current cycle you see, to a reference phase, that will also vary in a different way over x, for the traveling and standing wave cases. But regardless, at a point (any particular x) the pattern of current variation as time passes, will be a sinusoid, in either case. There is no difference in kind of current you would measure. The pattern of how this sinusoidal current varies in both phase and magnitude is very different in the two cases (standing and traveling waves), but you need both a phase reference and multiple locations to see the differences. The the definition of the word "current", in simplest form, is, the rate of charge movement past a point at some moment in time. An extension of this instantaneous and point definition might include a sinusoidal cyclic variation through time, by adding a frequency, phase and amplitude, to specify a common pattern of current over time, but still at a point. Adding in an additional function of position allows the extension of this definition of current over time to also include spacial variation of the time dependent pattern. But if you say the words "the current is different", and don't include a lot of additional verbiage to indicate that you are talking about the two dimensional pattern of the variation of current over time and location, some people are going to misunderstand you and argue based on picturing another definition of what might be legitimately meant by the word, "current". I made it clear what definition I was using for the word "current" (the instantaneous point definition) and you are arguing with me, while using some different definition. I realize that I am being pedantic, here, and stating the painfully obvious. But if your goal is to have other minds synchronize with the abstract thoughts rippling through your mind, you have to be pedantic. If you are just using this topic to argue, because you enjoy argument, then never mind. |
Current through coils
John Popelish wrote:
The pattern of how this sinusoidal current varies in both phase and magnitude is very different in the two cases (standing and traveling waves), but you need both a phase reference and multiple locations to see the differences. Exactly! And the multiple locations are available for us to measure. Since you like handicaps so much, how about just plucking out your eyeballs and chopping off your hands? :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John P. wrote, among other things,
"The pattern of how this sinusoidal current varies in both phase and magnitude is very different in the two cases (standing and traveling waves), but you need both a phase reference and multiple locations to see the differences. " Do you really need the phase reference? Traditionally (since the beginning of measuring them, and sometimes still today), standing waves on a uniform transmission line have been measured by finding a point of minimum amplitude (as measured by voltage, or alternatively by current) and a point of maximum amplitude, with no reference to phase. In fact, SWR was reasonably defined as the ratio of max/min amplitudes. If you know that the wave you're observing is a sinusoid and you have min and max amplitudes along the line, then you can resolve the wave into two travelling-wave amplitudes; you won't know which is which but you will know the two amplitudes. If there is but one source in the system, it's reasonable to think that the higher amplitude travelling wave was the one coming from the direction of that source. In fact, you don't even need to find the minimum and the maximum points. Again, given sinusoidal excitation and a uniform line, some small set of points with accurate amplitude measurement at each will suffice, since they will uniquely determine the amplitudes of the two waves and the line attenuation. You would have to know the spacing of the points and that they were dense enough that there is not a spacial aliasing problem (points distributed over more than 1/4 wavelength...). It's common to think of a standing wave as the result of two travelling waves, one in each direction, but another way to think of a standing wave pattern is as a pure standing wave plus a pure travelling wave. The minimum-amplitude represents the amplitude of the travelling-wave portion. The difference between max and min represents the amplitude of the standing wave portion. For some folk, it's enlightening to see an animation of the waves for several different values of SWR. Cheers, Tom |
Current through coils
K7ITM wrote:
John P. wrote, among other things, "The pattern of how this sinusoidal current varies in both phase and magnitude is very different in the two cases (standing and traveling waves), but you need both a phase reference and multiple locations to see the differences. " Do you really need the phase reference? Traditionally (since the beginning of measuring them, and sometimes still today), standing waves on a uniform transmission line have been measured by finding a point of minimum amplitude (as measured by voltage, or alternatively by current) and a point of maximum amplitude, with no reference to phase. In fact, SWR was reasonably defined as the ratio of max/min amplitudes. (snip) What I was trying to say is that to completely see (measure) all the differences between the current pattern in a standing wave versus a traveling wave (or any combination of traveling waves of different magnitudes in opposite directions, with or without losses, especially when there are discontinuities in the conductor, like loading coils) those observations would include phase versus position. In many practical cases, you can infer what you need to know about the two traveling waves by just taking amplitude measurements, as you suggest. |
Current through coils
K7ITM wrote:
In fact, you don't even need to find the minimum and the maximum points. Again, given sinusoidal excitation and a uniform line, some small set of points with accurate amplitude measurement at each will suffice, since they will uniquely determine the amplitudes of the two waves and the line attenuation. You would have to know the spacing of the points and that they were dense enough that there is not a spacial aliasing problem (points distributed over more than 1/4 wavelength...). Which points out, once again, that the phase information in a standing wave is contained in the amplitude, not in the phase. W7EL measured the *phase* of the standing-wave current which is known not to contain any information as it is close to unchanging all along a 1/2WL dipole or 1/4WL monopole. Yet he reported it as meaningful. So far, nobody has made meaningful phase shift measurements through a loading coil. It's common to think of a standing wave as the result of two travelling waves, one in each direction, but another way to think of a standing wave pattern is as a pure standing wave plus a pure travelling wave. One cannot get away from the fact that the pure standing wave is the superposition of equal amplitude traveling waves flowing in opposite directions. Some part of the forward traveling wave must be allocated to the standing wave function. That part of the traveling wave transfers no energy. |Ifor| - |Iref| = |Ifor'| the part of the forward traveling wave that is transferring energy. |Ifor| - |Ifor'| = |Ifor''| = |Iref| the part of the forward traveling wave that is contributing to the pure standing wave and transferring no energy. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
wrote: I'll have to think about that a while and how it might affect what I am saying. (snip) So here's the EZNEC example and an experiment that any properly equipped person can duplicate. That includes you and W7EL. I took W7EL's EZNEC file and changed wire #203 from 0.25' to 31.25'. At the 'tip' of the antenna, I installed a 439.2 ohm load that turns the antenna into a 90 degree long *traveling-wave* antenna. Note that the current magnitude at the top of the coil is identical to the current magnitude through the load resistor. The load resistor's value is very close to the calculated Z0 of the 31' #16 wire two feet above ground, using the formula for a single wire transmission line above ground. The graphic is at http://www.qsl.net/w5dxp/test316y.GIF The EZNEC file can be downloaded from: http://www qsl.net/w5dxp/test316y.EZ (snip) Excellent! Can you use this example, with varying frequency to explore your assertion that the time delay (frequency times phase shift) of the coil varies little over a significant range of frequencies up to self resonance, and that that delay is about 1/4 cycle of the self resonant frequency? A graph of delay versus frequency would be useful. It should show over what frequency range the coil acts mostly like a transmission line and where it acts mostly like something else (i.e. inductor, parallel resonant tank). |
Current through coils
EVERYTHING????
I thought there is/was a restriction that "Everything" must include "a significant portion of a wavelength". :-) Reg Edwards wrote: EVERYTHING has Inductance, Capacitance and Resistance, and therefore behaves as a transmission line. ---- Reg, G4FGQ |
Current through coils
John Popelish wrote:
Can you use this example, with varying frequency to explore your assertion that the time delay (frequency times phase shift) of the coil varies little over a significant range of frequencies up to self resonance, and that that delay is about 1/4 cycle of the self resonant frequency? I will do that when my energy level returns after getting home at 2 am this morning. Note that anyone can download the EZNEC file from http://www.qsl.net/w5dxp/test316y.EZ A graph of delay versus frequency would be useful. It should show over what frequency range the coil acts mostly like a transmission line and where it acts mostly like something else (i.e. inductor, parallel resonant tank). This coil, operated below its self-resonant frequency, has phase shift of 15.68 degrees or ~0.044 wavelength (delay of 7.4 nS). Dr. Corum says anything over 15 degrees requires the distributed network model. 15 degrees will transform 50 ohms to 54+j120 ohms, causing SWR to be erroneously reported as 7:1 instead of 1:1. That sounds like too large an error to me. Since the lumped-circuit model assumes a delay of zero, i.e. faster than light, seems the use of the lumped-circuit model results in 100% error, or infinite error if one calculates it the other way. :-) BTW, one of the principles on the other side of the argument sent me a file with a worm in it. I guess he wanted to extend the silence caused by my trip by bringing down my computer. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
This coil, operated below its self-resonant frequency, has phase shift of 15.68 degrees or ~0.044 wavelength (delay of 7.4 nS). Dr. Corum says anything over 15 degrees requires the distributed network model. 15 degrees will transform 50 ohms to 54+j120 ohms, causing SWR to be erroneously reported as 7:1 instead of 1:1. That sounds like too large an error to me. Since the lumped-circuit model assumes a delay of zero, i.e. faster than light, seems the use of the lumped-circuit model results in 100% error, or infinite error if one calculates it the other way. :-) Not if the lumped inductor model includes lumps of capacitance that represent the strays to ground. Lumped LC networks exhibit phase shift, also. BTW, one of the principles on the other side of the argument sent me a file with a worm in it. I guess he wanted to extend the silence caused by my trip by bringing down my computer. Never blame malice when ignorance will suffice. Even if you are wrong, you will sleep better. |
Current through coils
On Sun, 26 Mar 2006 15:12:23 GMT, Cecil Moore
wrote: Don't you find it strange that all the wire in the system occupies 90.01 - 15.68 = 74.33 degrees? Strange? 1. The current distribution shown on the web is different than the current distribution shown in the model; 2. -4.91 + -20.59 + -90.01 = -115.51 is different than 90.01 - 15.68 = 74.33 3. The coil Vf shown on the web is 0.1375 is different than eq (32) = 0.0078 4. refuting your own references (Corum²). not strange at all. |
Current through coils
John Popelish wrote:
Can you use this example, with varying frequency to explore your assertion that the time delay (frequency times phase shift) of the coil varies little over a significant range of frequencies up to self resonance, and that that delay is about 1/4 cycle of the self resonant frequency? Please don't put words in my mouth. What I have previously said is that the delay can be *ROUGHLY* calculated using the self- resonant frequency. I said something about +/- 50% accuracy. Here's what EZNEC reports as the phase shift through the coil in the traveling wave antenna previously tested at 5.89 MHz. 5.5 MHz: 14.1 deg, 5.89 MHz: 15.7 deg, 6 MHz: 16.2 deg, 7 MHz: 21.4 deg, 8 MHz: 29.5 deg, 9 MHz: 45.9 deg, 10 MHz: 89 deg, 11 MHz: 141.4 deg, 12 MHz: 163.0 deg, 13 MHz: 172.3 deg, 13.7 MHz: 183.82 deg. The linear delay calculation is off by 59%, not too far from my 50% rough estimate. Please note that the above values of delays reported by EZNEC are nowhere near the 3 nS measured by W8JI in the standing wave environment. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Sun, 26 Mar 2006 17:21:17 GMT, Cecil Moore
wrote: I said something about +/- 50% accuracy. The linear delay calculation is off by 59%, not too far from my 50% rough estimate. error is growing faster than the national debt. ;-) nowhere near the 3 nS measured by W8JI in the standing wave environment. On Sun, 26 Mar 2006 16:39:57 GMT, Cecil Moore wrote: delay of 7.4 nS Hmm, giving Tom the same grace of 59% reveals that the figures above, 7.4nS ±59% (4.4 - 11.77) and 3nS ±59% (1.77 - 4.77) overlap. The thing about error (especially when it is in a growth mode indicating loss of control over the experiment) is that you don't know where within the band of possible values that the actual value resides. So, comparing the one to the other, making a claim that the other is invalid, must necessarily invalidate both as they are convergent. Such is the legacy of poor quality control. It might be tempting to perform a Hail Mary save, by suddenly declaring they are both right. :-) but at 59% error, we can all agree that's a fantasy. Stretching your tolerance for error to fit your argument can lead to any conclusion. |
Current through coils
Richard Clark wrote:
1. The current distribution shown on the web is different than the current distribution shown in the model; Don't you know how to turn on the 'Current Phase' option when displaying EZNEC results. Do you need a tutorial? 2. -4.91 + -20.59 + -90.01 = -115.51 is different than 90.01 - 15.68 = 74.33 The phase of the source is referenced at zero degrees. The currents along the antenna are lagging the source current. -4.91 deg is the phase of the current at the bottom of the coil. -20.59 deg is the phase of the current at the top of the coil. -90.01 deg is the phase of the current at the end of the antenna. Trying to add those phases shows a lot of ignorance. 3. The coil Vf shown on the web is 0.1375 is different than eq (32) = 0.0078 Sorry, you're wrong. eq(32) for this coil yields a VF of ~0.033 which Dr. Corum claims to be accurate within about 10%. The coil VF on the web is at 5.89 MHz, *NOT* at the self-resonant frequency. 4. refuting your own references (Corum²). Dr. Corum's equation for the coil VF is at its *SELF-RESONANT* frequency, not anywhere else. Using it anywhere else is only a *VERY ROUGH* estimate. At the self resonant frequency reported by EZNEC, the VF calculates out to be ~0.055. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Clark wrote:
On Sun, 26 Mar 2006 15:12:23 GMT, Cecil Moore wrote: Don't you find it strange that all the wire in the system occupies 90.01 - 15.68 = 74.33 degrees? Strange? 1. The current distribution shown on the web is different than the current distribution shown in the model; 2. -4.91 + -20.59 + -90.01 = -115.51 is different than 90.01 - 15.68 = 74.33 3. The coil Vf shown on the web is 0.1375 is different than eq (32) = 0.0078 4. refuting your own references (Corum²). not strange at all. Hi Richard, Cecil never actually reads his references, he just gives them and hopes you won't read them either. If he'd bothered to look at figure 2 in the Corum reference he would have found that the Corums had in mind a shorted stub as a substitute for their Tesla coil. That's o.k., since it would lead to an inductance (jZc*tan(Betag*h)) which they could use in the time-honored way to resonate with the capacitance of the rest of the circuit. You're right, not strange at all. 73, Tom Donaly, KA6RUH |
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