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Current through coils
John Popelish wrote:
The only way I can see to do it is to go outside the coil and look at how the standing current nodes move. Standing wave phase is with respect to position, not time. Well John, you are obviously not up on the latest techniques. (But neither am I.) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote:
"Did you hear what he said about your wife?" Whatever he said is probably true. My ex-wife made off with $3 mil of my hard-earned dollars in 1984. I've never trusted a female since. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
"Phaseless signals". What an imaginative creation. Well not really, if you think about it, the phase of a DC signal can be considered to be zero everywhere. The phase of a standing wave current *is* zero everywhere on a 1/2WL thin-wire dipole. Seems to me, a standing- wave current indeed does have a lot in common with a DC current. But that might just be a coincidence. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
John Popelish wrote: "Did you hear what he said about your wife?" Whatever he said is probably true. My ex-wife made off with $3 mil of my hard-earned dollars in 1984. I've never trusted a female since. This factoid brings several apparently unrelated things into focus for me. |
Current through coils
John Popelish wrote:
Cecil Moore wrote: Whatever he said is probably true. My ex-wife made off with $3 mil of my hard-earned dollars in 1984. I've never trusted a female since. This factoid brings several apparently unrelated things into focus for me. Remember the Koala Pad? I was VP of Engineering and a couple of those patents are in my name. Koala Technologies could not survive the president's divorce and my divorce at the same time. The venture capitalists pulled the plug. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg wrote:
"Wanna bet?" Don`t bet against Reg. Phase shift aling the coil plus the phase shift along the conductors DOES add up to 90 degrees when the antenna is 1/4-wave resonant. Recall the purpose of the coil is electrically to make the too-short whip appear full-sized. The assembly is resonant when worked against the earth. Its plus and minus 90-degree reactances are equal in magnitude to each other. Best regards, Richard Harrison, KB5WZI |
Current through coils
Cecil,
I never in my wildest dreams said anything about Tom's measurements. (Perhaps in your dreams.) I don't believe that Tom set up a simple standing wave antenna and then tried to measure the phase of the standing wave. You seem to have forgotten, but a few days ago you were vehemently arguing that the bugcatcher coil in your mobile antenna must have X amount of phase shift. My comments, which may have proven too successful, dealt only with the basic fundamental properties of waves. That's the sort of thing that everyone should have learned in elementary school, but such knowledge seems to be fleeting for some people. 73, Gene W4SZ Cecil Moore wrote: wrote: It sounds like Cecil is trying to find a way to make his theory fit despite the fact that models and measurements show the phase shift is zero, and demanding I agree with his unusual theories like current that doesn't flow, phaseless signals, and in his latest post antennas behaving like dc circuits. Again, it is not my theory. It is the distributed network model known to succeed when the lumped-circuit model fails in the presence of standing waves. There is no useful phase information left in a standing wave current. DC current and standing wave current are equally 100% ineffective at measuring the delay through a coil. I have asked this technical question multiply times: How does one use a signal with unchanging phase to measure the delay through a coil? The answer is that one cannot. All that aside, it appears the main argument is Cecil's theory requires measuring current that doesn't flow ... No, using a signal with unchanging phase to try to measure delay is your main argument, not mine. I know it is foolish to measure a current with unchanging phase. Any phase measurement is meaningless. cos(kz)*cos(wt) doesn't possess phase information. One can tell that from the formula. Unlike you, Gene Fuller understands the meaning of those standing wave equation terms. Gene Fuller wrote: In a standing wave antenna problem, such as the one you describe, there is no remaining phase information. Any specific phase characteristics of the traveling waves died out when the startup transients died out. Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. Do you disagree with what Gene had to say? "PHASE IS GONE. KAPUT. VANISHED. CANNOT BE RECOVERED. NEVER TO BE SEEN AGAIN." In other words, one cannot use standing wave current to measure the delay through a coil. Delay doesn't exist in a standing wave current, i.e. "PHASE IS GONE." The worse part of that is he is demanding I answer something I cannot answer ... There's nothing wrong with admitting ignorance. Just please cease trying to disguise your ignorance as some technical fact. When are you going to correct the technical errors on your web page? 75m mobile bugcatcher loading coils possess a velocity factor of approximately 0.0175. They are about 6.6 inches long. The delay through that coil is ~0.128 wavelength at 4 MHz. That's a delay of 32 degrees. That's how much electrical length the coil is occupying when it is used on 4 MHz. |
Current through coils
"Gene Fuller" wrote: I never in my wildest dreams said anything about Tom's measurements. Of course not and I certainly didn't mean to imply otherwise. What you said was *objective and impersonal*, applicapable to anyone's measurements and also applies directly to Tom's earlier measurements. I don't believe that Tom set up a simple standing wave antenna and then tried to measure the phase of the standing wave. Maybe we should ask him. As I understand it, both Tom and Roy set up a simple loaded 1/4WL resonant *standing wave* monopole and measured the standing wave current at the bottom and top of the coil. EZNEC could have told them that they wouldn't measure any phase shift around the coil or anywhere else around along the antenna.. It's an easy mistake to make to look at the current displayed by EZNEC and picture that current flowing from the feedpoint to the tip while being 100% radiated in the process so the current falls to zero at the tip of the antenna. As we know, those are not the technical facts. The reflected wave is a large percentage of the forward wave. As seen from the graphic at: http://www.qsl.net/w5dxp/3freq.gif that standing wave current can have virtually any magnitude but has a phase that comes only in near-zero or near-180 degrees increments. I've been asking how to obtain phase information from a standing wave current. Nobody has answered. -- 73, Cecil, W5DXP |
Current through coils
Gene Fuller wrote: Cecil, I never in my wildest dreams said anything about Tom's measurements. (Perhaps in your dreams.) I don't believe that Tom set up a simple standing wave antenna and then tried to measure the phase of the standing wave. You seem to have forgotten, but a few days ago you were vehemently arguing that the bugcatcher coil in your mobile antenna must have X amount of phase shift. My comments, which may have proven too successful, dealt only with the basic fundamental properties of waves. That's the sort of thing that everyone should have learned in elementary school, but such knowledge seems to be fleeting for some people. Roy measured a real antenna for phase, I measured a moblile antenna for current. http://www.w8ji.com/agreeing_measurements.htm |
Current through coils
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Current through coils
wrote:
Roy measured a real antenna for phase, I measured a moblile antenna for current. http://www.w8ji.com/agreeing_measurements.htm Actually, I measured both phase and amplitude of the current at both ends of a toroidal inductor. It was measured at the base of a shortened vertical antenna, and also on the bench with the antenna replaced by lumped components having the same impedance as the antenna. The results were published in the October 2003 thread on this newsgroup. Roy Lewallen, W7EL |
Current through coils
This thread ran almost as long as "47KW CB mobile, was CW =
Engineer?" Not sure which holds the duration record. Cheers, Richard Harrison, KB5WZI |
Current through coils
Richard Harrison wrote:
This thread ran almost as long as "47KW CB mobile, was CW = Engineer?" Not sure which holds the duration record. Cheers, Richard Harrison, KB5WZI I counted almost 500 entries. Cecil had almost 25% of them. Dave N |
Current through coils
David G. Nagel wrote:
I counted almost 500 entries. Cecil had almost 25% of them. I kicked it off with "Current in loading coils". Reg then responded with "Current through coils" and the rest is history. When one is up against most of the r.r.a.a gurus, all at the same time, one needs to make a lot of postings. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
I counted almost 500 entries. Cecil had almost 25% of them.
Dave N =================================== - - - and I get the impression nobody learned anything! Problems should be handed over to the sewer rats in Rio de Janerio to sort out, rather than culling them. ---- Reg. |
Current through coils
Reg Edwards wrote:
- - - and I get the impression nobody learned anything! You think nobody learned anything from the fact that measuring standing wave current phase is meaningless? If nobody learned anything, they would no doubt still be contributing to the technical discussion. Here's what I think happened. Person A and Person B engage in an argument and both are wrong. Person A believes he cannot possibly be wrong so he digs in and argues his rigid position. Person B realizes that he may be wrong and uses the scientific method to fine tune his argument thus correcting any errors along the way. Which person has the advantage and is likely to win the argument? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Cecil Moore" wrote in message et... Reg Edwards wrote: - - - and I get the impression nobody learned anything! You think nobody learned anything from the fact that measuring standing wave current phase is meaningless? If nobody learned anything, they would no doubt still be contributing to the technical discussion. Here's what I think happened. Person A and Person B engage in an argument and both are wrong. Person A believes he cannot possibly be wrong so he digs in and argues his rigid position. Person B realizes that he may be wrong and uses the scientific method to fine tune his argument thus correcting any errors along the way. Which person has the advantage and is likely to win the argument? -- 73, Cecil http://www.qsl.net/w5dxp Hi Cecil I've read more than 80% of the posts in this thread. I still dont understand the objective. BUT, I sure have learned a few things, thanks to you guys who do what is being soughtafter. Jerry |
Current through coils
Hi Cecil I've read more than 80% of the posts in this thread. I still dont understand the objective. BUT, I sure have learned a few things, thanks to you guys who do what is being soughtafter. Jerry ======================================= Ah, but how do you know you learned the RIGHT things? Or what you learned was true and correct? The participants in the argument NEVER agreed on ANYTHING. So what can bystanders do? I learned far more about people than I did about current through coils. Quite interesting nevertheless. ---- Reg, G4FGQ. |
Current through coils
On Sat, 18 Mar 2006 19:57:32 GMT, Cecil Moore
wrote: Reg Edwards wrote: - - - and I get the impression nobody learned anything! You think nobody learned anything from the fact that measuring standing wave current phase is meaningless? If nobody learned anything, they would no doubt still be contributing to the technical discussion. Here's what I think happened. Person A and Person B engage in an argument and both are wrong. Person A believes he cannot possibly be wrong so he digs in and argues his rigid position. Person B realizes that he may be wrong and uses the scientific method to fine tune his argument thus correcting any errors along the way. Which person has the advantage and is likely to win the argument? I tried learning something. I didn't get to read the whole thread so may have missed the important part? When the measurements of the coil were done on the bench it seems that it was done with 50 ohms in and 50 ohms out. That hardly seems like it would give the same information as when the coil was in actual use as an antenna loading coil. Rather than a 50 ohm load how about if a load was placed at the end of the coil to simulate the antenna, a resistor and capacitor to take the place of the antenna impedance and reactance. Then measure the current in and out and the phase shift. 73 Gary K4FMX |
Current through coils
Jerry Martes wrote:
I've read more than 80% of the posts in this thread. I still dont understand the objective. Since the foundation of other's measurements was the use of standing wave current phase to prove the percentage of a wavelength occupied by a loading coil is zero, my objective was simple: To prove that the standing wave current, with its unchanging phase, cannot be used to make a valid measurement of the percentage of a wavelength occupied by a loading coil. I proved that using the standing wave current phase to measure the percentage of a wavelength occupied by a wire or a whip also yields an answer of zero. If the coil plus the whip both occupy a percentage of a wavelength equal to zero, all sorts of laws of physics are violated. Not to mention a full length 1/2WL wire dipole occupying a percentage of a wavelength equal to zero. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
I could have sworn that you were insisting the phase still had meaning in a standing wave environment. It only required the correct measurement technique. I am glad to see that you have now adopted the truth, even if the history appears a bit shaky. 73, Gene W4SZ Cecil Moore wrote: Jerry Martes wrote: I've read more than 80% of the posts in this thread. I still dont understand the objective. Since the foundation of other's measurements was the use of standing wave current phase to prove the percentage of a wavelength occupied by a loading coil is zero, my objective was simple: To prove that the standing wave current, with its unchanging phase, cannot be used to make a valid measurement of the percentage of a wavelength occupied by a loading coil. I proved that using the standing wave current phase to measure the percentage of a wavelength occupied by a wire or a whip also yields an answer of zero. If the coil plus the whip both occupy a percentage of a wavelength equal to zero, all sorts of laws of physics are violated. Not to mention a full length 1/2WL wire dipole occupying a percentage of a wavelength equal to zero. |
Current through coils
Gary Schafer wrote:
Rather than a 50 ohm load how about if a load was placed at the end of the coil to simulate the antenna, a resistor and capacitor to take the place of the antenna impedance and reactance. Then measure the current in and out and the phase shift. The measurement problem is harder than it looks. Here's a quote from "Field and Waves in Modern Radio", Ramo and Whinnery, 2nd edition, page 227. "Difficulties in applying these equations arise since the current and charge distributions are not known, but are determined by the field distributions which are calculated from the retarded potentials which depend upon current and charge distribution - a vicious circle! The exact solution of this problem is usually of prohibitive difficulty." -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
I could have sworn that you were insisting the phase still had meaning in a standing wave environment. I know that's what you thought, but you were mistaken. By thinking that, you accidentally posted some support for my side of the argument. Thanks very much. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Reg Edwards" wrote in message ... Hi Cecil I've read more than 80% of the posts in this thread. I still dont understand the objective. BUT, I sure have learned a few things, thanks to you guys who do what is being soughtafter. Jerry ======================================= Ah, but how do you know you learned the RIGHT things? Or what you learned was true and correct? The participants in the argument NEVER agreed on ANYTHING. So what can bystanders do? I learned far more about people than I did about current through coils. Quite interesting nevertheless. ---- Reg, G4FGQ. Hi Reg I note that you question my ability to know if I learned the Right Things. How do we ever know?? I wrote that I learned a FEW things. Let me be the judge about whats right for me. I dont know if you wrote the question about my learning the Right thing to impune my ability to sort out the Right from the NotRight, or you wrote to imply that were some statements made in the thread that werent right. I submit to you that if you find the need to show where any statement made in the antenna group that isnt True and Correct, you can correct them directly. By my standards, all the posts in this thread were worthy of being read. It is even possible that you learn something from these guys on the antenna group when you take time to read and think. Please dont stop trying to learn Reg, you are a great source of good information and you can improve if you try. Jerry |
Current through coils
Gary Schafer wrote: When the measurements of the coil were done on the bench it seems that it was done with 50 ohms in and 50 ohms out. That hardly seems like it would give the same information as when the coil was in actual use as an antenna loading coil. A bench test is fine. An inductor is an inductor. The only problem with a bench test is simulating the load impedance presented by the antenna and of course strong local fields generated by the antenna are missing, but the actual error can be reasonably small. However, inductors were measured in an actual antenna. I measured current, and Roy Lewallen measured phase and current. I couldn't measure time delay or phase in my actual antenna because I was measuring a mobile antenna. There wasn't any way to measure phase without perturbing the system and rendering any data unreliable. This long painful thread (it's been going on years now) started because K3BU claimed a loading inductor had most of the current in the first few turns. I made some measurements and posted them at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm These measurements show exactly what anyone who understands loading coils would expect, that it is stray C in comparison to load impedance on the inductor that determines any current taper, and that for a reasonable sized inductor the taper is very small. I wrote a description at: http://www.w8ji.com/mobile_and_loaded_antenna.htm I can't see anything in there that needs changed, based on what I've read here in this thread. Rather than a 50 ohm load how about if a load was placed at the end of the coil to simulate the antenna, a resistor and capacitor to take the place of the antenna impedance and reactance. Then measure the current in and out and the phase shift. I've done that also. You are absolutely correct Gary, it is possible to come very close with a lumped load on the inductor *except* of course the surroundings are different. The inductor test fixture I normally use is a large copper box made from blank double sided PC board sheets. It has vacuum caps (very high Q) and various detectors and probes. I have to characterize large inductors on occasion as part of designing RF systems. It's less scary than turning on a 50kW PA and having things misbehave at full power, or building a phasing system or phasing/ATU combo that doesn't work. 73 Tom |
Current through coils
wrote:
************************************************** ************** Please turn your technical expertise on this example which I have asked you about many times with no response from you: http://www.qsl.net/w5dxp/current.htm At the bottom of the page, the coil is seen to have 0.17 amps at the bottom and 2.0 amps at the top. With your lumped inductor way of thinking, how is that possible? ************************************************** *************** A bench test is fine. An inductor is an inductor. But the chosen valid model varies depending upon which inductor it is. Dr. Corum says the model must be changed over at 15 degrees of the self-resonant frequency. These are velocity inhibited slow- wave helical coils that we are talking about. And standing wave current is certainly not traveling wave current. Remember what Gene Fuller said? Please read it again. Gene said about standing wave current: Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. How can one use a signal where the phase is gone to measure phase? However, inductors were measured in an actual antenna. I measured current, and Roy Lewallen measured phase and current. You and Roy measured standing wave current the phase of which is unchanging over the coil and whip and entire antenna. You should have realized over the past week that those measurements were meaningless. EZNEC shows the same thing. Kraus reports the same thing. ONE CANNOT USE THE PHASE OF STANDING WAVE CURRENT TO MEASURE THE PART OF AN ANTENNA THAT A LOADING COIL REPLACES. ... and that for a reasonable sized inductor the taper is very small. The present argument is not about taper, it is about how much of a wavelength a loading coil occupies. One cannot measure that value using standing wave current as you and Roy did. Roy reported accurate phase measurements but standing wave current phase is meaningless since it has unchanging phase. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Gene Fuller wrote: I could have sworn that you were insisting the phase still had meaning in a standing wave environment. I know that's what you thought, but you were mistaken. By thinking that, you accidentally posted some support for my side of the argument. Thanks very much. Cecil, I am attaching a few of your quotes in this thread. Sorry to hear about your total loss of short term memory. [Direct quotes from March 5-7] Standing wave current is a net charge flow of zero. Standing wave current is DIFFERENT from traveling wave current. At any and every point, the standing wave current is NOT moving. Since it is not moving, there is NO net charge flow. ****** To tell the truth, standing waves are a product of the human mind. The forward and reflected waves couldn't care less about standing waves Surely you understand that standing waves in a transmission line don't flow - they just stand there, which is why they are called "standing waves". Exactly the same principle applies to standing wave antennas. The two traveling waves have to be analyzed separately and then superposed to obtain valid results. If you analyze net current without superposition, you are doing the same thing as superposing powers, which is a known no-no. ****** The currents that are doing the flowing are the underlying current components, the forward current and the reflected current and they are close to equal. Everything you say about a coil is true for the forward current and the reflected current. It is simply not true for the standing wave current which is just a conceptual construct and not a flowing phasor at all. If you really want to accurately apply the principles you are asserting, you must treat the forward current and reflected current separately and then superpose the results. Applying your above principle to standing wave current is akin to superposing power and that's a no-no. I have never seen such a wide-spread blind spot. [end quotes] 73, Gene W4SZ |
Current through coils
Gene Fuller wrote:
I am attaching a few of your quotes in this thread. Sorry to hear about your total loss of short term memory. I'm in a learning process here and using the scientific method to correct my mistakes. Isn't that what rational people do? [Direct quotes from March 5-7] Standing wave current is a net charge flow of zero. I was corrected on that one and already admitted my mistake. The charges obviously migrate from end to end in the antenna. Surely you understand that standing waves in a transmission line don't flow - they just stand there, which is why they are called "standing waves". Exactly the same principle applies to standing wave antennas. This means the same thing as your posting that phase is gone. A phasor requires a rotating phasor to exhibit flow in the real sense of the word. Standing wave current doesn't possess a rotating phasor so it is not flowing in the normal sense of current flow. If you think standing wave current is flowing, how do you explain 0.17 amps at the bottom of the coil and 2.0 amps at the top? http://www.qsl.net/w5dxp/current.htm bottom of page The two traveling waves have to be analyzed separately and then superposed to obtain valid results. Don't see anything wrong with that. If one uses the standing wave current phase to try to measure phase shift through a coil, one is making a mistake as has been demonstrated here. The currents that are doing the flowing are the underlying current components, the forward current and the reflected current and they are close to equal. Everything you say about a coil is true for the forward current and the reflected current. It is simply not true for the standing wave current which is just a conceptual construct and not a flowing phasor at all. You said it yourself, Gene, phase has disappeared from standing wave current. Do you understand the implications of your statements? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
Cecil Moore wrote: . . . The two traveling waves have to be analyzed separately and then superposed to obtain valid results. If you analyze net current without superposition, you are doing the same thing as superposing powers, which is a known no-no. Both those sentences are false. In a linear system like an antenna or transmission line, superposition applies. This means, among other things, that we can separately analyze the system's response to various components, and the sum of the results we get are the response to the sum of the excitation components. For example, we can split a current into two -- or more -- components, such as a forward traveling current wave and a reverse traveling current wave, with the actual current (or what Cecil calls "net" or "standing wave" current) at any point being the sum of the two. We can find the voltage across an inductor, for example, which results from the forward traveling current. Then we find the voltage across the inductor resulting from the reverse traveling current. Superposition tells us that the sum of those two voltages is what results from a current which is equal to the sum of the forward and reverse traveling current waves. We must get exactly the same result, in this example the voltage across the inductor, if we find it by adding the separate voltages due individually to the two current components, or if we find it directly as a result of the total current. We don't have to separate the current into two components then superpose the results as Cecil claims -- we get exactly the same result either way because superposition holds. This has nothing to do with attempted superposition of powers or other properties which don't fit into the boundaries of linear quantities. We're not restricted to splitting the current into a single forward and reverse wave, either. We can split it into many separate traveling waves, as well as any number of other combinations. As long as all the components add up to the actual total current, we'll get exactly the same result when we separately sum the responses to each individual component that we do when we simply look at the response to the total current. If Cecil's analysis shows, or his theory requires, that the result be different when adding the responses to traveling current waves than it is by calculating the response directly from the total current, then the analysis or theory is wrong. Superposition requires that the two results be identical. Roy Lewallen, W7EL |
Current through coils
Roy Lewallen wrote:
If Cecil's analysis shows, or his theory requires, that the result be different when adding the responses to traveling current waves than it is by calculating the response directly from the total current, then the analysis or theory is wrong. Superposition requires that the two results be identical. There is a phase shift through the coil for the individual phasors. When the phasors are superposed, that phase shift information disappears. That's what I meant by my statement. The results are the same but information is lost. Please see http://www.qsl.net/w5dxp/current.htm "Why the net current is not constant through a loading coil" and take a look at the phase of the net current. It is unchanging. Those phasors are copied directly from "Optics" by Hecht. What I was talking specifically about is the phase shift through the coil so let's discuss that one limited technical subject. The form of the forward traveling wave current is function(kz+wt) The form of the reflected traveling wave current is function(kz-wt) When we superpose those two waves we get the standing wave current. The form of the standing wave current is function(kz)*function(wt) A lot of information, including all phase information, has been lost in that superposition process. The standing wave current is obviously not like the traveling wave currents because the equations are different. As Gene Fuller said earlier, it has been stripped of all phase information by the superposition process. You pointed out a couple of days ago that the phase of the standing wave current is virtually constant from feedpoint to the tip of the antenna while the phase of the traveling waves are certainly not constant. I have asked this technical question before and no one has answered it. Given that the standing wave current would indicate a phase shift of zero in 45 degrees of a wire antenna, what does that imply for using the standing wave current to measure the number of degrees of the antenna occupied by the loading coil? If the standing wave current cannot determine the phase shift in a wire, why does anyone think it can determine the phase shift in a wire formed into a coil? Kraus and EZNEC tell us that the standing wave phase shift is zero from tip to tip in a 1/2WL thin-wire dipole. Why is it a surprise that if we replace part of that antenna with a loading coil the standing wave phase shift doesn't change and is still zero? What useful information does knowing that provide? Since the standing wave current phase is unchanging, how can it be used to determine how much of an antenna has been replaced by a loading coil? You and Tom have used standing wave current for your measurements. Delays and phases cannot be measured using standing wave current because standing wave current doesn't contain any phase related information. As Gene said, it lost all phase information in the superposition. All we can gather from the standing wave current is that the forward current and reflected current phasors are rotating in opposite directions. The delay experienced by the traveling waves is hidden by the superposition process. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Sun, 19 Mar 2006 04:57:54 GMT, Cecil Moore
wrote: Please see http://www.qsl.net/w5dxp/current.htm I refer to the diagram in the section entitled "What EZNEC Says About Current Distribution Using Inductive Loading Stubs" You use the diagram to assert that there is "not a lot of difference between inductive loading stubs and loading coils" by comparing the current distribution with another case. You show graphically the current on each side of the stub. You do not show the current in each wire of the stub or the sum of the currents in the stub. EZNEC calculates the currents in each wire of the stub? Aren't those currents a relevant detail that you have omitted from the diagram. Owen -- |
Current through coils
Owen Duffy wrote:
On Sun, 19 Mar 2006 04:57:54 GMT, Cecil Moore wrote: Please see http://www.qsl.net/w5dxp/current.htm I refer to the diagram in the section entitled "What EZNEC Says About Current Distribution Using Inductive Loading Stubs" You use the diagram to assert that there is "not a lot of difference between inductive loading stubs and loading coils" by comparing the current distribution with another case. You show graphically the current on each side of the stub. You do not show the current in each wire of the stub or the sum of the currents in the stub. EZNEC calculates the currents in each wire of the stub? Aren't those currents a relevant detail that you have omitted from the diagram. I don't quite follow the theory on the web page, but what does it predict should happen if there were no antenna at all, and the inductor were connected to a simple series RC circuit instead of the whip? I've taken the EZNEC model available there and modified it by replacing the whip with a wire to ground from the top of the coil (http://eznec.com/misc/test316_modified.EZ). I added a lumped impedance in that wire to represent the impedance of the vertical wire I deleted(*). The feedpoint impedance is the same as for the original model, and the currents at the top and bottom of the inductor are almost exactly the same as for the original model. Can the traveling wave analysis be used to explain the inductor currents in this model? Is traveling wave analysis necessary to explain them? (*) The impedance inserted in the new wire isn't equal to the impedance of the top wire driven against ground. The reason is that the new wire to ground does radiate some, does have significant impedance itself, and does interact with the inductor. The modified system, however, is quite obviously very different in radiating properties from the original, and isn't too different from a lumped RC load. Roy Lewallen, W7EL |
Current through coils
Cecil Moore wrote: Please turn your technical expertise on this example which I have asked you about many times with no response from you: http://www.qsl.net/w5dxp/current.htm At the bottom of the page, the coil is seen to have 0.17 amps at the bottom and 2.0 amps at the top. With your lumped inductor way of thinking, how is that possible? Yes it is possible. There is no difference between doing things as lumped components or standing wave models. The only disagreement is you seem to claim some very odd things about current not flowing, unless in the course of 400 posts you have corrected that. This entire thread reminds me of the Fractenna threads of years ago. 73 Tom |
Current through coils
Roy Lewallen wrote:
. . . I've taken the EZNEC model available there and modified it by replacing the whip with a wire to ground from the top of the coil (http://eznec.com/misc/test316_modified.EZ). I added a lumped impedance in that wire to represent the impedance of the vertical wire I deleted(*). The feedpoint impedance is the same as for the original model, and the currents at the top and bottom of the inductor are almost exactly the same as for the original model. Can the traveling wave analysis be used to explain the inductor currents in this model? Is traveling wave analysis necessary to explain them? (*) The impedance inserted in the new wire isn't equal to the impedance of the top wire driven against ground. The reason is that the new wire to ground does radiate some, does have significant impedance itself, and does interact with the inductor. The modified system, however, is quite obviously very different in radiating properties from the original, and isn't too different from a lumped RC load. Notice that the current into the grounded wire at the bottom of the coil is about 1 amp, and the current going into ground at the grounded end of the added wire is about 0.56 amp. So where is the extra current for the coil bottom wire coming from? The answer is displacement current from the coil. That is, the coil is capacitively coupled to ground, and this causes displacement current from the coil to ground. The effect is greatest at the end of the coil which is farthest from the source. A decent model of the coil is an L network, with a series L, and a shunt C to ground from the far end. This is all that's necessary to explain the drop in current from the bottom to the top; no current waves, standing or traveling, no transmission line analysis are required. If you're not convinced, try this. Change the ground type to free space. Then connect the bottoms of the two formerly grounded wires together with another wire. You'll see that the current at the top of the coil is now very nearly the same as at the bottom. We haven't changed any waves, antenna lengths, or anything else related to antennas or waves. All we've done is to eliminate the other side of the capacitor -- we've removed the C in the equivalent lumped L network. A simple lumped component model explains the difference between grounded and free space models just fine. How well does the traveling wave theory do at it? Roy Lewallen, W7EL |
Current through coils
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Current through coils
Owen Duffy wrote:
Cecil Moore wrote: Please see http://www.qsl.net/w5dxp/current.htm I refer to the diagram in the section entitled "What EZNEC Says About Current Distribution Using Inductive Loading Stubs" You use the diagram to assert that there is "not a lot of difference between inductive loading stubs and loading coils" by comparing the current distribution with another case. You show graphically the current on each side of the stub. You do not show the current in each wire of the stub or the sum of the currents in the stub. The currents in stubs cannot be displayed very well at full size in EZNEC just as the currents in coils cannot be displayed very well. Maybe an enlarged view would show it. I will try to do that. EZNEC calculates the currents in each wire of the stub? Aren't those currents a relevant detail that you have omitted from the diagram. Remember the present discussion is about the ability to use standing wave current phase to measure the electrical length of a wire or a coil. I have run the currents that you mention. The phase of the current is almost constant through the stubs. The phase of the current is almost constant through the coils. Would you like to see a list of the current at points through the stub Vs the current at points through the coil? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
Can the traveling wave analysis be used to explain the inductor currents in this model? In this new configuration, the traveling wave current encounters a short-circuit to ground instead of the open-circuit in a normal antenna. And that forward current is reflected by that short circuit. In the shorted case its phase doesn't change so the forward and reflected currents add instead of subtrace. But their phasors are still rotating in opposite directions. Please note that the phase shift in the standing wave current is almost zero throughout the system, i.e. standing wave phase information has still been lost. We still don't know the electrical length of the coil for the same reasons we didn't know it before. Below 'func' stands for 'function of'. The standing wave current reported by EZNEC is of the form: func(kz)*func(wt) = fun(kz+wt) + func(kz-wt) Is there any way in EZNEC to subtract out the func(kz-wt) reflected term and leave just the forward term? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Cecil Moore wrote: At the bottom of the page, the coil is seen to have 0.17 amps at the bottom and 2.0 amps at the top. With your lumped inductor way of thinking, how is that possible? Yes it is possible. There is no difference between doing things as lumped components or standing wave models. Please explain how 0.17 amps can be on the source side of a lumped inductor while 2.0 amps exists at the top of the inductor. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
In a linear system like an antenna or transmission line, superposition applies. ... We must get exactly the same result, ... If Cecil's analysis shows, or his theory requires, that the result be different when adding the responses to traveling current waves than it is by calculating the response directly from the total current, then the analysis or theory is wrong. Superposition requires that the two results be identical. Superposition does not require that all information be preserved through the superposition process. Here's an example: Two people are across the room from each other with a coax cable running between them. They each have two identical PSK modems but only one coax. When they use one modem pair, any information one sends is received 100% by the other. When they use the other modem pair, any information one sends is received 100% by the other. When they superpose the signals over the single coax line, all phase information is lost. The superposition results are the same but all phase information is lost in the process. The rules of superposition do not apply to the phase information content. The phase information is lost in the process of superposition. In like manner, the rules of superposition do not apply to the ability of a standing wave to detect phase shift. The phase information is lost in the process of superposition. One cannot use standing wave current phase to measure the electrical length of a wire or a coil. A 75m wire dipole is known to be close to 90 degrees long from the feedpoint to the tip. EZNEC says the current changes phase by 2.5 degrees. How can current change phase by only 2.5 degrees in an antenna wire known to be 90 degrees long? Since EZNEC's standing wave current cannot detect a phase shift in 90 degrees of wire, why should it detect a phase shift in a coil? If standing wave current measurements cannot detect a phase shift in 90 degrees of wire, why should anyone's measurements detect a phase shift in a coil? -- 73, Cecil http://www.qsl.net/w5dxp |
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