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Current through coils
Jerry Martes wrote:
I have a HP8405A Vector Voltmeter I'll give you and even pay the shipping if that is of any help with the measurements. Wow, thanks for the offer. That would certainly be more accurate than eyeballing an o'scope. Do you think the use of such would prove me right or wrong? Does the VV compare two signals and report the phase difference? Are the probes differential or coaxial? I've never used a VV. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Cecil Moore" wrote in message . com... Jerry Martes wrote: I have a HP8405A Vector Voltmeter I'll give you and even pay the shipping if that is of any help with the measurements. Wow, thanks for the offer. That would certainly be more accurate than eyeballing an o'scope. Do you think the use of such would prove me right or wrong? Does the VV compare two signals and report the phase difference? Are the probes differential or coaxial? I've never used a VV. -- 73, Cecil http://www.qsl.net/w5dxp Hi Cecil I dont know how to use a VV either. I got a couple of them from Pacific Missile Range surplus. One has a probe sheared off. I figured I could build a "pair of probes" to make that one work for myself. You are welcome to have the other. That one looks complete. It sure would be worth the effort to ship it to you if you'd like to have it. I cant guarentee that the 8405A works but I do know they are repairable. If you are willing to check it out, its yours. I downloaded a manual for the unit. E-mail me your address. Maybe you can tell me something about the unit after you figure it out. I have such a high respect for Roy and Wes that it is not possible for me to think they'd both be wrong while in agreement. And, I like to read your discussions on this group so much that I'd offer anything I can to assist your 'getting some measurements made'. I am absolutely sure all you guys will agree on this stuff after you make some measurements. You are all too bright to have such severe differences in understanding on this subject. Jerry |
Current through coils
Jerry Martes wrote:
It sure would be worth the effort to ship it to you if you'd like to have it. I hate to accept it for free. Maybe I could just borrow it for awhile? I have such a high respect for Roy and Wes that it is not possible for me to think they'd both be wrong while in agreement. So why are you offering a free VV to someone they both hate? :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Fri, 10 Mar 2006 04:23:03 GMT, Cecil Moore wrote:
Jerry Martes wrote: I have a HP8405A Vector Voltmeter I'll give you and even pay the shipping if that is of any help with the measurements. Wow, thanks for the offer. That would certainly be more accurate than eyeballing an o'scope. Do you think the use of such would prove me right or wrong? Does the VV compare two signals and report the phase difference? Are the probes differential or coaxial? I've never used The VVM probes are comprised of a quad diode sampling bridge followed by an FET amplifier. They are nominally coaxial, although without the BNC adapters, they have an exposed pin (very delicate) and at lower frequencies they can be used much as a high impedance scope probe is used. The instrument uses a phase-locked oscillator to drive the samplers with the "A" probe being the reference. One meter can be switched to display the amplitude of either channel and the second meter reads the phase difference between them. |
Current through coils
On Fri, 10 Mar 2006 05:10:24 GMT, Cecil Moore wrote:
Jerry Martes wrote: It sure would be worth the effort to ship it to you if you'd like to have it. I hate to accept it for free. Maybe I could just borrow it for awhile? I have such a high respect for Roy and Wes that it is not possible for me to think they'd both be wrong while in agreement. So why are you offering a free VV to someone they both hate? :-) I don't hate you. While I shook your hand at Flagstaff once, I don't know you well enough personally to get all worked about you one way or another. This is Usenet, not the real world. No sense taking it too seriously. |
Current through coils
On Fri, 10 Mar 2006 01:14:18 GMT, Cecil Moore wrote:
Wes Stewart wrote: Why do you persist at doing this? My post was in response to someone else and you feel it necessary to jump in with the same old bafflegab. This is a public forum. Why do you not respond to my posting on a technical level instead of resorting to an ad hominem attack? I have tons of technical references to support my position. Clearly, you were too busy trying to frame an argument to actually read what I wrote. I only respond to portions I disagree with, Wes. Why can't you and I have a simple, point by point, technical discussion? Which points? You are the master at selective editing. For example you stated: "Your graphs show standing wave current which doesn't flow...blah blah" When I show otherwise, snip, gone without reply. "We" need to plot no such thing. You may have such a need; I do not. You, nor your cohorts, are likely to understand what's really happening until you take a look at the individual underlying currents that superpose to form the standing wave current which doesn't flow at all since its phase angle is fixed at zero degrees. I have no "cohorts" here. This isn't the "Let's get Cecil" gang. Isn't a bunch of IEEE PhD's saying that "the lumped-circuit model fails in a standing-wave environment", enough evidence for you to consider that they know what they are talking about? I've worked with lots of PhD's. Hell I even had one working for me and his was in Nuclear Physics from Trinity College at Oxford. He was a lovely old guy, the quintessential Einstein type, who couldn't find his way to the men's room without directions. Another, younger one was so impressed with himself, it was impossible to have a conversation with him without him saying, "When I was working on my thesis..." Pass him in the hall and say, "Nice day today." He would reply, "Yes, it is but I remember a day back when I was working on my thesis..." Sorry, "A bunch of IEEE PhD's" impresses me less than a handful of the guys posting here. |
Current through coils
"Cecil Moore" wrote in message om... Jerry Martes wrote: It sure would be worth the effort to ship it to you if you'd like to have it. I hate to accept it for free. Maybe I could just borrow it for awhile? I have such a high respect for Roy and Wes that it is not possible for me to think they'd both be wrong while in agreement. So why are you offering a free VV to someone they both hate? :-) -- 73, Cecil http://www.qsl.net/w5dxp Hi Cecil There is no reason to ever return any of the stuff I send out. I actually enjoy knowing that someone appreciates this stuff. I dont pay $$ for it. It gets surplused by the government. My buddy buys it in bulk. I am able to refurbish alot of the surplus he buys, like 100 KW gen-sets, so he can re-sell the units back to them. Since I enjoy learning how to fix the broken stuff, I dont charge for my time. So, he lets me sort thru his "scrap piles". Everyone wins. But, I dont get to watch much TV because I keep too busy learning how to fix the stuff. Send me your shipping address. The HP 8405A will be in the mail within a day after I get the address. Do you have any use for a HP 8660 signal generator main frame, *no* plug-ins? That would sure be a nice generator to go with a Vector Voltmeter. I have 5 main frames but I havent been able to win an eBay bid for the plug-ins. Jerry |
Current through coils
"Wes Stewart" wrote in message ... On Fri, 10 Mar 2006 01:14:18 GMT, Cecil Moore wrote: Wes Stewart wrote: Why do you persist at doing this? My post was in response to someone else and you feel it necessary to jump in with the same old bafflegab. This is a public forum. Why do you not respond to my posting on a technical level instead of resorting to an ad hominem attack? I have tons of technical references to support my position. Clearly, you were too busy trying to frame an argument to actually read what I wrote. I only respond to portions I disagree with, Wes. Why can't you and I have a simple, point by point, technical discussion? Which points? You are the master at selective editing. For example you stated: "Your graphs show standing wave current which doesn't flow...blah blah" When I show otherwise, snip, gone without reply. "We" need to plot no such thing. You may have such a need; I do not. You, nor your cohorts, are likely to understand what's really happening until you take a look at the individual underlying currents that superpose to form the standing wave current which doesn't flow at all since its phase angle is fixed at zero degrees. I have no "cohorts" here. This isn't the "Let's get Cecil" gang. Isn't a bunch of IEEE PhD's saying that "the lumped-circuit model fails in a standing-wave environment", enough evidence for you to consider that they know what they are talking about? I've worked with lots of PhD's. Hell I even had one working for me and his was in Nuclear Physics from Trinity College at Oxford. He was a lovely old guy, the quintessential Einstein type, who couldn't find his way to the men's room without directions. Another, younger one was so impressed with himself, it was impossible to have a conversation with him without him saying, "When I was working on my thesis..." Pass him in the hall and say, "Nice day today." He would reply, "Yes, it is but I remember a day back when I was working on my thesis..." Sorry, "A bunch of IEEE PhD's" impresses me less than a handful of the guys posting here. Hi Wes The more I read your posts the more I like the way you think. Jerry |
Current through coils
Cecil Moore wrote: Please explain how a net current with a fixed constant non-rotating phase can possibly flow. Please explain how a wire with 1 amp flowing in one direction and 1 amp flowing in the other direction supports a net charge flow. Once again this indicates you are not familiar or comfortable with basics, and have gotten ahead of yourself by going off somehwre in a land of reflected waves. Now you are confused, and can't make sense of basics. The generator sees a reactive load. When the generator sees a reactive load, current and voltage are no longer in step. This is true all through the system from source to load. 3.) You also claim significant current phase shift exists between the terminals of a compact inductor operated well below self-resonance. Please define "compact" in terms of the number of degrees of phase shift measured using a traveling wave. Phase shift in what Cecil? This is how people get in trouble, make misstatements, and wind up blaming others for what they say. Here we are again, trying to work traveling and standing waves into a system too small to have anything stand when another significantly better analysis method would easily explain it all. You keep trying to define the "inductor" in terms of degrees related to standing waves like standing waves change the properties of the component. I can't remember the last time I called to order an inductor and they vendor asked me "what phase shift in degrees of standing wave 100uH inductor do you want?". It's very simple to measure current and voltage and the phase relationships in a two terminal device and prove you are wrong. I've got many technical references that disagree. If you can do that, why haven't you done that? I have done it and told you how, you ignore it. Roy has done it and told you how, you ignore it. I'm sure many thousands of people here and everywhere else understand in a reactive system voltage and current are not in phase. I'm equally sure many thousands of people, including lurkers here, understand a small inductor operated well below self-resonance has equal phase current entering one lead and leaving the other. The only way to get confused on that is if someone doesn't understand behavior of the basic component, gets in over his head and confuses himself trying to use a tool that doesn't work, and then lashes out at others and refuses to listen. The current flowing into one end and out of the other end of a small lumped inductor operated far below self-resonance is essentially equal in both phase and amplitude. Please define "small" as the number of degrees of phase shift measured using a traveling wave. There you go again! Back to traveling and standing waves. You say it isn't, I say it is, and I can prove it beyond any doubt to any open minded person. Here, you are just out and out lying since I never said that. Want to bet $1000 that you can prove I ever said that? I didn't think so. What is with this compulsion you have to lie about what I have said? Can't you win a technical argument without lying? There you go again, back to the lowest form of debate. If you can't understand something or get trapped, just call the other guy a liar. You very clearly said current in each terminal of the inductor has a different phase shift several times in your posts. I say I can easily build a loading coil that acts the same way. I can replace 40 or 60 degrees of electrical height with an inductor that has virtually no phase shift in current between the two terminals, and virtually the same current level. I can prove that also. I seriously doubt that. Please measure the phase shift using a traveling wave through any coil that accomplishes that function. I suspect you are being fooled by the current loop located inside the coil and the fact that you have been ignorantly been measuring the net standing wave current which is essentially irrelevant. I can't understand what you are saying or what your point is, other than you think I am being fooled by standing waves, I am ignorant, and anything I measure is irrelevant. Maybe someone else can help me with your last statement. I'm just not sure I can prove anything to someone who thinks a current transformer measures current that doesn't flow! I explained it to you, Tom, in another posting. If you don't understand it, you need technical help. At a fixed point on a wire (where no net current or net charge is flowing) that is experiencing a constant exchange of H-field energy with E-field energy every cycle, a toroidal pickup coil will certainly report the results of that orthogonal energy exchange between the fields even though there is no lateral flow of net current or net charge. That's why a standing-wave dipole radiates broadside and a traveling-wave dipole is an end-fire. Maybe someone else on this group can explain or understand what you are trying to say. Anyone help me here? What is Cecil saying in that last paragraph? What does the pattern of a radiating structure in the far-field have to do with current in a circuit with a reactor? 73 Tom |
Current through coils
Wes Stewart wrote:
Cecil Moore wrote: So why are you offering a free VV to someone they both hate? :-) I don't hate you. While I shook your hand at Flagstaff once, I don't know you well enough personally to get all worked about you one way or another. This is Usenet, not the real world. No sense taking it too seriously. I wasn't serious, Wes. That's why the smiley face. I apologize if my humor irritates anyone. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Wes Stewart wrote:
The VVM probes are comprised of a quad diode sampling bridge followed by an FET amplifier. They are nominally coaxial, although without the BNC adapters, they have an exposed pin (very delicate) and at lower frequencies they can be used much as a high impedance scope probe is used. Thanks, Wes. When you say "lower frequencies", does that include 4 MHz? The instrument uses a phase-locked oscillator to drive the samplers with the "A" probe being the reference. One meter can be switched to display the amplitude of either channel and the second meter reads the phase difference between them. I was planning to use toroidal pickups and a Lissajous figure for the phase measurement. Did you know "Lissajous figure" is described in my 1957 ARRL Handbook but not in my 2000 ARRL Handbook? My main concern is how to ensure there are no reflections present during the measurement. I need to put the 75m bugcatcher coil in an RF loop where current is flowing in only one direction. That's easy to draw on paper but I'm concerned about it. How would you set it up? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Wes Stewart wrote:
Cecil Moore wrote: "Your graphs show standing wave current which doesn't flow...blah blah" When I show otherwise, snip, gone without reply. Sorry, I completely missed it. I'll go back and try to find it. Sorry, "A bunch of IEEE PhD's" impresses me less than a handful of the guys posting here. Have you looked at the articles on the web pages I posted? Here's a funny quote, not previous quoted from: http://www.ttr.com/corum/index.htm "What frequency did you get in step 5? ... Is the difference within engineering accuracy ... less than 5%? If the answer is yes, then you may confidently use lumped-element modeling. However, if the answer is no, then, from the halls of Valhalla, old Wotan, himself, is thundering out over the battlements, '#*@&%!! ... Thor, you dumdum! You CAN'T use lumped circuit modeling!' ... [The coil has standing waves and is behaving as a distributed resonator.]" In case you missed it, here's what Walter Maxwell had to say about the subject: "If an inductance is in series with a line that has reflections, the current will NOT be the same at both ends of the inductor." "Consequently, circuit analysis will not work when both forward and reflected currents are present in a lumped circuit." -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
In case you missed it, here's what Walter Maxwell had to say about the subject: "If an inductance is in series with a line that has reflections, the current will NOT be the same at both ends of the inductor." "Consequently, circuit analysis will not work when both forward and reflected currents are present in a lumped circuit." Cecil, I really think you should let Walt speak for himself. You have a history of distorting facts and taking statements out of context, and may be discrediting Walt. Walt is too nice a person for me to stand by and let that happen. If anyone really thinks that as a stand-alone statement, it is not correct. I suspect he didn't get the full story or wasn't following a discussion closely, or you have snipped something out of context. It's very easy to take small areas out of context and make it seem like someone is saying something they are not. Any circuit analysis will work so long as the load impedances used in the analysis are the same as the load impedances presented at that point by an antenna. The behavior of any small two-terminal component REQUIRES currents to be essentially equal. It's only when the component has a third significant path to the outside world that currents can be unequal. If I have a small capacitor, current flowing in one lead is equal to current flowing out the other and the phase of each current is exactly equal. Same for an inductor. That's not a guess, that's a rule of how things always behave. I'm wondering if the real problem is some people spend too much time with transmission lines and antenna and not enough time with circuit components, and become rusty? In any event, you do enough damage to people's reputations Cecil. Please leave Walt alone. He will speak for himself if he likes. 73 Tom |
Current through coils
Cecil Moore wrote: The generator sees a reactive load. When the generator sees a reactive load, current and voltage are no longer in step. This is true all through the system from source to load. I didn't ask or say anything about voltage. The fact that you refuse to answer my technical questions speaks volumes. The fact you can't understand simple direct answers does the same. You asked how what I measured could happen, I answered. You either are choosing to ignore the answer becuase you don't like it, or you don't understand it. Please define "compact" in terms of the number of degrees of phase shift measured using a traveling wave. Phase shift in what Cecil? The measured phase shift is in a traveling wave through a 75m bugcatcher coil. How long does it take the traveling wave current to flow from one end of the coil to the other? Your lumped-circuit model presupposes instantaneous current flow for traveling waves. Let's measure the current delay in a traveling wave to see if your model is correct. If it is not correct, it is useless. When Roy measured current (and I did the same) using inductive coupling in a current trasformer, a method that requires a time-varying current to excite the secondary, you dismissed Roy's measurements with some odd response about him measuring current that doesn't flow. I already measured the phase of current, and it is nearly zero degrees. It seems obvious to me that when someone gives you and answer you don't like, you either personally attack that persona and call them a liar or you make up some lame excuse like "you measured current that doesn't flow". I don't know what others think, but it is starting to look to me like you either don't understand the basics of measurements or you are just unwilling to learn. You cannot even begin to understand the problem if you don't know that basic phase shift. I'm willing to bet that my 75m bugcatcher coil has at least a 40 nanosecond delay on 4 MHz which is a 60 degree current phase shift. I can measure that. My network analyzer measures time delays. The problem I see is if I take time from my busy schedule and measure it, you will either call me a liar or say I measured current that doesn't flow. Before measuring anything specific I'm going to warn you that I've measured group delays many times before, and the group delay in an inductor is significantly less than the group delay in a transmission line of the same conductor length. I know that from past experience. But if you promise to control yourself and not dismiss a measurement with personal attacks or insults, and promise to not do an about-face like you did with Roy and say "you really didn't measure current that moves with your thing that only measures changing current", I will do that. I really wish some of your ideas were correct. If they were correct, I would not have thousands of feet of coaxial cables coiled under my bench. I would not be forcing customers to cut long delay lines when their equipment could just use a simple wound up piece of enameled wire. If that measured delay is in the ballpark of 40 nanoseconds or more, it proves that your lumped-circuit model has failed and your invalid proof is presupposed in the invalid model. The only potential problem is your reaction to measurements. You keep trying to define the "inductor" in terms of degrees related to standing waves ... Not true, Tom, and just shows how confused you are about what I have said. For the Nth time: The phase of the standing wave current doesn't change up and down the entire length of a 1/2WL thin dipole. Why would anyone expect it to change at the ends of a loading coil? As far as I am concerned we can drop any discussion of standing wave current phase. It is meaningless. The phase that Roy measured was standing wave phase. It was already known and is completely irrelevant. I asked Roy to measure the traveling wave phase shift. He didn't. Does ANYONE on this newsgroup understand Cecil? I need help here. I have done it and told you how, you ignore it. Roy has done it and told you how, you ignore it. You guys are measuring standing wave current that doesn't flow and doesn't change phase. Your measurements are completely meaningless and your flawed model has you hoodwinked. What a silly statement. We are measuring a time-varying current that doesn't flow or change! The only way to get confused on that is if someone doesn't understand behavior of the basic component, gets in over his head and confuses himself trying to use a tool that doesn't work, and then lashes out at others and refuses to listen. That's an exact description of you and your lumped circuit analysis in a standing wave environment. Do you disagree with Walter Maxwell? Walt wrote: "If an inductance is in series with a line that has reflections, the current will NOT be the same at both ends of the inductor." "Consequently, circuit analysis will not work when both forward and reflected currents are present in a lumped circuit." Yes, if he wrote what you quoted and you didn't lift something out of context I totally disagree with him. The component is not the problem, Tom. The problem seems to be your feigning of total ignorance of the laws of reflection physics in order to avoid discussing the real problem. I don't think most qualified experienced people would think I am the ignorant one. There you go again! Back to traveling and standing waves. Yes, you are never going to understand what I am saying about standing-wave antennas until you discuss traveling and standing waves on the standing-wave antenna. Your lumped-circuit model is known to fail in the presence of standing waves. Nonsense. There you go again, back to the lowest form of debate. If you can't understand something or get trapped, just call the other guy a liar. No, it's a lot simpler than that. When you lie about something I said, I call you a liar. There you go again. Do you have any idea how statements like that make you look to others? You very clearly said current in each terminal of the inductor has a different phase shift several times in your posts. One more time. The standing wave current does NOT change phase at the ends of the coil. The standing wave current essentially does not change phase unless a dipole is longer than 1/2WL. The phase of the standing wave current is totally irrelevant. The forward traveling-wave current experiences a delay through the coil. The reflected traveling-wave current experiences a delay through the coil. This delay can be measured on the bench. If the delay is not negligible, your lumped-circuit model is useless because it presupposes a delay of zero. I can't understand what you are saying or what your point is, ... Please don't insult my intelligence or yours. Every one of us performed those experiments on the bench in college. Exactly what is it about bench measuring the RF current delay through a coil that you don't understand? I understand it fine. I don't think the problem is on my end. If it is, someone besides you will chime in and tell me. I'm afraid I don't trust your opinions very much. Maybe someone else can help me with your last statement. Do you even know what a standing wave current loop is? Do you? Maybe someone else on this group can explain or understand what you are trying to say. You must have missed EE203. :-) What is it about a continuous exchange of energy between the E-field and H-field at a fixed point on an antenna wire that you don't understand? That's just a characteristic of standing waves. Roy has used the same argument in the past to try to prove that reflected energy doesn't flow. But's it's the standing wave energy that doesn't flow. Are you confusing energy and current? Or are you just joking again? 73 Tom |
Current through coils
wrote:
Cecil Moore wrote: In case you missed it, here's what Walter Maxwell had to say about the subject: "If an inductance is in series with a line that has reflections, the current will NOT be the same at both ends of the inductor." "Consequently, circuit analysis will not work when both forward and reflected currents are present in a lumped circuit." Cecil, I really think you should let Walt speak for himself. Sorry, I don't care what you think. You and I (and Walt) know exactly who distorted the facts. If anyone really thinks that as a stand-alone statement, it is not correct. I suspect he didn't get the full story or wasn't following a discussion closely, or you have snipped something out of context. It's very easy to take small areas out of context and make it seem like someone is saying something they are not. Those are Walt's exact words, not mine. If you don't believe me, send him an email and ask him. The behavior of any small two-terminal component REQUIRES currents to be essentially equal. It's only when the component has a third significant path to the outside world that currents can be unequal. Wrong! Wrong! Wrong! Your lumped-circuit model presupposes that the currents are equal so you are begging the question. YOU CANNOT USE YOUR MODEL TO PROVE ITS OWN PRESUPPOSITIONS. I see you haven't yet read what Dr. Corum had to say on that subject. http://www.ttr.com/corum/index.htm If I have a small capacitor, current flowing in one lead is equal to current flowing out the other and the phase of each current is exactly equal. Same for an inductor. Sorry, that's just not true for inductors. In the real world, there is a traveling wave current delay through the coil that can easily be measured on the bench. That delay converts directly to a phase delay. You are simply mistaken, hoodwinked by your lumped-circuit model, which presupposes the proof of what you say above. You are once again, begging the question and assuming the proof without having proved anything. That's not a guess, that's a rule of how things always behave. BS, Tom. That's a rule from a model known to fail in the presence of standing waves. Models existing in your mind don't dictate reality. It is supposed to be just the opposite. I'm wondering if the real problem is some people spend too much time with transmission lines and antenna and not enough time with circuit components, and become rusty? The real problem is that you are looking for your keys under the streetlight instead of in the dark where you lost them. The real problem is that you are doing the same thing as the naive ham who tries to measure feedpoint impedance with an ohm-meter. The real problem is that you are using a tool known to fail under the conditions in which you are trying to use it. THE LUMPED-CIRCUIT MODEL FAILS IN THE PRESENCE OF STANDING WAVES! I know that. Walt knows that. Dr. Corum knows that. A number of lurkers on this newsgroup know that. Nikola Tesla obviously knew that in his 1897 patent application. In any event, you do enough damage to people's reputations Cecil. Please leave Walt alone. He will speak for himself if he likes. Please mind your own business. I have Walt's permission to quote his stuff. If he ever asks me to stop quoting him, I will. One wonders if your attitude would be different if Walt agreed with you? :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Fri, 10 Mar 2006 11:51:51 GMT, Cecil Moore wrote:
Wes Stewart wrote: The VVM probes are comprised of a quad diode sampling bridge followed by an FET amplifier. They are nominally coaxial, although without the BNC adapters, they have an exposed pin (very delicate) and at lower frequencies they can be used much as a high impedance scope probe is used. Thanks, Wes. When you say "lower frequencies", does that include 4 MHz? When I wrote last, I was nursing a big toe that had just suffered the trauma of having a 4' x 8' sheet of 3/4" plywood dropped on it edge on. So I didn't want to hobble into the shack to search for the manual. Now I have it before me. The nominal impedance of the probes is 100 Kohm shunted by 2.5 pF. If this doesn't upset your measurement then you're good to go. I think that when I was remembering probing circuits with the bare probes I was thinking of the HP Vector Impedance Meter more than the VVM. It was a lower frequency instrument designed for that purpose. The instrument uses a phase-locked oscillator to drive the samplers with the "A" probe being the reference. One meter can be switched to display the amplitude of either channel and the second meter reads the phase difference between them. I was planning to use toroidal pickups and a Lissajous figure for the phase measurement. Did you know "Lissajous figure" is described in my 1957 ARRL Handbook but not in my 2000 ARRL Handbook? Well, they gotta leave something out so they can included the latest PIC controlled-automatic-rig-to-computer-interface and coffeemaker doodad. My main concern is how to ensure there are no reflections present during the measurement. I need to put the 75m bugcatcher coil in an RF loop where current is flowing in only one direction. That's easy to draw on paper but I'm concerned about it. How would you set it up? Can't help you. |
Current through coils
Wes Stewart wrote: Cecil wrote: My main concern is how to ensure there are no reflections present during the measurement. I need to put the 75m bugcatcher coil in an RF loop where current is flowing in only one direction. That's easy to draw on paper but I'm concerned about it. How would you set it up? Can't help you. What Cecil needs to do is bias the coil with a DC bias current that safely exceeds the peak RF current. Then he would have RF current flowing in only one direction. 73 Tom |
Current through coils
"Cecil Moore" wrote in message et... Wes Stewart wrote: The VVM probes are comprised of a quad diode sampling bridge followed by an FET amplifier. They are nominally coaxial, although without the BNC adapters, they have an exposed pin (very delicate) and at lower frequencies they can be used much as a high impedance scope probe is used. Thanks, Wes. When you say "lower frequencies", does that include 4 MHz? The instrument uses a phase-locked oscillator to drive the samplers with the "A" probe being the reference. One meter can be switched to display the amplitude of either channel and the second meter reads the phase difference between them. I was planning to use toroidal pickups and a Lissajous figure for the phase measurement. Did you know "Lissajous figure" is described in my 1957 ARRL Handbook but not in my 2000 ARRL Handbook? My main concern is how to ensure there are no reflections present during the measurement. I need to put the 75m bugcatcher coil in an RF loop where current is flowing in only one direction. That's easy to draw on paper but I'm concerned about it. How would you set it up? -- 73, Cecil http://www.qsl.net/w5dxp Hi Cecil I have the Technical Manual for the HP 8405 (36 MB) and could send it to you with "Usendit" or "Skype". Jerry |
Current through coils
wrote: The fact you can't understand simple direct answers does the same. I love simple answers, Tom. What I don't like are simple-minded answers based on an invalid model. When Roy measured current (and I did the same) using inductive coupling in a current trasformer, a method that requires a time-varying current to excite the secondary, you dismissed Roy's measurements with some odd response about him measuring current that doesn't flow. The inductive coupling does NOT require a time-varying current. All it requires is a time-varying H-field. That standing wave H-field is indeed varying but it's not because current is moving laterally up or down the wire. That H-field is fixed at a point on the line exchanging energy with the E-field which is also fixed at the same point. If the H-field is not moving laterally up or down the wire (it isn't) then the current is NOT flowing. You must have missed that day in your fields and waves class. Take a metal rod. Slip a string through a washer and tie it. Loop the string onto the metal rod. Put a grommet on the rod on each side of the string to keep it in one place in the X dimension on the wire. Now, keeping the X dimension fixed, swing the loop in the plane of the Y and Z dimensions and look at it on edge. You are looking at a physical analogy of the standing wave current at a point on a wire. Is the string moving? Not in the X dimension which is constant and fixed by the grommets. At any point on a wire with standing waves, the E-field and H-field are not moving laterally up and down the wire. They are *stationary* at a point on the wire. All that is happening at that point is the E-field and H-field are swapping energy at the RF frequency. The current probe naturally picks up those stationary oscillating fields. You and Roy still don't understand what it was that was being measured.The current that you and Roy measured was not flowing. It was just standing there. That's why they call it a *standing* wave. The currents that are required to be constant through the coil are the traveling-wave currents. A standing wave is not at all a wave in the classic definition of EM waves. It is simply a superposition of two classic EM waves flowing in opposite directions. Here's an optical example of what is happening to you. The yellow light coming from your TV is an interference pattern between red, blue, and green light. You are measuring yellow light thinking that's a primary color. It is not. But you could use your yellow light measurement to estimate the strength of the primary colors. The standing-wave current is an interference pattern caused by superposition of forward and reflected current waves. Like the yellow light you are seeing, it is not primary, and like the yellow light, it is an artifact of interference.. In a wire in which one amp is flowing in one direction and one amp is flowing in the opposite direction, there is no net flow of current. Therefore, standing wave current has no net flow. That is obvious from its constant, fixed phase angle which doesn't change (much). I already measured the phase of current, and it is nearly zero degrees. The measured phase of the net standing wave current is near zero degrees whether a coil exists or not. All it means is that the net standing wave current is standing still. Basing your conclusions upon measurements of a current that is not even flowing is foolish. I don't know what others think, but it is starting to look to me like you either don't understand the basics of measurements or you are just unwilling to learn. You have been seduced by your model that is known to fail in the presence of standing waves. Why you cling to such a false prophet in the real world is beyond me. I can measure that. My network analyzer measures time delays. The problem I see is if I take time from my busy schedule and measure it, you will either call me a liar or say I measured current that doesn't flow. If you measure a traveling wave current, you will be measuring a current that is actually flowing. Your S12 phase shift measurement showed a -60 to -70 degree phase shift in a 100uH coil at one MHz. That measurement of yours has already proved that your lumped-circuit model is invalid. Why didn't you just use the zero degrees predicted by the lumped-circuit model instead of measuring it? :-) Before measuring anything specific I'm going to warn you that I've measured group delays many times before, and the group delay in an inductor is significantly less than the group delay in a transmission line of the same conductor length. I know that from past experience. I know that, Tom. The point is: If there is any appreciable delay through the coil, that fact violates the presuppositions of the lumped- circuit model. Therefore, a lumped-circuit model cannot be used to explain the characteristics of that real-world coil and especially not in a standing wave environment. But if you promise to control yourself and not dismiss a measurement with personal attacks or insults, and promise to not do an about-face like you did with Roy and say "you really didn't measure current that moves with your thing that only measures changing current", I will do that. I appreciate that and I would also appreciate it if you didn't pencil whip the results before reporting them. Please just be honest. I assume we are both after the truth. And be sure to measure a coil something of the size of a 75m bugcatcher coil. I think a 75m bugcatcher coil would show more of a delay than a toroidal inductor of the same inductive reactance. I really wish some of your ideas were correct. If they were correct, I would not have thousands of feet of coaxial cables coiled under my bench. I would not be forcing customers to cut long delay lines when their equipment could just use a simple wound up piece of enameled wire. Surely, you are familiar with helical transmision lines with a very, very small velocity factor. And Intel does use simple coils as delay lines in some of their PCB designs. Does ANYONE on this newsgroup understand Cecil? I need help here. They are there, Tom. But they just don't want to tangle with a junk yard dog. Most people don't have a thick enough skin to withstand your onslaughts. I get a couple of emails a week from those guys. One distinguished gentleman and well known ham said that you have never lost an argument, even when you were wrong. I know exactly what he means. What a silly statement. We are measuring a time-varying current that doesn't flow or change! It's magnitude changes but it indeed doesn't flow or change phase. It's magnitude changes because the E-field and H-field are continuously exchanging energy at the frequency of operation. If you understood the implications of a constant, fixed, unchanging phase, you would know that. Yes, if he wrote what you quoted and you didn't lift something out of context I totally disagree with him. So be it. Your lumped-circuit model is known to fail in the presence of standing waves. Nonsense. YOUR LUMPED-CIRCUIT MODEL IS KNOWN TO FAIL IN THE PRESENCE OF STANDING WAVES! What is it about that statement that you don't understand? Your lumped-circuit model presupposes conditions that don't exist in a standing wave environment. Therefore, it is invalid and another more powerful model must be chosen.Because your chosen model is invalid, the validity of everything you say is questionable. The lumped-circuit model is a subset of the distributed-network model. The distributed-network model is a subset of Maxwell's equations. If you don't understand the limitations of the model, you will choose to use it under the wrong circumstances. That's what you, Roy, and others have done. -- 73, Cecil, W5DXP |
Current through coils
On Fri, 10 Mar 2006 17:04:54 GMT, "Cecil Moore"
wrote: the RF current wave :-) |
Current through coils
Quoted from an e-mail exchange I am having:
However, I'd like you to reconsider your position concerning inductances in series with a line that has both forward and reverse currents flowing, as in short mobile antennas. As a result of two currents from the same source flowing in opposite directions, a standing wave is inevitable, hence different values of current at different points along the wire in the inductor. That is incorrect for the conditions we are outlining, and it is misleading Cecil. It has him lost in a world of reflections. You have gone outside the limits of the model by assuming, incorrectly, the inductor has no or little flux linkage from end-to-end and has large stray capacitance to the outside world compared to load impedance. The conductor used to build a inductor does not have current slowly winding its way along that path. There is no virtually no difference in phase delay in current at each end of a relatively compact inductor. It is very easy to measure that. It also have very little group delay compared to the group delay one would expect from a transmission line or antenna the same length. I know that because I have measured it hundreds of times. I have repeated a url below that Cecil posted on the rraa. The material in that url agrees with my position, and specifically states that circuit analysis is invalid when the model contains distributed currents, and admonishes that anyone who disbelieves this has forgotten the warning about the situation given in sophmore EE courses. The Tesla coil, by definition of how it works, violates all boundaries of the examples myself and others are giving Cecil. It does not apply to the discussion at all. The Tesla coil is intentionally of exceptionally long form factor. It has virtually an open circuit at the end, and is by operation self-resonant at the operating frequency. It has a very large amount of distributed capacitance compared to termination impedance, since the termination is an open. It is not operated at a fraction of self-resonance as people SHOULD know a good mobile loading coil is. It has no bearing at all on the discussion, any more than it would if I started measuring the plate choke from an AL1200 amplifier at the self-resonant frequency with an open termination, or a loading coil for a 75 meter antenna at the self-resonant frequency. Everyone (except Cecil) has been very careful to give the boundaries and describe the effects. The Tesla coil does not fit the boundaries described, and the secondary inductor in the Tesla coil behaves nothing like an inductor operated well below self resonance. http://www.ttr.com/corum/index.htm The very first paragraph of that reference should have been a red flag that it does not apply to this discussion. Here is what it says: "Can one model the physical operation of a Tesla coil appropriately with only lumped-element circuits? If not, why not? It was pointed out long ago that, at its operating frequency, a Tesla coil is NOT a lumped-element induction coil. Forget the quest for "many turns of fine wire". In fact, a Tesla coil has more in common with a cavity resonator than it does with a conventional inductor." The key words they use, and they even drew attention to the words by a type style change, "at its operating frequency, a Tesla coil is NOT a lumped-element induction coil". They were very clear about that, and go on to describe how it does behave like a normal induction coil. Everyone in the conversation has been very careful to clearly establish the boundary conditions that the behavior we are talking about is significantly below self-resonance, an inductor of compact form factor, and an inductor of good design. I can't understand why anyone would attempt to reference an article that, in the very opening, states the inductor is operating at self-resonance! I can't understand why anyone would reference an article that violates the boundaries of termination impedance outlined in the discussion, where it has been stated over and over again the inductor must be terminated in an impedance that is low compared to leakage impedances. I can't imagine anyone using a lossy Tesla coil as an antenna or part of an antenna system. Please read the opening paragraphs of the article you reference. 73 Tom |
Current through coils
On Fri, 10 Mar 2006 17:04:54 GMT, "Cecil Moore"
wrote: wrote: What Cecil needs to do is bias the coil with a DC bias current that safely exceeds the peak RF current. Then he would have RF current flowing in only one direction. I should have said: have the RF current wave flowing only in the forward direction.Wes knew what I meant. I did? |
Current through coils
Cecil Moore wrote:
wrote: What Cecil needs to do is bias the coil with a DC bias current that safely exceeds the peak RF current. Then he would have RF current flowing in only one direction. I should have said: have the RF current wave flowing only in the forward direction.Wes knew what I meant. I think a lot of the contention on this subject is based on little more than such multiple meanings for common term, "current". When you talk about current flowing, you seem to be thinking of current waves traveling along a conductor. Others seem to be saying "current" and thinking of charge movement. I think that only the second is technically correct (current is the movement of charge, not the traveling wave or standing wave pattern in that movement), but I think I understand what you are picturing. We switch to the short hand concept of calling a pattern of current changes a current every time we make an AC current measurement and refer to it as a non zero value, as we do with amperes (RMS). Standing waves involve no net wave travel in either direction, though anywhere except at the current nodes, charge is certainly moving back and forth along the conductor, during a cycle. Thus, there certainly are instantaneous currents in both directions (depending on location and instant) along any conductor sustaining a standing wave, everywhere, except at the current nodes. And everywhere, except at voltage nodes, half way between current nodes, charge is piling up (as electrons move toward every other current node) and spreading out as electrons moves away from the remaining current nodes) creating voltage changes. Traveling waves have a very similar charge movement as that which takes place half way between the nodes and peaks of the standing wave pattern. But there are no nodes or peaks, so the current swings between the same 2 values, everywhere along the conductor. Charge arrives from one direction, instead of from both directions and leaves in the other direction, each half cycle. Every other half cycle, the directions of arrival and departure reverse, even though the wave always moves in one direction. I am talking about conduction in wire, not EM waves in space, here. This current (movement of charge in either a standing wave or a traveling wave) creates H field and the changes in that H field can be monitored with a current transformer. But at any single point, current measured with a current transformer has no way of knowing if the current changes seen are the result of a standing wave or a traveling wave. In both cases, charge is seen to be moving in alternating directions. But if you slide the current transformer along the conductor, the current magnitude will vary if standing waves are responsible for the current, and remain, essentially constant, if traveling waves are its source. I apologize for stating the painfully obvious, but when basic terminology is the cause of misunderstanding, it sometimes helps to back up a step in the direction of a more basic view to uncover the origin of the misunderstanding. |
Current through coils
wrote :
That is incorrect for the conditions we are outlining, and it is misleading Cecil. It has him lost in a world of reflections. What is causing the misleading part is: THE LUMPED-CIRCUIT MODEL FAILS IN THE PRESENCE OF STANDING WAVES! There is no virtually no difference in phase delay in current at each end of a relatively compact inductor. Is a 75m bugcatcher coil a "relatively compact indictor"? If you say yes, you are stuck with its measured delay. If you say no, then we are not discussing the typical amateur radio mobile loading coil. Of course, one turn on a toroid is going to exhibit the characteristics you are presenting. But that is not a typical bugcatcher coil either. The Tesla coil, by definition of how it works, violates all boundaries of the examples myself and others are giving Cecil. It does not apply to the discussion at all. False: A 75m bugcatcher coil used as a 1/4WL resonator on 9-10 MHz meets the minimum requirements for a Tesla coil. It uses 1/6 wavelength of wire on 75m. I'll bet it would certainly arc at a kilowatt. The typical minimum Tesla system is a coil with a top hat sphere. It looks a lot like your 160m mobile antenna. :-) It is not operated at a fraction of self-resonance as people SHOULD know a good mobile loading coil is. A 75m bugcatcher coil is operating close enough to its self-resonant frequency that the self-resonant effects are certainly present. A 75m bugcatcher coil can be considered to be a lumped circuit impedance at 60 Hz but certainly not at 4000000 Hz. In fact, that is the whole question. At what frequency can the lumped circuit model be validly used on a 75m bugcatcher coil? I'm willing to bet that frequency is lower than 1000000 Hz. It has no bearing at all on the discussion, ... Wishful thinking on your part. .. In fact, a Tesla coil has more in common with a cavity resonator than it does with a conventional inductor." A 75m bugcatcher coil has more in common with a cavity resonator than it does with your lumped circuit inductance. "at its operating frequency, a Tesla coil is NOT a lumped-element induction coil". Neither is a 75m bugcatcher coil. Everyone in the conversation has been very careful to clearly establish the boundary conditions that the behavior we are talking about is significantly below self-resonance, an inductor of compact form factor, and an inductor of good design. A 75m bugcatcher coil used on 4 MHz is NOT significantly below the self-resonant frequency of 9-10 MHz. THE LUMPED-CIRCUIT MODEL FAILS IN A STANDING WAVE ENVIRONMENT! In the face of that simple technical fact, all other discussion is moot. Anyone wishing to validly model a 75m bugcatcher coil used on a mobile antenna is forced to choose a model that does not presuppose faster than light wave travel through a 75m bugcatcher coil. It's as simple as that. Tom, with a straight face, I want you to assert that the RF waves on a 75m bugcatcher mobile antenna are traveling faster than the speed of light. If it takes 125 nanoseconds for the forward current wave to make it from the end of the antenna and back to the feedpoint, then the lumped-circuit model yields invalid results. TDR anyone? -- 73, Cecil, W5DXP |
Current through coils
|
Current through coils
Cecil Moore wrote: A 75m bugcatcher coil used on 4 MHz is NOT significantly below the self-resonant frequency of 9-10 MHz. Yes it is, but no so far as to have perfectly equal currents at each end an zero phase shift in current. It is in the neither land between a Tesla coil (which is still nothing like my mobile antenna, but at least getting closer) and a idealized lumped component. THE LUMPED-CIRCUIT MODEL FAILS IN A STANDING WAVE ENVIRONMENT! In the face of that simple technical fact, all other discussion is moot. Anyone wishing to validly model a 75m bugcatcher coil used on a mobile antenna is forced to choose a model that does not presuppose faster than light wave travel through a 75m bugcatcher coil. It's as simple as that. Nonsense. You are ignoring the coupling mechanisim inside the inductor. Tom, with a straight face, I want you to assert that the RF waves on a 75m bugcatcher mobile antenna are traveling faster than the speed of light. If it takes 125 nanoseconds for the forward current wave to make it from the end of the antenna and back to the feedpoint, then the lumped-circuit model yields invalid results. TDR anyone? They are not travelling faster than light. What you (and the one or two others who seem to agree with you) repeatedly ignore or forget is magnetic flux couples one turn to another. A real inductor is always someplace between the two extremes of something like a radial mode helice (helically loaded whip) and an ideal lumped component. Since you have taken the path of totally forgetting or ignoring flux coupling, you are reaching incorrect conclusions. Using the Tesla coil model is a good example. Everyone is freely admitting there is *some* transmission line effect going on. There is some distrbuted component (a series of inductors shunted by capacitors) going on. Everyone (except you) is being careful to qualify remarks by specifying the inductor is operating well below self-resonance. If you weren't so pig-headed you could look at the measured data at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm ....and see that as inductors move towards self-resonance they do begin to display characteristics of transmission lines. It's too bad in three years you have claimed others made a measurement error, when in fact the error is in thinking all of the current in a loading coil slowly winds its way around turn by turn and the magnetic field linking turns does not cause charges in other turns to move long before current traveleing at light speed would wind through the copper path. Until you stop, put the beer away, and think about this a while you'll continue to butt your head up against people who KNOW how inductors behave. 73 Tom |
Current through coils
Wes Stewart wrote:
"Cecil Moore" wrote: Wes knew what I meant. I did? Hopefully anyone with an IQ above 80 knew that. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote:
Any discussion of inductors and waves needs to either select an example inductor for discussion, e.g., 75m bugcatcher mobile loading coil. or remain general enough to cover anything that might be called an inductor. e.g., Maxwell's equations. Certainly not a lumped-circuit model that presupposes that EM waves travel through anything and everything faster than the speed of light. Or else, endless and pointless arguments will ensue. Yep, notice how the inductors that Tom is talking keep getting smaller and smaller with time. Pretty soon they will indeed be point-sized inductors. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Cecil Moore wrote: A 75m bugcatcher coil used on 4 MHz is NOT significantly below the self-resonant frequency of 9-10 MHz. Yes it is, but not so far as to have perfectly equal currents at each end an zero phase shift in current. It is in the neither land between a Tesla coil (which is still nothing like my mobile antenna, but at least getting closer) and a idealized lumped component. That's about a 99% change in attitude from when we started this discussion a couple of years ago. At that time you were claiming that a 75m bugcatcher coil modeled as a lumped inductance with EZNEC showed zero change in current magnitude and phase and that was that. I'm glad to see the truth winning for a change. I think you are going to have to go a *LOT* lower in frequency than 4000000 Hz before a 75m bugcatcher coil can be treated as a lumped-inductance. THE LUMPED-CIRCUIT MODEL FAILS IN A STANDING WAVE ENVIRONMENT! In the face of that simple technical fact, all other discussion is moot. Anyone wishing to validly model a 75m bugcatcher coil used on a mobile antenna is forced to choose a model that does not presuppose faster than light wave travel through a 75m bugcatcher coil. It's as simple as that. Nonsense. You are ignoring the coupling mechanisim inside the inductor. That coupling mechanism works, at best, a lot lower than the speed of light and only on the voltage. In a high-Q inductor, the current is known to lag the voltage by a phase angle approaching 90 degrees. Do you have any idea what the velocity factor of a 75m bugcatcher coil is? I'll bet Reg can tell us. If the voltage is indeed traveling at the speed of light, the current is known to lag the voltage by a large number of degrees approaching 90 degrees for an ideal coil. The laws of physics strikes again. How can you bring yourself to ignore them? The voltage cannot travel faster than the speed of light and the current is lagging by, e.g. 60 degrees. It's hard not to suffer a 40 nS current wave delay through the coil on 4 MHz. I've told this to you before but you have avoided the subject like a plague. What you (and the one or two others who seem to agree with you) repeatedly ignore or forget is magnetic flux couples one turn to another. A real inductor is always someplace between the two extremes of something like a radial mode helice (helically loaded whip) and an ideal lumped component. You are talking about the E-field, not the H-field. I can agree with the E-field propagating at the speed of light but the H-field is known to lag the E-field by an angle approaching 90 degrees in the limit for an ideal inductor. Or is that another law of physics that you simply choose to ignore? Everyone is freely admitting there is *some* transmission line effect going on. There is some distrbuted component (a series of inductors shunted by capacitors) going on. Are you admitting that a 75m bugcatcher coil can be modeled as a transmission line with a Z0 and a VF? If so, you are giving up on your lumped-constant model. Actually, since the lumped-constant model is a subset of the distributed-network model, the lumped- constant model is very often wrong when the distributed-network model is correct. OTOH, it is impossible for the lumped-constant analysis to be right while the distributed-network analysis is wrong. So much for your choice of models. Everyone (except you) is being careful to qualify remarks by specifying the inductor is operating well below self-resonance. A 75m bugcatcher coil is NOT operating "well below" self-resonance. It is operating at 1/2 the self-resonant frequency. If one adds one foot at a time to the stinger above a 75m bugcatcher coil, at exactly what frequency does it cease to act like a "velocity inhibited slow-wave helical" and start acting like a lumped inductance? I propose that frequency is considerably lower than 1000000 Hz. If you weren't so pig-headed you could look at the measured data at: http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm You measured standing wave current, Tom. Your measurements are meaningless! Standing wave current has the same constant phase whether the coil exists or not. Your measurements prove absolutely nothing that is not already known. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote: You measured standing wave current, Tom. Your measurements are meaningless! Standing wave current has the same constant phase whether the coil exists or not. Your measurements prove absolutely nothing that is not already known. Nothing I have said has changed from what I've said for years. Now you have magnetic fields traveling slower than light speed in air, and have gone right back to the same nonsense of standing wave current. Please tell us all how you would measure the "traveling current" while ignoring "standing wave current". This ought to be good..... |
Current through coils
wrote:
Please tell us all how you would measure the "traveling current" while ignoring "standing wave current". Good question. One would ideally do it in a system without reflections. I am struggling with that concept right now. The best thought I have come up with so far is simple: coil +----////----+ | | source --- cap | --- | | +--/\/\/\/\--+ resistor I'm not a measurements guy so I could use some help. What's wrong with just reporting the measured the delay through your test coils? Your measured data already shows the current on one side of the coil to be different from the current on the other side of the coil. All we have to worry about now is the delay through the coils. If I've got your attention, let me repeat something I posted days ago. The forward current through the coil can indeed be assumed to be equal magnitude at both ends of the coil without much error. That should make you happy. The delay through the coil is whatever it is but it is nowhere near zero. I assume that makes you unhappy. The reflected current through the coil can indeed be assumed to be equal magnitude at both ends of the coil without much error. That should make you happy. The delay through the coil is whatever it is but it is nowhere near zero. I assume that makes you unhappy. The standing wave is the phasor sum of the forward wave and reflected wave. Its magnitude can vary from about double the forward current at a current loop to close to zero at a current node. I assume that makes you unhappy. The standing wave phase is close to constant and fixed near zero degrees within 1/4WL of the feedpoint. I assume that makes you happy. So three out of six results should make you happy and that's about all any mere mortal can hope for. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote:
When you talk about current flowing, you seem to be thinking of current waves traveling along a conductor. Others seem to be saying "current" and thinking of charge movement. I think that only the second is technically correct ... John, many thanks for some rationality from a cool head. Conventions aside, that sounds about right. So would you agree that if there's a forward current of one amp and a reflected current of one amp, the net charge movement is zero and therefore the standing wave current is not "going" anywhere? How can something with a constant fixed phase angle of zero degrees "go" anywhere? Standing waves involve no net wave travel in either direction, though anywhere except at the current nodes, charge is certainly moving back and forth along the conductor, during a cycle. That's unclear to me. Why can't the E-field and H-field simply be exchanging energy at a point rather than any net charge moving laterally? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote: What's wrong with just reporting the measured the delay through your test coils? Your measured data already shows the current on one side of the coil to be different from the current on the other side of the coil. All we have to worry about now is the delay through the coils. What measurement are you talking about? The one I did over two years ago that has been up on my web site since that time? Something on a bench? |
Current through coils
Cecil Moore wrote:
John Popelish wrote: When you talk about current flowing, you seem to be thinking of current waves traveling along a conductor. Others seem to be saying "current" and thinking of charge movement. I think that only the second is technically correct ... John, many thanks for some rationality from a cool head. Conventions aside, that sounds about right. So would you agree that if there's a forward current of one amp and a reflected current of one amp, the net charge movement is zero and therefore the standing wave current is not "going" anywhere? How can something with a constant fixed phase angle of zero degrees "go" anywhere? Standing waves involve no net wave travel in either direction, though anywhere except at the current nodes, charge is certainly moving back and forth along the conductor, during a cycle. That's unclear to me. Why can't the E-field and H-field simply be exchanging energy at a point rather than any net charge moving laterally? Cecil, I think I said all of that before the fun and games started. In any case I agree 100% with John. Let me try again to answer your question. This is all very basic textbook stuff. I claim not the slightest bit of credit for any of this. First, I hope we can agree that current is defined as the movement of charge. In this case the charge moves only in the direction of the wire, let's call it the z-direction. The generic equation for a forward traveling wave is simply: y = A cos (kz-wt) The generic equation for a reverse traveling wave is: y = B cos (kz+wt) One can add constant phase offsets to the cosine arguments, but it does not make any difference here. It just makes things look messy, especially in ASCII. The parameters k and w are not independent either, but again that does not really matter here. In the case of current we can say: If = Io cos (kz-wt) Ir = Io cos (kz+wt) I have set the "A" and "B" coefficients to the same value, Io, for simplicity. If the currents are not the same the math gets a little messier, but there is no fundamental difference. Keep in mind that the If and Ir refer to the current that moves along the z-direction, i.e., charge moving in the back-and-forth direction along the wire. The "f" refers to the forward "wave", and the "r" refers to the reverse "wave". The current in both cases is not "forward" or "reverse" but simply back-and-forth as in any AC condition. It is essential to separate the concepts of wave and current. They may be connected, but they are not the same, and they are not interchangeable. OK, now lets add these two traveling waves together to make a standing wave. This is a linear system, and superposition applies. We can simply add the components. The basic equation is: Isw = If + Ir = Io { cos (kz-wt) + cos (kz+wt) } Through the use of a standard trigonometric identity this can be reduced to: Isw = 2Io cos (kz) cos (wt) What can be seen immediately is that the standing wave current still has exactly the same time dependence that the traveling waves had. The magnitude of the current is now a function of z, unlike the constant magnitude in the traveling waves. The "current" is still defined as above, namely the charge that moves back-and-forth in the z-direction. The current oscillation factor (wt) is now decoupled from "z", unlike the traveling wave case. The "wave" is stationary. The current itself, however, behaves exactly the same as in the case of the traveling waves. Of course there are important differences in radiation patterns for traveling waves and standing waves. The magnitude of the current is different along the wire. However, except at the standing wave nodes, the standing wave current is very real and non-zero. I am almost embarrassed to write this, since surely you and most readers know all of this quite thoroughly. However, it appears you may have overlooked something. I hope this helps. 73, Gene W4SZ |
Current through coils
And, of course, since the net current is a function of distance along
the wire, it follows that in the case Gene described, charge in each section of wire goes through a cyclic, sinusoidal increase and decrease. In other words, the wire exhibits capacitance. See Reg's second sentence in the posting that started this whole set of insanity off. (One might call the current Reg mentions in the third sentence "displacement current" as is often done.) Yawn. (It's kind of fun to look at an animation of the case where the magnitude of If and Ir are not equal. It's pretty straightforward to program in Matlab or Scilab.) Cheers, Tom |
Current through coils
At great risk, let me try this approach.
I have a 100 turn 2" diameter #18 gauge wire air core inductor. There are 100 turns, so there is about 630 inches or 32 feet of wire in the coil. I have a Network Analyzer with port to port time delay measurement capability. It measures coaxial cables very well, and even clip leads. Cecil, please predict or guess the group delay of this inductor at 3.8 MHz. Tell us all what that group delay means for your wave theory. Just come close, and I will tell you what it measures. I can even print the plot just for you. 73 Tom |
Current through coils
wrote:
What measurement are you talking about? The one I did over two years ago that has been up on my web site since that time? Something on a bench? That one on your web site measured the standing wave current. We know the phase of the standing wave current is irrelevent since it is essentially the same whether the coil is in or out of the circuit. i.e. there is no such thing as standing wave current "delay" since the phase of the standing wave current is essentially fixed at (or near) zero degrees. You have measured the S12 delay for 100uH at 1 MHz to be -60 to -70 degrees. What we need is the equivalent of the S12 delay for current, rather than for voltage. What is the current delay througn the coil when no reflections are present? In other words, if the coil were installed in a traveling-wave antenna, like a terminated rhombic, what would the delay be through the coil? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
John Popelish wrote: When you talk about current flowing, you seem to be thinking of current waves traveling along a conductor. Others seem to be saying "current" and thinking of charge movement. I think that only the second is technically correct ... John, many thanks for some rationality from a cool head. Conventions aside, that sounds about right. So would you agree that if there's a forward current of one amp By this I assume you mean a traveling current wave with an RMS value of 1 amp. and a reflected current of one amp, Meaning a returning current wave with an RMS current of 1 amp. the net charge movement is zero and therefore the standing wave current is not "going" anywhere? Sorry, no. There is no net (average over one cycle) current, whether the wave is traveling or standing. In both cases the instantaneous current changes direction every half cycle at any given point. If there is a standing wave made of a 1 ampere RMS current wave and a 1 ampere RMS returning wave, then the standing wave current will vary from zero amperes RMS at current nodes to 2 amperes RMS at current peaks. Looking just at just current, and at only a single point, a traveling current wave and a standing current wave are indistinguishable. You cannot tell if the measured RMS current is made up of a wave traveling in one direction, or the sum of two waves traveling in opposite directions. How can something with a constant fixed phase angle of zero degrees "go" anywhere? The only way to understand a standing wave having a phase of zero degrees, that makes sense to me, is that it applies to all points between one current node and the next. The points between the next two nodes have a phase of 180 degrees (charge is moving in the opposite direction at all times) with respect to the points between the first two nodes. So, if you pick some point between a pair of current nodes, all other points along the standing wave must be either be in phase with the current at that point, or 180 degrees out of phase with it. In a standing wave, charge sloshes back and forth in opposite directions between alternate pairs of current nodes. Likewise, where the charge piles up and sinks (at the current nodes), voltage peaks occur because of the charge accumulation or shortage. Standing waves involve no net wave travel in either direction, though anywhere except at the current nodes, charge is certainly moving back and forth along the conductor, during a cycle. That's unclear to me. Why can't the E-field and H-field simply be exchanging energy at a point rather than any net charge moving laterally? In an isolated EM plane wave, I think this is the case, and displacement charge in space takes the place of conductor current. But when a wave is guided by a conductor, we can measure the charge sloshing back and forth in the conductor in response to those fields. Take a look at: http://galileo.phys.virginia.edu/cla...axwell_Eq.html about half way down. Here is an excerpt: (begin excerpt) "Displacement Current" Maxwell referred to the second term on the right hand side, the changing electric field term, as the "displacement current". This was an analogy with a dielectric material. If a dielectric material is placed in an electric field, the molecules are distorted, their positive charges moving slightly to the right, say, the negative charges slightly to the left. Now consider what happens to a dielectric in an increasing electric field. The positive charges will be displaced to the right by a continuously increasing distance, so, as long as the electric field is increasing in strength, these charges are moving: there is actually a displacement current. (Meanwhile, the negative charges are moving the other way, but that is a current in the same direction, so adds to the effect of the positive charges’ motion.) Maxwell’s picture of the vacuum, the aether, was that it too had dielectric properties somehow, so he pictured a similar motion of charge in the vacuum to that we have just described in the dielectric. This is why the changing electric field term is often called the "displacement current", and in Ampere’s law (generalized) is just added to the real current, to give Maxwell’s fourth -- and final -- equation. (end excerpt) |
Current through coils
Cecil,
Earlier you made comments about the time delay through a 75 meter loading inductor being somewhere around 60 nS or so. You have consistently disagreed with me when I said time delay through an inductor with tight mutual coupling from turn-to-turn is somewhat close to light speed over the physical length of the inductor, rather than the time it takes current to wind its way around through the copper. You didn't like my measurement of a small 100uH choke, and said a large inductor like a bug catcher coil is different. You predicted standing waves in that inductor. I have a 100 turn 2 inch diameter air wound inductor of pretty good quality. It is 10 inches long. Please tell all of us the time delay you expect in that inductor on 3.8 MHz. Please tell all of us what that delay means for your various changing theories about waves standing in that coil. I'll sweep the inductor from below the BC band up to 30MHz in a time measurement mode and post the printout of the sweep with scale values and markers that show time delays. 73 Tom |
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