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Current through coils
Gene Fuller wrote:
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. On the contrary, when kz is not linked by a plus or minus sign to wt, the wave doesn't move anymore. Maybe you need a review? Gene, you are a genius. Why didn't I think of that? I recognize that equation from "Optics", by Hecht. Pick any point, 'z', and see what you get. Hecht says, "It doesn't rotate at all, and the resultant wave it represents *DOESN'T PROGRESS THROUGH SPACE* - it's a standing wave." The RF equivalent of a standing wave of light that doesn't progress through space is an RF standing wave that doesn't progress through a wire. That's what I have been telling you guys. Standing waves don't move. Standing wave current doesn't flow! Even in empty space, a light standing wave doesn't progress through space, i.e. IT DOESN'T MOVE! That is on page 289 of "Optics", by Hecht, 4th edition. From "Fields and Waves ...", by Ramo & Whinnery, in describing the standing wave situation: "The total energy in any length of line a multiple of a quarter wavelength long is constant, *merely interchanging between energy in the electric field of the voltages and energy in the magnetic field of the currents*." Again, proof that standing wave energy doesn't flow. It just stands there being exchanged between the E-fields and the H-fields. That is from page 40 of "Fields and Waves in Communications Electronics", by Ramo, Whinnery, and Van Duzer. Now I did make a mistake in what I said earlier and I apologize for that. I said the energy in the E-field and H-field exchanges at a "point" on the line. Obviously, since a current maximum occurs at a voltage zero, that can't be true so I mis-spoke. Since the voltage maximum is 1/4 wavelength away from the current maximum, as Ramo & Whinnery say, one has to consider 1/4WL of line, and not a point as I said. Consider a 1/4WL section of line with a voltage maximum at Z and a current maximum at Z+(1/4WL). The current at Z is zero and the voltage at Z+(1/4WL) is zero. The net energy in that 1/4WL of line is constant. No net energy is flowing into or out of that 1/4WL of line. At some point the E-field energy is strongest toward the Z end and 1/4 cycle later, it is strongest toward the Z+(1/4WL) end. Since there is no net energy flow into or out of the line, there is no net current flow into or out of the line. 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. Sorry, you are wrong there, Gene. On that same page, Hecht says, "The standing wave does not move through space: it is clearly not of the form f(x +/- vt). For your equations that statement would be: The standing wave current does not move through the wi it is clearly not of the form f(z +/- wt). When you separate the 'z' function from the 'wt' function, the wave doesn't move anymore. It, well, it just stands there, like a good little standing wave. 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. And stationary as Hecht says. Your own equation indicates that it is stationary, i.e. not moving. I am almost embarrassed to write this, ... As you should be for not realizing that [Isw = 2Io cos (kz) cos (wt)] is "clearly not of the form f(z +/- wt)", i.e. of the form of a current traveling wave that moves. Time to refresh you memory on that subject. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
John Popelish wrote:
the net charge movement is zero and therefore the standing wave current is not "going" anywhere? Sorry, no. Gene just posted the equation for standing wave current. Isw = 2Io cos (kz) cos (wt) This is definitely not in the form of a traveling wave. Hecht, in "Optics" says the standing wave does not move through space. Presumably, for the same reason, a standing wave does not move through a wire. Looking just at just current, and at only a single point, a traveling current wave and a standing current wave are indistinguishable. True but if you know the equation above, then they are distinguishable. 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. Yes, the subject in context is 1/4WL monopoles or 1/2WL dipoles. 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. Yes, I was confused about that. If the question is changed to: "Why can't the E-field and H-field simply be exchanging energy within each 1/4WL rather than any net charge moving out of that 1/4WL?", it would make sense. Thanks John, for the refresher course. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
Good grief!!!! I said several times that the standing wave does not move. I also said the "wave" is not the same thing as the "current". The current is nonzero even though the wave is stationary. At this point it is obvious that you are just interested in causing a fuss, and not the slightest bit interested in reaching any sort of resolution of this item. Bye. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: 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. On the contrary, when kz is not linked by a plus or minus sign to wt, the wave doesn't move anymore. Maybe you need a review? Gene, you are a genius. Why didn't I think of that? I recognize that equation from "Optics", by Hecht. Pick any point, 'z', and see what you get. Hecht says, "It doesn't rotate at all, and the resultant wave it represents *DOESN'T PROGRESS THROUGH SPACE* - it's a standing wave." The RF equivalent of a standing wave of light that doesn't progress through space is an RF standing wave that doesn't progress through a wire. That's what I have been telling you guys. Standing waves don't move. Standing wave current doesn't flow! Even in empty space, a light standing wave doesn't progress through space, i.e. IT DOESN'T MOVE! That is on page 289 of "Optics", by Hecht, 4th edition. From "Fields and Waves ...", by Ramo & Whinnery, in describing the standing wave situation: "The total energy in any length of line a multiple of a quarter wavelength long is constant, *merely interchanging between energy in the electric field of the voltages and energy in the magnetic field of the currents*." Again, proof that standing wave energy doesn't flow. It just stands there being exchanged between the E-fields and the H-fields. That is from page 40 of "Fields and Waves in Communications Electronics", by Ramo, Whinnery, and Van Duzer. Now I did make a mistake in what I said earlier and I apologize for that. I said the energy in the E-field and H-field exchanges at a "point" on the line. Obviously, since a current maximum occurs at a voltage zero, that can't be true so I mis-spoke. Since the voltage maximum is 1/4 wavelength away from the current maximum, as Ramo & Whinnery say, one has to consider 1/4WL of line, and not a point as I said. Consider a 1/4WL section of line with a voltage maximum at Z and a current maximum at Z+(1/4WL). The current at Z is zero and the voltage at Z+(1/4WL) is zero. The net energy in that 1/4WL of line is constant. No net energy is flowing into or out of that 1/4WL of line. At some point the E-field energy is strongest toward the Z end and 1/4 cycle later, it is strongest toward the Z+(1/4WL) end. Since there is no net energy flow into or out of the line, there is no net current flow into or out of the line. 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. Sorry, you are wrong there, Gene. On that same page, Hecht says, "The standing wave does not move through space: it is clearly not of the form f(x +/- vt). For your equations that statement would be: The standing wave current does not move through the wi it is clearly not of the form f(z +/- wt). When you separate the 'z' function from the 'wt' function, the wave doesn't move anymore. It, well, it just stands there, like a good little standing wave. 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. And stationary as Hecht says. Your own equation indicates that it is stationary, i.e. not moving. I am almost embarrassed to write this, ... As you should be for not realizing that [Isw = 2Io cos (kz) cos (wt)] is "clearly not of the form f(z +/- wt)", i.e. of the form of a current traveling wave that moves. Time to refresh you memory on that subject. |
Current through coils
Cecil warned me that if I posted, the posting would be nit picked to
pieces. I`ve read correct postings describing the incident and reflected waves on a transmission line, and Maxwell`s secret of radiation (displacement current produces a magnetic field same as conduction current). All this may be relevant or not to some extent, but they don`t seem to resolve the current through a coil. Tom, W8JI wrote: "You have consistently disagreed with me when I said the 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 rakes to wind its way around the copper." That contradicts established experience. The property of reactance is to limit current flow. Inductive reactance limits by means of counter-emf which depends upon the rate at which current is changing in the coil. A-C current changes most rapidly at zero time (the axis crossings of the sine waveform). Lenz`s law says the counter-emf must oppose the growth of current in this case. Opposotion of the counter-emf causes the current to reach its maximum 1/4-cycle after the emf applied to the coil reaches its maximum. As almost everyone knows, the current lags by 90-degrees in a pure inductor. Make the turns coupling as tight as you can, the current is still delayed by 90-degrees. Now, it surely is possible to bypass a perfect inductor with a capacitor to mitigate a delay. I can`t repeat without retyping text on my screen, so the fact that I don`t retype everything only means I`m lazy. Right or wrong, W8JI may never lose an argument, but when he is clearly wrong it should be pointed out. Best regards, Richard Harrison, KB5WZI |
Current through coils
wrote:
Cecil, 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, No, I haven't, Tom. What you are describing is the voltage delay. I have never argued with you about the voltage delay through a coil. It occurs at the speed of light adjusted for VF. In EE101 everybody learns that the voltage leads the current through a coil. The question is by how much in a 75m bugcatcher coil? Have you ever seen a graph of the voltage vs current at the output of a series coil? It shows the current lagging the voltage by 90 degrees. It takes a series resonant capacitor to align the current with the voltage again. rather than the time it takes current to wind its way around through the copper. If you can find a posting of mine like that, I'll give you $100. If you can't find it, please admit you are fibbing again about what I have said. You didn't like my measurement of a small 100uH choke, I didn't say I didn't like it. You posted some results and then described those same results differently as time passed. At the moment, I have no idea what those results were. Was the -60 to -70 degree delay a voltage delay or a current delay? and said a large inductor like a bug catcher coil is different. You predicted standing waves in that inductor. Now we are getting to the truth. A 75m bugcatcher is closer to being a Tesla coil than it is to being a lumped-inductor. It satisfies R.W.P. King's advice that if the wire length used to make the coil exceeds 1/6 wavelength then, "an adequate representation of the reactance of a coil with a nonuniformly distributed current is NOT POSSIBLE in terms of a coil with a uniform current". The 75m bugcatcher uses very close to 1/6 wavelength of wire. And yes, standing wave antennas have standing waves so a 75m bugcatcher coil is emersed in a standing wave environment. Quoting Dr. Corum: "Lumped element representations for coils REQUIRE that the current is uniformly distributed along the coil - no wave interference and no standing waves can be present on lumped elements." I have a 100 turn 2 inch diameter air wound inductor of pretty good quality. It is 10 inches long. What is the inductance? What is the Q? 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. First please describe the circuit used to drive the coil, what other components are in the loop, and how you are picking off the two currents at the ends of the coil. Is your Network Analyzer equipped with current probes? If not, you are wasting your time. We already know the delay for the voltage will approximate the speed of light adjusted for VF. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
Good grief!!!! Good grief!!! I've already posted in another posting that I was mistaken about that. There is standing wave charge migrating from end to end in a 1/4WL monopole. Next time I have spaghetti, I'll give myself 20 licks with a wet noodle. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
Tom, W8JI wrote: "You have consistently disagreed with me when I said the 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 rakes to wind its way around the copper." That contradicts established experience. Tom seems to be confusing the effects of the E-field with the effects of the H-field. The E-field propagates at the speed of light through a coil. The H-field propagates at the speed of light through a capacitor. Make the turns coupling as tight as you can, the current is still delayed by 90-degrees. Can the actual current phase delay be estimated knowing the Q of the coil? I don't recall a formula for that. Now, it surely is possible to bypass a perfect inductor with a capacitor to mitigate a delay. Dang Richard, now you've told Tom how to run his experiment in order to obtain the results he predicts. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote: Now, it surely is possible to bypass a perfect inductor with a capacitor to mitigate a delay. Dang Richard, now you've told Tom how to run his experiment in order to obtain the results he predicts. :-) You say you will accept something, you ask for something to be done, and when it is offered you back up and stall, preparing advance excuses why it won't be done correctly and refusing to make a prediction. You've eaten up hours of my time and the only thing I've learned is you don't want to learn, and you are so unsure of yourself you'll avoid any prediction of how something will work any way you can. I'm just amazed you have to fall back on name calling, mubo-jumbo, and inuendo when someone offers to help you understand something. I'm all done with this too. 73 Tom |
Current through coils
Gene Fuller wrote: Cecil, Good grief!!!! I said several times that the standing wave does not move. I also said the "wave" is not the same thing as the "current". The current is nonzero even though the wave is stationary. At this point it is obvious that you are just interested in causing a fuss, and not the slightest bit interested in reaching any sort of resolution of this item. Bye. 73, Gene W4SZ Cecil also said he wanted a measurement. When I asked him to make a prediction, he made excuses why any result would be wrong and avoided any prediction. Like you, I now am sure there is no reason to get caught up in any further exchange with him. Whatever he is trying to do, it certainly isn't teaching or learning. 73 Tom |
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