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Current through coils
Different currents at each end of a coil are easily explained.
A coil has capacitance to its surroundings distributed along its length. And current flows from it radially. Every coil has length. Both L and C are distributed. Therefore the coil behaves as a transmission line. There are standing waves. Current and voltage both vary with length. The longer the line the greater the variation. The line has phase-shift, Zo and attenuation resulting from wire loss resistance and radiation resistance. The line can have a resonant length. It then becomes a short antenna. The whole business can be mathematically modelled. ---- Reg, G4FGQ. |
Current through coils
Reg Edwards wrote:
The whole business can be mathematically modelled. The point is that it cannot successfully be modeled with the lumped circuit model where the current is constant everywhere in the circuit. What would Kirchhoff have thought about a coil with 0.1 amp at the bottom and 0.7 amps at the top? It certainly doesn't mean that 0.6 amps is flowing sideways. All it means is that the relative phase of the forward current and reflected current changes through the coil and therefore the distributed network model needs to be used. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
Interesting. I am quite familiar with Kirchoff's equation in regard to voltages around a loop and his equation about currents at a node. Did I miss a third equation regarding currents around a loop? Hint: Kirchoff would not be the slightest bit bothered by this problem. Reg, as usual, has it completely correct. 73, Gene W4SZ Cecil Moore wrote: Reg Edwards wrote: The whole business can be mathematically modelled. The point is that it cannot successfully be modeled with the lumped circuit model where the current is constant everywhere in the circuit. What would Kirchhoff have thought about a coil with 0.1 amp at the bottom and 0.7 amps at the top? It certainly doesn't mean that 0.6 amps is flowing sideways. All it means is that the relative phase of the forward current and reflected current changes through the coil and therefore the distributed network model needs to be used. |
Current through coils
Gene Fuller wrote:
I am quite familiar with Kirchoff's equation in regard to voltages around a loop and his equation about currents at a node. Did I miss a third equation regarding currents around a loop? Nope, you missed an implication of Kirchhoff's current law. Unequal currents into and out of a passive black box implies the existence of a node inside the box. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
The whole business can be mathematically modelled. IF one uses the correct model. Here's an email I received today. Walter Maxwell, W2DU wrote: Hi Cecil, I just today found the (QRZ.com) discussion. I agree with your position 100%. It's as simple as this: If an inductance is in series with a line that has no reflections, the current will be the same at both ends of the inductor. 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. When reflections are present, a current node and a current loop can appear at separate points on an inductor simultaneously. Walt -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
Your response makes no sense at all. Unequal currents into and out of a passive black box implies charge storage, which generally means capacitance. You cannot have it any other way, with or without waves or reflections. Conservation of charge is one of the most fundamental laws in nature. Reg was correct. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: I am quite familiar with Kirchoff's equation in regard to voltages around a loop and his equation about currents at a node. Did I miss a third equation regarding currents around a loop? Nope, you missed an implication of Kirchhoff's current law. Unequal currents into and out of a passive black box implies the existence of a node inside the box. |
Current through coils
Gene Fuller wrote:
Your response makes no sense at all. Unequal currents into and out of a passive black box implies charge storage, which generally means capacitance. Boundary condition: There's nothing but wire inside the black box. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller weote:
"Conservation of charge is one of the most fundamental laws of nature." Unequal currents into and out of a passive black box are very simple to produce. Suppose the black box contains a simple transformer with a ratio other than one to one? The power can be constant but the voltage and current must be different on input and output. R-F is a-c, not d-c. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard Harrison wrote:
Gene Fuller weote: "Conservation of charge is one of the most fundamental laws of nature." Unequal currents into and out of a passive black box are very simple to produce. Suppose the black box contains a simple transformer with a ratio other than one to one? The power can be constant but the voltage and current must be different on input and output. R-F is a-c, not d-c. Best regards, Richard Harrison, KB5WZI Now explain how you'd do it with a box having only two terminals -- and assuming the box is very small compared to a wavelength. Roy Lew |
Current through coils
Roy Lewallen, W7EL wrote:
"Now explain how you`d do it with a box having only two terminals--" I`ll give the mathematician`s answer: "It`s of no interest. It`s already been solved." Cecil said he would put a coil in the box. I agree. Retardation between incident and reflected waves in each direction would in most cases cause a current difference between the two ends of the coil. Unlike the usual transmission line, the wire is coiled to get reactance into a small space. The effect is the same in that phase shift is distributed along the length of the wire. There is just more of it and and the intervals between maxima and minima are short. Impedance and therefore voltage along the vire is a function of site along the wire. There will be a standing wave pattern throughout the coil. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard,
After that response all I can say is, this newsgroup is sure good for entertainment. 73, Gene W4SZ Richard Harrison wrote: Roy Lewallen, W7EL wrote: "Now explain how you`d do it with a box having only two terminals--" I`ll give the mathematician`s answer: "It`s of no interest. It`s already been solved." Cecil said he would put a coil in the box. I agree. Retardation between incident and reflected waves in each direction would in most cases cause a current difference between the two ends of the coil. Unlike the usual transmission line, the wire is coiled to get reactance into a small space. The effect is the same in that phase shift is distributed along the length of the wire. There is just more of it and and the intervals between maxima and minima are short. Impedance and therefore voltage along the vire is a function of site along the wire. There will be a standing wave pattern throughout the coil. Best regards, Richard Harrison, KB5WZI |
Current through coils
Cecil,
This is getting more interesting by the moment. Have you now removed some of the well-known physical attributes of wire and transmission lines? Specifically, what happened to the L and C of the wire? I have no issue with the use of network theory, reflection coefficients, standing waves, or any other commonly used descriptions. However, none of these mathematical conveniences change the fundamental physical laws. If current, and therefore charge, appears to be unbalanced, then there must be charge storage somewhere. As Reg pointed out, the charge is stored in the capacitance of the coil. No need to invoke any magic incantations about networks and standing waves. In principle any of these problems can be solved with very basic equations found in any E&M text. In practice it is extremely cumbersome to do so, and that is why all of the network formulations have been developed. Just don't fall into the trap of thinking that any new physical behavior is created by the reflections and standing waves. I believe in previous messages you have referred to that thinking as "seduced by the math models." 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Your response makes no sense at all. Unequal currents into and out of a passive black box implies charge storage, which generally means capacitance. Boundary condition: There's nothing but wire inside the black box. |
Current through coils
Roy Lewallen wrote:
Now explain how you'd do it with a box having only two terminals -- and assuming the box is very small compared to a wavelength. Assume a one-wavelength dipole off-center fed 1/4WL from one end. Using EZNEC with 60 segments, feeding at segment number 15 is 24.2% from one end and that's close enough for this example. This is actually done in EZNEC with a 130 ft. dipole on 7.2 MHz and I'll email out that file upon request. I'm going to describe the current distribution in the following diagram with 60 segments running from left to right in *fixed font*. Eash dash corresponds to a segment in EZNEC and F is the feedpoint. seg L L seg 1 v v 60 --------------F--------------------------------------------- ^ ^ ^ N N N The current distribution is sinusoidal. N stands for 'node' which is a current minimum point. L stands for 'loop' which is a current maximum point. Since I'm limited to ASCII, the reader will need to imagine a current envelope drawn from seg 1 up to 'L', down to seg 30, back up to 'L', and back down to seg 60. I'll follow this posting up with actual EZNEC graphics posted to my web page. Now we are going to replace part of that wire with a 6" long coil. A 6" long coil on 7.2 MHz is about 1/3 of one percent of a wavelength so that should qualify as 'very small'. And, to illustrate another fact, I'm going to make the coil from 1/4 wavelength of wire, 33' on 40m, and try to model that using the helical coil feature of EZNEC. That may or may not violate an EZNEC design rule - I just don't know yet. But it doesn't change the concepts being presented here. Let me say this is a very rough approximation to what happens in the real world. The concepts are accurate. The values may be off by a relatively large percentage. The coil certainly distorts the current away from that near-perfect sinusoid and certainly doesn't radiate like the wire it replaces. But roughly, here will be the results of placing the bottom of the coil at seg 30: seg L L seg 1 v v 46 --------------F---------------////---------------- ^ ^ ^ N N N The current at the left end of the coil will be low because that is roughly the location of a current node (minimum). The current at the right end of the coil will be high because that is roughly the location of a current loop (maximum). If one considers the current flowing from left to right, more current will be flowing into the coil than is flowing out of it, like the current at: http://www.qsl.net/w5dxp/qrzgif35.gif This is a standing-wave antenna so the standing-wave current displayed by EZNEC is flowing hardly at all. That standing- wave current consists of two component phasors, rotating in opposite directions. That's why the phase of the standing-wave current is relatively constant. The standing-wave phasor, the superposition of the forward and reflected current phasors, rotates hardly at all, usually by just a few degrees from end to end in a 1/2WL dipole. If the dipole is made of 'thin wire', the phase of the standing-wave current is fixed at zero degrees. (Can a phasor that doesn't rotate be called a phasor?) Taking 1/4WL of the antenna wire and winding it into a high-Q coil above replaces *roughly* 90 degrees of the antenna. The radiation pattern certainly changes because the coil doesn't radiate much. But we are not concerned about radiation patterns in this discussion. We are concerned about the current at each end of the coil, the same current that we measure and the same current reported by EZNEC. That current is certainly not constant through the coil and THE DIFFERENCE IN THE MAGNITUDE OF THE CURRENT AT EACH END OF THE COIL DEPENDS UPON WHERE IT IS PLACED IN THE STANDING-WAVE SYSTEM. The traveling-wave current through a coil is close to equal at each end. The standing-wave current at each end of a coil is NOT equal unless we locate the center of the coil at a current node or at a current loop. In a bottom-loaded mobile antenna, the coil is located very near a current loop where the slope of the current is near zero. In fact, the net current peaks inside the bottom-loading coil. So the concept that net current at each end of a coil installed in a standing-wave environment is equal is just a myth, an old wives' tale that needs to be banned from ham radio. The coil does indeed cause considerable distortion away from the perfect cosine current wave exhibited by a thin wire. But the macro effects of that cosine wave still exist when a coil is installed. The current at each end of a coil installed in a standing-wave antenna depends upon its location in the system. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
Unlike the usual transmission line, the wire is coiled to get reactance into a small space. The effect is the same in that phase shift is distributed along the length of the wire. W8JI measured a 60 degree phase shift through a 100uH coil at 1 MHz. Consider that at one end of that coil the forward and reflected currents may be: Ifor = 0.55 amps at zero deg, Iref = 0.45 amps at zero deg. Inet = Ifor + Iref = 1 amp at zero degrees. At the other end of the coil, the forward and reflected currents may be: Ifor = 0.55 amps at +60 deg, Iref = 0.45 amps at -60 deg Inet = Ifor*cos(60) + Iref*cos(-60) Inet = 0.275 + 0.225 = 0.5 amps at zero deg Some items of note: 1. The forward current magnitude is the same at both ends 2. The forward current phase is shifted by 60 degrees 3. The reflected current magnitude is the same at both ends 4. The reflected current magnitude is shifted by -60 deg 5. The forward and reflected current phasors rotate in opposite directions 6. The net current phase is unchanged through the coil 7. The net current magnitude is changed by 100% from 0.5 amps to 1.0 amps. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
I have no issue with the use of network theory, reflection coefficients, standing waves, or any other commonly used descriptions. However, none of these mathematical conveniences change the fundamental physical laws. If current, and therefore charge, appears to be unbalanced, then there must be charge storage somewhere. Gene, the flaw is in your misunderstanding of the fundamental physical laws, not in those laws. We measure the net current at one end of a coil at 0.1 amp and we measure net current at the other end of the coil at 0.7 amps (my web page example). The net current *APPEARS* to be unbalanced, but appearances can be deceiving. THERE IS NO STEADY-STATE CHARGE STORAGE ANYWHERE IN THE SYSTEM. Does this violate any fundamental physical laws? Of course not. Here's why (neglecting losses): V*I*cos(theta) equals the same power at both ends of the coil. That proves there is no steady-state energy storage. V1*(0.7)*cos(theta1) = V2*(0.1)*cos(theta2) This is a distributed network. A lumped circuit analysis fails miserably when you try to use it in a standing- wave environment and you have just proved it. That is also the same mistake that W8JI and W7EL have been making. The forward current at the 0.7 amp point is 0.4 amps at zero deg. The reflected current at the 0.7 amp point is 0.3 amps at zero degrees. The net current is the phasor sum of those two component currents. Inet = (0.4 amps at zero deg) + (0.3 amps at zero deg) Inet = 0.7 amps at zero deg The forward current at the 0.1 amp point is 0.4 amps at 82 degrees. The reflected current at the 0.1 amp point is 0.3 amps at -82 degrees. The coil causes an 82 degree phase shift in both forward and reflected currents and since their phasors are rotating in opposite directions, the sign of their phase shifts are opposite. The net current at this end of the coil is: Inet = Ifor + Iref Inet = (0.4 amp at 82 deg) + (0.3 amp at -82 deg) Inet = 0.057 amps + 0.043 amps = 0.1 amp at zero deg The fundamental physical laws are perfectly valid as has been demonstrated here. It is your understanding of them that seems to be the problem. You seem to have been fooled by appearances and as a result, you chose the wrong model with which to try to solve the problem. The distributed network analysis was developed because the lumped circuit analysis falls apart under certain circumstances. One of those circumstances is the presence of standing waves like the ones that exist in a 75m mobile antenna. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller, W4SZ wrote:
"This is getting more interesting by the moment." There are plenty of coils in boxes which have different currents into and out of their two ends. A coil in a box used to be a common way to resonate a too-short 1/4-wave (90-degree) whip. A company I worked for had many Land Rovers, trucks, boats, and ships on and around the Argentine side of the island of Tierra del Fuego.These were equipped with H-F SSB tranceivers. Mobile amntenna was a stainless whip mounted atop a substantial fiberglass box. The box contained the loading coil which was accessible for preselecting the right coil tap to resonate the whip with the vehicle for a particular operating frequency. The box also contained a motor-driven band-switch to automatically change taps on the coil when the frequency was changed on the radio. I am well aware of the ability to resonate a 90-degree whip with no more than the proper coil in series with the short whip on a base insulator. I tuned every one of those coils for each of the frequencies we used in Argentina with my own hands. ON4UN has a graph, Fig 9-22 on page 9-15 of "Low-Band DX-ing" which shows current distribution of a base-loaded whip, In his example, the whip is 45-degrees long.. The loading coil provides the extra 45-degrees required for resonance. Current at the base of ON4UN`s whip is one amp times the cosine of 45-degrees, or 0.707 amp. The loading coil has an input of one amp. With 1 amp into the loading coil and 0.707 amp out of the loading coil, the coil definitely does not have the same current at both ends. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard Harrison wrote:
ON4UN has a graph, Fig 9-22 on page 9-15 of "Low-Band DX-ing" which shows current distribution of a base-loaded whip, In his example, the whip is 45-degrees long.. The loading coil provides the extra 45-degrees required for resonance. Current at the base of ON4UN`s whip is one amp times the cosine of 45-degrees, or 0.707 amp. The loading coil has an input of one amp. With 1 amp into the loading coil and 0.707 amp out of the loading coil, the coil definitely does not have the same current at both ends. It's not that perfect in the real world but the basic concept still applies. The actual current at the top of the coil is somewhat higher than 0.707 amp because the current inside the coil is greater than 1 amp. EZNEC says the current about 1/3 of the way up from the bottom of the coil is about 1.15 amp. The inductance of the coil forces the phase between the voltage and current to increase. To maintain the same V*I*cos(theta) power, the current must also increase. The high flux fields developed inside the coil somewhat distort the perfect current cosine wave found in a thin wire dipole so it is not quite as black and white as ON4UN indicates. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
If one considers the current flowing from left to right, more current will be flowing into the coil than is flowing out of it, ... Correction! Should say: If one considers the current flowing from left to right, more current will be flowing out of the coil than is flowing into it, ... -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
And now things must be getting boring again out in the Texas prairie, so here it comes again. Have fun, folks. Roy, you are like the novice who uses a DC ohm-meter to measure the feedpoint impedance of an antenna. You are using a lumped circuit analysis in the presence of standing waves, not realizing what an extreme technical blunder that really is. Worse yet, you belittle people who point out your blunder. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
I have lots of flaws, most of them unrelated to RRAA. But a lack of understanding of fundamental physical laws is not one of them. Gene, you proved beyond any doubt, during the rest of your posting, that you even though may quote the fundamental laws, you are misunderstanding those fundamental laws. I think Richard Harrison does understand. If you refuse to listen to me, then please listen to him. Current is generally accepted as the flow of charge. Standing wave current is a net charge flow of zero. Standing wave current is DIFFERENT from traveling wave current. At any and every point, the standing wave current is NOT moving. Since it is not moving, there is NO net charge flow. Please read, understand, and respond to the following simple example and questionai Lossless Transmission Line, SWR is infinite ------------------------------------------------- Ifor-- 1 amp --Iref 1 amp 1. Is there any net flow of charge? ______ 2. Is the current at a current maximum point equal to 2 amps? ______ 3. Is the current at a current minimum point equal to 0 amps? ______ 4. Is there any net flow of charge between the 2 amp point and the zero amp point? ________ 5. If I replace the 1/4WL section of wire with a 90 degree phase shifting coil, have I changed very much? _________ 6. If the current at one end of that coil is 0 amps and the current at the other end of that coil is 2 amps, is there any net flow of charge through the coil? ________ When the current is different at the ends of a simple two terminal device then the charge flow is different as well. That is definitely NOT true for standing wave current. There is ZERO net charge flow for standing wave current. And standing wave current is exactly what you are measuring in a standing wave antenna like a 75m mobile antenna. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
ON4UN has a graph, Fig 9-22 on page 9-15 of "Low-Band DX-ing" which shows current distribution of a base-loaded whip, In his example, the whip is 45-degrees long.. The loading coil provides the extra 45-degrees required for resonance. Those diagrams were highly misleading, and have been withdrawn from the current 4th edition. That whole introduction to short verticals has been completely rewritten and revised. The problem was that the current profiles of the full-size and loaded quarter-wave antennas were both drawn against a linear vertical scale of *phase*. This not only misrepresented the physical lengths of the lower and upper sections, it also misrepresented the length and effect of the coil. This presentation is highly misleading, and the first victim was the person who drew it, and then overlaid current profiles on it. (I don't think this was ON4UN. When someone sets out to produce a 500-page book, they have to quote some things on trust from other people; and it may take a few editions to iron out all the kinks. Much more to the point, ON4UN is right at the leading edge of his subject, and each edition contains something new and important.) The replacement diagrams in the 4th edition are much better. They show current profiles against *physical* height, and help bring out what's really happening. Current at the base of ON4UN`s whip is one amp times the cosine of 45-degrees, or 0.707 amp. The loading coil has an input of one amp. With 1 amp into the loading coil and 0.707 amp out of the loading coil, the coil definitely does not have the same current at both ends. You can't quite those figures in evidence, because they were never more than a speculation based on misunderstandings. When ON4UN came to think about it, he quite rightly changed his mind. This brings up another point that hasn't been mentioned so far in this discussion: there is an important difference between purely inductive loading, and the kind of loading you can get from any practical inductOR. Note the difference. An inductOR is a real-life electronic component, a coil of wire. InductANCE is its main electrical property - but it isn't the only one. When a shortened antenna is loaded by pure inductance, you find the following: 1. The magnitude and phase of the current flowing into the loading inductance are both the same as that of the current flowing out (this is a fundamental property of pure inductANCE). This means the current distributions in the sections above and below the loading inductance join up in a sharp kink. 2. What does go through a step change is the *voltage* across the inductance. This changes in both magnitude and phase. For a typical centre-loaded whip, the RF voltage is low in all of the bottom section, but above the loading inductance it's very high indeed. To repeat: this is the situation for loading with pure inductANCE. (Sorry to keep shouting "ANCE!" and "OR!" like that, but I'll bet someone still comes back with a reply that proves they didn't read what I actually wrote.) The diagram in ON4UN's 4th edition (Fig 9-44) shows these effects much better than I can describe them in words. The diagram came from an article by W7XC in QST for March 1990. I strongly recommend everyone to look at these diagrams... but please don't treat them as 'bible text'. Do your own thinking about it. A different viewpoint on loading inductANCE is given in an article by Boyer in 'Ham Radio'. This uses the 'antenna-transmission line analog' theory... and comes to exactly the same conclusions about the effects of loading inductANCE: it is simply there to resonate the capacitive reactance that arises from having physically shortened the antenna. (Ironically, ON4UN's worked examples and computer programs to calculate loading inductance have always been based on this approach; the conceptual error in early editions was only in that one diagram.) With a firm grip on the way that pure inductANCE loads an antenna, you are then in a good position to look at the differences that appear when you use a practical inductOR. With a real-life inductOR, you don't have pure inductANCE any more. It is embedded in a component that is made from some length of wire, wound into a coil that has a physical length and diameter, has capacitance between its own turns, and also has capacitance to the straight sections of antenna above and below it. The effects of the coil's inductANCE will still be there, but you can certainly expect to see a lot of detailed differences. But the practical differences can't possibly be understood without that basic understanding about inductANCE as a foundation. Without it, you're building your house on sand. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Ian White GM3SEK wrote:
1. The magnitude and phase of the current flowing into the loading inductance are both the same as that of the current flowing out (this is a fundamental property of pure inductANCE). That is a fundamental property of a pure inductance in a lumped circuit analysis which assumes a DC current or a pure traveling- wave current. It is NOT a fundamental property of a pure inductance if the current you are talking about is a net standing wave current. Your stated principle is simply false for a standing wave environment. In a transmission line, it is easy to install a coil that has zero current at one end and an amp of current at the other end. It simply doesn't apply in a standing wave environment - and a 75m bugcatcher loaded mobile antenna is a standing wave antenna. Please take a look at my example and questionaire to understand what is wrong with your above statement. The measured current at the bottom of a loading coil is primarily standing wave current. IT IS NOT FLOWING. The measured current at the top of a loading coil is primarily standing wave current. IT IS NOT FLOWING. Since neither of these two currents are flowing, they don't have to be equal. They just stand there. If I present to you a black box with zero amps at one terminal and one amp at the other terminal, what can we conclude? One possibility is 1/4 wavelength of coiled up coax with an infinite SWR. Please ponder that and apply it to your coil assertion above. The currents that are doing the flowing are the underlying current components, the forward current and the reflected current and they are close to equal. Everything you say about a coil is true for the forward current and the reflected current. It is simply not true for the standing wave current which is just a conceptual construct and not a flowing phasor at all. If you really want to accurately apply the principles you are asserting, you must treat the forward current and reflected current separately and then superpose the results. Applying your above principle to standing wave current is akin to superposing power and that's a no-no. I have never seen such a wide-spread blind spot. Take the transmission line example. ---------------------------X---------------------------- Ifor=1.0amp -- --Iref=1.0amp There's a black box at 'X'. Inside the black box is 1/4WL of coiled up transmission line. The current measured at left of the black box is zero amps. The current measured at the right of the black box is 2 amps. That doesn't violate any laws of physics. That obeys the laws of physics for a transmission line with reflections. You are measuring the currents at a current node and at a current loop. It's absolutely no big deal. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
A few questions. Do you have a reference that explains this "net standing wave current that does not flow"? Does this magical current have any other interesting properties besides the lack of charge flow? Do ordinary properties such as inductance and capacitance cease to function when dealing with "net standing wave current"? Do you really think it is a good idea to base detailed numerical analysis on these "conceptual constructs" as you call them? Do you have a convenient listing of your "conceptual contructs" so that we can avoid these battles in the future? 8-) 8-) 73, Gene W4SZ |
Current through coils
Cecil Moore wrote:
Ian White GM3SEK wrote: 1. The magnitude and phase of the current flowing into the loading inductance are both the same as that of the current flowing out (this a fundamental property of pure inductANCE). That is a fundamental property of a pure inductance in a lumped circuit analysis which assumes a DC current or a pure traveling- wave current. It is NOT a fundamental property of a pure inductance if the current you are talking about is a net standing wave current. Your stated principle is simply false for a standing wave environment. In a transmission line, it is easy to install a coil that has zero current at one end and an amp of current at the other end. Be very careful here. We're talking about the effect of cutting the physically shortened wire antenna, and inserting a loading device. This therefore has to be a TWO-terminal device. It simply doesn't apply in a standing wave environment - and a 75m bugcatcher loaded mobile antenna is a standing wave antenna. Please take a look at my example and questionaire to understand what is wrong with your above statement. The measured current at the bottom of a loading coil is primarily standing wave current. IT IS NOT FLOWING. The measured current at the top of a loading coil is primarily standing wave current. IT IS NOT FLOWING. Since neither of these two currents are flowing, they don't have to be equal. They just stand there. I'm sorry, but those last three paragraphs are simply contradictions in terms, which demonstrate their own illogicality. Electrical current is defined as a net rate of transfer of electrons, so by the very definition of the term there is literally no such thing as a non-flowing current (except when the current is exactly zero and the definition becomes moot). I seriously wonder if you understand what a standing wave is. It is simply a pattern of variation in current along the length of a transmission line, which is stable in time. If you pick any point along the transmission line or antenna wire, there is a simple net current characterized by one amplitude and one phase, relative to some other reference point. (In this whole discussion we discount the normal cyclic sinusoidal variation of instantaneous RF current which is happening everywhere in the system.) In our minds, we may choose to explain the causes of the standing wave by resolving the net physical current into conceptual forward and reverse components; but the physical system doesn't know what you are thinking. To be valid, your concept must do nothing more than explain what's seen to be happening; it cannot seek to affect it. At the point where you have to say that a measured (and therefore measurable) current does not flow, your concept is in trouble. If I present to you a black box with zero amps at one terminal and one amp at the other terminal, what can we conclude? One possibility is 1/4 wavelength of coiled up coax with an infinite SWR. Please ponder that and apply it to your coil assertion above. Your length of coiled up coax is a FOUR-terminal device, like Richard's transformer was. It isn't an applicable solution for this problem. The currents that are doing the flowing are the underlying current components, the forward current and the reflected current and they are close to equal. Everything you say about a coil is true for the forward current and the reflected current. It is simply not true for the standing wave current which is just a conceptual construct and not a flowing phasor at all. If you really want to accurately apply the principles you are asserting, you must treat the forward current and reflected current separately and then superpose the results. It is entirely *your* responsibility to ensure that your postulated forward and reflected currents obey the same circuit laws as the physical net current. If you cannot do that, your concept fails. Applying your above principle to standing wave current is akin to superposing power and that's a no-no. I have never seen such a wide-spread blind spot. Take the transmission line example. ---------------------------X---------------------------- Ifor=1.0amp -- --Iref=1.0amp There's a black box at 'X'. Inside the black box is 1/4WL of coiled up transmission line. The current measured at left of the black box is zero amps. The current measured at the right of the black box is 2 amps. That doesn't violate any laws of physics. The laws it violates are those of logic. Your black box is not allowed to sometimes have two terminals and sometimes need four. That obeys the laws of physics for a transmission line with reflections. You are measuring the currents at a current node and at a current loop. It's absolutely no big deal. Sorry, I just don't see it. But what I do see are the contradictions and inconsistencies of logic that you are forced to resort to, in order to arrive at the conclusion you've already decided upon. I think that proves the exact opposite. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Gene Fuller wrote:
Do you have a reference that explains this "net standing wave current that does not flow"? No, this is one of those topics that is supposed to be "obvious to the most casual observer" and not worthy of further comment. Why it is not obvious to you and others is beyond belief. Some- thing terrible has happened to the educational system since 1957 when I learned all these principles at Texas A&M. I assume that this is just a part of the "dumbing down" of the educational system that I keep hearing so much about. Incidentally, these concepts are obvious to Walter Maxwell. Does this magical current have any other interesting properties besides the lack of charge flow? It's not magical but yes, it's phasor value (if it has one) doesn't rotate which is prima facie evidence that it doesn't flow. Any flowing phasor has a rotation of omega (2*pi*f). The fact that standing waves don't have a rotation is proof that they don't flow. To tell the truth, standing waves are a product of the human mind. The forward and reflected waves couldn't care less about standing waves. Last time I talked to them, they didn't even know that each other existed except for the points in the transmission line where their constructive interference causes the wire to heat up. :-) Surely you understand that standing waves in a transmission line don't flow - they just stand there, which is why they are called "standing waves". Exactly the same principle applies to standing wave antennas. Do ordinary properties such as inductance and capacitance cease to function when dealing with "net standing wave current"? No, but one has to exercise caution and invoke the superposition principle to ascertain what is happening. The two traveling waves have to be analyzed separately and then superposed to obtain valid results. If you analyze net current without superposition, you are doing the same thing as superposing powers, which is a known no-no. Do you really think it is a good idea to base detailed numerical analysis on these "conceptual constructs" as you call them? All human thought is based on conceptual constructs. That's what makes us different from the rest of the animals. If you don't like "conceptual constructs", then go swim in a zoo pool with the alligators. :-) Do you have a convenient listing of your "conceptual contructs" so that we can avoid these battles in the future? Only dealing with one at the moment, Gene. The lumped circuit model falls apart unless you first apply it to the component currents and then superpose. The distributed network analysis was developed to avoid that very problem. So the only valid choices are to either use the lumped circuit analysis on the component currents and then superpose or use the distributed network analysis which, in the end, boil down to the same thing. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Ian White GM3SEK wrote:
Be very careful here. We're talking about the effect of cutting the physically shortened wire antenna, and inserting a loading device. This therefore has to be a TWO-terminal device. Yes, I realize that. Do you realize that the characteristic impedance of a single #14 wire 30 feet above ground is 600 ohms? That pesky ground return path raises its ugly head once again. It's impossible to install a two-terminal system 30 feet above *ground* and have it remain a two-terminal system. It's only a two-terminal system in your mind. Electrical current is defined as a net rate of transfer of electrons, so by the very definition of the term there is literally no such thing as a non-flowing current (except when the current is exactly zero and the definition becomes moot). You have hit the nail squarely on the head without realizing it. A non-flowing current doesn't exist in reality but that is exactly what you are measuring when you measure standing-wave current. The only things that exist in reality are the forward and reflected current. So you guys are basing your high and mighty concepts on something that doesn't even exist in reality. No wonder you are confused. You are measuring two currents flowing in opposite directions at the same time and don't realize it. I seriously wonder if you understand what a standing wave is. It is simply a pattern of variation in current along the length of a transmission line, which is stable in time. Nope, that's not what it is. For example, a current standing wave on a particular transmission line is the sum of one amp flowing in one direction and one amp flowing in the opposite direction. Exactly what is the net charge flow when identical currents are flowing in opposite directions? Let's see now, this is a really tough one. One amp flowing in one direction minus one amp flowing in the opposite direction. What could the result possibly be? :-) Hint: think DC to see what the net charge flow would be. If you pick any point along the transmission line or antenna wire, there is a simple net current characterized by one amplitude and one phase, relative to some other reference point. (In this whole discussion we discount the normal cyclic sinusoidal variation of instantaneous RF current which is happening everywhere in the system.) I suggest you review traveling wave phasors which rotate at omega (2*pi*f). A standing wave 'phasor' doesn't rotate at all so a standing wave current is not moving. I'm not even sure it is technically valid to call a standing wave current a "phasor" since it doesn't even possess a frequency characteristic. Please think about a perfectly stationary, non-revolving 'phasor' and then comment. Wouldn't a non-revolving phasor be DC? To be valid, your concept must do nothing more than explain what's seen to be happening; it cannot seek to affect it. The same thing applies to your concepts. So what do your concepts say about a phasor with an omega(2*pi*f) equal to zero as is the case for standing waves? Are standing waves really DC? Do they exist at all anywhere besides the human mind? At the point where you have to say that a measured (and therefore measurable) current does not flow, your concept is in trouble. Sorry, I have absolutely no idea what that means. Surely you have measured zero current at a standing wave current minimum where the forward current equals one amp and the reflected current equals one amp. Is that zero amps in the act of flowing? Your length of coiled up coax is a FOUR-terminal device, like Richard's transformer was. It isn't an applicable solution for this problem. If you include that pesky ground under antennas, it is. My electronics equation book contains a formula for the characteristic impedance of a single wire transmission line over ground. Is that invalid? Doesn't that sound very much like a dipole wire in the air? The laws it violates are those of logic. Your black box is not allowed to sometimes have two terminals and sometimes need four. An antenna system installed on this earth is always a four terminal system whether you like it or not. Haven't you ever seen those diagrams of the current return to ground from an antenna system? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Ian White GM3SEK wrote:
Electrical current is defined as a net rate of transfer of electrons, so by the very definition of the term there is literally no such thing as a non-flowing current ... I'm sorry, I forgot to provide a reference for your non-existant non-flowing current. On page 464 of "Antennas for All Applications", by Kraus and Marhefka, 3rd edition, it shows the current on a 1/2WL dipole along with its phase. The phase is *fixed* at zero degrees over the entire 1/2 wavelength. So what does an RF current with a fixed phase of zero degrees really mean? It means that the 'phasor', if it is indeed a phasor, doesn't flow. How could an RF current with a fixed phase of zero degrees manage to flow? e^wt would be zero. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
....[snip]....
The measured current at the bottom of a loading coil is primarily standing wave current. IT IS NOT FLOWING. ....[snip].... My obviously-overloaded must-be-pea-sized brain sure has trouble thinking of current which is NOT flowing, since my basic internal definition of "current" is something like "electrons flowing past a point". I'm enjoying reading this thread, but, what with all the difficulties my brain is having with such subtle points, I'm NOT learning much! -- --Myron A. Calhoun. Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
Current through coils
A coil inevitably occupies space.
In particular, one of its dimensions is length. Therefore it can be, and indeed for accurate modelling always should be, treated as a component having distributed L, C and R. It just makes the mathematics somewhat more complicated. Hyperbolic functions can be involved. Like a transmission line, a coil possesses Zo, phase-shift, attenuation and Q. It is why my coil-loaded antenna programs provide answers in the right ball-park although I havn't a clue about the rules which govern the American ball game. By the way, reflections and standing waves are irrelevant and don't enter the argument. Sorry Cecil! ---- Reg, G4FGQ. |
Current through coils
Myron,
I'm afraid Cecil has a fixation about standing waves and reflections. He brings them into arguments on every possible occasion. Nevertheless he is very convincing and manages to drag most people in. Give your brain a rest. Visit your nearest barber shop and tune up. You will feel much better. ---- Reg. |
Current through coils
Myron A. Calhoun wrote:
"--I`m not learning much." Alas, I`d wager I don`t have anything new for Professor Calhoun, but from some of the postings, what I write may be new in part to someone. Current is defined as movement of electrons through a conductor. Obviously, an incomplete definition. As we know, there is beam current in the vacuum of a CRT, and that at r-f, skin-effect forces most electrons to the surface so that most electron movement is on or very near the surface of the conductor rather than "through" it. When currents of equal amplitude and opposite direction meet at various points along a perfect transmission line, as they might after a perfect reflection of the incident wave, one might measure zero amps at cancellation points along the line. These would be distributed periodically as the waves, in fixed phase relation and equal and opposite currents, coincide. The measurement of zero amps occurs because the ammeter is measuring both currents simultaneously. If a directional coupler is used to measure the current in each direction separately, it will be found that the currents traveling in opposite directions are passing through each other without effect. Standing waves are more manifestation than anything else. There was a PBS TV Channel appeal tonight. It Quoted Einstein as saying: "Nothing happens until something moves". Incident and reflected waves move on a transmission line but standing waves are stationary and don`t move. So, it is the incident and reflected waves that make something happen. Not the stationary waves. Circulating energy within a transmission line causes standing waves. Without a reflection, they don`t exist. Energy must be accepted by an antenna to be radiated. It is best if it is accepted on the first pass so that there are no more losses on additional passes. A perfect match at the antenna accepts energy on the first pass. A mismatched antenna produces an SWR. Magnitude of the SWR is an indication of how much mismatch there is. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard Harrison wrote:
If a directional coupler is used to measure the current in each direction separately, it will be found that the currents traveling in opposite directions are passing through each other without effect. Standing waves are more manifestation than anything else. And this is equally true of standing wave antennas. Kraus goes as far as assuming the forward and reflected currents on a 1/2 wavelength thin-wire dipole are equal in magnitude so they must be close to equal in magnitude. I have estimated that the magnitude of the reflected current after the round trip to the end of the dipole and back to be in the ballpark of 90% of the forward current at the feedpoint. This entire episode of constant current through a loading coil is the result of thinking standing wave current flows. As you say it is a manifestation of our thinking process and our measurements. It doesn't flow at all. Incidentally, a horizontal dipole above earth can be analyzed as a single-wire transmission line system with the earth being the ground return path. Balanis says, "Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forwards and backwards) and represented by traveling wave currents If and Ib in Figure 10.1(a)." The forward current (If) through a loading coil is very close to constant magnitude. The reflected current (Ib) back through a loading coil is very close to constant magnitude. Their phasor sum is the standing wave current that we measure. There is no physics requirement that the phasor sum of the forward and reflected currents be of equal magnitude on both ends of the loading coil. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
By the way, reflections and standing waves are irrelevant and don't enter the argument. Sorry Cecil! I'm curious, Reg. With traveling wave energy flowing in both directions through a loading coil, how do you analyze it without taking the forward and reflected energy into account? All my reference equations have a term with a positive exponent for forward current and another term with a negative exponent for reflected current. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
I'm afraid Cecil has a fixation about standing waves and reflections. They are part and parcel of a distributed network analysis and are embedded in many transmission line equations. As far as the constant current through the coil goes: Neglecting losses, the forward current through a coil is constant magnitude with changing phase. The reflected current through a coil is constant magnitude with changing phase. Those conditions satisfy the necessary and sufficient conditions of the laws of physics concerning a coil. The laws of physics do not require the phasor sum of the forward current and reflected current to be constant magnitude. In fact, the laws of physics prohibit the standing wave current from being equal magnitude except at equidistant points from a current maximum or minimum. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore incorrectly posted:
W8JI measured a 60 degree phase shift through a 100uH coil at 1 MHz. Consider that at one end of that coil the forward and reflected currents may be: Ifor = 0.55 amps at zero deg, Iref = 0.45 amps at zero deg. Inet = Ifor + Iref = 1 amp at zero degrees. At the other end of the coil, the forward and reflected currents may be: Ifor = 0.55 amps at +60 deg, Iref = 0.45 amps at -60 deg Inet = Ifor*cos(60) + Iref*cos(-60) Inet = 0.275 + 0.225 = 0.5 amps at zero deg The above analysis clearly shows how wrong Cecil is, and how he invents reasons to support things. I NEVER measured a current shift of 60 degrees, and I never said I measured a current difference of 60 degrees. The phase shift I measured was in VOLTAGE. It simply shows the voltage is out of step with the current. It doesn't indicate current is shifted 60 degrees between each inductor terminal at all, and I never said it did. The current level at each end of the inductor was, as far as I can measure with test equipment, equal. This is another clear case of Cecil taking things out of context and mixing them with his idea that an inductor treats current differently, depending on what direction it "flows" (or whatever he is claiming, I certainly can't make sense of his arguments). It is always better to let people directly post what they say, and not have it run through a "Cecil Moore" filter. 73 Tom |
Current through coils
wrote:
I NEVER measured a current shift of 60 degrees, and I never said I measured a current difference of 60 degrees. The phase shift I measured was in VOLTAGE. It simply shows the voltage is out of step with the current. It doesn't indicate current is shifted 60 degrees between each inductor terminal at all, and I never said it did. The subject was Kraus' 180 degree current phase shifting coils. Here are you exact words (and all of your words about that measurement) quoted from qrz.com: By the way, I swept S12 phase with my network analyzer on a 100uH inductor a few hours ago while working on a phasing system. The phase shift through that series inductor was about -60 or -70 degrees on 1 MHz, crossing ZERO phase at self resonance (where loss became very high) near 18 MHz, and gradually increasing leading phase above 18MHz reaching 90 degrees and staying there well above resonance. I apologize for missing the small detail that S12 was a voltage measurement rather than a current measurement but I'm sure you can see how that was an honest mistake and easy to make. You didn't mention "voltage" at all in your posting and the context was current. I didn't recall until your objection here today that S12 is a voltage parameter measurement. But that leads to a question. Why were you using voltage measurements to try to disprove Kraus' statement about 180 degree current phase shifting coils. Quoting from: "Antennas for All Applications", Kraus and Marhefka, 3rd edition, page 824: "A coil (or trap) can also act as a 180 deg (current) phase shifter as in the collinear array ... The coil may also be thought of as a coiled-up 1/2WL element." The current level at each end of the inductor was, as far as I can measure with test equipment, equal. That sure doesn't make technical sense. If there was no phase shift in the current, then the voltage was lagging the current. But we know the current lags the voltage through an inductor by as much as 90 degrees in the ideal case. If the voltage is delayed by 60 degrees, then the current must necessarily be delayed by 60 degrees plus the lag to satisfy the laws of physics. If you will run the experiment using current probes, I assure you that the current will experience more of a phase shift than the voltage, just as the laws of physics predict. Which means there was more than a 60 deg current phase shift through the coil which makes my argument even stronger. Now, if you are talking only about the magnitude of the current then of course, the current was equal at both ends of the coil because reflected energy was absent for that measurement. IT IS THE PRESENCE OF REFLECTED ENERGY THAT MAKES FALSE YOUR ASSERTION ABOUT NET CURRENT. I think we are in perfect agreement about systems without reflections. This is another clear case of Cecil taking things out of context ... Not out of context, Tom. The entire quote is just above. The mistake was an honest one and easy to make. I'm only human. :-) and mixing them with his idea that an inductor treats current differently, depending on what direction it "flows" ... Sorry, I never said that. An inductor treats forward waves and reflected waves exactly the same according to the laws of physics. Your statement is more akin to your idea that standing wave current flows into the bottom of a coil and out the top. The coil treats all traveling waves exactly according to the laws of physics and exactly as you and I understand those laws of physics. I accept everything you say about traveling wave current through a coil. My argument with you is that a standing wave current is not a traveling wave current and doesn't behave like a traveling wave current. That seems rather obvious to me. 1. Just as you say, the forward traveling-wave current through a coil is of constant magnitude. Here's what Walter Maxwell says: "If an inductance is in series with a line that has no reflections, the current will be the same at both ends of the inductor." All three of us agree on that statment. 2. As in (1) above and just as you say, the reflected current through a coil is of constant magnitude. 3. There is no law of physics that requires the standing wave current to be equal at the top and bottom of a coil. In fact, such a requirement violates those laws of physics. Here's what Walter Maxwell says: "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. When reflections are present, a current node and a current loop can appear at separate points on an inductor simultaneously." Judging from what he has posted earlier, Richard Harrison agrees with those statements. There's an EZNEC graphic at: http://www.qsl.net/w5dxp/qrzgif35.gif Would you have us believe that 0.1+ amps is flowing into the bottom of the coil and 0.7+ amps is flowing out of the top of the coil? It is your concept that standing wave current flows that is the problem. Please explain how a current with a zero phase angle from tip to tip on a 1/2WL thin wire dipole can possibly flow without a rotating phase angle. It is always better to let people directly post what they say, and not have it run through a "Cecil Moore" filter. I agree, Tom, but you were not posting here so I quoted what I honestly thought you said over on qrz.com. I quoted the same thing on qrz.com over a number of days. You could have pointed out my mistake a lot sooner and saved me from making it here. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Walter Maxwell, W2DU wrote:
Hi Cecil, I just today found the (QRZ.com) discussion. I agree with your position 100%. It's as simple as this: If an inductance is in series with a line that has no reflections, the current will be the same at both ends of the inductor. 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. When reflections are present, a current node and a current loop can appear at separate points on an inductor simultaneously. Walt I think it would be better if Walt represented himself, unless he ASKED you to post that Cecil. Why not let Walt post what he thinks rather than someone else telling us what Walt thinks? We each should speak for ourselves and let other people speak for themselves. If Walt has something to say, I'm sure he will chime in. Drumming up support by writing what we **think** others say or mean seems pretty desperate. All of that aside, what does it matter who agrees or disagrees? Things work they way they work. All reliable measurements I've seen disagree with Cecil's theory. I can't believe anyone with experience in RF systems would think a physically small inductor (small in terms of wavelength) would have significantly unequal currents in the inductor or in the terminals of the inductor, especially any difference caused by "reflected waves". 73 Tom |
Current through coils
wrote:
I think it would be better if Walt represented himself, unless he ASKED you to post that Cecil. Walt isn't presently posting for reasons of his own. He certainly gave me permission to quote his email. I will ask him if he wants to defend his statements here. If Walt has something to say, I'm sure he will chime in. I'm sure he will if he feels so inclined. Drumming up support by writing what we **think** others say or mean seems pretty desperate. Those were Walt's words, not mine. (Your statement reeks of desperation, i.e. "Please don't quote any authorities who disagree with me.") All reliable measurements I've seen disagree with Cecil's theory. Simply not true, Tom, proving once again that you don't understand what I am saying. My "theory" explains exactly why neither you nor W7EL could get the current at the ends of the coil to be equal without creating a current maximum point inside the coil. If you would just take time to understand what I am saying, you wouldn't need to utter falsehoods about what I am saying. The standing wave net current at each end of the coil is indeed the same magnitude if a current maximum or current minimum point is located inside the coil. Walter Maxwell says: "When reflections are present, a current node and a current loop can appear at separate points on an inductor simultaneously." Does that sound like constant net current through a coil? Exactly what is it about Walt's statement that you don't understand? I can't believe anyone with experience in RF systems would think a physically small inductor (small in terms of wavelength) would have significantly unequal currents in the inductor or in the terminals of the inductor, especially any difference caused by "reflected waves". A 75m bugcatcher coil is about 0.2% of a wavelength and so qualifies as "physically small". The current at each end of that coil used with an eight foot whip is nowhere near equal. I cannot believe that anyone with experience in RF systems could utter such nonsense. (That logic is a double-edged sword.) I think you and others simply didn't realize that the current in a 75m mobile bugcatcher system is almost 100% a standing wave current and now you guys are desperately trying to cover up your mistake. Others have stopped responding instead of admitting their mistake. So I ask you again: How do you explain the flow of a current whose phase is unchanging (fixed at zero degrees in a thin wire dipole). Doesn't it take a rotating phasor for current to flow? That's a simple yes/no question. What do you want to bet that it goes unanswered? Incidentally, I posted a little questionaire a couple of days ago. The response to that questionaire has been zero. Why do you reckon all the gurus are afraid to respond? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
I think it would be better ... I forgot to ask you, Tom, why you trimmed out all the technical content from my posting and whinned about what was left? So I ask you once again: In the graphic at: http://www.qsl.net/w5dxp/qrzgif35.gif do you really expect anyone to believe that 0.1+ amp is flowing into the bottom of that coil and 0.7+ amp is flowing out of the top of the coil. If, as you say, net standing wave current actually flows, then miracles must be possible and the coil is creating energy. If, OTOH, net standing wave current just stands there then such results as reported by EZNEC are just the facts of physics. It is the forward current and reflected current that are doing the flowing and their magnitudes are indeed individually equal through the coil. -- 73, Cecil http://www.qsl.net/w5dxp |
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