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Current through coils
On Wed, 8 Mar 2006 23:37:57 -0600, (Richard
Harrison) wrote: Where is the myth? Hi Richard, From "The Man Who Shot Liberty Valance:" "This is the west, sir. When the legend becomes fact, print the legend." 73's Richard Clark, KB7QHC (coulda' been worse, I just finished watching 2 hours of Monty Python) |
Current through coils
"Cecil Moore" wrote Reg Edwards wrote: Has it ever occurred to you guys that a coil is a coil wherever it is used and always behaves in the same way. The coil always behaves in the same way. Unfortunately, the models used to explain the operation of the coil don't work in the same way. Please see: http://www.ttr.com/corum/index.htm ======================================== Cecil, thanks, I speed-read your extensive pointer. The whole thing could be summarised in one short sentence - "Coils are distributed transmission lines." The same general equations apply to coils of all dimensions, for any number of turns, at all frequencies, in all applications. There's no need to unnecessarily complicate things by artificially dividing them into lumped and other varieties. I had to skip over the bit about Smith Charts. As you are aware I don't know how to use one. It seems Tesla, with HIS coils, knew what it was all about and he couldn't use a Smith Chart either. ---- Reg. |
Current through coils
Richard Harrison wrote: Tom, W8JI wrote: "Thinking the inductor or loading coil represents 60 degrees of electrical length is EXACTLY where the big myth is at and it can easily be proven to be a myth!" Suppose the vertical is only 2/3 the height needed for self resonance, or 60-degrees high. The loading coil must replace about 30-degrees of missing antenna to bring the vertical to resonance. The myth is in thinking your 60-degree vertical is 90 degree resonant by virtue of an inductor "replaces about 30-degrees of missing antenna". It does not do that. Every real-world inductor behave to some extent as a transmission line, but unless the inductor is spatially large in terms of wavelength or unless the inductor has a termination impedance significantly higher than the shunting impedance caused by its own self-capacitance to the outside world the "transmission line" or radiation mode effects are negligible. The ultimate in misunderstanding is when people think the loading inductor replaces a missing electrical degree length, rather than understanding a reasonably compact inductor primarily inserts a reactance that compensates for the capacitive reactance of the antenna system. Does it have some other behavior based on the fact it is less than perfect? Of course. No one is saying it doesn't have some limited effects! If I have a 10 degree tall base loaded antenna it is a ten degree tall antenna. It is NOT 90 degree resonant antenna with "80 degrees of missing length" in the inductor, nor with that 80 degree long inductor behave like 80 degrees of antenna length would. The very incorrect concept that an inductor and loaded antenna acts as a "80 degree coil and ten degree antenna" (substitute the numbers you want) is what kicked this whole thing off several years ago. 73 Tom |
Current through coils
"Amos Keag" wrote
My 60 meter mobile antenna is 90 degrees long, 1/4 wavelength resonant at 18 +j0 ohms [MFJ analyzer]. etc _____________ But how much of that resistance term is the true radiation resistance of your short radiator, and how much is contributed by the coil and "ground plane" losses? Resonating an electrically short radiator with a loading coil doesn't change the radiation resistance of the short vertical antenna (whip) itself -- and the r-f current able to flow in that whip is the source of practically all of the useful radiation that system can produce. The loading coil makes it possible for a practical transmitter to deliver r-f power into that short antenna system, but doesn't change the fact that it is only the short radiator itself that provides the useful radiation. The system may have the net reactance of a resonant, 1/4-wave vertical, but it will still have the radiation resistance of the original, short radiator, and that radiation resistance is the primary determinant of system radiation efficiency when using these coil-loaded antennas. RF |
Current through coils
Ian White GM3SEK wrote:
. . . It is true that we agree on a lot of things, but there's only one reason for that: because physical reality is the same in Oregon, England and Scotland as it is in Georgia. There is a very high probability that it's the same in Texas too. No, I really think there's some kind of reality vortex in Texas. Adding to the already overwhelming evidence is the recent news that Tom DeLay overwhelmingly won the primary election so is well on the way to re-election. Reality is quite obviously different there. Roy Lewallen, W7EL |
Current through coils
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Current through coils
Richard Harrison wrote:
Suppose the vertical is only 2/3 the height needed for self resonance, or 60-degrees high. The loading coil must replace about 30-degrees of missing antenna to bring the vertical to resonance. Here's the reason why. In a standing wave antenna, like a mobile antenna, the forward current and the reflected current are 180 degrees out of phase at the tip of the antenna and their phasor sum is zero. That is one of the laws of reflection physics. Their phasors are rotating in opposite directions so they must each rotate 90 degrees to be in phase and additive at the feedpoint. That's simple geometry. Your above antenna loading coil must contribute ~60 deg to the rotation of the forward and reflected currents. There is nothing else existing in the antenna that can accomplish that absolutely necessary function. Where is the myth? The lumped circuit model is generating a logical blunder. That model presupposes no phase shift through an inductance. Therefore, there is no phase shift through an inductance. (Circular Logic) Fortunately, the coil ignores our mis-applied man-made model and performs the phase shift anyway. The actual myth is that there is no phase shift through a 75m bugcatcher coil. That myth is rampant on ham radio web pages. The lumped circuit model assumes the proof before a solution to the problem is even attempted. It is a common mistake, known as 'petitio principii', in the solution of logic problems (also known as 'begging the question'). Some folks have simply forgotten that the lumped circuit model presupposes that no reflections exist. It cannot be used in a standing wave antenna environment. Now that these folk have been reminded of the technical facts, it will be interesting to observe the results. Will the erroneous web page information be corrected? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
I had to skip over the bit about Smith Charts. As you are aware I don't know how to use one. The basics are really easy. Do you want to learn? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
David Shrader wrote: wrote: SNIPPED If I have a 10 degree tall base loaded antenna it is a ten degree tall antenna. It is NOT 90 degree resonant antenna with "80 degrees of missing length" in the inductor, nor with that 80 degree long inductor behave like 80 degrees of antenna length would. If I have a 15 degree long physical antenna, center loaded at 10 degrees, with 5 degrees above the coil I do have a 15 degree physical antenna. That does not mean the antenna is NOT 90 degrees elctrically long! If the antenna is 15 degrees long, it is 15 degrees long. I'm not even sure "90 degree resonant" is a viable phrase, or what it means. Can I have a series tuned circuit that is "90 degree resonant"? Is the radiation resistance the same as a 90 degree tall Marconi? Is the current distribution the same? If we go to twice the antenna's frequency is it 180 degree resonant? Does it have a current maximum in the center and HV at each end? This is as bad as the MFJ 20 foot tall vertical half-wave that covers 80 through 2 meters. Resonance requires that the reactive components cancel both in amplitude and phase! Each reactive component introduces phase shift into the system. The antenna, without a loading coil, is composed of three terms: resistance [radiation and loss], self capacitance, and self inductance. In a shortened antenna the self capacitance dominates and the resultant phase shift is NOT zero. It is required to add inductance to achieve resonance [phase shift = 0]. If an antenna is electrically 15 degrees long and the self inducance does not reduce the reactive phase shift to zero PHASE SHIFT MUST BE ADDED TO THE ANTENNA for resonance. This phase shift is accomplished by the loading coil. So what? No one disagrees with that. The series loading inductor corrects power factor, or brings voltage back in pahse with current. Nothing I've written or read disagrees with that. Now, when that antenna is fed with 1 ampere [Imax] at the base of the antenna and the feed current follows a cosine distribution to the base of the coil [I = Imax*cos(theta)][theta=10], you claim that the current exiting the coil is also Imax*cos(theta), or 98.5% of max value. However, if we start with zero current at the tip, a valid initial condition, and let current increase by a sine function then I = Imax*sin(theta1][theta1 = 5 degrees] The result is simply 9% of max value. There seems to be a disconnect here. 98.5% = 9% ????????? That's because you have failed to realize the antenna has a triangular distrubution ABOVE the coil. I suggest you look at this link: http://www.w8ji.com/Topload_Rad_res.bmp If I understand you correctly, then the measured value at the base of the 15 degree antenna is NOT 1 ampere but only 0.07 amperes. Your misunderstanding appears to be rooted in thinking the antenna above the loading reactor has a sine distribution. It does not. It is basically triangular. Unless distribution is correctly visualized, conclusions will be flawed. It take a certain number of ampere-feet to radiate a given amount of power as EM radiation. When the spatial distance of the radiating element is reduced, the current has to increase. This is just another way of saying radiation resistance decreases, and current increases. Therefore, I offer that the loading coil provides the required additional inductance for resonance. I'll agree with that. It corrects power factor. It forms a series resonant circuit with the capacitance presented by the antenna above the inductor. The only thing you are missing is the current curves are nowhere like you assume in the whip above the coil. It's very well documented in hundreds of peer reviewed engineering texts that current takes on a triangular distribution in a very short radiator, and that the intetgrated current over the length of that radiator for a given radiated power always equals the same ampere-feet. 73 Tom |
Current through coils
"Cecil Moore" wrote
It is physically 10 degrees tall. The physical height is what determines the radiation pattern. It is electrically 90 degrees long. The electrical length is what determines the feedpoint impedance. Where does that 90 degrees of electrical length come from if not partially from the coil? ________________ The intrinsic impedance of the radiator consists of its radiation resistance and its reactance. The proper loading coil can provide a net reactance at the feedpoint of the antenna system of ~ zero ohms, but that hasn't changed the radiation resistance of that short radiator. So the coil-loaded, short radiator is not really "electrically" ~90 degrees long -- it just has the reactance of an antenna that is ~90 degrees long. The coil-loaded, short radiator itself still doesn't have the radiation resistance of linear, 1/4-wave antenna. That remains a function of the electrical length of the whip, itself, apart from the effects of the coil. RF |
Current through coils
"Richard Fry" wrote in message ... So the coil-loaded, short radiator is not really "electrically" ~90 degrees long -- it just has the reactance of an antenna that is ~90 degrees long. But Richard, that is what is meant by "electrical" length, that it has the same phase shift as a ~90 degree antenna. -- 73, Cecil, W5DXP |
Current through coils
On Thu, 09 Mar 2006 08:32:44 -0500, David Shrader
wrote: wrote: SNIPPED If I have a 10 degree tall base loaded antenna it is a ten degree tall antenna. It is NOT 90 degree resonant antenna with "80 degrees of missing length" in the inductor, nor with that 80 degree long inductor behave like 80 degrees of antenna length would. I beg to differ. If I have a 15 degree long physical antenna, center loaded at 10 degrees, with 5 degrees above the coil I do have a 15 degree physical antenna. That does not mean the antenna is NOT 90 degrees elctrically long! Resonance requires that the reactive components cancel both in amplitude and phase! Each reactive component introduces phase shift into the system. The antenna, without a loading coil, is composed of three terms: resistance [radiation and loss], self capacitance, and self inductance. In a shortened antenna the self capacitance dominates and the resultant phase shift is NOT zero. It is required to add inductance to achieve resonance [phase shift = 0]. If an antenna is electrically 15 degrees long and the self inducance does not reduce the reactive phase shift to zero PHASE SHIFT MUST BE ADDED TO THE ANTENNA for resonance. This phase shift is accomplished by the loading coil. Now, when that antenna is fed with 1 ampere [Imax] at the base of the antenna and the feed current follows a cosine distribution to the base of the coil [I = Imax*cos(theta)][theta=10], you claim that the current exiting the coil is also Imax*cos(theta), or 98.5% of max value. Tom has quite adequately addressed this, however, if you go he http://www.k6mhe.com/n7ws and look at either Note 1 or 2 and then look at figures 1 and 2 this might change your mind about the current distribution. [snip] |
Current through coils
Cecil Moo
So the coil-loaded, short radiator is not really "electrically" ~90 degrees long -- it just has the reactance of an antenna that is ~90 degrees long. (R. Fry quote) But Richard, that is what is meant by "electrical" length, that it has the same phase shift as a ~90 degree antenna. _______________ So the definition of electrical length you use excludes radiation resistance? That resistance is the only parameter giving any antenna the ability produce useful EM radiation in a practical antenna system. And that resistance is a function of the physical properties and configuration of the radiator with respect to the operating frequency. Model a short vertical radiator in NEC, and check its impedance. If short enough, it could be something like 0.1 -j2500 ohms. Now add an inductive reactance to the system to reach resonance. NEC then will show 0.1 +/-0 ohms. Note that the radiation resistance term did not change. That short system is resonant, but it certainly won't have the practical radiation efficiency of a full, 1/4-wave, linear radiator, even though they both have the same "electrical length" by your definition. RF |
Current through coils
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Current through coils
"Richard Fry" wrote in message ... So the definition of electrical length you use excludes radiation resistance? Yes, of course a 60 degree coil obviously doesn't radiate like a 60 degree piece of wire. The 60 degrees is merely the phase shift that a traveling wave current undergoes while traveling through the coil. I hope this is not just a semantic problem. When someone says a coil replaces 60 degrees of an antenna, he certainly doesn't mean for radiation purposes (unless he is an absolute dummy). He simply means the coil causes a 60 degree phase shift in the forward current, much like a 60 degree length of wire. And that's all it means. Model a short vertical radiator in NEC, and check its impedance. If short enough, it could be something like 0.1 -j2500 ohms. Now add an inductive reactance to the system to reach resonance. NEC then will show 0.1 +/-0 ohms. Note that the radiation resistance term did not change. Of course not! Nobody is arguing otherwise. You are obviously confused about what I, and others, are saying. That short system is resonant, but it certainly won't have the practical radiation efficiency of a full, 1/4-wave, linear radiator, even though they both have the same "electrical length" by your definition. Is this a straw man? Nobody has said anything remotely resembling any argument otherwise. Electrical length doesn't have much to do with radiation. The radiation resistance and therefore efficiency, is closely associated with the physical length. Electrical length mainly has to do with phasor rotation. If a traveling wave current phasor rotates 90 degrees while flowing through a coil, the coil's electrical length is 90 degrees. That's a pretty simple concept. The coil can even be considered to be lossless and non- radiating in some relatively efficient antenna systems without introducing much of an error. -- 73, Cecil, W5DXP |
Current through coils
"Wes Stewart" wrote if you go he http://www.k6mhe.com/n7ws and look at either Note 1 or 2 and then look at figures 1 and 2 this might change your mind about the current distribution. Nobody is disputing the current rise through a coil. In fact, I have been pointing it out. The coil does distort the current away from the nice cosine envelope of a 1/2WL thin wire dipole. Your graphs show standing wave current which doesn't flow. (Its phase angle doesn't rotate.) Therefore, the magnitude of the standing wave current can be any value depending upon where it is located in the system. Wes, please take a look at http://www.qsl.net/qrzgif35.gif to find out why standing wave current can have any value and is thus unimportant. EZNEC plots the current in much the same way that you have. So are the EZNEC results wrong and yours right? The fact is that a standing wave current plot is close to meaningless. Why are we continuing to discuss standing wave current? What we need to plot is the forward traveling wave current and the reflected traveling wave current which are the two components of your standing wave current graphs. Do you have any simulation software that will plot the forward current and reflected current? Nobody is going to understand what is really happening until we get a plot of those two component waves or at least an estimated graph of the underlying superposed currents. In fact, how about your best estimate of a graph of forward and reflected currents through the coil including phase shifts? Only then are you likely to understand what we are talking about.. -- 73, Cecil, W5DXP |
Current through coils
Wes Stewart wrote:
Maybe part of the myth is that the antenna must be resonant to work. Nothing could be further from the truth. Has the radiator current distribution changed? No. Does the inductor in the L-network "make up" some number of electrical degrees in the radiator? Not from my viewpoint. I think there are two problems: 1.) Cecil wants everyone to start using reflection wave models to analyze every antenna system in the world. 2.) Many people think a very short monopole antenna that is resonant is still 90 electrical degrees long, and that the inductor makes up the missing number of degrees, and the current taper across that inductor is some form of sine shaped curve. Cecil is free to use whatever tools he likes. He doesn't work for me, and (thank God) I don't have to work for him! What he wants me or others to do is a moot point. I am concerned about the commonly held but very incorrect view that current travels through an inductor turn-by-turn, and that a loading inductor somehow shifts the phase of and/or level of current to "make up for missing degrees". My only concern is people not understanding how an inductor and short antenna actually behaves. That problem is worth attention. 73 Tom |
Current through coils
"Wes Stewart" wrote : Maybe part of the myth is that the antenna must be resonant to work. Nothing could be further from the truth. Can we agree that if the feedpoint impedance is purely resistive, then the antenna is resonant? How about this thought experiment: Assume a too short for resonance monopole, that has its feedpoint impedance made non-reactive by the insertion of a "base loading coil." All kinds of arguments, including this one, arise about what the role of the coil is, what its current distribution is, how it affects efficiency and so forth. To minimize these arguments, let's stop calling the inductor a "base loading coil" and call it part of an "L-network feedpoint matching network." Now the radiator isn't resonant and the resulting feedpoint reactance (and resistance) is matched separately with the external network. Has the radiator current distribution changed? No. Does the inductor in the L-network "make up" some number of electrical degrees in the radiator? Not from my viewpoint. This can be easily addressed by looking at a G5RV on 40m. On 40m, the feedpoint impedance at the dipole is about 500+j100 ohms. The parallel twinlead matching section is about 110 degrees long. The resonant impedance looking into the matching section is about 27+j0 ohms. So the G5RV matching section has indeed made up about 110 degrees needed by the antenna *system*. The tuned matching section has increased the electrical length of the antenna *system* by 110 degrees so its a pretty good match for coax.. The same goes for an antenna loading coil no matter where it is located. If the short whip antenna system needs 60 degrees to be matched (resonated) the coil provides 60 degrees of phase shift. That's all we are saying when we say the coil replaces 60 of degrees of an antenna system. And the basic argument is whether a lumped circuit analysis can be used on a coil when reflections are present. The answer is NO! If an antenna system needs 60 degrees to be resonant, it can be done in any number of ways. You can give it 60 degrees of transmission line or you can give it 60 degrees of coil. But please note that the 60 degrees of phase shift in the loading coil has no effect on the phase of the standing wave current. The phase of the standing wave current essentially doesn't change all up and down a 1/2WL dipole. Why would you expect it to change in a shortened monopole. The fact that it doesn't changing is essentially meaningless. It doesn't change whether a coil is present or not. -- 73, Cecil, W5DXP |
Current through coils
On Thu, 9 Mar 2006 11:03:24 +0000 (UTC), "Reg Edwards"
wrote: It seems Tesla, with HIS coils, knew what it was all about and he couldn't use a Smith Chart either. Tesla also experimented with over-the-air transmission of utility power to homes. He might have needed to know how to use a Smith Chart, or perhaps he needed a straight-jacket. |
Current through coils
For what it's worth --
I've avoided this discussion for two primary reasons. One is that it saddens me to see this "controversial" topic being brought up yet again after having been discussed at great length a number of times before. There's no reason I can see for it other than Cecil's religious zeal and dogged determination. The second reason is that I hate to be reminded how easily some people can be manipulated to wholly ignore well known physics and embrace alternate theories which are devoid of the ability to produce predictions or numerical results to demonstrate their validity. We live with it every day in our ordinary lives, seeing the astrology column in the newspaper (and learning that it's been a driving force behind top level government decisions), homeopathic remedies at the drug store, and so forth. It's hard to see it keep surfacing here also. Fortunately, some very good, honest, and knowledgeable people have been doing a very good job of presenting the facts. These include Tom, W8JI; Ian, G3SEK; Wes Stewart, N7WS; and Gene Fuller, W4SZ. Anyone who is truly interested in understanding the topic (which is fundamentally very simple) would do well to read what those folks have written and are writing. Because they're dealing with facts and well known phenomena, they can back up what they say with numbers and the ability to explain the phenomena you see. I'd like to add one note to particularly pay attention to Ian's postings on March 6 and 8 explaining the difference between an inductor and inductance. When I and others have spoken of a "physically small coil" we're talking about something resembling a pure inductance. As Ian and others have said, the first step in understanding this topic is to understand how the idealized component works. Only after that can you add the effects of coupling to external fields, which explain the current difference you typically do see between the ends of a real inductor loading an antenna. The red herring in this discussion is the attempt to attribute this effect to something fundamental about inductances, rather than the effect of external fields interacting with a real inductor of significant physical size. Part of this is understandable, because an inductor can be surprisingly small and still exhibit substantial current difference from one end to the other when in the field of a short antenna, because the field from the antenna is very intense. The field from the inductor is also quite large, making noticeable capacitive coupling nearly always present, which also provides a path for displacement current. So it's somewhat natural to assume that the current difference between ends is more fundamental than it really is. But the argument has been taken well beyond reason by the zeal to explain every phenomenon by means of reflecting waves and packets of average power. It's not necessary at all, and all that does is to provide a confounding factor to obscure the simplicity of what's really happening. Since the basis for this approach is largely contrived and devoid of the ability to produce quantitative results, it's easy to make pronouncements which can't be verified. It's pretty obvious that objects in motion come to rest naturally without any external force. You reach this conclusion by failing to separate the external force of friction from the inherent inertia of the object. The problem here is exactly the same -- people are failing to separate the phenomenon of external coupling from the inherent properties of inductance, and concluding that observed current differences between the ends of loading inductors are caused by some inherent property of inductance. I can imagine people arguing about the basic property of objects to spontaneously come to rest long after Newton proved it otherwise. Actually, I wouldn't even be surprised if there's some Newtonian Cecil who's still arguing about it. Roy Lewallen, W7EL |
Current through coils
"Roy Lewallen" wrote: A physically small inductor such as a toroid will function exactly the same in both cases. (I limited it to being physically small, since a larger inductor will interact with the antenna's field.) You're missing the point, Roy. It indeed does function the same way in both cases but if there are reflections present, your lumped circuit analysis rules are known to fail.Your analysis of both cases may be equally wrong in both cases. What is the traveling wave current delay through the coil in degrees? That's easy to measure. That current delay is the degrees that the coil supplies to the antenna. You can ignore any measurements involving standing wave current as being essentially meaningless. What is important is the traveling- wave current delay through the coil. Please measure it and report what it is for your 'physically small toroid'. Your lumped circuit analysis pre-assumes a zero delay through the coil. That delay is certainly not zero in the real world. -- 73, Cecil, W5DXP |
Current through coils
wrote:
1.) Cecil wants everyone to start using reflection wave models to analyze every antenna system in the world. No, I simply want you and others to stop using a known invalid model for every standing wave antenna system in the world. This is a quote from the first web page below: The capital letters are where the author used bold italics for emphasis. "... - no wave interferrence and no standing waves can be present on lumped elements. The problem has been that many experimenters working with self-resonant helices have PURSUED THE CONCEPT OF COIL SELF- CAPACITANCE WITHOUT REALLY UNDERSTANDING WHERE THE NOTION COMES FROM OR WHY IT WAS EVER INVOKED BY ENGINEERS. For that, they will have to go read R.W.P. King's wonderful old book, "Electromagnetic Engineering, McGraw-Hill, 1945. ... On page 465, the Harvard Professor points out that, for coils whose *wire length* exceeds 1/6 wavelength, ...'an adequate representation of the reactance of a coil with a nonuniformly distributed currentr is NOT POSSIBLE in terms of a coil with a uniform current [a lumped element inductance] ...' Period. Resonant FIELDS present surprises to engineers with limited training." Certainly sounds like he is talking about you, Tom. "Electronic Engineering" was written before you were born. Why are you ignorant of the technical facts presented in it? http://www.ttr.com/corum/index.htm http://www.ttr.com/TELSIKS2001-MASTER-1.pdf The .pdf paper is a pier-reviewed publication by the IEEE. Here's what it says about the model you have chosen to use. "Of course, the uniform current assumption has no validity for coils operating anywhere near self-resonance!" "The failure of any limped element circuit model to describe the real world lies at its core inherent *presupposition*: the speed of light is presumed to be infinite in the wave equation. ... Consequently, lumped element circuit theory does not (and cannot) accurately embody a world of second order partial differential equations in space and time." "The concept of coil "self-capacitance" is an attempt to circumvent transmission line effects on small coils when the current distribution begins to depart from its DC behavior." "There are a great number of formulae for coil self-capacitance. None are of particular value for quarter-wave helical resonators anywhere near the 90 degree point." "The delusion is that the short coil is then made to operate in the lumped element regime ...". That you refuse to give up on an invalid method in the face of overwhelming evidence is amazing. What he wants me or others to do is a moot point. Afraid of what you will find? The first web page above says: "Lumped circuit theory isn't absolute truth, it's only an analytical theory - and in these resonators we have the case where this sophmore theory fails experimentally." Do the experiment, Tom, and discover exactly how sophmorish you are being. I am concerned about the commonly held but very incorrect view that current travels through an inductor turn-by-turn, and that a loading inductor somehow shifts the phase of and/or level of current to "make up for missing degrees". Tom, that's what any matching network does. Loading coils are no exception. My only concern is people not understanding how an inductor and short antenna actually behaves. I am concerned about you not understanding, Tom. Don't you believe the information posted on those web pages above. Don't you think a peer-reviewed IEEE publication that disagrees with you is worth a second thought from you. Don't you think ignoring the knowledge published by experts in the field is a little naive? -- 73, Cecil, W5DXP |
Current through coils
"Roy Lewallen" wrote:
I've avoided this discussion for two primary reasons. One is that it saddens me to see this "controversial" topic being brought up yet again after having been discussed at great length a number of times before. There's no reason I can see for it other than Cecil's religious zeal and dogged determination. The reason is that you are wrong and I have provided expert testimony that you are wrong. I'm trying to stop you from speading false information so don't fault me for that. The fact that you refuse to have a technical discussion with me in spite of the numerous expert postings that prove you are using an invalid model, speaks volumes. The results of the spreading of lumped-circuit analysis myths is that you are hoodwinking the uninitiated. Fortunately, some very good, honest, and knowledgeable people have been doing a very good job of presenting the facts. These include Tom, W8JI; Ian, G3SEK; Wes Stewart, N7WS; and Gene Fuller, W4SZ. This is an argumentum ad verecundiam, a well known logical diversion and not a technical argument. I have quoted just as many experts and you have ignored them. In particular, R.W.P. King is quoted from "Electromagnetic Engineering": ... for coils whose *wire length* exceeds 1/6 wavelength, an adequate representation of the reactance of a coil is *NOT POSSIBLE* in terms of a coil with a uniform current [a lumped-element inductance]..." Roy, my 75m bugcatcher coil, made from 44 feet of wire, is more than 1/6 wavelength of wire. R.W.P. King says your lumped-circuit analysis is *NOT POSSIBLE*. He used bold print and underlined the words, *NOT POSSIBLE*. Ignoring the quotations from the true experts is just going to leave you ignorantly spreading old wives' tales. Is that really how you want to be remembered here? Why are all of you alleged "experts" unwilling to discuss technical quotes like R.W.P. King's above? Are you afraid that readers will discover your common mistake which Dr. Corum calls "sophomoric"? As Dr. Corum says: "There are no standing waves on a lumped element circuit component. (In fact, lumped-element circuit theory inherently employs the cosmological presupposition that the speed of light is infinite, as every EE sophomore should know." Why do you choose to absolutely ignore that technical knowledge? -- 73, Cecil, W5DXP |
Current through coils
Summary of design of a short loaded vertical antenna.
There is a 90-degree phase shift between the feedpoint and the tip of the antenna. With a short antenna most of the 90 degree phase shift is due to the loading coil which is, in effect, a transmission line. The transmission line has Zo, velocity, phase-shift and some attenuation due to radiation resistance plus wire loss resistance. Radiation resistance and phase-shift are directly proportion to coil length, as are L and C and wire resistance. Q = Omega*Total Inductance / Total R as is usual. Bandwidth = Resonant Freq / Q. Radiating efficiency takes into account wire resistance below the coil, coil resistance, resistance of the wire above the coil, plus ground loss resistance, plus the sum of the three radiation resistances. All resistances are referred to the antenna feedpoint. With short coils, radiation resistance of the coil is usually much less than that due to the length of the wires above and below it. With a helical antenna, wire loss resistance is always greater than its radiation resistance. At low HF, with a good set of ground radials, the loss resistance of coil wire usually predominates. At high HF, the ground loss usually predominates but the radiation resistance becomes important. The whole business is calculable. There are few rules of thumb. The only thing which is missing is the radiation pattern. If you don't already know what the radiation pattern is in the vertical plane then Eznec will attend to that. Actually, in the vertical plane, radiation is approximately proportional to the cosine of the elevation angle. The horizontal groundwave is stongest. Some of the parameters need not be explicitly calculated. EXAMPLE: Starting data: Height of antenna below coil = 2 metres = 79 inches. Diameter of antenna below coil = 25mm = 1 inch. Length of antenna above coil = 1 metre = 39 inches. Diameter of antenna above coil = 10mm = 0.4 inches. Length of coil = 152mm = 6 inches. Diameter of coil = 76mm = 3 inches. Overall antenna height = 3.152 metres = 124 inches = 10.3 feet. Ground electrode loss resistance = 5 ohms. Frequency = 3.8 MHz. Calculated data: Number of turns on coil = 53 Wire gauge = 13 or 14 awg. Radiating efficiency = 10 percent. Loss relative to full-size 1/4-wave vertical = 9.4 dB. Self-resonant frequency of the coil = 8.2 MHz. For maximum efficiency the coil is located at 50% of the overall antenna height. But there's not much extra loss by using base loading. For other calculated data use program LOADCOIL which is about 6 years old and I think I have lost the source code. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Current through coils
wrote in message oups.com... Cecil Moore wrote: What is the traveling wave current delay through the coil in degrees? That's easy to measure. That current delay is the degrees that the coil supplies to the antenna. You can ignore any measurements involving standing wave current as being essentially meaningless. What is important is the traveling- wave current delay through the coil. Please measure it and report what it is for your 'physically small toroid'. Your lumped circuit analysis pre-assumes a zero delay through the coil. That delay is certainly not zero in the real world. The problem with people doing work to verify this is even if several people measure something, Cecil will ignore results. I will accept what you find as long as long as the method to obtain the results is valid.. Roy's earlier measurements are virtually meaningless since he was measuring standing wave current which doesn't even flow (phase is constant and fixed around zero degrees). You guys always seem to make measurements that support your preconceived notions and avoid measurements that don't But you have already started what I am asking, Tom. You measured a voltage phase shift of 60 degrees through a 100uH coil at 1 MHz. The current is known to lag the voltage through a coil so the current phase delay is more than 60 degrees. I wouldn't be surprised to see it at 120+ degree lag in the current. So your own experiment proves you are wrong. How do you get away with such behavior without anyone noticing?. (Hint: there are a handful of knowledgeable lurkers who have noticed.) When you measured S12, was the load side of the coil looking into 50 ohms? In the web pages I previously posted, R.W.P. King, in "Electromagnetic Engineering", asserts that you cannot use a lumped circuit analysis on a coil containing 1/6 wavelength of wire. Your 100uH coil above exhibits 60 degrees of phase shift even for the voltage and that's 1/6 wavelength for voltage - even more for current. The lumped-circuit model assumes that the voltage is traveling at an infinite speed, faster than light. Since you believe so strongly in the lumped-circuit model, wonder why your measurement didn't reflect that fact? :-) -- 73, Cecil, W5DXP |
Current through coils
Cecil Moore wrote:
I will accept what you find as long as long as the method to obtain the results is valid.. Roy's earlier measurements are virtually meaningless since he was measuring standing wave current which doesn't even flow (phase is constant and fixed around zero degrees). Roy, Shame on you for measuring current that doesn't flow through a current transformer. 73 Tom |
Current through coils
wrote in message ups.com... Cecil Moore wrote: I will accept what you find as long as long as the method to obtain the results is valid.. Roy's earlier measurements are virtually meaningless since he was measuring standing wave current which doesn't even flow (phase is constant and fixed around zero degrees). Shame on you for measuring current that doesn't flow through a current transformer. Standing wave net current doesn't flow back and forth along the wire. That's why they call it a *standing* wave. Why don't you know that already? At any point on the wire, the H-fields and E-fields are exchanging energy at the frequency of operation. That's certainly enough reason for an inductive pickup to respond. Why is that a surprise to you or Roy? Because you two mistakenly thought net standing wave current flows and ignorantly measured it? All you measured was the orthogonal exchange of energy between the two fields. Nothing was moving except the underlying forward and reflected currents. Isn't this stuff taught anymore? What have you guys done - gotten together and elected yourselves into a club of omniscient gurus? Please take a look at the laws of reflection physics. It appears that you are ignorant of most of them. -- 73, Cecil, W5DXP |
Current through coils
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Current through coils
Cecil,
A few random comments: * I have done a number of "peer reviews" for IEEE and AIP publications as well as other publications. I have seen comments from the other reviewers. In general peer review is better than nothing, but in many cases it doesn't mean diddly. * The Tesla coil crowd seems to contain an unusually large fringe. I know nothing of the authors of your latest bible, but in any case I was not particularly impressed with their credentials or their paper. I love the part, "Lumped circuit theory isn't absolute truth, it's only an analytical theory about lumped models". As if their work is somehow absolute truth. (Back to the previous bullet: I have never seen any serious peer-reviewed paper that would contain such a statement.) * No one is his right mind would think that a Tesla coil with a gazillion closely spaced turns is equivalent to a bugcatcher coil. No one should think that an axial mode helical antenna is equivalent to an ordinary loading coil either. * You are waaaay too hung up on the subject of standing waves vs. traveling waves. You may have noticed that the standard treatments of antennas in texts and other references barely mention the terms. They merely discuss the actual current in the antenna. The fundamentally important entity in radiation is accelerated charge, just as Tom noted. At any point in an antenna, such as the loaded monopole discussed here, there is simply a current, not a traveling wave or a standing wave. If you could examine the antenna microscopically at a single point you would find electrons sloshing back and forth. You could not tell if the current was represented by a standing wave or a traveling wave. The standing wave description relates to the overall amplitude characteristic of the current when you look at the entire antenna. This amplitude characteristic is certainly important in calculation of details of the radiation field, but it does not change the fundamental property of radiation or the physical processes ongoing in the antenna. It is just plain silly to argue that a standing wave is totally inert and does not flow back and forth. * Distributed or network models are mathematically convenient for treating complex problems. However, they add precisely zero new information to the underlying physical reality described by Maxwell's equations. They offer no new physics beyond lumped models. They can be misapplied just the same as lumped models can be misapplied. It is generally best to drive a nail with a hammer, but a monkey wrench will also do the job. It is best to choose the most efficient tool, but that does not mean others won't work. 73, Gene W4SZ Cecil Moore wrote: wrote: 1.) Cecil wants everyone to start using reflection wave models to analyze every antenna system in the world. No, I simply want you and others to stop using a known invalid model for every standing wave antenna system in the world. This is a quote from the first web page below: The capital letters are where the author used bold italics for emphasis. "... - no wave interferrence and no standing waves can be present on lumped elements. The problem has been that many experimenters working with self-resonant helices have PURSUED THE CONCEPT OF COIL SELF- CAPACITANCE WITHOUT REALLY UNDERSTANDING WHERE THE NOTION COMES FROM OR WHY IT WAS EVER INVOKED BY ENGINEERS. For that, they will have to go read R.W.P. King's wonderful old book, "Electromagnetic Engineering, McGraw-Hill, 1945. ... On page 465, the Harvard Professor points out that, for coils whose *wire length* exceeds 1/6 wavelength, ...'an adequate representation of the reactance of a coil with a nonuniformly distributed currentr is NOT POSSIBLE in terms of a coil with a uniform current [a lumped element inductance] ...' Period. Resonant FIELDS present surprises to engineers with limited training." Certainly sounds like he is talking about you, Tom. "Electronic Engineering" was written before you were born. Why are you ignorant of the technical facts presented in it? http://www.ttr.com/corum/index.htm http://www.ttr.com/TELSIKS2001-MASTER-1.pdf The .pdf paper is a pier-reviewed publication by the IEEE. Here's what it says about the model you have chosen to use. "Of course, the uniform current assumption has no validity for coils operating anywhere near self-resonance!" "The failure of any limped element circuit model to describe the real world lies at its core inherent *presupposition*: the speed of light is presumed to be infinite in the wave equation. ... Consequently, lumped element circuit theory does not (and cannot) accurately embody a world of second order partial differential equations in space and time." "The concept of coil "self-capacitance" is an attempt to circumvent transmission line effects on small coils when the current distribution begins to depart from its DC behavior." "There are a great number of formulae for coil self-capacitance. None are of particular value for quarter-wave helical resonators anywhere near the 90 degree point." "The delusion is that the short coil is then made to operate in the lumped element regime ...". That you refuse to give up on an invalid method in the face of overwhelming evidence is amazing. What he wants me or others to do is a moot point. Afraid of what you will find? The first web page above says: "Lumped circuit theory isn't absolute truth, it's only an analytical theory - and in these resonators we have the case where this sophmore theory fails experimentally." Do the experiment, Tom, and discover exactly how sophmorish you are being. I am concerned about the commonly held but very incorrect view that current travels through an inductor turn-by-turn, and that a loading inductor somehow shifts the phase of and/or level of current to "make up for missing degrees". Tom, that's what any matching network does. Loading coils are no exception. My only concern is people not understanding how an inductor and short antenna actually behaves. I am concerned about you not understanding, Tom. Don't you believe the information posted on those web pages above. Don't you think a peer-reviewed IEEE publication that disagrees with you is worth a second thought from you. Don't you think ignoring the knowledge published by experts in the field is a little naive? -- 73, Cecil, W5DXP |
Current through coils
On Thu, 09 Mar 2006 17:51:48 GMT, "Cecil Moore"
wrote: "Wes Stewart" wrote if you go he http://www.k6mhe.com/n7ws and look at either Note 1 or 2 and then look at figures 1 and 2 this might change your mind about the current distribution. Nobody is disputing the current rise through a coil. In fact, I have been pointing it out. The coil does distort the current away from the nice cosine envelope of a 1/2WL thin wire dipole. 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. Your graphs show standing wave current which doesn't flow. (Its phase angle doesn't rotate.) Therefore, the magnitude of the standing wave current can be any value depending upon where it is located in the system. Wes, please take a look at http://www.qsl.net/qrzgif35.gif to find out why standing wave current can have any value and is thus unimportant. EZNEC plots the current in much the same way that you have. So are the EZNEC results wrong and yours right? The fact is that a standing wave current plot is close to meaningless. Why are we continuing to discuss standing wave current? Well, I certainly hope that EZNEC plots the current the same. If you would have read all that I wrote in the reference, you would have see: "The models were "built" using MultiNEC invoking EZNEC 3.0 (now 4.0) or double-precision NEC-2 as the calculating engines. The following graphics were all generated with MultiNEC." Among the other nice things that MultiNEC does is interface to many other analysis programs, EZNEC being my preferred one, and gives some other ways to present -the same data- in other forms. The data in the figures are EZNEC-calculated-data. Clearly, you were too busy trying to frame an argument to actually read what I wrote. What we need to plot is the forward traveling wave current and the reflected traveling wave current which are the two components of your standing wave current graphs. Do you have any simulation software that will plot the forward current and reflected current? Nobody is going to understand what is really happening until we get a plot of those two component waves or at least an estimated graph of the underlying superposed currents. "We" need to plot no such thing. You may have such a need; I do not. In fact, how about your best estimate of a graph of forward and reflected currents through the coil including phase shifts? Only then are you likely to understand what we are talking about.. If "we" includes you and me, I will never understand what "we" are talking about, although I am pretty sure what "I'm" talking about. Now, I've got to get back to something important; building a playhouse for my granddaughter. |
Current through coils
wrote:
Cecil Moore wrote: But you have already started what I am asking, Tom. You measured a voltage phase shift of 60 degrees through a 100uH coil at 1 MHz. The current is known to lag the voltage through a coil so the current phase delay is more than 60 degrees. I wouldn't be surprised to see it at 120+ degree lag in the current. So your own experiment proves you are wrong. How do you get away with such behavior without anyone noticing?. The only thing worth noticing is you are misrepresenting facts. I measured current with a small current transformer, and current at each end of the inductance was, as close as my two-channel vector voltmeter will resolve, equal in phase and equal in level. Here are your words cut and pasted 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, ... S12 is a voltage parameter. So did the coil show a "-60 or -70 degrees" voltage phase shift or not? Where does it say anything about "current with a small current transformer" in your posting? Last time I looked, a 100uH inductor was not a small current transformer. I assumed a current phase shift at first and you jumped on me about that. Now you say it was a current phase shift after all. If you want to be quoted correctly, you need to stop fibbing. Here's what I think happened in context. You were trying to prove Kraus wrong with his assertion that a 180 degree phasing coil can be thought of as 1/2WL of wire wound into a coil. You failed to realize that your posting was supporting my other point about phase shifts through coils. So you accidentally posted results that supported my side of the argument. Your lumped-circuit model predicts zero phase shift. My distributed network model predicts considerable phase shift. Your experiment yielded considerable phase shift and now you seek to deny it. However, it is there in all its glory on qrz.com for all to see. So feel free to deny it. The only thing worth noticing is you are misrepresenting facts. I never misrepresent facts as I understand them to exist. The fact that you absolutely refuse to engage me in a technical discussion speaks volumes. If I were wrong, you would simply engage me and prove me wrong with a technical argument as you have so many others. But If I am right, I fully understand your reluctance to engage me in a technical discussion. You can start the technical discussion by explaining the EZNEC results on my web page: http://www.qsl.net/qrzgif35.gif Why are all you gurus so reluctant to discuss that topic? I have asked you guys to respond to that graphic at least half a dozen times and got only one weak reply. Why the silence? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
wrote: The problem with people doing work to verify this is even if several people measure something, Cecil will ignore results. Indeed. Or alter his interpretation to fit the data. I can't help but point out that you guys are refusing to engage me in any technical discussion and refusing to respond to my technical quotes. All you do is engage in desperate ad hominem attacks hoping that your guru status will prevail. That's a pretty good indication that you have already lost the technical argument and know it. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
Cecil Moore wrote: . . . "... - no wave interferrence and no standing waves can be present on lumped elements. The problem has been that many experimenters working with self-resonant helices have PURSUED THE CONCEPT OF COIL SELF- CAPACITANCE WITHOUT REALLY UNDERSTANDING WHERE THE NOTION COMES FROM OR WHY IT WAS EVER INVOKED BY ENGINEERS. For that, they will have to go read R.W.P. King's wonderful old book, "Electromagnetic Engineering, McGraw-Hill, 1945. ... On page 465, the Harvard Professor points out that, for coils whose *wire length* exceeds 1/6 wavelength, ...'an adequate representation of the reactance of a coil with a nonuniformly distributed currentr is NOT POSSIBLE in terms of a coil with a uniform current [a lumped element inductance] ...' Period. Resonant FIELDS present surprises to engineers with limited training." Certainly sounds like he is talking about you, Tom. "Electronic Engineering" was written before you were born. Why are you ignorant of the technical facts presented in it? I have this book. The condition for the quoted result isn't simply that the length of wire in the coil be adequately long, but also that the coil be wound loosely enough so that the coupling between turns is poor enough to allow a particular nonuniform current distribution. It applies to a "loosely wound helix." The quote is within a section titled "'Lumped' Constants in Near-zone circuits", which contains a detailed analysis of just what conditions can cause an inductor to have unequal input and output currents, but primarily how the currents can be unequal even in the absence of an external field. In particular, the author describes an inductor in which the coupling between turns isn't sufficient to force equal currents at the coil ends. Qualitatively, this should be pretty obvious: If we begin with a long wire (in terms of wavelength), the current will vary along its length. As we wind it into a loose coil, mutual coupling between turns will create inductance and make the current more uniform, but with a distribution still resembling that of the straight wire. It's this situation that the quotation applies to -- an inductor so loosely wound that its current distribution resembles a straight wire more than an inductance. He does go on to say that if the winding is tighter but still not ideal, the resulting non-uniform current, which has a different distribution (greater at the center than at the ends), can be modeled by means of a lumped self capacitance. Only if we have perfect coupling between turns (as a toroid very nearly represents) will we truly have equal currents at input and output, for the reasons Tom recently explained. This is the idealized inductance which some of the contributers to this discussion are having trouble understanding. The mathematical treatment in King is quite complex. But nowhere does he mention any traveling, reflected, or standing current, power, or energy waves, or that an inductance behaves any differently in an antenna than in a lumped circuit. It simply isn't necessary or relevant to explaining the operation of either an ideal or non-ideal inductor. Nor does he dispute the fact that the currents into and out of an ideal inductance are equal. And of course there's no mention of the mysterious "resonant fields" which probably do surprise engineers, as does the metaphysics being promoted here. Roy Lewallen, W7EL |
Current through coils
Gene Fuller wrote:
* I have done a number of "peer reviews" for IEEE and AIP publications as well as other publications. I have seen comments from the other reviewers. In general peer review is better than nothing, but in many cases it doesn't mean diddly. Translation: If they don't agree with Gene Fuller, they don't mean diddly. :-) * No one is his right mind would think that a Tesla coil with a gazillion closely spaced turns is equivalent to a bugcatcher coil. On the contrary, Gene, my 75m bugcatcher meets the minimum definition of a Tesla coil on 9-10 MHz where it is 1/4WL self-resonant, i.e 90 degrees. It is a good 78 degrees on 75m which is not all that far from its self-resonant point. * You are waaaay too hung up on the subject of standing waves vs. traveling waves. So uttered by the priest of the high-and-mighty lumped-constant religious sect. :-) The lumped-circuit model is known to fail in a standing-wave environment. Anyone using it in a standing-wave environment is doomed to failure. Those are known facts. What is it about those statements that you don't understand? At any point in an antenna, such as the loaded monopole discussed here, there is simply a current, not a traveling wave or a standing wave. Gene, if you want to assert that the current on a standing wave antenna is not a standing wave, be my guest. The standing wave on a 1/2WL dipole is why it radiates broadside. If it were a traveling wave, it would be an end-fire. Standing wave current is NOT traveling wave current and vice versa. I'm not even sure that "standing-wave current" even meets the definition of "current". If it's not flowing, is it really current? It appears to me to be more of a wet dream than anything real. If you could examine the antenna microscopically at a single point you would find electrons sloshing back and forth. But we are not interested in Brownian motion, are we? We are only interested in the net charge flow and that is zero on a standing wave antenna with equal coherent currents flowing in opposite directions. You could not tell if the current was represented by a standing wave or a traveling wave. Say what? If voltage/current maximums/minimums exist, then a standing wave exists. Admittedly, if you were an individual electron, you would have trouble discerning the difference. But Gene, if you really are an individual electron, please explain to the group how you manage to depress the keyboard keys? It is just plain silly to argue that a standing wave is totally inert and does not flow back and forth. Where did that word, "inert", come from? Not from me. Do I smell a straw man arising? When you have equal magnitude coherent waves flowing in opposite directions in a wire, do you really want to assert that there is a net charge flow or a net current flow along the wire? If so, be my guest and please prove it. * Distributed or network models are mathematically convenient for treating complex problems. However, they add precisely zero new information to the underlying physical reality described by Maxwell's equations. Exactly correct! They offer no new physics beyond lumped models. Exactly incorrect. Lumped-circuit models are a subset of distributed- network models. Distributed-network models are a subset of Maxwell's equations. Lumped-circuit models are known to fail in the presence of standing waves. That is what the whole argument here is about. Some people have adopted the lumped-circuit model as their religion and they will attempt to put anyone who disagrees with them under house arrest, as happened to Galileo, e.g. W7EL has 'ploinked' me and uses his guru status to take unfair potshots at me from time to time. What we have on this newsgroup is a gang of junk yard dog gurus who don't care if they are right or wrong. They just attack anyone who disagrees with their postings whether right or wrong. (It's not ad hominem when it's the truth and any knowledgeable person following this discussion recognizes that as the truth.) I would like to request that everyone stop the ad hominem attacks, (me included), and engage in a civil gentlemanly technical discussion. If I am so wrong, I should be easy prey for 4+ distinguished gurus. OTOH, if I am right, I understand the reluctance to engage me on a technical level and fully understand the ad hominem attacks to be a face-saving necessity. So which will it be? The response to my technical quotes and assertions has, so far, been underwhelming. Shouldn't half a dozen omniscient gurus be able to dispatch a mere mortal grasshopper? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
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? "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. 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? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
It applies to a "loosely wound helix." Please define the point at which a "loosely wound helix" with a varying current turns into this lumped-circuit device that forces equal currents through the coil. Is a 75m bugcatcher coil a "loosely wound helix" or a "lumped-circuit"? (My 75m bugcatcher coil is about 1/6 wavelength of wire.) Only if we have perfect coupling between turns (as a toroid very nearly represents) will we truly have equal currents at input and output, for the reasons Tom recently explained. This is the idealized inductance which some of the contributers to this discussion are having trouble understanding. Unfortunately, an idealized inductance is like a lossless transmission line - it exists only in the human mind. What I would like to know is what is the real-world phase shift through your toroidal inductor when there is only a traveling wave (no standing wave). We can then use the laws of reflection physics to determine what effect that phase shift has on the amplitude of the standing wave current which is the phasor sum of the forward current and reflected current. I'm actually going to make those measurements as soon as I get off my old lazy ass. Seems to me that although a toroidal current pickup may not have the same magnitude characteristics because of variations in the permeability, the phase would suffer no such effects. Am I correct on that point? I'm somewhat handicapped in having no current probes for my 100 MHz Leader and acquiring them would put a big dent in my Social Security check. :-) What I am toying with is a 6m rhombic. I could run it as a terminated traveling-wave antenna or unterminate it and have a standing-wave antenna. I could move all kinds of coil(s) up and down the the elements to place them at nodes or loops or in-between and take measurements. What do you think? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Here are your words cut and pasted 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, ... S12 is a voltage parameter. So did the coil show a "-60 or -70 degrees" voltage phase shift or not? It did. Just as I posted here it did. Where does it say anything about "current with a small current transformer" in your posting? It didn't. As I kept telling you in that thread, I didn't want to talk to you until you were able to make a post without resorting to personal attacks. I also told you I was busy with work, and didn't have time to deal with the same old circular arguments with you. Last time I looked, a 100uH inductor was not a small current transformer. I assumed a current phase shift at first and you jumped on me about that. Now you say it was a current phase shift after all. If you want to be quoted correctly, you need to stop fibbing. Please stop trying to blame your mistakes on me! It's not my fault you assumed more than you read! I've been telling you all along current at each end of ANY small inductor has the same phase. I've been telling you all along I didn't want to talk to you until you learn to behave. Don't accuse me of lying because you made up a theory and it is dead wrong! It isn't MY fault you painted yourself in a corner by adjusting your theories to suit what you thought was said, when it wasn't even said. Here's what I think happened in context. You were trying to prove Kraus wrong with his assertion that a 180 degree phasing coil can be thought of as 1/2WL of wire wound into a coil. You failed to realize that your posting was supporting my other point about phase shifts through coils. "Here's what I think" is correct Cecil. In your mind Cecil, it's always all about the other guy failing, being wrong and knowing better, or being dishonest. So you accidentally posted results that supported my side of the argument. Your lumped-circuit model predicts zero phase shift. My distributed network model predicts considerable phase shift. Your experiment yielded considerable phase shift and now you seek to deny it. However, it is there in all its glory on qrz.com for all to see. So feel free to deny it. Anyone can read anything. I'd wager you anything you like multiple people on this list can make a small current transformer, measure current at each terminal of a compact inductor, and find the phase of current essentially the same at each end. It isn't about me Cecil. It isn't about Kraus. It isn't about QRZ. It isn't about Roy or anyone else. It's all about how a two terminal inductor acts! That can be proven over and over again, and it will always come out the same. Neither you nor I can change how things work. I never misrepresent facts as I understand them to exist. The fact that you absolutely refuse to engage me in a technical discussion speaks volumes. It does indeed. If you stayed away from personal attacks I would converse with you. I've told you that over and over again. People who say things on Internet they wouldn't say face to face wear on my nerves. I find it very difficult to remain civil when reading constant personal attacks. If I were wrong, you would simply engage me and prove me wrong with a technical argument as you have so many others. But If I am right, I fully understand your reluctance to engage me in a technical discussion. You can start the technical discussion by explaining the EZNEC results on my web page: 1.) We really can't have a good conversation until you stop the constant personal attacks, and until we agree on a few basics. 2.) You claim Roy measured current that doesn't flow. That area needs addressed. 3.) You also claim significant current phase shift exists between the terminals of a compact inductor operated well below self-resonance. It's very simple to measure current and voltage and the phase relationships in a two terminal device and prove you are wrong. Trying to divert the issue to me not following your commands and orders just won't go far. 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. You say it isn't, I say it is, and I can prove it beyond any doubt to any open minded person. 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'm just not sure I can prove anything to someone who thinks a current transformer measures current that doesn't flow! 73 Tom |
Current through coils
Hi Cecil I have a HP8405A Vector Voltmeter I'll give you and even pay the shipping if that is of any help with the measurements. Jerry "Cecil Moore" wrote in message om... Roy Lewallen wrote: It applies to a "loosely wound helix." Please define the point at which a "loosely wound helix" with a varying current turns into this lumped-circuit device that forces equal currents through the coil. Is a 75m bugcatcher coil a "loosely wound helix" or a "lumped-circuit"? (My 75m bugcatcher coil is about 1/6 wavelength of wire.) Only if we have perfect coupling between turns (as a toroid very nearly represents) will we truly have equal currents at input and output, for the reasons Tom recently explained. This is the idealized inductance which some of the contributers to this discussion are having trouble understanding. Unfortunately, an idealized inductance is like a lossless transmission line - it exists only in the human mind. What I would like to know is what is the real-world phase shift through your toroidal inductor when there is only a traveling wave (no standing wave). We can then use the laws of reflection physics to determine what effect that phase shift has on the amplitude of the standing wave current which is the phasor sum of the forward current and reflected current. I'm actually going to make those measurements as soon as I get off my old lazy ass. Seems to me that although a toroidal current pickup may not have the same magnitude characteristics because of variations in the permeability, the phase would suffer no such effects. Am I correct on that point? I'm somewhat handicapped in having no current probes for my 100 MHz Leader and acquiring them would put a big dent in my Social Security check. :-) What I am toying with is a 6m rhombic. I could run it as a terminated traveling-wave antenna or unterminate it and have a standing-wave antenna. I could move all kinds of coil(s) up and down the the elements to place them at nodes or loops or in-between and take measurements. What do you think? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Please stop trying to blame your mistakes on me! It's not my fault you assumed more than you read! I've been telling you all along current at each end of ANY small inductor has the same phase. Please define "small" in terms of the number of degrees of phase shift measured using a traveling wave signal. Don't accuse me of lying because you made up a theory and it is dead wrong! It isn't MY fault you painted yourself in a corner by adjusting your theories to suit what you thought was said, when it wasn't even said. Your diversions are comical and obvious, Tom. Thanks for the laugh. If you stayed away from personal attacks I would converse with you. Pot, Kettle. Kettle, Pot. Tom, your personal attacks are legend throughout the internet and world wide web. I know hams who are too terrified to respond to you even when you are wrong. 1.) We really can't have a good conversation until you stop the constant personal attacks, and until we agree on a few basics. Hard to accomplish since you define being proven technically wrong as a personal attack. 2.) You claim Roy measured current that doesn't flow. That area needs addressed. 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. 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. 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? 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. 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? 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'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. What school did you say you attended? -- 73, Cecil http://www.qsl.net/w5dxp |
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