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Current through coils
Cecil Moore wrote:
[snip] 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." Cecil, Interesting, The complete quote from Kraus on page 744 in my copy of his 2nd edition is: "A coil (or trap) can also act as a 180 degree phase shifter as in the collinear array of 4 in-phase lambda/2 elements in Fig. 16.30b. Here the elements present a high impedance to the coil which may be resonated without an external capacitance due to its distributed capacitance. The coil may also be though of as a coiled-up lambda/2 element." * It is possible that Kraus edited the comment in the 3rd edition, but I don't see the word "current" in this quote. It is considered good editorial form to indicate clearly when you have altered the original wording, unless you are trying to make a point, I suppose. * The coil in this case is self-resonant at the frequency of use. Do you use a self-resonant coil for your 80 meter bugcatcher? (Such a coil might be more appropriate for a pterodactyl catcher.) In any case, this has little to do with all of your rantings about loading coils. I suspect even at A&M they must have mentioned something about the characteristics of resonant circuits. * You might have noticed the prominent role of capacitance. I believe that was the item that spurred this thread. 73, Gene W4SZ |
Current through coils
Gene Fuller wrote:
Cecil Moore wrote: 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 complete quote from Kraus on page 744 in my copy of his 2nd edition is: "A coil (or trap) can also act as a 180 degree phase shifter as in the collinear array of 4 in-phase lambda/2 elements in Fig. 16.30b. Here the elements present a high impedance to the coil which may be resonated without an external capacitance due to its distributed capacitance. The coil may also be though of as a coiled-up lambda/2 element." * It is possible that Kraus edited the comment in the 3rd edition, but I don't see the word "current" in this quote. It is considered good editorial form to indicate clearly when you have altered the original wording, unless you are trying to make a point, I suppose. Gene, I assume you know it is common practice to insert words in parentheses in a quotation to make the meaning clear. Such words are understood not to be part of the quote. Since Kraus illustrated the current, not the voltage in Figure 23-21 and earlier in figures 14-2, 14-3, and 14-4, it is rather obvious that he was talking about a 180 degree current shift. Nowhere that I have seen does Kraus illustrate the voltage on a standing wave antenna or talk much about that voltage. Do you see the arrows drawn on the antenna in question? Do you not know that an arrow drawn on a line denotes current? And note that since all the current arrows are pointing to the right, there is a 180 degree current phase shift in each of those phase- shifting coils. However, I see I should have used brackets because Kraus was already using parentheses. I promise to do better next time. Again, there is hardly any technical content in your reply. You have refused to respond to the questions I listed for you in an earlier posting. One wonders why you are avoiding the technical issues. So I'll ask again. At http://www.qsl.net/w5dxp/qrzgif35.gif is an EZNEC simulation. How do you explain the 0.1+ amp of current 'flowing' into the bottom of the coil and 0.7+ amp of current 'flowing' out of the top of the coil. How, exactly, is the coil manufacturing extra current? Hint: such a thing happens all the time in a standing wave environment because standing wave current doesn't flow. How could it possibly flow with a constant fixed zero degree phase angle? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
What you are missing is the flux inside the coil links all the turns at light speed. When it does that, current appears at nearly the same instant of time (light speed over the spatial distance of the inductor) in all areas that are linked by flux. The flux coupling also tries to equalize currents throughout every area of the coil. Charge conservation also dictates that any current flowing into the coil has to be equalled by a like current flowing out the other terminal, less any displacement currents caused by stray capacitance (electric fields) to the outside world. We cannot have a two terminal "black box" with confined fields that behaves any other way, standing waves or not. The only flaws in having zero current phase shift and zero current difference are the less-than-perfect flux coupling and less-than-perfect confinement of the electric field. Any deviation from following perfect two-terminal rules are directly tied to the ratio of load impedance on the inductor to the stray capacitance to the outside world, and of course less than perfect flux linkage from end-to-end in the coil. People can often better understand the limits when things are taken to an extreme. Imagine a helical whip antenna. It is a very poorly constructed "loading coil". It has nearly infinite termination impedance at the open end, and very poor mutual coupling from turn to turn. The form factor is very distorted, far from being equal in diameter and length. The ratio of distributed capacitance to termination capacitance is very large, it can be nearly infinite. A loading inductor or helical whip like this behaves nearly like an antenna. The opposite would be a toroid, with a very compact form and almost total confinement of fields. Standing waves or not, as long as it is not near self-resonance it has evenly distributed current inside and at each terminal. Most well-designed efficient short antennas use a loading coil having very nearly equal currents at each terminal. Current equality actually is a good way to determine a properly designed loading coil. If you can stay on topic and we process only one point at a tme, I'm sure you will be able to learn how this works. If you see any flaw in how I just described inductor behavior, please point it out. Once we agree how an inductor works everything else will fall into place. 73 Tom |
Current through coils
wrote:
W8JI: I think it would be better if Walt represented himself, unless he ASKED you to post that Cecil. Cecil Moo 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. Odd you say that because Walt sent me this: Hi Tom, it's been a long time since we've talked. I'm sorry if you feel put upon. I had no idea that Cecil was going to put my response on QRZ, and my only intent in my comment to him was that with your broad knowledge in the area of this issue, I found it hard to believe you didn't understand it. I was simply incredulous, not critical. I'm sorry you perceived it as critical, as it certainly wasn't intended. In addition, Cecil should not have included that portion which was personal in his post to QRZ. Walt That doesn't sound like Walter gave you permission to me. 73 Tom |
Current through coils
Richard Harrison wrote:
A transmission line can`t be analyzed as a simple series circuit, because the current in the wires is not everywhere the same. Neither is the voltage. To analyze the line, each unit length must be examined. Each unit length produces a phase lag in the current on its wires. The voltage lags too. This can be totaled and the interference between the incident and reflected waves deternined to find the voltage and current at any point on the transmission line, Yes, and that also applies to a real-world loading coil installed in an environment of incident (forward) and reflected (backward) waves. Why this is so difficult for some people to understand is puzzling. All one has to do is use the superposition principle. Analyze the forward wave, analyze the reflected wave, and superpose the results. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
That doesn't sound like Walter gave you permission to me. Tom, I can't believe you have the balls to lie about such a thing when it is so easy to prove otherwise. Your behavior is unbelievably unethical. I simply cannot believe you are willing to go to these lengths to satisfy that insatiable ego of yours. W5DXP asks Walt: And Walt, would you mind if I add just your following comments to the thread on qrz.com and credit them to you? I trimmed out any reference to me or Tom. Walter Maxwell earlier wrote: 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. Walter Maxwell replied to the request: Fine with me, Cecil, but you might also add the point about the loop and node appearing simultanously when reflections are present--sorta puts the icing on the cake. Walt Tom, not only did Walt give me permission, he pointed out something that I had left out. You are being unbelievably unethical. You could have handled this in a private email to me but you are apparently willing to drag Walter Maxwell through the mud in order to spread your old wives' tales. Good grief, will you stop at nothing? I'm going to have to sign off and cool down. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
All personal issues and insults aside, before anyone does anything with any of this they would have to have a good feel for how an inductor behaves. Do you agree or disagree with my post about how an inductor behaves? 73 Tom |
Current through coils
wrote:
That doesn't sound like Walter gave you permission to me. He did give me permission. In a fit of anger, I made a posting that proves that fact. Upon reflection, after cooling down by taking a walk, I should not have made that posting and I have canceled it. Walter Maxwell is my friend and I don't want to drag the great man into your junk yard dog war. I respect him too much for that and regret making that posting. I just hope it didn't make it off my news-server before I canceled it. It is gone from my news-server. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
All personal issues and insults aside, before anyone does anything with any of this they would have to have a good feel for how an inductor behaves. I just asked my dog if she has a good feeling about how an inductor behaves. She wagged her tail in affirmation. Now please explain why feelings are important to this discussion. Do you agree or disagree with my post about how an inductor behaves? I disagree with you about how an inductor behaves in a standing wave environment. I agree with Walter Maxwell who said: "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." Sorry about that, but Walt gave me permission to quote him. Note the emphasis on 'NOT' in his statement. A 75m bugcatcher mobile system is a *STANDING WAVE ANTENNA*, so no, I don't agree with you at all as enumerated in my previous posting. Please don't ask me the same question over and over. I am not going to change my mind until you provid valid evidence to the contrary and so far, all you have done is prove your ethics leave something to be desired. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Wed, 08 Mar 2006 01:46:19 GMT, Cecil Moore wrote:
wrote: All personal issues and insults aside, before anyone does anything with any of this they would have to have a good feel for how an inductor behaves. I just asked my dog if she has a good feeling about how an inductor behaves. She wagged her tail in affirmation. ... Oh no Cecil, not another citation! Owen -- |
Current through coils
Hey folks, they have a word that's used occasionally that I think might be appropriate here, it is "chill". As in chill out. Things are getting more out of hand than normal. Some of you are adults, please start acting that way. Some people have been trying, possibly poorly, to be funny, forgive them. I could say more, but you get the idea. tom K0TAR |
Current through coils
Tom Ring wrote:
Some of you are adults, please start acting that way. Tom, I apologize profusely to everyone for losing my temper. I regret that every time it happens but that time never seems to be the final time. I canceled my posting made in anger. But please note that me losing my temper has absolutely no bearing on objective technical facts and has absolutely no effect at all on the validity of my technical arguments. Galileo probably lost his temper in front of the priests who placed him under house arrest. That made absolutely no difference in the scientific facts that he was asserting at the time. I am presenting my thoughts in front of the internet gurus in much the same manner as Galileo did to the priests. Hopefully, they will listen better than the priests did and not put me under house arrest. (But I have my Colt 45 ready just in case. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
That doesn't sound like Walter gave you permission to me. I have backtracked to try to find out what happened. I asked Walt's permission to post the following: Walter Maxwell wrote: 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. He agreed but suggested I also include his fourth statement which followed the above three statements. When reflections are present, a current node and a current loop can appear at separate points on an inductor simultaneously. When I went back to copy and paste bottom-up from his email in order to include his fourth assertion, I inadvertently copied one too many sentences at the top. It is true that I didn't have Walt's permission to publish that extra first sentence in his email. I regret that accidental mistake and wish I could take it back. And of course, neither Walt nor anyone else in the universe agrees with me 100%. But please note that accidentally including that first sentence doesn't change the technical content of Walt's other four assertions which should be allowed to stand as is until further notice. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Wed, 08 Mar 2006 00:29:14 GMT, Cecil Moore wrote:
Walter Maxwell earlier wrote: By accounts, Walt works both sides of the street for them. This Hustle & Flow of posts redefines the Academy award to "It's Hard Out Here for the Pimps" |
Current through coils
Do you agree or disagree with my post about how an inductor behaves? I disagree with you about how an inductor behaves in a standing wave environment. I agree with Walter Maxwell who said: "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." Then we can't go further with this Cecil, unless you can accurately explain WHY the behavior of an inductor changes when it is in an antenna, rather than in some other system where impedances are the same or very similar. It seems that Ian, Reg, Roy, and several others including myself all believe an inductor works the same way. If you convince one of us we are in error the others will surely follow! If you refuse to discuss the behavior or electrical characteristics of the component you are talking about, there really isn't anything we can talk about. In that case I suggest you leave my name out of things, and I'll do the same for you. When you are ready to talk about the root problem, I'll try to be here. 73 Tom |
Current through coils
wrote:
Do you agree or disagree with my post about how an inductor behaves? I disagree with you about how an inductor behaves in a standing wave environment. I agree with Walter Maxwell who said: "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." Then we can't go further with this Cecil, unless you can accurately explain WHY the behavior of an inductor changes when it is in an antenna, rather than in some other system where impedances are the same or very similar. It seems that Ian, Reg, Roy, and several others including myself all believe an inductor works the same way. And also, if the inductively loaded antenna is designed by the "antenna as transmission line" method (as used by Boyer and ON4UN for example) it clearly shows that the loading inductance is simply there to cancel the net capacitive reactance - in other words, it behaves in exactly the same way as you would in any other circuit. The irony is that Boyer *does* use the concept of reflected traveling waves in his basic explanation of how monopole antennas work. The difference is that he understood how to do it without tying himself in knots. 'Antenna Transmission Line Analog: a key to understanding antennas' by Joseph M Boyer (W6UYH, SK 1988). Ham Radio, April 1977 and May 1977. If you convince one of us we are in error the others will surely follow! Slip of the fingers there, Tom - there aren't any "followers" in that particular company. We are all fiercely independent-minded individuals, absolutely determined to do our own thinking and to get it right. 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. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
On Wed, 8 Mar 2006 11:41:38 +0000, Ian White GM3SEK
wrote: [snip] 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. Careful Ian, remember that our President calls Texas home, so the probability might not be so high after all. ;-) ps. I crossed paths with Joe Boyer a couple of times when we were both at Hughes. |
Current through coils
wrote:
Then we can't go further with this Cecil, ... That's simply not true. We can take this discussion to its logical conclusion if you are not afraid to continue it in logical order at a logical starting point. Starting with coils is like looking for your keys under the street light, instead of where you lost them, because that's where the light is better. Coil theory is not the problem. Standing wave current theory is the problem. Let's discuss the problem. If you refuse to discuss the behavior or electrical characteristics of the component you are talking about, there really isn't anything we can talk about. I'm not refusing to discuss anything as long as it is taken in logical order. Our disagreement extends much farther back into fundamental technical principles than just the subject of coil function. We actually may have no technical disagreement about coils. I believe our basic disagreement involves standing wave current, not coils, so standing wave current should be the topic of this initial discussion. For that, we need to first agree on the 1/2WL thin wire model of a dipole. Let's see what we can agree on. Can we agree on the following pertaining to a 1/2 wavelength thin wire dipole? The net current in a standing wave antenna is a standing wave. The net current displayed by EZNEC for a standing wave antenna is a standing wave. The net standing wave current is the phasor sum of the forward current traveling wave and the reflected current traveling wave. The principle of superposition applies to the two component waves. If we superpose the forward current traveling wave and the reflected current traveling wave, we obtain the net standing wave current. Let's take for instance, that 1/2WL thin wire dipole. The standing wave current distribution and phase appears in Figure 14-2 in Kraus and Figures 1.15 and 4.8 in Balanis. If the current at the feedpoint is 1 amp, the net standing wave current equals cosine(x) where 'x' is the distance in degrees away from the feedpoint. This topic of discussion will most likely reveal that our fundamental point of disagreement is standing wave current and not coils at all. So which points above do you agree/disagree with? References to Kraus are from "Antennas for All Applications", Kraus and Marhefka, 3rd edition. References to Balanis are from "Antenna Theory", Balanis, 2nd edition. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Ian White GM3SEK wrote:
And also, if the inductively loaded antenna is designed by the "antenna as transmission line" method (as used by Boyer and ON4UN for example) it clearly shows that the loading inductance is simply there to cancel the net capacitive reactance - in other words, it behaves in exactly the same way as you would in any other circuit. If that is true, you guys shouldn't have any difficulty proving me wrong and sending me back to the woodshed once and for all. If the above is not entirely true, please don't put me under house arrest until I present the truth as I see it. And certainly, call me on anything that is wrong. If you will keep listening with an open mind, I think I can show you that the words, "clearly", "simply", and "exactly", in your above statement are not entirely correct. -- Ian, no one has explained the antenna currents reported by EZNEC at: http://www.qsl.net/w5dxp/qrzgif35.gif How can 0.1+ amp of current be 'flowing' into the bottom of the coil and 0.7+ amp of current be 'flowing' out of the top of the coil. It's been days now and no one has offered an explanation. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
I received an email from someone (an attempted reply mail bounced) who thinks his mobile antenna is "90-degree resonant". The the upper portion of the antenna is physically 5 degrees long, the lower section 10 degrees, and the loading coil placed between the two about 1 degree long. He has tied himself in a knot picturing the system as being "90-degree" resonant, and thinking the inductor must make up the missing 74 degrees of antenna height. Here's a question for you, Tom. Assume for reference that the forward current phase is at 90 deg and the reflected current phase is at -90 deg at the tip of the antenna and then backtrack the two phasors to the feedpoint. The phasor currents are known to rotate in opposite directions. The question for you is: What is the phase of the forward current originating at the feedpoint? What is the phase of the reflected current returning to the feedpoint? Seems you are trying to tell us that the phase of the forward current at the feedpoint is at a phase angle of 90-16 = 74 degrees and the phase of the reflected current is -90+16 = -74 degrees at the feedpoint since, as you say, the antenna is 16 degrees long. Assuming angle F is the feedpoint phase of the forward current and angle R is the feedpoint phase of the reflected current: We know that net current at the feedpoint is Ifor*cos(F) + Iref*cos(R) According to your theory the net current would be Ifeedpoint = Ifor*cos(74) + Iref*cos(-74) = .028(Ifor+Iref) Since the feedpoint impedance is inversely proportional to the feedpoint current, the feedpoint impedance for your loaded vertical would be a lot higher than the feedpoint impedance for a 1/4WL vertical but we know it actually goes in the opposite direction. How do you resolve that contradiction? He also, as many people do, visualizes an inductror model where current winds its way through the copper from end to end. His exact words being: "Also, in colis(sic) of significant wire length the propagation time of current in the wire is still approximately 1 E-9 seconds/foot." For an ideal inductance, the voltage propagates through the coil at the speed of light. The current lags the voltage by as much as 90 degrees in an ideal inductance. For an ideal capacitance, the current propagates through the coil at the speed of light. The voltage lags the current by as much as 90 degrees in an ideal capacitance. It seems some have reached an unbendable conclusion without even understanding how an inductor works. It is not your understanding of how an inductor works that is the problem. It is your misunderstand of how standing wave current works that is the problem. Let's discuss the problem on the other thread in progress. We need to talk about the inductor, or this will go nowhere and in another three years pop right back up. You are looking for your keys under the street lamp instead of where you lost them, because the light is better. The inductor is NOT the problem. Your misunderstanding of standing waves is the problem. You fully understand how a coil works in the presence of a traveling wave. You do not understand how a coil works in the presence of standing waves, not because you lack understanding of a coil, but because you lack understanding of standing wave current. If you keep avoiding your area of misunderstanding, this will go nowhere. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Has it ever occurred to you guys that a coil is a coil wherever it is
used and always behaves in the same way. |
Current through coils
wrote:
It seems some have reached an unbendable conclusion without even understanding how an inductor works. It certainly seems you have reached an unbendable conclusion without even understanding how an inductor works in a standing wave environment. The following reference, emailed to me by a kind reader of this newsgroup, says exactly what I have been trying to say. I propose that a 75m bugcatcher loading coil is a "velocity inhibited slow-wave helical transmission line resonator". The only difference between it and a 1/4WL resonant Tesla coil is the radiating part of the antenna. I'll quote a few excerpts. http://www.ttr.com/corum/index.htm [begin quote] Tesla Coils and the Failure of Lumped-Element Circuit Theory by Kenneth L. Corum and James F. Corum, Ph.D. © 1999 by K.L. Corum and J.F. Corum In all of those [lumped] circuit models the current is analytically presupposed to be uniformly distributed along the wire in the coil ... There are no standing waves on a lumped element circuit component. However, a true Tesla coil (circa 1894) is a velocity inhibited slow-wave helical transmission line resonator: ... one needs transmission line analysis (or Maxwell's equations) to model these electrically distributed structures. Lumped circuit theory fails because it's a theory whose presuppositions are inadequate. Every EE in the world was warned of this in their first sophomore circuits course. This phenomenon is decisive. It occurs only on distributed resonators: it is impossible with any lumped circuit element! (The current has the same value at every point along a lumped-element.) To understand what is happening, consider a cylindrical helical coil of height H. The base is always forced to be a voltage node (it's grounded). The top is always a relative voltage loop at the odd quarter-wave resonances and a voltage node at the even (half-wave) resonances. These boundary conditions constrain the mode patterns on the structure (called spatial harmonics). We assert that velocity inhibited partially coherent forward and reflected RF traveling waves form interference patterns on the coil. [end quote] "Lumped circuit theory fails because it's a theory whose presuppositions are inadequate." Seems some EEs have forgotten that sophmore year warning. Using lumped circuit theory in the presence of standing waves is a form of "assuming the proof" or "begging the question" and is simply invalid. Quoting relevant material from Balanis: "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines. ... Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents If and Ib ..." -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
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 -- 73, Cecil http://www.qsl.net/w5dxp |
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 Dang Reg, I forgot to post the quote from that web page. Here it is: "Lumped element representations for coils require that the current is uniformly distributed along the coil - no wave interference and no standing waves can be present on lumped elements." Therefore, lumped element representations for coil CANNOT be used to analyze standing wave antennas. I wasn't the first to say that. Using a lumped element representation for a coil in a standing wave environment is "assuming the proof". Here's more information along those same lines. http://www.ttr.com/TELSIKS2001-MASTER-1.pdf -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Ian White GM3SEK wrote: And also, if the inductively loaded antenna is designed by the "antenna as transmission line" method (as used by Boyer and ON4UN for example) it clearly shows that the loading inductance is simply there to cancel the net capacitive reactance - in other words, it behaves in exactly the same way as you would in any other circuit. If that is true, you guys shouldn't have any difficulty proving me wrong and sending me back to the woodshed once and for all. If the above is not entirely true, please don't put me under house arrest until I present the truth as I see it. And certainly, call me on anything that is wrong. The only problem for the rest of us is that you seem to have unlimited energy and time :-) If you will keep listening with an open mind, I think I can show you that the words, "clearly", "simply", and "exactly", in your above statement are not entirely correct. There is one typo in that statement: I posted it part-way through changing from "In other words, you use the inductance in exactly the same way as you would in any other circuit" to "In other words, it [the inductance] behaves in exactly the same way as it does in any other circuit". I stand by both of those statements. -- Ian, no one has explained the antenna currents reported by EZNEC at: http://www.qsl.net/w5dxp/qrzgif35.gif How can 0.1+ amp of current be 'flowing' into the bottom of the coil and 0.7+ amp of current be 'flowing' out of the top of the coil. It's been days now and no one has offered an explanation. It's because you modeled a real-life coil, whose length and diameter are each a significant fraction of the size of the whole antenna. Nobody disputes that the currents at the two ends of a real-life coil are going to be different... but the reason is because of its other properties besides pure inductance. You are hung up on something far more fundamental. You are misrepresenting the fundamental electrical properties of inductance to make them fit your theory. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
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. That is only true if you say it about pure inductance. But a "coil" is a real-life component that has other properties like physical size, number of turns, self-capacitance and leakage inductance. A coil interacts electromagnetically with the circuit in which it finds itself, so it doesn't always behave in the same way. But pure inductance does. The difference between inductANCE and an inductOR - a real-life coil - is not just playing with words. There is a reason for having those two different words... and that reason is the key to this whole debate. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Reg Edwards wrote:
"Has it ever occurred to you guys that a coil is a coil however it is used and always behaves in the same way?" Yes! But when it is part of an antenna system, the system imposes energy upon the coil in ways which the coil does not control. "The system is the solution", AT&T used to say. John D. Kraus writes on page 176 of his 1950 edition of "Antennas": "The term transmission mode is used to describe the manner in which an electromagnetic wave is propagated along an infinite helix (that`s a coil, right?) as though the helix constituted an infinite transmission line or wave guide." Wave guides and transmission lines are subject to reflections. These produce the standing wave patterns exhibited in many text books. Kraus uses the helix very generally. To him it can collapse to a single loop or be stretched to a straight wire. When a "normal mode" helix (coil) is used as part of a antenna system, It radiates normal to the axis of the coil, similar to the manner it would were it stretched out to a straight wire. A reflection within the antenna system would return energy toward the generator, similar to the manner it would with straight wires. The same sort of interaction between incident and reflected waves must occur. There is no other way. These produce variatiations in both current and voltage in a periodic manner along the helix as described for transmission lines which should be familiar to all. The whole section of helical antennas in Kraus is interesting. Kraus is the inventor of the Axial mode helical antenna. I think he tells the story in his 3rd edition of how he went home and wound one up and tested it after being told by an expert of the times that such an antenna was impossible. Best regards, Richard Harrison, KB5WZI |
Current through coils
Ian White GM3SEK wrote:
SNIPPED A LOT You are hung up on something far more fundamental. You are misrepresenting the fundamental electrical properties of inductance to make them fit your theory. I agree with Cecil. An Inductor in a DC circuit under transient conditions has a classic L/R response. An inductor in a AC power line [60 Hz] acts as a classic inductor. An inductor in a LF antenna system acts as a classic inductor when the physical AND electrical dimensions are very small compared to a wavelength. An Inductor in a HF shortened antenna does NOT act like a classic inductor. It is a significant portion of the HF circuit and must be treated as such. My 60 meter mobile antenna is 90 degrees long, 1/4 wavelength resonant at 18 +j0 ohms [MFJ analyzer]. It is 10 degrees long from feedpoint to base of coil. Current into the coil is 98% of feedpoint current [cos 10 degrees]. The antenna is 5 degrees long from top of coil to top of antenna. The current at the top of coil calculates to 9% of feed current [sin 5 degrees]. Conclusion: the coil, at 75 degrees of the circuit, has to be treated differently from DC or LF models. |
Current through coils
"Ian White GM3SEK" 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. That is only true if you say it about pure inductance. ======================================== Ian, old boy, you are no better than the rest of the gaggle ! There's not one of the clever buggers who can design a coil-loaded whip for a given frequency using a pencil, paper and a pocket calculator. They have to copy an already existing, pre-tested, model after searching through the antenna comics. --- Reg. |
Current through coils
Ian White GM3SEK wrote:
There is one typo in that statement: I posted it part-way through changing from "In other words, you use the inductance in exactly the same way as you would in any other circuit" to "In other words, it [the inductance] behaves in exactly the same way as it does in any other circuit". I stand by both of those statements. Too bad you are standing by false statements. :-) Quoting: http://www.ttr.com/corum/index.htm "... one needs transmission line analysis (or Maxwell's equations) to model these electrically distributed structures. Lumped circuit theory fails because it's a theory whose presuppositions are inadequate. Every EE in the world was warned of this in their first sophomore circuits course." Seems you weren't listening that day, Ian. "Lumped element representations for coils require that the current is uniformly distributed along the coil - no wave interference and no standing waves can be present on lumped elements." It's because you modeled a real-life coil, whose length and diameter are each a significant fraction of the size of the whole antenna. A 75m bugcatcher coil is a real-life coil, Ian. Contrary to what W8JI asserts, it is a significant fraction of the size of the whole antenna. It uses 42 feet of wire, for goodness sake. You are hung up on something far more fundamental. You are misrepresenting the fundamental electrical properties of inductance to make them fit your theory. I am using distributed network theory known to work in a standing wave environment. You are using lumped element theory known to fail in a standing wave environment. A 75m bugcatcher mobile antenna is a standing wave environment. So exactly who is "misrepresenting the fundamental electrical properties of inductance to make them fit his theory"? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Amos Keag wrote:
I agree with Cecil. Good to hear. Conclusion: the coil, at 75 degrees of the circuit, has to be treated differently from DC or LF models. Yes, I just ran an experiment that would support that statement. My 75m bugcatcher coil is mounted on a one foot bottom section on my pickup. I'm sorry but I can't fasten the coil directly to the mount for reasons of clearance. But one foot at 75m is only about 1.5 degrees so let's call it negligible. I have one of those 12 foot telescoping whips from MFJ. It's great for portable operation from my pickup. It is adjustable from 2 feet to 12 feet. The first measurement I made was with no whip at all, just the bugcatcher sitting on top of a one foot bottom section. I used an MFJ-259B for the measurements connected through a two foot W2DU choke. Here are the results. resonant Stinger frequency 0' 6.7 MHz 2' 5.1 MHz 4' 4.3 MHz 6' 3.8 MHz 8' 3.5 MHz 10' 3.2 MHz 12' 3.0 MHz It's more than obvious that with a stinger length of 0', the coil is very close to 1/4WL and is NOT a lumped inductance. The current at the top of the coil is obviously zero. So moving down the frequency in 2' increments, exactly when does a coil made with 42 feet of wire become a lumped inductance in the presence of standing waves? http://www.ttr.com/corum/index.htm says never. When I get my MFJ current meter, I will actually measure the current at the top and bottom of the coil. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
There's not one of the clever buggers who can design a coil-loaded whip for a given frequency using a pencil, paper and a pocket calculator. Sure we can, Reg. Just design the coil too big and jumper the un-needed turns. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Hmm ... ARRL Antenna Book gives method ... No?
Cecil Moore wrote: Reg Edwards wrote: There's not one of the clever buggers who can design a coil-loaded whip for a given frequency using a pencil, paper and a pocket calculator. Sure we can, Reg. Just design the coil too big and jumper the un-needed turns. :-) |
Current through coils
"Cecil Moore" wrote Reg Edwards wrote: There's not one of the clever buggers who can design a coil-loaded whip for a given frequency using a pencil, paper and a pocket calculator. Sure we can, Reg. Just design the coil too big and jumper the un-needed turns. :-) ========================================== Dear Cecil, you know as well as I do, that pruning the coil is not DESIGN. It is a procedure done by people who are floundering about in the dark. Not by supposedly professionally qualified engineers who are participating in this discussion. Anybody, even a CB-er, can make an antenna with the top of the whip a mile long and then severely prune it until the antenna resonates at the pre-determined frequency, following a score of attempts to use coils of different dimensions and numbers of turns. But even the experimenting CB-er has to understand what he is doing. Not so the so-called professionals. It appears from this discussion the university-educated Ph.D professionals are the ones who are floundering about in the dark. Silly old-wives indeed. As I have said before, the standards of education in Western schools and universities are dropping to bits. Chinese, Japanese, Korean, Iraqian, Iranian, Afganistan, Indian, Pakistan, Vietnam and Indianesian school kids, not forgetting the half-starved sewer-rats of Rio-de-Janerio, are better at arithmetic. And, what is more important, what stems from it! If you are interested I am on Spanish, Valencia Red tonight. It is supposed to minimise cholesterol in the blood stream. ---- Your old pal, Reg. |
Current through coils
Reg Edwards wrote:
Dear Cecil, you know as well as I do, that pruning the coil is not DESIGN. I dunno about that, Reg. The Texas Bugcatcher guy made a living off of coils that were designed to require pruning. He even sold a pruning kit. If you are interested I am on Spanish, Valencia Red tonight. It is supposed to minimise cholesterol in the blood stream. Muy bueno. California Merlot here. Makes me forget about my cholesterol. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
My 60 meter mobile antenna is 90 degrees long, 1/4 wavelength resonant
at 18 +j0 ohms [MFJ analyzer]. It is 10 degrees long from feedpoint to base of coil. Current into the coil is 98% of feedpoint current [cos 10 degrees]. The antenna is 5 degrees long from top of coil to top of antenna. The current at the top of coil calculates to 9% of feed current [sin 5 degrees]. Conclusion: the coil, at 75 degrees of the circuit, has to be treated differently from DC or LF models. I don't know how you can reach that conclusion except by guessing. The inductor has some effective equivalent series impedance that includes resistance, reactance, and distributed capacitance. I can easily build an inductor for your antenna that tunes the antenna to resonance and when the top-whip is removed makes the lowest resonant many times higher than 75 degrees plus 10 degrees at 60 meters would appear. On the other hand I can probably, given enough time, build an inductor that might mislead us into thinking the coil inserted in the antenna acts like it is about 75 degrees long. 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! 73 Tom |
Current through coils
Reg Edwards wrote:
SNIPPED A LOT There's not one of the clever buggers who can design a coil-loaded whip for a given frequency using a pencil, paper and a pocket calculator. Hmm ... The capacitance of a short vertical monopole above a conducting plane is a straightforward EM problem [Em 101]. Hmm ... Resonance requires a series inductance where L is proportional to N^2 times D^2. [Circuits 101] Value of L can be adjusted using transmission line models for location along the monopole. The Zo of the monopole is proportional to the ln(len/dia minus a constant). [Antennas 101] Given a little time to review the particulars and refresh 60+ years of separation from EM 101 I think the method would work. But, I don't have a calculator. Would my old Pickett do? Does this mean I don't qualify as a "clever bugger"? |
Current through coils
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! Well then do it, Tom. But you are not allowed to use the lumped circuit model. You must use the distributed network model (or Maxwell's equations). I think the distributed network model proves otherwise. Could be you are the one spreading myths after using an invalid model. There's just no getting around it. The forward current undergoes approximately a 90 degree phase shift from the feedpoint to the end of a 75m mobile bugcatcher antenna. It is reflected there (180 degree phase shift) and becomes reflected current which undergoes approximately a 90 degree phase shift from the tip of the antenna back to the feedpoint. So from the start of the forward current wave to the return of the reflected current wave there is approximately a 360 degree shift in order to put the forward current and reflected current in phase so they can superpose constructively. If the straight element part of the antenna is 12 degrees, we can account for 12 + 180 + 12 = 204 degrees without the coil. The coil is the only other thing in the whole system. Where does the other 78+78=156 degrees of total phase shift come from if not from the coil? I've explained all of this to you many times. Might be a good time to start listening. You can prove this for yourself. Using current probes and your o'scope you can measure the traveling wave phase shift through a loading coil. That figure is approximately the electrical length that is replaced by the coil when it is installed in the antenna. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
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!" A vertical antenna is often driven against a reflecting ground system. It is desirable that it be self resonant at nearly 1/4-wavelength (90-degrees), in many instances, to eliminate reactive impedance to current into the antenna, avoid loading coil loss, and avoid bandwidth limitation which comes with high-Q coils. Even with its drawbacks, a base loading coil is often the practical way to resonate a too-short antenna. 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. 30-degrees is not an inductance value. An inductor is impure because it has resistance and capacitance in addition to inductance. Also, the inductance needed to replace the missing 30-degrees of antenna depends on where it is sited, high, low, or in-between. Siting affects performance as it determines current distribution along the antenna. Where is the myth? Best regards, Richard Harrison, KB5WZI |
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