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Current through coils
K7ITM wrote:
I REGULARLY model transmission lines as "lumped elements" and do NOT "presuppose that the speed of light" through them is infinite. I'm interested in knowing how you model a shorted quarter wavelength stub using the lumped element model. I REGULARLY model op amps as "lumped elements" and do NOT presuppose that the phase shift (and therefore propagation time) through them is infinite. I should hope not! You would never get a signal through them. :-) I REGULARLY model inductors as "lumped elements", and do not presuppose that they have no resistances and capacitances parasitic to their inductANCE. Then you are somehow applying a patch to the lumped element model. The basic lumped element model assumes no resistance and no capacitance. That's how the lumped inductance-only works in EZNEC. I find that my models very reliably predict the behaviour I actually observe in the circuits I build. I am served very well by the models I use. Do you use them on 75m bugcatcher coils and obtain an incorrect phase shift as W8JI and W7EL have done? By the way, what's EE203? The sophmore EE class alluded to by Dr. Corum. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
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Current through coils
Cecil Moore wrote:
K7ITM wrote: I REGULARLY model transmission lines as "lumped elements" and do NOT "presuppose that the speed of light" through them is infinite. I'm interested in knowing how you model a shorted quarter wavelength stub using the lumped element model. I REGULARLY model op amps as "lumped elements" and do NOT presuppose that the phase shift (and therefore propagation time) through them is infinite. I should hope not! You would never get a signal through them. :-) I REGULARLY model inductors as "lumped elements", and do not presuppose that they have no resistances and capacitances parasitic to their inductANCE. Then you are somehow applying a patch to the lumped element model. The basic lumped element model assumes no resistance and no capacitance. That's how the lumped inductance-only works in EZNEC. I find that my models very reliably predict the behaviour I actually observe in the circuits I build. I am served very well by the models I use. Do you use them on 75m bugcatcher coils and obtain an incorrect phase shift as W8JI and W7EL have done? By the way, what's EE203? The sophmore EE class alluded to by Dr. Corum. Cecil, there are two Corums and they're both Tesla coil crackpots. Secondly, Tom is right, you have to have capacitance to somewhere or your transmission line analogy becomes mired in absurdities. Third, it isn't enough to think something up in your head to make a convincing theory, you have to be able to predict behavior with it. Finally, you have to understand your subject before you even start thinking. I'm surprised you didn't even take the time to make a real coil and at least try to determine its characteristics before wasting everyone's time by starting this thread. 73, Tom Donaly, KA6RUH |
Current through coils
On Sat, 01 Apr 2006 19:26:42 GMT, Cecil Moore
wrote: Do you use them on 75m bugcatcher coils and obtain an incorrect phase shift as W8JI and W7EL have done? All measurements done by everyone are incorrect. Yours, by your own admission 59% in error, qualifies you for the Gold, Silver and Bronze medals of Olympian Mistakes. We can strike some Copper, Tin, and Lead medals, but you would scoop them up too. |
Current through coils
Tom Donaly wrote:
Cecil, there are two Corums and they're both Tesla coil crackpots. Secondly, Tom is right, you have to have capacitance to somewhere or your transmission line analogy becomes mired in absurdities. Would you guys please stop implying falsehoods and make an attempt to argue in good faith? I didn't say the capacitance didn't exist. I said it was a secondary effect to the superposition of the forward and reflected waves. That you are forced to twist what I said speaks volumes about your argument. Why don't you feel secure enough in your technical argument not to have to twist my words into something I didn't say? Third, it isn't enough to think something up in your head to make a convincing theory, you have to be able to predict behavior with it. I have predicted behavior on http://www.qsl.net/w5dxp/current.htm with text surrounding http://www.qsl.net/w5dxp/1WLDIP.GIF. That graphic is not disembodied as you claimed. It is surrounded with examples and text, more than enough proof for any rational person. The current at each end of a coil obviously depends upon where it is installed in the standing wave antenna system. Your wearing of blinders doesn't hide that technical fact from anyone except yourself. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Clark wrote:
All measurements done by everyone are incorrect. Yours, by your own admission 59% in error, ... Uhhhh Richard, those weren't measurements. Those were calculated results, using formulas out of books. The only measurements that I have made were of 1. self-resonant frequencies within the accuracy of an MFJ-259B and 2. standing wave phase measurements that agree with Kraus and EZNEC. The 59% accuracy was in my wild ass *guesses* as opposed to the 207% error in W8JI's phase *measurements*. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Sat, 01 Apr 2006 22:00:49 GMT, Cecil Moore
wrote: All measurements done by everyone are incorrect. Yours, by your own admission 59% in error, ... Uhhhh Richard, those weren't measurements. Those were calculated results, using formulas out of books. The crippling legacy of Xerox research. The only measurements that I have made were of 1. self-resonant frequencies within the accuracy of an MFJ-259B and 2. standing wave phase measurements Only indeed. Now there's some challenging qualification trials for an Olympic biathlon. that agree with Kraus Have you been sleeping with Kraus again? and EZNEC. Hmm, the same EZNEC you've impeached for accuracy? When we loop back to the top of this post to note the 59% error derived from work accomplished that "weren't measurements" and they agree with your "measurements" THAT just has to be another hallmark warning sign of bogus science - self validation. After 17,433 posts, you certainly work hard to convince yourself. ;-) |
Current through coils
Richard Clark wrote:
Have you been sleeping with Kraus again? Yes, I often sleep with Kraus and Balanis. You should try occasionally reading a reference book instead of watching The Three Stogies. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On 31 Mar 2006 16:34:07 -0800, wrote:
[snip] I'm sure the 800-post thread will continue another 800 posts. People must be bored. You've noticed :-) |
Current through coils
On Sat, 01 Apr 2006 18:37:35 -0700, Wes Stewart
wrote: On 31 Mar 2006 16:34:07 -0800, wrote: [snip] I'm sure the 800-post thread will continue another 800 posts. People must be bored. You've noticed :-) Boy, ain't that the truth. I'm putting into my kill filter. |
Current through coils
Tom Donaly wrote:
Cecil, there are two Corums and they're both Tesla coil crackpots. Secondly, Tom is right, you have to have capacitance to somewhere or your transmission line analogy becomes mired in absurdities. Third, it isn't enough to think something up in your head to make a convincing theory, you have to be able to predict behavior with it. Finally, you have to understand your subject before you even start thinking. I'm surprised you didn't even take the time to make a real coil and at least try to determine its characteristics before wasting everyone's time by starting this thread. 73, Tom Donaly, KA6RUH Tom, You, and everyone else is, as we put it in the midwest, and probably elsewhere, "****ing into the wind". You cannot win an argument with someone that does not acknowledge reality. tom K0TAR |
Current through coils
Tom Ring wrote:
You cannot win an argument with someone that does not acknowledge reality. I've found that out, Tom. None of you guys are willing to answer any technical questions about the material presented on my web page at: http://www.qsl.net/w5dxp/current.htm, in particular: http://www.qsl.net/w5dxp/1WLDIP.GIF The current through a coil placed in a standing wave environment either depends upon where it is placed in that environment or it doesn't. It's not rocket science. The gurus have refused to discuss at least 95% of my technical questions. No amount of personal wise cracks, like yours above, will erase that fact. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Tom Ring wrote: You cannot win an argument with someone that does not acknowledge reality. I've found that out, Tom. None of you guys are willing to answer any technical questions about the material presented on my web page at: http://www.qsl.net/w5dxp/current.htm, in particular: http://www.qsl.net/w5dxp/1WLDIP.GIF The current through a coil placed in a standing wave environment either depends upon where it is placed in that environment or it doesn't. It's not rocket science. The gurus have refused to discuss at least 95% of my technical questions. No amount of personal wise cracks, like yours above, will erase that fact. Cec; I hate to be the one to break it to you but you are the one they are talking about. When everyone says you are drunk, like down, your drunk. Dave N |
Current through coils
Early... too early... on Saturday morning, I wrote:
Tom Donaly wrote: What lumped circuit theory? It's a simplification and everyone knows it. Don't set up any more straw men than you have to, Cecil. It's a simplification of any real-life coil - but loading by pure-and-simple lumped inductance is also a vital test case. This form of loading is the simplest imaginable. If a theory about the behaviour of loaded antennas fails to give correct results for this very simplest test case, it cannot be valid... and all the further elaborations about real-life coils will not be valid either. Evidently I was in too much of a hurry to leave for the GMDX convention, because what I mean to write next was: "Cecil's theory does not work for this test case, " [ I definitely did type the word "not", but it accidentally disappeared from the version that was posted. ] So, from the top of the paragraph: Cecil's theory does not work for this test case, because it requires that basic electrical properties like current and inductance switch into a different kind of behaviour in what he calls a "standing wave environment". But it is an absolutely basic fact that the physical world does NOT change its behaviour according to the way we choose to think about it. If any theory requires that, it's an absolute proof that such theory is false. For the avoidance of doubt (as they say in Scottish legal documents): It certainly IS possible to analyse and predict the behaviour of coil-loaded antennas in terms of travelling and standing waves. My objection is specifically against Cecil's method, which is provably incorrect. Sorry for any confusion that typo may have caused. This corrected version is now fully consistent with what I meant to say. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Tom Ring wrote:
Tom Donaly wrote: Cecil, there are two Corums and they're both Tesla coil crackpots. Secondly, Tom is right, you have to have capacitance to somewhere or your transmission line analogy becomes mired in absurdities. Third, it isn't enough to think something up in your head to make a convincing theory, you have to be able to predict behavior with it. Finally, you have to understand your subject before you even start thinking. I'm surprised you didn't even take the time to make a real coil and at least try to determine its characteristics before wasting everyone's time by starting this thread. 73, Tom Donaly, KA6RUH Tom, You, and everyone else is, as we put it in the midwest, and probably elsewhere, "****ing into the wind". You cannot win an argument with someone that does not acknowledge reality. tom K0TAR If we don't pee into the wind Cecil will end up telling everyone his crackpot theories are received truth, and eventually we'll be reading them in _The ARRL Handbook_. I appreciate the fact that it's a waste of time, otherwise. Entertaining, though. Cecil's an interesting Character. 73, Tom Donaly, KA6RUH |
Current through coils
David G. Nagel wrote:
I hate to be the one to break it to you but you are the one they are talking about. I know that, Dave. At best it is the pot calling the kettle black. At worst, it's just another falsehood, one of many. The problem here is not "Current through coils". The problem is that a lot of the gurus are completely ignorant of the nature of standing wave current and refuse to alleviate their ignorance. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Ian White GM3SEK wrote:
Evidently I was in too much of a hurry to leave for the GMDX convention, because what I mean to write next was: "Cecil's theory does not work for this test case, " [ I definitely did type the word "not", but it accidentally disappeared from the version that was posted. ] Well there you have it, folks. Gurus don't even make typo mistakes. Some evil server removed that "not" on purpose from Ian's posting. Cecil's theory does not work for this test case, because it requires that basic electrical properties like current and inductance switch into a different kind of behaviour in what he calls a "standing wave environment". RF current switches from a different kind of behavior than DC current. Phase, capacitance, inductance, and wavelength all have to be taken into account in the steady-state analysis. That is a technical fact that I'm sure you appreciate. Why is it such a stretch to recognize that standing wave current behaves differently from traveling wave current? That standing wave current is different from traveling wave current is readily apparent from the equations. In the following equations, 'K' is used for a constant, 'z' is the linear distance up and down the line, and 'w' is omega. Forward traveling wave current = K1*cos(kz+wt) Reflected traveling wave current = K2*cos(kz-wt) Standing wave current = K1*cos(kz+wt) + K2*cos(kz-wt) = K3*cos(kz)*cos(wt) If tK1 = K2, then the standing wave doesn't move. Please dust off your old math books and realize what the above equations imply at a physical level. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Ian White GM3SEK" wrote in message ... From the beginning, then: snippydidudaa As we have seen, if the whip is loaded by pure inductance only, there is no change in current between the two terminals of the inductance - but there's a big step increase in voltage. At the upper terminal, the current is the same but the voltage is very high, so we're into a much higher-impedance environment. Reality check here. I need explanation how the above could happen. "Current stays the same ... and the big step increase in voltage." As far as "idiot" professors taught me, (current x voltage) = power. So, am I to discover that the pure inductance is better than perpetual motion amplifier of power? More power coming out of the coil than going in? Eureka!!! How could I overlook that? :-) As we go further up towards the top of the whip, current magnitude has to taper off to zero at the very top. This also means that the voltage magnitude has to increase even more as we approach the top of the whip. So it tapers across the straight piece of conductor, but not in the wound up conductor? Magine that! Reality check #2. Single-point loading by pure inductance has thus created almost all the major features that we see in a practical centre-loaded whip - particularly the big step change in voltage across the loading coil. So the "teaching" is that there is a big step change in the voltage across the coil, but no-way change in the current? Who's law, theory, invention is that? (We are still talking about real RF currents, not "my voltage" and "your invincible, steady, unchengeable current"?) What we don't see in a practical antenna are exactly equal current magnitudes and zero phase shift between the terminals of a real-life loading coil - but that is ONLY because a real-life coil is not a pure inductance. The harder we try to reach that ideal (by winding the coil on a high-permeability toroidal core which confines the external fields and allows the whole thing to become very small), the closer the currents at the bottom of the coil come to being equal. Solid theory and accurate measurements come together to support each other. The only gap between theory and practice is due to our inability to construct a pure inductance that has no other complicating properties. The whole argument is about REAL LIFE loading coil in the antennas. But you obviously ignored or not noticed that W9UCW also used toroid coil and found very similar results, about 40 - 60 % less current at the top end and NOT (just about) EQUAL as the arguments IS about. Who cares about or needs "pure" inductance? What for? Just to twist the argument that "gurus" were right? Gimme a break! If we can agree about pure inductive loading, we all have a firm place to stand. Then we can then put back those "other" complicating properties of a real-life loading coil, and see what difference they make. As firm as driving my Buick in the free space! Halooooo! Go measure it! See what it IS! Then if the coil IS hot at both ends, or you measure current almost equal at both ends, describe the experiment so we can verify it and we will rest our case and admit to be a bunch dummies stuck on stooooopid! (We are still talking about quarter wave resonant, loaded typical mobile antenna with loading coil about 2/3 up the 8 - 10 foot mast, no detours to la-la pure inductance in the vacuum with no resistance, free space no-nothing thing :-) And as Cecil mentioned, we are not disputing that there is no capacitance to the surroundings, or no losses through resistance and radiation amounting to SMALL (you put figure on it Richard) drop, versus more SIGNIFICANT (like 40 -60%) drop across the loading coil. I am sorry to beeing away for a zilion of posts, but real life is more important and I am trying to be in touch. I will try to find the W8JI response to my first (start from scratch) post in order to find where I went wrong, if he will engage in some technical discussion. I hate to be wrong. Happy second April foolsday! Yuri, K3BU.us [1] This principle of "conservation of charge" is also the underlying principle of Kirchhoff's current law. If you connect three ordinary wires together, the current flowing into the junction from one wire must be exactly and instantaneously balanced by the currents flowing in or out on the other two wires. If this was not so, there would have to be some means of adding, storing or losing electrons at the junction... which contradicts our initial assumption of three simple wires with no special properties. It is not strictly accurate to say that Kirchhoff's current law applies to pure inductance, but the underlying principle of "conservation of charge" does apply. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek What "other two wires"? I see RF current flowing through one wire (base) then another wire in series (coil) than another one in series (tip - whip) then "finding" the tip, aka END reflecting form it, and going back, creating standing wave with proper current AND voltage distribution according to sine (or if you like cosine) function. What about energy (power) conservation law? How can coil "make" more voltage at the top, while "having" the same current on the top as at the bottom? 73 + 88 from Yuri K3BU, jus' inquiring mind |
Current through coils
On Sun, 2 Apr 2006 16:00:16 -0400, "Yuri Blanarovich"
wrote: I am sorry to beeing away for a zilion of posts, but real life is more important and I am trying to be in touch. I will try to find the W8JI response to my first (start from scratch) post in order to find where I went wrong, if he will engage in some technical discussion. I hate to be wrong. Didn't you start a new thread to clear out the cobwebs? That seems to have gone the way of the dodo. Hi Yuri, Instead of chewing old gum over and over again, why not simply fulfill a promise offered two years ago? I hope it warms up, so I can get out, dig the car from the snow and do some experimenting. First experiment will be with 80m Hustler coil in order to use "standard" (lousy) typical coil. I will paste LCD strip thermometers on the coil to measure temperature changes at various positions, ends, middle. Experiment #1: I will drive DC current through the coil in order to generate heat and observe the temperatures across the coil. I predict that thermometers will be tracking each other very closely or be identical (ideal case). Experiment #2: I will insert the same coil in the Hustler mobile antenna, tune to resonance and fire 100W to it. I will observe temperatures between the end and center and between two ends. I expect difference indicating difference in current at various points. This will be the least disturbing measurement setup, no conductive nothing disturbing the coil or antenna. I am assuming LCD thermometer is RF transparent and I will verify that it does not detune the antenna/coil. Perhaps not very accurate, but sufficient to demonstrate the debated differences. The next measurements will be with current probes and RF ammeters. This will give more accurate values. Any problems with that? Yuri, K3BU.us No problems with that, but no results either. 73's Richard Clark, KB7QHC |
Current through coils
Yuri Blanarovich wrote:
"Ian White GM3SEK" wrote in message ... From the beginning, then: snippydidudaa As we have seen, if the whip is loaded by pure inductance only, there is no change in current between the two terminals of the inductance - but there's a big step increase in voltage. At the upper terminal, the current is the same but the voltage is very high, so we're into a much higher-impedance environment. Reality check here. I need explanation how the above could happen. "Current stays the same ... and the big step increase in voltage." As far as "idiot" professors taught me, (current x voltage) = power. So, am I to discover that the pure inductance is better than perpetual motion amplifier of power? More power coming out of the coil than going in? Eureka!!! How could I overlook that? :-) Your professor would have told you that you "overlooked" the phase shift in the voltage. The rest is just more of the same kind of name-calling. You didn't really read what I wrote, and you don't really want to hear any answers. All you really want is a shouting match. Well, tough, you don't get one. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Ian White GM3SEK wrote:
SNIPPED Your professor would have told you that you "overlooked" the phase shift in the voltage. SNIPPED Does this mean: "HERE WE GO AGAIN"? I was taught that there is a 90 degree phase shift in an inductor. But, in a loading coil there must be less than 90 degree phase shift because the top portion of the antenna still has a small, ~3 to 5 degree, phase shift required to achieve resonance. So, does the inductance have a 90 degree phase shift or an approximate 85+ degree phase shift. Voltage and current are in phase at the base and 90 degrees out of phase at the tip, at resonance, conclusion: less than 90 degree phase shift in the inductor. PLEASE EXPLAIN this physics anomaly! :-) |
Current through coils
Cecil Moore wrote:
Ian White GM3SEK wrote: Evidently I was in too much of a hurry to leave for the GMDX convention, because what I mean to write next was: "Cecil's theory does not work for this test case, " [ I definitely did type the word "not", but it accidentally disappeared from the version that was posted. ] Well there you have it, folks. Gurus don't even make typo mistakes. Some evil server removed that "not" on purpose from Ian's posting. In trying to respond to your points as clearly as possible, some parts of my previous posting went through several versions. I simply made a mistake in editing that particular sentence. I have already apologised for any confusion that might have caused. Cecil's theory does not work for this test case, because it requires that basic electrical properties like current and inductance switch into a different kind of behaviour in what he calls a "standing wave environment". RF current switches from a different kind of behavior than DC current. True, but irrelevant. You are asking for RF current to switch its behaviour while still being RF current. Phase, capacitance, inductance, and wavelength all have to be taken into account in the steady-state analysis. That is a technical fact that I'm sure you appreciate. Yes... Why is it such a stretch to recognize that standing wave current behaves differently from traveling wave current? That standing wave current is different from traveling wave current is readily apparent from the equations. In the following equations, 'K' is used for a constant, 'z' is the linear distance up and down the line, and 'w' is omega. Forward traveling wave current = K1*cos(kz+wt) Reflected traveling wave current = K2*cos(kz-wt) Standing wave current = K1*cos(kz+wt) + K2*cos(kz-wt) = K3*cos(kz)*cos(wt) If tK1 = K2, then the standing wave doesn't move. Please dust off your old math books and realize what the above equations imply at a physical level. Let's try it a different way. At any point located a distance z along the antenna, there is the normal cyclical variation in current I with TIME, so: I(t, z) = Ipk(z) cos(wt) where Ipk(z) is the peak value of the current at point z. The cos(wt) term represents the cyclical time dependence of the back-and-forth movement of electrons; it has no dependence on z. Ipk(z) is simply a scaling factor whose value depends only on the LOCATION of point z within the antenna. It has NO time dependence. The next issue to describe how Ipk varies with the location z along the wire. The aim of antenna analysis is to find out what the current distribution along the wire(s) actually is. All the rest of the antenna's properties can be calculated from this. Ipk(z) does not have to be a simple cosine function as you seem to assume above. A cosine function may be a good approximation for very simple (or simplified) cases; but when the antenna includes a physical discontinuity such as a loading coil, Ipk(z) will definitely NOT be a simple cosine function of distance z. So in general it will not be correct to bundle the z dependence into the same cosine function as (wt). There are several methods of finding the current distribution. If you choose a method based on forward, reflected and standing waves (which can be done), the "standing wave" is simply a plot of Ipk as a function of location z. Ipk(z) is a scalar quantity representing the peak magnitude of the current, and its only dependence is on LOCATION. It is not an alternating RF current because it has no time dependence. "Current" remains what it always was: simply the movement of charge (electrons). If it's an alternating RF current, the cos(wt) term describes how the charge moves cyclically forward and back past the observation point. A loading coil, the RF ammeter or the current-transformer measuring probe all respond to exactly the same cyclical back-and-forth movement of charge. In the standing wave analysis, the current is still the net movement of charge, ie the instantaneous difference between the forward and reflected currents. These vary together in time according to cos(wt). It is not possible to measure the "wrong kind" of current by mistake, because there is only one kind. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Richard Clark challenged me:
Didn't you start a new thread to clear out the cobwebs? That seems to have gone the way of the dodo. Hi Yuri, Instead of chewing old gum over and over again, why not simply fulfill a promise offered two years ago? Yea, the dodo was the contest I was trying to beat another record and then the fricken taxes came. I will dust off my whips and coils and do some 'sperimenting. But where are all the gurus? Nobody got mobile antenna and can do crude "feel the turns" 'speriment? Must be too busy with charger 'lectrons, Eh?! Yuri, K3BU |
Current through coils
"Ian White GM3SEK" wrote in message ... Yuri Blanarovich wrote: "Ian White GM3SEK" wrote in message ... From the beginning, then: snippydidudaa As we have seen, if the whip is loaded by pure inductance only, there is no change in current between the two terminals of the inductance - but there's a big step increase in voltage. At the upper terminal, the current is the same but the voltage is very high, so we're into a much higher-impedance environment. Reality check here. I need explanation how the above could happen. "Current stays the same ... and the big step increase in voltage." As far as "idiot" professors taught me, (current x voltage) = power. So, am I to discover that the pure inductance is better than perpetual motion amplifier of power? More power coming out of the coil than going in? Eureka!!! How could I overlook that? :-) Your professor would have told you that you "overlooked" the phase shift in the voltage. The rest is just more of the same kind of name-calling. You didn't really read what I wrote, and you don't really want to hear any answers. All you really want is a shouting match. Well, tough, you don't get one. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek Yep, when we try to argue the case, it ends up like this. So you know what I read, but you would not want to explain, enlighten this "dummy" what is going on, eh? Uhm, the phase shift is different for current and different for voltage, or you claim that current distribution curve would be way different from the voltage distribution curve? Can you draw the picture of current and voltage distribution in the case in question or provide the file for EZNEC or whateverNEC? Got it! Yuri, K3BU |
Current through coils
Yuri Blanarovich wrote:
"Ian White GM3SEK" wrote in message The rest is just more of the same kind of name-calling. You didn't really read what I wrote, and you don't really want to hear any answers. All you really want is a shouting match. Well, tough, you don't get one. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek Yep, when we try to argue the case, it ends up like this. So you know what I read, but you would not want to explain, enlighten this "dummy" what is going on, eh? I already told you what is going on, the best and most accurate way I know. It isn't easy, and it took some time to make it concise and clear. Your questions are based on a totally different way of looking at it, much of which I don't even accept as valid. Unfortunately that means I cannot answer them in any way that would make sense to me. Uhm, the phase shift is different for current and different for voltage, If you mean the phase differences across the coil, then this is one I can answer: yes, that is exactly what I mean. The phase difference across the coil is quite small for the current but much larger for the voltage. This is normal behaviour for inductance. When current is being pushed through an inductance into a small capacitance, it generates a high voltage across the inductance, and also a large phase shift in that voltage. That is the dominant feature when the inductance of your real-life loading coil drives current into the relatively short top section of the whip. Can you draw the picture of current and voltage distribution in the case in question or provide the file for EZNEC or whateverNEC? I did some drawings in a RadCom article - and we could certainly use a few diagrams here. It's late now and I have a tower to take down tomorrow... get back to you later. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Ian White GM3SEK wrote:
Cecil Moore wrote: RF current switches from a different kind of behavior than DC current. True, but irrelevant. You are asking for RF current to switch its behaviour while still being RF current. Standing wave RF current does not exhibit the same behavior as traveling wave RF current. If you understood the formulas, you would understand my statement. where Ipk(z) is the peak value of the current at point z. The cos(wt) term represents the cyclical time dependence of the back-and-forth movement of electrons; it has no dependence on z. Therefore, the phase of the standing wave current has no dependence on z. In fact, for a 1/2WL thin-wire dipole the phase is fixed at zero degrees no matter what is the value of z. Moral: Standing wave current phase cannot be used to measure the delay through a piece of wire, much less the delay through a coil. But that's exactly what W7EL measured. Now do you see why those measurements were meaningless? THE PHASE OF THE CURRENT IN AND AROUND A LOADING COIL HAS NO DEPENDENCE ON Z. Think about the implications of your statement. Ipk(z) is simply a scaling factor whose value depends only on the LOCATION of point z within the antenna. It has NO time dependence. There is an Ipk1(z) at the bottom of the coil. There is an Ipk2(z) at the top of the coil. Both of them have NO time dependence. Therefore, the phase shift between them CANNOT be used to determine the delay through a coil. The next issue to describe how Ipk varies with the location z along the wire. The aim of antenna analysis is to find out what the current distribution along the wire(s) actually is. All the rest of the antenna's properties can be calculated from this. Ipk(z) does not have to be a simple cosine function as you seem to assume above. I do NOT assume a simple cosine function. I have said many times that the fields of the loading coil warps the current waveform away from the simple cosine function. It puts a bump in the cosine curve but the fact remains that the current envelope magnitude contains the only phase information in the standing wave current. Above, you have essentially agreed with Gene Fuller that zero phase information exists in the standing wave current except in the magnitude. A cosine function may be a good approximation for very simple (or simplified) cases; but when the antenna includes a physical discontinuity such as a loading coil, Ipk(z) will definitely NOT be a simple cosine function of distance z. So in general it will not be correct to bundle the z dependence into the same cosine function as (wt). I suggest that the standing wave current for each segment of the antenna can be plotted as has been done at: http://www.k6mhe.com/n7ws/Loaded%20antennas.htm in figure 3 and that a cosine function can be plotted underneath that curve. Associating the bottom of the coil with one point on the cosine curve and the top of the coil with another point on the cosine curve will allow us to make a *rough* estimate of the delay through the coil. The cosine curve doesn't disappear - it is just warped by the current distribution through the coil. There are several methods of finding the current distribution. If you choose a method based on forward, reflected and standing waves (which can be done), the "standing wave" is simply a plot of Ipk as a function of location z. Ipk(z) is a scalar quantity representing the peak magnitude of the current, and its only dependence is on LOCATION. It is not an alternating RF current because it has no time dependence. Yet W7EL used that current with no time dependence to try to measure the delay through a coil. I don't recall you objecting. "Current" remains what it always was: simply the movement of charge (electrons). If it's an alternating RF current, the cos(wt) term describes how the charge moves cyclically forward and back past the observation point. A loading coil, the RF ammeter or the current-transformer measuring probe all respond to exactly the same cyclical back-and-forth movement of charge. Yes, but two RF ammeters gives us a different and more complete view of reality. In a traveling wave antenna, the two RF ammeters would read the same value. In a standing wave antenna, the values read by the two RF ammeters depend upon where they are located. In the 1WL standing wave antenna at: http://www.qsl.net/w5dxp/1WLDIP.GIF, an RF ammeter located at point B might read one amp. An identical RF ammeter located at point D will read zero amps. In the standing wave analysis, the current is still the net movement of charge, ie the instantaneous difference between the forward and reflected currents. There is no net transfer of energy in a pure standing wave. As Hecht says: "Its profile does not move through space." Nor does it move through a wire. Here's the above 1WLDIP.GIF wire replaced by a loading coil. |----1/4WL---|-1/4WL-|----------1/2WL------------| ------A------B-/////-D-------------fp------------- An RF ammeter placed at B may read one amp. An identical RF ammeter placed at D will read zero amps. How can one amp be "flowing" out of the top of the coil while zero amps is "flowing" into the bottom of the coil. That is standing wave current and it is NOT flowing. It is just standing still as explained by Hecht. These vary together in time according to cos(wt). It is not possible to measure the "wrong kind" of current by mistake, because there is only one kind. Sorry, you are wrong about that. A look at the equations while varying 'x' proves your statement is wrong. Please reference what Hecht said about those equations in another one of my postings. You have already admitted that there is more than one kind of current, e.g. DC Vs RF. It's time to admit that standing wave current and traveling wave current have different equations and therefore are different "kinds" of current. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Ian, GM3SEK wrote:
'There are several methods of finding current distribution." "I may be a fool, but I`n not the fool to be pitied because I disagreed with Terman. On page 893 of the 1955 edition of "Electronic and Radio Engineering" Terman writes: "An antenna can therefore be regarded as a resonant system with distributed constants. As a result, the impedance of an antenna behaves in much the same manner as does the impedance of a transmission line (see Sec. 4-7)." This is not news to many thread participants. Fig. 4-7 on page 96 shows an open-circuited transmission line. At the open circuit there is maximum voltage and zero current. Except for radiation and loss to heat, the typical standing-wave antenna would behave much the same as this ideal transmission line. Not only does Terman give voltage and current diagrams, he gives a phase diagram. It shows that whenever the voltage or current crosses the zero axis (changes sign) the phase angle changes abruptly by 180-degrees. Phase is unchanging between these inflection points. This agrees with what Cecil has said all along in this discussion. Best regards, Richard Harrison, KB5WZI |
Current through coils
Dave wrote:
I was taught that there is a 90 degree phase shift in an inductor. Dave, there is a phase shift between applied voltage and maximum current. That should not be confused with phase shift or phase difference in current at both ends of the inductor. , in a loading coil there must be less than 90 degree phase shift because the top portion of the antenna still has a small, ~3 to 5 degree, phase shift required to achieve resonance. So, does the inductance have a 90 degree phase shift or an approximate 85+ degree phase shift. No. What happens in an antenna is voltage and current are out-of-phase by some amount. This by definition means the antenna is reactive. The loading coil's primary function is to shift voltage in relationship to current, and compensate the relationship between voltage and current so they are back in phase. If the loading coil is physically large and has a good amount of displacement current flowing radially to space and objects around the antenna compared to through current, the coil would have a noticable difference in current at the bottom terminal and top terminal. The current also would also not be in phase when compared at each end. Voltage and current are in phase at the base and 90 degrees out of phase at the tip, at resonance, conclusion: less than 90 degree phase shift in the inductor. PLEASE EXPLAIN this physics anomaly! Again, you are comparing electrical degrees of the antenna with degrees phase shift between voltage and current in a circuit containing only a pure inductor. Degrees of antenna only deals with the length. It is a way of expressing length in terms of wavelength, with 360 degrees being a full wavelength. Degrees of phase angle in an antenna or any load is really just a comparison between voltage and current. It is not related to electrical degrees. Mixing those two very different things up is a source of great confusion. If we have a 10 degree tall antenna we really don't need an inductor that behaves like it is a 80 degree long antenna section to resonate the system, and the system is not "90-degree resonant". It is simply resonant. The antenna is 10 degrees long, and the coil is whatever it needs to be to bring voltage back in phase with current. Consider this. If I have a coil in series with a resistor and measure the input voltage as a reference point, the current at BOTH ends of the coil will lag voltage by a certain amount. If the coil has low capacitive reactance to the outside world compared to the load resistance, current at each end of the coil will be essentially equal. Phase shift in current at each end will be very low. It's only when the coil becomes physically large and has appreciable capacitive reactance to the outside world compared to the load impedance that it starts to show significant transmission line effects. Every bit of this is not difficult to understand if we really understand how an antenna behaves and how a coil behaves. The only source of wonderment and argument seems to come from people who want to make the inductor behave differently in an antenna than it behaves in other systems. It really isn't complicated at all. The very first post in this 900 plus post long thread explained it quite well, and it's been explained dozens of more times along the way. There is no reason to assign special properties to an inductor and make it behave differently in an antenna than it does in other systems. 73 Tom |
Current through coils
On Sun, 2 Apr 2006 18:34:11 -0400, "Yuri Blanarovich"
wrote: I will dust off my whips and coils and do some 'sperimenting. But where are all the gurus? Nobody got mobile antenna and can do crude "feel the turns" 'speriment? Must be too busy with charger 'lectrons, Eh?! Hi Yuri, This was YOUR self-appointed mission. If it doesn't count for much, or it has no relevancy, then say so and by all means drop it. This revisiting of old battleground cemeteries is stodgy tourism and I prefer Buenos Aires. Seeing Evita's tomb in the Recolleta is far more interesting than watching the grave robbing here. 73's Richard Clark, KB7QHC |
Current through coils
wrote:
If the loading coil is physically large and has a good amount of displacement current flowing radially to space and objects around the antenna compared to through current, the coil would have a noticable difference in current at the bottom terminal and top terminal. How does one amp at the top and zero amps at the bottom grab you? Please see my other postings. It's only when the coil becomes physically large and has appreciable capacitive reactance to the outside world compared to the load impedance that it starts to show significant transmission line effects. Which is certainly the case for a 75m bugcatcher coil. Every bit of this is not difficult to understand if we really understand how an antenna behaves and how a coil behaves. The only source of wonderment and argument seems to come from people who want to make the inductor behave differently in an antenna than it behaves in other systems. The 75m bugcatcher coil certainly behaves differently mounted one foot above a GMC pickup ground plane than it behaves in free space. The question is: which is more common? A GMC pickup or free space? There is no reason to assign special properties to an inductor and make it behave differently in an antenna than it does in other systems. There is no reason to assume an inductor behaves differently above a GMC truck ground plane than it behaves in free space??? Tom, would you please describe the free space that exists inside your head? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
Not only does Terman give voltage and current diagrams, he gives a phase diagram. It shows that whenever the voltage or current crosses the zero axis (changes sign) the phase angle changes abruptly by 180-degrees. Phase is unchanging between these inflection points. This agrees with what Cecil has said all along in this discussion. Kraus agrees. Yet W7EL used that unchanging phase to measure the delay through a loading coil. What's wrong with that picture? Some people, who no doubt have recognized their technical errors, simply refuse to discuss the technical subjects. Ian, OTOH, seems open to discussing those topics so please don't be too hard on him. An honest person deserves respect whether he is right or wrong. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Some people, who no doubt have recognized their technical errors, simply refuse to discuss the technical subjects. Ian, OTOH, seems open to discussing those topics so please don't be too hard on him. An honest person deserves respect whether he is right or wrong. In accordance with my goal of being honest, here is some ammunition for the other side of the argument. In Dr. Corum's IEEE paper he said regarding the Z0 of a loading coil: "It is worth noting that, for a helical anisotropic wave guide, the effective characteristic impedance is not merely a function of the geometrical configuration of the conductors (as it would be for lossless TEM coaxial cables and twin-lead transmission lines), but it is ALSO A FUNCTION OF THE EXCITATION FREQUENCY." I have been assuming that the Z0 of a loading coil didn't change much with frequency. Both Dr. Corum and EZNEC seem to disagree with that assumption. So, as is my practice, I am using the scientific method to adjust my concepts about that subject. I hope this proves that I am only interested in the technical facts which have not been proven one way or another as of this posting. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Richard Clark" wrote If it doesn't count for much, or it has no relevancy, then say so and by all means drop it. I think it is significant, not as much in "crummy" mobile vertical, as in antenna systems with loaded, shortened elements. I saw significant improvement in performance when replacing loading stubs in say KLM 3 el. 80m Yagi with coils. Performance and pattern improved significantly. If you stick wrong values in modeling program, the error will get only magnified. That's why this "bothers" me. I trust what W9UCW measured, and I want to do it myself, just to put the heated subject to rest with proper conclusions. Yuri |
Current through coils
Cec wrote, "How does one amp at the top and zero amps at the bottom
grab you? Please see my other postings." It grabs me that what you wrote in your other postings about capacitance to the outside world, " I didn't say there was no capacitance to the outside world. I said such is a secondary effect, not a primary effect, and for the sake of the present argument, can be ignored as secondary effects often are ignored," is all wet. And I still say that your other postings before that were saying you believed that there was NO capacitance to the outside world. It was the message they sent to me, loud and clear. Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out _for_ANY_abritrarily_short_time_period_, you have changed the net charge in that volume; if you pull out more electrons than go in, you have changed the net charge in that volume. If the current at the top and bottom, the only two conductors crossing the boundary of that volume, is different, that represents flow of charge into (and out of, in a cyclic fashion) that volume. I don't know what to call that except capacitance to the outside world. Yes, it's _distributed_ capacitance. But the key point is that it is THE reason--the WHOLE reason--for the difference in current between the top and the bottom, NOT a "secondary effect." In fact, when YOU say that the coil "behaves differently" in different external environments, you are AFFIRMING it as an important effect, for surely the presence or absence of some American gas guzzler (or is it Diesel guzzler?) strongly affects the capacitance to the outside world, and does not significantly affect internal capacitances (which in any event, being contained entirely within that volume, do NOTHING for storing net charge within the volume, because for those internal capacitances to store charge, what goes in one end comes immediately out the other end which is still inside the same volume and thus there is not any net change in charge within the volume). But the "other end" of capacitance to the gas guzzler or whatever is OUTSIDE the volume of the coil, thus EXACTLY accounting for the difference in current at the two leads going to the coil. -- I suppose they covered all that in a sophomore EE circuits class, but I wouldn't know. I suppose they also might have covered how a pure lumped model using only i(t)=C*dv(t)/dt and v(t)=L*di(t)/dt, with no time delay elements, can mimic lossless transmission line behaviour to any arbitrary degree of accuracy you want, but perhaps they don't try to hit you with that concept till later. I wouldn't know that, either...I just know it's true. I suppose it's a bit too much to ask all at once, but I do wish you could see that just because the specific value of the capacitance is different in different environments, it does not mean that I need a different model. The coil does not behave in some fundamentally different way. I only need to adjust the value of that capacitance within the model--or if you will, the parameters of the transmission-line-like behaviour, though other models may work as well in practical antenna analysis. The model stays the same; the parameters in the model change. When I change the value of a resistor, my model of a resistor doesn't change. It's still fundamentally v(t)=R*i(t). Only the value used for R changes. On a grander scale, when I include the parasitic effects of a real inductOR, I have more things to account for in the model than just inductANCE. Some of them are affected significantly by the environment in which I place the inductor. And even small changes in the values can have a profound effect on the overall system behaviour. That's especially true in a system operated near resonance where the Q is extremely high, such as a system in which there is only a standing wave. My only wish is that these musings will be useful to the lurkers trying to actually learn something, if there still happen to be any around. Cheers, Tom |
Current through coils
On Sun, 2 Apr 2006 23:24:05 -0400, "Yuri Blanarovich"
wrote: If you stick wrong values in modeling program, the error will get only magnified. That's why this "bothers" me. Hi Yuri, This is a most ambiguous "bothering" in that you haven't put any quantification to what the "error" leads to. No one can possibly expect perfection, and ±20% is possibly the best accuracy most hams can expect in measurement. We have all already identified that the "error" stemmed from an inappropriate application of lumped inductance in the place of a helix in modeling. This begs the question: "What's all the fuss over? What's to be proven? and How do we know when it has BEEN proven?" 73's Richard Clark, KB7QHC |
Current through coils
Tom, K7ITM wrote:
"Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out_for_ANY_arbitrarily_short_time_period_, you have changed the net charge in that volume;---." No. This is not charging a capacitor or a battery. Energy stored in an antenna system is in constant motion. Power delivered by the transmitter is neadly the same as that used by the load, (the antenna), plus that consumed by losses. Power is simply the in-phase volts times amps. It can have any impedance which is the ratio of in-phase volts to amps. Z in the general case can include reactance plus resistance and can give the apparent power. It is the ratio of volts to amps without regard to phase. The coil which has a great difference between the current at its ends most likely simply has different impedances at its ends. The power is nearly the same at both ends of the coil but the voltage to current ratios are different. Varying impredance along the RF path is a product of the interference between the incident and reflected waves. A standing-wave antenna typically has an open-circuit at its end or ends. The RF has no other option but to be returned toward the sender and make standing waves. The large number of possible incident and reflected wave combinatioms makes it very likely that the current at opposite ends of a coil inserted in the antenna system will be unequal. It`s the power in and out of a coil in an antenna system that`s likely to be nearly equal at both ends. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard H wrote,
"Tom, K7ITM wrote: "Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out_for_ANY_arbitrarily_short_time_period_, you have changed the net charge in that volume;---." No. ..." OK, I'm going to repeat it once mo If you shove more electrons into ANY volume than you remove, you have changed the charge within that volume. I do NOT care WHAT is in that volume. Current is the rate that charge is flowing past a point on a conductor. If the only way I have of getting charge into and out of a particular volume is through two wires, then the difference in current at every instant in time represents the time rate of change of charge within that volume. That is true INDEPENDENT of whether it is in an antenna, and it is INDEPENDENT of what's inside that volume. In fact, energy around an antenna is stored in electric and magnetic fields. These are inexorably linked to inductance along the conductors composing the antenna, and capacitance from these conductors to themselves and to any counterpoise or ground plane which may be part of the antenna--anything where electric field lines terminate. The charge per unit length along an antenna wire, be it resonant or not, be it a "standing wave" or a "travelling wave" antenna, varies with time. If it did not, then the current would necessarily be identical along the whole wire all the time. This all gets back to very basic definitions of charge, and current as the rate of flow of charge. It's all consistent with Maxwell, Gauss, Faraday, etc. and with waves both standing and travelling, and with "impredances" and all the rest. It's just amazing to me that some of you are fighting so hard against the very thing which has a chance of unifying your "wave" model with the realities of the electric and magnetic fields, and the associated capacitance and inductance along the antenna--indeed, along the wire itself, and not just along the coil. Without capacitance, there can be NO difference in current anywhere along the wire, because there is simply no place to put the charge implied by differing currents at differing locations. With capacitance and inductance, everything works just as it's supposed to--just as it DOES--and a properly developed wave theory will analyze it just fine, if that's your cup of tea. Cheers, Tom |
Current through coils
I don't understand what you are all on about, but, I side with K7ITM
"K7ITM" wrote in message Regards Mike. ups.com... Richard H wrote, "Tom, K7ITM wrote: "Given any volume, say a volume containing a Texas Bugcatcher coil and the air inside and immediately around it, if you push more electrons in than come out_for_ANY_arbitrarily_short_time_period_, you have changed the net charge in that volume;---." No. ..." OK, I'm going to repeat it once mo If you shove more electrons into ANY volume than you remove, you have changed the charge within that volume. I do NOT care WHAT is in that volume. Current is the rate that charge is flowing past a point on a conductor. If the only way I have of getting charge into and out of a particular volume is through two wires, then the difference in current at every instant in time represents the time rate of change of charge within that volume. That is true INDEPENDENT of whether it is in an antenna, and it is INDEPENDENT of what's inside that volume. In fact, energy around an antenna is stored in electric and magnetic fields. These are inexorably linked to inductance along the conductors composing the antenna, and capacitance from these conductors to themselves and to any counterpoise or ground plane which may be part of the antenna--anything where electric field lines terminate. The charge per unit length along an antenna wire, be it resonant or not, be it a "standing wave" or a "travelling wave" antenna, varies with time. If it did not, then the current would necessarily be identical along the whole wire all the time. This all gets back to very basic definitions of charge, and current as the rate of flow of charge. It's all consistent with Maxwell, Gauss, Faraday, etc. and with waves both standing and travelling, and with "impredances" and all the rest. It's just amazing to me that some of you are fighting so hard against the very thing which has a chance of unifying your "wave" model with the realities of the electric and magnetic fields, and the associated capacitance and inductance along the antenna--indeed, along the wire itself, and not just along the coil. Without capacitance, there can be NO difference in current anywhere along the wire, because there is simply no place to put the charge implied by differing currents at differing locations. With capacitance and inductance, everything works just as it's supposed to--just as it DOES--and a properly developed wave theory will analyze it just fine, if that's your cup of tea. Cheers, Tom |
Current through coils
"Richard Clark" wrote Hi Yuri, This is a most ambiguous "bothering" in that you haven't put any quantification to what the "error" leads to. No one can possibly expect perfection, and ±20% is possibly the best accuracy most hams can expect in measurement. We have all already identified that the "error" stemmed from an inappropriate application of lumped inductance in the place of a helix in modeling. This begs the question: "What's all the fuss over? What's to be proven? and How do we know when it has BEEN proven?" 73's Richard Clark, KB7QHC I think we are striving to improve our accuracy and reflection of reality in modeling antennas. We know that efficiency is proportional to the area under the current curve along the radiator. The "fatter" the curve, the better. This has been confirmed by the experimental measurements by varying position of the loading coil along the radiator and use of top hats. If the modeling program starts with wrong assumption (as we have seen using lumped inductance) and one uses multiple elements, like in vertical arrays or Yagis, then the results get skewed and we get wrong "recipe" for the antenna design. The biggest benefit would be in properly optimizing antenna design for the best rejection, F/B, cleanest pattern, which is more critical than just optimizing for max gain. Especially loaded arrays for low bands would benefit most. One could get good indication by comparing say 3 el loaded Yagi design with lumped inductance vs. loading stubs or solenoid model. Unfortunately, or fortunately, I am not retired, nor making living from the RF stuff and my time is limited to be working full time on this. My interest is to maximize the station and antenna design for contesting so I can try to cream some records. So far, it looks to me that this exercise is worthwhile if we can improve the accuracy of modeling and our understanding of the phenomena. Looks like lots of antennas would be damaged by the Midwest tornados, the ugly WX is heading our way. 73 Yuri, K3BU |
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