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Current through coils
"Gene Fuller" wrote: I did not say anything about W8JI's measurements. He had a completely different setup, and I had nothing to do with it. Didn't say you did and it's good that the two were unrelated - just wanted to point out the contradictions between your EZNEC results and W8JI's 3 nS measurements. I have uncovered a slight conceptual error in my traveling wave antenna simulation. I took care to eliminate reflections between the top of the coil and the load on the traveling wave wire. But I didn't do anything to eliminate reflections from the bottom of the coil. So the current phase at the load at the bottom of the coil is not from a traveling wave. It is instead from a standing wave or a combination of the two waves. The bottom section is one foot long. Knowing the frequency, e.g. 4 MHz, allows us to calculate the delay in that one foot of wire, i.e. 0.0041 WL = 1.5 degrees. So the current phase at the bottom of the coil is -1.5 degrees on 4 MHz. With the current phase at the top of the coil being 10.72 degrees, that gives a phase shift through the coil of 9.22 degrees which is equivalent to 6.4 nS, more than double W8JI's measured value still posted to his web page. -- 73, Cecil, W5DXP |
Current through coils
Cec, do you think that knowledge of reflected waves and phase angles
and propagation delays will enable an antenna designer to construct something that will win contests every time? ;o) I'd rather place my confidence in screwing an extra length on the top end of the loaded whip and damn the extra propagation delay. I nearly didn't post this. ---- Reg |
Current through coils
Cecil,
The numbers you quote below have no relationship to the numbers from the model I sent you. This is the third time you have "accidentally" screwed with the model. 73, Gene W4SZ Cecil Moore wrote: The bottom section is one foot long. Knowing the frequency, e.g. 4 MHz, allows us to calculate the delay in that one foot of wire, i.e. 0.0041 WL = 1.5 degrees. So the current phase at the bottom of the coil is -1.5 degrees on 4 MHz. With the current phase at the top of the coil being 10.72 degrees, that gives a phase shift through the coil of 9.22 degrees which is equivalent to 6.4 nS, more than double W8JI's measured value still posted to his web page. -- 73, Cecil, W5DXP |
Current through coils
Gene Fuller wrote:
The numbers you quote below have no relationship to the numbers from the model I sent you. This is the third time you have "accidentally" screwed with the model. It was no accident. Those numbers are from your model modified to an 8.5 ft. tall antenna. *Our original agreement was an 8 ft. tall antenna.* Your antenna was almost 50% longer, and that was a violation of the agreed upon boundary conditions. If you made it 50 feet tall the delay through the coil would be even smaller. I'll send you the modified files. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy, W7EL wrote:
"I maintain there`s no such group as "other coils", but that coils act quite differently depending on their physical sizes and the amount of coupling between turns." I wrote: "That`s how the experts say the coil in a TWT works, and is no different from other coils." All coils aren`t inside TWTs, but all coils do create inductance. Bill Orr wrote this concerning the coil in a Traveling Wave Tube: "Figure 25 is a simplified sketch of a basic helix-type TWT tube. Spaced closely around the beam is a circuit, in this case a helix of tightly wound wire, capable of propagating a slow wave. The r-f energy travels along the wire at the velocity of light, because of the helical path, the energy progresses along the length of the tube at a considerable slower veloity than is determined primarily by the pitch of the helix." Terman wrote this concerning the coil in a TWT: "The beam is shot through a long, loosely wound helix, and is collected by an electrode at anode potential as shown." Lenkurt wrote: "The RF signal travels as a surface wave around the turns of the helix, toward the collector, at about the velocity of light. The forward or axial velocity is slower, of course, because of the pitch and diameter of the helix." Orr`s example was a helix of tightly wound wire. Terman`s example was a long, loosely wound helix, and Lenkurt did not specify how tight or loosely the coil was wound. In all cases the coil retarded the signal well below the velocity of light along the axis that the electron beam traveled so that the beam could keep up with the signal along the path. The beam needs to be speeded as well as slowed for velocity modulation. Point is that group velocity does not exceed the velocity of light even in W8JI`s coil no matter how he makes it. There is no way to coerce actual energy to exceed the velocity of light. It would turn into a pumpkin or something. Also, electric current follows the course of maximum potential difference and that`s along the conductor supplying the electrons. The wave impels electrons to move in the conductor. Kraus wrote: "The helical antenna, which is discussed in this chapter, may be regarded as the connecting link between the linear antenna and the loop antenna, discussed in preceeding chapters. The helical antenna is the general form of antenna of which the linear and the loop are special cases. Thus, a helix of fixed diameter collapses to a loop as spacing approaches zero. On the other hand, a helix of fixed spacing between turns straightens out into a linear conductor as the diameter approaches zero. This thread has been about a coil loaded whip. This is a standing wave antenna. When the signal gets to the antenna tip it has no where else to go but return over the path which brought it. The coil has an incident wave impinging from the transmitter and an out-of-phase signal reflected from its tip. These two waves have the same origin so they are locked in step to make standing waves in both voltage and current. These determine the ratios of voltage to current at each point along the signal route. In this respect the coil behaves as a conductor in the antenna. It has more opposition to the signals traversing it than a straight wire but the volts and amps at each of its ends can obviously be very different. Thus, current in one end of the coil can be very different from the current at the other end of the same coil. Best Regards, Richard Harrison, KB5WZI |
Current through coils
From all that, I gather that your answer is "yes", that you do believe
that the current in a small inductor with close turn spacing (i.e., one where the fields from the turns couple well) flows around and around along the wire at near the speed of light, resulting in a delay from end to end approximately equal to the wire length divided by the speed of light. Or did I misinterpret what you said, and you don't believe this? Roy Lewallen, W7EL Richard Harrison wrote: Roy, W7EL wrote: "I maintain there`s no such group as "other coils", but that coils act quite differently depending on their physical sizes and the amount of coupling between turns." I wrote: "That`s how the experts say the coil in a TWT works, and is no different from other coils." All coils aren`t inside TWTs, but all coils do create inductance. . . . |
Current through coils
Rot, W7EL wrote:
"From all that, I gather your answer is Yes." I believe the wave is guided by the wire in its path and takes no shortcut along the axis of a coil. Best regards, Richard Harrison, KB5WZI |
Current through coils
Roy Lewallen wrote:
From all that, I gather that your answer is "yes", that you do believe that the current in a small inductor ... There's those buzz words "small inductor" again. We are talking about 75m bugcatcher coils, not "small inductors". Small inductors have a high self-resonant frequency. We are talking about large inductors operated relatively near their self-resonant frequencies. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a couple of calibrated current probes, and a dual-channel scope, will you believe the results? Or would you rather have someone else make the measurement or do it yourself? Roy Lewallen, W7EL Richard Harrison wrote: Rot, W7EL wrote: "From all that, I gather your answer is Yes." I believe the wave is guided by the wire in its path and takes no shortcut along the axis of a coil. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard Harrison wrote:
Rot, W7EL wrote: "From all that, I gather your answer is Yes." I believe the wave is guided by the wire in its path and takes no shortcut along the axis of a coil. If 100% of the flux from each and every coil physically linked 100% of each and every other coil, the current would indeed skip from one end of the coil to the other without interference. That is the basic presupposition of the lumped-circuit model. Quoting Dr. Corum: "Lumped element circuit theory assumes that there are no wave interference phenomena present, ...", i.e. no superposition of forward and reflected waves, i.e. no standing waves. Continuing the quote: "This is manifested by two phenomena: 1. The current distribution function is spatially uniform across each element. 2. The spatial phase delay between circuit extremities is zero." One has to imagine that W8JI's 2" dia x 12" length 100 uH coil links 100% of the flux in coil number 1 with coil number 100 a foot away and vice versa. That's quite an imagination but W8JI did measure a 3 nS delay, virtually instantaneous, so it must be true. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
It'll be easy enough to show that's false. If I set up a simple measurement with a piece of Air-Dux in series with a resistor, a couple of calibrated current probes, and a dual-channel scope, will you believe the results? Or would you rather have someone else make the measurement or do it yourself? You will, no doubt, chose a piece of Air-Dux so small that all the flux is linked to every coil. Instead of a small Air-Dux coil, use a 75m bugcatcher coil mounted over a ground plane and see what you get. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
To nobody in particular.
If the propagation time along a coil is equal to the time taken for the current to travel along the length of wire in the coil at the velocity of light, then, at a given frequency, if a half-wavelength of wire is wound into a coil it should become self-resonant at that frequency. But it isn't. The coil resonates at a different frequency which depends on the length and diameter of the coil as well as on the length of wire. Just make a coil, measure its resonant frequency, then measure the length of wire it contains. There will be no direct relationship between resonant frequency and length of wire. The same experiment can be carried out using pencil and paper. The resonant frequency will be directly related to wire length only when the coil is stretched out straight. And only then. ---- Reg. |
Current through coils
Roy Lewallen wrote:
It'll be easy enough to show that's false. If I set up a simple measurement with a piece of Air-Dux in series with a resistor, a couple of calibrated current probes, and a dual-channel scope, will you believe the results? Or would you rather have someone else make the measurement or do it yourself? Sorry for the double posting, but I just thought of an experiment that will settle everything. Take W8JI's 100 uH coil. Keep the spacing between coil 1 and coil 100 the same at one foot. Get rid of all the other coils leaving only coil 1 and coil 100 separated by one foot of air. Use coil 1 as the primary coil and measure the coupling from coil 1 to coil 100. If it is 100%, you will have made believers out of everyone and we can stop this silly argument. The lumped circuit theory says that all the flux in coil 1 links to coil 100 one foot away just as if they were both tightly wrapped around a toroid. So there's the challenge. Simply prove that 2" dia coils one foot apart in air transfer all the energy from one coil to the other. Piece of cake. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Sat, 1 Apr 2006 00:59:10 +0100, "Reg Edwards"
wrote: To nobody in particular. To nobody in reply. If the propagation time along a coil which has been described as a transmission line is equal to the time taken for the current to travel along the length of wire in the coil at the velocity of light, then, at a given frequency, um, yes. if a half-wavelength of wire is wound into a coil which has been described as a transmission line it should become self-resonant at that frequency. But it isn't. Maybe it is - within ±59% (after fudging the Vf) Cecil's theories allows for so many possibilities ;-) |
Current through coils
Reg Edwards wrote:
The coil resonates at a different frequency which depends on the length and diameter of the coil as well as on the length of wire. Yes, that's why inductive loading is more efficient than linear loading. The inductor has the advantage of adjacent wire flux coupling. However, the farther away in space that a particular coil is located from a reference coil, the lower the coupling. I just issued a challenge to anyone to prove that the coupling between 2" dia coils separated by one foot of air is 100%. If anyone can do that, I will admit I am wrong. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Clark wrote:
Cecil's theories allows for so many possibilities ;-) I would have loved to have invented the distributed network model, but it was proven valid and in widespread use long before I was born. But apparently, it has been forgotten in the past half-century. The results are otherwise intelligent engineers trying to use an unchanging standing wave phase to measure the phase shift through a loading coil in a standing wave antenna system, not realizing that the phase of the standing wave current cannot even be used to measure the phase shift in a piece of wire (since it is virtually unchanging). -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote: To nobody in particular. If the propagation time along a coil is equal to the time taken for the current to travel along the length of wire in the coil at the velocity of light, then, at a given frequency, if a half-wavelength of wire is wound into a coil it should become self-resonant at that frequency. But it isn't. The coil resonates at a different frequency which depends on the length and diameter of the coil as well as on the length of wire. Just make a coil, measure its resonant frequency, then measure the length of wire it contains. There will be no direct relationship between resonant frequency and length of wire. Thanks Reg, but I'm sure most people already understand that. I think those who have been following this thread and who don't understand that are beyond help. As a matter of fact if we all just go back to the very first post you made, we'll see nothing has changed from what you initially said. I'm sure the 800-post thread will continue another 800 posts. People must be bored. 73 Tom |
Current through coils
Cecil, W5DXP wrote:
"Actually, they are wondering how you are going to prove 100% coupling between coil #1 and #100 in your 100 uH coil such that the result was 1 nS delay over that one foot length." Yes. I think turn-to-turn capacitance doesn`t amount to much and won`t bypass the coil as you have 100 small capacitors in series, so their sum approaches zero. The speed of the wave is almost 984 feet per microsecond. At 75 meters (4 MHz), 1/4-wave is about 60 feet, and this corresponds to 90-degrees. The delay corresponding to the time required to establish current in the coil to induce voltage seems trivial to me. Almost instantaneous transmission between the first and last coil turns should be possible were they tightly coupled. But, I think Cecil is on to something. I`ve played with antique radios using front panel adjustment to control distance between two coils on the same axis to control their mutual impedance. You only had a couple inches of adjustment which was enough to seriously decouple the coils. 12-inch separation would surely have almost completely decoupled them. This much separation was not available as I`m sure it is unnecessary. Best regards, Richard Harrison, KB5WZI |
Current through coils
Richard Harrison wrote:
. . . Almost instantaneous transmission between the first and last coil turns should be possible were they tightly coupled. . . . Oops, wait a minute. Just a couple of hours ago you said the current would have to wind its way around each turn, following the wire from one end to the other, and that it would take nearly the wire length divided by the speed of light. Have you changed your mind about how inductors work? Roy Lewallen, W7EL |
Current through coils
Cecil Moore wrote:
Roy Lewallen wrote: It'll be easy enough to show that's false. If I set up a simple measurement with a piece of Air-Dux in series with a resistor, a couple of calibrated current probes, and a dual-channel scope, will you believe the results? Or would you rather have someone else make the measurement or do it yourself? Sorry for the double posting, but I just thought of an experiment that will settle everything. Take W8JI's 100 uH coil. Keep the spacing between coil 1 and coil 100 the same at one foot. Get rid of all the other coils leaving only coil 1 and coil 100 separated by one foot of air. Use coil 1 as the primary coil and measure the coupling from coil 1 to coil 100. If it is 100%, you will have made believers out of everyone and we can stop this silly argument. The lumped circuit theory says that all the flux in coil 1 links to coil 100 one foot away just as if they were both tightly wrapped around a toroid. So there's the challenge. Simply prove that 2" dia coils one foot apart in air transfer all the energy from one coil to the other. Piece of cake. 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. 73, Tom Donaly, KA6RUH |
Current through coils
Tom Donaly wrote:
Cecil Moore wrote: So there's the challenge. Simply prove that 2" dia coils one foot apart in air transfer all the energy from one coil to the other. Piece of cake. 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 not a straw man if someone actually believes it. We have a 2" dia. x 12" long coil. That's a length to diameter ratio of 6/1. There's no way coil 1 links all its flux to coil 100. Yet the *measured* delay through that coil was 3 nS. EZNEC says the delay through a better linked 70 uH coil is 6.22 nS. Have you noticed that the coils having instantaneous propagation times have been getting smaller and smaller and more conceptual rather than real? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote: It's not a straw man if someone actually believes it. We have a 2" dia. x 12" long coil. That's a length to diameter ratio of 6/1. There's no way coil 1 links all its flux to coil 100. Cecil sure is selective in presenting data. He alters dimensions and anything else that gets in his way. He dismisses EZNEC when it disagrees with him (he did that just a dozen or two posts ago), he uses it when it suits him. What a character! |
Current through coils
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. Cecil's theory does 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. (Away now to the GMDX Convention, so no replies till Monday.) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
On Sat, 01 Apr 2006 00:25:48 GMT, Cecil Moore
wrote: But apparently, it has been forgotten in the past half-century. Classic 5th sign of bogus science being offered. 5. The discoverer says a belief is credible because it has endured for centuries ... our ancestors possessed miraculous remedies that modern science cannot understand. Hi Tom, How could I possibly find this boring? It isn't every day that you find someone channeling Ramtha from the antediluvian 1950s to design antennas. OK, so it is a cheesy sort of K-Mart channeling. 73's Richard Clark, KB7QHC |
Current through coils
wrote:
He alters dimensions ... I don't remember the exact dimensions of your coil so you might refresh my memory. Was it 100 turns at 8 TPI? I have the same coil stock in a 50 uH version. As far as the EZNEC files go, I created them. Gene altered they away from the agreed upon length specifications. I altered them back and corrected a mistake I made in the traveling wave configuration. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Ian White GM3SEK wrote:
It's a simplification of any real-life coil - but loading by pure-and-simple lumped inductance is also a vital test case. It only tests the validity of the lumped-circuit model. It does NOT test the validity of the real world. Testing the validity of the real world is best left to metaphysicians, not engineers. 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. Whoa there, Ian. You are confusing cause and effect. If the lumped inductance fails to give correct real-world results, then it must be abandoned in favor of a more powerful model, e.g. the distributed network model. You are making my argument for me. Do you really believe a 2" dia x 12 inch coil has 100% flux linkage between coil 1 and coil 100? 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. Exactly! Choosing to think about an inductance as "lumped" does NOT change the behavior of the coil. The behavior of the coil is what it is. Choosing to think about it as "lumped" is often an over-simplification, a fantasy existing only in someone's mind. 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. The distributed network model, a superset of the lumped circuit model, is "provably incorrect" after being accepted and tested for more than a century??? By all means, please prove it incorrect. That should be very interesting - overturning a century of acceptance. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote: The distributed network model, a superset of the lumped circuit model, is "provably incorrect" after being accepted and tested for more than a century??? By all means, please prove it incorrect. That should be very interesting - overturning a century of acceptance. Ian, It seems to me Cecil now agrees the system can be modeled as a lumped components and loads and we do not need to use standing waves. At least that's what it sounds to me like what he is saying now. 73 Tom |
Current through coils
Cecil,
That's quite remarkable. You issued a "challenge" to design and report on a loading coil for 4 MHz, with a whip of 8 feet. I responded with a solution that used a whip length of 10 feet. I did not "alter" anything, and I told you exactly what I did. What came back in return? Three separate times you altered my file and reported back here that something was incorrectly designed, illegal, or just plain different. You did not acknowledge the changes you made until I complained. (EZNEC did not change the coil pitch or connect the bottom of the coil to the top of the coil.) I don't have a copy of the IEEE Dictionary, but I believe the correct descriptive word for your action is dishonesty. -73 Gene W4SZ Cecil Moore wrote: wrote: He alters dimensions ... I don't remember the exact dimensions of your coil so you might refresh my memory. Was it 100 turns at 8 TPI? I have the same coil stock in a 50 uH version. As far as the EZNEC files go, I created them. Gene altered they away from the agreed upon length specifications. I altered them back and corrected a mistake I made in the traveling wave configuration. |
Current through coils
Gene Fuller wrote:
Cecil, That's quite remarkable. You issued a "challenge" to design and report on a loading coil for 4 MHz, with a whip of 8 feet. I responded with a solution that used a whip length of 10 feet. I did not "alter" anything, and I told you exactly what I did. What came back in return? Three separate times you altered my file and reported back here that something was incorrectly designed, illegal, or just plain different. You did not acknowledge the changes you made until I complained. (EZNEC did not change the coil pitch or connect the bottom of the coil to the top of the coil.) I don't have a copy of the IEEE Dictionary, but I believe the correct descriptive word for your action is dishonesty. I wasn't complaining about Cecil altering your coil's dimensions Gene. I was complaining about him altering the coil I measured and altering the context of what I say. What you say about him altering your data is true, but I want you to know that *I'm first*. .... woops.....I'm not first! I just remembered this: http://www.w8ji.com/agreeing_measurements.htm Roy's first. You're way down the list Gene. Get back in line. 73 Tom |
Current through coils
Roy, W7EL wrote:
"Just a couple of hours ago you said the current would have to wind its way atound each turn, following the wire from one end to the other, and it would take nearly the wire length divided by the speed of light." Yes, and I`m still convinced that is the case in an air cored r-f coil that is long because the coupling between ends of the coil isn`t enough to bypass the delay of the coil. I posted speculations on bypassing the delay in the coil. Capacitance between turns is too small over the length of the coil, said to be about one loot, and about 100 turns. Tom, W8JI had said that magnetic coupling between the start and finish of the coil bypassed the time delay of following the path of the wire. Well, nothing happens instantly when voltage is applied across a coil. 90-degrees after the voltage has crossed the zero axis on its way up, the current does the same. It lags the voltage by 90-degrees. It`s the current which induces a voltage in the coil and this is delayed by the forces predicted by Lenz`s law. 90-degrees at 4 MHz equates to about the time required for a radio wave to traverse about 60 feet of thin wire. 100 turns of wire on a 2-inch form requires about 52 feet of wire. The current travels from start to finish on the coil before the current reaches its maximum in the coil and before energy could be effectively induced from one end of the coil to the other. The wave velocity is about 984 feet per microsecond. These are just musings aloud and confirm my speculation that signal progress is through conduction on the surface of the wire of the coil. Best regards, Richard Harrison, KB5WZI |
Current through coils
|
Current through coils
Heck, Cecil, I don't see Ian saying that a proper distributed model is
incorrect at all. I see him saying that YOUR model is incorrect! -- For the record, YOU and YOUR below translate to Cecil and Cecil's. YOUR model doesn't have any capacitance to the outside world, as YOU have posted and repeated till you are perhaps blue in the face. (No charge storage translates very directly to no capacitance, in case anyone could have missed that.) Because of that YOUR model has, guess what, ZERO time delay along the coil. It is ONLY through a combination of both inductance AND capacitance that you get propagation velocities equal to or less than the speed of light. NOTE that in freespace, the speed of light, c, is exactly equal to 1/sqrt(epsilon_naught * mu_naught) -- and the units of epsilon_naught (freespace permittivity) are FARADS per meter, and mu_naught (freespace permeability) are HENRIES per meter. A coil increases the henries per meter, but somehow we seem to have gotten in YOUR model to some space around the coil in which the permittivity is _zero_ so that we don't have any capacitance in YOUR model. That would be a good trick, but it's not one that Ian and I are buying. I suppose that W8JI and Tom D and Roy and Wes and Reg and Gene and John P and probably the two Richards and some others are ALSO not buying. Why, even the detailed Tesla coil calculations I've seen consider the distributed capacitance to the outside world, in great detail. I'd bet that the authors of those calculations would ALSO not buy your model. Putting it another way, propagation of an EM wave requires an interchange of energy between electric and magnetic fields. With zero permittivity, there would be no energy stored in the electric field, and no EM wave. (In a TEM transmission line, it's often said that the energy is stored in capacitance and inductance along the line, but that's no different than saying the energy is stored in electric and magnetic fields.) It amazes me that you fought so hard for a distributed model in which that capacitance to the outside world is missing, but insist that the resulting model allows a non-zero time delay. That's YOUR model; it's all in the stuff YOU have posted for anyone that wants to go look at it. By denying the capacitance in the model, YOU are the one who doesn't accept what's been know since Maxwell and Faraday and Tesla and... But YOUR model isn't any use to me, and it seems that it's no use to Ian. We'd prefer a model that actually accounts for all the currents correctly, and actually allows for a delay along a transmission-line structure. Then, knowing it's an ACCURATE model when we can verify through specific measurements that it agrees to an acceptable level with those cases we measured, we can look at ways to use that model as-is, or to use a model which makes life easier for us which matches the very accurate one closely enough for our purposes. (Not only does YOUR model with no capacitance to the outside world have zero propagation delay, but it ALSO leads to a line with infinite impedance, which I'm ALSO not buying, though with zero delay, the line impedance really doesn't matter. Also notice that with no capacitance to the outside world in that area, the model collapses to exactly the one YOU are arguing AGAINST, except that the straight sections of antenna are apparently not in the zero-permittivity area, so we need to keep them separated...it leads to a very strange model, indeed!) And please note that in the paragraphs above, the only models specifically mentioned are DISTRIBUTED ones, so don't go giving me any bull**** about the other kind. And you can save any bull**** about accepting the fact of capacitance to the outside world, because your postings repeatedly say otherwise. |
Current through coils
wrote:
It seems to me Cecil now agrees the system can be modeled as a lumped components and loads and we do not need to use standing waves. A 100% false statement but we are accustomed to such from W8JI. Since the lumped circuit model is a subset of the distributed network model, if there is any disagreement between the two models, the distributed network model wins every time. They are both right under certain conditions and the lumped circuit model is wrong under certain conditions. Quoting from: http://www.ttr.com/corum/index.htm "There are no standing waves [allowed] on a lumped element circuit component. ... for coils whose WIRE LENGTH exceeds 1/6WL", the distributed network model is required. Quoting from: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf Concerning the *impedance only* of a loading coil: "The formula will NOT (and, being lumped, can not) give the voltage magnification by VSWR dur to physically true current standing waves on the structure ... If impedance is the only item of interest, the empirical Medhurst approximation is acceptable out to about 60 degrees." But we haven't been arguing about impedance. We have been arguing about phase. Here's what the above paper says about phase shift through a loading coil. "Further, the voltage distribution passes from the loop of a sinusoid (at 90 degrees) to the linear portion of the sinusoid (for heights less than 15 degrees)." It is necessary to use the distributed network model if the phase shift through the coil is greater than 15 degrees. Continuing the quote: "Lumped elements 'have no physical dimensions and no preferred orientation in space; they can be moved around and rotated at will.' Not so for real world coils. ... The concept of coil 'self capacitance' is an attempt to circumvent transmission line effects on small coils when the current distributions begins to depart from its DC behavior." -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
You issued a "challenge" to design and report on a loading coil for 4 MHz, with a whip of 8 feet. I responded with a solution that used a whip length of 10 feet. No, you didn't! You responded with a antenna length of 11.775 feet, 3.775 feet longer than the agreed upon 8 foot antenna. It wasn't the whip that was to be 8 feet, it was the entire antenna. I made that perfectly clear early on so it would match the mobile antennas in the ARRL Antenna Handbook. You did not acknowledge the changes you made until I complained. Of course I did. Go back and read my postings about such. It wasn't until you complained that I sent you the corrected EZNEC files. I made a severe blunder in the traveling wave model and you copied my blunder. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
I was complaining about him altering the coil I measured and altering the context of what I say. I was doing it from memory, Tom, which may be faulty. As I remember, you coil was 2" dia and 100 turns at 8 TPI. If that's not right, what was it? http://www.w8ji.com/agreeing_measurements.htm Roy's first. You're way down the list Gene. Get back in line. Telling Roy about his abortive use of standing wave current phase to try to measure phase shift when there is zero phase shift in a wire or in a coil is just stating the technical facts. As far as measuring phase through a coil goes, neither you nor W7EL has any clue as to how to make valid measurements. You guys really need to listen to Gene Fuller who said: Regarding the cos(kz)*cos(wt) term in a standing wave: Gene Fuller, W4SZ wrote: In a standing wave antenna problem, such as the one you describe, there is no remaining phase information. Any specific phase characteristics of the traveling waves died out when the startup transients died out. Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. The so-called "phase reversal" in longer antennas is not really about phase either. It is merely a representation of the periodic sign reversal seen in a cosine function. What is it about Gene's posting that you and W7EL don't understand? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
100 turns of wire on a 2-inch form requires about 52 feet of wire. 52 feet of wire on 4 MHz is 0.21 WL. Dr. Corum says anything over 0.17 WL requires the distributed network model. The 3 nS delay measured by W8JI through that coil is simply technically impossible except in his mind. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Clark wrote:
"The apparent capacitance based on reported resonances and modeled reactance is on the order of 12 -14 pF." Have you calculated the self-capacitance of a 2in x 12in single-layer coil for yourself? The length to diameter ratio is 6. H = .92 D = 5 cm HD = 4.6 pF by the formula on page 451 of the "Radiotron Designer`s Handbook". Course, formulas are a dime a dozen and disputed. Best regards, Richard Harrison, KB5WZI |
Current through coils
Why, yes, in fact it is true that I don't agree in every case with the
unknown guru you've placed on a pedestal above all reproach. So there. It is also true that I do not agree with your (mis)interpretation of what your unknown guru has written. I REGULARLY model transmission lines as "lumped elements" and do NOT "presuppose that the speed of light" through them is infinite. 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 REGULARLY model analog to digital converters as "lumped elements" and do NOT presuppose that the result comes out at the same time as the signal that goes in. I REGULARLY model inductors as "lumped elements", and do not presuppose that they have no resistances and capacitances parasitic to their inductANCE. 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. By the way, what's EE203? It's very likely that I missed not only that day but all such days. You yourself may well be presupposing something that isn't true. Cheers, Tom |
Current through coils
K7ITM wrote:
YOUR model doesn't have any capacitance to the outside world, as YOU have posted and repeated till you are perhaps blue in the face. (No charge storage translates very directly to no capacitance, in case anyone could have missed that.) I do wish you guys would argue in good faith. ***STRAWMAN ALERT*** 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. Because of that YOUR model has, guess what, ZERO time delay along the coil. No, transmission lines have negligible capacitance to the outside world and their time delays are NOT zero. You straw man is just not believable. It is ONLY through a combination of both inductance AND capacitance that you get propagation velocities equal to or less than the speed of light. Yes, and that capacitance can be either internal or external. I'm ignoring the rest of your posting because it is based on the false premises of your straw man. But you get an 'A' in Obfuscation 101. It amazes me that you fought so hard for a distributed model in which that capacitance to the outside world is missing, ... It is *NOT* missing. That is just your straw man. It is just secondary to the addition of the forward and reflected current phasors. At a point where the the forward and reflected current phasors add up to zero, it's hard for anything else to contribute much of an effect. -- 73, Cecil http://www.qsl.net/w5dxp |
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