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Current through coils
Roy Lewallen wrote:
-- we get exactly the same result either way because superposition holds. Thinking that the result is the same and that nothing gets lost during superpositon is a misconception. Consider the following. PSK modem A--------------------------------------PSK modem B When a single signal flows from A to B, perfect information transfer occurs. When a single signal flows from B to A, perfect information transfer occurs. Now superpose the two information streams. ZERO information transfer occurs. Superposition is not magic and the result is not the same. The superposition of forward and reflected currents cause 100% loss of phase information in the standing wave current phase measurement. It is analogous to the problem above. A standing wave current cannot be used to determine the delay through a coil. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Sun, 19 Mar 2006 12:41:43 GMT, Cecil Moore
wrote: Owen Duffy wrote: Cecil Moore wrote: Please see http://www.qsl.net/w5dxp/current.htm I refer to the diagram in the section entitled "What EZNEC Says About Current Distribution Using Inductive Loading Stubs" You use the diagram to assert that there is "not a lot of difference between inductive loading stubs and loading coils" by comparing the current distribution with another case. You show graphically the current on each side of the stub. You do not show the current in each wire of the stub or the sum of the currents in the stub. The currents in stubs cannot be displayed very well at full size in EZNEC just as the currents in coils cannot be displayed very well. Maybe an enlarged view would show it. I will try to do that. Or even words that explain that the diagram is incomplete, that there are currents flowing in the stub wires, and that they don't balance each other so they participate in the antenna's total current moment. The currents in the stubs is an explanation for the difference in the currents in the main radiator at each side of the stub connection. Is it fair to say that though the diagram may resemble the first diagram on the page, to some extent, the reason they are similar is that the second one is incomplete. EZNEC calculates the currents in each wire of the stub? Aren't those currents a relevant detail that you have omitted from the diagram. Remember the present discussion is about the ability to use standing wave current phase to measure the electrical length of a wire or a coil. I have run the currents that you mention. The phase of the current is almost constant through the stubs. The phase of the current is almost constant through the coils. Would you like to see a list of the current at points through the stub Vs the current at points through the coil? No thanks, I didn't ask the question without creating a model and inspecting the currents. The phase of the currents is only one dimension. Though the phase of the current in adjacent segments in all wires (including the stubs) is commonly similar (except where a phase reversal occurs), in general, the magnitude and phase of paired stub segments that effectively form a transmission line section are not equal in magnitude and phase. My point is really about whether the subject diagram supports your argument, especially if it is incomplete and if it misrepresents the scenario. Owen -- |
Current through coils
wrote This long painful thread (it's been going on years now) started because K3BU claimed a loading inductor had most of the current in the first few turns. I am back after loooong absence here and see more misinformation coming from Tom, W8JI. I claimed that current in the antenna coil is NOT CONSTANT (or near) as he claimed. The case was of electrical quarter wave vertical radiator (as loaded mobile antenna) and that the current is distributed, varying across the coil as I have experienced, W9UCW has measured and Cecil has explained. The refresher is at http://www.k3bu.us/loadingcoils.htm The thread is "painful" because some people try to subvert the reality and keep clinging to wrong "reality" and some try to set the record straight.. This misinformation keeps being perpetuated in literature and it even crept into the latest ON4UN 4th edition of Low Band DXing (see page 9-33). The significance of properly realizing the current distribution in the loading coil is in how the modeling programs treat the phenomena and major screw-up will show up in multi element loaded antenna systems, where error will multiply and give false results. There are few more statements slightly out of true on W8JI pages, but would have to be left for later time. I apologize for being away from this NG, my AOL provider dumped NG and I am slowly dumping AOL and will migrate to optonline.net and back to NG. Also business and other QRM keeps me away, but I hope is that "tings" will improve. 73 to all Yuri, K3BU www.K3BU.us www.TeslaRadio.org |
Current through coils
Cecil Moore wrote:
Roy Lewallen wrote: -- we get exactly the same result either way because superposition holds. Thinking that the result is the same and that nothing gets lost during superpositon is a misconception. Consider the following. PSK modem A--------------------------------------PSK modem B When a single signal flows from A to B, perfect information transfer occurs. When a single signal flows from B to A, perfect information transfer occurs. Now superpose the two information streams. ZERO information transfer occurs. Superposition is not magic and the result is not the same. The superposition of forward and reflected currents cause 100% loss of phase information in the standing wave current phase measurement. It is analogous to the problem above. A standing wave current cannot be used to determine the delay through a coil. Cecil, that's the worst analogy I've ever read in my life. 73, Tom Donaly, KA6RUH |
Current through coils
Yuri Blanarovich wrote:
wrote This long painful thread (it's been going on years now) started because K3BU claimed a loading inductor had most of the current in the first few turns. I am back after loooong absence here and see more misinformation coming from Tom, W8JI. I claimed that current in the antenna coil is NOT CONSTANT (or near) as he claimed. The case was of electrical quarter wave vertical radiator (as loaded mobile antenna) and that the current is distributed, varying across the coil as I have experienced, W9UCW has measured and Cecil has explained. Yuri, Why don't you explain in a few words how you think the loading coil works? Also, why do you think a mobile antenna is "90 degrees long" when it has a loading coil? The loading coil, if well-designed and of compact size, doesn't have to have any significant current taper. The exception would be if the antenna above the coil has small capacitance compared to distributed capacitance from the coil to space or to ground. Do you still disagree with this? 73 Tom |
Current through coils
Owen Duffy wrote:
The currents in the stubs is an explanation for the difference in the currents in the main radiator at each side of the stub connection. Just as are the currents in the coils. Is it fair to say that though the diagram may resemble the first diagram on the page, to some extent, the reason they are similar is that the second one is incomplete. I sent you a .gif file giving you the full perspective. My point is really about whether the subject diagram supports your argument, especially if it is incomplete and if it misrepresents the scenario. The phase shift through the stub is the same as through the coil is the same as through the wire. It is simply zero according to the standing wave current phase which is incapable of measuring phase. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Yuri Blanarovich wrote:
I claimed that current in the antenna coil is NOT CONSTANT (or near) as he claimed. Only one out of a dozen tests run by W8JI and W7EL showed the currents to be equal. All the other tests showed the currents to be *unequal*. The significance of properly realizing the current distribution in the loading coil is in how the modeling programs treat the phenomena and major screw-up will show up in multi element loaded antenna systems, where error will multiply and give false results. The helix option in EZNEC supports the notion that the currents are hardly ever equal. If a coil is installed at a standing wave current maximum or minimum the currents can be equal. If the coil is installed at a point where the slope of the current is maximum, the difference in the currents at each end will be maximum. That's pretty simple physics. The currents at each end of a coil in a standing wave environment depends upon where it is installed. I provided an example where the current "into" the bottom of the coil was 0.17 amps and the current "out of" the top of the coil was 2.0 amps. W8JI said the lumped-circuit inductance could explain that so I asked him to explain it to all of us. So far, no response. Wonder how a model that assumes faster than light propagation of waves and absolutely equal current magnitude and phase is going to explain a 1.8 amp difference and a phase shift of 180 degrees? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Tom Donaly wrote:
Cecil, that's the worst analogy I've ever read in my life. The PSK signals lose phase when they are superposed. The forward and reflected currents lose phase when they are superposed. Looks like a perfect analogy to me. Do you disagree with Gene Fuller? 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. Do you disagree with Gene? How can Tom and Roy possibly use a signal whose phase cannot be recovered to measure phase? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Owen Duffy wrote: The currents in the stubs is an explanation for the difference in the currents in the main radiator at each side of the stub connection. Just as are the currents in the coils. Is it fair to say that though the diagram may resemble the first diagram on the page, to some extent, the reason they are similar is that the second one is incomplete. I sent you a .gif file giving you the full perspective. My point is really about whether the subject diagram supports your argument, especially if it is incomplete and if it misrepresents the scenario. The phase shift through the stub is the same as through the coil is the same as through the wire. It is simply zero according to the standing wave current phase which is incapable of measuring phase. For anyone who is foolish enough to believe Cecil when he says that all phase information is lost when two oppositely traveling waves create a standing wave, consider the following, adapted from Georg Joos book _Theoretical Physics_: consider two traveling waves going in opposite directions represented mathematically by Ae^i(wt-kx) + Ae^i(wt+kx+d) where A is the same amplitude for both waves, i is the square root of -1, k is 2*pi/wavelength, w is the radian frequency, t is time, x is distance, and d is the phase difference between the two waves. This is just another way of writing 2Acos(kx+d/2)(e^i(wt+d/2). Notice that the part cos(kx+d/2) still contains the phase information? If Cecil were any kind of experimentalist he could easily tease the phase information out of any standing wave on his antenna system. 73, Tom Donaly, KA6RUH |
Current through coils
Roy wrote, "... That is, the coil is capacitively coupled to ground,
and this causes displacement current from the coil to ground." In fact, if there were no such current -- if there were no capacitance from the coil to the world outside the coil -- then the time delay through the coil, calculated from tau = sqrt(L*C), would be zero. It is exactly this current that allows there to be a transmission-line behaviour and a corresponding time delay. That's not to say, however, that a physically very small loading coil with practically no capacitance to ground would not work as a loading coil. It just wouldn't have a transmission line behaviour worth mentioning. It is also exactly this displacement current from a large coil that allows the current at one end of the coil to be substantially different from the current at the other end. Cheers, Tom |
Current through coils
Cecil Moore wrote:
Tom Donaly wrote: Cecil, that's the worst analogy I've ever read in my life. The PSK signals lose phase when they are superposed. The forward and reflected currents lose phase when they are superposed. Looks like a perfect analogy to me. Do you disagree with Gene Fuller? 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. Do you disagree with Gene? How can Tom and Roy possibly use a signal whose phase cannot be recovered to measure phase? But Cecil, it can be recovered. See my earlier remarks. 73, Tom Donaly, KA6RUH |
Current through coils
Tom Donaly wrote:
This is just another way of writing 2Acos(kx+d/2)(e^i(wt+d/2). Notice that the part cos(kx+d/2) still contains the phase information? If Cecil were any kind of experimentalist he could easily tease the phase information out of any standing wave on his antenna system. I have previously teased that information from that equation. Perhaps you forgot. It's how to determine the exact phase shift along a thin-wire 1/2WL dipole. I showed how to do that days/weeks/years ago. It's the *phase* of the standing wave current that does not yield any phase information. I have been very careful with that caveat in my statements. cos(kx+d/2) indeed does still contain the phase information. If you will re-read my postings, you will see that I said the *PHASE* term of the reflected current doesn't contain any phase information. FYI, that's the e^i(wt+d/2) term and that part is what Roy used to make his phase measurements which has been my objection for years. It's all archived on Google. It is I, not Roy or Tom, who used the phase information in cos(kx+d/2) to determine phase. When the term containing the phase information is actually used, the delay through the coil is shown to be in the tens of degrees. In the 1/2WL thin-wire dipole, the phase shift between two points is arc-cos(amplitude1) - arc-cos(amplitude2). The only phase information is, as you and Gene Fuller rightly assert, in the amplitude of the standing wave current, NOT in the phase of the standing wave current that Roy measured. If the e^i(wt+d/2) term is used, as Roy and Tom have done, it suffers from the absence of any phase information at all. Gene Fuller said it all days ago: 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. i.e. there's no remaining phase information in e^i(wt+d/2) term. The only "phase" remaining is the cos (kz) term, which is really an amplitude description, not a phase. i.e. there is phase information in the cos(k+d/2) term, but that's not the part of the wave that Roy and Tom were using to determine delay through the coil. I have been hoping someone would jump in who understood the math. To summarize: cos(kx+d/2) is proportional to the *amplitude* of the standing wave current. When I used the amplitude of the standing wave current to estimate the phase, the gurus objected. e^i(wt+d/2) is proportional to the phase of the standing wave current and, ironically contains no phase information, just as Gene asserted. Yet, this is what Roy chose to measure in trying to determine the phase shift through a coil and that's the entire problem with his measurements. He was expecting to measure zero phase shift and he did because there was no phase shift information available from his measurement of the e^i(wt+d/2) term. I told Roy a long time ago, in general, how to calculate the phase shift from the cos(kx+d/2 amplitude term but he replied with "gobbledygook" or some such. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
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Current through coils
K7ITM wrote:
In fact, if there were no such current -- if there were no capacitance from the coil to the world outside the coil -- then the time delay through the coil, calculated from tau = sqrt(L*C), would be zero. It is exactly this current that allows there to be a transmission-line behaviour and a corresponding time delay. Tom, have you read what Dr. Corum had to say about that on page 8 of http://www.ttr.com/corum/index.htm? Here's a partial quote: "The problem has been that many experimenters working self-resonant helices have pursued the concept of coil self- capacitance without really understanding where the notion comes from or why it was ever invoked by engineers." -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
I think what everyone has forgotten is a large amount of current taper in a loading coil of a short monopole, while possible, is a good indicator of a very poor antenna design. While zero current taper in a loading coil is a good indicator of a confused engineer, unless of course, there's a current maximum inside the coil or a very large top hat. The current taper depends upon where the coil is installed in the standing wave antenna system. Some positions can result in current flowing into both ends of the coil at the same time, just like a transmission line. But the delay through an HF loading coil is *NEVER* 3 nS. Say Tom, you were going to explain to us how the lumped-circuit inductor theory handles a coil with 0.17 amps at zero degrees at the bottom of the coil and 2.0 amps at 180 degrees at the top. We are still waiting. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Tom Donaly wrote:
But Cecil, it can be recovered. See my earlier remarks. Yes, it can be recovered and I showed how years ago. Roy and Tom rejected that approach and instead reverted to measuring the phase of the standing wave current which is known to contain zero phase information. Go figure. Seriously, I showed those two how to calculate the phase shift in a 1/2WL thin-wire dipole using an arc-cos function. They responded with a personal attack. It's all on Google. If you will check my past postings on Google, you will find me saying, if the current at the base of the coil is one amp, we can estimate the phase shift through the coil by arc-cos(It) where It is the current out of the top of the coil. That is admittedly a very rough estimate since the coil distorts the current away from a perfect cosine envelope but it is closer than measuring the phase of a signal whose phase is known to be unchanging. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
I've been trying to tell Yuri (and others) that for three years now. 73 Tom Tom. You tell that to the RF ammeters installed on the vertical, W9UCW's pictures on my page! You can mumbo-jumbo all the theory, you can dream of, but reality shows that in the say, quarter wave vertical, with loading coil the current at both ends of the coil is different. Cecil explained the various situation depending where the coil is placed within the radiator and at overall antenna curve. Try this test, no meters necessary (perhaps the aquarium strip thermometer): Take your 80m Hustler antenna with Hustler loading coil and whip. At the resonant frequency put about 600 Watts to it for a while. Stop transmitting and go feel (or read the temperature on the strips) the coil, bottom end and the top end. Same temperature? Temperature is proportional to the current flow (same diameter wire) - warmer end - more current. Then test two: Keep the RF flowing until heat shrink tubing on the coil starts melting. Where does it melt first? Bottom of the coil or nicely uniformly as you claim it should? Then answer Cecil question about his demonstration of different currents at the ends! The rest is on my web page as I mentioned, with pictures. 73 Yuri, www.K3BU.us |
Current through coils
Tom Donaly wrote:
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. I think that if Gene believes that, he should redo his math. Tom, the math equations that you posted supports Gene's assertions 100%. They are essentially identical to the same equations that Gene posted. Many thanks to both of you guys for posting the technical facts. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
K7ITM wrote:
Roy wrote, "... That is, the coil is capacitively coupled to ground, and this causes displacement current from the coil to ground." In fact, if there were no such current -- if there were no capacitance from the coil to the world outside the coil -- then the time delay through the coil, calculated from tau = sqrt(L*C), would be zero. It is exactly this current that allows there to be a transmission-line behaviour and a corresponding time delay. Yes. And this, not the C across the coil, is what should be used for transmission line formulas when treating an inductor as a transmission line. When the ground was removed and replaced by a wire, the transmission line properties of the coil changed dramatically, while the C across the coil didn't change significantly. That's not to say, however, that a physically very small loading coil with practically no capacitance to ground would not work as a loading coil. It just wouldn't have a transmission line behaviour worth mentioning. It is also exactly this displacement current from a large coil that allows the current at one end of the coil to be substantially different from the current at the other end. Yes again, with one slight modification. You'll note from the EZNEC models that the current actually increases some as you go up from the bottom of the inductor. This is the effect noted by King which is due to imperfect coupling between turns. It results in currents at both ends being less than at the center. A transmission line can be represented by a series of L networks with series L and shunt C. You can achieve any desired accuracy by breaking the total L and C into enough L network sections. The requirement for validity is that the length of line represented by each section must be very small relative to a wavelength. For the example coil, a single section is entirely adequate at the 5.89 MHz frequency of analysis. However, at some higher frequency this model won't be adequate, and either more L sections or a distributed model is necessary. If the reasons for this aren't obvious, many texts cover it quite well. No special "traveling wave" analysis is required. I spent several years of my career designing very high speed TDR and sampling circuits, which involved a great deal of modeling. At the tens of GHz equivalent bandwidths of the circuitry, even very small structures such as chip capacitors and short connecting runs often had to be treated as transmission lines. One of the skills important to building an accurate model which would run in a reasonable amount of time, particularly on the much slower machines being used in the earlier part of that period, is determining when a lumped L, pi, or tee model is adequate and when a full-blown transmission line model has to be used(*). My models were used in the development of quite a number of circuits that were successfully produced in large numbers. (*) One of the characteristics of the SPICE programs at the time was that the time step was never longer than the delay of the shortest transmission line in the model. So if you willy-nilly modeled everything as a transmission line, you'd end up with an excruciatingly short time step and consequently unnecessarily long calculation time. Roy Lewallen, W7EL |
Current through coils
Cecil Moore wrote: K7ITM wrote: In fact, if there were no such current -- if there were no capacitance from the coil to the world outside the coil -- then the time delay through the coil, calculated from tau = sqrt(L*C), would be zero. It is exactly this current that allows there to be a transmission-line behaviour and a corresponding time delay. Tom, have you read what Dr. Corum had to say about that on page 8 of http://www.ttr.com/corum/index.htm? Here's a partial quote: "The problem has been that many experimenters working self-resonant helices have pursued the concept of coil self- capacitance without really understanding where the notion comes from or why it was ever invoked by engineers." Cecil, You keep trying to drag something from a self-resonant helice into a loading coil discussion. The two are nearly at opposite extremes in behavior, but even at that the self-resonant helice can be analyzed with standar L/C analysis. It's just another way to analyze things, and it's just one way of doing it. 73 Tom |
Current through coils
Yuri Blanarovich wrote: Tom. You tell that to the RF ammeters installed on the vertical, W9UCW's pictures on my page! 1.) I can build an antenna that has greatly uneven currents at the ends of the loading coil, but the antenna rea above the inductor is wasted and the system will be less efficient than a properly designed system. 2.) The meters are large and have a good deal of self-capacitance compared to the capacitance at the point where they are connected, and are directly connected to the antenna. Bad idea to base a whole concept of how an antenna works on something like that. You can mumbo-jumbo all the theory, you can dream of, but reality shows that in the say, quarter wave vertical, with loading coil the current at both ends of the coil is different. It can be different, but in a well designed system it is essentially the same. The only difference is caused by displacement currents, and that is a result of stray capacitance. Wind a good coil that has low self-C to the outside world compared to the antenna hanging above the coil, and the problem of large uneven current goes away. Cecil explained the various situation depending where the coil is placed within the radiator and at overall antenna curve. I doubt that. If he explained it in those terms he was missing some important points. Try this test, no meters necessary (perhaps the aquarium strip thermometer): Take your 80m Hustler antenna with Hustler loading coil and whip. At the resonant frequency put about 600 Watts to it for a while. Stop transmitting and go feel (or read the temperature on the strips) the coil, bottom end and the top end. Same temperature? Temperature is proportional to the current flow (same diameter wire) - warmer end - more current. Are you saying thermal effects have no bearing? It's getting pretty dangerous to write a theory based only on a Hustler mobile coil with almost no stinger above the coil. One of the reasons the Hustler works so poorly is the distributed capacitance in the coil is large compared to the tiny stinger above the coil. The Hustler has narrow bandwidth and poor efficiency because of the coil design. Then test two: Keep the RF flowing until heat shrink tubing on the coil starts melting. Where does it melt first? Bottom of the coil or nicely uniformly as you claim it should? I never claimed uniformly in ALL coils. I set boundaries as to the conditions. I can replace that Hustler coil with another coil and ruin your theory about standing waves and missing antenna degrees. 73 Tom |
Current through coils
wrote in message oups.com... Yuri Blanarovich wrote: Tom. You tell that to the RF ammeters installed on the vertical, W9UCW's pictures on my page! 1.) I can build an antenna that has greatly uneven currents at the ends of the loading coil, but the antenna rea above the inductor is wasted and the system will be less efficient than a properly designed system. 2.) The meters are large and have a good deal of self-capacitance compared to the capacitance at the point where they are connected, and are directly connected to the antenna. Bad idea to base a whole concept of how an antenna works on something like that. You can mumbo-jumbo all the theory, you can dream of, but reality shows that in the say, quarter wave vertical, with loading coil the current at both ends of the coil is different. It can be different, but in a well designed system it is essentially the same. The only difference is caused by displacement currents, and that is a result of stray capacitance. Wind a good coil that has low self-C to the outside world compared to the antenna hanging above the coil, and the problem of large uneven current goes away. Cecil explained the various situation depending where the coil is placed within the radiator and at overall antenna curve. I doubt that. If he explained it in those terms he was missing some important points. Try this test, no meters necessary (perhaps the aquarium strip thermometer): Take your 80m Hustler antenna with Hustler loading coil and whip. At the resonant frequency put about 600 Watts to it for a while. Stop transmitting and go feel (or read the temperature on the strips) the coil, bottom end and the top end. Same temperature? Temperature is proportional to the current flow (same diameter wire) - warmer end - more current. Are you saying thermal effects have no bearing? It's getting pretty dangerous to write a theory based only on a Hustler mobile coil with almost no stinger above the coil. One of the reasons the Hustler works so poorly is the distributed capacitance in the coil is large compared to the tiny stinger above the coil. The Hustler has narrow bandwidth and poor efficiency because of the coil design. Then test two: Keep the RF flowing until heat shrink tubing on the coil starts melting. Where does it melt first? Bottom of the coil or nicely uniformly as you claim it should? I never claimed uniformly in ALL coils. I set boundaries as to the conditions. I can replace that Hustler coil with another coil and ruin your theory about standing waves and missing antenna degrees. 73 Tom Yea Tom, it all started with ALL coils, it is MY theory and you can ruin MY theory. Riiiight! It's getting pathetic. Yea, meters are too big, Hustler is crapy, Cecil is wrong, and you never claimed uniformly in all coils, just those that you have. Reality is wrong, your "theory" is right! Rrrrright!!! But what a coincidence that what W9UCW measured, jives with what Cecil calculated. Hmmm! ANSWER Cecil's question about his modeled example. I guess when someone is stuck on something and dunt gitit, its tough! I am just waiting how you will come around, dancing around in mumbo-jumbo circles and then will become guru on how current IS different in the loading coils. Happened in the past, will happen again. You are WRONG, reality proves it, regardless of your detours. BTW, what engineering degree, from what university do you have or PE that gives you right to put labels like "JI Engineering" on your products? bada BUm |
Current through coils
Correction:
Roy Lewallen wrote: K7ITM wrote: . . . It is also exactly this displacement current from a large coil that allows the current at one end of the coil to be substantially different from the current at the other end. [I wrote:] Yes again, with one slight modification. You'll note from the EZNEC models that the current actually increases some as you go up from the bottom of the inductor. This is the effect noted by King which is due to imperfect coupling between turns. It results in currents at both ends being less than at the center. Tom's statement doesn't need modification, it's correct as written. Imperfect coupling between turns causes current which is different at the ends than in the middle. Tom said, correctly, that displacement current is the cause of the currents at the ends being different from each other. Roy Lewallen, W7EL |
Current through coils
Tom, W8JI wrote:
"What you are missing is the flux inside the coil links all the turns at light speed. When it does that, current appears at nearly the same instant of time (light speed over the spatial distance of the inductor) in all areas that are linked by flux." Are any famous authors protagonists of that theory? One author, Bill Orr, W6SAI writes in the 22nd edition of "Radio Handbook" on page 5.11: "Spaced closely around the beam (in a TWT) 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 but, because of the helical path, the energy progresses along the length of the tube at a considerably lower velocity that is determined by the pitch of the helix. Maybe Varian has a paper on this (just my speculation). Best regards, Richard Harrison, KB5WZI |
Current through coils
Yuri Blanarovich wrote: Yea Tom, it all started with ALL coils, it is MY theory and you can ruin MY theory. What is your theory Yuri? You didn't explain it. 73 Tom |
Current through coils
Roy Lewallen wrote:
When the ground was removed and replaced by a wire, the transmission line properties of the coil changed dramatically, while the C across the coil didn't change significantly. Moral: The self-resonant frequency of a loading-coil needs to be measured in the mobile antenna system, no on the bench. Yes again, with one slight modification. You'll note from the EZNEC models that the current actually increases some as you go up from the bottom of the inductor. This is the effect noted by King which is due to imperfect coupling between turns. It results in currents at both ends being less than at the center. It results in a deviation away from the perfect cosine envelope exhibited by a 1/2WL thin-wire dipole. In any case, the delay through a 75m bugcatcher coil is tens of degrees, not 3 nS. If the reasons for this aren't obvious, many texts cover it quite well. No special "traveling wave" analysis is required. The self-resonant frequency of that modeled coil is around 9 MHz. Since the coil is 90 degrees at 9 MHz, it would be ~59 degrees at 5.9 MHz. Dr. Corum suggests a 15 degree limit at which the lumped-circuit model needs to be abandoned in favor of the distributed-network model or Maxwell's equations. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
You keep trying to drag something from a self-resonant helice into a loading coil discussion. My 75m bugcatcher coil is self-resonant around 6.7 MHz so it meets the minimum requirement for a Tesla coil at 6.7 MHz. 4 MHz is 60% of the Tesla coil self-resonant frequency. The coil is known to possess a 90 degree delay at 6.7 MHz. That would make the delay ~60 degrees at 4 MHz. Dr. Corum suggests a 15 degree limit for the lumped-circuit model. The two are nearly at opposite extremes in behavior, but even at that the self-resonant helice can be analyzed with standar L/C analysis. Unfortunately, that's not true. One cannot assume the presuppositions of one's model without proof. The "standar L/C analysis " assumes the delay through a coil is zero, i.e. faster than light. The delay through a self-resonant coil is known to be 90 degrees. That "standar L/C" model is invalid at the self-resonant frequency where the coil is acting like a 1/4WL open-circuit transmission line stub. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Yuri Blanarovich wrote: Cecil explained the various situation depending where the coil is placed within the radiator and at overall antenna curve. I doubt that. If he explained it in those terms he was missing some important points. I never claimed uniformly in ALL coils. I set boundaries as to the conditions. I can replace that Hustler coil with another coil and ruin your theory about standing waves and missing antenna degrees. Take your 1/4WL electrical antenna and put another 1/4WL bottom section beneath it. The current "flowing" into the bottom of the coil will be higher than the current "flowing" out of the top of the coil. Please explain that. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Richard Harrison wrote:
Are any famous authors protagonists of that theory? In "Fields and Waves in Modern Radio", Ramo and Whinnery, 2nd edition, there is a section titled: "9-16 The Idealized Helix and Other Slow-Wave Structures". Quoting: "A rough picture would convince one that the wave should follow the *wire* with about the velocity of light, ..." From the IEEE Dictionary: "slow-wave circuit - A circuit whose phase velocity is much slower than the velocity of light. For example, for suitably chosen helixes the wave can be considered to travel on the *wire* at the velocity of light but the phase velocity is less than the velocity of light by the factor that the pitch is less than the circumference." a 75m bugcatcher loading coil is a slow wave structure with a velocity factor around 0.017 (calculated and measured). -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote in message oups.com... Yuri Blanarovich wrote: Yea Tom, it all started with ALL coils, it is MY theory and you can ruin MY theory. What is your theory Yuri? You didn't explain it. 73 Tom Nice twist again! (That was sarcasm and take on your comment about ALL coils) I didn't produce any MY theory. I simply realized that there is something weird (effect) when I burned heatshrink tubing on the bottom of my Hustler 80m coil, W9UCW measured and did experimenting with that and brought to our attention that there is significant difference in the current distribution across the loading coil. W5DXP put some explanations on as far as mechanism of the effect. I give credit where its due, I didn't produce any theory, I simply tried to bring attention to the effect, tried to find explanation and set the record straight for the benefit of hams, who were misled for decades (including myself), provide (with others) correction pointers so we can correctly model antennas and get better, more accurate results. If W7EL can capture the effect and provide tool to model the loading coil (lumped inductance) as what the hairpin of the same inductance does, we have a major improvement in modeling and designing loaded antennas and arrays. Sooo, we have the effect, we have some measurements to quantify it and we have explanations going back to Dr. Nikola Tesla and we are trying to set the record straight and correct the years of false information in the ham literature, going back to J. Belrose first article in ancient QST. What you have? Misinformation on your web site and refusing to admit that you could be wrong (again). Not answering technical questions, nitpicking on things to confuse and cloud the issue "proving" that you are right. Funny how you object to "personal" attacks, when it is the first thing you do when someone posts something that doesn't jive with your understanding of the subject. Been there, you have done it to me few times. Tom, it's not personal attack on YOU, it is correction ("attack") on what you (wrong) say and parade on your web site. The bottom line is, that you claim that loading antenna coil behaves according to "DC circuit laws" and has the same (or almost) current at both ends. When in reality there is quite a difference (talking about case of say quarter wave loaded radiator). The significance is, that the efficiency of the antenna is proportional to the area under the current distribution curve. If that distribution is portrayed wrongly (not showing, calculating drop of current across the coil) then we get false results, which will be magnified in multielement loaded array. So you can keep up the mumbo-jumbo and cloud the issue all you want, reality is there and won't go away. One more experiment that "scientwists" can do: Stick some neon bulbs at the bottom and top of the coil with equal "tail", or just move the neon bulb along the coil whil holding in your hand. I bet you would see that there is noticeable difference in brightness from top to bottom, top being brighter, meaning higher voltage. We know (not mine theory) that if voltage is higher then the current has to be lower, meaning that current at the bottom of the coil is higher than on the top. Meaning that it is not EQUAL as W8JI is insisting on. Nice science project for a 7th grader kid of a ham. (To avoid mumbo-jumbo detours - we are talking say 80m mobile Hustler or similar quarter wave antenna at resonant frequency). No need for phasors, distributed this or that, inside or outside of the coil wire and other "clouds". Can you answer questions that are posted, instead of sidestepping them and nitpicking on unrelated stuff? That's just MY theory, I may be wrong, and I would admit it, if I am shown the right. So can you ANSWER Cecil's question? Where did you get the engineering degree and usage of "JI Engineering"? Yuri, www.K3BU.us |
Current through coils
Yuri, why not try program LOADCOIL.
Its just what you've been waiting for. Download from website below. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Current through coils
wrote:
1.) I can build an antenna that has greatly uneven currents at the ends of the loading coil, but the antenna rea above the inductor is wasted and the system will be less efficient than a properly designed system. Anyone with EZNEC can answer the question for himself. For the following EZ files, the currents at the bottom and top of the coil are viewed by clicking on the "Load Dat" button. Load 1 is at the bottom of the coil and Load 2 is at the top of the coil. The loads are both zero so they have no effect on the antenna system and are used only to report the current at that point. I previously modeled a bottom-loaded 5.89 MHz mobile antenna. That EZNEC file is available at: http://www.qsl.net/w5dxp/test316.EZ Taking that antenna and *changing nothing* except adding 1/4WL of wire to the top of the whip, yields the EZNEC file at: http://www.qsl.net/w5dxp/test316c.EZ The antenna has been changed from a base-loaded 1/4WL antenna to a base-loaded 1/2WL antenna using the same coil in the same relative position to the source and ground. The changes in the currents through the coil are obvious. The frequency was not changed so the coil occupies the same percentage wavelength of the antenna in both examples. In the first example, we have 1.01 amps at the bottom of the coil and 0.6984 amps at the top of the coil. That's fairly typical for mobile antennas at the 5.89 MHz frequency and agrees with the measurements presented so far. Now, changing nothing except the whip length by adding 40 feet (1/4WL) of whip, in the second example we have 1.239 amps at the bottom of the coil and 2.068 amps at the top of the coil. How does the lumped-circuit model explain that one? More current "flowing" into the coil than is "flowing" out of the coil just by adding 40' of wire to the top of the antenna? The coil occupies the same electrical length in both examples because they are at the same frequency. The current through the coil depends upon where it is physically installed relative to the standing waves existing at the point of installation. Using what EZNEC tells us about the self-resonant frequency near 9 MHz, we can calculate the delay through the coil as ~59 degrees. Thus the coil occupies ~0.16 wavelength. (The wire used to wind the coil is ~0.24 wavelength if stretched out straight.) Nobody said it was a 1:1 replacement but someone said it was *NOT* a replacement at all. I would encourage the experimenters to add 1/4WL of whip to their previously measured mobile antenna systems and make additional measurement. That is, of course, after matching the source to the new impedance. Please report the results here. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cec, who the heck is Dr Corum?
Is he yet another Bible writer? Nobody's ever heard of him. What makes you think he is right? Is it just because you think he agrees with YOU? And you may have taken him out of context and misquoted him anyway. ---- Reg. |
Current through coils
Everybody quotes from Bibles.
Which reduces the authors to the same standard of conversation as transpires on this newsgroup. Has nobody any confidence in what he is saying and feels in need of support from the angeles. ------------------------------------------------------------------- |
Current through coils
Reg Edwards wrote:
Cec, who the heck is Dr Corum? Nobody's ever heard of him. Reg, in Mexico, it's known as a "Tequila Sunrise". In your case, it must be a "Chardoney Sunrise". :-) If you've never heard of him, it's your own fault. http://www.ttr.com/corum/index.htm http://www.ttr.com/TELSIKS2001-MASTER-1.pdf - URLs posted here a number of times. Do a web search to understand his far-reaching influence in matters of a technical nature. What makes you think he is right? He makes sense and his equations agree with my rough measurements within 14%. I suspect my measurements are off by at lease 10%. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Reg Edwards wrote:
Has nobody any confidence in what he is saying and feels in need of support from the angeles. "angeles"? Resorting to Spanish is no help. The present question is, "can EZNEC be trusted"? We already know your opinion. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
"Cecil Moore" wrote Reg Edwards wrote: Has nobody any confidence in what he is saying and feels in need of support from the angeles. "angeles"? Resorting to Spanish is no help. The present question is, "can EZNEC be trusted"? We already know your opinion. :-) ======================================== Dear Cec, - - - and what is my opinon which everybody is supposed to know? C'mon then. Be truthful. Out with it! ---- Reg. |
Current through coils
Reg Edwards wrote:
- - - and what is my opinon which everybody is supposed to know? C'mon then. Be truthful. Out with it! Your opinion of EZNEC is recorded for posterity on Google. Who am I to embellish it? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
wrote: 1.) I can build an antenna that has greatly uneven currents at the ends of the loading coil, but the antenna rea above the inductor is wasted and the system will be less efficient than a properly designed system. Anyone with EZNEC can answer the question for himself. In accordance with my policy of correcting my mistakes using the scientific method and updating my presentations to have the most impact, I have revised the bottom of the web page at http://www.qsl.net/w5dxp/current.htm Can there be any question about the lumped-circuit model failing in a standing wave environment after viewing that information? -- 73, Cecil http://www.qsl.net/w5dxp |
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