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Current through coils
Thanks, Tom, for taking the trouble to go through the numbers. As I said
earlier, most of us know, and all engineers certainly should know, superposition requires that results from an analysis using the total current must be the same as the sum of the results from separate analyses using forward and reflected currents (or any other components whose sum is the total current). Your analysis shows this, as it should. Roy Lewallen, W7EL |
Current through coils
On Sat, 25 Mar 2006 17:43:08 +0000, Ian White GM3SEK
wrote: First, several years ago, came the shocking observation that the current into a coil is not the same as the current out of it. Somewhere along the debate, this practical measurement was then expressed to be in conflict with Kirchhoff's theories. ... So much has been said in this debate - and this is at least the third or fourth re-make of the whole show - that I honestly cannot remember if the exact words that Richard reports were ever used. Hi Ian (if you are still with us), I stumbled upon the context in this snipe hunt: On Sun, 05 Mar 2006 20:03:14 GMT, Cecil Moore wrote: What would Kirchhoff have thought about a coil with 0.1 amp at the bottom and 0.7 amps at the top? It certainly doesn't mean that 0.6 amps is flowing sideways. To explain the application of "snipe hunt," this is a term suggesting that someone is being set upon a fool's mission (an impossible goal employing absurd tools). In the Navy is was catching sea bats, or being on mail buoy watch. 73's Richard Clark, KB7QHC |
Current through coils
Richard Clark wrote:
On Sat, 25 Mar 2006 17:43:08 +0000, Ian White GM3SEK wrote: First, several years ago, came the shocking observation that the current into a coil is not the same as the current out of it. Somewhere along the debate, this practical measurement was then expressed to be in conflict with Kirchhoff's theories. ... So much has been said in this debate - and this is at least the third or fourth re-make of the whole show - that I honestly cannot remember if the exact words that Richard reports were ever used. Hi Ian (if you are still with us), Yeah, still here... and still wondering why... I stumbled upon the context in this snipe hunt: On Sun, 05 Mar 2006 20:03:14 GMT, Cecil Moore wrote: What would Kirchhoff have thought about a coil with 0.1 amp at the bottom and 0.7 amps at the top? It certainly doesn't mean that 0.6 amps is flowing sideways. To explain the application of "snipe hunt," this is a term suggesting that someone is being set upon a fool's mission (an impossible goal employing absurd tools). In the Navy is was catching sea bats, or being on mail buoy watch. And here, it's about chasing single isolated comments. Moral: don't hunt snipe unless you see a whole flock of 'em. -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek |
Current through coils
Richard Clark wrote: I stumbled upon the context in this snipe hunt: On Sun, 05 Mar 2006 20:03:14 GMT, Cecil Moore wrote: What would Kirchhoff have thought about a coil with 0.1 amp at the bottom and 0.7 amps at the top? It certainly doesn't mean that 0.6 amps is flowing sideways. I think everyone here except Cecil knows where the current goes. If Cecil admits to displacement currents, he has to also admit his argument about reflected waves is incomplete. 73 Tom |
Current through coils
If the lurkers think one can add or subtract the forward current
at both ends of the coils, as you did, I feel sorry for them. -- 73, Cecil http://www.qsl.net/w5dxp I feel sorry for anyone who has to deal with you on a daily basis. No wonder your wife split. |
Current through coils
Roy Lewallen wrote:
Thanks, Tom, for taking the trouble to go through the numbers. As I said earlier, most of us know, and all engineers certainly should know, superposition requires that results from an analysis using the total current must be the same as the sum of the results from separate analyses using forward and reflected currents (or any other components whose sum is the total current). Your analysis shows this, as it should. Roy, would you please explain what is the technical significance of Tom's superposing the forward wave of 1 amp at zero degrees at the bottom of the coil with the forward wave of 1 amp at 45 degrees at the top of the coil when those two currents are separated in space by 12 inches and separated in time by 45 degrees of a cycle? Doesn't the superposition principle require the two signals to exist in the same space-time? The misconceptions being presented here are unbelievable but apparently exist in the engineering community. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
Richard Clark wrote: I stumbled upon the context in this snipe hunt: Cecil Moore wrote: What would Kirchhoff have thought about a coil with 0.1 amp at the bottom and 0.7 amps at the top? It certainly doesn't mean that 0.6 amps is flowing sideways. I think everyone here except Cecil knows where the current goes. Those are standing wave currents, Tom. What is it about func(kx)*func(wt) that you don't understand? Take a look at the standing wave current distribution on a one wavelength dipole at: http://www.qsl.net/w5dxp/1WLDIP.GIF The position in which a coil is installed in the standing wave environment determines the magnitudes and phases of the currents at the top and bottom of the coil. No magic displacement current is required. If magic displacement current is not required in a transmission line, why is it required in a coil? Hint: because the lumped-circuit model is flawed. If Cecil admits to displacement currents, he has to also admit his argument about reflected waves is incomplete. We can assume zero displacement current without much changing anything. In the example at the top of this posting, there sure isn't 0.6 amps of displacement current. I'm beginning to believe that you don't understand superposition of forward and reflected waves. That would explain a lot. In the above example, the forward and reflected currents superpose to 0.7 amps at the top of the coil. That is simply closer to the standing wave current maximum point. No displacement current required. The forward and reflected currents superpose to 0.1 amp at the bottom of the coil. That is simply closer to the standing wave current minimum point. No displacement current required. Exactly the same thing happens along a transmission line with reflections. There's negligible displacement current between the 0.1 amp point and the 0.7 amp point on a transmission line. For exactly the same reason, there can be negligible displacement current in the coil. The forward current and reflected current superpose in a coil just as they do in a transmission line. If you would use the proper model and you will not need to resort to any magic displacement current which is just a patch on a gaping hole in the flawed lumped-circuit model. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
I feel sorry for anyone who has to deal with you on a daily basis. The distributed network model, with its superposition of forward and reflected waves, explains everything without having to resort to displacement currents. The distributed network model is more powerful than the lumped circuit model. The lumped circuit model is a subset of the distributed network model. When the two models agree, all is well. When the two models disagree, the distributed network model is right and the lumped circuit model is wrong. You assume displacement currents exist because your model requires them, not because they exist in reality. The distributed network model illustrates just how unimportant displacement currents really are. In the distributed network model, displacement currents are often omitted as negligible. In a high-Q coil, in a standing wave environment, radiation from and losses in the coil are often negligible and can be ignored. The large part of what happens to the standing wave current is simply superposition of the forward and reflected waves. No magic explanations required. The delay through a real world 75m bugcatcher coil, predicted by the distributed network model, is tens of degrees, not the faster than light speed predicted by the lumped circuit model. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
K7ITM wrote: Cecil is unable (and believes it is impossible) to determine the net charge in the volume containing the coil as a function of time (to within a constant, at least), even though the the wires in which we know the currents are the only way for charge to get in and out of that volume. THERE IS NO RF BATTERY STORING ENERGY! THERE IS ZERO LONG TERM ACCUMULATION OF CHARGE! Neglecting losses, energy in exactly equals energy out over the long term. The fact that 2 amps of standing wave current exists at the bottom of the coil and 1.4 amps of standing wave current exists at the top of the coil doesn't imply any long term accumulation of charge. Long term accumulation of charge in a coil is impossible. Cecil, I believe the long term average current is also zero. Therefore all of these coils and antennas are totally inert. Problem solved. It is a mystery why the discussion randomly switches from degrees of phase and nanoseconds of time delay to long term averages, RMS, and "net" something or other. If you don't understand accumulation of charge in *every* AC and RF circuit then there is little hope that you will ever get to an understanding of the now-infamous "current through coil" problem. 73, Gene W4SZ |
Current through coils
Gene Fuller wrote:
If you don't understand accumulation of charge in *every* AC and RF circuit then there is little hope that you will ever get to an understanding of the now-infamous "current through coil" problem. I understand the movement of charge within a cycle, Gene. But it is irrelevant to the discussion and just another one of your strawmen erected as a diversion away from the relevant issues. Why do you think such a transparent diversion would work? During a cycle, energy is obviously exchanged between the E-fields and H-fields. For a 1/4WL antenna, that means migration from end to end. But everything being discussed so far are RMS values. EZNEC reports and displays RMS values of current. All of the measurements reported so far were RMS values. There is no net storage of energy in the coil based on the product of the RMS voltage and the RMS current. Everything about RMS standing wave current can be understood simply by superposing the RMS values of forward and reflected current. func(kx+wt) + func(kx-wt) = func(kx) * func(wt) You were the one who posted that information. I don't think you quite realized what a boost that was for the distributed network model. The lumped circuit model has no provisions for accomodating the above equation and presupposes faster than light propagation. Your next logical diversion will probably be - trying to track the position and velocity of an individual electron in an antenna. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil,
Your response shows you don't understand, or more likely, you are faking a non-understanding. Charge storage is virtually equivalent to voltage. Are you suggesting that there is no RMS voltage in these configurations? And as to your point about my "boost" of the distributed model: I am neither boosting nor de-boosting any particular model. I don't believe there is another person participating in this thread who is claiming one model trumps the other, except you. Each model has its place, but that place is dictated only by mathematical convenience. It could be really tedious to set up complex problems with the less convenient model, but that does not mean it cannot be done. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: If you don't understand accumulation of charge in *every* AC and RF circuit then there is little hope that you will ever get to an understanding of the now-infamous "current through coil" problem. I understand the movement of charge within a cycle, Gene. But it is irrelevant to the discussion and just another one of your strawmen erected as a diversion away from the relevant issues. Why do you think such a transparent diversion would work? During a cycle, energy is obviously exchanged between the E-fields and H-fields. For a 1/4WL antenna, that means migration from end to end. But everything being discussed so far are RMS values. EZNEC reports and displays RMS values of current. All of the measurements reported so far were RMS values. There is no net storage of energy in the coil based on the product of the RMS voltage and the RMS current. Everything about RMS standing wave current can be understood simply by superposing the RMS values of forward and reflected current. func(kx+wt) + func(kx-wt) = func(kx) * func(wt) You were the one who posted that information. I don't think you quite realized what a boost that was for the distributed network model. The lumped circuit model has no provisions for accomodating the above equation and presupposes faster than light propagation. Your next logical diversion will probably be - trying to track the position and velocity of an individual electron in an antenna. :-) |
Current through coils
If you guys want to see Cecil in action in other forums,
look at his behavior in this thread: http://www.qrz.com/ib-bin/ikonboard....T;f=5;t=115870 This is obviously a deeply personal issue with Cecil, and has nothing to do with science or trying to communicate. No matter what happens here, Cecil will run off someplace else and report everyone supports him and give some personal argument why. I suspect that is becuase he really hasn't a leg to stand on technically and he knows it. 73 Tom |
Current through coils
Gene Fuller wrote:
Your response shows you don't understand, or more likely, you are faking a non-understanding. Charge storage is virtually equivalent to voltage. Are you suggesting that there is no RMS voltage in these configurations? Gene, everyone knows that an inductor stores energy during part of a cycle and gives up that same energy, minus losses, during the other part of the cycle. That knowledge is irrelevant to the present discussion. Your attempt at a diversion is more than transparent. Why don't you discuss the real issues? I don't believe there is another person participating in this thread who is claiming one model trumps the other, except you. I suspect those people know when the lumped circuit model fails. Your own posting about standing wave current phase proved that W7EL's phase measurements were meaningless. Here's what you said: Regarding the func(kx)*func(wt) standing wave current term: 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. That is technical fact. Thanks for stating it. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
wrote:
This is obviously a deeply personal issue with Cecil, and has nothing to do with science or trying to communicate. Technical facts *are* a deeply personal issue with me. So I ask you the same question he When are you going to correct the technical errors on your web page? The delay through a 75m mobile bugcatcher coil is tens of degrees, not faster than the speed of light. Your chosen model has you hoodwinked into assuming the proof. Its presuppositions cannot be used as proof of anything which is all the proof you have ever presented. Please note that nobody has made valid measurements of the delay through a loading coil. The closest thing to a valid measurement presented thus far is the EZNEC simulation on my web page at: http://www.qsl.net/w5dxp/current.htm which I updated just this morning. I'm hoping some objective person will make the traveling wave measurements and report them here. And I'm willing to predict it won't be the people defending the lumped circuit model for fear of what they will measure. No matter what happens here, Cecil will run off someplace else and report everyone supports him and give some personal argument why. I suspect that is becuase he really hasn't a leg to stand on technically and he knows it. Neither you, not anyone else, has been able to poke a hole in the distributed network/reflection model. Wonder why that is? When there is a disagreement between the distributed network model and the lumped circuit model, the distributed network model wins every time because that is prima facie evidence that the lumped circuit model has ceased to function under the given conditions. Why are your postings so lacking in technical content? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Mon, 27 Mar 2006 13:42:12 GMT, Cecil Moore
wrote: We can assume zero displacement current without much changing anything. You can also guarantee the injected slop, then you can roll back on your heels and utter "not much is changed." This has all the irony of Galileo fighting for his right to mumble: "If we assume we revolve around Mercury.... then that's close enough isn't it?" Vatican: Less than 59% error, fer sure. Is that your final answer? Exactly the same thing happens along a transmission line with All of your claims of accuracy fall wildly short of "exactly." ;-) If you would use the proper model and you will not need to resort to any magic displacement current which is just a patch on a gaping hole in the flawed lumped-circuit model. Let's see, this logic flows from the original misapplication of Kirchhoff's laws, forcing them onto the lumped load, and then blaming the lumped load for its poor application. Thread buster umpty-ump. |
Current through coils
wrote:
I suspect that is becuase he really hasn't a leg to stand on technically and he knows it. I asked you to discuss the technical issues associated with: http://www.qsl.net/w5dxp/1WLDIP.GIF - so I'm not the one avoiding discussion of the technical issues. Would it help if I paid you a fee to discuss those technical issues? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
Everything about RMS standing wave current can be understood simply by superposing the RMS values of forward and reflected current. Boing! You might want to think about that sentence for a while. |
Current through coils
Please note that nobody has made valid measurements of the delay
through a loading coil. The closest thing to a valid measurement presented thus far is the EZNEC simulation on my web page: ======================================= Dear Antagonists, Why go to the great hazardous trouble of measuring it when it can easily be calculated from physical dimensions of the coil. Velocity V = 1 / Sqrt( L * C ) metres per second where L and C are henrys and farads per metre. Therefore Seconds Delay = Coil Length in metres / Velocity. OK, I admit it's an approximation because coil turns couple one part of the 'line' to another a short distance away. It is not unconnected with proximity effect. This does not occur in a normal transmission line. But the approximation holds. See and amuse yourselves with program TRANCOIL. ---- .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... |
Current through coils
John Popelish wrote:
Cecil Moore wrote: Everything about RMS standing wave current can be understood simply by superposing the RMS values of forward and reflected current. Boing! You might want to think about that sentence for a while. Let me rephrase. Everything about RMS standing wave current can be understood simply by superposing the values of the forward and reflected current phasors whose phasor length is (usually) represented by their RMS values. The phasor arrow length is customarily the RMS value of the phasor so the superposition of phasors turns out to result in an RMS value. That's what I meant. When EZNEC says the source current is 1.0 amp at zero degrees, that is an RMS value. If the source voltage is 50 volts at zero degrees, multiplying voltage by current will yield the power input, i.e. 50 watts. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
|
Current through coils
Reg Edwards wrote:
Therefore Seconds Delay = Coil Length in metres / Velocity. So what is it for a 25 turn coil, 12 inches long, 6 inches in diameter, made from #16 wire? EZNEC says it depends upon the frequency. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
On Mon, 27 Mar 2006 17:17:04 GMT, Cecil Moore
wrote: How much do you need to be paid This was already asked and answered. Must be the gringo form of bartering a deal. No wonder the immigration problem has never gone away with the Republicans in charge. "How much would you pay for a tall fence 3000 miles long?" If its built by the Army Corps of Engineers to Katrina standards? |
Current through coils
Cecil Moore wrote:
John Popelish wrote: Cecil Moore wrote: Everything about RMS standing wave current can be understood simply by superposing the RMS values of forward and reflected current. Boing! You might want to think about that sentence for a while. Let me rephrase. Everything about RMS standing wave current can be understood simply by superposing the values of the forward and reflected current phasors whose phasor length is (usually) represented by their RMS values. Better. As I said, earlier, This thread has drawn me back to re-reading "Zen and the Art of Motorcycle Maintenance". If you haven't read it, I highly recommend it. Here is a passage that jumped out at me, last night. "The real purpose of scientific method is to make sure Nature hasn't misled you into thinking you know something you don't actually know. There's not a mechanic or scientist or technician alive who hasn't suffered from that one so much that he's not instinctively on guard. That's the main reason why so much scientific and mechanical information sounds so dull and so cautious. If you get careless or go romanticizing scientific information, giving it a flourish here and there, Nature will soon make a complete fool out of you. It does it often enough anyway even when you don't give it opportunities. One must be extremely careful and rigidly logical when dealing with Natu one logical slip and an entire scientific edifice comes tumbling down. One false deduction about the machine and you can get hung up indefinitely." More at: http://www.public.iastate.edu/~stuga...ntena nce.pdf |
Current through coils
John Popelish wrote:
"The real purpose of scientific method is to make sure Nature hasn't misled you into thinking you know something you don't actually know." Hmmmm, anyone we know? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Cecil Moore wrote:
John Popelish wrote: "The real purpose of scientific method is to make sure Nature hasn't misled you into thinking you know something you don't actually know." Hmmmm, anyone we know? Potentially everyone you know. Oh wait... We really don't know anyone. We only pretend we do. |
Current through coils
So what is it for a 25 turn coil, 12 inches long, 6 inches in diameter, made from #16 wire? EZNEC says it depends upon the frequency. -- 73, Cecil ================================== Use both programs and compare the results. Make the coil 1 metre long, 500 turns, and diameter 25.4 mm (1 inch). Give the programs something to get their teeth into. How does EZNEC make its calculations? If you don't know you are placing your faith in a mirage. ---- Reg. |
Current through coils
On Mon, 27 Mar 2006 18:58:16 +0100, "Reg Edwards"
wrote: If you don't know you are placing your faith in a mirage. Now there's a commendation for your own work. No wonder we don't see any correspondence from you with actual values for the coils offered. Lords Plushbottom and Kelvinator might let you serve in the black gang, moving coal on one of those transatlantic cable layers - but they certainly wouldn't expect a practical answer to: "How many shovels full today Reggie?" "If your lordships will forgive me, but you can find out by downloading my unzipped SHUVFULL.EXE and entering many fascinating variables." "I say, Plushbottom old son, we must ask the Boatswain to check the coal bunkers for hidden bottles of Sack." Who would've guessed that the comedic possibilities still lingered after 600 postings. ;-) |
Current through coils
Reg Edwards wrote:
Please note that nobody has made valid measurements of the delay through a loading coil. The closest thing to a valid measurement presented thus far is the EZNEC simulation on my web page: ======================================= Dear Antagonists, Why go to the great hazardous trouble of measuring it when it can easily be calculated from physical dimensions of the coil. Velocity V = 1 / Sqrt( L * C ) metres per second where L and C are henrys and farads per metre. Therefore Seconds Delay = Coil Length in metres / Velocity. OK, I admit it's an approximation because coil turns couple one part of the 'line' to another a short distance away. It is not unconnected with proximity effect. This does not occur in a normal transmission line. But the approximation holds. See and amuse yourselves with program TRANCOIL. It's hard to tell from this, but are you still claiming that the end-to-end C of an inductor is the C of an equivalent transmission line? Or even an approximation? Does your program assume this? Roy Lewallen, W7EL |
Current through coils
Reg Edwards wrote:
. . . How does EZNEC make its calculations? If you don't know you are placing your faith in a mirage. A bit more than a mirage -- you're placing your faith in a program (NEC-2) which has been in daily use by hundreds to thousands for nearly 30 years, and has been used for designing countless antennas, several of which you almost certainly use daily. But anyone interested in knowing how EZNEC does its calculations can get a highly detailed answer from the NEC-2 manual, available free at http://www.si-list.org/NEC_Archives/nec2prt1.pdf. Or, if interested in the general method (method of moments), there's a very good and easy to understand explanation in the second and later editions of Kraus' _Antennas_. I'm sure there are some good (and undoubtedly also bad) explanations of the moment method on the web, also. Roy Lewallen, W7EL |
Current through coils
Cecil,
I don't remember why you chose a frequency of 5.89 MHz for all of your analysis, but in any case I believe that frequency is slightly out of the 75 meter band. The FCC will be calling. 8-) I tried to adjust the frequency downward, but the segment length limit is reached for the coil model. I redrew the coil with only six segments per turn, rather than eight. Now the frequency can be lowered to about 3.94 MHz without EZNEC guideline check warnings. In order to get the 90 degree phase curve I extended the horizontal wire to about 55 feet. (not sure why this matters if the antenna is purely a terminated traveling wave antenna, but, hey, no loose ends.) The result from EZNEC is that the phase shift in the coil is about 9 degrees. You might observe that this shift is a bit smaller than the "tens of degrees" noted below, and it is also smaller than the guru-inspired transition point of 15 degrees. I would like to model a coil more typical of common use than the strange beast you designed, but the segment length limits in the NEC engine seem to preclude such models. (I have never seen a mobile coil that is 12 inches high, 6 inches in diameter, with 2 turns per inch.) If I was the cynical sort I might think that your choice of coil dimensions and frequency were picked to get a phase shift of 16 degrees, which is just over the guru limit. But since I am a straightforward kind of guy I won't think such thoughts. 73, Gene W4SZ Cecil Moore wrote: Technical facts *are* a deeply personal issue with me. So I ask you the same question he When are you going to correct the technical errors on your web page? The delay through a 75m mobile bugcatcher coil is tens of degrees, not faster than the speed of light. |
Current through coils
Gene Fuller wrote:
. . . I tried to adjust the frequency downward, but the segment length limit is reached for the coil model. I redrew the coil with only six segments per turn, rather than eight. Now the frequency can be lowered to about 3.94 MHz without EZNEC guideline check warnings. . . . Of the Guideline Check warnings, the one about short segment length can most often be ignored without a problem. If in doubt and where practical, do a test case. For example, model the inductor with a wire through the middle directly connecting top and bottom and with a source in the middle. Note how the source reactance changes with frequency to see that it follows what it should theoretically do. Another test you should run when in doubt is the Average Gain test, described in the manual. Either is probably adequate to have confidence in the results. The Guideline Check warnings are based on NEC-2 recommendations. I've found that you can often make segments much shorter than the recommendations without causing a problem. Roy Lewallen, W7EL |
Current through coils
Reg Edwards wrote:
How does EZNEC make its calculations? If you don't know you are placing your faith in a mirage. It uses the Moment Method (MM) sometimes called the Method Of Moments (MOM). It's described in Kraus and Balanis and credited to Roger Harrington in the 1960's. Each segment in EZNEC is assumed to have constant current. In the aforementioned 8-sided coil, there are 200 segments, each with an assumed constant current. The standing wave current in each segment depends upon where it is inserted in the standing wave environment as shown at: http://www.qsl.net/w5dxp/1WLDIP.EZ -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
Gene, I want to commend you on a rational, mostly technical, posting. Hopefully, others will follow your lead. I don't remember why you chose a frequency of 5.89 MHz for all of your analysis, but in any case I believe that frequency is slightly out of the 75 meter band. The FCC will be calling. 8-) :-) Here's the history. I tried to model my 75m bugcatcher coil in EZNEC. It appears to be impossible without violating EZNEC's guidelines. So I changed the coil from 4 TPI to 2 TPI. That moved the resonant frequency from 3.8 MHz to 5.9 MHz, close enough to the 60m band that I thought no one would object. Do you think the FCC calls everyone who uses EZNEC to model an antenna out of the amateur bands? :-) I tried to adjust the frequency downward, but the segment length limit is reached for the coil model. I redrew the coil with only six segments per turn, rather than eight. Now the frequency can be lowered to about 3.94 MHz without EZNEC guideline check warnings. Hey, great. In order to get the 90 degree phase curve I extended the horizontal wire to about 55 feet. (not sure why this matters if the antenna is purely a terminated traveling wave antenna, but, hey, no loose ends.) I found the same thing. Seems no matter how one changes things, it appears to be a diverging series. The main goal is to get the reflections reduced to a low level, maybe not to eliminate them entirely. The result from EZNEC is that the phase shift in the coil is about 9 degrees. Yes, but that's for a coil designed for a 6 MHz antenna. You need to add a lot of turns to make it typical of a 4 MHz coil. Doubling the turns would make for an 18 degree phase shift - a detail you seem to have missed. Please expand the coil until it resonates an 8 foot antenna on 4 MHz and repeat your findings. You might observe that this shift is a bit smaller than the "tens of degrees" noted below, and it is also smaller than the guru-inspired transition point of 15 degrees. Of course, a 60m mobile coil used on 75m is going to have a smaller phase shift. But you dropped a bit in your logic, Gene. What you need to do is go back and create a coil that resonates an 8 foot antenna on 4 MHz. Then do your phase calculations. When you do that, the delay in the larger coil will turn out to be tens of degrees. Could you email me your EZNEC file? (Hopefully, without the worm/virus I received from someone else recently.) I would like to model a coil more typical of common use than the strange beast you designed, but the segment length limits in the NEC engine seem to preclude such models. (I have never seen a mobile coil that is 12 inches high, 6 inches in diameter, with 2 turns per inch.) We do the best we can do with the tools we have. Actually, I have seen such a coil at one of the CA 75m shootouts. It was made out of half-inch copper tubing. If I was the cynical sort I might think that your choice of coil dimensions and frequency were picked to get a phase shift of 16 degrees, which is just over the guru limit. But since I am a straightforward kind of guy I won't think such thoughts. I tried to model my 4 TPI 75m bugcatcher coil. EZNEC would have none of that. So I modeled what I could. The phase shift of 16 degrees was a complete coincidence, but interesting, no? -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Roy Lewallen wrote:
Of the Guideline Check warnings, the one about short segment length can most often be ignored without a problem. The problem that Gene and I are having is the spacing between adjacent segments. EZNEC won't allow me to do a 4 TPI coil. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Hi Roy,
Thanks. I went back and bravely ran the original coil model, ignoring the guideline checks. The difference in results from the two coil models, eight-sided and six-sided, was in the noise. (Or at least well below the new RRAA error guideline of 59%.) Emboldened by this apparent success I tried to substitute the now-famous W8JI coil; 100 turns, 2 inch diameter, 10 inch length. This time the overall 500 segment count was the limiter (I am cheap), so I had to make the coil four-sided. The delay through this coil was about 9 degrees at 5.89 MHz and about 6 degrees at 3.9 MHz. Sooooo, the bottom line for the 17,000 posts in this thread is that the pure lumped-circuit toroidal coil analog might be just a slight bit stingy, but it comes pretty close to reality. The full-bore transmission line model for the coil works as well, but it does not appear to add much useful information. The real phase shifts are well below the 15 degree transition point claimed by the Tesla coil crowd. I am sure none of this is news for you or for most others. Cecil has thanked me on several occasions for bringing up the standing wave equations. I now must return the favor by thanking him for setting up the traveling wave model. It did not prove his point, but it helped bring clarity to the issue. I am confident that this will not be the end of this immortal thread, but it is now quite clear through simulation that the entire issue is much ado about very little. 73, Gene W4SZ Roy Lewallen wrote: Gene Fuller wrote: . . . I tried to adjust the frequency downward, but the segment length limit is reached for the coil model. I redrew the coil with only six segments per turn, rather than eight. Now the frequency can be lowered to about 3.94 MHz without EZNEC guideline check warnings. . . . Of the Guideline Check warnings, the one about short segment length can most often be ignored without a problem. If in doubt and where practical, do a test case. For example, model the inductor with a wire through the middle directly connecting top and bottom and with a source in the middle. Note how the source reactance changes with frequency to see that it follows what it should theoretically do. Another test you should run when in doubt is the Average Gain test, described in the manual. Either is probably adequate to have confidence in the results. The Guideline Check warnings are based on NEC-2 recommendations. I've found that you can often make segments much shorter than the recommendations without causing a problem. Roy Lewallen, W7EL |
Current through coils
Cecil Moore wrote:
Roy Lewallen wrote: Of the Guideline Check warnings, the one about short segment length can most often be ignored without a problem. The problem that Gene and I are having is the spacing between adjacent segments. EZNEC won't allow me to do a 4 TPI coil. Gee, I wonder why that is? 73, Tom Donaly, KA6RUH |
Current through coils
Gene Fuller wrote:
Cecil has thanked me on several occasions for bringing up the standing wave equations. I now must return the favor by thanking him for setting up the traveling wave model. It did not prove his point, but it helped bring clarity to the issue. Uhhh Gene, you still need to add turns to the 6 MHz coil to bring it down to 4 MHz with an 8 foot antenna. No fair reporting the half of the results that agree with your preconceptions while ignoring the half of the results that disagree. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Tom Donaly wrote:
Cecil Moore wrote: The problem that Gene and I are having is the spacing between adjacent segments. EZNEC won't allow me to do a 4 TPI coil. Gee, I wonder why that is? My real-world 75m bugcatcher coil is 4 TPI. That EZNEC won't model it is discouraging. -- 73, Cecil http://www.qsl.net/w5dxp |
Current through coils
Gene Fuller wrote:
Emboldened by this apparent success I tried to substitute the now-famous W8JI coil; 100 turns, 2 inch diameter, 10 inch length. This time the overall 500 segment count was the limiter (I am cheap), so I had to make the coil four-sided. The delay through this coil was about 9 degrees at 5.89 MHz and about 6 degrees at 3.9 MHz. Sooooo, the bottom line for the 17,000 posts in this thread is ... You wish that was the bottom line. Here's some mud in your eye. 1. I have always been talking about my 75m bugcatcher coil which is about 6"x6" and designed for actual mobile use. W8JI's coil is nowhere near what the average ham uses for a 75m bugcatcher coil. It is much too fragile for long-term mobile use. It can't even be considered to be a "bugcatcher" because one Texas- sized bug and it is destroyed. 2. You haven't installed that coil in an 8 foot 75m mobile antenna so you don't know what the delay is in an 8 foot 4 MHz system. Please feel free to try again - no cigar at the present time. -- 73, Cecil http://www.qsl.net/w5dxp |
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