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On his web site, Yuri quoted W9UCW as measuring the currents at the ends
of a toroid mounted at the base of the antenna as being 100 mA at the bottom and 79 at the top. You must, then, believe these measurements to be in error. Roy Lewallen, W7EL Not! Here what Yuri has on his web site, quote by W9UCW: "Because of the constant claim that this must be due to the fact that the coil is so big compared to a wavelength, I measured the in and out current on a TOROIDAL loading coil used on a 20m mobile antenna. It was a 78" base mast (including spring and mount) with a 38" top whip (including 12" of alum. tubing for adjustment). Below --100ma & Above --79ma When I moved the coil to the top of the mast and made a horizontal "X" top hat to resonate it back on the same freq, I got Below --100ma & Above --47ma So, It happens even in a totally shielded loading coil with miniscule power going thru it! Kirchoff has no laws about current being the same on both ends of inductors. His current law is about one POINT in a circuit and his voltage law is about a closed loop." He described exactly how it was done, definitely not at the base. Yuri |
That's a pretty good theory, Yuri. I'd like to know where you got this "Cosine law" you keep talking about. From ancient Greeks I presume, it was way before my time. ON4UN has it shown in his book and pictures. Current in the radiator Ir = Imax x cos Alpha where Imax is the maximum current (like on the bottom of quarter wave radiator) Alpha is the angle (distance) in degrees like from 0 to 90 in quarter wave radiator. I can't seem to find mention of any such _law_ anywhere but on this newsgroup. It is one of the first things in trigonometry books, look into your high school library. Does that mean I should throw away my method of moments software because I don't need it any more? No, keep it. It is good for number of things, like arguing against reality. If you threw it away, what would you use as an argument? And what is a current drop? I've heard of voltage drops and cough drops but never current drops. It is right next to voltage drops. If it drops from one of the component to the other, that is called current drop across the component, like loading coil in the antenna, or coil in PI network, or in RF chokes, etc. Finally, how do you measure the "current in the radiator (in degrees)?" Why not use amperes like everyone else? We use amperes like everyone else. My ammeters are calibrated in A. Radiator length can be expressed in electrical degrees, if Roy claims that it can't be expressed in electrical length. Like quarter wave vertical would be 90 deg., half wave dipole would be 180 deg, Full wave quad would be 360 deg or 2 x 180 deg (same thing :-) I won't believe your theory, Yuri, until you and Cecil take the time to present it in terms of field theory. Since you guys have taken EM classes in college you should have no trouble doing this, right? You can worship what you wish, itsa free country. Or you can measure things and then you can choose whom to believe and where to send your contribution. 73, Tom Donaly, KA6RUH Yuri, K3BUm |
I think I'm learning something, but I'm getting a headache trying to follow
you guys! de jerry... "Roy Lewallen" wrote in message ... Can I conclude from this that if I were to make a coil with more or less inductance, then I would see a current difference between the ends of the coil? So tell you what. If you'll pull out your equations and calculate the expected current difference, I'll replace the coil with one of 100 ohms reactance and remeasure. How much current difference (magnitude andd phase, of course) between the ends of a 100 ohm inductor at the base of that same antenna? Roy Lewallen, W7EL Cecil Moore wrote: Yuri Blanarovich wrote: Judging by description, I would guess that there wasn't much difference. The feedpoint of the radiator alone is 35-j185. The impedance of the loading toroid is 0.6+j193. Assuming perfect predictability, that gives the antenna system a feedpoint impedance of 35.6+j8, i.e. it is *longer* than resonant. That moves the current maximum point inside the toroid making the current in and out even closer to equal. If a coil is installed at a current maximum point or a current minimum point, the current in and out will be the same. If a coil is installed at a place where the slope of the current envelope is positive, the current will actually increase through the coil. |
So, as a successful and award-winning engineer, what do you calculate as being the ratio of currents across my inductor, and how did you calculate it? Roy Lewallen, W7EL Judging by the picture, I wouldn't be able to include all the variables present in the setup. I will first measure it in same way as W9UCW did, about 2/3 up the mast and no wires hanging. Yuri |
Roy Lewallen wrote: Yuri, the inductor I put at the base of the antenna "replaced" something like 20 - 45 degrees, Nope, it didn't, Roy. Your 33' vertical was already equivalent to a 50' vertical apparently due to extraneous loading. I calculate that your coil replaced 18 degrees of wire with a current maximum point located inside the coil. -- 73, Cecil http://www.qsl.net/w5dxp In that case, If the feedpoint current was at 0 deg of the radiator length, and coil replaces 18 deg of wire, the cos 18 deg = 0.951 which should make difference, drop in the coil current 5% (or half, 2.5 deg?) Providing current maximum is exactly at the bottom end of the coil. Yuri, K3BU.us |
I think I'm learning something, but I'm getting a headache trying to follow you guys! de jerry... It not our fault, it is them :-) Yuri |
2.5 deg?)
make that 2.5%?) |
Well, what would it be if my setup was perfect?
Roy Lewallen, W7EL Yuri Blanarovich wrote: So, as a successful and award-winning engineer, what do you calculate as being the ratio of currents across my inductor, and how did you calculate it? Roy Lewallen, W7EL Judging by the picture, I wouldn't be able to include all the variables present in the setup. I will first measure it in same way as W9UCW did, about 2/3 up the mast and no wires hanging. Yuri |
I apologize. I read and was referring to the same quote, and interpreted
it to mean that the first measurement was made with the coil at the base of the antenna. So where was it -- 78" from the bottom? Roy Lewallen, W7EL Yuri Blanarovich wrote: On his web site, Yuri quoted W9UCW as measuring the currents at the ends of a toroid mounted at the base of the antenna as being 100 mA at the bottom and 79 at the top. You must, then, believe these measurements to be in error. Roy Lewallen, W7EL Not! Here what Yuri has on his web site, quote by W9UCW: "Because of the constant claim that this must be due to the fact that the coil is so big compared to a wavelength, I measured the in and out current on a TOROIDAL loading coil used on a 20m mobile antenna. It was a 78" base mast (including spring and mount) with a 38" top whip (including 12" of alum. tubing for adjustment). Below --100ma & Above --79ma When I moved the coil to the top of the mast and made a horizontal "X" top hat to resonate it back on the same freq, I got Below --100ma & Above --47ma So, It happens even in a totally shielded loading coil with miniscule power going thru it! Kirchoff has no laws about current being the same on both ends of inductors. His current law is about one POINT in a circuit and his voltage law is about a closed loop." He described exactly how it was done, definitely not at the base. Yuri |
I'm sorry, I didn't catch the step where you got from cos(18 degrees) =
0.951 to 2.5%. Roy Lewallen, W7EL Yuri Blanarovich wrote: 2.5 deg?) make that 2.5%?) |
I apologize. I read and was referring to the same quote, and interpreted it to mean that the first measurement was made with the coil at the base of the antenna. So where was it -- 78" from the bottom? Roy Lewallen, W7EL Yes, mast 78" - coil - 38" top whip we keep saying, looking at typical mobile antenna with loading coil about 2/3 up the quarter wave radiator. The lower the frequency, more loading, more pronounced effect. Caution, using toroid current transformers with scope leads would detune the antenna setup and introduce errors. You can get away with this at the base, but any stray capacitance up the radiator will detune it and skew the results. Need to use thermal RF current ammeters or current probe with detector and small meter together, no wires. Yuri, K3BU |
I'm sorry, I didn't catch the step where you got from cos(18 degrees) = 0.951 to 2.5%. Roy Lewallen, W7EL Just (in case) speculating that because of reflected wave either 5 or 2.5% reduction. I have not done the measurements yet. Yuri |
Thanks for the clarification.
I'm not entirely convinced that the ammeter is the best idea. There are enough internal wires and coils to introduce a real possibility of error when in close proximity to an inductor. It shouldn't be as much of a problem with a toroid, but I'm still a little leery. I agree it would be difficult to do the measurements well with a scope anywhere but at the base of the antenna. Current probes and a detecting meter might be ok, but you'd have to take a lot of care to avoid making an unintentional loop which would couple to the inductor, and you'd have to calibrate the potentially nonlinear detector. Phase information would be lacking, too. I'm waiting for Cecil's response, since by his theory, as I understand it, we should be able to get a decent phase shift through an inductor at the base of an antenna providing the antenna is significantly longer than a quarter wavelength. And if I understand your theory, we should be able to see a full 30% change in magnitude and 45 degree change in phase in the current through a base mounted inductor, if it's loading a 45 degree radiatior to resonance. Am I correct? I could measure that with the same setup but with an antenna removed from the mount. And 30% and 45 degrees should be much easier to resolve with any accuracy than the 2.5 or 5 percent you predict for the setup I did measure. Incidentally, I take it that your prediction for the setup I did measure includes an 18 degree phase shift of current from input to output of the inductor? Roy Lewallen, W7EL Yuri Blanarovich wrote: I apologize. I read and was referring to the same quote, and interpreted it to mean that the first measurement was made with the coil at the base of the antenna. So where was it -- 78" from the bottom? Roy Lewallen, W7EL Yes, mast 78" - coil - 38" top whip we keep saying, looking at typical mobile antenna with loading coil about 2/3 up the quarter wave radiator. The lower the frequency, more loading, more pronounced effect. Caution, using toroid current transformers with scope leads would detune the antenna setup and introduce errors. You can get away with this at the base, but any stray capacitance up the radiator will detune it and skew the results. Need to use thermal RF current ammeters or current probe with detector and small meter together, no wires. Yuri, K3BU |
Incidentally, I take it that your prediction for the setup I did measure
includes an 18 degree phase shift of current from input to output of the inductor? Roy Lewallen, W7EL Yes, I used Cecil estimate/calculation and taking cos 18 = 0.951056516 which is 4.8943483% Yuri |
Roy Lewallen wrote:
So now you're saying that any coil at the base of a short vertical antenna, regardless of its value, will have equal currents at the input and output? No, I didn't say that. I wish you would read what I say. If the coil is a low reactance (not many degrees) and the current maximum point is inside the coil, the two currents will tend to be equal. Ok, suppose I make the measurement at, say, 10 MHz, where the coil is no longer at the current maximum. Tell you what. I'll set up a 33 foot wire vertical, to eliminate the difficulty of the mounting arrangement. I'll furnish you the base impedance at 10 MHz, and even let you choose the inductor value. Be sure and choose a value that will clearly illustrate your point. Using the fine education you received from Balanis et al, calculate the current into and out of the inductor (phase and magnitude), and I'll set it up and measure it. Since it is a fair amount of work on my part, though, I'd like to do a dry run first, using, say, the base impedance predicted by EZNEC. Then, after you've shown us how you make the calculations, I'll build the antenna and do the measurement. I'd hate to go to the considerable trouble of setting it up and find that you somehow aren't able to do the calculation. I can't do the calculation because I don't know the attenuation factor. Do you think my inability to do the calculation proves anything about what's happening in reality at the antenna? You guys need to turn loose of the concept that what happens or doesn't happen on a piece of paper dictates reality. I can describe a base-loaded configuration that will demonstrate the principle. Take a 75m bugcatcher coil, one of the 6"x6" models, and choose a stinger that resonants the antenna in the 75m-80m band. Then measure the in and out currents at a frequency a little below resonance. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Yuri Blanarovich wrote:
If the feedpoint current was at 0 deg of the radiator length, and coil replaces 18 deg of wire, the cos 18 deg = 0.951 which should make difference, drop in the coil current 5% (or half, 2.5 deg?) Providing current maximum is exactly at the bottom end of the coil. It wasn't. The coil made the antenna too long so the current maximum was inside the coil. But this points up a measurement problem. I doubt that these measurements are 5% accurate. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Ok. So far, we have your calculation that the output current should be
5% smaller, and 18 degrees shifted in phase (lagging, I presume) from the input; and Cecil's, that the output current should equal the current, both in phase and magnitude. I don't know if Richard is going to do the calculation or not, so I'll wait a little longer. Anyone else like to hazard a prediction? Roy Lewallen, W7EL Yuri Blanarovich wrote: Incidentally, I take it that your prediction for the setup I did measure includes an 18 degree phase shift of current from input to output of the inductor? Roy Lewallen, W7EL Yes, I used Cecil estimate/calculation and taking cos 18 = 0.951056516 which is 4.8943483% Yuri |
Cecil Moore wrote:
Roy Lewallen wrote: . . . So in the past, you've predicted no difference, something like 20 or 45 degrees phase shift, or an indeterminate amount. It's good to see you've settled on one figure. There are three possibilities listed earlier. What happens with a coil depends upon where it is located. Please read that over and over until it soaks in. That's the problem. The more times I read what you've posted, the more confused I've gotten. My inductor was placed at the antenna base because I could measure the currents there with reasonable accuracy. Yep, you are looking for your keys under the streetlight because the light is better there than it is where you really lost the keys. You have a unique talent for turning an honest effort at being truthful and accurate into an insult, as you did with Ian. On his web site, Yuri quoted W9UCW as measuring the currents at the ends of a toroid mounted at the base of the antenna as being 100 mA at the bottom and 79 at the top. You must, then, believe these measurements to be in error. If the toroid is not mounted at a current maximum point, i.e. if the feedpoint impedance is slightly capacitive, then those figures could be accurate. I didn't pay any attention to them. Could be his coil causes a larger phase shift than your coil. You making your antenna too long ensured that the current maximum point would fall inside the coil. Whether you realize it or not, you are biasing the outcome of your experiment to agree with your pre-conceived (sacred cow) notions. This is precisely why I've given you the opportunity to choose the inductor for the 10 MHz test. You choose it so that it will best illustrate what you say is true. Shucks, I even encourage you to do the experiments yourself. . . . Roy Lewallen, W7EL |
Cecil Moore wrote:
Roy Lewallen wrote: So now you're saying that any coil at the base of a short vertical antenna, regardless of its value, will have equal currents at the input and output? No, I didn't say that. I wish you would read what I say. If the coil is a low reactance (not many degrees) and the current maximum point is inside the coil, the two currents will tend to be equal. I did read what you said. You said that it wouldn't exhibit a phase shift if placed at a current maximum. The current at the base of a short vertical antenna is at its maximum there. So now if you're saying that it *won't* exhibit a phase shift if placed at the base of a short antenna, let's try this. Suppose I remount my antenna to eliminate the shunting effect of the mounting, and do my measurements at 3.8 MHz as before. Suppose the base input Z is, say, 35 -j380. You choose any inductor value you'd like, that will best illustrate your method, and tell me what output to input current ratio to expect. Ok, suppose I make the measurement at, say, 10 MHz, where the coil is no longer at the current maximum. Tell you what. I'll set up a 33 foot wire vertical, to eliminate the difficulty of the mounting arrangement. I'll furnish you the base impedance at 10 MHz, and even let you choose the inductor value. Be sure and choose a value that will clearly illustrate your point. Using the fine education you received from Balanis et al, calculate the current into and out of the inductor (phase and magnitude), and I'll set it up and measure it. Since it is a fair amount of work on my part, though, I'd like to do a dry run first, using, say, the base impedance predicted by EZNEC. Then, after you've shown us how you make the calculations, I'll build the antenna and do the measurement. I'd hate to go to the considerable trouble of setting it up and find that you somehow aren't able to do the calculation. I can't do the calculation because I don't know the attenuation factor. What "attenuation factor" is it you need? Is it something that can be measured? If not, how about an equation or prediction with the "attenuation factor" as a variable? We can estimate a probable range of values, then see if the measurement results are within them. Do you think my inability to do the calculation proves anything about what's happening in reality at the antenna? You guys need to turn loose of the concept that what happens or doesn't happen on a piece of paper dictates reality. I hope to demonstrate what constitutes reality by theoretical analysis and by measurement. Where I come from, that counts much more than arm-waving, insulting, and vague explanations. Ultimately, each of the readers of these exchanges will decide what to believe, and I'm sure you will have convinced some. I can describe a base-loaded configuration that will demonstrate the principle. Take a 75m bugcatcher coil, one of the 6"x6" models, and choose a stinger that resonants the antenna in the 75m-80m band. Then measure the in and out currents at a frequency a little below resonance. I have no disagreement that a "bugcatcher" coil, or any coil of physically significant size, will exhibit a phase shift and magnitude change of current from one end to the other. Where we disagree is that you believe that a physically very small inductor will also exhibit this. I don't. I'm proposing a test which will show, with reasonable certainty, which viewpoint is correct. I fully expect every test I make to bring forth a flurry of objections. So I'm giving you the opportunity to choose the inductor which will best illustrate your point of view. I want to limit the parameters of the test to conditions I think I can measure with reasonable accuracy. With the equipment I've got, that pretty much limits me to doing measurements at the antenna base. But I think (although I'm still not sure) that you're now saying that there should be a substantial current difference between the input and output of a small inductor at the base of an antenna, if the antenna and inductor are properly chosen. So, you choose. And if you won't make the measurement, I will. Roy Lewallen, W7EL |
The absolute accuracy of the measurement isn't important. All that
matters is the accuracy of the ratio of currents at input and output, which is a lot easier to get with reasonable accuracy. What I'm looking for now, however, is your recommendation for a test which will clearly show the current ratio you claim will happen, of such a magnitude that the result will be clear even in the presence of a few percent error. Based on my measurements of currents with both probes on the same lead, and averaging results with probes reversed, I think I can measure the ratio within about 2% at ratios near 1, and resolve phase shifts of a few degrees. If you can come up with a test that'll produce 30% amplitude change and 45 degrees phase shift, I guarantee I tell whether the result is closer to that or to the zero amplitude change and zero phase shift I predict. Roy Lewallen, W7EL Cecil Moore wrote: Yuri Blanarovich wrote: If the feedpoint current was at 0 deg of the radiator length, and coil replaces 18 deg of wire, the cos 18 deg = 0.951 which should make difference, drop in the coil current 5% (or half, 2.5 deg?) Providing current maximum is exactly at the bottom end of the coil. It wasn't. The coil made the antenna too long so the current maximum was inside the coil. But this points up a measurement problem. I doubt that these measurements are 5% accurate. |
Roy Lewallen wrote:
and Cecil's, that the output current should equal the current, both in phase and magnitude. Hold the presses! That was a rounded off ballpark value. You haven't told us what the feedpoint impedance is yet so an accurate estimate is impossible so far. Is the feedpoint impedance 35.6+j8? Is that the impedance into which you are shoving one amp? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote:
That's the problem. The more times I read what you've posted, the more confused I've gotten. Use EZNEC to display the current distribution for a 102 ft center-fed dipole on 20m. Assume the origin is the feedpoint. Turn the current phase on. You have 270 degrees of a cosine wave for the current to the right of the feedpoint. You have a current maximum at zero degrees and 180 degrees. The current magnitude decreases to zero in the first 90 degrees. The current magnitude increases to a maximum negative value in the second 90 degrees. The current magnitude decreases to zero in the third 90 degrees. Where one locates a loading coil and how many degrees it replaces will determine the magnitude and phase of the current into the coil and the current out of the coil. There are three possibilities. You have a unique talent for turning an honest effort at being truthful and accurate into an insult, as you did with Ian. Roy, honest efforts are not always valid and the truth sometimes hurts. This is precisely why I've given you the opportunity to choose the inductor for the 10 MHz test. You choose it so that it will best illustrate what you say is true. Shucks, I even encourage you to do the experiments yourself. I have some 1.5" diameter, 6 tpi stock. Get a one foot stinger and use enough of that kind of stock to resonate on 10 MHz. I guarantee the current will be different into and out of the coil. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote:
What I'm looking for now, however, is your recommendation for a test which will clearly show the current ratio you claim will happen, of such a magnitude that the result will be clear even in the presence of a few percent error. Assuming the test is on 10 MHz, use a one foot stinger and enough 1.5" diameter, 6 tpi air-core stock to resonate the vertical on 10 MHz. I guarantee there is a difference in current in and out of the coil. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy, W7EL wrote:
"Other predictions would be welcome, too, such as Yuri`s based on the "missing antenna length" theory of inductor current." It`s desirable to resonate a standing-wave antenna to reduce impediment to antenna current. In the 19th edition of the ARRL Antenna Book, there is a section on "Base Loading and Center Loading" beginning on page 16-4. First point is that current is not uniform in a ground mounted whip because the bottom section of the whip is closest to the ground, and so has more capacitance to the ground. Next point is that raising the coil up in the whip improves current distribution. The high voltage which boosts capacitive current is moved farther away from the earth or ground plane. Lower voltage below the coil has less capacitive current between the earth and whip than before the coil was boosted. Current below the coil is now almost uniform. Table 1 gives coil values for base loading and center loading an 8-ft whip in amateur bands between 1.8 and 29 MHz. There is a CD-ROM attached to the rear cover of the ARRL Antenna Book which includes a program, MOBILE.EXE, for optimization of coil placement. There is much practical information in this Antenna Book section. I`d speculate it was tried and proved useful before it was included in the Antenna Book. Has anyone found faults? Best regards, Richard Harrison, KB5WZI |
Roy Lewallen wrote:
I did read what you said. You said that it wouldn't exhibit a phase shift if placed at a current maximum. I'm sorry, there is a misunderstanding that is my fault. When I say "current is the same.", I'm implying magnitude only. That's a convention left over from my college days and may not be a convention any longer. If I said anything at all about phase, I used the word, "phase", in my posting. So I will stop omitting the word, "magnitude", when I am talking about magnitude. So do a system reset on what you think I said. There is always a phase shift through a real-world inductor. Whether it can be measured accurately is another matter. When I said: "If the current maximum point is located in the middle of a coil, the current (implied magnitude) in and out of a coil will be equal.", I was implying current magnitude only. I didn't imply or say anything about phase unless I used the word, "phase" in the sentence. I also have not said anything about the phase of the currents into and out of your toroidal inductance except to say it replaces approximately 18 degrees of antenna. The current at the base of a short vertical antenna is at its maximum there. So now if you're saying that it *won't* exhibit a phase shift if placed at the base of a short antenna, let's try this. As you can see above, I never said anything like that. Suppose I remount my antenna to eliminate the shunting effect of the mounting, and do my measurements at 3.8 MHz as before. Suppose the base input Z is, say, 35 -j380. You choose any inductor value you'd like, that will best illustrate your method, and tell me what output to input current ratio to expect. I am still leery about your ability to separate small phase shifts from noise. We need to make the inductor large enough to ensure the phase shift measurements are above the noise level. I have no disagreement that a "bugcatcher" coil, or any coil of physically significant size, will exhibit a phase shift and magnitude change of current from one end to the other. Huh?????? I thought that was what the argument was all about. What triggered this whole discussion was W8JI's alleged assertion that a loading coil like a bugcatcher doesn't affect the current at all. Where we disagree is that you believe that a physically very small inductor will also exhibit this. I don't. The effect of a very small inductor may be too small to measure in the presence of strong fields and noise. Ask yourself, at exactly what value of inductor does the phase shift completely disappear? +j1? +j10? +j100? +j1000? What is the crossover point from some phase shift to zero phase shift? Can you measure a phase shift of 0.1 degree at HF? Zero phase implies faster than light propagation through the coil. -- 73, Cecil, W5DXP |
"Roy Lewallen" wrote in message ... I did read what you said. You said that it wouldn't exhibit a phase shift if placed at a current maximum. The current at the base of a short vertical antenna is at its maximum there. So now if you're saying that it *won't* exhibit a phase shift if placed at the base of a short antenna, let's try this. Naturally, the inductance of the coil and the resistance of the circuit determine how much of a phase shift there will be. But the amount of resulting change in current magnitude will depend on where on the cosine curve this shift occurs. A 10 degree phase shift from 40 to 50 degrees generates almost an order of magnitude greater change in current that it does shifting from 0 to 10 degrees. Obviously, the closer the center of the coil is to zero (or 180) degrees, the smaller the resulting differential in current across the coil. 73, Jim AC6XG |
Hopefully your skills extend beyond looking up values in books, to being
able to do actual calculations. Given the measured antenna impedance I reported and the inductor I used, what should we expect as the ratio (magnitude and phase) of output to input current at the two inductor leads? Roy Lewallen, W7EL Richard Harrison wrote: Roy, W7EL wrote: "Other predictions would be welcome, too, such as Yuri`s based on the "missing antenna length" theory of inductor current." It`s desirable to resonate a standing-wave antenna to reduce impediment to antenna current. In the 19th edition of the ARRL Antenna Book, there is a section on "Base Loading and Center Loading" beginning on page 16-4. First point is that current is not uniform in a ground mounted whip because the bottom section of the whip is closest to the ground, and so has more capacitance to the ground. Next point is that raising the coil up in the whip improves current distribution. The high voltage which boosts capacitive current is moved farther away from the earth or ground plane. Lower voltage below the coil has less capacitive current between the earth and whip than before the coil was boosted. Current below the coil is now almost uniform. Table 1 gives coil values for base loading and center loading an 8-ft whip in amateur bands between 1.8 and 29 MHz. There is a CD-ROM attached to the rear cover of the ARRL Antenna Book which includes a program, MOBILE.EXE, for optimization of coil placement. There is much practical information in this Antenna Book section. I`d speculate it was tried and proved useful before it was included in the Antenna Book. Has anyone found faults? Best regards, Richard Harrison, KB5WZI |
So, you've retracted your prediction. What's your new one, then?
Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: I did read what you said. You said that it wouldn't exhibit a phase shift if placed at a current maximum. I'm sorry, there is a misunderstanding that is my fault. When I say "current is the same.", I'm implying magnitude only. That's a convention left over from my college days and may not be a convention any longer. If I said anything at all about phase, I used the word, "phase", in my posting. So I will stop omitting the word, "magnitude", when I am talking about magnitude. So do a system reset on what you think I said. There is always a phase shift through a real-world inductor. Whether it can be measured accurately is another matter. When I said: "If the current maximum point is located in the middle of a coil, the current (implied magnitude) in and out of a coil will be equal.", I was implying current magnitude only. I didn't imply or say anything about phase unless I used the word, "phase" in the sentence. I also have not said anything about the phase of the currents into and out of your toroidal inductance except to say it replaces approximately 18 degrees of antenna. The current at the base of a short vertical antenna is at its maximum there. So now if you're saying that it *won't* exhibit a phase shift if placed at the base of a short antenna, let's try this. As you can see above, I never said anything like that. Suppose I remount my antenna to eliminate the shunting effect of the mounting, and do my measurements at 3.8 MHz as before. Suppose the base input Z is, say, 35 -j380. You choose any inductor value you'd like, that will best illustrate your method, and tell me what output to input current ratio to expect. I am still leery about your ability to separate small phase shifts from noise. We need to make the inductor large enough to ensure the phase shift measurements are above the noise level. I have no disagreement that a "bugcatcher" coil, or any coil of physically significant size, will exhibit a phase shift and magnitude change of current from one end to the other. Huh?????? I thought that was what the argument was all about. What triggered this whole discussion was W8JI's alleged assertion that a loading coil like a bugcatcher doesn't affect the current at all. Where we disagree is that you believe that a physically very small inductor will also exhibit this. I don't. The effect of a very small inductor may be too small to measure in the presence of strong fields and noise. Ask yourself, at exactly what value of inductor does the phase shift completely disappear? +j1? +j10? +j100? +j1000? What is the crossover point from some phase shift to zero phase shift? Can you measure a phase shift of 0.1 degree at HF? Zero phase implies faster than light propagation through the coil. -- 73, Cecil, W5DXP |
The feedpoint impedance without the inductor was 35 - j185. The inductor
was 0.6 + j192. Sorry, I had left it up to you to add the two together, to get 35.6 + j7 ohms. It would be nice to have something better than a ballpark value, since I think I can get the ratio of output to input to within a couple of percent or so, and resolve two or three degrees of phase shift. Anything more precise than that, though, I won't be able to resolve anyway. Which is why the next test might be better, since you'll be choosing the inductor size to make the shift very apparent. Won't you? So what's your new, more precise prediction of the output:input current ratio (magnitude and phase) for the system I did measure? Incidentally, I've now also made a measurement using the same system on the bench, substituting a series RC with the same Z as the antenna feedpoint for the antenna. You've stated that you expect to see a difference between this setup and the antenna (the former being "lumped" and the latter "distributed"). Do you, Yuri? How about you, Richard? If so, what should I be seeing for the ratio of output:input current in the lumped setup? Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: and Cecil's, that the output current should equal the current, both in phase and magnitude. Hold the presses! That was a rounded off ballpark value. You haven't told us what the feedpoint impedance is yet so an accurate estimate is impossible so far. Is the feedpoint impedance 35.6+j8? Is that the impedance into which you are shoving one amp? |
Roy Lewallen wrote:
So, you've retracted your prediction. What's your new one, then? No, you misunderstood my prediction. I cannot make an accurate prediction until you tell us the feedpoint impedance of the antenna including the coil. Is it 34.6+j8 or what? You have told us the feedpoint impedance of the antenna without the coil and the impedance of the coil but we still don't have an accurate measurement for the feedpoint impedance of the antenna including the coil. Did you measure it? If not, any estimate is not going to be very accurate. -- 73, Cecil, W5DXP |
Jim, it sounds like you're firmly in the camp that believes that a phase
and/or magnitude shift will occur from one terminal to the other of a physically very small inductor. Your participation in the predictions will be welcome. Perhaps you can also propose an inductor I can put at the base of a short antenna that would guarantee a large phase shift which would be large and easily seen in a measurement. Roy Lewallen, W7EL Jim Kelley wrote: "Roy Lewallen" wrote in message ... I did read what you said. You said that it wouldn't exhibit a phase shift if placed at a current maximum. The current at the base of a short vertical antenna is at its maximum there. So now if you're saying that it *won't* exhibit a phase shift if placed at the base of a short antenna, let's try this. Naturally, the inductance of the coil and the resistance of the circuit determine how much of a phase shift there will be. But the amount of resulting change in current magnitude will depend on where on the cosine curve this shift occurs. A 10 degree phase shift from 40 to 50 degrees generates almost an order of magnitude greater change in current that it does shifting from 0 to 10 degrees. Obviously, the closer the center of the coil is to zero (or 180) degrees, the smaller the resulting differential in current across the coil. 73, Jim AC6XG |
Yes, I did measure it. But how much difference in your prediction would,
say, +/- 10 ohms of reactance make -- I can't guarantee my measurements any closer than that in any case. So why not make your predictions for 35 - j2 and 35 + j18, and let's see just how much difference it makes. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: So, you've retracted your prediction. What's your new one, then? No, you misunderstood my prediction. I cannot make an accurate prediction until you tell us the feedpoint impedance of the antenna including the coil. Is it 34.6+j8 or what? You have told us the feedpoint impedance of the antenna without the coil and the impedance of the coil but we still don't have an accurate measurement for the feedpoint impedance of the antenna including the coil. Did you measure it? If not, any estimate is not going to be very accurate. -- 73, Cecil, W5DXP |
Cecil Moore wrote in message ...
Roy Lewallen wrote: I did read what you said. You said that it wouldn't exhibit a phase shift if placed at a current maximum. I'm sorry, there is a misunderstanding that is my fault. When I say "current is the same.", I'm implying magnitude only. That's a convention left over from my college days and may not be a convention any longer. If I said anything at all about phase, I used the word, "phase", in my posting. So I will stop omitting the word, "magnitude", when I am talking about magnitude. So do a system reset on what you think I said. There is always a phase shift through a real-world inductor. Whether it can be measured accurately is another matter. When I said: "If the current maximum point is located in the middle of a coil, the current (implied magnitude) in and out of a coil will be equal.", I was implying current magnitude only. I didn't imply or say anything about phase unless I used the word, "phase" in the sentence. I also have not said anything about the phase of the currents into and out of your toroidal inductance except to say it replaces approximately 18 degrees of antenna. The current at the base of a short vertical antenna is at its maximum there. So now if you're saying that it *won't* exhibit a phase shift if placed at the base of a short antenna, let's try this. As you can see above, I never said anything like that. Suppose I remount my antenna to eliminate the shunting effect of the mounting, and do my measurements at 3.8 MHz as before. Suppose the base input Z is, say, 35 -j380. You choose any inductor value you'd like, that will best illustrate your method, and tell me what output to input current ratio to expect. I am still leery about your ability to separate small phase shifts from noise. We need to make the inductor large enough to ensure the phase shift measurements are above the noise level. I have no disagreement that a "bugcatcher" coil, or any coil of physically significant size, will exhibit a phase shift and magnitude change of current from one end to the other. Huh?????? I thought that was what the argument was all about. What triggered this whole discussion was W8JI's alleged assertion that a loading coil like a bugcatcher doesn't affect the current at all. Where we disagree is that you believe that a physically very small inductor will also exhibit this. I don't. The effect of a very small inductor may be too small to measure in the presence of strong fields and noise. Ask yourself, at exactly what value of inductor does the phase shift completely disappear? +j1? +j10? +j100? +j1000? What is the crossover point from some phase shift to zero phase shift? Can you measure a phase shift of 0.1 degree at HF? Zero phase implies faster than light propagation through the coil. Cecil Is not the group straying somewhat from the initial discussion on E ham? That discussion that started all this was with regard to a whip antenna and the coil on it. Why has the discussion been pulled away from the original coil to a torroid of all things ? The basic discussion was on a inductor of length which can be considered a major part of the antennas length. It is this situation that Yuri stated that he measured a current difference at the inductors end, to which Tom replied that it was probably capacitive coupling to ground, so even Tom did not dispute the possibility of a current drop per Yuri's measurements ! Maneuvering to to a toroid style of inductance is placing darkness over the original statement, probably to prevent the application of light by others. Now the playing on words is intruding again ( phase ) so I suggest that in that atmosphere one should relate to a inductive network to prevent the accusation of a 'pure' inductance which is a whole different ball game as conditions imposed in the solution of such a network is certainly not the same. Best regards and have fun. Please do not pull into the discussion the root of minus one or all the answers given by the application of a quadratic equation since many will go crazy by taking them to the lab and measuring them. Grin Art |
Roy Lewallen wrote:
So what's your new, more precise prediction of the output:input current ratio (magnitude and phase) for the system I did measure? I don't see any way to make a precise prediction given that the antenna doesn't exhibit the expected characteristics of a 33' vertical on 75m. I don't see that your experiment makes a lot of difference now that you have said that a 75m bugcatcher coil causes a current magnitude change and a phase shift. That was the original argument. -- 73, Cecil, W5DXP |
Art Unwin KB9MZ wrote:
Is not the group straying somewhat from the initial discussion on E ham? That discussion that started all this was with regard to a whip antenna and the coil on it. Why has the discussion been pulled away from the original coil to a torroid of all things ? Because someone can't stand to be wrong? -- 73, Cecil, W5DXP |
So your math is good only for an ideal antenna? That's a sad state of
affairs. Ok, let's suppose I build an ideal antenna that's about 33 feet high, with a feedpoint impedance of 35 - j370 ohms at 3.8 MHz. Choose an inductor value and let me know what the output:input current ratio would be for that inductor at the base of the antenna. Assume that the inductor is physically very small. You have such a clear understanding of what's happening, it should be a simple calculation. Then I'll do my best to build the antenna and make the measurement. Or you can. Roy Lewallen, W7EL Cecil Moore wrote: Roy Lewallen wrote: So what's your new, more precise prediction of the output:input current ratio (magnitude and phase) for the system I did measure? I don't see any way to make a precise prediction given that the antenna doesn't exhibit the expected characteristics of a 33' vertical on 75m. I don't see that your experiment makes a lot of difference now that you have said that a 75m bugcatcher coil causes a current magnitude change and a phase shift. That was the original argument. -- 73, Cecil, W5DXP |
Chuckle.
I'm continually amazed at how different our backgrounds are. Whenever I've encountered a complex system I don't understand, I try to begin with a simple system, to make sure I understand it first. Only after I know how a simple one will behave do I have a chance of understanding the more complex one. This is the method adopted by virtually all the capable engineers I've had the pleasure to work with over the years. In contrast, complexity is embraced by people who have a need to conceal a lack of understanding. By resisting simplification and constantly pleading that the system is too complex to analyze, fundamental understanding isn't required, and one can never be shown to be wrong. If the best you can do in any case is to give vague answers and wave hands, it doesn't really make any difference whether you understand it or not -- it's impossible to tell. On the other hand, if it's necessary to actually calculate values (as I've had to do for years as a design engineer) and truly understand what's happening, there's no way I'll be able to do it for a complex system if I can't even do it for a simple one. As for standing to be wrong, I'm willing to post my measurements and my predictions, and be wrong. So far, only Yuri has joined me. And, Art, I'm surprised at your objecting to my bringing up the dreaded complexity of -- gasp -- phase. You should rejoice, because it gives me twice the opportunity to show just how wrong I am. If the small inductor shows a measureable phase shift from input to output, I'll be just as wrong as I'll be if it shows a magnitude change. So I've doubled the odds I'll fall on my face. At the same time, it puts Cecil at no extra risk at all, since he won't venture a prediction of either magnitude or phase, and I feel confident in my assumption that you won't, either. I'm the only one (except Yuri, who has bravely given a range of magnitude values at least) who *can* be wrong, and including phase makes it all the more likely. Surely, that should cheer you up a bit. Roy Lewallen, W7EL Cecil Moore wrote: Art Unwin KB9MZ wrote: Is not the group straying somewhat from the initial discussion on E ham? That discussion that started all this was with regard to a whip antenna and the coil on it. Why has the discussion been pulled away from the original coil to a torroid of all things ? Because someone can't stand to be wrong? -- 73, Cecil, W5DXP |
Roy Lewallen wrote:
So your math is good only for an ideal antenna? That's a sad state of affairs. Heck, I'll just supply you with ten dimensions and virtual photons and see just how well your math works. :-) This discussion has very little to do with math equations. The orbits of the planets got along just fine before man ever walked the earth and came up with the math to explain them. Reality rules! Here's what Einstein said: "One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike ..." Ok, let's suppose I build an ideal antenna that's about 33 feet high, with a feedpoint impedance of 35 - j370 ohms at 3.8 MHz. Choose an inductor value and let me know what the output:input current ratio would be for that inductor at the base of the antenna. Assume that the inductor is physically very small. Why? The argument is/was about bugcatcher coils which are NOT small. Who uses a physically small toroid in his center-loaded mobile antenna? Not that it wouldn't be an interesting experiment. Roy, it appears to me that you are trying to win the last battle after the war is over, like the South did weeks after Lee surrendered. Please feel free to proceed with whatever mission that you are trying to complete. Whatever it is, it is a diversion from the original argument based on W8JI's alleged assertion that the current magnitude and phase doesn't change through an HF mobile antenna's loading coil. That argument has been lost. It appeared that you jumped in and defended W8JI and called everyone who disagreed, "ignorant engineers", or something to that effect. The issue between you and me was settled when you posted that you had no argument with current magnitude and phase changes through HF mobile antenna loading coils. (Now if we can just get W8JI to agree with you.) -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Roy Lewallen wrote in message ...
Chuckle. I'm continually amazed at how different our backgrounds are. Whenever I've encountered a complex system I don't understand, I try to begin with a simple system, to make sure I understand it first. Only after I know how a simple one will behave do I have a chance of understanding the more complex one. This is the method adopted by virtually all the capable engineers I've had the pleasure to work with over the years. In contrast, complexity is embraced by people who have a need to conceal a lack of understanding. By resisting simplification and constantly pleading that the system is too complex to analyze, fundamental understanding isn't required, and one can never be shown to be wrong. If the best you can do in any case is to give vague answers and wave hands, it doesn't really make any difference whether you understand it or not -- it's impossible to tell. On the other hand, if it's necessary to actually calculate values (as I've had to do for years as a design engineer) and truly understand what's happening, there's no way I'll be able to do it for a complex system if I can't even do it for a simple one. As for standing to be wrong, I'm willing to post my measurements and my predictions, and be wrong. So far, only Yuri has joined me. And, Art, I'm surprised at your objecting to my bringing up the dreaded complexity of -- gasp -- phase. You should rejoice, because it gives me twice the opportunity to show just how wrong I am. From my point of view you are rarely wrong and should be admired on how knoweledgable you have become despite insurmountable hardships that make mine a a Sunday morning walk despite the war. I agreed with your posting regarding an inductance but then realised that Yuri was talking about what is really a network and thus he could take measurements. Now I am hoping that Yuri will get a true explanation of what he has observed which in the real world is a circuit containing capacitance,resistance and inductance and where he is unable to separate the parts as you are doing on paper. From an engineering stand point I am not willing to discard fundamentals as you would suggest as their use provides solutions even to one such as I who wasted my younger year by not going to school. My point is that you are playing with Yuri because he used the term inductance instead of a circuit which would then prevented your present tack. For some reason you take offense at that suggestion given in the starting post nd I really do not know why until you come up with an explosive point.. Regards Art If the small inductor shows a measureable phase shift from input to output, I'll be just as wrong as I'll be if it shows a magnitude change. So I've doubled the odds I'll fall on my face. At the same time, it puts Cecil at no extra risk at all, since he won't venture a prediction of either magnitude or phase, and I feel confident in my assumption that you won't, either. I'm the only one (except Yuri, who has bravely given a range of magnitude values at least) who *can* be wrong, and including phase makes it all the more likely. Surely, that should cheer you up a bit. Roy Lewallen, W7EL Cecil Moore wrote: Art Unwin KB9MZ wrote: Is not the group straying somewhat from the initial discussion on E ham? That discussion that started all this was with regard to a whip antenna and the coil on it. Why has the discussion been pulled away from the original coil to a torroid of all things ? Because someone can't stand to be wrong? -- 73, Cecil, W5DXP |
Roy Lewallen wrote:
If the small inductor shows a measureable phase shift from input to output, I'll be just as wrong as I'll be if it shows a magnitude change. And if the small inductor shows a phase shift too small to be measured, you will have invented faster than light transmission because inches per nanosecond is easy to measure nowadays. Heck, my old bench scope will display two nanoseconds per division. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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