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#301
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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! =----- |
#302
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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! =----- |
#303
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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! =----- |
#304
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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 |
#305
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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 |
#306
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"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 |
#307
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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 |
#308
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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 |
#309
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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? |
#310
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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 |
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