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#341
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Can we make a physically small "phase reversing coil" that has 180
degree phase shift between its ends? If so, how? Roy Lewallen, W7EL Richard Harrison wrote: Cecil, W5DXP wrote: "Here is the diagram in 23-21b." Thanks, Cecil. My copy of Kraus is new and I`d not yet read page 824. Kraus says: "The coil may also be thought of as a coiled-up halfwave element." I like his preceding sentence: "Here the elements present a high impedance to the coil which may be resonated without external capacitance due to its distributed capacitance." A "phase reversing coil" does present a 180-degree phase shift between its ends. Best regards, Richard Harrison, KB5WZI |
#342
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Jim Kelley wrote:
"Roy Lewallen" wrote in message ... You've said that because the inductor I chose is something like 4% larger than necessary to resonate the antenna, the magnitude and phase shift from input to output would be very nearly zero (although the reasoning is contrary to conventional electrical circuit theory, and I don't follow it at all). Don't know. Didn't say it. Can't help. I apologize. I looked back at what I thought you had said, and I was mistaken. So what I'm asking for is an inductor value which would exhibit a large enough phase and/or magnitude shift that would be easily seen in a measurement. Do we agree that the amount of differential will depend on the number of 'degrees missing' from the length of the antenna? No. In a few minutes, I'll post a description of a more recent measurement I made that refutes this. Of course, elementary circuit theory refutes it also, which is the basis for my disagreement. Do we agree that the position of the loading coil plays a significant. role in determining how much of a current differential will appear across it? If you're talking about a physically long coil, yes. If you're talking about a physically small coil, no. But if you believe that the amount of antenna the coil "replaces" determines the differential, wouldn't this be true regardless of the placement of the coil in the antenna? I'll be constructing a more ideal 33 foot vertical in the near future, and making similar measurements at 3.8 MHz. So if its feedpoint impedance is, let's say, 35 - j370, what would be the input to output current ratio (magnitude and phase) for a physically very small base inductor of, say, +j300 ohms? If it's very small, then pick an inductor value which would exhibit a substantial inpututput current ratio. Are you going to insist that it be one of these ferrite core jobs, or is it more like ones on a HF6V? Is there something about a "ferrite job" that makes it follow different rules? But the answer is no to both. I insist on using a physically small toroid wound on a powdered iron core. Only after people understand how a physically small inductor works will they have any chance of understanding how a physically long one does. Roy Lewallen, W7EL |
#343
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Today's project was to construct and measure a more idealized antenna.
The antenna is 33 feet high, made of #16 insulated wire. I put out 23 radials on the surface of the wet ground. Radials were of various lengths, most about 30 feet long. The feedpoint impedance of the antenna, measured with a GR bridge, was 15.8 - j437 ohms at 3.8 MHz. Allowing 3% lengthening effect for insulation, EZNEC says a lossless vertical of that height and diameter should have an input Z of 7.5 - j478. 8.3 ohms loss resistance is reasonable for that number of radials, and the somewhat lower than predicted reactance is likely due to the fact that the radial wires were grouped together as they came up a few inches to the antenna base, and not immediately coming in contact with the ground. That would add a bit of inductive reactance. I wound an inductor on a T-106-6 core as before, but with more turns, for a measured Z of 1.3 + j387 ohms. After putting it in series with the antenna at the base, the base impedance measured 17.1 - j54 ohms. This is only 4 ohms from the expected reactance, and spot on the expected resistance, so measurements are consistent. Analyzing verticals with EZNEC, made from #16 wire at 3.8 MHz, shows that: -- An antenna 63.2' high is resonant. -- An antenna 35.9' high has a feedpoint reactance of -j437 ohms. -- An antenna 59.35' high has a feepoint reactance of -j54 ohms. With a resonant height of 63.2', you could say that 63.2' is "90 electrical degrees" as far as the antenna is concerned. So you might say that my inductor has "replaced 33.4 electrical degrees" of the antenna. Using Yuri's cosine rule, we should then expect the inductor output current to be cos(33.4 deg) times the input current, or 16.5% less. Also, we should expect to see those 33 degrees of "replaced antenna" as phase shift from the input to the output of the inductor. That is, the current change from the input to output of the inductor is the same as it would be for the portion of the antenna it "replaces". (I think Jim Kelley subscribes to this theory also, but I'm not sure.) In contrast, conventional electrical circuit theory predicts no current difference between the input and output for a physically very small inductor with no radiation or stray coupling. I saw about 3% in the previous measurement, which I believe can be attributed to stray capacitance. So I predicted that we should see about twice that amount with the higher valued inductor used for this experiment (387 vs 192 ohms reactance). I didn't see any measurable phase shift between input and output before, so I didn't expect to see it this time. So for this test, there's quite a difference in predictions for output:input current -- **Yuri's method predicts a reduction of output current magnitude of 16.5% and a phase shift of 33 degrees. **I predict around 6% magnitude reduction (due to stray C) and no measurable phase shift (less than 2 or 3 degrees). I have very high confidence that my measurements are good enough to resolve the difference between these two possibilities. Would anyone care to comment before I post the measurement results? And, Yuri, please correct me if I've misinterpreted your theory. Roy Lewallen, W7EL |
#344
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Roy, W7EL wrote:
"Can we make a physically small "phase reversing coil" that has 180 degree phase shift between its ends? If so, how?" Yes. Kraus was discussing collinear arrays composed of 1/2-wave elements interconnected by phase inverters to keep the currents in all elements in-phase, that is, flowing in the same direction. More than the phase delay of the coil is involved. Its self-capacitance is involved in making a parallel resonant circuit at the operating frequency. The phase relations would be the same for a smaller inductance shunted with a larger capacitance. Two reasons for using self resonance; simplicity and wider bandwidth with the low-C circuit. These parallel resonant circuits replace short-circuit 1/4-wave stubs in some collinears. Best regards, Richard Harrison, KB5WZI |
#345
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I apologize if the reason for my delay in posting measurement results is
seen as being to embarrass people. That's not at all the purpose. The intent is simply to force people to make numerical predictions based on their theories, rather than explaining the results after the fact. As it turns out, Yuri is the only one confident enough of his theory to make a numerical prediction(*). I happen to believe it's wrong, but by making it he's earned my respect. A theory can be tested only if it predicts results which can be tested. Whether it turns out to be right or wrong, we learn from it. Those who've waffled and dodged the issue aren't in my opinion worthy of the respect Yuri is. When all this is done, I hope that readers come away with some assurance that circuit theory does work and can be applied to antenna problems -- provided that the assumptions made for the components are valid. If all that's taken away is a feeling that I've been doing this to try and embarrass people, then it's been worse even than a monumental waste of time. I really did have other things I wanted to do today besides make antenna measurements, and I spent the time doing it only in the hope that it would open some eyes. Roy Lewallen, W7EL (*) I've really solicited predictions only from people who don't agree with conventional circuit theory, and believe that there will be a difference in current from input to output. So there are also a number of people who agree with me that conventional circuit theory holds, but haven't explicitly made a prediction. Richard Clark wrote: . . . But such is the gamesmanship that is being conducted, from the start. The withholding of data to embarrass correspondents is not uncommon. Lord knows how many I've embarrassed with simpler topics (the current crew being only a subset). However, I generally restrain my participation such that those threads are smaller. Otherwise the posting of: . . . |
#346
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Reg Edwards wrote:
A design which 'exceeds' specified performance is as poor as one which 'under exceeds'. It would have cost money and space to add the circuits to bring the measurable jitter up to the RS232 specification allowable threshold. You really think I should have done that? -- 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! =----- |
#347
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Roy Lewallen wrote:
Now, that's quite an insult, based on a total lack of information about my career and what I've accomplished. Why is it OK for you to insult my engineering capabilities but not vice versa? How does it feel? I'm going to do my best to ignore Cecil's postings from here on. They're abusive and insulting. Yours were abusive and insulting first and second. I did this one just to let you know how your insults feel. If you will stop saying things to me like, "I am continually amazed at how truly ignorant some engineers are ...", I will not feel the need to retaliate. -- 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! =----- |
#348
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Roy Lewallen wrote:
Can we make a physically small "phase reversing coil" that has 180 degree phase shift between its ends? If so, how? Why are you so hung up on physically small coils? The subject is center-loading coils on mobile antennas, like bugcatchers. -- 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! =----- |
#349
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Roy Lewallen wrote:
When all this is done, I hope that readers come away with some assurance that circuit theory does work and can be applied to antenna problems -- provided that the assumptions made for the components are valid. Roy, isn't everything moot after Kraus tells us that an antenna coil can cause a 180 degree phase reversal? Plus his graph of current in a loaded antenna that shows a step function in the current at the loading coils? The entire purpose of this discussion was to determine if the following statement, allegedly made by W8JI, is true or false. "This is in any book, including the ARRL Handbook. If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." That's the very clear statement that was questioned by Yuri. And you have already proved it not to be true even with your toroidal coil. Incidentally, given a 180 degree phase reversing coil, the current is flowing into both ends at the same time. -- 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! =----- |
#350
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Would anyone care to comment before I post the measurement results? And, Yuri, please correct me if I've misinterpreted your theory. Roy Lewallen, W7EL It is not my theory. My argument with W8JI and his followers: is the current in typical loading coil in quarter wave radiator same at both ends or does it drop with distance from the feedpoint. I have made temperature observations, W9UCW measured the difference, W5DXP provided some explanation. Based on Cecils analysis of data you provided, and on my understanding of the phenomena I guestimated drop in current in your setup. No theory, no mathematical procedure (yet) just attempt (using degrees replaced by coil in a radiator) at explanation of what is happening. I will measure things myself, try to verify previous measurements and then come up with conclusions and "theory". So far Cecils (and ON4UN book) theory seems to be closest to the truth. As far as your measurements, it appears that you are trying to use the worse case extreme situation (feed point, toroid) to prove your case. Why don't you use thermo ammeters or current probe without leads and normal coil and do it on typical mobile whip antenna. Here is the info on homebrew current probe: http://www.isd.net/~lyle/currprob/currprob.htm I am going to build one too, it is handy to check the current while sliding along the radiator, which easier than inserting ammeter. I posted my 7 points, so far not one argument against, had few agreements. What's this guessing game anyway? Why don't you try to prove that W9UCW measurements are off the rocker? Yuri, K3BU |
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