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Roy Lewallen wrote:
In the absence of radiation, all the charge that flows into an inductor has to flow out, a point I and (much more eloquently) Ian and others have tried to make, but which is lost on some of the most vocal contributors to the newsgroup. This concept doesn't seem to fit neatly into some of the preconceived theories, so is simply being ignored. In the end, any theory that truly explains observed phenomena has to work with physically vanishingly small inductors, for which the currents in and out must be equal, as well as larger ones. What a lot of people are missing is that a relatively constant forward current flows into the bottom of the coil and out the top. That current is reflected from the tip of the antenna and a relatively constant reflected current flows into the top of the coil and out the bottom. The current at the bottom and top of the coil is the phasor sum of those two currents and cannot help but be different for the typical mobile bugcatcher antenna. The net total current is the sum of those two currents and even if the component currents are constant, their phasor sum will differ because the phase of the component currents are changing in opposite directions across the bugcatcher coil. The cosine current distribution on a standing-wave antenna is just a standing wave caused by the superposition of forward and reflected current. For a vanishingly small inductor, the phase shift through the inductor is near zero and indeed results in the same current on both sides of the inductor so the theory works just fine. -- 73, Cecil http://www.qsl.net/w5dxp "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines ... Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents If and Ib ..." _Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489 ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Gene Fuller wrote:
Yes, but Tom modified his statement shortly thereafter. Tom admitted his statement was wrong? When and where? -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Cecil,
You are using fightin' words, but I will play along. (I said "modified", not "wrong".) I followed the URL quoted on Yuri's web site, http://www.eham.net/articles/5998 It appears to me that W8JI made his first comment on this topic on August 7, 2003. The "ALWAYS" exchange with Yuri took place on August 10. Over the next week there were numerous messages. W8JI explained how there could be a current change if the coil exhibited capacitive coupling, yada, yada, yada. On August 17 W8JI posted a summary which clearly outlined his position. This is essentially the same position that has been detailed on his web site. I don't care one way or the other about just how the personality battle started. You may see it differently than I do. However, it seems pretty clear, with the exception of one hyperbolic "always" comment, W8JI fully understands that the current can be different at the ends of a real-world coil. I am not going to engage in a semantics battle with you or anyone else. If you don't agree with my interpretation that's fine with me. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Yes, but Tom modified his statement shortly thereafter. Tom admitted his statement was wrong? When and where? |
Wes, N7WS wrote:
"Could you describe in more detail what the "pictures" are saying." My edition of "Low-Band DXing" is copyrighted in 1994. The "pictures" are graphs of current distribution on (6) different 1/4-wave vertical antennas: 1) full size 2) base loaded 1/8-wave of wire 3) capacitive hat loaded 1/8-wave 4) center loaded 1/16-wave wire above & below 5) continuously loaded (all coil) antenna 6) combined top and base loading of short vertical The current distribution graphs are in a section (2.1) titled "Radiation Resistance" In every case , the current tapers lower from feedpoint end to the loading coil`s end nearer the open end of the antenna. Devoldere discusses the various loading methods. Devoldere says the full size 1/4-wave vertical has a radiation resistance of 36.6 ohms. His 50% length base loaded example has a radiation resistance of 6.28 ohms. His top loaded example has a radiation resistance of 18.3 ohms. His center loaded example has a radiation resistance of 22.1 ohms Radiation resistance is our goal. Radiation resistance versus total resistance (radiation+loss resistances) is the antenna efficiency. The all coil antenna has a calculated radiation resistance of 16.4 ohms. The point is that all loading coils show less current at the top than at the bottom because that`s the way it is, superposition. Now that we`ve been re-Bushed, I`ve had time to answer Wes` question. Best regards, Richard Harrison, KB5WZI |
Cecil,
I cannot speak directly for Tom Donaly, but you and I are about 99% in DISagreement over physics. One more time: Current, charge, voltage, E-field, and H-field are different physical entities. They are related, but they are not interchangeable. No amount of E-field, H-field, or voltage can create or destroy charge. Current is the movement of charge. At any point in space that charge must either keep moving (Kirchhoff's current law) or it must be stored (continuity equation). There is absolutely no other choice, period. Your traveling wave/standing wave model is intuitive, but otherwise useless. Many authors reference such a model, but no one seems to use it for serious calculations. You have started quoting Balanis: "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines ... Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents If and Ib ..." _Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489 I do not have easy access to the Balanis book at this time. Does he go on to actually perform antenna calculations such as actual current distributions and radiated fields? I found the table of contents for this edition of his book, and it appears that Chapter 10 is a chapter on traveling wave antennas, not basic dipoles. If so, then it is likely that Balanis is merely trying to tie the entire world of antennas together to give a warm and fuzzy feeling to the reader. Every detailed professional treatment of antenna theory and modeling I have found starts with Maxwell's equations, and quickly gets immersed in integral equations, Green's functions, and other messy stuff. Why would people do this if the mere application of a couple of traveling waves would provide the correct answers? Do you have a reference to an analytic treatment using the traveling wave model that could give results comparable to NEC2? If so, I would sure like to find that reference. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Antennas work the same way. Any change in current along the antenna must be accompanied by a change in stored charge. The net (total) current on a standing-wave antenna is the phasor sum of the forward current and reflected current and can change simply because it is part of a standing wave. The change in net current at the tip of a standing-wave antenna simply means that the energy has moved from the H-field into the E-field. |
Gene Fuller wrote:
On August 17 W8JI posted a summary which clearly outlined his position. This is essentially the same position that has been detailed on his web site. Point is, W8JI has never retracted his false statement. What he has missed is that all those effects he lists affect both the forward and reflected currents on a standing-wave antenna. The major effect in the change in NET current is simply the superposition of the forward and reflected waves with their differing phases from end to end in the antenna. -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Gene Fuller wrote:
Cecil, I cannot speak directly for Tom Donaly, but you and I are about 99% in DISagreement over physics. One more time: Current, charge, voltage, E-field, and H-field are different physical entities. They are related, but they are not interchangeable. No amount of E-field, H-field, or voltage can create or destroy charge. Current is the movement of charge. At any point in space that charge must either keep moving (Kirchhoff's current law) or it must be stored (continuity equation). There is absolutely no other choice, period. Your traveling wave/standing wave model is intuitive, but otherwise useless. Many authors reference such a model, but no one seems to use it for serious calculations. You have started quoting Balanis: "The current and voltage distributions on open-ended wire antennas are similar to the standing wave patterns on open-ended transmission lines ... Standing wave antennas, such as the dipole, can be analyzed as traveling wave antennas with waves propagating in opposite directions (forward and backward) and represented by traveling wave currents If and Ib ..." _Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489 I do not have easy access to the Balanis book at this time. Does he go on to actually perform antenna calculations such as actual current distributions and radiated fields? I found the table of contents for this edition of his book, and it appears that Chapter 10 is a chapter on traveling wave antennas, not basic dipoles. If so, then it is likely that Balanis is merely trying to tie the entire world of antennas together to give a warm and fuzzy feeling to the reader. Every detailed professional treatment of antenna theory and modeling I have found starts with Maxwell's equations, and quickly gets immersed in integral equations, Green's functions, and other messy stuff. Why would people do this if the mere application of a couple of traveling waves would provide the correct answers? Do you have a reference to an analytic treatment using the traveling wave model that could give results comparable to NEC2? If so, I would sure like to find that reference. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: Antennas work the same way. Any change in current along the antenna must be accompanied by a change in stored charge. The net (total) current on a standing-wave antenna is the phasor sum of the forward current and reflected current and can change simply because it is part of a standing wave. The change in net current at the tip of a standing-wave antenna simply means that the energy has moved from the H-field into the E-field. As usual, Cecil is very selective of his quotes. Balanis uses a highly mathematical approach in most of his book, supplemented by many graphs and charts. Cecil's quote, like his quote of Tom Rauch on loading coils is only a very small part of the total. 73, Tom Donaly, KA6RUH |
Gene, W4SZ wrote:
"Do you have a reference to an analytic treatment using the traveling wave model that could give results comparable to NEC2?" NEC2 must agree with reality else it is worthless. Terman agrees with Balanis and is only wrong when theory is revoked. Terman says on page 866 of his 1955 edition: "A wire antenna is a circuit with distributed constants; hence the current distribution in a wire antenna that results from the application of a localized voltage follows the principles discussed in Chap. 4, and depends upon the antenna length, measured in wavelengths; the terminations at the ends of the antenna wire; and the losses in the system. The current distribution is also affected by the ratio of wire length to diameter in situations where the antenna is unusually thick. (see Kraus, Schelknoff, and Friis) Under most circumstances, the losses are sufficiently low and the ratio of wire length to diameter sufficiently great so that to a first approximation the current distribution can be taken as that for a line with zero losses; it then has the characteristics discussed in Sec. 4-5." Sec. 4-5 is titled: "The Effect of Attenuation on Voltage and Current Distribution - Lossless Lines" This is in Chapter 4, "Transmission Lines". Best regards, Richard Harrison, KB5WZI |
Richard,
What in the world are you babbling about???? Nothing I wrote conflicts with Terman or Balanis. Did you see a ghost message from me that I did not write? 73, Gene W4SZ Richard Harrison wrote: Gene, W4SZ wrote: "Do you have a reference to an analytic treatment using the traveling wave model that could give results comparable to NEC2?" NEC2 must agree with reality else it is worthless. Terman agrees with Balanis and is only wrong when theory is revoked. Terman says on page 866 of his 1955 edition: "A wire antenna is a circuit with distributed constants; hence the current distribution in a wire antenna that results from the application of a localized voltage follows the principles discussed in Chap. 4, and depends upon the antenna length, measured in wavelengths; the terminations at the ends of the antenna wire; and the losses in the system. The current distribution is also affected by the ratio of wire length to diameter in situations where the antenna is unusually thick. (see Kraus, Schelknoff, and Friis) Under most circumstances, the losses are sufficiently low and the ratio of wire length to diameter sufficiently great so that to a first approximation the current distribution can be taken as that for a line with zero losses; it then has the characteristics discussed in Sec. 4-5." Sec. 4-5 is titled: "The Effect of Attenuation on Voltage and Current Distribution - Lossless Lines" This is in Chapter 4, "Transmission Lines". Best regards, Richard Harrison, KB5WZI |
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