|
Richard Clark wrote:
Hence, the first statement above was a troll. Nope, just a statement of fact, contradicting W8JI's assertion that the current has to be the same at both ends of a coil in order to satisfy Kirchhoff's laws. I'm finding it hard to ascertain which side you are on, Richard - reality or W8JI's? Come to think of it, the only thing upon which you have ever disagreed with me is my style, not my technical assertions. -- 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 =--- |
For those who really want to learn
about loading coils on small antennas, go to Tom Rauch's web page and learn how a real engineer deals with the problem. 73, Tom Donaly, KA6RUH Yea, that current across the coil is constant. Can you specify what engineering degree Tom has, from what school? Yuri |
On Wed, 03 Nov 2004 16:53:00 -0600, Cecil Moore
wrote: reality or W8JI's? Come to think of it, the only thing upon which you have ever disagreed with me is my style, not my technical assertions. |
On Wed, 03 Nov 2004 16:53:00 -0600, Cecil Moore
wrote: Come to think of it, the only thing upon which you have ever disagreed with me is my style, not my technical assertions which side you are on, reality or your own? |
Tom Donaly wrote:
Since when has anyone claimed it's impossible to make a coil that has a non-constant current distribution? Tom, W8JI claimed such in the following quote from eHam.net: "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." Maybe you should catch up on the argument before you expose your ignorance of the argument any farther. Tom's above assertion is what the argument was/is all about. Your posting proves that you are ignorant of what the argument is all about. You guys sure go out of your way to pat yourselves on the back for proving something no one has ever argued about. You are continuing to exhibit your ignorance. W8JI (your hero) asserted the above quotation that the current flowing in one terminal of an inductor "ALWAYS" equals the current flowing out the other terminal. Are you going to back him up on that assertion or not? For those who really want to learn about loading coils on small antennas, go to Tom Rauch's web page and learn how a real engineer deals with the problem. Tom Rauch is the person who made the above assertion of which you are obviously ignorant. Please alleviate your ignorance and get back to us. Do you really believe that, for an inductor, "the current flowing in one terminal ALWAYS equals the current flowing out the other terminal"? It's a simple yes/no question and it's time for you to $hit or get off the pot. -- 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 =--- |
Yuri Blanarovich wrote:
For those who really want to learn about loading coils on small antennas, go to Tom Rauch's web page and learn how a real engineer deals with the problem. Yea, that current across the coil is constant. Can you specify what engineering degree Tom has, from what school? Not only that, can he defend this assertion of Tom Rauch in his response to your posting on eHam.net? "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." Has the definition of "ALWAYS" changed while I wasn't looking????? -- 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 =--- |
Richard Clark wrote:
Cecil Moore wrote: Come to think of it, the only thing upon which you have ever disagreed with me is my style, not my technical assertions which side you are on, reality or your own? The aliens instructed me to deliver this knowledge to earthlings. -- 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 =--- |
"My patience is getting thin" was also a joke. Seems it fell flat.
|
On Wed, 03 Nov 2004 17:32:22 -0600, Cecil Moore
wrote: The aliens instructed me to deliver this knowledge to earthlings. Any Eric Cartman DNA in your bloodline? |
Cecil Moore wrote:
Tom Donaly wrote: Since when has anyone claimed it's impossible to make a coil that has a non-constant current distribution? Tom, W8JI claimed such in the following quote from eHam.net: "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." Maybe you should catch up on the argument before you expose your ignorance of the argument any farther. Tom's above assertion is what the argument was/is all about. Your posting proves that you are ignorant of what the argument is all about. You guys sure go out of your way to pat yourselves on the back for proving something no one has ever argued about. You are continuing to exhibit your ignorance. W8JI (your hero) asserted the above quotation that the current flowing in one terminal of an inductor "ALWAYS" equals the current flowing out the other terminal. Are you going to back him up on that assertion or not? For those who really want to learn about loading coils on small antennas, go to Tom Rauch's web page and learn how a real engineer deals with the problem. Tom Rauch is the person who made the above assertion of which you are obviously ignorant. Please alleviate your ignorance and get back to us. Do you really believe that, for an inductor, "the current flowing in one terminal ALWAYS equals the current flowing out the other terminal"? It's a simple yes/no question and it's time for you to $hit or get off the pot. Go to Tom's home page and read _everything_ he wrote about loading coils and come back here and tell us what he really thinks. 73, Tom Donaly, KA6RUH |
"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal." I think that is true. If you define current as electron flow, then the fields and radiation that a large coil may be subjected to, will not increase or decrease the number of electrons that the coil contains. As such, the amount of electrons entering the base of the coil, will equal the same number exiting the coil, with time displacement. Consider a large physically long capcitor, with multiple plates. One can use this as a loading element. There is no electron flow between plates. However there is "displacement" current between the plates that has no physical meaning. Now what? The capacitor will be just affected as a coil. So, from the conservation of electron flow I don't know what to believe. 73 Gary N4AST |
|
"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal." I think that is true. If you define current as electron flow, then the fields and radiation that a large coil may be subjected to, will not increase or decrease the number of electrons that the coil contains. As such, the amount of electrons entering the base of the coil, will equal the same number exiting the coil, with time displacement. I think you've just proven that all antennas must have a constant current distribution on their driven element... the same argument can probably be made about a piece of straight wire! More generally: I'd like to propose a thought experiment, which I think may cause you to reconsider your conclusions. The experiment: start with a straight length of wire 1/4 wavelength long (minus a bit) at a frequency of interest. Install it over an infinite ground plane and feed it at the base. You've got a resonant "1/4 wavelength" monopole. I think most people will agree that the net-current distribution in said monopole is tolerably close to being a cosine function - highest at the feedpoint, and lowest near the tip. Mark two positions on the wire, 1/3 and 2/3 of the way along its length. Consider the three sections of wire to be the "base", "mid", and "tip" sections. I think most people will agree that the net currents at the two ends of the "mid" section are not equal. We haven't changed the cosine-like current distribution by simply marking the third-of-the- way points. Now... take the "2/3" point, and pull it back (or down) towards the base of the antenna, by some small amount... say, 1% of the length of the "mid" section. Leave the "1/3" point right where it was. There's now a small amount of slack in the "mid" wire. Shape the "mid" section into a small-diameter helix, with uniform spacing between the turns, so that the helixing of the wire just takes up the slack. The antenna has now been shortened slightly, and some inductance has been added to the "mid" section. Add or subtract wire at the end of the "tip" to bring the antenna back into resonance. Now... are the net currents at the "1/3" and "2/3" points suddenly equal? Or, are they still unequal (but perhaps different from what they were when the mid section was straight)? If unequal, by how much? Now, continue repeating this process... pull the "2/3" point back towards the base by the same amount you did before (1% of the original length of the "mid" section), re-coil the "mid" section into a helix to take up the slack, adjust the length of the "tip" to re-resonate the antenna, and re-evaluate the net currents at the "1/3" and "2/3" points. You can do this "shorten and re-resonate" step a total of 100 times, at which point the "mid" section has no physical length and is a "pure" inductance. [Let me know what page you find it on in the Digi-Key catalog, please!] You may use any strategy you wish for deciding how many turns are in the helix at each step, and what its diameter is at each step, as long as you're consistent and as long as all of the slack is used up each time. So... we now have a total of 101 sets of measurements... all the way from "mid is a straight length of wire" to "mid is a pure inductance having no physical length". We could graph "difference in net current between points 1/3 and 2/3" on the Y axis, and "number of shortening steps taken" along the X axis. Question: exactly how many shorten/re-coil/re-trim steps must we go through, before the net currents at the two ends of the mid-section / helix / coil become the same (mathematically identical, assuming zero resistance in the wire)? -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
|
Gary,
There is not the slightest bit of mystery in the "conservation of electron flow". An important relationship in electromagnetics is the so-called continuity equation. In simple terms this is an expansion of Kirchhoff's current law. It says that any current imbalance at a point in space must be compensated by a change in the stored charge at that point in space. You can see the exact equation in any mid-level text on E&M. This is how capacitors work. Current flows in but does not pass through the gap between the plates. Instead, charge is stored on the plates. It is sometimes convenient to describe this behavior in terms of displacement current through the gap, but of course no electrons actually pass between the capacitor plates. Antennas work the same way. Any change in current along the antenna must be accompanied by a change in stored charge. The antenna acts as a capacitor. Everyone talks about high voltage at the tips of a dipole antenna, but perhaps fewer people understand there is a buildup of stored charge as well. 73, Gene W4SZ JGBOYLES wrote: "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." I think that is true. If you define current as electron flow, then the fields and radiation that a large coil may be subjected to, will not increase or decrease the number of electrons that the coil contains. As such, the amount of electrons entering the base of the coil, will equal the same number exiting the coil, with time displacement. Consider a large physically long capcitor, with multiple plates. One can use this as a loading element. There is no electron flow between plates. However there is "displacement" current between the plates that has no physical meaning. Now what? The capacitor will be just affected as a coil. So, from the conservation of electron flow I don't know what to believe. 73 Gary N4AST |
You have to use some care in applying the conservation of charge to a
system that includes radiation or other manifestations of displacement current. Imagine a capacitor with widely spaced plates. Charge flows into one plate of the capacitor, and an equal amount of charge flows out of the other plate. You have to include both plates in the system when counting up the total amount of charge that's conserved. Similarly, in the case of a radiating coil, you have to count the charge that flows on all nearby and distant conductors as a result of the (field created by) the charge flowing on the inductor. That is, some of the charge that flows into a radiating inductor flows out of other nearby and distant conductors. 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. Roy Lewallen, W7EL JGBOYLES wrote: "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." I think that is true. If you define current as electron flow, then the fields and radiation that a large coil may be subjected to, will not increase or decrease the number of electrons that the coil contains. As such, the amount of electrons entering the base of the coil, will equal the same number exiting the coil, with time displacement. Consider a large physically long capcitor, with multiple plates. One can use this as a loading element. There is no electron flow between plates. However there is "displacement" current between the plates that has no physical meaning. Now what? The capacitor will be just affected as a coil. So, from the conservation of electron flow I don't know what to believe. 73 Gary N4AST |
Yes, but Tom modified his statement shortly thereafter.
Are you guys actually interested in antennas, or is this just some sort of ****ing contest? (Clearly a rhetorical question.) 73, Gene W4SZ Cecil Moore wrote: Tom, W8JI claimed such in the following quote from eHam.net: "If you look at HOW an inductor works, the current flowing in one terminal ALWAYS equals the current flowing out the other terminal." |
Reg Edwards wrote:
"My patience is getting thin" was also a joke. Seems it fell flat. Oops, sorry Reg. I'm guilty of what I accused you of. -- 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 =--- |
Tom Donaly wrote:
Go to Tom's home page and read _everything_ he wrote about loading coils and come back here and tell us what he really thinks. Once again, the argument is not about what is on Tom's web page. The argument is about what Tom asserted in his argument with Yuri on eHam.net. Diverting attention to his web page is just, well, an obvious diversion of the issue. If I say there is no God on eHam.net and don't say it on my web page does that prove I never said it? You said: Since when has anyone claimed it's impossible to make a coil that has a non-constant current distribution? When was August 10, 2003: In Search of 'The Perfect Mobile Antenna': Reply by W8JI on August 10, 2003 Yuri, You are like to call names, insult people, and argue rather than take the time to learn basic electronics. 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. THE VOLTAGE can be (and is) different on each end of the inductor, NOT the current. During that argument, W8JI presented the lumped inductance in EZNEC as proof of the above statement. -- 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:
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. -- 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 =--- |
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 |
|
Gene Fuller wrote:
I cannot speak directly for Tom Donaly, but you and I are about 99% in DISagreement over physics. That's just a straw man, Gene. You school and my school probably taught 99% the same physics. You and I are not that far apart at all. THERE ARE NO CONTRADICTIONS BETWEEN THE PHYSICS YOU USE AND THE CONCEPTS I AM PRESENTING. It only appears that way to you because you haven't taken the time to understand those concepts. Are there standing waves on a standing wave antenna? Are standing waves caused by the superposition of forward and reflected waves? Absolutely nothing new or different there. Current, charge, voltage, E-field, and H-field are different physical entities. They are related, but they are not interchangeable. Straw man alert! I resent any implication that I said they were interchangeable. I agree with you about the above quantities. No amount of E-field, H-field, or voltage can create or destroy charge. Straw man alert! I resent any implication that I said charge could be destroyed. I agree with what you said about 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. EXACTLY! And that is exactly what you and W8JI are missing. The familiar cosine current distribution on a dipole is a standing wave, i.e. the net current in that standing wave is not moving. Therefore, the net current doesn't obey your rules above. The net current is just an artifact of superposition of the forward current wave with the reflected current wave. It is the forward current and reflected current that is moving. Until you and Tom understand the nature of standing-wave antennas, you will never understand the nature of the current(s) through a loading coil installed in the middle of a standing wave antenna. Kurt N. Sterba made the same mistake in this month's Worldradio article. In a standing-wave antenna, the net current doesn't flow and RF current cannot stand still. The current is zero at the tip of a standing wave antenna not because all the energy has been radiated and/or conducted away by displacement currents. The current is zero because all the energy at that point is contained in the E-field. The forward H-field and the reflected H-field cancel each other at the tip of a standing wave antenna. If you really think there is zero energy at the tip of a mobile antenna, please grab it while power is applied. Your traveling wave/standing wave model is intuitive, but otherwise useless. Until you take the time to conceptually understand standing wave antennas, there is absolutely no chance of you understanding what happens when a loading coil is inserted in a standing wave antenna. 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. If what Balanis said is false, please present some proof. 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. There are some problems that do not lend themselves very well to a quantitative analysis. That's why simulation modeling is so popular with antennas and Blackjack. However, the difficulty of a quantitative analysis should not turn your brain into concrete such that you reject the associated qualitative analysis. All of these qualitative concepts are presented in textbooks. I have only quoted a handful of them. -- 73, Cecil, W5DXP |
Cecil,
There is complete contradiction between the physics you have concocted and the real world. I perfectly understand your concepts. They are great for explanations and handwaving, but little else. Until you understand the basics of the first few chapters in any physics (E&M) textbook there is no hope for agreement. Little more for me to say. 73, Gene W4SZ Cecil Moore wrote: Gene Fuller wrote: I cannot speak directly for Tom Donaly, but you and I are about 99% in DISagreement over physics. That's just a straw man, Gene. You school and my school probably taught 99% the same physics. You and I are not that far apart at all. THERE ARE NO CONTRADICTIONS BETWEEN THE PHYSICS YOU USE AND THE CONCEPTS I AM PRESENTING. It only appears that way to you because you haven't taken the time to understand those concepts. Are there standing waves on a standing wave antenna? Are standing waves caused by the superposition of forward and reflected waves? Absolutely nothing new or different there. Current, charge, voltage, E-field, and H-field are different physical entities. They are related, but they are not interchangeable. Straw man alert! I resent any implication that I said they were interchangeable. I agree with you about the above quantities. No amount of E-field, H-field, or voltage can create or destroy charge. Straw man alert! I resent any implication that I said charge could be destroyed. I agree with what you said about 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. EXACTLY! And that is exactly what you and W8JI are missing. The familiar cosine current distribution on a dipole is a standing wave, i.e. the net current in that standing wave is not moving. Therefore, the net current doesn't obey your rules above. The net current is just an artifact of superposition of the forward current wave with the reflected current wave. It is the forward current and reflected current that is moving. Until you and Tom understand the nature of standing-wave antennas, you will never understand the nature of the current(s) through a loading coil installed in the middle of a standing wave antenna. Kurt N. Sterba made the same mistake in this month's Worldradio article. In a standing-wave antenna, the net current doesn't flow and RF current cannot stand still. The current is zero at the tip of a standing wave antenna not because all the energy has been radiated and/or conducted away by displacement currents. The current is zero because all the energy at that point is contained in the E-field. The forward H-field and the reflected H-field cancel each other at the tip of a standing wave antenna. If you really think there is zero energy at the tip of a mobile antenna, please grab it while power is applied. Your traveling wave/standing wave model is intuitive, but otherwise useless. Until you take the time to conceptually understand standing wave antennas, there is absolutely no chance of you understanding what happens when a loading coil is inserted in a standing wave antenna. 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. If what Balanis said is false, please present some proof. 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. There are some problems that do not lend themselves very well to a quantitative analysis. That's why simulation modeling is so popular with antennas and Blackjack. However, the difficulty of a quantitative analysis should not turn your brain into concrete such that you reject the associated qualitative analysis. All of these qualitative concepts are presented in textbooks. I have only quoted a handful of them. -- 73, Cecil, W5DXP |
Richard Harrison wrote:
"A wire antenna is a circuit with distributed constants; Terman, Kraus, Balanis, ... what do they know? :-) Apparently, a lot of the otherwise knowledgeable people on this newsgroup have forgotten that the formula for the characteristic impedance of a single-wire transmission line is 138*log(4h/d) where h is the height of the wire above ground and d is the diameter of the wire. There's no difference between that single-wire transmission line and a lot of ham antennas. That single-wire transmission line radiates just like an antenna. 1/2WL of #16 wire 24 feet in the air has a Z0 of 600 ohms. If that center-fed dipole were terminated at each end with a 600 ohm load, it would be a traveling-wave antenna with a feedpoint impedance of 600 ohms. Take away the loads and there's a match to 50 ohm coax at the feedpoint. The only difference in those two antennas is that removing the loads turned the antenna into a standing-wave antenna and reflections are arriving back at the feedpoint, lowering the feedpoint impedance. Any coil installed in a standing wave antenna is going to be subjected to both forward and reflected currents. There is no hope of understanding the current in a loading coil without understanding the component currents flowing both directions through the loading coil. -- 73, Cecil, W5DXP |
Gene Fuller wrote:
Nothing I wrote conflicts with Terman or Balanis. And nothing I wrote conflicts with your physics. -- 73, Cecil, W5DXP |
Richard Cl;ark wrote:
"The radiation resistance of an antenna is NOT necessarily the same as the drivepoint impedance of the antenna." True, but for many resonant antennas they are identical. Fundamentally, the radiation resistance is the value when inserted in series with an antenna will consume the same power as that radiated. Unless otherwise specified, the radiation resistance is referred to a current maximum point in an ungrounded antenna, and to the base of a grounded antenna. See 1955 Terman page 890 and 1950 Kraus page 143. They agree. All of ON4UN`s loaded antennas have maximum current at their drivepoints and they are resonant, so their feedpoint resistance coincides with their radiation resistance in all the instances diagrammed in the current distribution chart for short loaded verticals. ON4UN starts with 1A current to the base of all antennas and the current declines from that value. Its value is the cosine of the number of degrees from the feedpoint in most cases. Best regards, Richard Harrison, KB5WZI |
Gene Fuller wrote:
There is complete contradiction between the physics you have concocted and the real world. That's simply a false statement and your agenda seems to be personal rather than technical. Whose sacred cow am I goring? I say there are standing waves on a standing wave antenna. You disagree "completely" with everything I say. So, Gene, please prove that standing waves are absent on a standing wave antenna. After that, please explain why they are called "standing wave" antennas. Also explain why you think Terman, Kraus, and Balanis are wrong in their explanations of how standing waves exist on standing wave antennas. -- 73, Cecil, W5DXP |
|
Arguing about the "true" meaning of radiation resistance is pointless.
If you'll look through various respected texts and references, you'll see that it's used by different authors in different ways. (I posted some specific examples quite a long time ago on this newsgroup -- I'll find and repost if anyone is interested.) Some authors refer it to a current loop; others use it to describe the feedpoint resistance, at resonance or not. In "folded" antennas, it can mean either the "unfolded" resistance or the transformed feedpoint resistance. The only common thread in usage is that it always represents a sink for the power which is radiated, so this is the only "true" meaning of the term. The greatest danger in being careless about usage is in blindly using some formula such as a common one for efficiency, Efficiency = Rr / (Rr + Rl). This works only if Rr and Rl are referred to the same point. For example, if used for a folded dipole or unipole, both Rr and Rl must be as measured at the feedpoint, where they're both transformed by the "folding" process; or both defined as properties of the unfolded antenna. Using the "folded" value of one and "unfolded" value of the other leads to incorrect conclusions about efficiency -- conclusions which been successfully used to sell antennas. A given antenna doesn't have a single "inherent" or "fundamental" value of radiation resistance -- it's different at every point along an antenna, and the term can be legitimately used to describe the radiation "loss" component at any point. So whenever there's a chance of misunderstanding, it's important to say exactly what you mean by "radiation resistance" -- that is, where on the antenna this equivalent resistance is -- whenever you use the term. Roy Lewallen, W7EL Richard Harrison wrote: Richard Cl;ark wrote: "The radiation resistance of an antenna is NOT necessarily the same as the drivepoint impedance of the antenna." True, but for many resonant antennas they are identical. Fundamentally, the radiation resistance is the value when inserted in series with an antenna will consume the same power as that radiated. Unless otherwise specified, the radiation resistance is referred to a current maximum point in an ungrounded antenna, and to the base of a grounded antenna. See 1955 Terman page 890 and 1950 Kraus page 143. They agree. All of ON4UN`s loaded antennas have maximum current at their drivepoints and they are resonant, so their feedpoint resistance coincides with their radiation resistance in all the instances diagrammed in the current distribution chart for short loaded verticals. ON4UN starts with 1A current to the base of all antennas and the current declines from that value. Its value is the cosine of the number of degrees from the feedpoint in most cases. Best regards, Richard Harrison, KB5WZI |
Richard Clark wrote:
The drivepoint Z is NOT the "radiation resistance" irrespective of loading transformation. You can build a very small radiator, load it to resonance and it offers extremely poor efficiency. The ARRL Antenna Book says the feedpoint impedance of an 8 foot center-loaded mobile antenna on 80m is 22 ohms while the radiation resistance is 0.8 ohms. -- 73, Cecil, W5DXP |
The ARRL Antenna Book says the feedpoint impedance of an
8 foot center-loaded mobile antenna on 80m is 22 ohms while the radiation resistance is 0.8 ohms. ===================================== Cec, There you (in the plural) go again - using handbooks as bibles. Written by technically ill-educated amateurs and professionals, no different from yourselves, who can't agree on ANYTHING beyond V=I/R. These threads sure have entertainment value. Not quite hilarious, too serious, but well worth a speed-read, ;o) Cec, I'm on deep red, South African Western Cape, Pinotage-Shiraz tonight. You should try some. Makes a change from Californian, Texan and John Wayne, six-shooter politics. ---- Yours, Reg, G4FGQ |
| All times are GMT +1. The time now is 01:28 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com