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Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Tue, 8 Jan 2008 19:57:18 -0500, "AI4QJ" wrote:
measures delta I**2 or delta V**2 What is delta, specifically as you use it here? 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On 8 Jan, 17:26, "AI4QJ" wrote:
"Richard Clark" wrote in message ... Now, if you want to discard EZNEC (which for some odd reason you seem to approach method of moments with a sneer), conventional methods would still bear out the same results. The NEC program is just a computer model, for discussion purposes only. I think there are far too many variables in real life for the program to take into account. It may be valuable but I am not yet convinced it is infallible. Lord knows I've sat at the bench doing it the conventional way for thousands of measurements. That is the only way to do it in my opinion. I am not very convinced that the NEC models can be used as a first source to support any proposals in these discussions although they are useful as a secondary level of corroboration. Although we accept them because we are usually too busy to perform hardware measurements, at least one should consider exactly how one "would" or "could" make a hardware emasurement in real life. The less likely you are able to measure in real life, the more likely your proposal is heavy on abstractions and light on reality. For example. I think the more significant recent developments in quantum theory, such as "string theory", although they may attract a lot of research dollars to fund professors at our Universities, are actually quite useless in practice because no one will ever be able to prove it true by empirical measurments. I can say "God created the universe" which may seem plausible until I am challenged to prove the existence of God, which I cannot now and never will be able to do. Belief requires faith or even a suspension of logical thought, neither of which I am prepared to do for science. I've probably made more physical measurements in a day, than anyone here has in a lifetime. Others, don't bore us with indignities about all your SWR meter readings in reply to that last statement. * :-) So now to the shoe you dropped: I know this was not your main point, it was just an aside, but I don't agree with it What was my main point, and how is yours conflict with it? You were arguing about an SWR on a NEC model being 8:1, due, I have heard, to an erroneous assumption of Zo. No problem with me. But when you made an assertion that I thought could not be measured easily, I hesitated to take it true using faith based science. As you can see, the NEC model falls apart by making one simple erroneous assumption. Or was it? You can argue about that. That is the problem with these models, nobody is so intelligent that they are free of errors and no model is infallible either. Is yours a philosophical triviality so common to these threads, or does it come with physical measurements experience? It is philosophical as above but I do not consider it trivial. To me it was not a waste of time; thanks for the exchange Richard. AI4QJ Oh my! I wish I was as eloquent as you. You would explained the problem so much better than I did. When an assumption was made in addition to the use of Maxwell's laws it was to make the program conform with known results. And then the assuption made regarding sino soidal current flow was made is found to be in error, thus the absolute validity of the programs comes into question. Were they generated to follow Maxwells laws explicably or were they made to reflect empirical results? I suspect that Maxwells laws overode external human influences imposed by the programmer who are not infallable Best regards Art Unwin...KB9MZ...xg (uk). |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
Dave wrote:
"AI4QJ" wrote in message ... The VSWR meter on the ham rig is merely looking at the balance of forward and reflected "power" and it is calibrated to read it out as VSWR (or SWR). It may as well say "ISWR"; it is all the same thing. But it is not measured by sensing either voltage ot current going into the antenna...it measures the delta power. how do you measure 'power'?? you don't. and no swr meter in the world measures 'power'. they all take samples of voltage and/or current and drive a simple meter circuit that just happens to be calibrated in units of watts because thats what most users of cheap meters want to see. they could just as easily be calibrated in volts or amps referenced to 50 ohms SWR meters calibrated in watts? Really, where? However, I do find it enough that my watt meter reads 2.5 KW and my linear is 5 KW--loaded lightly to achieve the 2.5 KW. Somehow it just makes sense ... and, I am running it into a dummy load--of course! :-D Regards, JS |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Tue, 8 Jan 2008 20:26:03 -0500, "AI4QJ" wrote:
"Richard Clark" wrote in message .. . Now, if you want to discard EZNEC (which for some odd reason you seem to approach method of moments with a sneer), conventional methods would still bear out the same results. The NEC program is just a computer model, Hi Dan, "Just a" is a familiar dismissal for almost anything offered. Without corroborating evidence for the fear that is associated with its usage; then such an expression is a totem or religious chant to chase away spirits. "Computer model"s are as useful as they are predictive. EZNEC conforms to NEC which in turn conforms to field tests. The chain of evidence is quite strong and I have yet to hear of any real-life design that has defied NEC analysis. for discussion purposes only. I think there are far too many variables in real life for the program to take into account. It may be valuable but I am not yet convinced it is infallible. "Infallible" is a feeble demand to the gods for proof of their existence. I very seriously doubt you have ever encountered anything infallible in your life, so why start now? This desire for guarantee is usually a crutch for the turmoil of nervous youth. A computer model is explicitly not "real life" except to the extent by which it is included as a parameter. You don't name anything in particular that troubles you about "real life," so you don't appear to be looking for assurance, just negation. NEC has certainly responded to "real life" through the iterations of its successive designs (something that Roy may have more to say). There are explicit allowances for Ohmic loss of the conductor, and dielectric loss of insulation. Also added is the issue of the proximity of earth, and NEC offers similar parameter controls for describing it. In fact, you (or anyone) is probably far more ignorant of the characteristics of the earth in their "real life" than would be the problem of NEC to successfully model it. As to this last statement, the problem with modeling is far more operator error borne than computer borne. If you have any suspicions, gripes, grief, or indecision, it can frequently be laid at the feet of the designer. That is why I use the designer's own designs to split open their logic to reveal the corruption. If the model lacks interior fidelity, it is not the fault of NEC. Any review of EZNEC's help files will quickly reveal there are many trip points that can result in low accuracy, or outright errors. These can be investigated by simply asking for the model and examining it yourself. I revealed a couple from Cecil's offering: a strongly earth associated design modeled against a perfect earth; remote stimulus. I explicitly described changes of one or two parameters (expressly demanded by Cecil) and revealed that Traveling Wave antennas have Standing Waves upon them. This is hardly a monumental observation - except when it upsets the horse cart of celebrity. If you want to remain unconvinced, that is a rather passive activity of low participation and little information. I would suspect that of the 6 billion inhabitants of earth, there are 6 billion like you, but they don't write here. Their motivations lie elsewhere where they participate in activities to their interests. What was my main point, and how is yours conflict with it? You were arguing about an SWR on a NEC model being 8:1, due, I have heard, to an erroneous assumption of Zo. Well, with nothing more substantial than that, this is not a particularly condemning point. You should note that you are trapped by your own passivity into accepting other people's "word for it." This is an odd position to be in when you are writing in a community of Modelers who exchange designs for review and can either confirm or deny claims against rather more substantial evidence than what was overheard. No problem with me. But when you made an assertion that I thought could not be measured easily, I hesitated to take it true using faith based science. As you can see, the NEC model falls apart by making one simple erroneous assumption. Or was it? You can argue about that. That is the problem with these models, nobody is so intelligent that they are free of errors and no model is infallible either. You would stand to learn far more by examining the model yourself than have me swear on my credentials. You could stand to learn far more by asking for data instead of pondering the emotional chemistry of writing to a newsgroup, or second guessing how a model might fail. Those that stand to lose the most in celebrity, rarely offer correlating data or respond in true faith to enquiry for details. This is, after all, the point of the exchange of correspondence where celebrities post merely to pronounce their claims a spark of invention to be validated here. That just isn't the way it works here, or in "real life" either. 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Tue, 8 Jan 2008 20:38:40 -0500, "AI4QJ" wrote:
"Richard Clark" wrote in message .. . On Tue, 8 Jan 2008 19:57:18 -0500, "AI4QJ" wrote: measures delta I**2 or delta V**2 What is delta, specifically as you use it here? The delta between what is sent forward and what is reflected back. If the delta is zero, SWR = 1:1. Hi Dan, I was trying to untangle this expression from your statement: I have not seen a meter that appears to directly measure the ratio of Vmax forward/Vmax reflected or Imax forward/Imax reflected, which *would* be a direct SWR measurement. How does you lack of exposure to such an instrument impact this thread? Do you need it for assurance? Does it demonstrate something lacking in other methods of determination? I've already written to a method of determining not only SWR but the phase of reflections using one meter, switched between three points along a line (or probed directly). Such a method does not deny the accuracy of other methods or reveal any more information. In short, what significance is there in a "direct SWR measurement?" My skill at it is hardly remarkable until you get to some rather obscure situations (and a lot of what is obscure here passes as discovery of the ages stuff, but those discoverers lack the skill). 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
AI4QJ wrote:
The NEC program is just a computer model, for discussion purposes only. I think there are far too many variables in real life for the program to take into account. It may be valuable but I am not yet convinced it is infallible. . . Exactly the same can be said of any of the other models we successfully use daily. "Resistances", "impedances", "capacitances", and other objects we routinely use in circuit analysis, are "just" models of real objects. Likewise, the equations we use for solving all kinds of problems, including transmission line and circuit analysis problems, are "just" models of actual behavior. Ohm's law is "just" a model of the relationship among V, I, and Z. The fundamental equations relating currents and fields, Maxwell's equations, and all other equations used in engineering are "just" models of real behavior. *All* models are subject to intelligent use. A person modeling a real resistor as a pure resistance at 50 GHz will get just as bad results as a person modeling a dipole on a circuit board in a smart key in a pocket as a free-space dipole. No model, not even a simple resistance, is infallible -- even it can be misused by someone not having the underlying knowledge necessary to apply it. So of course computer models aren't infallible either. But there are many, many real life antennas which can be modeled with great accuracy with NEC. I use EZNEC regularly myself in my consulting work to design antennas, and find very good correlation with anechoic chamber pattern tests, network analyzer impedance tests, and performance results. So do the many aerospace companies, military organizations, space agencies, universities, research labs, domestic and international broadcasters, and many other companies that use EZNEC daily to help design real antennas that work as predicted. But those aren't the only people successfully modeling with EZNEC -- a large number of amateurs successfully use it also. I'm not sure what it is that makes models inherently less accurate or believable if the equations are solved with a computer than if they're solved by some other method. Perhaps you could explain. Roy Lewallen, W7EL |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
Richard Clark wrote:
. . . "Computer model"s are as useful as they are predictive. EZNEC conforms to NEC which in turn conforms to field tests. The chain of evidence is quite strong and I have yet to hear of any real-life design that has defied NEC analysis. I don't think you said quite what you meant. There are many real-life designs which are beyond NEC's (and hence EZNEC's) ability to analyze. One common example is a microstrip (patch) antenna; NEC has no way to account for the dielectric. A user with even minimal knowledge should realize the significance of this shortcoming, and not expect to be able to get accurate results from a model with the dielectric excluded. However, and I think this is probably what you meant, the accuracy of NEC is strikingly good whenever a model can be constructed that does a good job of mimicking the real antenna. All this really proves are two things: 1. The fundamental electromagnetic equations solved by NEC are sound, and 2. Most of the bugs have been worked out of the code, so it correctly solves the equations. The equations solved by NEC can't be solved in closed form. That means there is no formula into which you can plug numbers and calculate a result. The method it uses can be done manually for very simple cases and with very limited accuracy -- see Kraus' _Antennas_, 2nd Edition or later, for a good example. A number of very simple antennas with simple geometry can be analyzed using approximations which have been developed over the years, but they're usually strictly limited to a narrow range of conditions. For example, there have been many methods developed for finding the input impedance of a simple, straight dipole of various lengths and diameters. (I have a large collection of papers and references on this topic, accumulated before MININEC became available.) All are based on approximations, and some are better than others at certain lengths and diameters. None are terribly good over a wide range, and bending the elements, for example, invalidates any of the methods. Now, why should we expect results from these methods to be better in some way than results from NEC, "just" a computer model, when NEC can solve the problem for any length, diameter, and shape, to an arbitrary degree of accuracy, in a fraction of a second? Roy Lewallen, W7EL |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Tue, 8 Jan 2008 22:17:40 -0500, "AI4QJ" wrote:
"Richard Clark" wrote in message .. . Those that stand to lose the most in celebrity, rarely offer correlating data or respond in true faith to enquiry for details. This is, after all, the point of the exchange of correspondence where celebrities post merely to pronounce their claims a spark of invention to be validated here. That just isn't the way it works here, or in "real life" either. Your entire post seems to indicate that, in order to participate in this newsgroup, you must use EZNEC. Hi Dan, No, it explicitly informs you that if you don't have any modeler, you are only guessing. Modelers offer solutions that I doubt you could obtain through your own efforts. Forget about all those tiresome formulae and the concept building; you need not know how a standing wave works or the mathematics thereof. Forget? Well, this certainly describes someone who will certainly contribute to pilot error. I dare say, those who are eminently familiar with how a standing wave works, or the math, use modelers. Those who don't know how a standing wave works, or the math, are rather flat-footed. I'm sure it was a boon for you when the slide rule was replaced by the electronic calculator, leaving your mind free from having to wrestle with the true science and mathematics that is going on with your engineering problems and just let the machine do it for you. Fortunately, I don't pursue issues that don't survive a simple rationality check. This can even eclipse the need of a slide rule with a few figures sketch on a paper, and some simple computations. If you make a stupid mistake, don't fret, somebody will correct the parameters and re-run the program until it fits. No need to understand maxwell, calculus, vectors, phasors, just let the program do it all for your using the brute force method of moments. Transistors are dirt cheap and efficient calculations are no longer necessary. No need for analog computers. Just plug it into a method of moments calculator and you are done. Ah, but the introduction of this last quote is significant: the mistake is caught. One needn't be a conductor to enjoy music. On the other hand, a conductor is eminently qualified (if one can use the word) to enjoy music. What's missing with this, of course, is the part your grey matter is supposed to do. Grey matter can take a permenent vacation. Again, you have already revealed a thought process of recognizing a mistake. Stupid or otherwise is merely a value to the problem, not to the process of obtaining the solution. I see no problem using a NEC to confirm a calculation or concept. But you seem to advocate its exclusive use as the only authoritative, indeed, available, tool. I am still waiting for you to reveal something that does it better. Simply throwing brain cells at it hasn't offered us much product here - except when the internal logic of some proclamation fails on the starting blocks. Of course, I disagree and think that rraa still has room for real math and scientific concepts and indeed there is room for NEC. However, if the choice is given to prefer one over the other, I prefer the former because creative design does not occur by arbitrary and random use computer problems such as NEC, CADAM and the like, it comes from scientific method which requires human thought. A long and winding road, that. But cursing at air traffic because it gets others there faster doesn't make blisters on your feet ennobling, especially when you are as likely to arrive at the wrong destination as any air traveler. 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On 8 Jan, 19:01, Roy Lewallen wrote:
AI4QJ wrote: The NEC program is just a computer model, for discussion purposes only. I think there are far too many variables in real life for the program to take into account. It may be valuable but I am not yet convinced it is infallible. . . Exactly the same can be said of any of the other models we successfully use daily. "Resistances", "impedances", "capacitances", and other objects we routinely use in circuit analysis, are "just" models of real objects. Likewise, the equations we use for solving all kinds of problems, including transmission line and circuit analysis problems, are "just" models of actual behavior. Ohm's law is "just" a model of the relationship among V, I, and Z. The fundamental equations relating currents and fields, Maxwell's equations, and all other equations used in engineering are "just" models of real behavior. *All* models are subject to intelligent use. A person modeling a real resistor as a pure resistance at 50 GHz will get just as bad results as a person modeling a dipole on a circuit board in a smart key in a pocket as a free-space dipole. No model, not even a simple resistance, is infallible -- even it can be misused by someone not having the underlying knowledge necessary to apply it. So of course computer models aren't infallible either. But there are many, many real life antennas which can be modeled with great accuracy with NEC. I use EZNEC regularly myself in my consulting work to design antennas, and find very good correlation with anechoic chamber pattern tests, network analyzer impedance tests, and performance results. So do the many aerospace companies, military organizations, space agencies, universities, research labs, domestic and international broadcasters, and many other companies that use EZNEC daily to help design real antennas that work as predicted. But those aren't the only people successfully modeling with EZNEC -- a large number of amateurs successfully use it also. I'm not sure what it is that makes models inherently less accurate or believable if the equations are solved with a computer than if they're solved by some other method. Perhaps you could explain. Roy Lewallen, W7EL Answer why Maxwells laws must have a proviso added when they are considered LAWS nOT theory but law When you jump the traffic lights you have broken the law. Maybe your exception has a good reason but by its very use you have invalidated the laws that you are seeking to abide by.This does not mean that the program does not reproduce actual antennas because numourous modifications to make sure that it does. Doing this is tantamount to saying that Maxwells laws need the help of experts such as your self. Seems like a good job is being done but it doesn't change the facts. You have taken the lead offered by Maxwell but have reserved the right to modify these laws to obtain a better computor model. Why was this deviation added when the discharge of a capacitor is in no way sino-soidal? Same goes for a inductor. Explain your deviation from the laws of Maxwell! As a computor programmer you never gave credence to other antenna programs that produced tipped radiators for maximum gain for the polararisation required? You stayed quiet to protect the sales of your own program and thus by your silence allowed true facts to be distorted on this newsgroup. There were many opportunities for you to say that Eznec confirmed this finding but you said nothing, which in itself is a insult to ham radio. You modified Maxwell's laws and that is prohibited in mathematics if one is to follow a mathematical law which you then invalidate. Nothing personal intended, just a statement of facts as I see them. I will accept factual changes if you deign to point them out in detail so they can be confirmed or denied. Art |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Tue, 8 Jan 2008 22:24:09 -0500, "AI4QJ" wrote:
The measurement itself will change the SWR significantly once you start adding probes to the antenna. Hi Dan, I've done it with remote, fiber optic probes. If this is another absolutism about "change" then my being on the same planet will disturb that certainly. 73's Richard Clark, KB7QHC |
r.r.a.a WARNING!!!
On 7 Jan, 18:39, "AI4QJ" wrote:
"art" wrote in message ... On 6 Jan, 18:39, "AI4QJ" wrote: "art" wrote in message .... "Did you ever think that your post would last this long? Obviously the regular contributors in this group cannot handle the truth and thus will not consult anything.Now the experts are argueing over the term SWR a very, very, deep discussion revealing things unknown to the amateur community at this time. [...]" Hello Art, the concept of SWR is extremely misunderstood even by people with degrees in electronics engineering. It is assumed to be simple, yet many people get it wrong. Indeed, a good understanding is essential for antenna development. I do not fault anyone for not understanding the concept because standing waves, simple as they may seem, are actually expressed as the product of a cos wave over distance and a sine wave over time. Many things are happening over the length of the antenna as the function is operating. If you think of it, it is the essence of space-time and it may be productive for you to consider it even more broadly in your own hypotheses, more broadly that is by possibly incorporating the mechancial SWR analogues to voltage/current SWR's and who knows what new ideas may come to mind with your model. I don't understand a lot of this talk about waves bouncing which is fortunate. Icould not possibly stay on a thread where everybody is talking past each other and then changing the subject as they didn't understand the subject in the first place. In ham radio nothing is believed if it is contrary to the norm.This bouncing wave thing will never come to closure as all participants are deaf. As *far as me getting involved all the answers involved in my description of radio are known facts in the scientific world and fully coroberated. Heck they are even corroberated by existing antenna computor programs and actual tests. I can't see how these waves fit in with classical science so it must be another invented science that it referes to. Now if the trend changed to debate the voracity of existing accepted data is proved to be incorrect then they would have my attention but the group is not competant enough for that trail. Regards Art You are a mechanical engineer, right? Consider acoustic "radiation". Pluck a guitar string; the fundamental wavelength of the sound your hear (and its harmonics) will be related to the length of the string and the speed of the wave in the string (not the speed of sound) which depends on the tension and density of the string. f*length = v. The 'radiation resistance' is the string's standing wave pushing against the air and producing sound energy from applied kinetic energy stored in the *vibrating string*. The musical note you hear does move at the speed of sound. This is somewhat analagous to an antenna. Now I agree that to be a musician it is not neccesary to understand these principles but to design guitar strings (antennas) it would be advantageous to understand it (though not mandatory). In order to discuss the reasons why certain guitar strings work better or sound different than others, it is essential to understand this and to understand it, you must first understand what an acoustic standing wave is. You are working on an antenna model; you may be a ham and you may even be designing antennas but you do not know how standing waves work. It is not compusory. You can still operate and design antennas without knowing how this works. But, *it sounds like you need some more tools. You are dealing with EM fields and waves and you are also dealing with vibrations of particles making your model, if it works, almost as related to a mechancial wave as an electrical wave...a combination of both? I think on the track that you are on, which is not real clear to me, I would advise getting out the physics books and getting familiar with these concepts...they are not only EE related, there is an ME analog (as there often is for fundamental EE problems).- Hide quoted text - - Show quoted text - I was being facietious in my comments regarding the change of direction to SWR. If it upset you I apologise,as I do to David and Richard with their comments with respect to SWR meters and I thus withdraw said comment. Best regards Art |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
AI4QJ wrote:
The NEC program is just a computer model, for discussion purposes only. I think there are far too many variables in real life for the program to take into account. It may be valuable but I am not yet convinced it is infallible. Oh darnit! Here I went and built several antennas designed with Eznec, and they have worked just like the program said they would. I guess I'll have to take the remaining ones down, since I was only supposed to discuss them, not actually make and use them. Thanks for the correction! - 73 de Mike N3LI - |
Standing morphing to travelling waves, and other stupid notions
On Jan 8, 2:39 pm, Jim Kelley wrote:
But when you write the equation for the superposition of traveling waves and claim that resultant standing wave is a different kind of electromagnetic wave, that is a misguided point of view. That's not true unless you consider Eugene Hecht to be misguided. He said standing waves are so different from traveling waves that they probably shouldn't even be considered to be waves at all since they are not even moving. Standing waves could hardly be any different from traveling waves and tend to create strange illusions in human brains. I have plotted the envelopes of the waves at http://www.w5dxp.com/TravStnd.gif Those waveforms could hardly be any different yet you asserted that they are linked by a trig identity. A standing wave is not only different from an EM traveling wave, it cannot correctly even be called an EM wave because it is not moving at the speed of light in the medium, a technical requirement for EM waves. I have asked you to prove your assertion that, using your trig identity, cos(kx-wt) = cos(kx)+cos(wt). Where is that proof? ... you almost inevitably end up lying ... Misunderstanding you and repeating it back to you is not lying. Neither are my personal opinions proof of lying. I joke a lot but lying is against my ethics and religion. Being called a liar by liar is unacceptable proof. Would it be too much to ask to post one of my alleged lies instead of hoping that your handwaving and implications will accomplish that underhanded trick. P.S. I'm on my daughter's computer posting from Google. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Jan 8, 3:54 pm, art wrote:
Yes 50/60 is frequency just like 10 metrrs. Now go homw and cut the wire in the kitchen to make it an open circuit Now ham r5adio says the cuyrrent will turn around where you cutt it and it will go back. Well science has not seen a trace of this new frequency of 100, 110 0r 220 line double its frequency to twice what it was before. Art, please think about what you are saying. The wavelength of 20 MHz is 70 ft. The wavelength of 60 Hz is 16,400,000 feet (3100 miles). There is a power factor correcting capacitor every city block or so on the 60 Hz system, i.e. approximately every 0.00003 wavelength. Are there any power factor correcting capacitors hanging on a 20m dipole? If the standing wave power factor was corrected on a 20m dipole, the standing waves would disappear just like they do on the power wires. Correcting the power factor on a standing wave dipole antenna would turn it into a traveling wave antenna and there would be no reflections from the end of the dipole. Our 50/60 Hz power distribution systems are overwhelmingly traveling wave systems. The power companies simply don't allow reflections to exist because they don't get paid for reflected energy and they sure don't want it coming back to the generator. If you had a 60Hz generator feeding a low-loss 3100 mile open- circuited transmission line, you would certainly observe a forward wave, reflected wave, and standing wave all obeying the distributed network reflection model rules. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
.. A standing wave is not only different from an EM traveling wave, it cannot correctly even be called an EM wave because it is not moving at the speed of light in the medium, a technical requirement for EM waves. Cecil, I showed you exactly how the energy in a standing wave travels at the speed of light. Did you miss that message, or are you just pretending it didn't happen? Neither you nor your buddy Hecht are likely to overturn more than 100 years of successful use of standing waves. 8-) 73, Gene W4SZ |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Jan 8, 9:19 pm, Richard Clark wrote:
I explicitly described changes of one or two parameters (expressly demanded by Cecil) and revealed that Traveling Wave antennas have Standing Waves upon them. This is hardly a monumental observation - except when it upsets the horse cart of celebrity. You wasted your time, Richard. Everyone should already know that there are received reflected waves of all different frequencies on a traveling wave antenna. However, they can all be completely ignored since we are only interested in the one frequency on which we are transmitting *and* in the direction to which we are transmitting. Introducing all the other extraneous frequencies and directions that exist is an act of desperation. In particular, we are not interested in the received standing waves that are incident upon our terminated rhombic when they are coming from the side or back of the antenna. That they exist proves absolutely nothing of value. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
On Jan 9, 2:42 pm, Gene Fuller wrote:
I showed you exactly how the energy in a standing wave travels at the speed of light. Did you miss that message, or are you just pretending it didn't happen? I don't think I missed it, Gene, but it is possible. There is no net energy movement in a standing wave because the forward Poynting vector, Pz+, and reverse Poynting vector, Pz-, are equal magnitude and opposite directions. Therefore, no net energy movement is possible in a standing wave. In contrast to that standing wave, there is always net energy movement in a traveling wave. If you can prove net energy movement in a standing wave, you will have violated the definition of a standing wave. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
On Jan 8, 2:39 pm, Jim Kelley wrote: But when you write the equation for the superposition of traveling waves and claim that resultant standing wave is a different kind of electromagnetic wave, that is a misguided point of view. That's not true unless you consider Eugene Hecht to be misguided. Of course it's true, and Dr. Hecht does post here. He said standing waves are so different from traveling waves that they probably shouldn't even be considered to be waves at all since they are not even moving. On what page has Dr. Hecht written "a standing wave is a different kind of electromagnetic wave"? Those waveforms could hardly be any different yet you asserted that they are linked by a trig identity. I asserted that expression for the sum of traveling waves and the expression for the resulting standing wave pattern are related by trig identity, as per page 140 of the 28th Edition of the CRC Standard Mathematical Tables Handbook. A standing wave is not only different from an EM traveling wave, it cannot correctly even be called an EM wave because it is not moving at the speed of light in the medium, a technical requirement for EM waves. The 'wave' which stands is merely an amplitude envelope for the waves which move. It's not a "different kind of electromagnetic wave." If you were to instead characterize a 'standing wave' as a different kind of interference pattern, then we would in fact be in agreement. ac6xg |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Wed, 9 Jan 2008 11:48:12 -0800 (PST), Cecil Moore
wrote: On Jan 8, 9:19 pm, Richard Clark wrote: I explicitly described changes of one or two parameters (expressly demanded by Cecil) and revealed that Traveling Wave antennas have Standing Waves upon them. This is hardly a monumental observation - except when it upsets the horse cart of celebrity. You wasted your time, Richard. Everyone should already know that there are received reflected waves of all different frequencies on a traveling wave antenna. However, they can all be completely ignored since we are only interested in the one frequency on which we are transmitting *and* in the direction to which we are transmitting. Introducing all the other extraneous frequencies and directions that exist is an act of desperation. In particular, we are not interested in the received standing waves that are incident upon our terminated rhombic when they are coming from the side or back of the antenna. That they exist proves absolutely nothing of value. Hi Dan, I want you to take this quote above and observe that it offers nothing of data, and certainly says nothing of any model (except by the slightest of inference), and there is nothing of a practical measurement. It does touch on the gray matter you aspire to keep active in the game, but only to recite homilies that do not attend the discussion. One could as easily demand that Ohm's law describes conduction, but say nothing about current, voltage, or resistance. Yes, all very true about Ohm, but hardly dismissive of prior models presented or their data that they deliver (by whatever means), nor how the sum of these typical engineering considerations fails to conform to the logic of Cecil's proposed argument. By the points: !. different frequencies is not an issue, only one has ever been expressed; 2. direction is not an issue, excitation is by degree only, nothing changes the energy distribution in relative phases nor period; 3. termination was not my issue (although I conformed to Cecil's demand that it should be) as I had already accounted for it; 4. they (Standing Waves) exist may be nothing of value, but only for a desperate celebrity who discounts his argument, impeaches his models and disinherits their data. If you still find EZNEC a poor mechanism to support an argument through its means of presenting what you might call suspect data, then the quoted response to my posting above, has to be light years further from a rational conclusive demonstration. ;-) 73's Richard Clark, KB7QHC |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
On Jan 9, 2:42 pm, Gene Fuller wrote: I showed you exactly how the energy in a standing wave travels at the speed of light. Did you miss that message, or are you just pretending it didn't happen? I don't think I missed it, Gene, but it is possible. There is no net energy movement in a standing wave because the forward Poynting vector, Pz+, and reverse Poynting vector, Pz-, are equal magnitude and opposite directions. Therefore, no net energy movement is possible in a standing wave. In contrast to that standing wave, there is always net energy movement in a traveling wave. If you can prove net energy movement in a standing wave, you will have violated the definition of a standing wave. -- 73, Cecil, w5dxp.com So do we now have a new requirement for waves and photons that there must be *net* energy flow? Who cares what the average or *net* is. Think *instantaneous* if you want to understand photons. After all, they don't stand still, and they don't interact with each other. You claimed that standing waves cannot be real waves because they cannot obey photon rules. I easily demonstrated that idea is incorrect. The message was sent on January 3, at 4:32 pm, in the thread " Standing-Wave Current vs Traveling-Wave Current". 73, Gene W4SZ |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
Cecil Moore wrote:
On Jan 8, 3:54 pm, art wrote: Yes 50/60 is frequency just like 10 metrrs. Now go homw and cut the wire in the kitchen to make it an open circuit Now ham r5adio says the cuyrrent will turn around where you cutt it and it will go back. Well science has not seen a trace of this new frequency of 100, 110 0r 220 line double its frequency to twice what it was before. Art, please think about what you are saying. The wavelength of 20 MHz is 70 ft. The wavelength of 60 Hz is 16,400,000 feet (3100 miles). There is a power factor correcting capacitor every city block or so on the 60 Hz system, i.e. approximately every 0.00003 wavelength. Are there any power factor correcting capacitors hanging on a 20m dipole? If the standing wave power factor was corrected on a 20m dipole, the standing waves would disappear just like they do on the power wires. Correcting the power factor on a standing wave dipole antenna would turn it into a traveling wave antenna and there would be no reflections from the end of the dipole. Our 50/60 Hz power distribution systems are overwhelmingly traveling wave systems. The power companies simply don't allow reflections to exist because they don't get paid for reflected energy and they sure don't want it coming back to the generator. If you had a 60Hz generator feeding a low-loss 3100 mile open- circuited transmission line, you would certainly observe a forward wave, reflected wave, and standing wave all obeying the distributed network reflection model rules. -- 73, Cecil, w5dxp.com Cecil, That is an interesting tale, but mostly baloney. When you get back to the wilds of Texas go check out some rural power lines. Count the number of power factor correcting capacitors you see. I bet it is a lot less than the equivalent of one per city block. Power factor correcting capacitors are intended to correct for reactive loads, such as motors, not for reflections or standing waves on open ended power transmission lines. But you already know that. 73, Gene W4SZ |
Standing morphing to travelling waves, and other stupid notions
Before Cecil jumps on the typo, see below. My profuse apologies.
Jim Kelley wrote: Cecil Moore wrote: On Jan 8, 2:39 pm, Jim Kelley wrote: But when you write the equation for the superposition of traveling waves and claim that resultant standing wave is a different kind of electromagnetic wave, that is a misguided point of view. That's not true unless you consider Eugene Hecht to be misguided. Of course it's true, and Dr. Hecht does post here. and Dr. Hecht does not post here. He said standing waves are so different from traveling waves that they probably shouldn't even be considered to be waves at all since they are not even moving. On what page has Dr. Hecht written "a standing wave is a different kind of electromagnetic wave"? Those waveforms could hardly be any different yet you asserted that they are linked by a trig identity. I asserted that expression for the sum of traveling waves and the expression for the resulting standing wave pattern are related by trig identity, as per page 140 of the 28th Edition of the CRC Standard Mathematical Tables Handbook. A standing wave is not only different from an EM traveling wave, it cannot correctly even be called an EM wave because it is not moving at the speed of light in the medium, a technical requirement for EM waves. The 'wave' which stands is merely an amplitude envelope for the waves which move. It's not a "different kind of electromagnetic wave." If you were to instead characterize a 'standing wave' as a different kind of interference pattern, then we would in fact be in agreement. ac6xg |
Standing morphing to travelling waves, and other stupid notions
Cecil Moore wrote:
... P.S. I'm on my daughter's computer posting from Google. -- 73, Cecil, w5dxp.com Cecil: Break down and buy a laptop (even a used one.) Make sure it has a wireless card or, get a USB wireless dongle (make sure the laptop has USB ports!) Jiwire(http://www.jiwire.com) can be used to find any free wireless hotspots in the areas you are in, or even paid ones--for that matter. Without you, it's too boring ... Sometimes this is better than an Indiana Jones movie! You know, the type of movies where the natives want his head on a stick. LOL Warm regards, JS |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Jan 9, 11:03*am, Michael Coslo wrote:
AI4QJwrote: The NEC program is just a computer model, for discussion purposes only. I think there are far too many variables in real life for the program to take into account. It may be valuable but I am not yet convinced it is infallible. * * * * Oh darnit! Here I went and built several antennas designed with Eznec, and they have worked just like the program said they would. * * * * I guess I'll have to take the remaining ones down, since I was only supposed to discuss them, not actually make and use them. Thanks for the correction! * * * * - 73 de Mike N3LI - But you may have a problem discussing on the ng exactly "why" they work. Why would you want to discuss an antenna if you don't care "how" it works, you only care "that" it works? There are some people that operate at 27MHz who don't care how their radios work, only that they can peg your meter at 10 pounds. |
Standing morphing to travelling waves, and other stupid notions
On Jan 9, 2:42*pm, Gene Fuller wrote:
Cecil Moore wrote: . A standing wave is not only different from an EM traveling wave, it cannot correctly even be called an EM wave because it is not moving at the speed of light in the medium, a technical requirement for EM waves. Cecil, I showed you exactly how the energy in a standing wave travels at the speed of light. Did you miss that message, or are you just pretending it didn't happen? Neither you nor your buddy Hecht are likely to overturn more than 100 years of successful use of standing waves. 8-) 73, Gene W4SZ Semantics. The standing wave doesn't 'travel' anywhere, much less at the speed of light. However, it does vibrate. Each vibration cycle occurs at a frequency that, when multiplied by its wavelength, would be equal to the speed of light. I find this an interesting concept. |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
Roger Sparks wrote:
Using the reflection point as the zero reference seems to correspond with an observation you made about the end of the line controlling the SWR. The choice of zero reference is entirely arbitrary; any point on the line, or off the line, for that matter, can be used. I used the input end of the line as the x = 0 reference, so my equations are correct only when that reference is used. The choice of a reference has no effect on the SWR or any other aspect of line operation; it simply modifies the equations. For example, my equations for the first forward and first reflected voltage wave we vf1(t, x) = sin(wt - x) vr1(t, x) = Gl * sin(wt + x) and for the second set: vf2(t, x) = Gs * sin(wt - x) vr2(t, x) = Gs * Gl * sin(wt + x) where here I've explicitly shown the source and load reflection coefficients as Gs and Gl respectively. They were 0.5 and 1 in my second analysis (the one with a 150 ohm resistor at the source). The more general case where the line is some length L, rather than the integral number of wavelengths in the example, vf1(t, x) = sin(wt - x) vr1(t, x) = Gl * sin(wt + x - 2L) vf2(t, x) = Gs * Gl * sin(wt - x - 2L) vr2(t, x) = Gs * Gl^2 * sin(wt + x - 4L) In general, (1) vfn(t, x) = (Gs * Gl)^n * sin(wt - x - 2nL) (2) vrn(t, x) = Gl * (Gs * Gl)^n * sin(wt + x - (2n + 1)L) where L is expressed in the same units as x and wt (degrees or radians). These equations are correct with x being the distance from the input end of the line. You could, as I mentioned, use a different reference, for example x' = L - x, where L is the line length in radians or degrees (same units as x and wt). Then you have, simply by substituting L - x' for x: vf1(t, x') = sin(wt - L + x') vr1(t, x') = sin(wt + L - x' - 2L) = sin(wt - L - x') and so forth, and for the general case, (3) vfn(t, x') = (Gs * Gl)^n * sin(wt + x' - (2n + 1) * L) (4) vrn(t, x') = (Gs * Gl)^n * sin(wt - x' - 2nL) or, you can use x for the forward wave and x' for the reverse wave or vice-versa in order to reference to the point the wave was reflected from or where it will be reflected from. Any combination of the equations is equally valid and will give correct results. You can't, however, simply redefine the reference point without a corresponding change in the equation. In general, equation 1 and equation 3 will give different results if you put in the same value for x and x'; likewise equations 2 and 4. There are some special cases, as you showed, where you can change the reference without modifying the equations and not have any impact on the sum of the waves. However, you can see from the equations that this won't usually work. The general case with complex reflection coefficients and arbitrary line length is mathematically a little more difficult than the simple example I worked earlier. Not only does each reflection have a different amplitude than the previous one, it also has a different phase angle, due to the line length and the reflection coefficients. Consequently, the simple a / (1 - r) formula I used for summing the infinite series of waves can't be applied to the equations in the form I used. This is where a change to phasor notation is really beneficial, since the phase delay simply becomes e raised to an imaginary exponent which can be treated more conveniently than its constituent sine and cosine functions. With phasor notation, the summing formula can be used even for the general case to find the steady state results from the individual reflected waves. There's a very excellent treatment of this in Chipman's _Transmission Lines_ (Schaum's Outline Series). He does just about exactly what I did in my earlier posting, except for the general case and using phasors rather than time representations. It's an excellent text and reference, and I highly recommend it for anyone seriously interested in transmission lines. Roy Lewallen, W7EL |
Standing morphing to travelling waves. was r.r.a.a LaughRiot!!!
Art wrote:
"Yes 50/60 is frequency just like 10 meters." What is wrong with that statement? The frequency corresponding to 10 meters is 30 million cycles per second. The wavelength corresponding to 50 Hz is 6 million meters. A point a few meters from another along a 50 Hz line must have the same voltage as that of the other point on the line a few meters away because the 50 Hz wave changes its value so slowly as compared with wave velocity, about 300 million meters per second. At the same distance between points on a 30 MHz line, the voltages of two points are surely different at the same instant because the wave changes its value rapidly. Cut a line carying HF of 30 MHz and the voltage doubles at the open circuit while the current is completely reflected, making a sum of zero amperes at the cut. Best regards, Richard Harrison, KB5WZI |
Standing morphing to travelling waves, and other stupid notions
Jim Kelley, AC6XG wrote:
"On what page has Dr. Hecht written "A standing wave is a different kind of electromagnetic wave?" In "Schaum`s College Physics Outline" by Bueche & Hecht on page 214 is written: "Standing Waves:....These might better not be called waves at all since they do not transport energy and momentum." Best regards, Richard Harrison, KB5WZI |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On 9 Jan, 11:36, Cecil Moore wrote:
On Jan 8, 3:54 pm, art wrote: Yes 50/60 is frequency just like 10 metrrs. Now go homw and cut the wire in the kitchen to make it an open circuit Now ham r5adio says the cuyrrent will turn around where you cutt it and it will go back. Well science has not seen a trace of this new frequency of 100, 110 0r 220 line double its frequency to twice what it was before. Art, please think about what you are saying. The wavelength of 20 MHz is 70 ft. The wavelength of 60 Hz is 16,400,000 feet (3100 miles). There is a power factor correcting capacitor every city block or so on the 60 Hz system, i.e. approximately every *0.00003 wavelength. Are there any power factor correcting capacitors hanging on a 20m dipole? If the standing wave power factor was corrected on a 20m dipole, the standing waves would disappear just like they do on the power wires. Correcting the power factor on a standing wave dipole antenna would turn it into a traveling wave antenna and there would be no reflections from the end of the dipole. Our 50/60 Hz power distribution systems are overwhelmingly traveling wave systems. The power companies simply don't allow reflections to exist because they don't get paid for reflected energy and they sure don't want it coming back to the generator. If you had a 60Hz generator feeding a low-loss 3100 mile open- circuited transmission line, you would certainly observe a forward wave, reflected wave, and standing wave all obeying the distributed network reflection model rules. -- 73, Cecil, w5dxp.com Thank you for responding Cecil as well as not being abusive. Still looking at the first statement as I cannot move on without closure. Your point about a antenna having a open circuit at the top is a troubling point for me. For a given frequency the wave travells a certain distance forward and the a certain distance back.What you are saying is if the antenna is short then the wave or current flow will always about turn. Thus it is the length of the antenna by your statement is what turns around the current regardless of the frequency applied. Thus if I reduced the antenna to 1 inch length the current will turn around multiple times by the time that a period for say 10 metres has expired. Since the current supplied travels on the outside of the antenna it will be radiating all the time ( as I understand what you are saying) without pulsating . I suppose you can prove this being a electrical person! For me it is the time that the antenna is actually radiating for a given frequency that is important so perhaps you will kindly relate travel distance, time taken with the period duration of the frequency applied? There will be efforts to change the subject under discussion which would make this one small point last a few years but I do think it is worth clarifying for all so a solid base can be built. I would appreciate it if you would clarify what sort of antenna we are referring to ie a full electrical wave or a half electrical wave (resonant or otherwise )so that I may relate to either a series circuit or a parallel circuit such that the discussion is neatly enclosed to prevent deviation. Very Best Regards Art Unwin |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
Corrections:
The equations I gave aren't adequate for complex reflection coefficients, which I didn't explicitly state. Also, I inadvertently omitted a multiplying factor in two equations. Roy Lewallen wrote: . . . For example, my equations for the first forward and first reflected voltage wave we vf1(t, x) = sin(wt - x) vr1(t, x) = Gl * sin(wt + x) and for the second set: vf2(t, x) = Gs * sin(wt - x) vr2(t, x) = Gs * Gl * sin(wt + x) where here I've explicitly shown the source and load reflection coefficients as Gs and Gl respectively. They were 0.5 and 1 in my second analysis (the one with a 150 ohm resistor at the source). The above equations are valid only for purely real reflection coefficients, as in the analysis I did. The more general case where the line is some length L, rather than the integral number of wavelengths in the example, vf1(t, x) = sin(wt - x) vr1(t, x) = Gl * sin(wt + x - 2L) vf2(t, x) = Gs * Gl * sin(wt - x - 2L) vr2(t, x) = Gs * Gl^2 * sin(wt + x - 4L) In general, (1) vfn(t, x) = (Gs * Gl)^n * sin(wt - x - 2nL) (2) vrn(t, x) = Gl * (Gs * Gl)^n * sin(wt + x - (2n + 1)L) For complex reflection coefficients, vf1(t, x) = sin(wt - x) vr1(t, x) = |Gl| * sin(wt + x - 2L + /_Gl) vf2(t, x) = |Gs * Gl| * sin(wt - x - 2L + /_(Gs * Gl)) vr2(t, x) = |Gs * Gl^2| * sin(wt + x - 4L + /_(Gs * Gl^2) In general, (1) vfn(t, x) = |(Gs * Gl)^n| * sin(wt - x - 2nL + /_((Gs * Gl)^n)) (2) vrn(t, x) = |Gl * (Gs * Gl)^n| * sin(wt + x - (2n + 1)L + /_(Gl * (Gs * Gl)^n) where /_(qty) is the phase angle of qty. where L is expressed in the same units as x and wt (degrees or radians). These equations are correct with x being the distance from the input end of the line. You could, as I mentioned, use a different reference, for example x' = L - x, where L is the line length in radians or degrees (same units as x and wt). Then you have, simply by substituting L - x' for x: vf1(t, x') = sin(wt - L + x') vr1(t, x') = sin(wt + L - x' - 2L) = sin(wt - L - x') and so forth, and for the general case, (3) vfn(t, x') = (Gs * Gl)^n * sin(wt + x' - (2n + 1) * L) (4) vrn(t, x') = (Gs * Gl)^n * sin(wt - x' - 2nL) A Gl term was inadvertently omitted from the equations for vr. With that error corrected, and with complex reflection coefficients, vf1(t, x') = sin(wt - L + x') vr1(t, x') = |Gl| * sin(wt + L - x' - 2L + /_Gl) = sin(wt - L - x' + /_Gl) and so forth, and for the general case, (3) vfn(t, x') = |(Gs * Gl)^n| * sin(wt + x' - (2n + 1) * L + /_((Gs * Gl)^n) (4) vrn(t, x') = |Gl * (Gs * Gl)^n| * sin(wt - x' - 2nL + /_(Gl + (Gs + Gl)^n)) The reflection coefficient phase terms are easily handled in phasor analysis, in the same manner as the phase term related to the line length. Roy Lewallen, W7EL |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
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Standing morphing to travelling waves, and other stupid notions
On Jan 9, 3:30 pm, Gene Fuller wrote:
So do we now have a new requirement for waves and photons that there must be *net* energy flow? It's not a new requirement, Gene, just a very old requirement of physics. Photonic, i.e. EM waves, do not flow back and forth as you are implying. As long as the medium is homogeneous, i.e. doesn't change, a photon travels at the speed of light in one direction in a medium. So yes, net energy flow is absolutely a requirement for photons. EM waves *are* photons and do not vibrate back and forth in a medium. They travel in one direction at the speed of light in the medium until they encounter an impedance discontinuity. Virtually any physics book with a diagram of the EM wave E-field and H-field will show the direction of travel as one direction without the "one step forward and one step back" concept that you are proposing. You claimed that standing waves cannot be real waves because they cannot obey photon rules. I easily demonstrated that idea is incorrect.v All you demonstrated was your ignorance of the nature of photons. Your analysis was incorrect. You are seeing the standing wave illusion and assuming an impossibility of physics. It is very clear that you and others simply do not understand the nature and physics of photons and photonic waves. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
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Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
Roy Lewallen wrote:
Corrections: The equations I gave aren't adequate for complex reflection coefficients, which I didn't explicitly state. Also, I inadvertently omitted a multiplying factor in two equations. ... Roy Lewallen, W7EL Or, in honest terms, "forget about anything 'unifying', to make this ten gorilla float it is going to take tons of "special cases." In my humble opinion, complete proof "something is missing." I do NOT claim to know what that "something" is, only that it is QUITE obvious! Regards, JS |
Standing morphing to travelling waves, and other stupid notions
On Jan 9, 3:13 pm, Jim Kelley wrote:
On what page has Dr. Hecht written "a standing wave is a different kind of electromagnetic wave"? Since I didn't say that Dr. Hecht said that, it must be a rhetorical question. Here's what Dr. Hecht did say: In "Schaum`s College Physics Outline" by Bueche & Hecht on page 214 is written: "Standing Waves:....These might better not be called waves at all since they do not transport energy and momentum." (Thanks to Richard Harrison for that quote.) I agree with Dr. Hecht. Standing waves should not be called waves at all since they do not meet the definition and requirements for EM waves. I asserted that expression for the sum of traveling waves and the expression for the resulting standing wave pattern are related by trig identity, as per page 140 of the 28th Edition of the CRC Standard Mathematical Tables Handbook. Sorry Jim, that's not what you said. You asked if I recognized the trig identity that (presumably) equated a standing wave to a traveling wave. If that was not your meaning, it is time to say exactly what meaning I was supposed to assume. The 'wave' which stands is merely an amplitude envelope for the waves which move. Key word there is "waves". A standing wave is NOT self sufficient - it requires the superposition of a forward-traveling wave and a reverse- traveling wave. A standing wave loses its EM wave identity in the process of that superposition and apparently creates an illusion capable of mass hysteria. To alleviate that hysteria, one has only to compare the equations for standing waves and traveling waves or the corresponding graphs of those functions to see that they are hardly anything alike. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Jan 9, 3:33 pm, Gene Fuller wrote:
When you get back to the wilds of Texas go check out some rural power lines. Count the number of power factor correcting capacitors you see. I bet it is a lot less than the equivalent of one per city block. Power factor correcting capacitors are intended to correct for reactive loads, such as motors, not for reflections or standing waves on open ended power transmission lines. Within the city limits of my home town of Madisonville, TX, there is approximately one capacitor every city block. I had one in my front yard. But the exact number and distances do not matter one iota. Those capacitors exist to neutralize the inductive reactance in the system at the load. I use exactly the same method to twist the feedpoint impedance of my 75m Bugcatcher to 50 ohms. You said: "Power factor correcting capacitors are intended to correct for reactive loads," :-) Reactive loads cause reflections. The opposite reactance reduces reflections. Does that scheme of matching a transmission line to a load sound familiar? :-) My Bugcatcher antenna has about 25=j25 ohm feedpoint impedance on 40m. I install a -j50 cap from antenna to ground to achieve 50+j0 at the feedpoint. That's exactly what the power company capacitors do. Reflections *ARE* power factor problems. When the power company brings the power factor to unity, they have eliminated reflections and turned the system into a traveling wave energy delivery system. That you do not recognize the similarity between VARS and standing waves is really strange indeed. Standing waves contain nothing except VARS. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
On Jan 9, 7:48 pm, art wrote:
Thus it is the length of the antenna by your statement is what turns around the current regardless of the frequency applied. The feedpoint impedance of these standing wave antennas can be closely approximated by Zfp = (Vfor+Vref)/(Ifor+Iref) where all values are phasors. For instance, the reflected voltage will be out of phase with the forward voltage at the feedpoint for a resonant 1/2WL dipole while the reflected current will be in phase with the forward current. The feedpoint impedance of a 1/2WL dipole is very close to (|Vfor|-|Vref|)/(|Ifor|+|Iref|). See if you can figure it out for other lengths of dipoles. -- 73, Cecil, w5dxp.com |
Standing morphing to travelling waves, and other stupid notions
Just what is a "wave", anyway? Are there different "kinds" of
electromagnetic wave? If so, what are they? Does a "wave" have to travel in order to be a "wave", or can it just "vibrate" or "oscillate"? Or just "stand"? Most of my references call a standing wave a "pattern". Is a "pattern" a "wave"? Can a "wave" be a "pattern"? That should be good for another few hundred posts, at least. Sheesh. Roy Lewallen, W7EL |
Standing morphing to travelling waves, and other stupid notions
After reading this, I understand why you find Art's material interesting.
But, what's a "wave"? Roy Lewallen, W7EL AI4QJ wrote: "Roy Lewallen" wrote in message ... Just what is a "wave", anyway? Are there different "kinds" of electromagnetic wave? If so, what are they? Does a "wave" have to travel in order to be a "wave", or can it just "vibrate" or "oscillate"? Or just "stand"? Most of my references call a standing wave a "pattern". Is a "pattern" a "wave"? Can a "wave" be a "pattern"? That should be good for another few hundred posts, at least. Sheesh. Roy Lewallen, W7EL Roy, The standing wave is the mathematical sum of the forward and reflected waves. This sum is a superposition wave. The components of the superposition wave no longer exist by themselves; they form part of the summation which is the non-traveling "standing wave". Like its forward and reverse components (each containing "real" power) that would have been traveling waves prior to superposition, and which have now ceased to exist, the summation wave is also a real wave that vibrates at a frequency that, when multiplied by its wavelength, equals c (but traveling nowhere), and stored with "imaginary" or "reactive" power, where the real power components have been changed to reactive power components. Energy is conserved. The real energy in the traveling waves has been changed temporarily to potential or reactive VA (Cecil calls it VAR....same thing) energy until it dissipates into the radiation resitance by the radiation of photons/waves through free space (ignoring ohmic losses which also dissipate real power). After dissipation of each photon or wave into free space (where E=hf, take your pick) from the theoretical radiation resistor, the generator (transmitter) source must replenish energy into the antenna to keep the standing wave stored-energy system oscillating and then depleting into radiation. Without constant replenishment from the generator, the standing wave diminishes to zero. It is like an inductor, capacitor and radiation "resistor", all connected in parallel, and whose impedance is the radiation resistance of the antenna, which itself is related to the impedance of free space and the geometry of the antenna (as you know). What is not intuitive is where the other terminal of the "radiation resistor" is connected. But that is indeed where the traveling wave from the dissipated standing wave 'travels' to. That is where I find Art's material interesting. I do not think I have ever seen a depiction of this phenomenon that can be conceptualized but I think Art is trying. OK, go ahead. Lock, load and fire ;-) AI4QJ |
Standing morphing to travelling waves. was r.r.a.a Laugh Riot!!!
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