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Question about "Another look at reflections" article.
On Jun 6, 10:13*pm, lu6etj wrote:
On 6 jun, 18:00, Keith Dysart wrote: On Jun 6, 9:45*am, Cecil Moore wrote: On Jun 5, 6:28*pm, Keith Dysart wrote: There are indeed negative values. These occur when the energy is flowing in the other direction, ... Let's take a close look at the illusion that you are seeing and not comprehending. Observe a snapshot of the instantaneous power envelope of a traveling wave. It is a sinusoidal envelope with peak instantaneous power levels and zero instantaneous power levels. When it is traveling in the forward direction we consider that to be positive power. When it is traveling in the reverse direction, we consider that to be negative power. It is only a directional *convention* not proof that negative power exists. The only waves that can exist as waves on a transmission line are traveling waves. Ahhh. I see part of your problem. You are thinking envelopes. You need to change your point of view to be a particular point on the line. At this point, there is a function that describes the voltage: V(t). It may or may not be a sinusoid. There is a function for the current: I(t). And from these can trivialy be derived a function for power: P(t)=V(t)I(t). When I clip my instantaneous voltmeter across a line and measure 0 for all time, I can confidently say that no energy is flowing, for there is not. I am curious as to what you would answer? In "Optics", Hecht says instantaneous power is "of limited utility." You seem to have discovered that limit, stepped over it, and stepped in it. :-) Well, Hecht may have his limitations when dealing with Optics, but there is no reason to expect these same limitations to apply to circuit analysis. ...Keith Hi folks, good night (from here). I do not disagree with anything you have written, but I do think it is much too early to introduce Poynting vectors and lossy conductors to the discussion. Hello Keith, Yes, I understand your comment, I introduced Poynting vector only because both, energy and power, are scalars and we can not talk about scalars having direction without get in conceptual troubles; flux of power instead, have direction because surface vector presence in its definition gives directive characteristics to power crossing an imaginary surface. Slanted flux of electromagnetic power (Poynting) due resistive conductor simply seems to me a good example of a power flux in a TL not totally coincident with axial direction to provide a little more supporting to "directive" notion of Power Flux. However IMHO power flux do not seems to me more complicated than power, work, voltage, potential, energy, E and H fields, etc. All of them -I believe- are not very simple stuff :(, but they are very funny and interesting, indeed...!! :D. What do you think? My interests lie in understanding the behaviour of transmission lines to a level necessary to predict their basic behaviour. I did not find that I needed power flux to achieve this so I have not explored it. I suspect that you are right and it is an interesting topic. ..... Please would you mind tell me why "sine wave" it is not a correct use of "wave" word. The only dictionary I have = "Oxford *advanced english dictionary of current english defines wave as: "move to and fro, up and down", I believe also in english there are word qualifiers (sine, traveling, standing, etc) who specify the precise meaning of them in diverse contexts. Am I wrong about this?. Sine wave. Square wave. Triangle wave. Sawtooth wave. Waveform. Waveshape. 'Wave' seems to fit well with many words. I do not see a problem. .... Sorry by my insistence about convenience of discuss about "models". Please let me bring a citation: "At times, two quite differents models may serve equally well, but eventually one is usually found to prevail, not because it is right, but because it is both more convenient and more logically constructed. After all, models are constructed for convenience in thinking and recording, not as photographic images of nature" (From "Electromagnetic Engineering", Ronold W.P. King (PhD), page 94. McGraw Hill.1946). It seems to me that all is well as long as the model is used properly in the contexts in which it yields answers which are adequately accurate. .... I studied "Principle of Conjugates Impedance Matching" in my early student days and the "mirror reflection" explained by Walter Maxwell in his article agree with my undestanding about "where the reflected waves go" because to balance magnitudes it is necessary that they found a full mismatch on its way (path?) to generator. My own limited analisis led me to the same notion even without conjugate match if I calculate Incident and reflected voltages values in a half wave TL (as my early thread example), As I said, reading Cecil's web page quarter wave line examples led me to considerate another possible representations of the problem, in addition Owen's own ideas about it also made me consider the issue from another point of view. When I was trying to understand the behaviour of reflections in transmission lines, I found it extremely valuable to consider waveforms other than sinusoids. Step functions into open, shorted and properly terminated lines were quite enlightening. The arithmetic is much easier to perform than for sine waves and some of the results rather surprising. For example, apply a step function from a matched generator to an open transmission line. After the step makes one round trip, there will be a constant voltage everywhere on the line and the current will be zero everywhere. The wave reflection will show that there is a constant forward wave which is summed with a constant reflected wave to produce the constant voltage on the line. This is a strong example of why there is not necessarily power in the forward and reflected wave. Other interesting thought experiments are pulses and pulse trains. Arrange the timing so that a forward pulse collides with a reflected in the middle of the line. What are the voltages and currents that would be observed? Try alternating positive and negative pulses. And lastly, inject signals simultaneously from both ends of a transmission line. What is the result? When doing these, I would compute the power provided by the source and dissipated in the source resistor (I tend towards ideal Thevenin generators to simplify the analysis, though it is worth occasionaly doing the same with Norton), the energy stored in the line and the energy being dissipated in the load resistor, if there is one. Dealing with all of this in the time domain can help make the energy flows clear. These simple thought experiments definitely helped my understanding. Some of the assertions that have been made can be shown to be false when tested with these waveforms and analysis. ....Keith |
Question about "Another look at reflections" article.
On Jun 6, 3:40*pm, Keith Dysart wrote:
In the past you have insisted that only average powers were relevent. Does this mean you are ready to look at power (i.e. energy flow) in the time domain? Your concepts violate the laws of physics so no, I am not going to discuss it with you until you correct your numerous technical blunders. You need to give up on waves that violate Maxwell's equations. You need to give up on the occurrence of reflections where reflections are impossible. You need to give up on the concept that photons obey your every whim. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 6, 3:48*pm, Keith Dysart wrote:
You do seem to mention looking in the mirror quite frequently, as if it had something to do with understanding the behaviour of a transmission line. Are you aware that visible light and RF waves are identical phenomena, just at different frequencies? An RF transmission lines operates much the same as fiber optics. When I clip my instantaneous voltmeter across a line and measure 0 for all time, I can confidently say that no energy is flowing, for there is not. I am curious as to what you would answer? I have already answered. I agree with you that there is no NET energy flowing across that boundary. All it means is that the forward Poynting vector and reverse Poynting vector are of equal magnitudes. The reflection coefficient at that zero voltage point is zero so reflections are impossible. Yet, your concept requires a reflection at every node - which violates the laws of physics. Until you eliminate those magical metaphysical functions from your concepts, they are "of limited utility", to quote Hecht. Again, you are saying that there is zero traffic on the Golden Gate Bridge because the northbound vehicles equal the southbound vehicles. There is zero NET traffic, but such information is worthless. Someone still has to repair the bridge. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 6, 9:13*pm, lu6etj wrote:
I studied "Principle of Conjugates Impedance Matching" in my early student days and the "mirror reflection" explained by Walter Maxwell in his article agree with my undestanding about "where the reflected waves go" because to balance magnitudes it is necessary that they found a full mismatch on its way (path?) to generator. My own limited analisis led me to the same notion even without conjugate match if I calculate Incident and reflected voltages values in a half wave TL (as my early thread example), As I said, reading Cecil's web page quarter wave line examples led me to considerate another possible representations of the problem, in addition Owen's own ideas about it also made me consider the issue from another point of view. Miguel, you might be surprised to know that I got the constructive/ destructive interference concepts first from Walter Maxwell's, "Reflections". Take a look at "Sec 4.3 Reflection Mechanics of Stub Matching". Walt says: "The destructive wave interference between these two complementary waves at the stub point causes a complete cancellation of energy flow in the direction toward the generator." "Conversely, the constructive wave interference produces an energy maximum in the direction toward the load, resulting from the sum of the two reflected waves and the source wave." Walt clearly understands that wave cancellation, interference, and redistribution of reflected energy back toward the load is involved with his "conjugate mirror" and virtual-short-circuit concepts. So you see the concept of wave cancellation of complimentary reflected waves at a Z0-match didn't come first from me. The concept of all of that energy involved in wave cancellation changing direction and joining the forward wave didn't come first from me. I only resorted to the field of optics to gain additional technical information and expanded on Walt's original "Reflections" concepts in my article. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
Keith Dysart wrote:
These simple thought experiments definitely helped my understanding. Some of the assertions that have been made can be shown to be false when tested with these waveforms and analysis. ...Keith Here is a thought experiment for you. A C E +----\/\/\--+--/\/\/\--+--/\/\/\--+--/\/\/\--+ | | --- - - --- | B | D | F | +-----------+-----||---+---||-----+----------+ | | Four resistors, equal value. Four DC sources, equal value. Voltage A-B = 0, no power past here. Voltage C-D = 0, no power past here. Voltage E-F = 0, no power past here. No power crossing the boundaries on either side of the resistor between A and C. The resistor is not directly connected to a supply, how is it dissipating power, if any? (Yes, I do know the answer.) |
Question about "Another look at reflections" article.
On Jun 7, 10:11*pm, Cecil Moore wrote:
On Jun 6, 3:40*pm, Keith Dysart wrote: In the past you have insisted that only average powers were relevent. Does this mean you are ready to look at power (i.e. energy flow) in the time domain? Your concepts violate the laws of physics so no, I am not going to discuss it with you until you correct your numerous technical blunders. You need to give up on waves that violate Maxwell's equations. You need to give up on the occurrence of reflections where reflections are impossible. You need to give up on the concept that photons obey your every whim. -- 73, Cecil, w5dxp.com It took a lot of words to say "no, I am not ready." It is too bad, because the time domain is quite enlightening. ....Keith |
Question about "Another look at reflections" article.
On Jun 8, 5:30*am, joe wrote:
Here is a thought experiment for you. Does anyone know of a better Google solution to reading an ASCII schematic than copying from Google and pasting to Notepad? -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 8, 6:04*am, Keith Dysart wrote:
It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On 8 jun, 09:54, Cecil Moore wrote:
On Jun 8, 6:04*am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. -- 73, Cecil, w5dxp.com Good day. Sorry for the large extension of this post, my friends... My interests lie in understanding the behaviour of transmission lines to a level necessary to predict their basic behaviour. I did not find that I needed power flux to achieve this so I have not explored it. I suspect that you are right and it is an interesting topic. OK. I understand. I suposse you are more interested in "know how". When I complained about "the bench" at Richard, I was thinking on so many "know how" working years in my life. Today, I have more time to the "know WHYs" and I am trying to take my chance... :) A knowledge on Smith Chart (or software equivalent tools) using, solve most (if not all) of our ham practical and professional situations and provide enough basic theory for design purposes, I think in such sense I agree with you about it; however seems to me this topic thread have dealt a little more in the why's than the how's :) Look, several years ago many hams in my country -Argentine- came from technical schools, I become a ham in my seventeens (1969) when I was a very young electronic technician student. Here we have three fundamental educative levels: Primary, secondary (college?) and terciary (university). In secondary and terciary levels one of the first matters we study is physics. If we study electronics -on RF speciality-, only when we reach later study years of each level we learn transmission lines in the frequency domain with infinite lattices of RLCG, Telegrafer's equations solution, Smith charts, impedances, reactances, etc. If you do not go to study any RF especialities, the only knowledge you will have about transmission lines will be the physics ones. Physics models teach us the associated phenomena reffering basically to electromagnetic fields = we learn about, E field, H field, power and energy in more basics terms that frequency domain later more advanced studies. We do not learn typical AC models in basic physics (as you can see in Resnick-Hallyday books, for example, I can not give you college's references books because I study from local authors). In addition at very early physical mechanics courses we learn stationary and traveling waves, superposition principle and late, interference, in optics. Probably this is not the way to approaching to this topic that medium Ham employ because our natural ansiety to put the rig to work :D but seems to be a consensus about what is more basic and what more complex in formal pedagogic/understanding approaches to this matters. May be for that some of us tend to emphasize in directional power flux and other similar "ugly stuff" to analize transmission line questions, Perhaps for this reason it is easy and illustrative to me the Cecil's bridge car analogy about net energy flux, in addition, energy fluxes crossing areas results very intuitive to me because I can easily visualize (imagine) thousands of them hit and cross my body all the time. Sun light and infrared energy flux, light in houses, streets lights, sky diffused light, RF waves from broadcast and Hams, cellular phones, etc. Instead it is not so ease visualize in such intuitive context a single point with a permanent zero voltage (or E field, better) all the time. Measurement of interference phenomenom requires much more sofisticated and special reductive technics to simplify the problem. One of this technics it is, for example, voltage measurement on a transmission line point with a zero volt pure AC voltage node; but as Cecil et al said, a zero voltage point does not implicate not power flux crossing that point, that is a very known wave interference phenomenom, it is a little easy to visualize it if we remember that fields are "force fields" -fields are forces acting on testing devices- (charges, compass needles, etc), as we learnt in Coulomb laws. Fields being forces let us intuite that having two horses pulling a rock in right angles results in rock moving on a direction resulting of composition of that forces. Seem to be only one force acting in movement direction but are two!. also you can have both horses pulling in opposite directions, then we do not measure any movement and we could think there is not any force acting on the rock!, but our zero force measurement do not implicate there are not two horse pulling the rock! , zero net force it is different of zero force, I think we agree in that. I believe I undestand your reasoning: P=V*I, = not V, not P!, it is OK. But power not represent the internal system energy, power implicate "energy developed = work/time", you need energy (applied during certain time, then "power") to accelerate a charge, but the charge can have cinetic energy of its own; then, zero volt line point simply are a point where not any energy it is ADDED to the charges. not a point where there is not have (or not can have) preexistent electric energy (current) flowing; why zero volt net force field point would be stop travelling wave energy flow?; think of zero volt line point as a zero potential energy point, not acceleration in it, as the lowest part of a roller coaster... Incidentally, Poynting vector is defined as "speed of energy flux by unity of area", it is a different thing that power developed on interchange of energy phenomena such electric energy converted to heat or chemical reaction or movement, if we remember what we learn about P=V*I in Joule law (electric to heat transformation) it is a little more evident its transforming (not transport) energy context. Thus, transmited power its different than "developed power" in the other sense (perhaps here my translation not be clear enough). What is your opinion? Miguel Ghezzi LU6ETJ PS: I have some more things in my inkwell about models used on our issue but I have to leave it for future postings :) |
Question about "Another look at reflections" article.
On Jun 8, 4:20*pm, lu6etj wrote:
I believe I undestand your reasoning: P=V*I, = not V, not P!, it is OK. But power not represent the internal system energy, power implicate "energy developed = work/time", you need energy (applied during certain time, then "power") to accelerate a charge, ... One comment here. "Power" is defined differently in pure physics vs engineering. In physics, power requires work to be done. In engineering, one definition of power is energy passing a point in a unit of time, i.e. the energy doesn't have to be used up to be defined as power. One might think of it as potential power waiting to be used. These two quite different definitions of "power" are at the root of a lot of disagreements. For RF engineers we should probably honor "The IEEE Dictionary" definition: "power - the rate of generating, transferring, or using energy". Since energy cannot be destroyed, all energy that has been generated and is so far unused, is in the process of being transferred. Thus any reflected energy in a transmission line that is in the process of being transferred will be used (lost to heat or radiated) during the transient state following key-up. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 8, 10:30*am, joe wrote:
Here is a thought experiment for you. * * * * * * * * * *A * * * * *C * * * * *E * * * *+----\/\/\--+--/\/\/\--+--/\/\/\--+--/\/\/\--+ * * * *| * * * * * * * * * * * * * * * * * * * * * *| * * * --- * * * * * * * * * * * * * * * * * * * * * - * * * *- * * * * * * * * * * * * * * * * * * * * * --- * * * *| * * * * * B * * | * *D * | * * *F * * * * *| * * * *+-----------+-----||---+---||-----+----------+ * * * * * * * * * * * * *| * * * *| Four resistors, equal value. Four DC sources, equal value. Voltage A-B = 0, no power past here. Voltage C-D = 0, no power past here. Voltage E-F = 0, no power past here. No power crossing the boundaries on either side of the resistor between A and C. The resistor is not directly connected to a supply, how is it dissipating power, if any? (Yes, I do know the answer.) the first step of the analysis of this circuit is to combine the 4 voltage sources into a single source, thus rendering point b,d,f irrelevant. you can then analyze for the currents and voltages through the 4 resistors easily and show that current flows one way through all 4 of them equally. circuits 101, 2nd day. |
Question about "Another look at reflections" article.
On Jun 8, 6:30*am, joe wrote:
Keith Dysart wrote: These simple thought experiments definitely helped my understanding. Some of the assertions that have been made can be shown to be false when tested with these waveforms and analysis. ...Keith Here is a thought experiment for you. * * * * * * * * * *A * * * * *C * * * * *E * * * *+----\/\/\--+--/\/\/\--+--/\/\/\--+--/\/\/\--+ * * * *| * * * * * * * * * * * * * * * * * * * * * *| * * * --- * * * * * * * * * * * * * * * * * * * * * - * * * *- * * * * * * * * * * * * * * * * * * * * * --- * * * *| * * * * * B * * | * *D * | * * *F * * * * *| * * * *+-----------+-----||---+---||-----+----------+ * * * * * * * * * * * * *| * * * *| Four resistors, equal value. Four DC sources, equal value. Voltage A-B = 0, no power past here. Voltage C-D = 0, no power past here. Voltage E-F = 0, no power past here. No power crossing the boundaries on either side of the resistor between A and C. The resistor is not directly connected to a supply, how is it dissipating power, if any? (Yes, I do know the answer.) Very nice. How about: A C E +------+--/\/\/\--+--/\/\/\--+----+ | | | | | | | B | D | F | +------+-----||---+---||-----+----+ | | In any case, ABCD do not form a network, being, in fact, two disjoint networks. All bets are off. Consider: +------+--/\/\/\--+--/\/\/\--+----+ | | | | | | | B | D | F | +------+-----||---+---||-----+----+ | | | ----- --- | | A C E +------+--/\/\/\--+--/\/\/\--+----+ | | | | | | | | | | +------+-----||---+---||-----+----+ | | There can be current flowing at C and at D, as well as a large voltage difference between C and D, but these have nothing to do with each other and are not an indication of energy flow. For Cecil, using Google Groups, look for 'Options' and select 'Fixed Font'. ....Keith |
Question about "Another look at reflections" article.
On Jun 8, 8:54*am, Cecil Moore wrote:
On Jun 8, 6:04*am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. I assume that you do not consider that the problems you propose to be ones "whose basic premises violate the laws of physics". Consider then, the problem you propose in http://www.w5dxp.com/nointfr.htm. A time domain analysis (http://sites.google.com/site/keithdysart/ radio6), demonstrates that the analysis presented in http://www.w5dxp.com/nointfr.htm results in the wrong answers. Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. ....Keith |
Question about "Another look at reflections" article.
On Jun 8, 8:33*pm, Keith Dysart wrote:
Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. Everything I covered is covered in "Optics", by Hecht. If you can locate a flaw, you need to convince Hecht (and Born & Wolf) to expand their reference books to cover your pet subjects that they consider "of limited utility". -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On 8 jun, 22:33, Keith Dysart wrote:
On Jun 8, 8:54*am, Cecil Moore wrote: On Jun 8, 6:04*am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. I assume that you do not consider that the problems you propose to be ones "whose basic premises violate the laws of physics". Consider then, the problem you propose inhttp://www.w5dxp.com/nointfr.htm.. A time domain analysis (http://sites.google.com/site/keithdysart/ radio6), demonstrates that the analysis presented inhttp://www.w5dxp.com/nointfr.htm results in the wrong answers. Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. ...Keith Hi Cecil. Yes, good comment, definitions of terms specifying their meanings in each context avoid innecessary disagreements. I think that it is an essential predialogal "must". Keith: I just saw your web page = http://sites.google.com/site/keithdysart/radio3 where you seems disagree (please correct me if I am wrong) with our ideas about superposition principle. I search examples in the Net -for not paid the price of my hard and slow translations ;)- What do you think about them? http://www.physics.ucla.edu/demoweb/...rposition.html http://www.phy.ntnu.edu.tw/ntnujava/...php?topic=18.0 73 Miguel Ghezzi - LU6ETJ |
Question about "Another look at reflections" article.
On Jun 8, 11:27*pm, lu6etj wrote:
On 8 jun, 22:33, Keith Dysart wrote: On Jun 8, 8:54*am, Cecil Moore wrote: On Jun 8, 6:04*am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. I assume that you do not consider that the problems you propose to be ones "whose basic premises violate the laws of physics". Consider then, the problem you propose inhttp://www.w5dxp.com/nointfr.htm. A time domain analysis (http://sites.google.com/site/keithdysart/ radio6), demonstrates that the analysis presented inhttp://www.w5dxp.com/nointfr..htm results in the wrong answers. Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. ...Keith Hi Cecil. Yes, good comment, definitions of terms specifying their meanings in each context avoid innecessary disagreements. I think that it is an essential predialogal "must". Keith: I just saw your web page =http://sites.google.com/site/keithdysart/radio3 where you seems disagree (please correct me if I am wrong) with our ideas about superposition principle. I search examples in the Net -for not paid the price of my hard and slow translations ;)- What do you think about them? http://www.physics.ucla.edu/demoweb/...osition/waveSu... http://www.phy.ntnu.edu.tw/ntnujava/...php?topic=18.0 Superposition works just fine for voltage and current, but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. From any circuit analysis, superposition is used to find the voltages and the currents, and then the resulting total voltages and currents are used to compute powers. Doing it in the other order does not work. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. ....Keith |
Question about "Another look at reflections" article.
On Jun 9, 7:44*am, Keith Dysart wrote:
On Jun 8, 11:27*pm, lu6etj wrote: On 8 jun, 22:33, Keith Dysart wrote: On Jun 8, 8:54*am, Cecil Moore wrote: On Jun 8, 6:04*am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. I assume that you do not consider that the problems you propose to be ones "whose basic premises violate the laws of physics". Consider then, the problem you propose inhttp://www.w5dxp.com/nointfr..htm. A time domain analysis (http://sites.google.com/site/keithdysart/ radio6), demonstrates that the analysis presented inhttp://www.w5dxp.com/nointfr.htm results in the wrong answers. Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. ...Keith Hi Cecil. Yes, good comment, definitions of terms specifying their meanings in each context avoid innecessary disagreements. I think that it is an essential predialogal "must". Keith: I just saw your web page =http://sites.google.com/site/keithdysart/radio3 where you seems disagree (please correct me if I am wrong) with our ideas about superposition principle. I search examples in the Net -for not paid the price of my hard and slow translations ;)- What do you think about them? http://www.physics.ucla.edu/demoweb/...osition/waveSu... http://www.phy.ntnu.edu.tw/ntnujava/...php?topic=18.0 Superposition works just fine for voltage and current, but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. From any circuit analysis, superposition is used to find the voltages and the currents, and then the resulting total voltages and currents are used to compute powers. Doing it in the other order does not work. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. ...Keith I should have mentioned that the two references you provide are superposing amplitude (i.e. voltage or current) and not power. |
Question about "Another look at reflections" article.
On Jun 9, 6:44*am, Keith Dysart wrote:
Superposition works just fine for voltage and current, but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. It is invalid to try to use superposition on scalar values. There is a particular way to obtain the total power from the superposition of two EM waves. It's called the power density equation and contains an interference term, the sign of which tells us whether destructive, constructive, or zero interference results when the two EM waves are superposed. It agrees perfectly with calculating the total power from the voltage and current end products of superposition. It would explain everything that Roy is missing in his food-for-thought article. I first saw this equation in Dr. Best's QEX article. Ptot = P1 + P2 + 2*SQRT(P1*P2)*cos(A) where A is the angle between the electric fields (voltages) of the two superposed waves. We get the same equation when we square the s-parameter equations. (b1)^2 = (s11*a1 + s12*a2)^2, where (b1)^2 is the reflected power toward the load. (s11*a1 + s12*a2)^2 = (s11*a1)^2 + (s12*a2)^2 + 2(s11*a1)(s12*a2) If it is not obvious, this is the same equation as the power density equation above. The interference term in the squared s-parameter equation contains phasors whose dot product involves cos(A), where A is the angle between those two phasors. More s-parameter information available below - Please note pages 16 and 17 involving powers. http://www.sss-mag.com/pdf/hpan95-1.pdf -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
Keith Dysart wrote:
On Jun 8, 11:27 pm, lu6etj wrote: On 8 jun, 22:33, Keith Dysart wrote: On Jun 8, 8:54 am, Cecil Moore wrote: On Jun 8, 6:04 am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. I assume that you do not consider that the problems you propose to be ones "whose basic premises violate the laws of physics". Consider then, the problem you propose inhttp://www.w5dxp.com/nointfr.htm. A time domain analysis (http://sites.google.com/site/keithdysart/ radio6), demonstrates that the analysis presented inhttp://www.w5dxp.com/nointfr.htm results in the wrong answers. Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. ...Keith Hi Cecil. Yes, good comment, definitions of terms specifying their meanings in each context avoid innecessary disagreements. I think that it is an essential predialogal "must". Keith: I just saw your web page =http://sites.google.com/site/keithdysart/radio3 where you seems disagree (please correct me if I am wrong) with our ideas about superposition principle. I search examples in the Net -for not paid the price of my hard and slow translations ;)- What do you think about them? http://www.physics.ucla.edu/demoweb/...osition/waveSu... http://www.phy.ntnu.edu.tw/ntnujava/...php?topic=18.0 Superposition works just fine for voltage and current, but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. From any circuit analysis, superposition is used to find the voltages and the currents, and then the resulting total voltages and currents are used to compute powers. Doing it in the other order does not work. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. ...Keith I think the issue is the assertion there is no energy flow when I or V is 0 is where people disagree. I've tried to show with very simple (EE101) circuits that just because v = 0 at some points in a circuit there is still energy flowing. But, nobody apparently saw that. The leap from v=0 to energy flow=0 is the source of contention. Just because the amount of power sourced in one part of a circuit matches the power dissipated in that portion does not mean that all the power sourced in a portion of a circuit stayed in that portion to be dissipated there. The whole rest of the circuit is involved. When you do your Spice evaluation you only see the _net_ results of the underlaying evaluation and note the _apparent_ lack of energy flow. By selecting situations that give the results you want, you are reinforcing the misperception. If the generators did not put out identical pulses would you see the same lack of energy transfer? A linear system, where superposition applies should not change based on minor changes to the signals in it. Limiting any analysis to steady state sine waves or uniform pulse trains may cause you to reach the wrong conclusions. |
Question about "Another look at reflections" article.
On Jun 8, 11:05*pm, Cecil Moore wrote:
On Jun 8, 8:33*pm, Keith Dysart wrote: Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. Everything I covered is covered in "Optics", by Hecht. If you can locate a flaw, you need to convince Hecht (and Born & Wolf) to expand their reference books to cover your pet subjects that they consider "of limited utility". Let us follow the chain: 1. Hecht writes a book on OPTICS that includes some models. 2. Cecil reads the book. 3. Cecil interprets his readings. 4. Cecil applies his interpretations of the models to transmission lines. 5. Cecil draws some conclusions on the behaviours. 6. Keith, using basic circuit theory, reflection coefficients and analysis in the time domain, shows that Cecil's conclusions do not align with expected behaviours. 7. Cecil says any disagreement with Cecil's conclusions is a disagreement with Hecht. I suggest the error is more likely in steps 2 to 5; Hecht is, after all, well respected. In particular, 4. seems like a candidate. It is quite possible that Hecht understood the limitations of his models and that these models do not align with the detailed behaviour on a transmission line, though they might be completely adequate for the behaviours with light that Hecht was addressing in Optics. One must always be careful when applying a model in a different domain. Cecil ....Keith |
Question about "Another look at reflections" article.
On Jun 9, 8:26*am, Keith Dysart wrote:
6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. I suspect that your instantaneous virtual power must necessarily obey the conservation of energy principle but I am not going to waste my time trying to prove it. Hecht and I seem to agree 100% that *average* energy flow obeys the laws of physics. May I suggest that you read "Optics", by Hecht and post anything with which you disagree. I, and others, stopped taking you seriously when you said that an equal magnitude of the forward Poynting vector and the reflected Poynting vector proves that zero energy is crossing the boundary (without adding that it is zero NET energy). You have probably ruined your technical reputation with such nonsense. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 9, 8:26*am, Keith Dysart wrote:
6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I had to run an errand and, as usual, the answer popped into my head. The problem has to do with the definition of "power". If, in a flat system, one measures 100 watts at 100 points between the source and the load, does that mean that there are 10,000 watts of power available to be dissipated or radiated? Of course not! That is your conceptual error. Keith, your instantaneous virtual power is not *real* power until it is dissipated (or radiated). Thus your instantaneous virtual power is not required to obey the conservation of energy principle and all bets are off. If your instantaneous virtual power seems to violate the laws of physics, it is simply because you are counting it too many times or too few times. Instantaneous virtual power is *absolutely irrelevant* until it is dissipated or radiated. In my resistive-source/resistive-load (no radiation) example, nothing of value actually happens until power is dissipated in one of the two resistors. I have accounted for all the power being dissipated in the two resistors. Your V(t)*V(t) instantaneous power doesn't matter unless it is being dissipated and surprise!, it is not, i.e. your instantaneous power doesn't *count* until it is dissipated. Please feel free to try again. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On 9 jun, 13:23, Cecil Moore wrote:
On Jun 9, 8:26*am, Keith Dysart wrote: 6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. I suspect that your instantaneous virtual power must necessarily obey the conservation of energy principle but I am not going to waste my time trying to prove it. Hecht and I seem to agree 100% that *average* energy flow obeys the laws of physics. May I suggest that you read "Optics", by Hecht and post anything with which you disagree. I, and others, stopped taking you seriously when you said that an equal magnitude of the forward Poynting vector and the reflected Poynting vector proves that zero energy is crossing the boundary (without adding that it is zero NET energy). You have probably ruined your technical reputation with such nonsense. -- 73, Cecil, w5dxp.com Good evening. (sunny and cold day, here) Superposition works just fine for voltage and current, And electromagnetic waves... We also study TL in physics with a electromagnetic model (E-H fields). but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. Yes. As Cecil pointed, power not apply to superposition because it is a scalar magnitude. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. Because my interpretation of this sentences on the wave page: What happens when the signals from two identical generators at each end of a transmission line collide in the middle? Term "collide" without quotes suggest (to me) interaction (as particles). I learnt travelling waves do not "collides" in space (or linear mediums), simply they crossing each other (as ghosts).( I do not be sure about this translation) or, quoting UCLA web page note, "Wave maintain their integrity upon overlapping (without themselves being permanently changed)". Does energy cross the midpoint of the transmission line? ..... The plot shows that the voltage in the middle of the transmission line is always zero (that's femtoVolts on the left, not a bad representation for 0 in a simulation). Recalling that Power = (Volts times Amps), if the voltage is always 0, then there is no power. With no power, no energy is crossing the middle of the transmission line. My interpretation of last sentence (and reading technical controversy with Cecil and K1TT in thread) make me think that it does not match to superposition principle (except when there are not any travelling waves in system, of course). (I do not considered here spice application to travelling wave model issues). Please tell me if you agree with Java applets linked -applied to TL travelling waves- to clarify my understanding of your proposition. 73 Miguel Ghezzi - LU6ETJ PS: I hope to have some time today to make simple test of my own about Cecil, and Roy's web page examples cited on early posts of this thread. |
Question about "Another look at reflections" article.
On Wed, 9 Jun 2010 11:37:18 -0700 (PDT), lu6etj
wrote: Good evening. (sunny and cold day, here) Hi Miguel, I've been wondering about your time of day and climate comments until I realized you live in the outskirts of Buenos Aires. I visited there a few years ago (and Iguazú Cataratas). Amazing city. (Most stupendous water falls imaginable.) 73's Richard Clark, KB7QHC |
Question about "Another look at reflections" article.
On Jun 9, 8:33*am, Cecil Moore wrote:
On Jun 9, 6:44*am, Keith Dysart wrote: Superposition works just fine for voltage and current, but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. It is invalid to try to use superposition on scalar values. You may wish to rethink this assertion, otherwise... Go.... Do not pass Go. Do not collect 200$. ....Keith |
Question about "Another look at reflections" article.
On Jun 9, 8:55*am, joe wrote:
Keith Dysart wrote: On Jun 8, 11:27 pm, lu6etj wrote: On 8 jun, 22:33, Keith Dysart wrote: On Jun 8, 8:54 am, Cecil Moore wrote: On Jun 8, 6:04 am, Keith Dysart wrote: It is too bad, because the time domain is quite enlightening. Nothing wrong with a time domain analysis but analyzing problems whose basic premises violate the laws of physics is a waste of my time and yours. I assume that you do not consider that the problems you propose to be ones "whose basic premises violate the laws of physics". Consider then, the problem you propose inhttp://www.w5dxp.com/nointfr..htm. A time domain analysis (http://sites.google.com/site/keithdysart/ radio6), demonstrates that the analysis presented inhttp://www.w5dxp.com/nointfr.htm results in the wrong answers. Perhaps you could locate a flaw in the time domain analysis. Finding a flaw would pretty much settle the matter. ...Keith Hi Cecil. Yes, good comment, definitions of terms specifying their meanings in each context avoid innecessary disagreements. I think that it is an essential predialogal "must". Keith: I just saw your web page =http://sites.google.com/site/keithdysart/radio3 where you seems disagree (please correct me if I am wrong) with our ideas about superposition principle. I search examples in the Net -for not paid the price of my hard and slow translations ;)- What do you think about them? http://www.physics.ucla.edu/demoweb/...osition/waveSu.... http://www.phy.ntnu.edu.tw/ntnujava/...php?topic=18.0 Superposition works just fine for voltage and current, but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. From any circuit analysis, superposition is used to find the voltages and the currents, and then the resulting total voltages and currents are used to compute powers. Doing it in the other order does not work. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. ...Keith I think the issue is the assertion there is no energy flow when I or V is 0 is where people disagree. I've tried to show with very simple (EE101) circuits that just because v = 0 at some points in a circuit there is still energy flowing. But, nobody apparently saw that. The leap from v=0 to energy flow=0 is the source of contention. Just because the amount of power sourced in one part of a circuit matches the power dissipated in that portion does not mean that all the power sourced in a portion of a circuit stayed in that portion to be dissipated there. The whole rest of the circuit is involved. When you do your Spice evaluation you only see the _net_ results of the underlaying evaluation and note the _apparent_ lack of energy flow. By selecting situations that give the results you want, you are reinforcing the misperception. *If the generators did not put out identical pulses would you see the same lack of energy transfer? Of course not, because then there would be. And the measurement of voltage and current would show it to be so. P=VI holds. If one selects a V and I that are not appropriately related then one does not compute a useful power, though the units may still be J/s. As an illustrative example, if I measure the voltage across my stove and the current through my light, I can multiply them together to get watts, but it does not mean much. A linear system, where superposition applies should not change based on minor changes to the signals in it. Agreed. The computations done with the altered signals will successfully predict the altered outcome. Limiting any analysis to steady state sine waves or uniform pulse trains may cause you to reach the wrong conclusions Yes, and no. I suggest that the models that are claimed to successfully predict the behaviour for sinusoids should also successfully predict the behaviour for simpler examples. Otherwise the models are suspect. So I use the simpler examples to show that the models break down. ....Keith |
Question about "Another look at reflections" article.
On Jun 9, 12:23*pm, Cecil Moore wrote:
On Jun 9, 8:26*am, Keith Dysart wrote: 6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. Ahhh, so you are only claiming that 'on average', the energy does not enter the PA or 'on average' the energy is reflected. The finer grained time domain analysis, reveals that some energy does enter the PA, but that it comes back out again to keep the average the same. So if you want to live with the coarser, less complete models, that is fine as long as you understand the limitations of your model. It would be good if you were to articulate these limitations to the readers to reduce confusion. Of course, if you are happy with averages, it is not obvious to me why you want to bother with separating the signal in to forward and reflected. Why not just use the overall average energy flowing towards the load. ....Keith |
Question about "Another look at reflections" article.
On Jun 9, 2:37*pm, lu6etj wrote:
On 9 jun, 13:23, Cecil Moore wrote: On Jun 9, 8:26*am, Keith Dysart wrote: 6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. I suspect that your instantaneous virtual power must necessarily obey the conservation of energy principle but I am not going to waste my time trying to prove it. Hecht and I seem to agree 100% that *average* energy flow obeys the laws of physics. May I suggest that you read "Optics", by Hecht and post anything with which you disagree. I, and others, stopped taking you seriously when you said that an equal magnitude of the forward Poynting vector and the reflected Poynting vector proves that zero energy is crossing the boundary (without adding that it is zero NET energy). You have probably ruined your technical reputation with such nonsense. -- 73, Cecil, w5dxp.com Good evening. (sunny and cold day, here) Superposition works just fine for voltage and current, And electromagnetic waves... We also study TL in physics with a electromagnetic model (E-H fields). Yes, of course. but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. Yes. As Cecil pointed, power not apply to superposition because it is a scalar magnitude. Not quite. It does not apply to power because it does apply to voltages. If one doubles the voltage, one gets 4 times the power. There is no way to make superposition (which is simply addition) simultaneously work for voltage and power. As for scalars... Superposition works quite fine for circuit analysis with scalars. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. Because my interpretation of this sentences on the wave page: What happens when the signals from two identical generators at each end of a transmission line collide in the middle? Term "collide" without quotes suggest (to me) interaction (as particles). I learnt travelling waves do not "collides" in space (or linear mediums), simply they crossing each other (as ghosts).( I do not be sure about this translation) or, quoting UCLA web page note, "Wave maintain their integrity upon overlapping (without themselves being permanently changed)". Superposition is a mathematical trick that allows the solution of the problem. It does not mean that the pulses pass through each other, though that is one of the visualizations. Consider a point on the line where the current is always 0, no electrons cross this point nor does any energy. Did the pulses cross through such a point? The voltage envelope appears to, but does that mean the pulse did? Does energy cross the midpoint of the transmission line? ..... The plot shows that the voltage in the middle of the transmission line is always zero (that's femtoVolts on the left, not a bad representation for 0 in a simulation). Recalling that Power = (Volts times Amps), if the voltage is always 0, then there is no power. With no power, no energy is crossing the middle of the transmission line. My interpretation of last sentence (and reading technical controversy with Cecil and K1TT in thread) make me think that it does not match to superposition principle (except when there are not any travelling waves in system, of course). (I do not considered here spice application to travelling wave model issues). Please tell me if you agree with Java applets linked -applied to TL travelling waves- to clarify my understanding of your proposition. I have no issues with the applets. They show voltage waves crossing each other and appropriately use superposition to derive the results. Like many optical illusions, there are multiple ways to visualize what is happening. The second one for example can also be seen as the two pulses bouncing off of each other. The response would be identical if the transmission line was cut at the point of collision. These two simulations do not claim to show energy moving all the way down the line in both directions, nor do they superpose powers. So they look fine. ....Keith |
Question about "Another look at reflections" article.
On 9 jun, 23:55, Keith Dysart wrote:
On Jun 9, 2:37*pm, lu6etj wrote: On 9 jun, 13:23, Cecil Moore wrote: On Jun 9, 8:26*am, Keith Dysart wrote: 6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. I suspect that your instantaneous virtual power must necessarily obey the conservation of energy principle but I am not going to waste my time trying to prove it. Hecht and I seem to agree 100% that *average* energy flow obeys the laws of physics. May I suggest that you read "Optics", by Hecht and post anything with which you disagree. I, and others, stopped taking you seriously when you said that an equal magnitude of the forward Poynting vector and the reflected Poynting vector proves that zero energy is crossing the boundary (without adding that it is zero NET energy). You have probably ruined your technical reputation with such nonsense. -- 73, Cecil, w5dxp.com Good evening. (sunny and cold day, here) Superposition works just fine for voltage and current, And electromagnetic waves... We also study TL in physics with a electromagnetic model (E-H fields). Yes, of course. but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. Yes. As Cecil pointed, power not apply to superposition because it is a scalar magnitude. Not quite. It does not apply to power because it does apply to voltages. If one doubles the voltage, one gets 4 times the power. There is no way to make superposition (which is simply addition) simultaneously work for voltage and power. As for scalars... Superposition works quite fine for circuit analysis with scalars. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. Because my interpretation of this sentences on the wave page: What happens when the signals from two identical generators at each end of a transmission line collide in the middle? Term "collide" without quotes suggest (to me) interaction (as particles). I learnt travelling waves do not "collides" in space (or linear mediums), simply they crossing each other (as ghosts).( I do not be sure about this translation) or, quoting UCLA web page note, "Wave maintain their integrity upon overlapping (without themselves being permanently changed)". Superposition is a mathematical trick that allows the solution of the problem. It does not mean that the pulses pass through each other, though that is one of the visualizations. Consider a point on the line where the current is always 0, no electrons cross this point nor does any energy. Did the pulses cross through such a point? The voltage envelope appears to, but does that mean the pulse did? Does energy cross the midpoint of the transmission line? ..... The plot shows that the voltage in the middle of the transmission line is always zero (that's femtoVolts on the left, not a bad representation for 0 in a simulation). Recalling that Power = (Volts times Amps), if the voltage is always 0, then there is no power. With no power, no energy is crossing the middle of the transmission line. My interpretation of last sentence (and reading technical controversy with Cecil and K1TT in thread) make me think that it does not match to superposition principle (except when there are not any travelling waves in system, of course). (I do not considered here spice application to travelling wave model issues). Please tell me if you agree with Java applets linked -applied to TL travelling waves- to clarify my understanding of your proposition. I have no issues with the applets. They show voltage waves crossing each other and appropriately use superposition to derive the results. Like many optical illusions, there are multiple ways to visualize what is happening. The second one for example can also be seen as the two pulses bouncing off of each other. The response would be identical if the transmission line was cut at the point of collision. These two simulations do not claim to show energy moving all the way down the line in both directions, nor do they superpose powers. So they look fine. ...Keith- Ocultar texto de la cita - - Mostrar texto de la cita -- Ocultar texto de la cita - - Mostrar texto de la cita - Hello Keith: I believe I just understand where is the problem You are talking about "Superposition Theorem" of circuit theory and we are talking about "Superposition pinciple of waves". There are not the same stuff. Please read this page from "Physics for scientists and engineers with modern physics" book to aliviate my translation :) http://books.google.com.ar/books?id=...uantum&f=false Uf, what a large link!! If do not works search on page 501 of Google books with the appointed title. Note = "Two travelling waves can pass trough each other without being destroyed or even altered". (Op. Cit.). (Please pay attention to pond example). The applet there do not represent an opticall illusion, You can experiment with different shape opposite end launched pulses in a rope to verify that do not collide but pass through each other. It is a usual student laboratory work on applied physics. 73 Miguel ghezzi LU6ETJ PS: Yes Richard I live outside of Buenos Aires city. I hope you have been welcome on your visit to Argentine... and... what do you think of our beautiful girls, ah? ;D |
Question about "Another look at reflections" article.
On 10 jun, 01:45, lu6etj wrote:
On 9 jun, 23:55, Keith Dysart wrote: On Jun 9, 2:37*pm, lu6etj wrote: On 9 jun, 13:23, Cecil Moore wrote: On Jun 9, 8:26*am, Keith Dysart wrote: 6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. I suspect that your instantaneous virtual power must necessarily obey the conservation of energy principle but I am not going to waste my time trying to prove it. Hecht and I seem to agree 100% that *average* energy flow obeys the laws of physics. May I suggest that you read "Optics", by Hecht and post anything with which you disagree. I, and others, stopped taking you seriously when you said that an equal magnitude of the forward Poynting vector and the reflected Poynting vector proves that zero energy is crossing the boundary (without adding that it is zero NET energy). You have probably ruined your technical reputation with such nonsense. -- 73, Cecil, w5dxp.com Good evening. (sunny and cold day, here) Superposition works just fine for voltage and current, And electromagnetic waves... We also study TL in physics with a electromagnetic model (E-H fields). Yes, of course. but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. Yes. As Cecil pointed, power not apply to superposition because it is a scalar magnitude. Not quite. It does not apply to power because it does apply to voltages. If one doubles the voltage, one gets 4 times the power. There is no way to make superposition (which is simply addition) simultaneously work for voltage and power. As for scalars... Superposition works quite fine for circuit analysis with scalars. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. Because my interpretation of this sentences on the wave page: What happens when the signals from two identical generators at each end of a transmission line collide in the middle? Term "collide" without quotes suggest (to me) interaction (as particles). I learnt travelling waves do not "collides" in space (or linear mediums), simply they crossing each other (as ghosts).( I do not be sure about this translation) or, quoting UCLA web page note, "Wave maintain their integrity upon overlapping (without themselves being permanently changed)". Superposition is a mathematical trick that allows the solution of the problem. It does not mean that the pulses pass through each other, though that is one of the visualizations. Consider a point on the line where the current is always 0, no electrons cross this point nor does any energy. Did the pulses cross through such a point? The voltage envelope appears to, but does that mean the pulse did? Does energy cross the midpoint of the transmission line? ..... The plot shows that the voltage in the middle of the transmission line is always zero (that's femtoVolts on the left, not a bad representation for 0 in a simulation). Recalling that Power = (Volts times Amps), if the voltage is always 0, then there is no power. With no power, no energy is crossing the middle of the transmission line. My interpretation of last sentence (and reading technical controversy with Cecil and K1TT in thread) make me think that it does not match to superposition principle (except when there are not any travelling waves in system, of course). (I do not considered here spice application to travelling wave model issues). Please tell me if you agree with Java applets linked -applied to TL travelling waves- to clarify my understanding of your proposition. I have no issues with the applets. They show voltage waves crossing each other and appropriately use superposition to derive the results. Like many optical illusions, there are multiple ways to visualize what is happening. The second one for example can also be seen as the two pulses bouncing off of each other. The response would be identical if the transmission line was cut at the point of collision. These two simulations do not claim to show energy moving all the way down the line in both directions, nor do they superpose powers. So they look fine. ...Keith- Ocultar texto de la cita - - Mostrar texto de la cita -- Ocultar texto de la cita - - Mostrar texto de la cita - Hello Keith: I believe I just understand where is the problem *You are talking about "Superposition Theorem" of circuit theory and we are talking about "Superposition pinciple of waves". There are not the same stuff. Please read this page from "Physics for scientists and engineers with modern physics" book to aliviate my translation :) http://books.google.com.ar/books?id=...01&lpg=PA501&d... Uf, what a large link!! If do not works search on page 501 of Google books with the appointed title. Note = "Two travelling waves can pass trough each other without being destroyed or even altered". (Op. Cit.). (Please pay attention to pond example). The applet there do not represent an opticall illusion, You can experiment with different shape opposite end launched pulses in a rope to verify that do not collide but pass through each other. It is a usual student laboratory work on applied physics. 73 Miguel ghezzi LU6ETJ PS: Yes Richard I live outside of Buenos Aires city. I hope you have been welcome on your visit to Argentine... and... what do you think of our beautiful girls, ah? ;D- Ocultar texto de la cita - - Mostrar texto de la cita - Before I forget... Here is early mornig and I am ready for bed (I'm nocturnal habits). I want give a QSL to Cecil's comment on Maxwell article and Joe's example in CC. Also, noblesse oblige, I recall that Cecil make this comment in a very early post in this thread: Yes, standing waves are hard to visualize, but there is indeed same- cycle interference involving forward waves and reflected waves. There is a certain delay from the source signal to the load and back that can be calculated if one chooses. The wave reflection model is closer to Maxwell's equations than is the lumped-circuit model where EM waves propagate instantaneously. Pointing to differences between lumped constants circuit theory models (superposition theorem) and TL issues. I aknowledge his linked page = http://www.google.com/url?sa=D&q=htt...06V-3Vix1MXnrA where it said: "There are no standing waves on a lumped element circuit component. (In fact, lumped-element circuit theory inherently employs the cosmological presupposition that the speed of light is infinite, as every EE sophomore should know. See, e.g., - Electric Circuits, by J.W. Nilsson, Addison-Wesley, 1983, p. 3.)" Probabily Cecil had in mind this controversy when I submitted my question to this newsgroup. He will correct me if I am wrong. Thank you very much, and now, I am go to ZZZZZZZ...! Miguel |
Question about "Another look at reflections" article.
On Wed, 9 Jun 2010 21:45:05 -0700 (PDT), lu6etj
wrote: PS: Yes Richard I live outside of Buenos Aires city. I hope you have been welcome on your visit to Argentine... and... what do you think of our beautiful girls, ah? ;D Ah! Cherchez la femme. We did a lot of walking around town (stayed in the Emperador across from Estación Retiro) and there were certainly crowds of them on Av (Calle?) Florida and along Av 9 de Julio (24 lanes of traffic as I remember with trying to cross from the Opera house Teatro Colón). In the back of my mind was that Buenos Aires enjoys the world's highest pedestrian death rate. One large truck replaced it horn with the sound of someone screaming. (The memories are starting to flood back.) It was strange to see Spanish headlines about the capture of Saddam Husein in his spider hole. An out-of-America experience much like the evening when I was standing on the quay in Acapulco, waiting for the Liberty launch back to my ship, and a wave of talk spread through our group that Nixon had just resigned. However, returning to pretty girls, when I was in Caracas ten years ago, I was told the poor lived up in the hills that surround the city like a fish bowl and the girls got plenty of exercise climbing them. Gave them Miss Universe figures. As for Buenos Aires hospitality, too much food (huge steaks) at the wrong hours. When we went to a restaurant at 9PM, it was like we were arriving for high tea. How gauche of us. Later, we were satisfied to enjoy empanadas in the late afternoon and call it dinner. We also took the train from Estación Constitución down to La Plata to see the Catedral. Dinner nearby was Wiener Schnitzel. Enjoyed walking through Recoleta (and seeing the cemetery). Also got out to Abasto to see Carlos Gardel's neighborhood (love his Tango, his singing gets better every year). It was great! 73's Richard Clark, KB7QHC |
Question about "Another look at reflections" article.
On Jun 9, 9:11*pm, Keith Dysart wrote:
On Jun 9, 8:33*am, Cecil Moore wrote: It is invalid to try to use superposition on scalar values. You may wish to rethink this assertion, otherwise... Go.... Do not pass Go. Do not collect 200$. Keith, virtually everyone (except you) knows that English is a contextual language and that the entire context cannot be repeated every time a sentence is uttered. You know and I know that the context is EM waves. The obvious context of my statement is: "It is invalid to try to use EM wave superposition on scalar values, since scalar values are not EM waves." If you feel forced to resort to crap like that, it indicates that you have already lost any argument. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 9, 9:29*pm, Keith Dysart wrote:
Ahhh, so you are only claiming that 'on average', the energy does not enter the PA or 'on average' the energy is reflected. Of course, you already knew that because I have never said otherwise. I have stated my opinion more than once that instantaneous (virtual) power is not worth discussing. Here is what I said on my web page: "Please note that any power referred to in this paper is an AVERAGE POWER. Instantaneous power is beyond the scope of this article, irrelevant to the following discussion, and "of limited utility" according to Eugene Hecht. [4]" I have an ample library and cannot find any reference to instantaneous (virtual) power other than it is "of limited utility", as Hecht noted. Most of the references imply that paying close attention to the reality of instantaneous (virtual) power can lead one down a primrose path to false assumptions. The finer grained time domain analysis, reveals that some energy does enter the PA, but that it comes back out again to keep the average the same. So what? If it is not dissipated or radiated, it doesn't matter to anyone (except you). It would be good if you were to articulate these limitations to the readers to reduce confusion. I have always said that I was talking about power dissipation in a source resistor or load resistor (or radiation), but you already knew that. I have said that instantaneous virtual power is irrelevant and not worth discussing. Here is a question for you. Given that P(t)=V(t)*I(t), we measure 10 watts at each of 10 points within a single cm., five just inside a source and five just outside the source. Does that mean we have 100 watts in that single cm.? What is the physical meaning of being able to measure an infinite amount of power given an infinite number of measurement points? -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 10, 1:48*am, lu6etj wrote:
"There are no standing waves on a lumped element circuit component. (In fact, lumped-element circuit theory inherently employs the cosmological presupposition that the speed of light is infinite, as every EE sophomore should know. See, e.g., - Electric Circuits, by J.W. Nilsson, Addison-Wesley, 1983, p. 3.)" It probably should have said: "By a (possibly invalid) definition only, there are no standing waves on a lumped element circuit component, even though standing waves might exist in reality". Note that Dr. Corum is NOT saying that there are no standing waves. He is simply repeating the false assumptions of the lumped-element circuit model. In his other paper, he says that if a circuit is electrically longer than about 15 degrees and phase is important, the lumped- element circuit model should not be used. Any lumped-element circuit analysis can be caused to fail simply by increasing the source frequency. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On Jun 10, 2:55*am, Keith Dysart wrote:
On Jun 9, 2:37*pm, lu6etj wrote: On 9 jun, 13:23, Cecil Moore wrote: On Jun 9, 8:26*am, Keith Dysart wrote: 6. Keith, using basic circuit theory, reflection coefficients and * *analysis in the time domain, shows that Cecil's conclusions do not * *align with expected behaviours. I must have missed the posting where you proved RF waves do not obey the *average* power density (irradiance) equation from "Optics", by Hecht. Neither Hecht nor I have ever said anything about instantaneous virtual power except that it is "of limited usefulness". Nothing you have posted about instantaneous virtual power has disagreed or disproved anything that I have said about *average* power where I simply quoted Hecht. I suspect that your instantaneous virtual power must necessarily obey the conservation of energy principle but I am not going to waste my time trying to prove it. Hecht and I seem to agree 100% that *average* energy flow obeys the laws of physics. May I suggest that you read "Optics", by Hecht and post anything with which you disagree. I, and others, stopped taking you seriously when you said that an equal magnitude of the forward Poynting vector and the reflected Poynting vector proves that zero energy is crossing the boundary (without adding that it is zero NET energy). You have probably ruined your technical reputation with such nonsense. -- 73, Cecil, w5dxp.com Good evening. (sunny and cold day, here) Superposition works just fine for voltage and current, And electromagnetic waves... We also study TL in physics with a electromagnetic model (E-H fields). Yes, of course. but is mostly invalid for power. Attempting to apply superposition to power will lead to inaccurate results. Yes. As Cecil pointed, power not apply to superposition because it is a scalar magnitude. Not quite. It does not apply to power because it does apply to voltages. If one doubles the voltage, one gets 4 times the power. There is no way to make superposition (which is simply addition) simultaneously work for voltage and power. As for scalars... Superposition works quite fine for circuit analysis with scalars. I am curious as to what I wrote on the web page that suggested disagreement with the superposition principle. Because my interpretation of this sentences on the wave page: What happens when the signals from two identical generators at each end of a transmission line collide in the middle? Term "collide" without quotes suggest (to me) interaction (as particles). I learnt travelling waves do not "collides" in space (or linear mediums), simply they crossing each other (as ghosts).( I do not be sure about this translation) or, quoting UCLA web page note, "Wave maintain their integrity upon overlapping (without themselves being permanently changed)". Superposition is a mathematical trick that allows the solution of the problem. It does not mean that the pulses pass through each other, though that is one of the visualizations. Consider a point on the line where the current is always 0, no electrons cross this point nor does any energy. Did the pulses cross through such a point? The voltage envelope appears to, but does that mean the pulse did? Does energy cross the midpoint of the transmission line? ..... The plot shows that the voltage in the middle of the transmission line is always zero (that's femtoVolts on the left, not a bad representation for 0 in a simulation). Recalling that Power = (Volts times Amps), if the voltage is always 0, then there is no power. With no power, no energy is crossing the middle of the transmission line. My interpretation of last sentence (and reading technical controversy with Cecil and K1TT in thread) make me think that it does not match to superposition principle (except when there are not any travelling waves in system, of course). (I do not considered here spice application to travelling wave model issues). Please tell me if you agree with Java applets linked -applied to TL travelling waves- to clarify my understanding of your proposition. I have no issues with the applets. They show voltage waves crossing each other and appropriately use superposition to derive the results. Like many optical illusions, there are multiple ways to visualize what is happening. The second one for example can also be seen as the two pulses bouncing off of each other. The response would be identical if the transmission line was cut at the point of collision. only in the very special case of the far end being an open or short circuit and the line being lossless. simulate it for a more general case of a load other than those and see what happens. |
Question about "Another look at reflections" article.
On 25 mayo, 03:35, Richard Clark wrote:
On Mon, 24 May 2010 17:17:41 -0700 (PDT), lu6etj wrote: PSE, with the due respect and consideration toward you an the distinguished colleagues and friends, Would you mind return to the original question? (sorry if it is not this the most polite form to ask it) Hi Miguel, I presume by "original question" you mean: On Mon, 24 May 2010 13:06:19 -0700 (PDT), lu6etj wrote: Absorb the reflected power or amortiguate the effects of variyng load impedance? The answer is YES. Now, if you mean by absorb that all absorbtion results in heat, then the answer is NO. If you mean by absorb that all energy is combined in a load, then the answer is YES. The difference between YES and NO is the PHASE differences of the two energies that are combined. 73's Richard Clark, KB7QHC Hello folks. (I am learnig new greetings...) Hi Cecil: Yesterday I was making some calculations based in your article "An energy Analysis of a Simple Ideal Source, Part:1 Zero Average Interference" I have checked your and Roy results using three methods: Mathematical solution using the TL Zin obtained from clássical formulas. Spice simulation with equivalent lumping element resulting of the above cited formulas, and Spice simulation with a RG8U TL loaded with RL's of your and Roy examples.. In all cases results agree between different methods and with your examples (I do.not want to seem pedantic with this last comment ;) ) For this discussion would be relevant the results corresponding to sixth column of your article using a quarter wave line. They a 0 - 8 - 22 - 50 - 88.9 - 128 and 200 W (190 W the last one with Spice TL simulation). Since the refflection coefficient has not changed, if I do not misunderstood the premises, quarter wave line PRs do not seems agree with the hipothesis of Pref adding in Rs with Pfor. I think that is what Ro. Lewallen denote in his "Food for thought: Forward and reverse power" example. Frankly, I think there are somthing wrong in my interpretation because you (all) should have already performed these checks. I remember you have said something about that your work (article) was not finished yet. I confess actually I have not yet entirely clear your differences but I hope to capture it more accurately. 73 - Miguel LU6ETJ PS: Hey Richard, I'm glad you liked our city, girls and steaks :) well you like Gardel (me too) and I like so much your old and classic jazz music. Billie Holiday... she is one of my favorites. A friend of me living in Caracas now tell me the gift of fifteen for girls consists of the operation to put silicones. must be very dangerous for heart patients, a lot more dangerous than Buenos Aires street traffic ;) (SRI, I can not translate = "waiting for the Liberty launch back to my ship", give me a hand PSE) |
Question about "Another look at reflections" article.
On Thu, 10 Jun 2010 20:04:14 -0700 (PDT), lu6etj
wrote: (SRI, I can not translate = "waiting for the Liberty launch back to my ship", give me a hand PSE) Hi Miguel, I was in the Navy from 1968 to 1975. Our president Richard Nixon resigned from the presidency in 1974. My ship was in transit between Charleston, South Carolina to go to the naval ship yard for overhaul in Bremerton, Washington (state), near Seattle (where I live). On the way, we spent 5 days in the harbor of Acapulco. We were "anchored out," which means resting at anchor in the bay instead of tied up at a pier. The only way to get back and forth was by a smaller boat (carries about 75 people). That boat is called a launch. That name is qualified with Liberty because those who used it were going on Liberty. In the Navy, Liberty means "time off" or "free time," which means we can leave work and do what we want to until 0800 the next day. If we have to be back by midnight, it is called "Cinderella Liberty." I was one of the senior Metrologists in the Fleet Electronics Calibration Laboratory aboard the USS Holland, AS-32 (now tied up in retirement in Bremerton). I did precision measurement and calibration of RF standards and maintained a Cesium Beam Standard (atomic clock) that set the time for the "Boomers" (nuclear submarines). Later, after the Navy, I added physical standards (length, pressure, tension, temperature, torque, smoothness, incline...) to my resumé. I try to catch as many movies from Argentina as possible (I like Ricardo Darín as an actor, and love "Nueve Reinas"). One of my degrees is Cinema (the other is English). Another title I like (since it is about an out-of-work programmer) is "Una Sombra ya Pronto Serás." Sometimes that title works here too. Héctor Olivera, the director, has done some interesting things. 73's Richard Clark, KB7QHC |
Question about "Another look at reflections" article.
On Jun 10, 10:04*pm, lu6etj wrote:
For this discussion would be relevant the results corresponding to sixth column of your article using a quarter wave line. They a 0 - 8 - 22 - 50 - 88.9 - 128 and 200 W (190 W the last one with Spice TL simulation). I'm sorry, Miguel, using a "quarter wave line" is a mistake. You should be using a lossless 1/8WL line. The results in my article are based on a 1/8WL (45 deg) lossless line, NOT on a 1/4WL (90 deg) line. *Please re-run your Spice simulation using a 1/8WL line* and report back to us. When the line is 1/8WL long, the reflected wave arrives back at Rs 90 degrees out of phase with the forward wave and cos(90) = 0, so the interference term is zero and all the reflected power is dissipated in the source resistor. For the special case where cos(A)=0, i.e. the interference term is zero, the power density equation reduces to: Prs = Pfor + Pref + 0 Nowhere in my article did I use a 1/4WL line so please don't say that your Spice results disagree with my chart. It is perfectly understandable that your 1/4WL results do not agree with my 1/8WL results. -- 73, Cecil, w5dxp.com |
Question about "Another look at reflections" article.
On 11 jun, 11:06, Cecil Moore wrote:
On Jun 10, 10:04*pm, lu6etj wrote: For this discussion would be relevant the results corresponding to sixth column of your article using a quarter wave line. They a 0 - 8 - 22 - 50 - 88.9 - 128 and 200 W (190 W the last one with Spice TL simulation). I'm sorry, Miguel, using a "quarter wave line" is a mistake. You should be using a *lossless 1/8WL line. The results in my article are based on a 1/8WL (45 deg) lossless line, NOT on a 1/4WL (90 deg) line. *Please re-run your Spice simulation using a 1/8WL line* and report back to us. When the line is 1/8WL long, the reflected wave arrives back at Rs 90 degrees out of phase with the forward wave and cos(90) = 0, so the interference term is zero and all the reflected power is dissipated in the source resistor. For the special case where cos(A)=0, i.e. the interference term is zero, the power density equation reduces to: Prs = Pfor + Pref + 0 Nowhere in my article did I use a 1/4WL line so please don't say that your Spice results disagree with my chart. It is perfectly understandable that your 1/4WL results do not agree with my 1/8WL results. -- 73, Cecil, w5dxp.com Yes it is OK I am not saying your article use 1/4, In a previous post I said with 1/8 lambda TL, results support your idea of Pref dissipating on Rs (is correct my interpretation of your idea?). Yesterdey I posted results calculated for a 1/4 lambda TL to comparing both ponting to 1/4 lambda results did not agree with a Pref dissipating on RS. Then, I thought you are not intending generalize the very common notion of.Pref returnig to generator but seem to me you are hypothesizing there are different mechanisms dealing with Pref depending of the line length. Is It OK? (Meanwhile I will take a look at the new thread to look if I can find exactly what is the heart of this question ;) ) 73 - Miguel - LU6ETJ PS: Thanks Richard, I would not have guessed it without your help. Really a very interesting electronics job! I'm glad you're interested in our films.. Of course here I grew up with the ubiquitous Hollywood movies and I am very familiar with it and his old and popular TV series. Before I go to bed this early morning I visited your QTH vía Google streets panoramic photographies. Also I saw David -K1TTT- watching his computer screen via his robotic webcam. I shake hands in front of my PC monitor to greet him but did not see me :D |
Question about "Another look at reflections" article.
On Jun 11, 4:11*pm, lu6etj wrote:
Then, I thought you are not intending generalize the very common notion of.Pref returnig to generator but seem to me you are hypothesizing there are different mechanisms dealing with Pref depending of the line length. Is It OK? Yes, a 1/8WL line is a *SPECIAL CASE* where zero interference exists. In the power density equation: Ptot = P1 + P2 + 2*SQRT(P1*P2)*cos(A) if A = 90, then cos(A) = 0 and there is no interference term and no interference. When you go to a 1/4WL line, it is no longer a special case where cos(A)=0 and I have not published anything on my web page about that condition. -- 73, Cecil, w5dxp.com |
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