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what happens to reflected energy ?
On Jun 24, 3:25*pm, Cecil Moore wrote:
On Jun 24, 9:20*am, lu6etj wrote: Oh, I'm so sorry Cecil, I should have written "However I can not visualize a simple PHYSICAL mechanism/example to generate such system in a TL". Anyway, your additional info it is very useful to me. Thanks. The physical mechanism is the Z01==Z02 impedance discontinuity with its associated reflection coefficient, rho. We can see that reflection on a TDR so it is indeed a PHYSICAL mechanism. -- 73, Cecil, w5dxp.com don't forget the OTHER physical mechanism that is necessary, superposition... the ability to add voltages, currents, and fields in linear circuits and media. |
what happens to reflected energy ?
On Jun 24, 9:42*am, Cecil Moore wrote:
On Jun 24, 5:17*am, Keith Dysart wrote: I assume you will claim that there is now “constructive interference” rather than the previous “destructive interference”, but the line conditions are the same. How does the “reflected power” know if it should construct or destroy? The phase is the same. That's easy to answer. The Norton equivalent is a current source so currents should be used in the calculations. The phase angles between the two current components are 180 degrees different from the phase angles between the two voltage components. If the interference between voltages is constructive, the interference between currents will be destructive. Hint: the reflected current phasor is 180 degrees out of phase with the reflected voltage phasor because of the direction of travel of the reflected wave. As a result of directional convention, the power in the reflected wave is negative. So destructive interference for forward/reverse voltages is constructive interference for forward/reverse currents and vice versa. An SWR voltage maximum (constructive voltage interference) is an SWR current minimum (destructive current interference) and an SWR voltage minimum (destructive current interference) is an SWR current maximum (constructive voltage interference). Very inventive. And the wave just knows the difference between the 50ohm generator that is constructed in the Thevenin style and the 50ohm generator constructed in the Norton style. Amazing waves. And now the explanation for the mixed constant power mixed Thevenin/ Norton generator is ...? ....Keith |
what happens to reflected energy ?
On Jun 24, 10:39*am, Cecil Moore wrote:
On Jun 24, 5:27*am, Keith Dysart wrote: This equation is problematic. Firstly, it mixes power with voltage since theta is the angle between the voltage waveforms. You apparently don't understand what happens when one takes the dot product of two voltage phasors (and divides by Z0). The result is watts but the math involves the cosine of the angle between the two voltage phasors. All competent EEs should already know that. As K1TTT said, "why not just do the whole thing with voltages?" Because the title of this thread is: "What happens to reflected energy?", not what happens to reflected voltages? Doing the whole thing with voltages allows the obfuscation of interference to be swept under the rug. Because some of you guys don't recognize interference when it is staring you in face? I was taught to recognize interference between voltage phasors at Texas A&M in the 1950s. What happened to you guys? Here's a short lesson about dot products of voltage phasors and the resulting interference between the two voltages. Vtot = V1*V2 Vtot^2 = (V1*V2)^2 Vtot^2/Z0 watts = (V1*V2)^2/Z0 watts There will be the two obvious power terms, V1^2/Z0 and V2^2/Z0, representing the powers in the individual waves before superposition. There will be a third, additional interference term whose dimension is watts that *requires the dot product* between the two phasor voltages. Therefore, your objection is apparently just based on ignorance of the dot product of two voltage phasors. This mixing is bad form and clearly demonstrates the incompleteness of the power based analysis. Good grief! This "bad form" has been honored in the field of optical physics for at least a century. It was taught in EE courses 60 years ago. I don't know what has happened in the meantime. Walter Maxwell explains interference in section 4.3 in "Reflections" and obviously understands the role of interference in the redistribution of energy. The second is that there are two solutions depending on whether the positive or negative root is used? Why is one discarded? Is this numerology at work? Negative power is just a convention for "negative" direction of energy flow. Still does not explain why you choose only the positive root. Especially when you let the result be negative as a consequence of cos(theta). All EEs are taught in our engineering courses to ignore the imiginary root when calculating resistance, energy, or power. For instance, the Z0 for the 1/4WL matching section between R1 and R2 needs to be SQRT(R1*R2). When you perform that math function, do you really go on a world-wide search demanding a transmssion line with a negative Z0? Please get real. Thirdly, it only produces the correct answer for average energy flows. If the instantaneous energy flows are examined, the results using this equation do not align with observations. You forgot to add that instantaneous energy is as useless as tits on a boar hog, or as Hecht said, putting it mildly: "of limited utility". I always get a chuckle when you write this. It makes me think of a kid, who, upon being told that he can not have his favourite dessert until he finishes his brussel sprouts, declares that he has always hated that dessert. You might study why the real power folk prefer three phase to single. It all has to do with instantaneous power. Might not make a difference for light, but it sure helps the understanding at RF and lower. And your analysis still only produces the correct answers for the average and still gets the instantaneous wrong. I do see the benefit of repeating "of limited utility". It appears to me that instantaneous energy is just a mathematical artifact inside a process requiring integration in order to bear any resemblence to reality. Omit the integration and the process loses touch with reality. Instantaneous energy has zero area under the curve until the intergration process has been performed. A zero area represents zero energy. Otherwise, when you integrate from zero to infinity, the result would be infinite energy. Do you have any kind of reference for your treatment of instantaneous power? As I suggested above, have a look at the benefit of three phase over single. ....Keith |
what happens to reflected energy ?
On Jun 24, 11:25*am, Cecil Moore wrote:
On Jun 24, 9:20*am, lu6etj wrote: Oh, I'm so sorry Cecil, I should have written "However I can not visualize a simple PHYSICAL mechanism/example to generate such system in a TL". Anyway, your additional info it is very useful to me. Thanks. The physical mechanism is the Z01==Z02 impedance discontinuity with its associated reflection coefficient, rho. We can see that reflection on a TDR so it is indeed a PHYSICAL mechanism. But then what explains the reflection at the generator that presents Z0 to the line? ....Keith |
what happens to reflected energy ?
On 24 jun, 12:25, Cecil Moore wrote:
On Jun 24, 9:20*am, lu6etj wrote: Oh, I'm so sorry Cecil, I should have written "However I can not visualize a simple PHYSICAL mechanism/example to generate such system in a TL". Anyway, your additional info it is very useful to me. Thanks. The physical mechanism is the Z01==Z02 impedance discontinuity with its associated reflection coefficient, rho. We can see that reflection on a TDR so it is indeed a PHYSICAL mechanism. -- 73, Cecil, w5dxp.com Hello Cecil. I will try another translation because I think I could not explain well my question. We can see energy maximuns and nulls with simple experiments with light. We set a double slits experiment and we see light flowing in same direction reinforcing and cancellating in maximuns and minimuns on screen. You name it "redistribution", the energy "dissapearing" from nulls reappears on maximuns (Sorry, I use this horrifying light example too because physics books have such unhealthy trend to explain wave interference) In a TL, instead, total destructive interference in one point would mean energy stop flowing from that point forwards (is it OK say "forwards"?) and reverse its flow direction doubling his value, is it OK?. You name it "redistribution" too, not reflection. Well, my question was how we can set (devise) an experiment to get such behaviour in a TL? We need add (or put) in this point a source of energy to make the interference (the second slit light source from the light example, or the other front wave in a diffraction example), how to, here?. Light experiments is easy because we put both independent coherent light sources near each other illuminating the screen but here I can not visualize how put them. I hope I was explain better my question. 73 Miguel |
what happens to reflected energy ?
On 24 jun, 17:54, K1TTT wrote:
On Jun 24, 3:25*pm, Cecil Moore wrote: On Jun 24, 9:20*am, lu6etj wrote: Oh, I'm so sorry Cecil, I should have written "However I can not visualize a simple PHYSICAL mechanism/example to generate such system in a TL". Anyway, your additional info it is very useful to me. Thanks. The physical mechanism is the Z01==Z02 impedance discontinuity with its associated reflection coefficient, rho. We can see that reflection on a TDR so it is indeed a PHYSICAL mechanism. -- 73, Cecil, w5dxp.com don't forget the OTHER physical mechanism that is necessary, superposition... the ability to add voltages, currents, and fields in linear circuits and media. I mentioned same comment in another post. We use superposition principle in two different contexts. Superposition theorem in circuit theory, and wave superposition. Wave (traveling) superposition deals with f(t,x,y,z) and usually with puntual magnitudes, E, H, D, B, etc) while circuit theory deals with a subset f(t) phenomena and with integrated magnitudes (V, I). Sometimes that becomes a confused issue :) Miguel |
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what happens to reflected energy ?
On Jun 25, 7:46*am, lu6etj wrote:
On 24 jun, 17:54, K1TTT wrote: On Jun 24, 3:25*pm, Cecil Moore wrote: On Jun 24, 9:20*am, lu6etj wrote: Oh, I'm so sorry Cecil, I should have written "However I can not visualize a simple PHYSICAL mechanism/example to generate such system in a TL". Anyway, your additional info it is very useful to me. Thanks. The physical mechanism is the Z01==Z02 impedance discontinuity with its associated reflection coefficient, rho. We can see that reflection on a TDR so it is indeed a PHYSICAL mechanism. -- 73, Cecil, w5dxp.com don't forget the OTHER physical mechanism that is necessary, superposition... the ability to add voltages, currents, and fields in linear circuits and media. I mentioned same comment in another post. We use superposition principle in two different contexts. Superposition theorem in circuit theory, and wave superposition. Wave (traveling) superposition deals with f(t,x,y,z) and usually with puntual magnitudes, E, H, D, B, etc) while circuit theory deals with a subset f(t) phenomena and with integrated magnitudes (V, I). Sometimes that becomes a confused issue :) Miguel NO, superposition is always the same. it is the linear addition of currents or fields in a linear media. it works the same for circuits as for em waves. the big problem are the people who confuse the formulas for adding powers with adding fields or currents/voltages and forget the phase terms. the other big problem is keith who seems to want to separate his waves into separate time and space variables and leaves out the requirement that wave functions must be dependent on both space AND time. basically any solution to the wave equations derived from maxwell's laws must be of the form f(t-x/v). this leads him to the erroneous conclusions he gets from trying to compare his batteries to wave propagation. this is the same problem people have with standing waves, they have separate dependence on t and x, so they can't travel and can't transport energy. |
what happens to reflected energy ?
On Jun 24, 8:39*pm, Keith Dysart wrote:
Very inventive. And the wave just knows the difference between the 50ohm generator that is constructed in the Thevenin style and the 50ohm generator constructed in the Norton style. Amazing waves. Repeating myself - it is not necessary for you to imagine magical smart waves. Ignorant people invent magic and metaphysics to explain away their ignorance. All you need to do is to alleviate your ignorance concerning the laws of physics which those ordinary EM waves are obeying. *Externally*, it doesn't matter whether you use voltage superposition, current superposition, or EM field superposition - the results are identical. Every EE professor I ever had warned me about trying to look inside a Thevenin or Norton source at the power dissipation in the source resistor. For instance, their internal dissipations are exactly opposite for shorts and opens so exactly why should you expect the internal interference levels to be the same? When the Thevenin source is dissipating all the power inside the source from being connected to a *short-circuit*, it is experiencing total constructive interference. When the Norton source is dissipating all the power inside the source from being connected to an *open- circuit*, it is experiencing total constructive interference - opposite external conditions causing exactly the same phenomenon inside the two source boxes. And now the explanation for the mixed constant power mixed Thevenin/ Norton generator is ...? Neither the Thevenin equivalent source nor the Notron equivalent source is "constant power". The Thevenin equivalent source is a constant voltage source with a series source resistor and the Norton equivalent source is a constant current source with a shunt source resistor. A constant power source is conceivable but it would either need a circulator plus load, have a pretty sophisticated feedback system, or be driving an ideal instantaneous antenna tuner. -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 24, 8:58*pm, Keith Dysart wrote:
Still does not explain why you choose only the positive root. Of course it does. In the power density equation, choosing the negative root would lead to a violation of the conservation of energy principle. When one of the roots is obviously impossible in reality, a rational person chooses the other root. You might study why the real power folk prefer three phase to single. It all has to do with instantaneous power. I am a "real power folk", Keith. My first EE degree was in power generation and transmission. Three-phase puts less stress on the system by eliminating the hills and valleys in the energy flow common with traveling waves. But why do you believe that three-phase power transmission is relevant to ham radio? Are you running three-phase RF? Maxwell's equations don't even work for your mashed-potatoes version of energy. That should tell you something. -- 73, Cecil, w5dxp.com |
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