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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 |
what happens to reflected energy ?
On Jun 24, 8:59*pm, Keith Dysart wrote:
But then what explains the reflection at the generator that presents Z0 to the line? Your error is in assuming it is a reflection. It is NOT a reflection which, by definition, involves one wave. It is a redistribution of energy due to superposition which, by definition, involves two or more waves. In a system designed to eliminate reflections at the source, ALL of the redistribution of reflected energy back toward the load is due to superposition accompanied by interference. From the FSU web site: "... when two waves of equal amplitude and wavelength that are 180- degrees ... out of phase with each other meet, they are not actually annihilated, ... All of the ... energy present in these waves must somehow be recovered or redistributed in a new direction, according to the law of energy conservation ..." Nothing said about *reflection* (involving a single wave). It is all about the meeting (superposition) of two waves which can cause the redistribution of energy. It may look somewhat like a reflection but it is technically NOT a reflection. -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 25, 2:13*am, lu6etj wrote:
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?. In our ham transmission line systems, the goal is to accomplish total destructive interference toward the source, i.e. zero reflected energy incident upon the source. So let's talk about destructive interference toward the source and constructive interference toward the load. You name it "redistribution" too, not reflection. By definition, reflection is something that happens to a single wave. By definition, superposition involves two or more waves. The redistribution that I am talking about can include both reflection and superposition if both are present. Depending upon the system configuration, both may be present, both may be absent, or one exist without the other. Well, my question was how we can set (devise) an experiment to get such behaviour in a TL? I've presented it before and it is a simple Z0-match involving a 1/4WL matching section. 50w-----50 ohm------+------1/4WL 300 ohm------1800 ohm load On the source side, rho at '+' is 0.7143 Using a TDR, we can verify that there is indeed a reflection from the 50/300 ohm impedance discontinuity. What happens to that reflection during steady-state? What happens to Vfor1(rho) = 50v(0.7143) = 35.7v? What happens to Pfor1(rho^2) = 50w(0.51) = 25.5w? -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
"Cecil Moore" wrote ... On Jun 24, 8:59 pm, Keith Dysart wrote: But then what explains the reflection at the generator that presents Z0 to the line? Your error is in assuming it is a reflection. It is NOT a reflection which, by definition, involves one wave. It is a redistribution of energy due to superposition which, by definition, involves two or more waves. In a system designed to eliminate reflections at the source, ALL of the redistribution of reflected energy back toward the load is due to superposition accompanied by interference. From the FSU web site: "... when two waves of equal amplitude and wavelength that are 180- degrees ... out of phase with each other meet, they are not actually annihilated, ... All of the ... energy present in these waves must somehow be recovered or redistributed in a new direction, according to the law of energy conservation ..." Nothing said about *reflection* (involving a single wave). It is all about the meeting (superposition) of two waves which can cause the redistribution of energy. It may look somewhat like a reflection but it is technically NOT a reflection. In the Hertz dipole the reflection take place but in the loop antenna "two waves of equal amplitude and wavelength that are 180-degrees ... out of phase with each other meet," But the both cases are the same. At the meeting the energy is radiated and the electrons emitted because in the meeting place the voltage is doubled. The electronic circuit theory do not use EM. S*. |
what happens to reflected energy ?
On 25 jun, 08:30, K1TTT wrote:
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.- Ocultar texto de la cita - - Mostrar texto de la cita - NO, superposition is always the same I did not say that things were fundamentally different, I said "context" it is different, as "substraction" in mathematics, you can not subtract a natural number bigger from a smaller one in natural field, but you can do it in integer field, we have to apply (comply?) contextual rules with such operations. Otherwise I agree with what you say. 73 |
what happens to reflected energy ?
On 25 jun, 10:00, Cecil Moore wrote:
On Jun 25, 2:13*am, lu6etj wrote: 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?. In our ham transmission line systems, the goal is to accomplish total destructive interference toward the source, i.e. zero reflected energy incident upon the source. So let's talk about destructive interference toward the source and constructive interference toward the load. You name it "redistribution" too, not reflection. By definition, reflection is something that happens to a single wave. By definition, superposition involves two or more waves. The redistribution that I am talking about can include both reflection and superposition if both are present. Depending upon the system configuration, both may be present, both may be absent, or one exist without the other. Well, my question was how we can set (devise) an experiment to get such behaviour in a TL? I've presented it before and it is a simple Z0-match involving a 1/4WL matching section. 50w-----50 ohm------+------1/4WL 300 ohm------1800 ohm load On the source side, rho at '+' is 0.7143 Using a TDR, we can verify that there is indeed a reflection from the 50/300 ohm impedance discontinuity. What happens to that reflection during steady-state? What happens to Vfor1(rho) = 50v(0.7143) = 35.7v? What happens to Pfor1(rho^2) = 50w(0.51) = 25.5w? -- 73, Cecil, w5dxp.com Sorry. Cecil, I do not catch you (final numeric example), would you mind give to me a more explanatory/explicit answer? (the rest OK). 73 Miguel |
what happens to reflected energy ?
On Jun 25, 8:24*am, Cecil Moore wrote:
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. That's the time domain. Variation in the instantaneous energy flow. Not quite 'as useless as tits on a boar hog, or as Hecht said, putting it mildly: "of limited utility"'. ....Keith |
what happens to reflected energy ?
On Jun 25, 9:00*am, Cecil Moore wrote:
On Jun 25, 2:13*am, lu6etj wrote: 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?. In our ham transmission line systems, the goal is to accomplish total destructive interference toward the source, i.e. zero reflected energy incident upon the source. So let's talk about destructive interference toward the source and constructive interference toward the load. You name it "redistribution" too, not reflection. By definition, reflection is something that happens to a single wave. By definition, superposition involves two or more waves. The redistribution that I am talking about can include both reflection and superposition if both are present. Depending upon the system configuration, both may be present, both may be absent, or one exist without the other. Well, my question was how we can set (devise) an experiment to get such behaviour in a TL? I've presented it before and it is a simple Z0-match involving a 1/4WL matching section. 50w-----50 ohm------+------1/4WL 300 ohm------1800 ohm load On the source side, rho at '+' is 0.7143 Using a TDR, we can verify that there is indeed a reflection from the 50/300 ohm impedance discontinuity. What happens to that reflection during steady-state? What happens to Vfor1(rho) = 50v(0.7143) = 35.7v? Using superposition, when you add Vrev2(tau) to Vfor1(rho) you get zero. With zero voltage comes 0 energy transfer. For further learning, do not just examine steady state, but also examine how it gets to steady state. Using a lattice diagram, examine what happens as the first reflection and then each re-reflection arrives at '+'. Determine how Vrev2(tau) slowly builds to equal Vrev1 and cancels it, using the simple addition of superposition. While this process is occurring, there is a Vrev1 which decreases after each round trip in the second line section. This is all done with simple addition. No need for products and square roots. For further marks, decide whether you should think of Vrev2 as an infinite sum of reverse waves or is it okay to think of it as one sum that slowly accumulates. Which is it really? Same question for Vfor2. What happens to Pfor1(rho^2) = 50w(0.51) = 25.5w? Once you have computed total Vrev1 using simple superposition, it is easy to compute that the "reverse power", Prev1, is 0. Do you really need rho^2 to understand what goes on in a transmission line? ....Keith |
what happens to reflected energy ?
On Jun 25, 7:30*am, K1TTT wrote:
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.- Hide quoted text - I see that the stress induced by considering DC waves is causing you to misinterpret my writings. May I suggest an alternate exploration for you. Assuming that you accept TDR and know how to use Reflection Coefficients to compute voltage and current reflections, then consider what happens when a rectangular pulse is launched from a matched generator in to a transmission line. For simple reflection coefficients like 0, 1, and -1 compute the reflected pulse. For both the forward and reflected direction compute the voltage and current on the line before the pulse arrives, as it passes and after it has passed. Compute the energy in the pulse, and how long a distance it occupies on the transmission line. Compute the power as the pulse is passing. Be sure you know what happens to the pulse when it re-enters the generator. For simplicity, assume a generator constructed using the Thevenin circuit. Make sure all the results are in agreement; especially, the energy delived by the source and the energy dissipated in the various resistors. Now make the pulse longer and longer... until it looks like a step function. And do the computations again. Determine if the results agree with those I previously presented for the DC example. ....Keith PS: Barring errors, they will. |
what happens to reflected energy ?
On Jun 26, 12:22*am, Keith Dysart wrote:
On Jun 25, 7:30*am, K1TTT wrote: 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.- Hide quoted text - I see that the stress induced by considering DC waves is causing you to misinterpret my writings. May I suggest an alternate exploration for you. Assuming that you accept TDR and know how to use Reflection Coefficients to compute voltage and current reflections, then consider what happens when a rectangular pulse is launched from a matched generator in to a transmission line. For simple reflection coefficients like 0, 1, and -1 compute the reflected pulse. For both the forward and reflected direction compute the voltage and current on the line before the pulse arrives, as it passes and after it has passed. Compute the energy in the pulse, and how long a distance it occupies on the transmission line. Compute the power as the pulse is passing. Be sure you know what happens to the pulse when it re-enters the generator. For simplicity, assume a generator constructed using the Thevenin circuit. Make sure all the results are in agreement; especially, the energy delived by the source and the energy dissipated in the various resistors. Now make the pulse longer and longer... until it looks like a step function. And do the computations again. Determine if the results agree with those I previously presented for the DC example. ...Keith PS: Barring errors, they will. why would i want to do all that work? there is no way that my answers will agree with your misconceptions. you'll just come up with an even uglier generator to try to make it fit. oh, and by the way, your fancy 2 generator and 2 resistor 'constant power' source isn't what you think it is. go back to basic circuits 101 and you will find that any linear network like that can be reduced to either a simple one source one impedance norton or thevenin equivalent. in your example it is identical to a 50v voltage source in series with a 50ohm resistor... deriving the norton equivalent is left for the student. |
what happens to reflected energy ?
On Jun 25, 4:00*pm, Keith Dysart wrote:
That's the time domain. Variation in the instantaneous energy flow. What you seem to be missing is that the *energy content* of power (total joules) must be conserved but the instantaneous power (joules/ second) does not have to be conserved as you have argued numerous times in numerous examples. The only question that needs to be answered is: In a system designed to eliminate reflections and interference, does all the reflected energy eventually get dissipated in the source resistor. The answer is yes because there is nowhere else for it to go. There is no conservation of power principle and that includes instantaneous power. So it is irrelevant what/where instantaneous power might do/go during a single cycle. Now I understand that instantaneous power dictates some physical design considerations as in waveguides. But since instantaneous power does not fall under the conservation of energy principle, it is simply irrelevant to the present discussion. What happens over a complete cycle is what is relevant. However, in any and every case, it is energy that is conserved, not power. How many joules are in that dt sliver of time when the instantaneous power is 100 watts? It's those joules that must be conserved, not the instantaneous power. You didn't answer my previous question. If you measure 100 watts of instantaneous power at 100 places within an inch of each other, does that mean there is 10000 watts of instantaneous power in that one inch of wire? That is the only logical conclusion based on your argument and assertions. Any argument based on the conservation of power is doomed to fail. Please get real. Not quite 'as useless as tits on a boar hog, or as Hecht said, putting it mildly: "of limited utility"'. One could argue that tits on a boar hog are not completely useless and, therefore, instantaneous energy is exactly as useless (or exactly as useful) as tits on a boar hog. (Hint: Without the existence of the tit gene in the male, female hogs would probably not have tits.) -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 25, 6:47*pm, Keith Dysart wrote:
Now this I agree with. Superpose volts, current and fields to your heart's content. Just don't attempt it for power. Nobody except you, using instantaneous power, has attempted to superpose power. The Power-Density/Interference equation does NOT superpose power because it contains the interference term. If the interference term were omitted than it would be an attempt to superpose power, but I have never omitted the interference term except when it was zero. You should study the design of the generator described previously and repeated below, for your convenience: Can you make your redistribution explanation work for this one? Here's what your schematic looks like. How about a web page graphic instead? http://www.w5dxp.com/Keith.JPG -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 25, 7:07*pm, Keith Dysart wrote:
Using superposition, when you add Vrev2(tau) to Vfor1(rho) you get zero. With zero voltage comes 0 energy transfer. Completing your above sentence: With zero voltage comes 0 energy transfer *in the direction of travel of the original waves that were superposed*. Assuming that you believe in the conservation of energy principle, what happened to the energy in the two component voltage waves necessary for their existence before they cancel each other? If they didn't contain any energy, they would be zero but we know they are not zero, i.e. they are 35.7 volts each. That original wave energy is redistributed and *transfered* in the opposite direction, the only other direction available in a transmission line. One cannot argue with a forked tongue that the superposed waves never existed in the first place because that would violate the laws of physics and superposition. Do you really need rho^2 to understand what goes on in a transmission line? Not using rho^2 is why you are so confused. If you actually cared where the energy goes, you would be forced to use rho^2 or at least multiply the superposition component voltages and currents to obtain the power in the superposition component wavefronts. In the earlier example, the impedance discontinuity has a physical voltage reflection coefficient of 0.7143 and a physical power reflection coefficient of 0.51. If you consider the steady-state power conditions, you will calculate a virtual power reflection coefficient of 0.0 and a virtual voltage reflection coefficient of 0.0. Which reflection coefficient is correct? Obviously, physical trumps virtual every time. The 50v source voltage reflected at the 0.7143 reflection coefficient is 35.7 volts and it exists in a 50 ohm environment. Simple math yields the power = (35.7)^2/50 = 25.5 watts. Where did the energy in that 25.5 watt EM wave go? One can obtain the same value by calculating the current: 1a(0.7143) = 0.7143. Power = 35.7(0.7143) = 25.5 watts. So you can get by without using rho^2 but to determine where the energy is going, one needs to at least multiply the EM traveling-wave voltage by the EM traveling-wave current (or calculate the ExH Poynting vectors). In fact, this would be a good application for your instantaneous power calculations. Where is the energy going that is in the instantaneous power being reflected by the impedance discontinuity? -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 25, 3:27*pm, lu6etj wrote:
Sorry. Cecil, I do not catch you (final numeric example), would you mind give to me a more explanatory/explicit answer? I previously had a senior moment and changed contexts in the middle of a posting and I apologize for any confusion. Would you enlighten me as to the area of the discussion that you don't catch? Do you understand physical reflection and transmission coefficients and their effect on voltage, current, and power? -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 26, 7:41*am, K1TTT wrote:
On Jun 26, 12:22*am, Keith Dysart wrote: On Jun 25, 7:30*am, K1TTT wrote: 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.- Hide quoted text - I see that the stress induced by considering DC waves is causing you to misinterpret my writings. May I suggest an alternate exploration for you. Assuming that you accept TDR and know how to use Reflection Coefficients to compute voltage and current reflections, then consider what happens when a rectangular pulse is launched from a matched generator in to a transmission line. For simple reflection coefficients like 0, 1, and -1 compute the reflected pulse. For both the forward and reflected direction compute the voltage and current on the line before the pulse arrives, as it passes and after it has passed. Compute the energy in the pulse, and how long a distance it occupies on the transmission line. Compute the power as the pulse is passing. Be sure you know what happens to the pulse when it re-enters the generator. For simplicity, assume a generator constructed using the Thevenin circuit. Make sure all the results are in agreement; especially, the energy delived by the source and the energy dissipated in the various resistors. Now make the pulse longer and longer... until it looks like a step function. And do the computations again. Determine if the results agree with those I previously presented for the DC example. ...Keith PS: Barring errors, they will. why would i want to do all that work? * It would be an opportunity for you to deepen your understanding of the behaviour of transmission lines. there is no way that my answers will agree with your misconceptions. * I am not convinced. You have not yet found any errors in my expositions, so if you do not make any errors, I expect we will agree on the outcome, though perhaps not on the interpretation, for you disagree when I say "do not assign TOO much reality to the energy in reflected waves. You seem to want your reflected waves to always transport energy, but are unhappy that this leads to a line that was originally excited with a step function having energy flowing in both directions even though the current is zero all along the line. Cecil simply sidesteps these little inconveniences by refusing to consider anything other than sinusoidal RF excitation and by refusing to consider any time based analysis. Such is not the path to understanding, deep or otherwise. you'll just come up with an even uglier generator to try to make it fit. My generators are pretty simple. So far I have only used 3: Thevenin, Norton, and one with an interesting constant input power characteristic. oh, and by the way, your fancy 2 generator and 2 resistor 'constant power' source isn't what you think it is. *go back to basic circuits 101 and you will find that any linear network like that can be reduced to either a simple one source one impedance norton or thevenin equivalent. * You have confused a bit, models with implementation. As I said in the original: "Consider a generator constructed as below". I am not using an equivalent circuit, but a construction. Only when dealing with the actual construction is it valid to examine the internal energy flows. An "equivalent" circuit is equivalent for external behaviour but not necessarily for internal, so I avoid them when examining the internals. ....Keith |
what happens to reflected energy ?
On Jun 27, 5:49*pm, Keith Dysart wrote:
On Jun 26, 7:41*am, K1TTT wrote: On Jun 26, 12:22*am, Keith Dysart wrote: On Jun 25, 7:30*am, K1TTT wrote: 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.- Hide quoted text - I see that the stress induced by considering DC waves is causing you to misinterpret my writings. May I suggest an alternate exploration for you. Assuming that you accept TDR and know how to use Reflection Coefficients to compute voltage and current reflections, then consider what happens when a rectangular pulse is launched from a matched generator in to a transmission line. For simple reflection coefficients like 0, 1, and -1 compute the reflected pulse. For both the forward and reflected direction compute the voltage and current on the line before the pulse arrives, as it passes and after it has passed. Compute the energy in the pulse, and how long a distance it occupies on the transmission line. Compute the power as the pulse is passing. Be sure you know what happens to the pulse when it re-enters the generator. For simplicity, assume a generator constructed using the Thevenin circuit. Make sure all the results are in agreement; especially, the energy delived by the source and the energy dissipated in the various resistors. Now make the pulse longer and longer... until it looks like a step function. And do the computations again. Determine if the results agree with those I previously presented for the DC example. ...Keith PS: Barring errors, they will. why would i want to do all that work? * It would be an opportunity for you to deepen your understanding of the behaviour of transmission lines. there is no way that my answers will agree with your misconceptions. * I am not convinced. You have not yet found any errors in my expositions, so if you do not make any errors, I expect we will agree on the outcome, though perhaps not on the interpretation, for you disagree when I say "do not assign TOO much reality to the energy in reflected waves. You seem to want your reflected waves to always transport energy, but are unhappy that this leads to a line that was originally excited with a step function having energy flowing in both directions even though the current is zero all along the line. Cecil simply sidesteps these little inconveniences by refusing to consider anything other than sinusoidal RF excitation and by refusing to consider any time based analysis. Such is not the path to understanding, deep or otherwise. you'll just come up with an even uglier generator to try to make it fit.. My generators are pretty simple. So far I have only used 3: Thevenin, Norton, and one with an interesting constant input power characteristic. oh, and by the way, your fancy 2 generator and 2 resistor 'constant power' source isn't what you think it is. *go back to basic circuits 101 and you will find that any linear network like that can be reduced to either a simple one source one impedance norton or thevenin equivalent. * You have confused a bit, models with implementation. As I said in the original: "Consider a generator constructed as below". I am not using an equivalent circuit, but a construction. Only when dealing with the actual construction is it valid to examine the internal energy flows. An "equivalent" circuit is equivalent for external behaviour but not necessarily for internal, so I avoid them when examining the internals. ...Keith but the equivalent points out that your statements about it sourcing constant power is incorrect. i have also pointed out that your statements about your 'step wave' are obviously incorrect because you have applied assumptions that are only valid in the sinusoidal steady state to a step function that can never be in steady state. neither can your pulses for that matter, so all the assumptions are worthless, you must do the complete analysis including the summations for the infinite fourier decomposition of your step or pulses to get the full picture... in a transient analysis. as was pointed out if you go VERY far into the future with a battery connected to an open circuit piece of coax there can be no currents and therefore no waves propagating in the line. its only in the detailed transient analysis that you haven't done where you will see the propagating steps going back and forth. |
what happens to reflected energy ?
On Jun 27, 12:49*pm, Keith Dysart wrote:
Cecil simply sidesteps these little inconveniences by refusing to consider anything other than sinusoidal RF excitation and by refusing to consider any time based analysis. That's simply false. Using Fourier analysis, I reduce anything other than a sinusoid to multiple sinusoidal RF excitations, perform the sinusoidal analysis, and then use superposition to find the answer. I also reject any example where Maxwell's equations do not work. Your insistance that magical waves can somehow exist during DC steady-state violates the known laws of physics. EM waves CANNOT exist during DC steady-state because electrons are traveling at a constant velocity. You can measure DC voltage with an AC voltmeter but that doesn't change DC voltage to AC voltage. -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 26, 9:05*am, Cecil Moore wrote:
On Jun 25, 4:00*pm, Keith Dysart wrote: That's the time domain. Variation in the instantaneous energy flow. What you seem to be missing is that the *energy content* of power (total joules) must be conserved but the instantaneous power (joules/ second) does not have to be conserved as you have argued numerous times in numerous examples. In any region, the energy flowing in (i.e. power) to the region minus the energy flowing out (i.e. power) is equal to the additional energy per unit time (i.e. power) being stored in the region. While not called the "conservation of power law" it is an obvious corollary to "conservation of energy". The only question that needs to be answered is: In a system designed to eliminate reflections and interference, does all the reflected energy eventually get dissipated in the source resistor. The answer is yes because there is nowhere else for it to go. The obvious alternative is that the computed energy in the reflected wave is sometimes just a figment. Or is something else happening with the step function example? Not to mention that in your 1/8 wavelength example (http:// www.w5dxp.com/nointfr.htm) you do not explain where the energy is stored so that it can be returned at a different time. There is no conservation of power principle and that includes instantaneous power. So it is irrelevant what/where instantaneous power might do/go during a single cycle. Such declarations do permit an easy out, despite not aligning with reality. Now I understand that instantaneous power dictates some physical design considerations as in waveguides. But since instantaneous power does not fall under the conservation of energy principle, it is simply irrelevant to the present discussion. What happens over a complete cycle is what is relevant. If that is the case, the whole concept of reflected energy seems somewhat bogus. Over a whole cycle, the power delivered by the generator is passed on towards the load. If that is all you want to know, then there is no need at all for "reflected power". However, in any and every case, it is energy that is conserved, not power. Yes. But see the related corollary above. How many joules are in that dt sliver of time when the instantaneous power is 100 watts? It's those joules that must be conserved, not the instantaneous power. Still having problems with mapping the concepts from calculus to the real world, I see. You didn't answer my previous question. If you measure 100 watts of instantaneous power at 100 places within an inch of each other, does that mean there is 10000 watts of instantaneous power in that one inch of wire? That is the only logical conclusion based on your argument and assertions. No more than "If you measure 100 watts of *average* power at 100 places within an inch of each other, does that mean there is 10000 watts of *average* power in that one inch of wire?" But it is a way of thinking that you like to use to distract yourself from the really interesting results. Any argument based on the conservation of power is doomed to fail. Please get real. Please study the corollary above. Not quite 'as useless as tits on a boar hog, or as Hecht said, putting it mildly: "of limited utility"'. One could argue that tits on a boar hog are not completely useless and, therefore, instantaneous energy is exactly as useless (or exactly as useful) as tits on a boar hog. (Hint: Without the existence of the tit gene in the male, female hogs would probably not have tits.) So which is it? Is instantaneous energy flow a useful concept? Or is it not? You previously suggested an understanding of the value (when I mentioned "real power folk"), but seem to continue to want to argue its complete lack of usefulness. And to stop besmirching Hecht, it seems most probable that his comment was in the context of optics. After all, the book had that title. ....Keith |
what happens to reflected energy ?
On Jun 26, 9:20*am, Cecil Moore wrote:
On Jun 25, 6:47*pm, Keith Dysart wrote: You should study the design of the generator described previously and repeated below, for your convenience: Can you make your redistribution explanation work for this one? Here's what your schematic looks like. How about a web page graphic instead? http://www.w5dxp.com/Keith.JPG That does present a bit of a challenge to decipher. Try using groups.google.com to read the message. After opening the topic, scroll to the top and click "Options" which should be found in the same header as the Topic. Click "Fixed font". This significantly improves readability. ....Keith |
what happens to reflected energy ?
On Jun 26, 9:49*am, Cecil Moore wrote:
On Jun 25, 7:07*pm, Keith Dysart wrote: Using superposition, when you add Vrev2(tau) to Vfor1(rho) you get zero. With zero voltage comes 0 energy transfer. Completing your above sentence: With zero voltage comes 0 energy transfer *in the direction of travel of the original waves that were superposed*. Assuming that you believe in the conservation of energy principle, what happened to the energy in the two component voltage waves necessary for their existence before they cancel each other? The fundamental question is: "did they have energy?" Let us express this as a hypothesis: Hypothesis 1: The component voltage waves have energy. Then it should follow that we can trace this energy and discover where it goes. At least three examples have been proposed where the energy can not be properly traced: Example 1: Step function applied to a transmission line. After the line settles, a forward and reflected voltage wave continue on the line but no energy is being transferred. Example 2: On a line with infinite VSWR no energy crosses a voltage minimum or maximum. Example 3: With the 1/8 wavelength line described in http://www.w5dxp.com/nointfr.htm the energy can not be properly accounted for on a moment by moment basis. Only one counter-example was needed to disprove the hypothesis, three have been found. There may be more. Hypothesis is disproved. No matter how many examples are found that support the hypothesis, the hypothesis is still disproved. ....Keith |
what happens to reflected energy ?
On 27 jun, 11:37, Cecil Moore wrote:
On Jun 25, 3:27*pm, lu6etj wrote: Sorry. Cecil, I do not catch you (final numeric example), would you mind give to me a more explanatory/explicit answer? I previously had a senior moment and changed contexts in the middle of a posting and I apologize for any confusion. Would you enlighten me as to the area of the discussion that you don't catch? Do you understand physical reflection and transmission coefficients and their effect on voltage, current, and power? -- 73, Cecil, w5dxp.com Thanks Cecil: Examples of you that I saw in recent weeks were about interferences generated by a single real generator and reflections, resulting, for example, in constructive/destructive interference responsible of changes in energy flow direction starting from the line point where those interferences occurs. In a nutshell: In post 127 I asked you for an example/experiment based in TWO real generators to assimilate it to more familiar double slit interference phenomenom (TWO coherent sources) rendering energy redistribution inside one dimensional TL space, two sources in tridimensional space gives maximuns and nulls on screen (redistribution). Well, I ask you for identical example in unidimensional space rendering a phenomenom similar as reflection (one wave) but with interference (two waves). Sorry I do not know how better translate my question to english words. I not catched your answer because it does not match my question :) Thank you very much in advance. Miguel - LU6ETJ PS: On Google interface, inside thread's tittle = options you can select fixed text, to correctly see ASCII drawings. |
what happens to reflected energy ?
On Jun 27, 1:38*pm, Keith Dysart wrote:
In any region, the energy flowing in (i.e. power) to the region minus the energy flowing out (i.e. power) is equal to the additional energy per unit time (i.e. power) being stored in the region. While not called the "conservation of power law" it is an obvious corollary to "conservation of energy". I'm sorry, that is simply not true for power. The energy content of a 1us pulse containing one joule and the energy content of a one sec pulse containing one joule are equal and that one joule is all that must be conserved. The 1us pulse containing 1,000,000 watts can be converted to a one second pulse containing 1 watt. Where did the other 999,999 watts go??? Energy has been conserved but the power changed from 1,000,000 watts to 1 watt using exactly the same energy. Perhaps this characteristic of power is what you are missing. Also, all the energy can be conserved in reactance while power falls to absolute zero. This often happens during a fraction of a cycle. That is what is wrong with you trying to track instataneous power - it doesn't work unless one standardizes to at least one cycle. Within each fraction of a cycle, any principle of conservation of power will surely be violated. If it appears that power is ever conserved, it is only by accident. Such is the case with many megacycles/second where the result of a fraction of a cycle will have a negligible effect on the joules/sec. The obvious alternative is that the computed energy in the reflected wave is sometimes just a figment. And God created the heavens and earth in six days and rested on the seventh. I'm glad you are happy with your faith-based physics. In the field of real-world physics, EM waves cannot exist without ExH energy. The only way to win this argument is to prove to everyone that they are not really detecting reflected waves containing energy when they look at themselves in the mirror. Good luck on that one. Question: How were the first three days measured before the creation of the sun on the 4th day? Not to mention that in your 1/8 wavelength example (http://www.w5dxp.com/nointfr.htm) you do not explain where the energy is stored so that it can be returned at a different time. Energy is stored in the transmission line and delivered as needed to satisfy the conservaton of energy principle. Years ago, I showed how energy can flow *into the source* (negative power) during a fractional part of a cycle in a conjugately matched system. Such declarations do permit an easy out, despite not aligning with reality. If you can take one joule per microsecond (1 megawatt) and conserve that one megawatt of power over a century, you can get rich selling it. Let us know when you get your patent on conservation of power. :-) Good Grief! If that is the case, the whole concept of reflected energy seems somewhat bogus. Over a whole cycle, the power delivered by the generator is passed on towards the load. If that is all you want to know, then there is no need at all for "reflected power". But, as you can grok from the subject of this thread, that is not all that is needed to know. The last gasp of the loser is that it didn't matter anyhow. Reflected energy has always mattered to optical physicists who know it obeys the laws of physics. Now it seems to matter to some hams. If it doesn't matter to you, why do you continue posting? And to stop besmirching Hecht, it seems most probable that his comment was in the context of optics. After all, the book had that title. Hint: RF waves are covered in every physics book whose title is "Light". There is absolutely no difference, from a physics standpoint, between a coherent light wave and a coherent RF wave except for frequency. The both obey exactly the same laws of physics which you seem to concede for visible light but not for light at RF frequencies. -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 27, 2:23*pm, Keith Dysart wrote:
Example 1: Step function applied to a transmission line. After the * * * * * *line settles, a forward and reflected voltage wave * * * * * *continue on the line but no energy is being transferred. As far as I am concerned, if Maxwell's equations don't work on an example, it might as well be ignored. There is nothing during DC steady-state that allows Maxwell's equations to work because there are no EM waves during DC steady-state. Why don't you already know that? I can take your approach and do you one better. Please prove that you exist. If you cannot prove that you exist, then nothing you say is of any consequence. See, I can do it also. Example 2: On a line with infinite VSWR no energy crosses a * * * * * *voltage minimum or maximum. Completely false assumption. You are back to asserting that since the north-bound traffic equals the south-bound traffic on the Golden Gate Bridge that there is no traffic and no bridge maintenance is required. When are you going to give up on that irrational wet dream of yours? No *NET* energy crosses at a voltage zero or current zero point. That doesn't make the north-bound energy equal to zero and doesn't make the south-bound energy equal to zero. It just makes them equal. Just because there is no NET traffic flow on the Golden Gate Bridge doesn't mean there is zero traffic flow in both directions. Please stop clowning around with such absurb notions. Example 3: With the 1/8 wavelength line described in * * * * * *http://www.w5dxp.com/nointfr.htmthe energy can not be * * * * * *properly accounted for on a moment by moment basis.. There is no conservation of power principle. If you would track the RF joules and the conversion of RF joules to heat instead of the joules/ second, everything would become clear to you. As it is, you are laboring under some serious misconceptions about the laws of physics. Power simply doesn't balance within a single cycle - because it doesn't have to - because there is no conservation of power principle. People who don't learn from their mistakes are doomed to commit the same mistakes over and over. Keith, you seem to be all output and no input. Please enable your input channels for a change. -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 27, 2:20 pm, K1TTT wrote:
but the equivalent points out that your statements about it sourcing constant power is incorrect. You might like to actually test it. The two sources are always delivering 100W. With an open circuit load: The current source is delivering 100 W to the parallel source resistor. The voltage source delivers nothing. Total: 100W With a shorted load: The voltage source is delivering 100W to the series source resistor. The current source delivers nothing. Total: 100W With a 50 ohm load: The voltage source is delivering 50W. The current source is delivering 50W. Total: 100W The load is receiving 50W. Each generator resistor is dissipating 25W. i have also pointed out that your statements about your 'step wave' are obviously incorrect because you have applied assumptions that are only valid in the sinusoidal steady state to a step function that can never be in steady state. I am not sure where you think there is an error. Perhaps you can point them out in the following example: Generator: - 100V step in to an open circuit - 50 ohm source impedance Line: - 50 ohm - open circuit Generator is commanded to produce a step. This will produce 50 V and 1 A at the line input which will propagate down the line. The open end of the line has a reflection co-efficient of 1.0. Just before the 50 V step reaches the end of the line, the whole line will be at 50 V and 1 A will be flowing everywhere. The 50 V step hits the end and is reflected, producing a 50 V step (on top of the 50V already there) which propagates back to the generator. In front of the 50 V step, the current is still 1 A (which provides the charge necessary to produce the reverse propagating 50 V step. Behind the step, the current is 0. When the reverse 50 V step (which is actually a step from 50V to 100V) reaches the generator, the source impedance matches the line impedance so there is no further reflection. The line state is now 100V and 0A all along its length. The settling time was one round-trip. The generator is still producing the step, so the forward step voltage wave is still 'flowing' and being reflected so there is still a reflected step voltage wave, each of 50 V. Since the generator open circuit voltage is 100 V and the line voltage is now 100 V, current is no longer flowing from the generator to the line. Does this agree with your understanding? I have snipped the rest of your post since until the above is agreed, there is no sense in proceeding further. ....Keith |
what happens to reflected energy ?
On Jun 27, 2:26*pm, Cecil Moore wrote:
On Jun 27, 12:49*pm, Keith Dysart wrote: Cecil simply sidesteps these little inconveniences by refusing to consider anything other than sinusoidal RF excitation and by refusing to consider any time based analysis. That's simply false. Using Fourier analysis, I reduce anything other than a sinusoid to multiple sinusoidal RF excitations, perform the sinusoidal analysis, and then use superposition to find the answer. You need to expand your solution space. Some problems are so much easier to solve in the time domain. I can't even imagine doing some problems in the frequency domain. Let's see: I turn on my flashlight maybe once per week, so the fundamental is 1.6e-6 Hz, and say the risetime is 1 millisecond -- my head hurts already -- that's about 600,000,000 harmonics to be computed. No wonder you give up on some problems so readily. I also reject any example where Maxwell's equations do not work. Your insistance that magical waves can somehow exist during DC steady-state violates the known laws of physics. It is not my insistence. It follows from the math. Besides if you convert it to the frequency domain you should be happy that they exist since they then align with your understandings. EM waves CANNOT exist during DC steady-state because electrons are traveling at a constant velocity. Are you sure you meant this? The electron velocity changes? Or did you mean the wave velocity? Nope. That does not work either. You can measure DC voltage with an AC voltmeter but that doesn't change DC voltage to AC voltage. And for especial fun... Why are you sure DC is so special? v(t)=A cos(wt) describes a sinusoid. It has the parameter w to specifiy the frequency. Set it to 0, and voila: DC. It falls right out of the same definition as is used for a sinusoid. It is a sinusoid. ....Keith |
what happens to reflected energy ?
On 27 jun, 17:39, Keith Dysart wrote:
On Jun 27, 2:20 pm, K1TTT wrote: but the equivalent points out that your statements about it sourcing constant power is incorrect. You might like to actually test it. The two sources are always delivering 100W. With an open circuit load: The current source is delivering 100 W to the parallel source resistor. The voltage source delivers nothing. Total: 100W With a shorted load: The voltage source is delivering 100W to the series source resistor. The current source delivers nothing. Total: 100W With a 50 ohm load: The voltage source is delivering 50W. The current source is delivering 50W. Total: 100W The load is receiving 50W. Each generator resistor is dissipating 25W. i have also pointed out that your statements about your 'step wave' are obviously incorrect because you have applied assumptions that are only valid in the sinusoidal steady state to a step function that can never be in steady state. I am not sure where you think there is an error. Perhaps you can point them out in the following example: Generator: - 100V step in to an open circuit - 50 ohm source impedance Line: - 50 ohm - open circuit Generator is commanded to produce a step. This will produce 50 V and 1 A at the line input which will propagate down the line. The open end of the line has a reflection co-efficient of 1.0. Just before the 50 V step reaches the end of the line, the whole line will be at 50 V and 1 A will be flowing everywhere. The 50 V step hits the end and is reflected, producing a 50 V step (on top of the 50V already there) which propagates back to the generator. In front of the 50 V step, the current is still 1 A (which provides the charge necessary to produce the reverse propagating 50 V step. Behind the step, the current is 0. When the reverse 50 V step (which is actually a step from 50V to 100V) reaches the generator, the source impedance matches the line impedance so there is no further reflection. The line state is now 100V and 0A all along its length. The settling time was one round-trip. The generator is still producing the step, so the forward step voltage wave is still 'flowing' and being reflected so there is still a reflected step voltage wave, each of 50 V. Since the generator open circuit voltage is 100 V and the line voltage is now 100 V, current is no longer flowing from the generator to the line. Does this agree with your understanding? I have snipped the rest of your post since until the above is agreed, there is no sense in proceeding further. ...Keith Sorry, I ommited aknowledge to you I understoond your example and what you mean with: "What happens to Vfor1(rho) = 50v(0.7143) = 35.7v? " "What happens to Pfor1(rho^2) = 50w(0.51) = 25.5w? " (Last represent the cancellating (interference?) term of transmitted power (1.Rho^2) towards generator from the reflected power from the load to render VRef1=0 (doing the accounts with phasorial V-I math, though I suppose will give similar results employing the eq-1 of your World Radio article, but I am not sure if I'm catching it very well yet. Have you P1, P2, P3 and P4, for your 100 W example, to clear it? ) Miguel |
what happens to reflected energy ?
On 27 jun, 19:05, lu6etj wrote:
On 27 jun, 17:39, Keith Dysart wrote: On Jun 27, 2:20 pm, K1TTT wrote: but the equivalent points out that your statements about it sourcing constant power is incorrect. You might like to actually test it. The two sources are always delivering 100W. With an open circuit load: The current source is delivering 100 W to the parallel source resistor. The voltage source delivers nothing. Total: 100W With a shorted load: The voltage source is delivering 100W to the series source resistor. The current source delivers nothing. Total: 100W With a 50 ohm load: The voltage source is delivering 50W. The current source is delivering 50W. Total: 100W The load is receiving 50W. Each generator resistor is dissipating 25W. i have also pointed out that your statements about your 'step wave' are obviously incorrect because you have applied assumptions that are only valid in the sinusoidal steady state to a step function that can never be in steady state. I am not sure where you think there is an error. Perhaps you can point them out in the following example: Generator: - 100V step in to an open circuit - 50 ohm source impedance Line: - 50 ohm - open circuit Generator is commanded to produce a step. This will produce 50 V and 1 A at the line input which will propagate down the line. The open end of the line has a reflection co-efficient of 1.0. Just before the 50 V step reaches the end of the line, the whole line will be at 50 V and 1 A will be flowing everywhere. The 50 V step hits the end and is reflected, producing a 50 V step (on top of the 50V already there) which propagates back to the generator. In front of the 50 V step, the current is still 1 A (which provides the charge necessary to produce the reverse propagating 50 V step. Behind the step, the current is 0. When the reverse 50 V step (which is actually a step from 50V to 100V) reaches the generator, the source impedance matches the line impedance so there is no further reflection. The line state is now 100V and 0A all along its length. The settling time was one round-trip. The generator is still producing the step, so the forward step voltage wave is still 'flowing' and being reflected so there is still a reflected step voltage wave, each of 50 V. Since the generator open circuit voltage is 100 V and the line voltage is now 100 V, current is no longer flowing from the generator to the line. Does this agree with your understanding? I have snipped the rest of your post since until the above is agreed, there is no sense in proceeding further. ...Keith Sorry, *I ommited aknowledge to you I understoond your example and what you mean with: "What happens to Vfor1(rho) = 50v(0.7143) = 35.7v? " "What happens to Pfor1(rho^2) = 50w(0.51) = 25.5w? " (Last represent the cancellating (interference?) term of transmitted power (1.Rho^2) towards generator from the reflected power from the load to render VRef1=0 (doing the accounts with phasorial V-I math, though I suppose will give similar results employing the eq-1 of your World Radio article, but I am not sure if I'm catching it very well yet. Have you P1, P2, P3 and P4, for your 100 W example, to clear it? *) Miguel- Ocultar texto de la cita - - Mostrar texto de la cita - Or if you prefer, tell me if in your article: P1=48.98 W; P2=53.15 W; P3=51.02 W; P4=51.02 W |
what happens to reflected energy ?
On Jun 27, 4:01*pm, Cecil Moore wrote:
On Jun 27, 1:38*pm, Keith Dysart wrote: In any region, the energy flowing in (i.e. power) to the region minus the energy flowing out (i.e. power) is equal to the additional energy per unit time (i.e. power) being stored in the region. While not called the "conservation of power law" it is an obvious corollary to "conservation of energy". I'm sorry, that is simply not true for power. The energy content of a 1us pulse containing one joule and the energy content of a one sec pulse containing one joule are equal and that one joule is all that must be conserved. The 1us pulse containing 1,000,000 watts can be converted to a one second pulse containing 1 watt. Perhaps some of your difficulty is revealed in your phraseology. A pulse does not 'contain' power. It can deliver energy at some rate. If the pulse is rectangular, the rate will be constant for the duration of the pulse. With some other profile, the rate will vary over the duration of the pulse. Perhaps a simple analogy would help. Near my house is a 50 m water tower with a bunch of pipes connected to the bottom. The rate at which water is added to the tower is always equal to the sum of the rates flowing in on all the pipes (assume positive flow raises the level in the tank, while negative flow reduces it). Rephrased, for greater certainty: At any instant in time, the rate at which water is being added to the tower is always equal to the sum of the rates flowing in on all the pipes. At any instant in time, all the water (and flows) can be accounted for. Same for energy (and energy flow). snip The obvious alternative is that the computed energy in the reflected wave is sometimes just a figment. And God created the heavens and earth in six days and rested on the seventh. Some do say, but this appears to be rather a non-sequitor. I'm glad you are happy with your faith-based physics. In the field of real-world physics, EM waves cannot exist without ExH energy. Perhaps, then, you are simply arguing that these are not EM waves since they do not have ExH energy? The only way to win this argument is to prove to everyone that they are not really detecting reflected waves containing energy when they look at themselves in the mirror. Good luck on that one. Question: How were the first three days measured before the creation of the sun on the 4th day? Continuing with non-sequitors? Not to mention that in your 1/8 wavelength example (http://www.w5dxp.com/nointfr.htm) you do not explain where the energy is stored so that it can be returned at a different time. Energy is stored in the transmission line and delivered as needed to satisfy the conservaton of energy principle. Nope. That also failed to account for the energy when observed in the time domain. See http://sites.google.com/site/keithdysart/radio6. Years ago, I showed how energy can flow *into the source* (negative power) during a fractional part of a cycle in a conjugately matched system. Such declarations do permit an easy out, despite not aligning with reality. If you can take one joule per microsecond (1 megawatt) and conserve that one megawatt of power over a century, you can get rich selling it. Let us know when you get your patent on conservation of power. :-) Good Grief! If that is the case, the whole concept of reflected energy seems somewhat bogus. Over a whole cycle, the power delivered by the generator is passed on towards the load. If that is all you want to know, then there is no need at all for "reflected power". But, as you can grok from the subject of this thread, that is not all that is needed to know. The last gasp of the loser is that it didn't matter anyhow. Reflected energy has always mattered to optical physicists who know it obeys the laws of physics. Now it seems to matter to some hams. If it doesn't matter to you, why do you continue posting? Did I miss something? Was it not you who said "What happens over a complete cycle is what is relevant."? And to stop besmirching Hecht, it seems most probable that his comment was in the context of optics. After all, the book had that title. Hint: RF waves are covered in every physics book whose title is "Light". There is absolutely no difference, from a physics standpoint, between a coherent light wave and a coherent RF wave except for frequency. The both obey exactly the same laws of physics which you seem to concede for visible light but not for light at RF frequencies. Several differences: - Transmission lines work down to DC - At lower RF, it is possible to independantly measure voltage and current This allows a better understanding of the behaviour, not constrained by the capabilities of the mearsuring instruments. ....Keith |
what happens to reflected energy ?
On Jun 27, 4:27*pm, Cecil Moore wrote:
On Jun 27, 2:23*pm, Keith Dysart wrote: Example 1: Step function applied to a transmission line. After the * * * * * *line settles, a forward and reflected voltage wave * * * * * *continue on the line but no energy is being transferred. As far as I am concerned, if Maxwell's equations don't work on an example, it might as well be ignored. There is nothing during DC steady-state that allows Maxwell's equations to work because there are no EM waves during DC steady-state. Why don't you already know that? I always thought that Maxwell's equations were more complete than that and worked all the way down to DC. Two of them do not even include time and nothing says that a derivative with respect to time can't be 0. I can take your approach and do you one better. Please prove that you exist. If you cannot prove that you exist, then nothing you say is of any consequence. See, I can do it also. From the above, you have proved that I exist. Thank you. Example 2: On a line with infinite VSWR no energy crosses a * * * * * *voltage minimum or maximum. Completely false assumption. You are back to asserting that since the north-bound traffic equals the south-bound traffic on the Golden Gate Bridge that there is no traffic and no bridge maintenance is required. When are you going to give up on that irrational wet dream of yours? No *NET* energy crosses at a voltage zero or current zero point. That doesn't make the north-bound energy equal to zero and doesn't make the south-bound energy equal to zero. It just makes them equal. Just because there is no NET traffic flow on the Golden Gate Bridge doesn't mean there is zero traffic flow in both directions. Please stop clowning around with such absurb notions. I suppose, but then you have to give up on P(t)=V(t)*I(t), generally considered to be a rather fundamental equation. Example 3: With the 1/8 wavelength line described in * * * * * *http://www.w5dxp.com/nointfr.htmtheenergy can not be * * * * * *properly accounted for on a moment by moment basis. There is no conservation of power principle. There is no mention of power above; simply energy. Are you saying that conservation of energy only applies some of the time? If you would track the RF joules and the conversion of RF joules to heat instead of the joules/ second, everything would become clear to you. As it is, you are laboring under some serious misconceptions about the laws of physics. Power simply doesn't balance within a single cycle - because it doesn't have to - because there is no conservation of power principle. In your example, the RF energy does seem to disappear and re-appear, when tracked on a moment by moment basis. People who don't learn from their mistakes are doomed to commit the same mistakes over and over. Keith, you seem to be all output and no input. Please enable your input channels for a change. Well, it would help if you could actually find and articulate a flaw in http://sites.google.com/site/keithdysart/radio6. ....Keith |
what happens to reflected energy ?
On Jun 27, 4:42*pm, Keith Dysart wrote:
It is not my insistence. It follows from the math. Unfortunately for your arguments, math models do not dictate reality. If the math model doesn't match reality, it is invalid. Your math models obviously do not match reality. Are you sure you meant this? The electron velocity changes? Or did you mean the wave velocity? Nope. That does not work either. Yes, acceleration and deceleration of electrons (in the conductor) is required for EM waves to even exist. That's an obvious change in electron velocity. Is that another fact of physics that shoots your theory down? I repeat: EM waves are impossible during DC steady-state. -- 73, Cecil, w5dxp.com |
what happens to reflected energy ?
On Jun 27, 6:59*pm, Keith Dysart wrote:
From the above, you have proved that I exist. Thank you. Nope, I believe you are only a figment of my imagination. Please prove that you actually exist. I suppose, but then you have to give up on P(t)=V(t)*I(t), generally considered to be a rather fundamental equation. I have absolutely no problem with giving up on the conservation of power principle in which no rational technical person can possibly believe. Are you saying that conservation of energy only applies some of the time? No, I am saying that if you cannot balance the energy equation at all times, you have made a mistake. You are not tracking joules. You are attempting to track watts which can appear and disappear at any time. The only condition where watts can be tracked is over an integer multiple of complete cycles. That's why watts can be tracked when the frequency is in the MHz. Trying to track instantaneous watts within a fraction of a cycle is a moronic attempt at power superposition, a no- no that we all learned in EE101. In your example, the RF energy does seem to disappear and re-appear, when tracked on a moment by moment basis. No, the power can disappear and re-appear but the energy cannot. You have not even come close to tracking the energy. Well, it would help if you could actually find and articulate a flaw inhttp://sites.google.com/site/keithdysart/radio6. The flaw is your belief in a conservation of power principle that doesn't exist. Instantaneous power is not required to obey any conservation principle. What you are doing on that web page is attempting to superpose powers apparently without a clue. Superposition of power is a no-no. The power density equation allows us to accomplish the addition of *average* powers taking interference into effect. I know of no such mathematical equations for instantaneous power and your instantaneous power superposition technique is obviously invalid. -- 73, Cecil, w5dxp.com |
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