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Do you mean the mashed-potatoes energy equations where the wave energy components are completely ignored? Calling the steady state solution "mashed-potatoes" is ridiculous. I'm not calling the solutions ridiculous. I am calling some of the conceptual conclusions ridiculous. For instance, since the *net* Poynting vector equals delivered source watts, there are zero watts in the reflected wave even though there are joules in the reflected wave moving at the speed of light. If you want to know what happens during the transient, you MUST start from the original differential equation that describes how the fields were set up in the line in the first place, but it doesn't matter in the steady state. The answer is the same. Not according to some of the gurus posting here. The joules supplied during the initial transient state are being swept under the steady-state rug. Witness "Food For Thought #1" on www.eznec.com I don't want to have to do it but one of these days I think it might be necessary. What you will find is that there is exactly the energy in the transmission line required to support the real speed-of-light forward traveling wave and the real speed-of-light reflected traveling wave - no more and no less. The argument that there is no more energy in a transmission line with reflections than is being supplied by the source is simply false. The Poynting vector in a mismatched line has been worked out by me, here, and I'd appreciate comments on the MATH. http://en.wikipedia.org/wiki/User ![]() What about the forward Poynting vector, Pz+, and the reflected Poynting vector, Pz-. Reference page 291, "Fields and Waves ...", Ramo and Whinnery, 2nd edition? My claim is that that's it. That's all. No handwaving, no setting up steady state startup and claiming that that energy remains in the line. The real part of the Poynting vector represents real power flux and the imaginary part represents reactive power flux. To get the energy that exists in the line you just add it all up... The forward wave's average Poynting vector is real. The reflected wave's average Poynting vector is real. Adding two real power flow vectors is a lot easier than integrating a power flow vector with real and imaginary parts. And, bottom line, one obtains exactly the same results with 10% of the work. Subtract the reverse Poynting vector from the forward Poynting vector to determine the net power. Add the two Poynting vectors and multiply by the length in seconds of the feedline to determine the total energy. What could be simpler? Am I wrong, Cecil et. al? No, you are correct but you are going around the world to get from California to New York. My method, supported by Ramo and Whinnery, can be done in much less time and can be more easily understood by people not familiar with your method. By the time you get out your calculator, I can have your answer waiting for you and it will be the same answer you get after wasting a lot of time. When the SWR is infinite, there is no energy in the line associated with flowing power. None at all. The reflection coefficient is 1, and all energy in the line is associated with circulating power (reactance only, as you would expect from a stub) You are, of course, talking about *net* "flowing" power. But your answer is exactly the same as component forward power in real joules/sec plus component reflected power in real joules/sec. And thinking in terms of those real component powers is a lot easier than your imaginary stuff. Pz+ - Pz- = Pz-tot sourced and delivered (Pz+ + Pz-)* feedline length in seconds = total feedline energy There is also a physics problem with the imaginary concept. EM wave energy must necessarily move at the speed of light. A small amount of TV modulation will prove that those forward and reflected waves are still moving end to end at the speed of light and still transferring information. -- 73, Cecil http://www.w5dxp.com |
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