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Cecil Moore wrote:
Roger wrote: Cecil Moore wrote: Assume a constant power source and you will get the results that Roy is talking about. No, because you would find two waves of equal voltage and current traveling in opposite directions, always arriving at exactly out of phase, at the source. No, because a *constant power source* is pumping joules/second into the system no matter what voltage or current it requires to move those joules/second into the system. It's like the power source in "Forbidden Planet". Now the question here is "Do the waves bounce off one another?" Waves do NOT "bounce" off one another. At a physical impedance discontinuity, the component waves can superpose in such a way as to redistribute their energy contents in a different direction. (Redistribution of energy in a different direction in a transmission line implies reflections.) In the absence of a physical impedance discontinuity, waves just pass through each other. www.mellesgriot.com/products/optics/oc_2_1.htm micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html There is a third possibility. The interaction of the two waves can establish a very high resistance, so high that no current flows-zero. Does this place us at a logical impasse, with current reversing and voltage doubling at in one argument (at the open end), but not doubling at the source end? No, the voltage will double at the source end when stability is reached after one full cycle (in the 1/2 wave example). Logically then, we must recognize that our source voltage WILL NOT remain constant following the arrival of the reflected wave. Certainly this is what we find when we retune our transmitters after changing frequency. What would be the logic of insisting that the input voltage be held constant to the 1/2 wave example after it is shown that the reflected wave must interact with the incoming wave give a very high impedance at the source? 73, Roger, W7WKB |
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