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Derivation of Reflection Coefficient vs SWR
On Feb 5, 2:41*pm, Cecil Moore wrote:
Keith Dysart wrote: How does this reflected wave of 6.25 W affect the already present forward wave of 25 W when it arrives back at the generator. It affects it not one iota. The forward power remains the same, the forward voltage remains the same and the forward current remains the same. This is the meaning of no reflection. Maybe a more drastic example will help. * * * * * * Rs * * * Vg * * * * * * * * * * Vl * * * *+----/\/\/-----+----------------------+ * * * *| * *50 ohm * * * * * * * * * * * * * | * * * *| * * * * * * * * * * * * * * * * * * / * * * Vs * * * * * * * * 90 degrees * * * * *\ * Rl * *100 cos(wt) * * * * * 50 ohm line * * * * / *1 ohm * * * *| * * * * * * * * * * * * * * * * * * \ *load * * * *| * * * * * * * * * * * * * * * * * * | * * * *+--------------+----------------------+ * * * gnd Current through the source: Is = 0.0392 cos(wt). The source is supplying 1.96 watts. That is all the power available to the entire system. You say the forward power is 25 watts and that none of the reflected power is reflected at the source. How can there be 25 watts of forward power when the source is supplying only 1.96 watts and none of the reflected energy is joining the forward wave? The answer would be clear to you if you were to complete the analysis. Please compute: Pfor Pref Vfor Vref at the point Vg, both before and after the reflected wave makes it back to the point Vg. When you find (as you will), that Pfor and Vfor do not change when the reflected wave returns, it should be difficult to assert that the reflected wave is re-reflected at Vg. If the reflected wave was re-reflected at Vg, there would necessarily be a change to Vfor and Pfor. ...Keith |
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