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Roger Sparks wrote:
Yes, in nature the returning power will affect the frequency of the source. If the reflected wave is a sine wave coherent with the forward wave, why would the frequency change when they are superposed? GND--Vs--x--Rs--------45deg 50 ohm----short 100v 50ohm This circuit has an impedance of 73.5 + J44.1 ohms at the point x. Energy sinking into the source occurs during the cycle. It is not an illusion. I got a different impedance value but for purposes of discussion, all that matters is that the impedance is NOT 50 ohms. Let's assume your impedance is correct. That means the ratio of reflected power to forward power at point 'x' is 0.1452 in the 50 ohm environment. Why would reflected energy flowing back through the source be considered "energy sinking". Why cannot the reflected energy flow back through the source unimpeded by the 0+j0 impedance and be reflected by the short to ground on the other side? That same thing happens all the time to standing wave current on the outside of the coax braid. Why do the laws of physics change inside a source? In this example, we are delivering 100 watts to Rs. With a power reflection coefficient of 0.1452, the forward power has to be 117 watts making the reflected power equal to 17 watts at point 'x'. That reflected power of 17 watts is not absorbed by the source. It flows back through the source, unimpeded by the 0+j0 impedance, and is reflected by the short to ground. It joins the 100 watts being generated by the source to become the forward wave of 117 watts. No absorbing of energy required - just good old distributed network physics. Once this 17 watt wave is tracked back through the source, reflected, and superposed with the 100 watts being generated by the source, all will become clear without any power absorption by the source being necessary. Here's a diagram of what's happening. 100w 100w GND--------Vs----------Rs--------45deg----------short 17w-- 117w-- 50w-- --17w --17w --50w All energy flows balance perfectly and there is no absorption by the source. -- 73, Cecil http://www.w5dxp.com |
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