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Derivation of Reflection Coefficient vs SWR
Keith Dysart wrote:
So, contrary to Cecil's assertion, an analysis based on 'no reflections at the source', has not resulted in any violation of conservation of energy. This is good. Again your analysis violates the conservation of energy principle. The only way to balance your energy equation is for your source to supply 25 joules/sec. IF THE REFLECTED WAVE IS NOT REFLECTED FROM THE SOURCE, IT FLOWS THROUGH THE SOURCE RESISTOR AND IS DISSIPATED IN THE SOURCE RESISTOR. THAT REFLECTED WAVE ENERGY IS THEREFORE NOT AVAILABLE TO THE FORWARD WAVE. You cannot eat your reflected wave and have it too. The standard equation is: Psource = Pfor - Pref = Pload But you have taken away the reflected energy and dissipated it in the source resistor. So your new equation becomes: Psource = Pfor + ???????? 18.75w = 25w + ________ You say the source power is 18.75 joules/sec and the forward power is 25 joules/sec. If none of the reflected energy is available to the forward wave, where did the extra 6.25 joules/sec come from? Is it sheer coincidence that the reflected wave is associated with 6.25 joules/sec that are now missing from the above equation? Here is an example of the reflected wave flowing through a circulator resistor and being dissipated. Source---1---2----45 deg 50 ohm feedline---150 ohm load 25w \ / 18.75w | 50 ohms 6.25w But in this example Psource = Pfor in order to satisfy the conservation of energy principle which your example does not. -- 73, Cecil http://www.w5dxp.com |
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Derivation of Reflection Coefficient vs SWR
On Feb 5, 10:44*am, Cecil Moore wrote:
Keith Dysart wrote: So, contrary to Cecil's assertion, an analysis based on 'no reflections at the source', has not resulted in any violation of conservation of energy. This is good. Again your analysis violates the conservation of energy principle. The only way to balance your energy equation is for your source to supply 25 joules/sec. IF THE REFLECTED WAVE IS NOT REFLECTED FROM THE SOURCE, IT FLOWS THROUGH THE SOURCE RESISTOR AND IS DISSIPATED IN THE SOURCE RESISTOR. THAT REFLECTED WAVE ENERGY IS THEREFORE NOT AVAILABLE TO THE FORWARD WAVE. Not sure that shouting helps. I do not find any unbalances with the energy. See below. You cannot eat your reflected wave and have it too. The standard equation is: Psource = Pfor - Pref = Pload Yes. Indeed. And just changing to use my terminology... Pgenerator = Pfor - Pref = Pload For the example at hand... Pgenerator = 18.75 Pfor - Pref = 18.75 Pload = 18.75 And the source provides 50 W of which 31.25 is dissipated in the source resistor and 18.75 is delivered to the line (Pgenerator, above). All seems well with world and no energy is left unaccounted. But you have taken away the reflected energy and dissipated it in the source resistor. So your new equation becomes: Psource = Pfor + ???????? 18.75w *= 25w *+ ________ As your original equation above Psource = Pfor - Pref 18.75 = 25 - 6.25 I do not see any issues. When the source was first turned on, 25 J/s flowed from the generator into the line. Pfor = 25 W After the reflected wave makes it back to the generator, 25 - 6.25 - 18.75 J/s are flowing in the line. Pfor - Pref = 18.75 W And the generator output has also reduced from 25 W to 18.75 W, so all is still in balance. I am having difficulty determining where you think there is a violation of the conservation of energy principle. ...Keith PS Do not be fooled by the numerology where 25 + 6.25 gives 31.25. For the 35 degree line, the corresponding numbers are Ps = 41.449507 Prs = 22.699502 Pg = 18.75 Pf = 25 Pr = 6.25 Pl = 18.75 Pg = Pf - Pr = Pl Ps = Prs + Pg All as expected. No missing energy. |
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