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| Transmission Line Question - RF Cafe Forums | ||||||
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Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
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Below are all of the forum threads, including all the responses to the original posts. mikerauh Post subject: Transmission Line Question Posted: Fri Mar 07, 2008 2:46 pm Lieutenant Joined: Fri Mar 07, 2008 2:29 pm Posts: 3 In his book, Prof. Guillermo Gonzalez writes: V(x)=V+(x) + V-(x) and I(x)=I+(x) - I-(x) Why is there a minus sign in the second equation? The equations say the voltage at a point on the transmission line is the sum of the forward wave voltage V+(x) and the reflected wave voltage V-(x). But the current is the difference of the current of the forward wave I+(x) and the current of the reflected wave I-(x). It seems to me the voltage and the current are vector quantities, i.e. they have a phase. So why the minus sign? Why not just sum them? Mike Rauh Top fred47 Post subject: Posted: Fri Mar 07, 2008 4:30 pm General Joined: Wed Feb 22, 2006 3:51 pm Posts: 104 If I understand it correctly, it's to make the direction of the power flow work out correctly. Power doesn't really have a phase, but power flow definitely has a direction, and I think the signs are set up to give that. Hope this helps! Fred Top mikerauh Post subject: Posted: Fri Mar 07, 2008 5:18 pm Lieutenant Joined: Fri Mar 07, 2008 2:29 pm Posts: 3 Fred, You are correct. The apparent current has to be defined as the incident wave current minus the reflected wave current to get the power relationships right. Thank you. Mike Posted 11/12/2012 | ||||||
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