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I'm taking an EE course where we have been studying transmission lines, among other things. I know that when I am driving an unmatched load, there will be a reflected wave. figure from the Popovic manual

My question is where exactly does this wave travel? Is it along the top or the bottom conductor? On the one hand, I thought current returns on the bottom conductor. Does this mean that the insulator on a coax cable, for instance, is the only thing protecting me from the AC voltage? On the other hand, if both waves travel on the top conductor, how isn't there interference? Or is that what causes there to be a standing wave?

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  • \$\begingroup\$ In an AC situation current returns alternately on both conductors. \$\endgroup\$ – Andy aka May 11 '16 at 17:17
  • \$\begingroup\$ ... What does KCL tell you about where it travels? \$\endgroup\$ – Ignacio Vazquez-Abrams May 11 '16 at 17:17
  • \$\begingroup\$ The concept of "current returning" in a transmission line must be rethought of, we are no longer using a lumped model for the circuit. \$\endgroup\$ – Varun Sep 4 '17 at 14:38
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Where exactly does this wave travel? Is it along the top or the bottom conductor?

Both. The potential difference or voltage that evolves according to the wave equation is a potential difference between the two conductors. It doesn't exist on one conductor without reference to the other one.

On the other hand, if both waves travel on the top conductor, how isn't there interference? Or is that what causes there to be a standing wave?

You are correct, the standing wave is the result of interference between the forward and reverse travelling waves.

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As shown in your diagram, the voltage difference is simply a potential between the two conductors. It is shown in the diagram as V(z). If you grounded the bottom conductor then you could consider the voltage to be ~0V in the bottom conductor and V(z) in the top.

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