This is a simple circuit showing two mismatched transmission lines. The first line is 75 ohms, and the second line is 500 ohms. Waves traveling down the first line are reflected at the boundary, causing a standing wave on the line, which is a wave that oscillates but does not appear to travel. It is actually the combination of two waves (the initial wave, and the reflected wave) traveling in opposite directions.
The second line is properly terminated, so there are no reflections on that one.
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