I'm confused why sometimes when we look at the termination effect on a transmission line, we don't consider the overall input impedance looking into the transmission line including the load? For example, I have this:
We say, the voltage at node A before the wave propagates down the transmission line is only 1/2 of Vin because we treat it as voltage divider of Rs and Zo (voltage at node A = Vi * Zo/(Rs + Zo)). Why in this case we are not considering the total Zin (blue, the impedance looking into the transmission line) for the voltage divider? Why do we only use Zo to form voltage divider with Rs? But, sometimes, why do we try to calculate for Zin? Thanks.