alex

I've been alone in summer, I've been alone in spring

Regardless of the season, whatever it would bring

It never really mattered, for I never stopped to sing

The essay nobody asked for, but I've been reading about for around a week, and now can explain very easily and intuitively.

When electricity flows from a region with low impedance to a region with high impedance, a reflection of the signal passes back up the cable towards the source. This tends to make the most intuitive sense to people - after all, the high impedance region is easy to imagine as a traffic jam, and the ripple going up the line is just all the electrons having to slam their brakes. We've seen this before.

However, you get an identical ripple when going from a region with high impedance to a region with low impedance, which kind of mangles that analogy. You don't see traffic jams in regions where the speed limit goes up, just in places where it goes down.

And so for that, we're going to have to break the signal into two parts.

V=IR is bread and butter, but nobody accounts for those in time. Everyone does DC steady state analysis, and this is slightly weirder. So in a line with low impedance to high, you just look at how much V (voltage) you need to push the same amount of current (I). Since R is getting bigger, you now run out of voltage before you run out of current. So all the voltage gets used up, some of the current gets used up, and the current that no longer has enough voltage to get pushed forward can't enter the new material and thus bounces backwards up the line. The reverse happens with high to low. You now run out of current (I) before you run out of voltage (V) because R got smaller and energy must be conserved, so you get a voltage wave that bounces up the line. So any time R changes you have too much of either current or voltage and the extra gets sent back.