I have a different, and possibly more relevant question for you "scope wizards." What does the waveform look like when it reaches the MOTOR? Assuming that you're running a modern, can-motored loco; and further assuming that the electronic E-unit (or Legacy motor driver, or PS3 motor driver) does some "chopping" of it's own, you could end up with a waveform that's nasty, brutish, and short. Or possibly a motor that's starved for power.
A long time ago when my Dad had a scope handy, we looked at the waveforms coming out of the basic Lionel electronic E-unit from a 1980s starter set loco, and also the waveform from a K-Line K-3003 train set 4-6-2. The K-Line's was much more interesting, it seemed to increase the duty cycle proportional to an increase in the input voltage. I wasn't able to capture images then, but with the advent of Legacy, PS3, etc., this experiment might be worth repeating.
What you have posted so far is interesting and informative, thanks for sharing!
