To be clear: we are trying to visualize the green curve in the yellowish frame in this picture compose from screenshots in Ben Watson's simulation
link:
https://i.postimg.cc/c4LcZ7cV/screenshot-27.pngIf I got the sizes right (I skimmed through the video this time and I don't remember if he said the dimensions explicitly), Watson simulated a strip 9cm long and half a cm wide.
It takes 15-20 ps for light at 2.98 x 10^10 cm/s to cross the strip.
At 820 ps, ie 620 ps after the switch on, the charge has redistributed itself along the wire (can we infer a velocity factor of about 0.5?).
The times will be different in the experiment. If 50 cm were separating generator on one side and load+scope on the other, we will have to wait 1.5 - 2 ns for the green line to rise. And then some 130 ns for the charge redistribution to reach the load.
What we see on the scope is the big green step (that in this tiny line starts at 820 ps). What I am dubious about is: is the setup capable of revealing that small step that starts 20 ps after the "switch" is closed?
In the real world, with the probe cable, and the scope attached we do not have just the load. What happens to that tiny current when we attach the whole equipment?
Also, wouldn't it be required to have the scope on the load side, without any connection to the generator?
This looks like a delicate measure: we are not operating the transmission line from one of its ends, the effect is small in itself and might be killed by the instrument, the geometry of the setup is important (for example, if you bring the coax for the load and the generator in the same scopes-- they are what? One inch apart? We must make them half a meter, one meter apart). We might also have to consider the propagation along the probes (what does that do to the feeble charge whose effects we are trying to measure?).