Hello
I come through this tutorial about transmission lines

The idea is to put two transmission lines with resistive load
-first TL = 50 ohm,
- Second TL = 70.71 ohm
- the load is 100 ohm
The output is like this

When I played with these setting, I found that there is a problem if I put the second TL = 50 ohm, the output is like noise !! Why?

is there a basic document about that theory?
Thanks

 

Look at the numbers describing the Y axis. Do you see how close they are? The "noise" is just an artifact of the mathematical engine because the difference between the points of the curve is at the limit of the precision of the numbers used.