# Transmission Lines in time domain

This video represents the potential and the intensity of two different Transmission Lines (TLs) joined in cascade.   This simulation is made using the Finite Different Time Domain (FDTD) method, which allows us to visualize what happens when the time goes by.

What can we see? A step signal feeds the first TL and the line is excited by certain potential. At t=2s, the step arrives to the discontinuity between the two TLs. Two waves appear: one wave is generated in the second line to forward direction and another wave advances to the backward direction. The first TL has a bigger transmission speed than the second.  The wave in the second line arrives at t=8s  to a certain load and a backward wave is produced that come back to the discontinuity.

Let‘s look a little more inside. We can make some affirmations. Try to understand why:

–          The two lines are lossless.

–          The two lines have different transmission speed and different impedance.  The impedance of the first line is smaller than the second one.

–          The load at the end of the second TL has a real value smaller than the impedance of the second line

–          The generator is matched to the first TL.