Transmission Line Problem

Hi,

I have a doubt regarding the transmission line effect. In the textbook
it says the transmission line effect is only considered when the
rising/falling edges are smaller than 2.5*t, where t is the propagation
time for the waveform goes from one end to the other. Therefore the
transmission line can be assumed to be long enough.

Now my question is: what happens if the tranmission line is not long
enough. If the rise time of the waveform is quite large and the
transmission line is not long enough, how to model the transmission line
effect? What will happen under such a situation?

Kuan

 

When the transmission line is too short, the entire line behaves more like a
lumped element.

Essentially the propagation wave gets to the other end and back again before
the input waveform has completed
its transition.

Essentially all of the Transmission line effects (echos, reflection,
mismatching) happen on a small percentage
of the total voltage. With any reasonable decay parameters, the
"Transmission Line" effects are not seen.