How Do You Sketch Voltage and Current Waveforms for a Coaxial Transmission Line?

[tim9000]

Homework Statement

As seen in picture: A coaxial transmission line has a characteristic impedance of 50 Ω, propagation
velocity of 200m/μs, length of 400m, and is terminated by a load resistance, RR =
16.7 Ω. At the sending end the line is connected to a pulse generator that has an
internal resistance of 150 Ω and produces a 40 V, 1 μs long pulse at time, t=0. Sketch
the sending end voltage and current waveforms for 0≤t≤15 µsec.

Homework Equations

The Attempt at a Solution

I'm not sure how to approach this, I'm assuming it has something to do with the inductance and capacitance found from Z = Sqrt(L/C), does anyone have any thoughts?
Thanks

 

[rude man]

IMO this is a very difficult assignment. It would be so even if the input were an infinite-duration pulse, in which case a lattice diagram could be used. Not sure if this type of diagram could be adapted for a finite-duration pulse (duration < L/v). Should in theory but wouldn't want to try it.

The basic idea of course is that
1. the outgoing wave V and I moves with velocity v, I = V/Z_0;
2. the returning wave V' and I' are related by the load reflection coefficient;
3. the returning wave, added to the ingoing wave, force a new V and I at the source, which will depend on the source impedance;
etc.

This keeps going until the input pulse goes back to zero V.

 

[tim9000]

thanks

I see, thanks anyway.
Though what does the internal resistance of the pulse generator have to do with it?

 

[rude man]

I see, thanks anyway.
Though what does the internal resistance of the pulse generator have to do with it?

The 150 ohm source resistance determines the fraction of the reflected pulse (back to the source) sent back out again as a new pulse in the +x direction. Us your experssion for the reflection coefficient with Z_0 = 50 ohms and Z_L = 150 ohms.