# Homework Help: Transmission line Sketch

1. Apr 27, 2014

### tim9000

1. The problem statement, all variables and given/known data

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.

2. Relevant equations

3. 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

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2. Apr 27, 2014

### 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.

3. Apr 27, 2014

### tim9000

thanks

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

4. Apr 27, 2014

### rude man

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.