# Homework Help: Transmission Line

1. Dec 1, 2013

### sandy.bridge

1. The problem statement, all variables and given/known data
Attached is the problem. I am a little confused as to how I should be approaching this type of problem. If I Determine the input impedance for the first segment of transmission line and load impedance on the right, is that going to be in parallel with $Z_L$ on the left? I am assuming that "effective impedance" is referring to that total input impedance at the left of the diagram, but I am unsure.

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2. Dec 2, 2013

### rude man

1. What is the impedance looking into the 1/4 wave xfmr? (Pretend there's just the xfmr and end-termination).
2. So is that in parallel with the 1st 25 ohm resistor or ???
3. You should wind up with just a 50 ohm xmsn line and a yet-to-be-determined termination, from which you can come up with the reflection coefficient.
.

3. Dec 2, 2013

### sandy.bridge

Number two is the very issue that I was having. I determined the input impedance of the 1/4 transformer and end impedance of 25 ohm to be $Z_i=(50Ω)^2/25Ω$. I believe this input impedance looking to the right would then be in parallel with $Z_L$ at the second termination on the left side and that results in 20Ω. Is that logical so far?

Last edited: Dec 2, 2013
4. Dec 2, 2013

### rude man

You are doing fine. I'm wondering why that isn't obvious to you. You're looking into the 1/4 wave xfmr and you see 100 ohms, and your end is in parallel with the first 25 ohm load.

5. Dec 2, 2013

### sandy.bridge

Sorry this is all super new to me. It makes sense now. I get an effective impedance of 20ohms and a total reflection coefficient of -0.429

6. Dec 2, 2013

Right on!