# Determine attenuation of voltage in transmission line

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1. Mar 19, 2015

### FDTD

Hello,

So I have a circuit where I input a square pulse with a source impedance and load impedance (which are just pure resistors) each of which can be varied and a transmission line circuit connecting them which is made up of resistors, capacitors, inductors in a lumped element model. I set the load impedance to open circuit and vary the source impedance until Vin (the voltage after the source impedance but at the input to the transmission line) shows only a transmitted pulse and single reflected pulse on an oscilloscope.

This is what I believe is source matching where the source impedance is equal to the characteristic impedance. What I am trying to calculate is the attenuation of the voltage from the input to the output and hence the attenuation coefficient. If I say the transmitted pulse is V1 and the reflected pulse is V2 BUT the reflected is a combination of V1 and the backward travelling wave. As I understand it the attenuation is for forward or reverse travelling wave only. So do I just subtract one from the other and use the difference to work out the attenuation coefficient? i.e. V3=V2 - V1 and so attenuation is V3/V1?

I am very new to this so any help or guidance would be appreciated! Thanks!

2. Mar 22, 2015

### tech99

Are you sending a square pulse and can you see the reflected pulse coming back? What do you see?