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Transmission Line interview problem?

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davyzhu

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Hi all,

There is a interview problem.

A voltage source with internal impedance Z_source = 50 OHm is connected to a transmission line with Z = 50 OHm. Z_load is also 50 OHm.
The voltage source generates a single voltage step 1V.
What will be the voltage level on the load?

Is there any intuitive method to solve such Transmission Line problem?

Any suggestions will be appreciated!
Best regards,
Davy
 

I think it should be 0.5V.

Added after 1 minutes:

Because the resistance of the line is 50 and load is also 50 so no reflection. But the source resistance is 50 as well. So only 0.5v is on the line and the load.
 

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    davyzhu

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hi,
well here the important point is that -->if the load that is connected to the circuit have an impedance different form the line's characteristic impedance then the energy trying to be transmitted to the end of the line cant be fully transmitted.
So some part of reflection could be faced but ur circuit is exactly opposite.
This way an infinitive loop is build,it will go and come back infinitive times.

so the potential energy that will travel inf.
V= Vo .e^(-zφ)
I=Io.e^(-φz)

Zi=Zo.[(ZL+Zo.tanh.φ.e)/(Zo+ZL.tanh.φ.L)]
 

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    davyzhu

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As the T-line is terminated in its characteristic impedence hence the impedence seen by the source is equal to the characteristic impedence which is 50.hence the total voltage will be divided equally between source impedence and load.
SO THE VOLTAGE AT LOAD WILL BE 0.5 Volts.take care
 

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    davyzhu

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it will be definitely 0.5 v in the steady state
but not before the time required for the wave to reach the load i.e. the length of the line

since source ,load, characteristic impedance are seame the steady state will reach faster

it is a typ. problem in EMI/EMC subject
 

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    davyzhu

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