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- Thread starter agata78
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- #2

gneill

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- #3

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Calculate the characteristic impedance (Z0) of the two port network shown below:

In this example :

R1 = 40 ohm

R2 = 40 ohm

R3 = 20 ohm

V1 = I1 (R1+R2)

Then, Z11 = V1/I1 = R1+R3 = 40+20 = 60 ohm

V2 = V1 (R3 / R1+R3) = I1 (R3+ R1) (R3 / (R1+R3)) = I1 R3

Then, Z21 = V2 / I1 = R3 = 20 ohm

Am I correct so far?

In this example :

R1 = 40 ohm

R2 = 40 ohm

R3 = 20 ohm

V1 = I1 (R1+R2)

Then, Z11 = V1/I1 = R1+R3 = 40+20 = 60 ohm

V2 = V1 (R3 / R1+R3) = I1 (R3+ R1) (R3 / (R1+R3)) = I1 R3

Then, Z21 = V2 / I1 = R3 = 20 ohm

Am I correct so far?

Last edited:

- #4

gneill

Mentor

- 20,925

- 2,866

Calculate the characteristic impedance (Z0) of the two port network shown below:

In this example :

R1 = 40 ohm

R2 = 40 ohm

R3 = 20 ohm

V1 = I1 (R1+R2)

Then, Z11 = V1/I1 = R1+R3 = 40+20 = 60 ohm

V2 = V1 (R3 / R1+R3) = I1 (R3+ R1) (R3 / (R1+R3)) = I1 R3

Then, Z21 = V2 / I1 = R3 = 20 ohm

Am I correct so far?

Sure. Note that you can drive a port with a current source rather than a voltage source. This might make some of your work easier, not having to fiddle about with voltage dividers and determining the input current separately.

For example, for Z21 if you drive I1 into the first port then the output voltage on the second port is clearly V2 = I1*20Ω, yielding V2/I1 = 20Ω.

- #5

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Zoc= R1 + R2 = 40 + 20 = 60Ω

Zso = (R1 * R2 ) /( R1 + R2 ) + R1

Zso= (40 + 20) / (40+ 20 ) + 40

Zso= 800/ 60 + 40 = 13.333+ 40 = 53.333Ω

Zor= √ Zoc Zsc = √60 + 53.333= √ 113.333 = 10.645 Ω

I hope im on right path this time

- #6

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But the key moment when I was learning 2 port neworks is that Z and Y (I think dont have access to my notes atm) are bassically you just doing Mesh and Nodal Analysis

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I don't want to start going down the wrong track.

- #8

The Electrician

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Zoc= R1 + R2 = 40 + 20 = 60Ω

Zso = (R1 * R2 ) /( R1 + R2 ) + R1

Zso= (40 + 20) / (40+ 20 ) + 40

Zso= 800/ 60 + 40 = 13.333+ 40 = 53.333Ω

Zor= √ Zoc Zsc = √60 + 53.333= √ 113.333 = 10.645 Ω

I hope im on right path this time

The part in red is incorrect. You have Zor = sqrt(Zoc) + Zsc

It should be Zor = sqrt(Zoc * Zsc) = sqrt(60 * 53.333) = sqrt(3200) = 56.57

- #9

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Zso = (R1 * R2 ) /( R1 + R2 ) + R1

Zso = (40 + 20) / (40+ 20 ) + 40

Zso = 800/ 60 + 40 = 13.333+ 40 = 53.333Ω

Zor = √ Zoc Zsc = √60 x 53.333 = √ 3200 = 56.568

Characteristic Impedance = 56.57 Ω

- #10

The Electrician

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This is correct.

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