Home Forums Bug Reports Impedance Smith Chart Plotting Error

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  • #624
    Jess_Stuart
    Participant

    I created a simple Qucs schematic to illustrate this problem.   I am using a voltage controlled dependent current source to drive a transmission line and load resistance.  The idea is to drive the transmission line and load with a 1 Amp current, then plot the impedance (voltage when I=1A) on a Smith Chart.  However, when I use the formula Gamma = (ZL-Z0)/(ZL+Z0)  the smith chart plots the reflection coefficient outside of the unit circle.  When I plot the formula for 1/Gamma = (ZL+Z0)/(ZL-Z0)  the plot looks correct.  This is just a problem with using the dependent sources; Driving the load with a swept-frequency AC current source does not exhibit this problem.

    I need to compare the frequency If several slightly different circuits, and to do that, I need to use dependent current sources that are all controlled by the same swept-frequency voltage source.

    I have a workaround (by plotting 1/Gamma) and am not stuck at the moment, but I feel this is a bug that needs fixing.

    I am using QucsStudio version 3.3.2 on Windows 10, 64-bit.

     

    • This topic was modified 1 week, 3 days ago by Jess_Stuart.
    • This topic was modified 1 week, 3 days ago by Jess_Stuart.
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    #628
    QucsStudio
    Keymaster

    The input current has the wrong polarity! It doesn’t flow into the transmission line,

    because the arrow at the input of the voltage-controlled current source points upwards

    and therefore, gets a negative voltage.

    You can either flip the voltage source, set the voltage to -1V or the transconductance to -1S.

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