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Help: Finding Load Impedance & Reflection Coefficient using SWR

Discussion in 'Radio and Communications' started by doughng, Aug 23, 2010.

  1. doughng

    doughng New Member

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    I have an exercise I'm working on during my holiday, and it seems I dont get it. Can you kindly help;

    In a laboratory experiment conducted on a 50 ohms lossless transmission line terminated in an unknown load impedance, it is found that the SWR is 2.0. The successive voltage minima are 25 cm apart, and the first minimum occurs at 5cm from the load. Find (a.) the load impedance (b.) the reflection coefficient of the load (c.) Where would the first voltage minimum be located on if the load were replaced by a short-circuit?

    Here's my working:
    Distance between successive voltage minima is a half-wavelenght i.e.
    λ= 2 x 0.25m = 0.5m
    β= 2π/λ = 4π rad/m


    |Γ| =S − 1/S + 1
    = 2-1/2+1 = 0.3


    θL= 2βlmin − π,
    = 2 x 4π rad/m x 0.05m - π
    = -0.6π rad
    Γ= 0.33e(-j0.6π) (Ans)


    But from the textbook where I found the problem, reflection coefficient is 0.3e(j4.41) and the Load impedance is: 33.75 - j23.75 ohms...can anyone please help?


    Thanks
     

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