Characteristic impedance equation - why is there a negative sign?

Discussion in 'General Electronics Chat' started by sp2821, Jul 23, 2015.

  1. sp2821

    Thread Starter New Member

    Jan 8, 2014
    12
    0
    Why is there a negative sign in below equation?

    upload_2015-7-23_18-7-56.png

    If I understand correctly, definition of characteristic impedance of a transmission line is a ratio of incident voltage wave to incident current wave OR reflected voltage wave to reflected wave current.

    Since both reflected waves upload_2015-7-23_18-3-15.png and upload_2015-7-23_18-3-29.png are traveling in same direction,
    shouldn't it be upload_2015-7-23_18-9-28.png ?
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,067
    3,837
    Honestly, it is a question of semantics and perspective. Here is a good and simple explanation from Wikipedia...

    upload_2015-7-23_20-6-46.png
     
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