Impedance discontinuity close to power amp

Discussion in 'General Electronics Chat' started by dbickham, Apr 14, 2010.

  1. dbickham

    Thread Starter New Member

    Apr 14, 2010
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    I've got a VLF transmission line with a possible impedance discontinuity 1000ft from the PA, so only a small fraction of a wavelength away, but the total transmission line length is significant relative to the wavelength. So my question is, do rules of an electrically short transmission line apply so that I can basically ignore this? It would make sense that no standing wave can develop in the portion of the line before the discontinuity, but do I need to worry about reflections at my PA output? Thanks!
     
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    It will change the impedance seen by the amp, so also probably changing the power output to some amount.
     
  3. dbickham

    Thread Starter New Member

    Apr 14, 2010
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    Thanks rjenkins. Is that the only effect? No reflected power at the PA?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    How bad is the impedance mismatch?
     
  5. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    A discontinuity a small fraction of a wavelength from the amp would have a similar effect to the same fault directly at the amp output.

    If the fault is either a short or open circuit, then either near zero or infinite impedance at the amp, so a pretty high level of reflected power.
     
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  6. dbickham

    Thread Starter New Member

    Apr 14, 2010
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    SgtWookie -
    This is actually more of a hypothetical for now. I'm doing a splice job on an accidentally severed cable, so I'm thinking of "what ifs" if the splice job is done poorly.
     
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