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Measuring complex output impedance

Discussion in 'General Electronics' started by Lord Snooty, May 16, 2004.

  1. Lord Snooty

    Lord Snooty Guest

    Does anyone have a nice simple technique for measuring both parameters of the
    complex output impedance of a signal source, like an amplifier? I'm interested
    in the MHz domain if that's relevant. I would want to model the source as
    having a voltage source connected in series with one real impedance R and one
    imaginary reactance jX.

    Andrew
     
  2. Externet

    Externet Guest

    Hi Andrew.
    I do not know if you are referring to the output circuitry of a final
    amplifier or to the load conncted at its output.
    Complex measurements are not to be measured with simple intruments,
    but there is an instrument that behaves well, it really shines light
    on unknown parameters for RF antennas. I have the MFJ249 and behaves
    great.

    http://www.mfjenterprises.com/products.php?catid=49

    Search for reports on the MFJ259B; it may suit your expectations.
    Miguel
     
  3. I didn't know that any such thing even existed. I had always thought
    that the _output_ impedance of a circuit was always purely resistive and
    that any reactance that is created is due to trying to feed that into
    another device with a different characteristic impedance.
     
  4. Externet

    Externet Guest

    Hi.
    I would say if the output specifications on a RF amplifier is "output
    impedance = 50 ohms"; it is not purely resistive, or it would be
    specified as "output resistance = 50 Ohms"

    Miguel
     
  5. Karl Uppiano

    Karl Uppiano Guest

    I've seen it written "output impedance = 50 + j0" to indicate pure
    resistance.
     
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