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Discussion in 'Electronic Basics' started by Mark-T, Nov 17, 2005.

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  1. Mark-T

    Mark-T Guest

    What is a balun, and what for?

    How is it different than any other transformer?


  2. Balun = Balanced to Unbalanced. It is used to convert a balanced
    line to single ended, or vice versa.
  3. Bob Myers

    Bob Myers Guest

    The answer in this case is in the name: a "balun" is a device
    for converting between an unbalanced line and a balanced
    load, or vice-versa. Hence, BALanced-to-UNbalanced
    (transformer, although not all "baluns" are transformer-like
    devices - you can make a balun for a given frequency from
    the right length of transmission line, f'rinstance). Pretty common
    in antenna/transmission line work.
    For the transformer type, it's not, really, in the basic
    theory of the thing - it's more in how it's connected, and
    in practice that generally it is intended for high-frequency,
    fairly broadband operation (very high, compared to power
    transformers and the like).

    Bob M.
  4. JeffM

    JeffM Guest

    What is a balun, and what for?
    The most common ones have 75 ohm coax on one end
    and 300 ohm flat lead on the other.
    US TV Channel 13 == 216 MHz
    Channel 83 == 890 MHz
  5. Indeed. A typical balun would appear as a dead-short to a mains
    frequency signal.

  6. You've never seen a line isolation transformer?
  7. Mark-T

    Mark-T Guest

    So the primary has one side grounded, while the secondary
    goes to the inputs of a diff. amp, with center tap to ground?

  8. Bob Myers

    Bob Myers Guest

    Why assume a grounded center tap? Better to say that
    the primary - or input side - has one end connected to the
    "ground" or reference used for the unbalanced output of
    whatever you're connecting to, and the output side is
    connected to a balanced input - for instance, perhaps it
    feeds a dipole antenna. No need for a "ground" at all
    on the output side!

    Bob M.
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