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How to Design a Balun

A balun is an electric transformer that couples two sides of an electrical circuit. One side of the electrical circuit contains an electrical signal that is balanced with respect to electrical ground, while the other side of the circuit contains an unbalanced electrical signal. Merging the two circuit sides gives the "balun" its name. Baluns are typically used to produce maximum power transfer by matching the impedence on one side of the circuit with the impedence on the other side of the circuit. Calculate the necessary ratio of wire turns on the primary side of the balun transformer to the secondary side of the balun transformer to accomplish this matching.

Things You'll Need

  • Input impedence measurement
  • Output impedence measurement
  • Calculator
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Instructions

    • 1

      Divide the output impedence measurement by the input impedence measurement and write this value down. For example, if you wish to create a balun that matches a 75-ohm input to a 300-ohm output, the number you would record is 4, which is equal to 300 ohms/75 ohms.

    • 2

      Calculate the square root of the number recorded in Step 1. The calculated square root is the turns ratio that the balun must have for maximum power transfer. For the example above, the turns ratio is 2 (equal to the square root of 4).

    • 3

      Convert the calculated square root into a fraction; this fraction will serve as the primary-to-secondary turns ratio of the balun transformer. For the example above, the primary must have twice as many wire turns around the transformer core as does the secondary.


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