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For related information on the subject, see also our articles on common mode interference and impedance matching.


The balun is a device (often a transformer) that can:

  • match a balanced antenna (dipole) to an unbalanced feedline (coax)
  • match an unbalanced antenna (quarter-wave vertical) to a balanced feedline
  • electrically isolate the feedline
  • choke common-mode currents (caused by unbalanced antennas)

Although a balun can quench common-mode currents, it doesn't necessarily transform impedances.

Tuned Stub

Folded Balun

Pawsey Stub
Coax balun
Split coax balun