S.M.R.C.C. Web Tools for Radio Amateurs


Impedance Calculators


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Open Wire Feeder Impedance Calculator

  • Use the "Spin Buttons" to adjust the values in the box.


  • Type in a Radius and Spacing and press "Calculate"

The characteristic impedance of the line is displayed in the last box and the blue dots under the panel show the proportions of the cable providing (Radius+Spacing) < 80

Radius Spacing Z0



  • The "Radius" and "Spacing" should be in the same units

    • If the wire radius is in "mm" then the spacing should be in "mm"

    • If the wire radius is in 16ths of an inch then the spacing should be 16ths of an inches

  • The calculator assumes bare (Un-insulated) wire. Any insulation will introduce an error into the result.

    •  but the above results are reasonably accurate where the spacing is large compared to the thickness of the insulation.