# Coax Impedance Calculations

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(Partly from http://www.electronics-lab.com/blog/?p=18953 )

In deriving the formula for characteristic impedance resistance per unit length can be neglected. The impedance can be found from the values of capacitance per unit length (C/h) and the inductance per unit length (L/h):

where D is the diameter inside diameter of the shield, d is the outside diameter of inner conductor, h is the length of the cable, and e is the dielectric constant of the insulator.

The series inductance per unit length, in Henrys per meter, is given by:

(See http://en.wikipedia.org/wiki/Impedance_of_free_space )

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