Transmission lines calculator

This transmission line calculator calculates the impedance at input and attenuation of a given transmission line once terminated with the given load.

All the math involved is well explained and documented by Dan AC6LA on his site. The K values for the various transmission lines are also copied from his Transmission Line Details windows software which I recommend to download and try for much more complete information.

Load R, Ω:
Load X, Ω:
Freq. MHz:
Length unit:
Cable type:
Gen. R, Ω:
Gen. X, Ω:
Z0, Ω:


The information below describes the meaning of the data that can be entered in the program:

  • Load R – resistive component of the load (i.e. the antenna)
  • Load X – reactive component of the load; this can be positive or negative
  • Freq. – required frequency in MHz
  • Length unit – select your favorite unit (meters or feet)
  • Length – lenght of the transmission line in the unit selected above
  • Gen. R – resistive component of the generator (i.e. your radio), usually 50; it will be used to calculate the VSWR seen by it
  • Gen. X – reactive component, same as above (usually 0)
  • Cable type – type of the cable; select “custom” to insert custom data (see Z0, VF, K0, etc. below)
  • Z0, VF, K0, K1 and K2 – line parameters that describe the transmission line; they can be edited only by selecting “custom” cable type


The information below describes the meaning of the data reported by the calculator:

  • Cable type – cable type selected for this calculation
  • Length – length of the cable, expressed in the selected measurement unit
  • Z at input – impedance of the cable at other end: this is the result of the impedance transformation done by the transmission line
  • Generator Z – impedance selected for the generator, usually 50+j0 (it has effects only on “VSWR at gen”)
  • VSWR at load – VSWR that the transmission line encounters at load according to its characteristic impedance
  • VSWR at gen – VSWR seen by a generator that is designed for “Generator Z” impedance (usually 50+j0)
  • True Zo – true characteristic impedance of the transmission line (usually shows a little reactive component)
  • Matched loss – loss in dB due to cable attenuation when the load is perfectly matched
  • Total loss – true loss in dB accounting also extra loss due to mismatch; if the load is perfectly matched to the line characteristic impedance, it is identical to “Matched loss”


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