Transmission Line Loss RF Calculator Free Online Resources Link

This calculator computes the matched line loss for a transmission line using a model calibrated from data for the transmission line types built in to the calculator. It also gives an estimate of the mismatched loss if the mismatch is specified. Mismatch can be specified as:

  • the impedance at the load end of the line;
  • the admittance at the load end of the line;
  • the impedance looking into the line from the source;
  • the admittance looking into the line from the source;
  • the VSWR at the source end of the line;
  • the VSWR at the midpoint of the line; or
  • the VSWR at the load end of the line; or
  • the load end VSWR - bad case Zload (Zload=Zo/VSWR).
The calculation of loss using VSWR is an approximation that is reasonably accurate on long lines with low VSWR and low loss. The methods using the impedance of the load or looking into the line produce accurate answers, and are the only way to get reasonably accurate answers with high VSWR or short lines.

The models for most lines are from the manufacturers published specifications, and are dependent on the quality of that data for their accuracy.

The models for generic open wire lines are theoretical values for air dielectric lines. There are a couple of generic types derived from the ARRL reference tables, and an indicative figure on Zip Cord. In each case, the results form identifies the source of the data.

The model used for matched line loss in a length of line is:


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