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.
Input
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
Output
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”
