TLLC help


This calculator is designed to model the common configuration where a transmitter which is designed for a particular load impedance, is connected to a an antenna of that impedance, over transmission line of the same characteristic impedance.

The calculator allows specification of the transmission line loss 'upstream' and 'downstream' from the measurement point. It is intended to provide a simple analysis of the system at the transmitter and at the antenna where a directional wattmeter is used to take measurements in the system at some convenient intermediate point.

Input values / formats

The input fields may support flexible input format. In general, the formats supported include traditional floating point number (50.00), scientific notation (5.05E1).

Complex numbers must be entered as floating point cartesian format  with a leading j on the imaginary part, and no leading, embedded or trailing spaces. The imaginary part is optional if it is zero. For example 5.1-j34.2, 43, 1e-8.

The calculator will not accept zero for an impedance or admittance, use a very small (eg 1e-8) or very large (1e8) impedance or admittance as appropriate for open circuit or short circuit.

Model variables

Transmission line type

The transmission line type  is a line description selected from the TLLC database.


Length of transmission line specified as either metres, feet, degrees or wavelengths. The results calculates the electrical length in wavelengths and degrees.


Frequency in Megahertz.


The type of mismatch modelled, it may be NONE, Average VSWR, Zload or Zin. Note that specifying a negative value for the real component of impedance, or an impedance for Zin that results in negative Rload will prevent calculation of some results.

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 impedance looking into the transmission line from the generator end.

Input format is a rectangular format complex value (eg 3.23-j45.1) with no spaces , the imaginary part is optional (eg 1e-8).


The impedance terminating the transmission line opposite to the generator end.


The complex reflection coefficient GAMMA at the input, expressed in polar format magnitude<angle (angle in degrees). GAMMA is for the actual Zo as calculated, not nominal Zo.


The complex reflection coefficient GAMMA at the load, expressed in polar format magnitude<angle (angle in degrees). GAMMA is for the actual Zo as calculated, not nominal Zo.

Average VSWR

The average VSWR over the transmission line. 


A title for results documentation purposes only.


Code is the unique key used in the TLLC database for entries.

Data source

A short identification of the source of the transmission line characteristics.


The characteristic impedance of the transmission line at the modelled frequency.

Velocity factor

The velocity factor of the transmission line at the modelled frequency.

Line loss (matched)

The line loss under matched conditions at the modelled frequency.

Line loss

The total line loss under the mis-matched conditions at the modelled frequency.


The ratio of real power delivered to the load to the real power into the transmission line at the generator end, expressed as a percentage.


The complex load impedance.

gamma (γ)

The complex line propagation constant at the modelled frequency.

k1, k2

The loss model coefficients.

Many other programs use the same type of model for transmission line loss. This calculator displays the values of k1 and k2 based on the length units selected on this form and frequency in Hz.

To use the values of k1 and k2 in other calculators, you may need to adjust the values. For example:

Correlation coefficient (r)

The correlation coefficient from the regression analysis to determine k1, k2.


Use at your own risk, not warranted for any purpose. Do not depend on any results without independent verification.

© Copyright: Owen Duffy 1995, 2021. All rights reserved. Disclaimer.