TWLLC help

Overview

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

Conductivity

Conductivity of the conductor material in S/m.

Rel permeability

Relative permeability of the conductor material.

Diameter

Diameter of the round conductors.

Spacing

Centre to centre spacing of the round conductors

Velocity factor

Velocity factor of the line as described.

Twist rate

The number of full twists per meter in a twisted pair.

Loss tangent

Loss tangent of the dielectric. If the space around and between the conductors is partially filled, use an adjusted value to allow for the partial fill if needed. (Hint: calibrate the model using the adjustment to permittivity above.)

Length

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

Frequency

Frequency in Megahertz.

Mismatch

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.

Zin

The impedance looking into the transmission line from the generator end.

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

GAMMAin

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.

Title

A title for results documentation purposes only.

Code

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

Zo

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.

Efficiency

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.

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 distance in metres and frequency in Hz.

Disclaimer

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