Transmission Line Characteristics
The applet demonstrates the properties of both lossy and lossless transmission lines with adjustable characteristic impedance under various
conditions of complex source and load impedances.
There are two displays, selected from the drop-down menu; the first plots the voltage and impedance functions along the line, and the second plots the available power and line input VSWR as a function of frequency.
In both cases, the source and load complex impedances may be varied.
Moving the mouse across the displays indicates the plot values relative to the mouse position along the line.
Signal frequency, the line electrical length, and the line loss/wavelength are applet variables.
Varying the source and load reactances as ratios of the impedance magnitudes allows modification of the impedances from purely resistive through to purely reactive.
The complex impedance component values are displayed at the bottom of the display.
Varying source impedance does not affect the response of the line, but does effect the voltage and current magnitudes and in turn the efficiency of power transfer to the load.
An interesting case occurs if the line impedance differs from the system design impedance. For example, a 100Ω line loaded by a system-matched load of 50Ω produces an input VSWR ranging from 1.0 to 4.0 depending upon the signal frequency and line length.
On the other hand, a system-matched 50Ω line loaded by 100Ω has a VSWR of 2.0 independent of line length or frequency.
Other cases of interest can be reviewed using the applet, including the effects of line loss.
Line loss per wavelength is scrollbar adjustable and the corresponding total line loss is tabulated on the left of the display.
Chapter 1 - Introduction