School of Physics Lecture Demonstration Manual

Ei-5 Transmission Line

Published: Tuesday 14 March 2006 - Updated: Tuesday 29 March 2011


To demonstrate some basic properties of transmission line theory.



Click on pictures to enlarge.

Transmission Line Pic


A narrow pulse (0.4microsec duration at 200kHz ) is sent down a long coaxial cable and the pulse and the reflected pulse is displayed on the C.R.O. The shape and polarity of the reflected pulse is observed under the following terminations.

An electrical pulse travelling along a coaxial wire may be compared to a pulse on a spring. The reflected pulse will depend on the terminating impedance. The reflected pulse in this demonstration changes from positive (open circuit) to negative (short circuit case) and almost disappears when a trim potentiometer is adjusted to match the characteristic impedance of the coaxial wire.

Safety notes

Electrical safety 


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