Ei-5 Transmission Line

Aim

To demonstrate some basic properties of transmission line theory.

Apparatus

  • Coaxial wire
  • C.R.O.
  • Signal Generator

Transmission Line

Transmission Line Setup.

Description

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.

  • Open ended.
  • Short circuited.
  • A potentiometer allowing adjustment to the characteristic impedance.

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.