To demonstrate some basic properties of transmission line theory.
- Coaxial wire
- Signal Generator
Transmission Line Setup.
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.