Author Lim, Chee Hok
Title Distortion and designing of signals propagating in a coaxial cable.
Institute Thesis (M.Sc.) National Institute of Education, Nanyang Technological University
Year 2003
Supervisor Foong, See Kit
Call no. TK5102.9 Lim
Voltage or current waves travelling along a transmission line suffer distortion in their waveform, which may be due to energy dissipation and wave dispersion during the transmission from one end to the other. The objectives of this project include the study of the distortions of a square waveform along a coaxial cable, and the designing of the waveform to be sent such that the waveform after distortion is the desired square waveform. Only the effects of dissipation and dispersion on the waveforms were considered in this project.

Two methods were used in the study of waveform distortion and the designing. The first method is based on the waveform of sinusoidal travelling wave having an amplitude which decreases exponentially in the propagating direction, and a phase velocity that varies with the frequency. By the use of Fourier series, the effects of dissipation and dispersion on each component wave were considered and the distorted waveform was computed. Knowing the line parameters and hence the propagation characteristics, the Fourier components of the waveform that should be sent could be constructed from the corresponding components of the desired square waveform at a predetermined point.

The second method is based on the path integral solution of the telegrapher's equation which relates the distorted waveform to the dissipation-free waveform at the same point along the line. By this relationship, we obtained the distorted waveform from the dissipation-free square waveform by considering the effect of dissipation and dispersion on the Fourier components. On the other hand, by setting the distorted waveform in this relationship as the desired square waveform, we determined the dissipation-free waveform which was then used as the designing waveform to be sent.

Experiments to measure the waveform distortion and tests for square designing waveform based on the first method were carried out. Results showed that the waveform designing has improved the distorted waveform, namely the deviation of distorted waveform from its original waveform has been reduced. In addition, the observation of distorted waveform has shown fairly good agreements with the expected distorted waveform, in terms of the decreasing amplitude with distance travelled and the speed of propagation. Results showed that the method of designing was able to overcome the waveform distortion with an approximate capability of 2/3.