Data suggest that continuous time signals and systems (CTSS), and its underlying concepts, can be difficult for students to grasp. CTSS and Electromagnetics courses at certain universities experience drop/failure rates 2-3 times higher than other required courses. Likewise, the phenomenon of absorption and dispersion is only briefly discussed in most undergraduate Electromagnetic and CTSS textbooks. This paper proposes a new teaching technique of simulating and modeling the attenuation and dispersion in a communication cable using low pass filters on a signals processing board.
In our study, we used a RG-59 60 meters coaxial cable. With a function generator and an oscilloscope, we were able to observe dispersion and attenuation at high frequencies. We then used a gain-phase analyzer to measure the attenuation and phase shift produced by the cable as a function of frequency. Our results suggest the frequency response of the cable is very much like a low pass filter. The students can use the response to construct a set of filters on a signals processing board that will approximate the dispersion and attenuation observed in the cable, thus gain a better understanding of both concepts.
The attenuation and dispersion can also be modeled by students using Fourier Series. At the input, any periodic square pulse signal can be expressed as a weighted sum of infinite number of sine and cosine functions. At the output, the individual frequency components are modified with a new amplitude and phase term based on the measured frequency response of the cable, and combined to give a distorted signal.
One goal is to provide a hands on learning experience for students in order to reinforce their understanding of attenuation and dispersion. Another is to reinforce the concept of Fourier analysis in modeling the input and output signals, and gain an appreciation for how a linear system modifies the amplitude and phase of a signal to produce an output signal. In this case, the dispersion and attenuation are undesired effects of the coaxial cable which can distort the output signal at higher frequencies. Lastly, the construction of the filters allows students to see how two different systems with the same transfer function can produce a closely similar output signal from an input signal.
We would prefer a poster session presentation.
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