# ECE 391: Transmission Lines Winter Term 2019

2. (a) The voltage amplitude of a sinusoidal wave at the input of a 200m long transmission line is Vin = 5V. The far end of the line is matched (no reflected waves are excited) and the voltage is measured as Vout = 3V. What is the attenuation in (i) dB/m, (ii) Np/m? (b) A coaxial cable has a specified attenuation constant of ↵ = 0.05dB/m. Specify the attenuation constant in (i) dB/cm, (ii) Np/m, (iii) dB/100ft. How much is the voltage amplitude of a single traveling sinusoidal wave attenuated after 100 meters? Give your answer in %, dB, and nepers.

3. A lossless 50⌦ transmission line of length zr = 50m (vp = 30cm/ns) is terminated in (a) ZT = Z0/4, (b) ZT = 4Z0, (c) L = 398nH, (d) C = 79.6pF. Using Matlab, plot the voltage and current standing-wave patterns on the line for f = 7.5MHz and specify the voltage standing-wave ratio for each of the cases (a)-(d). The amplitude of the incident wave is 10V. Use one graph for all voltage plots and one for current plots.

4. A lossless 50⌦ coax of length zr = 5m (r = 2.25) is terminated in an impedance ZT = (70j30)⌦. (a) What is the standing-wave ratio on the line? (b) Using Matlab, plot the voltage and current standing-wave patterns on the line for f0 = 10 MHz. (c) Determine the input impedance of the line if the operating frequency is (i) f0 = 10 MHz, (ii) f0 = 20 MHz, (iii) f0 = 30 MHz.

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