MULTIPLE CHOICES QUESTIONS IN Communications Engineering By: S. S. Cuervo & K. L. N. Suello 400 Solved Problems TRANSMISSION LINES 1. A parallel wire line spaced at 1.27 cm has a diameter of 0.21 cm. what is the characteristic impedance? a. 300 ohms b. 400 ohms c. 500 ohms d. 600 ohms 2. In a coaxial line if the inner diameter is 0.51 Encoded by: cm and the center conductor has a diameter Pante, Riel Djoshua P. of 0.22 cm. what is the characteristic impedance? a. 50.1 ohms b. 50.2 ohms c. 50.3 ohms d. 50.4 ohms 3. A strip line is formed using a multilayer Table of Contents board (dielectric constant = 2). The center track is 0.15 inch wide and 0.005 inch thick Transmission Lines 65 problems and the PC board first layer thickness is 0.05 solved inch thick, with an overall board thickness Radio Wave Propagation 39 problems of twice the single layer. What is the solved characteristic impedance? Antenna 68 problems solved a. 14.7 ohms Noise 71 problems b. 14.8 ohms solved c. 14.9 ohms Amplitude Modulation 101 problems d. 15.0 ohms solved 4. In an improperly loaded transmission line, Frequency Modulation 56 problems determine the power reflected from the load solved if the incident power at the load is 500 W and the reflection coefficient is 0.71. ________________ a. 252.04 W Total = 400 problems b. 252.05 W solved c. 252.06 W d. 252.07 W 5. In wire communications system, calculate the return loss in dB, if the load impedance is 600 ohms and the characteristic impedance of the line is 300 ohms. a. 9.52 dB b. 9.53 dB c. 9.54 dB d. 9.55 dB a. 2.13 b. 2.14 6. The VSWR on a loss free line of 50 ohm c. 2.15 characteristic impedance is 4.2. Determine d. 2.16 the value of the purely resistive load 12. What is the characteristic impedance of a impedance which is known to be larger than coaxial cable using a solid polyethylene 50 ohms. dielectric having a relative permeability of 2.3, an inner conductor of 1 mm diameter a. 210 ohms and an outer conductor of diameter 5mm? b. 211 ohms c. 212 ohms a. 63.4 ohms d. 213 ohms b. 63.5 ohms 7. A micro strip line is formed using a 0.095 c. 63.6 ohms inch thick PC board, with a bottom ground d. 63.7 ohms plane and a single 0.15 inch wide, 0.008 13. Calculate the velocity factor of a coaxial inch thick track on the top. What is its cable used as a transmission line, with the characteristic impedance? characteristic impedance of 50 ohms; capacitance is 40 pF/m, and inductance a. 72.1 ohms equal to 50microH/m. b. 72.2 ohms c. 72.3 ohms a. 0.0745 ft d. 72.4 ohms b. 0.0746 ft 8. Determine the impedance of a balanced 2 c. 0.0747 ft wire with unequal diameters d1 = 12 mm d. 0.0748 ft and d2 = 10 mm. the spacing between wires 14. What is the actual length in feet of a one is 30mm. quarter wavelength of a coaxial cable with a velocity of 0.69 at 40 MHz? a. 35.35 M ohms b. 35.36 M ohms a. 4.23 ft c. 35.37 M ohms b. 4.24 ft d. 35.38 M ohms c. 4.25 ft 9. For a parallel wire line, determine the d. 4.26 ft conductance if the conductivity is 200 x 10-6 15. What is the actual length in feet of one half S/m and the conductor diameter spacing is wavelengths of a coax with velocity factor 10mm. of 0.63 at 28 MHz? a. 1.23mS/m a. 11.07 ft b. 1.24mS/m b. 11.08 ft c. 1.25mS/m c. 11.09 ft d. 1.26mS/m d. 11.10 ft 10. What is the characteristic impedance of an 16. What is the actual length in feet of one open line with conductors 4 mm in diameter quarter wavelength of a coax with a velocity separated by 15 mm? factor of 0.68 at 39 MHz? a. 241.52 ohms a. 5.577 ft b. 241.53 ohms b. 5.576 ft c. 241.54 ohms c. 5.575 ft d. 241.55 ohms d. 5.574 ft 11. The forward power in a transmission line is 17. What is the actual length in feet of a one half 150 W and the reverse power is 20 W. wavelength of a coax with a velocity factor Calculate the SWR on the line. of 0.61 at 27 MHz? constant of 2.56 a. 11.10 ft b. 11.11 ft a. 98 ohms c. 11.12 ft b. 99 ohms d. 11.13 ft c. 100 ohms 18. What is the actual length in feet of a one half d. 101 ohms wavelength of a coax with a velocity factor 24. What is the characteristic impedance of a of 0.59 at 26 MHz? single wire with diameter d = 0.25 mm placed at the center between grounded a. 11.16 ft parallel planes separated by 1 mm apart? b. 11.17 ft The wire is held by a material with a c. 11.18 ft velocity factor of 0.75. d. 11.19 ft 19. What is the actual length in feet of a one a. 71 ohms quarter wavelength of a coax with a velocity b. 72 ohms factor of 0.695 at 42 MHz? c. 73 ohms d. 75 ohms a. 4.05 ft 25. What is the phase coefficient of a b. 4.06 ft transmission line at the frequency of 10 c. 4.07 ft MHz if the velocity of propagation is 2.5 x d. 4.08 ft 108m/s? 20. An amplifier with a 20 dB gain is connected to another with 10 dB gains by means of a a. 0.25rad/m transmission line with a loss of 4 dB; if a b. 0.26rad/m signal with a power level of 14 dBm were c. 0.27rad/m applied to the system, calculate the power d. 0.28rad/m output. 26. Determine the conductance of a two wire open line with the following parameters; D a. 11dBm = 4 in; d = 0.1 in. and p = 2.6 x108 ohms-m. b. 12dBm c. 13dBm a. 2.75 x 10-9 S/m d. 14dBm b. 2.76 x 10-9 S/m 21. An attenuator has a loss of 26 dB. If a power c. 2.77 x 10-9 S/m of 3 W is applied to the attenuator, find the d. 2.78 x 10-9 S/m output power. 27. What is the input impedance of a transmission line if its characteristic a. 7.54mW impedance is 300 ohms and the load is 600 b. 7.55mW ohms? Assume a quarter wavelength c. 7.56mW sections only. d. 7.57mW 22. What would be the approximate series a. 149 ohms impedance of a quarter wave matching line b. 150 ohms used to match a 600 ohms feed to 70 ohms c. 151 ohms antenna? d. 152 ohms 28. Determine the standing wave ratio of a 300 a. 204. 94 ohms ohms line whose load is 400 + j150 ohms. b. 204.95 ohms c. 204.96 ohms a. 1.67 d. 204.97 ohms b. 1.68 23. What is the impedance of a balance 4 wire c. 1.69 with a diameter of 0.25 cm and spaced 2.5 d. 1.70 cm apart using an insulator with a dielectric 29. What proportion of the incident power is reflected back for the load for a 75 ohms line terminated with ZL = 50 – j25 ohms. a. 7.6 cm b. 7.7 cm a. 7.82% c. 7.8 cm b. 7.83% d. 7.9 cm c. 7.84% 36. Calculate the SWR of the line if the d. 7.85% characteristic impedance of the line is 75 30. What is the attenuation of a 50 ohms coaxial ohms and is terminated by 50 ohms. cable if it has a resistance of 0.121 ohms/m? a. 1.4 a. 1.21 x10-3Np/m b. 1.5 b. 1.22 x10-3Np/m c. 1.6 c. 1.23 x10-3Np/m d. 1.7 d. 1.24 x10-3Np/m 37. A transmitter sends a 5 W of power to a 75 31. Find the inductance of a 5 meter length ohms line. Suppose the transmitter and the transmission line if its characteristic line is matched but the load is not. impedance is 52 ohms and the capacitance is Determine the power absorbed by the 75pF/m. reflection is 0.75. a. 1.013uH a. 2.1821 W b. 1.014uH b. 2.1822 W c. 1.015uH c. 2.1823 W d. 1.016uH d. 2.1825 W 32. An open wire transmission line with a 2 mm 38. A generator sends a 250 W of power down a diameter each separated by 12 mm. calculate line. If the SWR of the line is 2.5, determine the characteristic impedance. the power absorbed by the load. a. 297 ohms a. 204.0 W b. 298 ohms b. 204.1 W c.