This is the Coaching materials in Transmission Lines and Antennas Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Transmission Lines and Antennas Coaching Materials Part 1
1. The minimum value that a characteristic impedance of an air dielectric parallel-wire could have is
83 ohms.*
2. Velocity factor of coaxial cables vary from
0.6 to 0.8*
3. Typical value of the velocity factor of an open-wire transmission is
0.9*
4. When the load absorbs all the power transmitted, it means that the load impedance is
equal to Zo of the line.*
5. When no power is applied to a transmission system, the VSWR is
equal to zero.*
6. The characteristic impedances commonly available are
75 ohms and 50 ohms.*
7. The 50-ohm RG-58 coaxial cable is used in
cheapernet or thin-wire Ethernet.*
8. The 50-ohm double-shielded RG-11 coaxial cable is used in
thicknet or thick-wire Ethernet.*
9. A flat conductor separated from a ground plane by an insulating dielectric material
Microstrip.
10. A flat conductor sandwich between two ground planes.
Stripline
11. What connecting link is used to transfer energy from a radio transmitter to its antenna located on the mast of a ship?
Transmission line.
12. What term is used for the end of a transmission line that is connected to a transmitter?
Input end, generator end, transmitter end, sending end and source.
13. What term is used for the end of a transmission line that is connected to an antenna?
Output end, receiving end, load end, and sink.
14. Name two of the three uses of a two-wire open line.
Power lines, rural telephone lines, and telegraph lines.
15. What are two primary disadvantages of a two-wire open line?
High radiation losses and noise pickup.
16. What type of transmission line is often used to connect a television set to its antenna?
Twin-lead.
17. What is the primary advantage of the shielded pair?
The conductors are balanced to ground.
18. What the two types of coaxial lines in use today?
Air coaxial (rigid) and solid coaxial (flexible).
19. What is the chief advantage of the air coaxial line?
The ability to minimize radiation losses.
20. List the two common type of waveguides in use today.
Cylindrical and rectangular.
21. What are the three types of line losses associated with transmission lines?
Copper, dielectric and radiation.
22. Losses caused by skin effect and I 2 R (power) loss are classified as what types of loss?
Copper loss.
23. What type of losses cause the dielectric material between the conductors to be heated?
Dielectric loss.
24. What is the range of characteristic impedance of lines used in actual practice?
Between 50 and 600 ohms.
25. Two types of waves are formed on a transmission line. What names are given to these waves?
Incident waves from generator to load. Reflected waves from load to generator.
26. On an open-ended transmission line, the voltage is always zero at what distance from each end of the line?
One-fourth the distance from each end of the line.
27. A non-resonant line is a line that has no standing waves of current and voltage on it and is considered to be flat. Why is this true?
The load impedance of such a line is equal to Zo.
28. At what point on an open-circuited rf line do voltage peaks occur?
At ½ wavelength from the end and at every ½ wavelength along the line.
29. What is the square of the voltage standing wave ratio called?
Power standing-wave ratio (pswr)
30. What does vswr measure?
The existence of voltage variations on a line.
31. Determine the characteristic impedance for an air dielectric two-wire parallel transmission line with a D/r ratio of 12.22?
300 ohms.
32. Determine the characteristic impedance for an RG-59A coaxial cable with the following specifications: d=0.025 inches, D=0.15 inches, and dielectric constant of 2.23
72 ohms
33. Determine the characteristic impedance for an RG-59A coaxial cable with the following specifications: L = 0.118 uH/ft and C = 21 pF/ft
75 ohms.
34. For a given length of RG 8A/U coaxial cable with a distributed capacitance of 96.6pF/m, a distributed inductance of 241.56 nH/m, and a relative dielectric constant of 2.3, determine the velocity of propagation and the velocity factor;
2.07x10^8m/s; 0.69
35. For a transmission line with an incident voltage of 5V and a reflected voltage of 3V, determine the reflection coefficient and the SWR.
r=0.6, SWR=4
36. A pulse is transmitted down a cable that has a velocity of propagation of 0.8c. The reflected signal is received 1us later. How far down the cable is the impairment?
120 m.
37. Using TDR, a transmission line impairment is located 3000m from the source. For velocity of propagation of 0.9c, determine the time elapsed from the beginning of the pulse to the reception of the echo.
22.22 us
38. Determine the impedance of λ/4 line to match 600ohm feed to 75 ohm antenna. 212 ohm
39. If a cable has a velocity factor of 0.8, what length of cable is required for a 90 degree phase shift at 100 meters?
0.6 meters
40. The scientist who profounded the theory of electromagnetic radiation James
Maxwell*
41. Antenna radiated power is ______ of the antenna current.
proportional to the square (I^2)
42. Antenna field strength is _____ to the antenna current.
directly proportional (I)
43. Antennas assuming having similar size, has largest gain.
Parabolic*
44. Antenna whose technical equivalent is λ/4 line is open circuited.
Dipole*
45. Marconi type of antenna is a grounded _____ vertical antenna.
λ/4*
46. Antenna used in mobile communications, mounted on vehicles.
Marconi*
47. Antenna used for radiating AM broadcast band.
λ/2 vertical antenna.*
48. Electrical length of a Marconi antenna needed for AM broadcasting can be increased by
using series loading of capacitor.*
49. The SI unit of magnetic field intensity.
Ampere/meter*
50. The radio wavelength known as ______ falls within the medium frequency range
hectrometric waves*
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