Communications Engineering Mastery Test 8: ECE Pre-Board

This is 100 items set of Practice Examination 8 in Communications Engineering (Electronics Systems and Technology) composed of previous Board Exams Questions. Read each questions and choices carefully! Choose the best answer. In the actual board, you have to answer 100 items in Communications Engineering within 5 hours. You have to get at least 70% to pass the subject. Communications Engineering is 30% of the total 100% Board Rating along with Mathematics (20%), General Engineering and Applied Sciences (20%) and Electronics Engineering (30%). Familiarize each and every questions to increase the chance of passing the ECE Board Examination.

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1. What is the refractive index of an ionospheric layer with 100 x 10⁵ free electrons per m³?

Assume frequency to be at 20 MHz.

• A. 0.99
• B. 0.15
• C. 0.78
• D. 0.85

2. “Each point on a spherical wavefront may be considered a source of secondary spherical wavefronts”. This is known as the

• A. Snell’s law
• B. D’Alembert’s principle
• C. Appleton’s theory
• D. Huygen’s principle

3. What is meant by the term deviation ratio?

• A. The ratio of the audio modulating frequency to the center carrier frequency.
• B. The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.
• C. The ratio of the carrier center frequency to the audio modulating frequency.
• D. The ratio of the highest audio modulating frequency to the average audio modulating frequency.

4. What is the major cause of selective fading?

• A. Small changes in the beam heading at the receiving station.
• B. Large changes in the height of the ionosphere, as experience at the receiving station.
• C. Time differences between the receiving and transmitting stations.
• D. Phase differences between radio wave components of the same transmission, as experienced at the receiving station.

5. What phenomenon causes the radio-path horizon distance to exceed the geometric horizon?

• A. E-layer skip.
• B. D-layer skip.
• C. Auroral skip.
• D. Radio waves may be bent.

6. What propagation condition is usually indicated when a VHF signal is received from a station over 500 miles away?

• A. D-layer absorption
• B. Faraday rotation
• C. Tropospheric ducting
• D. Moonbounce

7. What is meant by the term modulation index?

• A. The processor index.
• B. The ratio between the deviation of a frequency modulated signal and the modulating frequency.
• C. The FM signal-to-noise ratio.
• D. The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.

8. The bending of radio waves passing over the top of a mountain range that disperses a weak portion of the signal behind the mountain is

• A. eddy-current phase effect
• B. knife-edge diffraction
• C. shadowing
• D. mirror refraction effect

9. What is the wavelength of a signal at 500 MHz?

• A. 0.062 cm
• B. 6 meters
• C. 60 cm
• D. 60 meters

10. What is included in the total resistance of an antenna system?

• A. Radiation resistance plus space impedance
• B. Radiation resistance plus transmission resistance
• C. Transmission line resistance plus radiation resistance
• D. Radiation resistance plus ohmic resistance

11. What are electromagnetic waves?

• A. Alternating currents in the core of an electromagnet
• B. A wave consisting of two electric fields at right angles to each other
• C. A wave consisting of an electric field and a magnetic field at right angles to each other
• D. A wave consisting of two magnetic fields at right angles to each other

12. The band of frequencies least susceptible to atmospheric noise and interference is:

• A. 30 – 300 kHz
• B. 300 – 3000 kHz
• C. 3 – 30 MHz
• D. 300 – 3000 MHz

13. What is the relationship in degrees of the electrostatic and electromagnetic fields of an antenna?

• A. 0 degree
• B. 45 degrees
• C. 90 degrees
• D. 180 degrees

14. For a space wave transmission, the radio horizon distance of a transmitting antenna with a height of 100 meters is approximately:

• A. 10 km
• B. 40 km
• C. 100 km
• D. 400 km

15. What is meant by referring to electromagnetic waves as horizontally polarized?

• A. The electric field is parallel to the earth.
• B. The magnetic field is parallel to the earth.
• C. Both the electric and magnetic fields are horizontal
• D. Both the electric and magnetic fields are vertical

16. What is meant by referring to electromagnetic waves as having circular polarization?

• A. The electric field is bent into a circular shape.
• B. The electric field rotates
• C. The electromagnetic wave continues to circle the earth
• D. The electromagnetic wave has been generated by a quad antenna

17. If a transmitting antenna is 100 meters high and a separate receiving antenna is 64 meters high, what is the maximum space wave communication distance possible between them?

• A. 18 km
• B. 72 km
• C. 164 km
• D. 656 km

18. A receiver is located 64 km from a space wave transmitting antenna that is 100 meters high. Find the required height of the receiving antenna.

• A. 36 meters high
• B. 64 meters high
• C. 100 meters high
• D. 182.25 meters high

19. Which of the following is not one of the natural ways a radio wave may travel from transmitter to receiver?

• A. Ground wave
• B. Microwave
• C. Sky wave
• D. Space wave

20. Which of the following terrain types permits a ground wave to travel the farthest?

• A. Salt water
• B. Fresh water
• C. Sandy
• D. Rocky

21. What is the input terminal impedance at the center if a folded dipole antenna?

• A. 300 ohms
• B. 72 ohms
• C. 50 ohms
• D. 450 ohms

22. What is the term used to describe a spread spectrum communications system where the center frequency if a conventional carrier is altered many time per second in accordance with a pseudo-random list of channels?

• A. Frequency hopping
• B. Direct sequence
• C. Time-domain frequency modulation
• D. Frequency compandored spread spectrum

23. What is the velocity factor for non-foam dielectric 50 or 75 ohm flexible coaxial cable such as RG 8, 11, 58 and 59?

• A. 2.70
• B. 0.66
• C. 0.30
• D. 0.10

24. If a transmission line has a power loss of 6 dB per 100 feet, what is the power at the feed point to the antenna at the end of a 200 foot transmission line fed by a 100 watt transmitter?

• A. 70 watts
• B. 50 watts
• C. 25 watts
• D. 6 watts

25. What determines the velocity factor in a transmission line?

• A. The termination impedance
• B. The line length
• C. Dielectrics in the line
• D. The center conductor resistivity

26. What term is used to describe a spread spectrum communications system in which a very fast binary bit stream is used to shift the phase of an RF carrier?

• A. Frequency hopping
• B. Direct sequence
• C. Binary phase-shift keying
• D. Phase compandored spread spectrum

27. Which of the following frequency bands is best suited for ground wave propagation?

• A. 30 to 300 kHz
• B. 300 kHz to 3 MHz
• C. 3 MHz to 30 MHz
• D. 30 MHz to 300 MHz

28. Which of the following frequency bands is best suited for sky wave propagation?

• A. 30 to 300 kHz
• B. 3 MHz to 30 MHz
• C. 30 MHz to 300 MHz
• D. 3 GHz to 30 GHz

29. What is the seventh harmonic of a 100 MHz quarter wavelength antenna?

• A. 14.28 MHz
• B. 107 MHz
• C. 149 MHz
• D. 700 MHz

30. Which if the following layers of the ionosphere has no effect on sky wave propagation during the hours of darkness?

• A. D
• B. E
• C. F₁
• D. F₂

31. Skip distance can be maximized by using the ____ radiation angle possible and the ____ frequency that will be refracted at that angle.

• A. lowest, lowest
• B. lowest, highest
• C. highest, lowest
• D. highest, highest

32. What is the meaning of the term “velocity factor” of a transmission line?

• A. The ratio of the characteristic impedance of the line to the terminating impedance
• B. The index of shielding for coaxial cable.
• C. The velocity of the wave on the transmission line multiplied by the velocity of light in a vacuum.
• D. The velocity of the wave on the transmission line divided by the velocity of light in a vacuum.

33. What is the term for the ratio of actual velocity at which a signal travels through a line to the speed of light in a vacuum?

• A. Velocity factor
• B. Characteristic impedance
• C. Surge impedance
• D. Standing wave ratio

34. Why is the physical length of a coaxial cable transmission line shorter than its electrical length?

• A. Skin effect is less pronounced in the coaxial cable
• B. RF energy moves slower along the coaxial cable
• C. The surge impedance is higher in the parallel feed line
• D. The characteristic impedance is higher in the parallel feed line

35. What would be the physical length of a typical coaxial transmission line that is electrically one-quarter wavelength long at 14.1 MHz?

• A. 20 meters
• B. 3.51 meters
• C. 2.33 meters
• D. 0.25 meter

36. To obtain the most reliable sky wave propagation the ____ should be used.

• A. Lowest useable frequency (LUF).
• B. Maximum useable frequency (MUF).
• C. Optimum useable frequency (OUF).
• D. Critical frequency

37. What is the deviation ratio for an FM-phone signal having a maximum frequency swing of plus or minus 5 kHz and accepting a maximum modulation rate of 3kHz?

• A. 60
• B. 0.16
• C. 0.6
• D. 1.66

38. Tropospheric scatter is a method of sky wave propagation for which of the following frequency bands?

• A. 300 kHz to 3 MHz
• B. 3 MHz to 30 MHz
• C. 30 MHz to 300 MHz
• D. 300 MHz to 3 GHz

39. What is the frequency range of an aircraft’s radio altimeter?

• A. 962 MHz to 1213 MHz
• B. 329.15 MHz to 335.00 MHz
• C. 4250 MHz to 4350 MHz
• D. 108.00 MHz to 117.95 MHz

40. What type of transmission is radiated from an aircraft’s radio altimeter antenna?

• A. An amplitude modulated continuous wave
• B. A pulse position modulated UHF signal
• C. A differential phase shift keyed UHF signal
• D. A frequency modulated continuous wave

41. The polarization of a radio wave:

• A. Is perpendicular to the electrostatic field of the antenna
• B. Is the same direction as the electrostatic field of the antenna.
• C. Is the same direction as the magnetic field of the antenna.
• D. Is perpendicular to both the electrostatic and magnetic fields of the antenna.

42. A coaxial cable has 7dB of reflected power when the input is 5 watts. What is the output of the transmission line?

• A. 5 watts
• B. 2.5 watts
• C. 1.25 watts
• D. 1 watt

43. When is it useful to refer to an isotropic radiator?

• A. When comparing the gains of directional antennas
• B. When testing a transmission line for standing wave ratio
• C. When (in the northern hemisphere) directing the transmission in a southerly direction
• D. When using a dummy load to tune a transmitter

44. Most AM broadcasts employ ___ polarization while most FM broadcasts employ ___ polarization of the radio wave.

• A. vertical, vertical
• B. vertical, horizontal
• C. horizontal, vertical
• D. horizontal, horizontal

45. How does the gain of a parabolic dish type antenna change when the operating frequency is doubled?

• A. Gain does not change
• B. Gain is multiplied by 0.707
• C. Gain increases 6 dB
• D. Gain increases 3 dB

46. What is the frequency range of an aircraft’s Very High Frequency (VHF) communications?

• A. 118.000 MHz to 136.975 MHz (worldwide up to 151.975 MHz)
• B. 108.000 MHz to 117.95 MHz
• C. 329.15 MHz to 335.00 MHz
• D. 2.0000 MHz to 29.999 MHz

47. What is a selective fading effect?

• A. A fading effect caused by small changes in beam heading at the receiving station.
• B. A fading effect caused by phase differences between radio wave components of the same transmission, as experienced at the receiving station.
• C. A fading effect caused by large changes in the height of the ionosphere, as experienced at the receiving station
• D. A fading effect caused by time differences between the receiving and transmitting stations.

48. If the velocity of propagation in a certain medium is 200x10⁶ m/s, what is its refractive index?

• A. 1.3
• B. 1.5
• C. 1.27
• D. 0.67

49. What is the resultant field strength at the receiving antenna in space wave propagation under case 2?

• A. 0
• B. ξ_d
• C. 2ξ_d
• D. 3ξ_d

50. The decimetric wave is using what method of propagation?

• A. Ground wave
• B. Space wave
• C. Sky wave
• D. Tropospheric wave

51. What is the typical frequency used for communicating to submerged submarines?

• A. 100 Hz
• B. 500 Hz
• C. 4 kHz
• D. 200 Hz

52. Which frequency bands can be refracted during the day by the D layer?

• A. VLF
• B. MF
• C. LF
• D. Both VLF and LF

53. What height of an ionized layer is determined from the time interval between the transmitted signal and the ionospheric echo at vertical incidence?

• A. Virtual height
• B. Apparent height
• C. Actual height
• D. Effective height

54. During the night when the F₂ layer combines with F₁ layer it falls to what approximate height?

• A. 250 km
• B. 350 km
• C. 300 km
• D. 400 km

55. Which of the following is considered the most frequently used transmission line?

• A. Two-wire open line
• B. Twin lead
• C. Rigid coaxial line
• D. Flexible coaxial line

56. The antenna effective height is ____ to ____ of the actual height.

• A. ½ to 2/3
• B. ½ to ¾
• C. ¼ to 2/3
• D. ¼ to ¾

57. What is the propagation velocity of a signal in a transmission line whose inductance and capacitance are 5μH/m and 20μF/m respectively?

• A. 100 x 10³ m/s
• B. 100 m/s
• C. 10 x 10³ m/s
• D. 100 x 10⁶ m/s

58. What is the phase coefficient in radians per unit length of a transmission line at the frequency of 10 MHz if the velocity of propagation is 2.5 x 10⁸ m/s?

• A. 0.25
• B. 2.5
• C. 0.35
• D. 3.5

59. Determine the conductance of a two-wire open line with the following parameters: D = 4 in., d = 0.1 in. and ρ = 2.6x10⁸ Ω-m.

• A. 2.76 x 10^-9 S/m
• B. 2.76 x 10^-6 S/m
• C. 2.76 x 10^-12 S/m
• D. 2.76 x 10^-3 S/m

60. What is the input impedance of a transmission line if its characteristic impedance is 300 Ω and the load is 600 Ω? Assume a quarter wavelength section only.

• A. 150 kΩ
• B. 150 mΩ
• C. 150 Ω
• D. 2 Ω

61. Determine the standing wave ratio of a 300-Ω line whose load is 400+j150 Ω.

• A. 3.55
• B. 1.67
• C. 5.53
• D. 3.35

62. What is the optimum volume per person of rooms for speech?

• A. 2.8
• B. 3.1
• C. 4.2
• D. 5.1

63. What happens to the beamwidth of an antenna as the gain is increased?

• A. The beamwidth increases geometrically as the gain is increased.
• B. The beamwidth increases arithmetically as the gain is increased.
• C. The beamwidth is essentially unaffected by the gain of the antenna.
• D. The beamwidth decreases as the gain is increased.

64. A superhet receiver has an IF of 455 kHz and is experiencing image-channel interference on a frequency of 1570 kHz. The receiver is tuned to

• A. 1115 kHz
• B. 660 kHz
• C. 2025 kHz
• D. 910 kHz

65. What is the end impedance of a half-wave dipole?

• A. 73 Ω
• B. 72 Ω
• C. 250 Ω
• D. 2500 Ω

66. What volume of the chamber is required to measure absorption coefficient at 100 Hz?

• A. 125 m³
• B. 50 m³
• C. 150 m³
• D. 352 m³

67. What is the optimum reverberation time at 500 Hz for a cinema?

• A. 0.8 – 1.2 sec.
• B. 0.9 – 1.3 sec.
• C. 0.6 – 0.8 sec.
• D. 0.45 – 0.55 sec.

68. An FM receiver whose intermediate frequency is 10.7 MHz, is experiencing image channel interference from a station transmitting on 121.1 MHz. If the local oscillator is tracking above, the receiver is tuned to

• A. 131.8 MHz
• B. 110.4 MHz
• C. 142.5 MHz
• D. 99.7 MHz

69. A 1 Mhz carrier is amplitude modulated by a pure 200-Hz audio test tone. Which of the following combinations of frequencies represent the total content of the AM signal?

• A. 1 MHz and 200 Hz
• B. 1 MHz and 1000.2 kHz
• C. 999.8 kHz, 1000 kHz, and 1000.2 kHz
• D. 999.8 kHz and 1000.2 kHz

70. What establishes the receiver bandwidth?

• A. RF amplifier
• B. Mixer
• C. Local oscillator
• D. IF amplifier

71. What noise type is observable between 8 MHz to somewhat above 1.43 GHz or up to 1.5 GHz?

• A. Solar noise
• B. Space noise
• C. Galactic noise
• D. Cosmic noise

72. Flicker noise is a poorly understood form of noise which may be completely ignored about above ____.

• A.100 Hz
• B. 200 Hz
• C. 400 Hz
• D. 500 Hz

73. What is the typical gain of a rhombic antenna?

• A. Between 15 to 60
• B. Between 20 to 90
• C. Between 50 to 75
• D. Between 10 to 25

74. What illumination factor is normally considered in computing parabolic antenna gain in microwave communications?

• A. 0.54
• B. 0.65
• C. 0.75
• D. 0.85

75. How many voice band channels are there in a superjumbo group?

• A. 600
• B. 900
• C. 10,800
• D. 3,600

76. In acoustics, what is the reference pressure in lb/ft² unit?

• A. 2x10^-5
• B. 0.0002
• C. 2.089
• D. 2.980

77. Which of the following characterizes a properly terminated transmission line?

• A. The line loss is minimum.
• B. The standing wave ratio is minimum.
• C. The input impedance is twice the load impedance.
• D. The standing wave ratio is one.

78. What is the meaning of forward power?

• A. The power traveling from the transmitter to the antenna.
• B. The power radiated from the top of an antenna system.
• C. The power produced during the positive half of an RF cycle.
• D. The power used to drive a linear amplifier.

79. What organization has published safety guidelines for the maximum limits of RF energy near the human body?

• A. The American National Standards Institute (ANSI).
• B. The Environmental Protection Agency (EPA).
• C. The Federal Communications Commission (FCC).
• D. The Institute Of Electrical and Electronics Engineers (IEEE).

80. When no signal is being received, the loudspeaker is not entirely silent as a result of the presence of

• A. parasitic oscillations in some of the receiver stages.
• B. negative feedback in each stage.
• C. spurious frequencies as a result of improper neutralization.
• D. internal receiver noise.

81. When measuring a transmitter’s frequency against a suitable standard, the frequency to be measured is taken from the

• A. oscillator stage
• B. intermediate amplifier
• C. buffer stage
• D. final RF stage

82. When the is the ionosphere most ionized?

• A. Dusk
• B. Midnight
• C. Dawn
• D. Midday

83. Cellular radios use FM with a maximum deviation of

• A. ± 30 KHz
• B. ± 75 KHz
• C. ± 25 KHz
• D. ± 12 KHz

84. What device measures the angle between two radio frequencies and also the direction of propagation of a wave?

• A. Densimeter
• B. Absorption wavemeter
• C. Goniometer
• D. Ergometer

85. An automated ship-to-shore distress alerting system using satellites and advanced terrestrial communications systems.

• A. GPS
• B. Iridium system
• C. INMARSAT
• D. GMDSS

86. What antenna can be used to minimize the effect of Faraday rotation of polarization?

• A. Dipole
• B. Parabolic
• C. Helical
• D. Rhombic

87. The presence of standing waves on a transmission line is the result of

• A. a high level of attenuation on the line.
• B. terminating the line by a resistive load equal in value to the surge impedance
• C. reducing the input power to below its critical level.
• D. an impedance mismatch between the load and the line.

88. What device measures rf power by measuring the heat the rf power generates?

• A. Calorimeter
• B. Goniometer
• C. Spectrum meter
• D. Oscilloscope

89. What is considered the most efficient mode in terms of energy transfer in waveguides?

• A. Dominant mode
• B. Normal mode
• C. Conventional mode
• D. Vertical mode

90. In acoustics, _____ is the apparent change in frequency or pitch when a sound source moves either toward or away from a listener.

• A. flanking
• B. reverberation
• C. Doppler effect
• D. echo

91. Which of the following wavelengths where absorption of electromagnetic waves becomes peak due to vibrational resonances in the water vapor molecule?

• A. 1.35 cm and 1.7 mm
• B. 1.5 mm and 5mm
• C. 1.35 dm and 1.7cm
• D. 1.5 cm and 5 mm

92. Oxygen molecule absorption peaks to electromagnetic wave are at what wavelengths?

• A. 1.35 mm and 1.7 μm
• B. 1.35 cm and 1.7 mm
• C. 5 cm and 2.5 cm
• D. 5 mm and 2.5 mm

93. The approximate single-hop nighttime range of F₂ layer is ____.

• A. 3000 km
• B. 3840 km
• C. 4130 km
• D. 2350 km

94. What ionospheric layer has a daytime approximate critical frequency of 8 MHz?

• A. F₂ layer
• B. F₁ layer
• C. E layer
• D. D layer

95. In cellular system, _____ defines the geographic distance that is required between cells using identical frequencies in order to avoid interference between the radio transmissions at these cells.

• A. frequency-reuse ratio
• B. distance-to-reuse ratio (D/R)
• C. reuse format plan ratio
• D. reuse factor

96. What do you call the ability of a mobile phone to change from one channel (frequency) to another?

• A. Frequency agility
• B. Frequency handoff
• C. Frequency handover
• D. Frequency switch

97. What mathematical plane figure is ideal in cellular system design and engineering it graphically and functionally depicts overlapping radio coverage between and among adjacent cell base stations?

• A. Hexagon
• B. Octagon
• C. Pentagon
• D. Nonagon

98. In cellular system, the average lead time to install a new base station is approximately ____ months to a year.

• A. 4
• B. 5
• C. 6
• D. 10

99. What is considered the threshold of audibility at 3000 Hz?

• A. 10^-12 W/m²
• B. 10^-16 W/m²
• C. 10^-12 W/cm²
• D. 10^-15 W/cm²

100. At one atmospheric pressure, what is the approximate speed of sound in steel?

• A. 5150 m/s
• B. 5150 ft/s
• C. 4990 m/s
• D. 4990 ft/s

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