# Communications Engineering Mastery Test 18: ECE Pre-Board

(Last Updated On: April 2, 2021) This is 100 items Practice Examinations set 18 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.

#### Start the Test Yourself Exam 18

Choose the letter of the best answer in each questions.

1. What determines the bandwidth of a transmitted AM signal?

a. the maximum modulation amplitude

b. the lowest frequency component of the intelligence

c. the lowest modulation amplitude

d. the highest frequency of the modulating signal

Solution:

2. A receiver has two uncoupled tuned circuits before the mixer, each with a Q of 75. The signal frequency is 100.1 MHz, and the IF is 10.7MHz. The local oscillator uses low side injection. Calculate the image rejection ratio in dB.

a. 58.60 dB

b. 29.30 dB

c. 62.48 dB

d. 31.24 dB

Solution:

3. If the SWR is equal to one, what type of load transmission line has?

a. purely reactive

b. purely resistive

c. purely capacitive

d. purely inductive

Solution:

4. Waveguides are generally used above ______.

a. 20 MHz

b. 100 MHz

c. 200 MHz

d. 1000 MHz

Solution:

5. Which of the following is most often transmitted in a binary (two-level) digital mode?

a. USB emission

b. ISB emission

c. FSTV emission

d. CW emission

Solution:

6. An important operational point in the SPADE system is that the carriers are _____.

a. voice operated

b. suppressed

c. filtered

d. always present

Solution:

7. Which of the following is not necessarily an advantage of FM over AM?

a. less modulation power is required

b. lower bandwidth is required

c. better noise immunity

d. the transmitted power is more useful

Solution:

8.  The process of ____ is used to overcome the degradation of the S/N ratio.

a. suppression

b. companding

c. regeneration

d. equalization

Solution:

9. Group 3 fax uses what type of modulation?

a. QAM

b. PSK

c. Vestigial sideband

d. FM

Solution:

10. What portion of the TV signal is used to synchronize the video information on the recording tape?

a. the vertical sync

b. the horizontal sync

c. the vertical deflection coil

d. the raster line

Solution:

11. The most common unit of noise measurement in white noise voltage testing.

a. NPR

b. dBW

c. dBrn

d. dBm

Solution:

12. The first Philippine Agila I will have how many transponders?

a. 36

b. 48

c. 24

d. 14

Solution:

13. Echo suppressors are used on all communication system when the round-trip propagation exceeds

a. 50 ms

b. 30 ms

c. 100 ms

d. 1 ms

Solution:

14. The GSM cellular radio system uses GMSK in a 200-kHz channel, with a channel data rate of 270.833 kb/s. Calculate the minimum transmitted frequency if the carrier (center) frequency is exactly 880 MHz.

a.  880.0677 MHz

b. 879.93229 MHz

c. 879.86458 MHz

d. 880.1354 MHz

Solution:

15. 20 Angstroms is equivalent to how many microns?

a. 2000

b. 0.002

c. 0.02

d. 200

Solution:

16. Second level of SONET multiplexing system with a total capacity of 32,256 channels.

a. OC-1

b. OC-48

c. OC-2

d. OC-49

Solution:

17. If the incident voltage wave to an open-ended transmission line is 40 V and the reflected voltage wave is 25 V, what is the percentage of power reflected?

a.  46.3%

b. 62.5%

c. 28.4%

d. 39.1%

Solution:

18. Two resistors rated 5 ohms and 10 ohms are connected in series and are connected in series and are at 27 degrees Celsius. Calculate their combined thermal noise voltage for a 10 kHz bandwidth.

a. 0.05 microvolts

b. 0.005 microvolts

c. 0.05 millivolts

d. 0.5 millivolts

Solution:

19. The localizer transmitter operates in the frequency range of _____.

a. 328-336 MHz

b. 108-112 MHz

c. 30-300 MHz

d. 70-120 MHz

Solution:

20. How can unwanted ringing and audio instability be prevented in a multi-section op-amp RC audio filter circuit?

a. restrict both gain and Q

b. restrict gain, but increase Q

c. restrict Q but increase gain

d. increase both gain and Q

Solution:

21. What is the power output of Personal Communications System..

a. 10 mW

b. 75 mW

c. 150 mW

d. 10 W

Solution:

22. At what position on the color triangle will saturated yellow will be found?

a. between red and blue

b. between blue and green

c. between green and red

d. near the center

Solution:

23. A transmitter operates from a 12 V supply, with a collector current of 2 A. The modulation transformer has a turns ratio of 4:1. What is the load impedance seen by the audio amplifier?

a. 6

b. 37

c. 54

d. 96

Solution:

24. Which of the following is most affected by noise?

a. PSK

c. FSK

d. QAM

Solution:

25. Two or more receivers are used on a single antenna.

a. space diversity

b. frequency diversity

c. hybrid diversity

d. polarization diversity

Solution:

26. Frequency range for high frequencies (HF).

a. 300 kHz –  3 MHz

b. 3 MHz – 30 MHz

c. 300 MHz – 3 GHz

d. 3 GHz – 30 GHz

Solution:

27. Hartley’s law states that

a. the maximum rate of information transmission depends on the channel bandwidth.

b. redundancy is essential

c. the maximum rate of information depends on the depth of modulation.

d. only binary code may be used

Solution:

28. Doubling the power means

a. 6-dB gain

b. 3-dB loss

c. 3-dB gain

d. 6-dB loss

Solution:

29. The receiver equalizer in a synchronous modem is called

a. a compromise equalizer

b. a statistical equalizer

d. an impairment equalizer

Solution:

30. Small rooms can resonate at certain audible frequencies, this condition is called

a. Bathroom Tenor Effect

b. Doppler Effect

c. Resonance Effect

d. Dumpling Effect

Solution:

31. The most common CRT readout where the radar is at the center and a radius rotates to reveal reflected targets as blips.

a. B Scan

b. PPI

c. Circular polarized array

d. Phased Array

Solution:

32. Phase jitter is a form of incidental phase modulation which occurs at a ___ rate or lower, commonly found in power supplies.

a. 650 Hz

b. 100 Hz

c. 500 Hz

d. 300 Hz

Solution:

33. For airplane and navigation, the preferred frequency band is ____.

a. VLF

b. UHF

c. SHF

d. EHF

Solution:

34. A system to allow users to log on to a distant host by emulating a dumb terminal; part of the TCP/IP suite.

a. SNA

b. virtual circuit

c. Telnet

d. FTP

Solution:

35. Polarization of a discone antenna.

a. vertical

b. horizontal

c. circular

d. spiral

Solution:

36. When is the effectivity of E.O. 436?

a. September 11,1997

b. September 6,1997

c. September 9,1997

d. September 18,1997

Solution:

37. Use of fiber for all of a telephone system except for the subscriber loop.

a. FDDI

b. FTTC

c. FITL

d. SONET

Solution:

38. A taxi company uses a central dispatcher with an antenna at the top of a 15m tower, to communicate with the taxi cabs. The taxi antennas are on the roofs of the cars, approximately 1.5m above the ground. Calculate the maximum communication distance between two taxis.

a. 10.1 km

b. 21.0 km

c. 7.3 km

d. 17.7 km

Solution:

39. Fold over distortion or aliasing is

a. eliminated by filtering out frequencies below 400 Hz

b. another name for crosstalk

c. the presence of spurious frequencies caused by having too high frequencies in the sampled signal

d. none of these

Solution:

40. Highest frequency that can be used for skywave propagation between two given points on Earth.

a. Critical frequency

b. MUF

c. Cutoff frequency

d. Skip frequency

Solution:

41. What power density is required to produce an electric field strength of 100 volts per meter in air?

a. 0.26 W/m2

b. 13.26 W/m2

c. 26.5 W/m2

d. 0.52 W/m2

Solution:

42. A satellite transmitter with 8 W power operates at 4 GHz with an antenna gain of 40 dBi. The receiver, 40,000 km away has an antenna gain of 50 dBi. If the overall loss is 6dB, find the ERP.

a. 40.85 dBW

b. 42.15 dBW

c. 45.15 dBW

d. 37.85dBW

Solution:

43. A _____ connection provides a dedicated link between two devices.

a. point-to-point

b. multipoint

c. primary

d. secondary

Solution:

44. A unique serial number which identifies mobile stations internationally and is allocated by the manufacturer and then registered by the network operators.

a.  IMSI

b. MSISDN

c. IMEI

d. TMSI

Solution:

45. Which of the following frequency is likely to be associated with AM radio broadcast?

a. 1000 kHz

b. 100 MHz

c. 500 MHz

d. 10 GHz

Solution:

46. In a TV picture tube, what is the purpose of the large picture tube voltage?

a. attracts electrons toward face of the tube

b. repels electrons away from the tube

c. create huge magnetic field

d. good raster production

Solution:

47. For best low-level noise performance in the X-band, an amplifier should use

a. a bipolar transistor

b. a Gunn diode

c. a step-recovery diode

d. an IMPATT diode

Solution:

48. What is the emission C3F?

a. RTTY

b. SSB

c. Television

d. Modulated CW

Solution:

49. One sone is equivalent to how many phons?

a. 0 phons

b. 15 phons

c. 40 phons

d. 20 phons

Solution:

50. Cassegrain feed is used with a parabolic reflector to ____.

a. reduce the size of the main reflector

b. increase the gain of the system

c. increase the beamwidth of the system

d. allow the feed to be placed at a convenient point

Solution:

51. The European standard for synchronous transmission over a fiber-optic network.

a. SONET

b. SDH

c. T carrier

d. E carrier

Solution:

52. The angle between electric and magnetic fields in a waveguide is

a. 90°

b. 0°

c. 180°

d. 45°

Solution:

53. Stores the data of all mobile stations that are currently staying in the administrative area of the associated MSC.

a.  HLR

b. VLR

c. AUC

d. EIR

Solution:

54. The permissible power in kW of stations II-A during nighttime is

a. 0.25 – 50

b. 10 – 50

c. 1 – 5

d. none of these

Solution:

55. What modulation is normally used with digital data?

a. AM

b. FM

c. SSB

d. QPSK

Solution:

56. Use Carson’s rule to compute for the bandwidth that would be required to transmit a baseband signal with a frequency range from 300 Hz to 3 kHz using WBFM with a maximum deviation of 75 kHz.

a. 150.6 kHz

b. 78 kHz

c. 75.3 kHz

d. 156 kHz

Solution:

57. Total bit rate of a T3 carrier system.

a. 1.544 Mbps

b. 6.312 Mbps

c. 44.736 Mbps

d. 27.176 Mbps

Solution:

58. LORAN system has

a. gliding path localizer

b. homing path

c. path retracer

d. master/slave

Solution:

59. Standard mismatching in microwave circuits have SWR from

a. 0.5:1 to 2:1

b. 1:0.5 to 2:1

c. 1.2:1 to 2:1

d. 1.33:1 to 2:1

Solution:

60. A short-lived aspect of a signal such as the attack and decay of musical notes.

a. treble

b. transducer

c. transient

d. volume

Solution:

61. What is the function of a DAC?

a. it changes an analog signal into a digital one

b. it serves as a detector for PM

c. it operates as a slope detector for SSB

d. none of these

Solution:

62. The VRB Board is composed of a Chairman, a Vice Chairman and ___ members.

a. 10

b. 18

c. 22

d. 25

Solution:

63. Which of the following LAN topology is the fastest?

a. bus

b. star

c.  ring

d. square

Solution:

64. In channel 16, the 3.58 MHz color signal is transmitted at the frequency of

a. 474.83 MHz

b. 477.25 MHz

c. 486.83 MHz

d. 495.75 MHz

Solution:

65. A buffer amplifier is

a. a double tuned amplifier

b. a high gain dc amplifier

c. a cathode follower stage

d. none of the choices

Solution:

66. A data-compression scheme that replaces repeated characters or bit patterns with a code indicating the character or pattern and the number of repetitions.

a. ARQ

b. FEC

c. Huffman coding

d. run-length encoding

Solution:

67. The efficiency of an ideal klystron is closer to

a. 25%

b. 50%

c. 75%

d. 90%

Solution:

68. A receiver connected to an antenna whose resistance is 50 ohms has an equivalent noise resistance of 30 ohms. What is the receiver’s noise temperature?

a. 116 K

b. 174 K

c. 163.8 K

d. 464 K

Solution:

69. In a CATV system, Head End Processor as RF input/output terminal match should have ___ dB.

a. 16

b. 18

c. 20

d. 22

Solution:

70. Electronic mail and the CCITT X.400 set of recommendations would be handled by which layer of the OSI model?

a. Network

b. Application

d. Presentation

Solution:

71. What type of radiator normally drives a corner reflector?

a. half-wave

b. despun

c. marconi

d. isotropic

Solution:

72. What is the church dB SPL with speech reinforcement only?

a. 90

b. 80 – 85

c. 95 – 100

d. 100 – 105

Solution:

73. Which of the following operating frequencies is used for the modern LORAN navigational system?

a. LORAN C: 100kHz

b. LORAN D: 10.2 kHz

c. LORAN A: 1950 kHz

d. LORAN B: 900 kHz

Solution:

74. Antennas which are not properly terminated

a. Isotropic

b. Non-resonant

c. Whip

d. Resonant

Solution:

75. Listing of date and time of events, programs, equipment, tests, malfunctions and corrections in communications system.

a. File

b. Documentation

c. Reporting

d. Log

Solution:

76. When the modulating frequency is doubled, the modulation index is halved, and the modulating voltage remains constant. The modulation system is

a. AM

b. PM

c. FM

d. any of these

Solution:

77. Calculate the color subcarrier frequency for TV channel 11.

a. 198.25 MHz

b. 190.83 MHz

c. 205.25 MHz

d. 202.83 MHz

Solution:

78. What kind of an antenna is used with a PPI radar?

a. slotted waveguide

b. discone

c. log-periodic

d. phase array

Solution:

79. A data highway in LAN, which allows work stations to be connected to a common line where all messages pass stations on the way to their destination.

a. CSMA/CD

b. bus

c. ring

d. star

Solution:

80. Iridium satellite system has a mean elevation above Earth for about how many miles?

a. 370 miles

b. 420 miles

c. 650 miles

d. 780 miles

Solution:

81. A transmission line capable of handling high-powered signal is

a. waveguide

b. stripline

c. coax

d. microstrip

Solution:

82. Modal dispersion is caused by the

a. dependence of wavelength on index of refraction

b. dependence of propagation constant on index of refraction

c. dependence of propagation constant on the wavelength

d. dependence of the propagation constant on mode number

Solution:

83. Which signal has color information for 1.5 MHz bandwidth?

a. I

b. Y

c. R-Y

d. B-Y

Solution:

84. It is a protocol used to connect the other packet switching network.

a.  X.75

b. X.25

c.  X.50

d. X.400

Solution:

85. In what frequency bands does marine radar operate?

a. C

b. Ka

c. S

d. Ku

Solution:

86. Known in the United States as RS-232 but defines only the functions of its interface circuits.

a.V.23

b. V.24

c. V.31

d. V.32

Solution:

87. Calculate the maximum efficiency of an asynchronous communication system using ASCII with seven data bits, one start bit, one stop bit and one parity bit.

a. 78%

b. 70%

c. 88%

d. 90%

Solution:

88. A receiver has a sensitivity of 0.5 uV and a blocking dynamic range of 70 dB. What is the strongest signal that can be present along with a 0.5 uV signal without blocking taking place?

a. 5 V

b. 158 pV

c. 50 fV

d. 1.58 mV

Solution:

89. A dipole antenna has a radiation resistance of 67 ohms and a loss resistance of 5 ohms, measured at the feed point. Calculate the efficiency.

a.  7.46%

b. 92.53%

c. 93.05%

d. 64.22%

Solution:

90. In a microwave system, the antenna sees a sky temperature of 150K, and the antenna feedline has a loss of 3 dB. Calculate the noise temperature of the antenna/feedline system, referenced to the receiver input.

a. 205 K

b. 233.33 K

c. 182 K

d. 220 K

Solution:

91. A province in the Philippines has an area of 3000 km. it has to be covered by cellular mobile telephone service using cells with a radius of 2 km. assuming hexagonal cells, fin the number of cell sites needed.

a. 154

b. 216

c. 145

d. 217

Solution:

92. The telephone network is being converted to digital operation primarily to

a. carry digital data

b. reduce costs

c. improve speech quality

d. increase system capacity

Solution:

93. One-hundred ninety microbars of pressure variation is equal to

a. 130 dBSPL

b. 115.56 dBSPL

c. 41.58 dBSPL

d. 119.6 dBSPL

Solution:

94. A shorted half-wave line at the operating frequency acts like a(an)

a. capacitor

b. inductor

c. series resonant

d. parallel resonant

Solution:

95. Which type of fiber-optic cable has the least modal dispersion?

a. single-mode step-index

b. multimode step-index

Solution:

96. What bad electrical effect happens when the switch-hook is opened?

a. a high voltage transient is generated

b. the line is shorted out

c. the line is opened

Solution:

97. What is proper measurement of average power emitted by a pulsed laser?

a. energy x time

b. Pulse energy x repetition rate

c. Pulse energy/repetition rate

d. Peak power x pulse length

Solution:

98. Subcarriers that are arranged so that the channels occupying adjacent frequency bands with some frequency space between them is

a. guard bands

b. null bands

c. band gaps

d. void bands

Solution:

99. Quantization noise can be reduced by

a. taken samples at a faster rate

b. using a PCM system

c. increasing the number of levels during sampling

d. using higher amplitude signals

Solution:

100. A broadcast TV channel has a bandwidth of 6 MHz. Ignoring noise, calculate the maximum data rate that could be carried in a TV channel using a 8-level code and determine the minimum possible signal-to-noise ratio in dB for the calculated data.

a. 24 Mbps, 48 dB

b. 48 Mbps, 24 dB

c. 36 Mbps, 18 dB

d. 18 Mbps, 36 dB