You dont have javascript enabled! Please enable it! Communications Engineering Mastery Test 16: ECE Pre-Board

# Communications Engineering Mastery Test 16: ECE Pre-Board

This is 100 items Practice Examinations set 16 in Communications Engineering (Electronics Systems and Technology) composed of previous Board Exams Questions. Read each question and choice 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 question to increase the chance of passing the ECE Board Examination.

#### Start the Test Yourself Exam 16

Choose the letter of the best answer in each question.

1. A TDM system

a. needs lower bandwidth

b. gives low signal-to-noise ratio

c. uses simple circuits as compared to FDM systems

d. none of the choices

Solution:

2. When a quarter-wave section transmission line is terminated by a short circuit and is connected to an RF source at the other end, its input impedance is

a. inductive

b. capacitive

c. resistive

d. equivalent to a parallel resonant LC circuit

Solution:

3. The frequency normally used for ionospheric transmission is known as _____.

a. Optimum Working Frequency

b. MUF

c. Critical Frequency

d. Nominal Frequency

Solution:

4. How far from the transmitter could a signal be received if the transmitting and receiving antennas were 40 m and 20 m respectively, above level terrain?

a. 45 km

b. 60 km

c. 15 km

d. 20 km

Solution:

5. The agreed standard for measuring loudness is the loudness sensation produced by a 100 Hz sine wave, ____ dB above the listenerโs threshold level.

a. 10 dB

b. 20 dB

c. 30 dB

d. 40 dB

Solution:

6. What diode makes a good low noise detector at higher microwave frequencies?

a. Schottky

b. Gunn

c. Led

d. PIN

Solution:

7. What is the number of channels of a cellular system with an allocated spectrum of 25 MHz and with a channel of 30 kHz bandwidth?

a. 833

b. 240

c. 1000

d. 666

Solution:

8. How many seconds does a facsimile transmit a standard page?

a. 5

b. 10

c. 20

d. 25

Solution:

9. What is the flicker noise voltage of a carbon composition resistor?

a. 0.01 ฮผV to 0.2 ฮผV

b. 0.1 ฮผV to 2 ฮผV

c. 0.02 ฮผV to 0.2 ฮผV

d. 0.2 to 2 ฮผV

Solution:

10. Which of the following frequency will not be found in the output of the normal TV receiver tuner?

a. 4.5 MHz

b. 41.25 MHz

c. 45.75 MHz

d. 55.25 MHz

Solution:

11. An amplifier has a noise figure of 2 dB. What is its equivalent noise temperature?

a. 192.8 K

b. 169.6 K

c. 158.5 K

d. 179.2 K

Solution:

12. VSAT was made available in

a. 1979

b. 1989

c. 1981

d. 1983

Solution:

13. The TV picture size increases

a. voltage for the picture tube anode increases

b. voltage required for picture tube anode decreases

c. voltage required for picture tube anode does not change

d. none of the choices

Solution:

14. What is the maximum data rate for a fiber optic system?

a. 1 Gbps

b. 10 Gbps

c. 100 Gbps

d. 1000 Gbps

Solution:

15. Which of the following affects the bandwidth of an optical fiber?

a. refractive index

b. modal dispersion

c. splicing

d. material dispersion

Solution:

16. An FM modulator has kf = 30 kHz/V and operates at a carrier frequency of 175 MHz. Find the output frequency for an instantaneous value of the modulating signal equal to 150 mV.

a. 174.9955 MHz

b. 174.94 MHz

c. 175.06 MHz

d. 175.0045 MHz

Solution:

17. The function of serrations in the composite video waveform is to

a. equalize the charge in the integrator before the start of the vertical retrace

b. help vertical synchronization

c. help horizontal synchronization

d. simplify the generation of the vertical sync pulse

Solution:

18. In telecommunications, short-haul connections refer to a connection exceeding ____ km.

a. 150 km

b. 200 km

c. 250 km

d. 250 km

Solution:

19. In a single-gun color CRT, what electron beam travels straight through the tube?

a. red

b. green

c. blue

d. yellow

Solution:

20. What is the transmission rate of a system for transmitting the output of a microcomputer to a line printer operating at a speed of 30 lines/minute? Assume that the line printer has 8 bits of data per character and prints out 80 characters and prints out 80 characters/line?

a. 800 bps

b. 400 bps

c. 320 bps

d. 640 bps

Solution:

21. What is the approximate bandwidth occupied by the chrominance video signal for color TV?

a. 0.8 MHz

b. 1.8 MHz

c. 6.0 MHz

d. 1.6 MHz

Solution:

22. Refraction of waves is relatively insignificant at frequencies above about

a. 1 MHz

b. 10 MHz

c. 100 MHz

d. 1000 MHz

Solution:

23. A triple conversion superheterodyne receiver, diode mixer stages are

a. operated in the linear region

b. operated in the nonlinear region

c. operated as Class-A amplifier

d. operated in Class-C amplifier

Solution:

24. The number of OC-1 signals within a SONET OC-3 signal is

a. 3

b. 6

c. 9

d. 12

Solution:

25. Find the cutoff frequency for the TE10 mode in the air-dielectric waveguide with an inside cross-section of 2 cm by 4 cm.

a. 7.51 GHz

b. 3.75 GHz

c. 1.88 GHz

d. 2.15 GHz

Solution:

26. What two DTMF tones are generated when the digit 8 is pressed?

a. 852 Hz, 1336 Hz

b. 941 Hz, 1336 Hz

c. 852 Hz 1477 Hz

d. 941 Hz, 1477 Hz

Solution:

27. When did ISO adapt the seven-layer OSI model?

a. 1983

b. 1973

c. 1963

d. 1953

Solution:

28. The originator of the Sabine reverberation equation.

a. Wallace C. Sabine

b. Lawrence C. Sabine

c. Allan C. Sabine

d. Willie C. Sabine

Solution:

29. Frequency frogging is used in carrier system to

a. reduce distortion

b. reduce crosstalk

c. conserve frequency

d. conserve bandwidth

Solution:

30. The standard for the 7-layer model for Open System Interconnection.

a. X.75

b. X.200

c. X.400

d. X.500

Solution:

31. A church has an interval volume of 90.05 ft3 (2,550 m3). When it contains 2,000 customary sabines of absorption (186 metric sabines), what will be its reverberation time in seconds.

a. 2.0

b. 2.2

c. 2.5

d. 3.0

Solution:

32. If the spectrum is shifted in frequency with no other changes, this is known as

a. frequency multiplication

b. sideband movement

c. baseband reorientation

d. frequency translation

Solution:

33. The beam width angle of a parabolic dish antenna _____ the dish diameter.

a. decrease with increase in

b. decrease with decrease in

c. independent of

d. is equal to

Solution:

34. What is the dB SPL of an auditorium with contemporary music?

a. 80 โ 95

b. 85 โ 90

c. 95 โ 100

d. 100 โ 105

Solution:

35. The spectrum user fee (SUF) charge by NTC for PTE such as CMTS operators is ____ Philippine pesos per one Megahertz BW efficiency.

a. 100,000

b. 500,000

c. 1,000,000

d. 5,000,000

Solution:

36. One factor in the accuracy of a reconstructed PCM signal is the _______.

a. signal bandwidth

b. carrier frequency

c. number of bits used for quantization

d. baud rate

Solution:

37. What is the capture area of the dipole operated at 75 MHz?

a. 4 mm2

b. 2 m2

c. 2.088 m2

d. 4.088 m2

Solution:

38. Assuming there is negligible noise, what would be the data rate of one satellite transponder used for binary data transmission?

a. 72 Mbps

b. 144 Mbps

c. 36 Mbps

d. 108 Mbps

Solution:

39. In preparing the power budget for fiber optics system, it is customary to include the margin of safety to compensate for variations in source, losses due to bends and for repair splices. What is the typical margin of safety used?

a. 1-5 dB

b. 5-10 dB

c. 10-15 dB

d. 15-20 dB

Solution:

40. CMTS operators are encouraged by NTC to improve the drop call rate of _____ after one year of start of operation.

a. 2%

b. 4%

c. 5%

d. 7%

Solution:

41. The Planned European Satellite Navigation System known as Galileo has ____ number of constellation satellites.

a. 3

b. 24

c. 30

d. 66

Solution:

42. If the modulation index of an AM wave is doubled, the antenna current is also doubled, the AM system being used is

a. H3E

b. J3E

c. C3F

d. A3E

Solution:

43. The gain of the isotropic antenna is ______.

a. 0 dB

b. 3 dB

c. 10 dB

d. 12 dB

Solution:

44. What is the frequency deviation of the cellular telephone system?

a. ยฑ 5 kHz

b. ยฑ 30 kHz

c. ยฑ 12 kHz

d. ยฑ 75 kHz

Solution:

45. A collector-modulated Class C amplifier has a carrier output power Pc of 100 W and an efficiency of 70%. Calculate the transistor power dissipation with 100% modulation.

a. 214 W

b. 75 W

c. 150 W

d. 64 W

Solution:

46. Microphone used in telephone handset

a. carbon microphone

c. dynamic microphone

d. resistance microphone

Solution:

47. It is an alpha-numeric code based on five binary values.

a. Quinta Code

b. Gray Code

c. Baudot Code

d. ASCII

Solution:

48. Cellphones receives in the band from

a. 860 โ 880 MHz

b. 870 โ 890 MHz

c. 870 โ 880 MHz

d. 860 โ 890 MHz

Solution:

49. Which of the following is not an application of microwave cavities?

a. band pass filter

b. band stop filter

c. oscillator frequency control

d. detector

Solution:

50. Find the Doppler shift caused by a vehicle moving towards a radar at 60 mph, if the radar operates at 10 GHz.

a. 1.78 kHz

b. 4.01 kHz

c. 3.92 kHz

d. 1.96 kHz

Solution:

51. Poynting vector gives which of the following?

a. intensity of the magnetic field

b. intensity of the electric field

c. direction of polarization

d. rate of energy flow

Solution:

52. Why are visible light LEDs not used in fiber optics?

a. it has high losses

b. it has short wave

c. it has low attenuation

d. it has weak signals

Solution:

53. Probability density function of thermal noise

a. Poisson

b. Binomial

c. Gaussian

d. None of the choices

Solution:

54. The rays comprising a mode that all passes through the longitudinal, or z-axis of the fiber core, are called ______.

a. skew rays

b. convergent rays

c. meridional rays

d. divergent rays

Solution:

55. What is the maximum power that can be obtained from a microwave semiconductor?

a. 1 W

b. 500 mW

c. 10 W

d. 4 W

Solution:

56. A typical PBX configuration is _______.

a. Bus Topology

b. Star Topology

c. Ring Topology

d. Mesh Topology

Solution:

57. How many bits would be required to define all the characters for a 54-key computer terminal?

a. 4

b. 5

c. 6

d. 8

Solution:

58. ______ is a voice operated device that inserts a high loss in the opposite direction of transmission of the talking party.

a. Hybrid

b. 2-wire circuit

c. Echo suppressor

d. VNL

Solution:

59. Which of the following application advantages of radar beacons is false?

b. target identification

c. more accurate tracking of enemy targets

d. very significant extension of the maximum range

Solution:

60. What device is located between the magnetron and the mixer and prevents received signals from entering the magnetron?

a. TR box

b. ATR box

c. RF attenuator

d. resonant cavity

Solution:

61. Which of the following is a function of an amplitude limiter in an FM receiver?

a. amplify low frequency signals

b. To reduce the amplitude of the signal

c. To eliminate any change in the amplitude of the received FM signal

d. None of the choices

Solution:

62. What is the maximum power output of a CB A3E emission?

a. 4 W

b. 10 W

c. 3 kW

d. 10 kW

Solution:

63. For a transmission line giving a maximum rms voltage reading of 50 V at one point and a minimum rms voltage reading 25 V at another point. What is the VSWR of the line?

a. 2

b. 4

c. 1

d. 5

Solution:

64. In a cellular radio, the duplexer is a

a. ferrite isolator

b. waveguide assembly

c. pair of TR/ATR tubes

d. pair of sharp bandpass filters

Solution:

a. GaAs FET

b. Magnetron

c. Gunn diode

d. Klystron

Solution:

66. Commonly used electro โ optic crystal for polarization modulation

a. Lithium Niobate

b. Tourmaline

c. Sodium Chlorate

d. Sphalerite

Solution:

67. Which of the following modulating system is inherently most noise resistant?

a. PCM

b. PPM

c. FM

d. DSB

Solution:

68. Compression ratio used by time assignment speech interpolation

a. 2:1

b. 4:1

c. 3:2

d. 4:3

Solution:

69. The chrominance processing circuits are deactivated when monochrome broadcasts are received by the

a. NOT gate

b. Color killer

c. One-shot MV

d. SAW filter

Solution:

70. An FM detector produces a peak-to-peak output voltage of 1.2 V from an FM signal that is modulated to 10 kHz deviation by a sine wave. What is the detector sensitivity?

a. 60 ฮผV/Hz

b. 12 ฮผV/Hz

c. 120 ฮผV/Hz

d. 53 ฮผV/Hz

Solution:

71. If an FET is used as the first AF amplifier in a transistor receiver, this will have the effect of

a. improving the effectiveness of the AGC

b. reducing the effect of negative-peak clipping

c. reducing the effect of noise at low modulation depths

d. improving the selectivity of the receiver

Solution:

72. What is the reference tone level for dBa using the pure test tone?

a. -90 dBm

b. -82 dBm

c. -85 dBm

d. -67 dBm

Solution:

73. In a waveguide, ______ is a specific configuration of electric and magnetic fields that allows a wave to propagate.

a. set-up

b. coupler

c. channel

d. mode

Solution:

74. The middle marker in an ILS is approximately _____ from the runway threshold

a. 75 m

b. 1050 m

c. 5000 m

d. 7200 m

Solution:

75. The distance between consecutive maxima and minima is given by

a. ฮป/2

b. 2ฮป

c. ฮป

d. ฮป/4

Solution:

76. Where is a color burst found?

a. front porch

b. back porch

c. blanking porch

d. synch porch

Solution:

77. The frequency band used in marine and aeronautical communications using satellites are within the ___ band. (also known as the L band)

a. 350 MHz – 10GHz

b. 1000 – 2450 MHz

c. 3490 โ 8610 MHz

d. 1530 – 2700 MHz

Solution:

78. Flat-topped rectangular pulses must be transmitted in radar to (indicate the false statement)

a. Allow a good maximum range

b. Make the returned echoes easier to distinguish from noise

c. Prevent frequency changes in the magnetron

d. Allow accurate range measurement

Solution:

79. A local loop has a resistance of 1 kiloohms, and the telephone connected to it has an off-hook resistance of 200 ohms. Calculate the voltage across the telephone when the phone is off-hook.

a. 16 V

b. 48 V

c. 4 V

d. 8 V

Solution:

80. MP3 is a format for compressing music which delivers almost CD quality sound. In MP3, a ____ minute song can be stored in about 3 megabytes of storage quality.

a. 1

b. 2

c. 3

d. 4

Solution:

81. A disadvantage of direct FM is the need for

a. AGC

b. AFC

c. a frequency synthesizer

d. phase modulation

Solution:

82. Single sideband reduced carrier emission type.

a. H3E

b. R3E

c. J3E

d. B8E

Solution:

83. What is the main problem in receiving a suppressed carrier transmission or a single sideband transmission?

a. the receiver needs to reinsert the missing carrier

b. the gain of the amplifier must be high

c. the selectivity of the receiver must be good

d. there must be three detectors

Solution:

84. A radio channel has a bandwidth of 10 kHz and a signal-to-noise ratio of 15 dB. What is the maximum data rate that can be transmitted using any system?

a. 31.6 kbps

b. 50.3 kbps

c. 40 kbps

d. 15.8 kbps

Solution:

85. When a block of data is transmitted, and if no error is detected, a _____ is sent back to the transmitter.

a. NAK

c. DQPSK

d. ACK

Solution:

86. What is the part of a switching system that establishes transmission paths between pairs of terminals?

a. Switching Bridge

b. Switching Trunk

c. Switching Array

d. Switching Network

Solution:

87. If the transmitter and the receiver rise times were 0.5 ns and 1.5 ns respectively, and the fiber rise time was 25 ps, the system rise time would be approximately

a. 25.05 ns

b. 1.42 ns

c. 1.58 ns

d. 5.19 ns

Solution:

88. A device used for abating the noise accompanying the flow of gas through a pipe.

a. Helmholtz Resonator

b. Muffler

c. Acoustic Chamber

d. Acoustic Filter

Solution:

89. In cable TV, after what channel does Hyperband start?

a. 7

b. 13

c. 36

d. 64

Solution:

90. What is the reason for using pre-emphasis?

a. reduce noise reception

b. to increase noise figure

c. reduce S/N ratio

d. increase selectivity

Solution:

91. How many significant sidebands are present in FM if the modulation index is 1.0?

a. 2

b. 3

c. 4

d. 5

Solution:

92. An advantage of optic fiber rejecting an induced noise signals from magnetic field or solar storms flux.

a. electric hazard

b. cross talk

c. immunity to noise

d. shielding

Solution:

93. Transmission lines when connected to antennas have

b. resistive load whose resistance is greater than the characteristic impedance of the line

c. resistive load whose resistance is less than the characteristic impedance of the line

d. resistive load at the resonant frequency

Solution:

94. Anomalous propagation of radio waves is caused by ______.

a. super refractive duct

b. meteorological factors

c. troposcatter

d. ducting

Solution:

95. Television receiver antenna is usually ______.

a. loop type

b. yagi antennas

c. parabolic dishes

d. none of the choices

Solution:

96. The signal power at the input to an amplifier is 100ฮผW and the noise power is 1 ฮผW. At the output, the signal power is 1 W and the noise power is 30 mW. What is the amplifier noise figure, as a ratio?

a. 4.8

b. 2.4

c. 3.0

d. 9.5

Solution:

97. The graded โ index multimode optical fiber has a core diameter of _____ nm

a. 0.5

b. 0.05

c. 0.005

d. 5

Solution:

98. On a basic synchro system, the angular information is carried on

a. dc feedback signal

b. stator lines

c. deflection coils

d. rotor lines

Solution:

99. What is the carrier frequency of an FM station with channel number of 300?

a. 107.5 MHz

b. 101.1 MHz

c. 107.9 MHz

d. 99.5 MHz

Solution:

100. Indoor equipment and devices for Wireless Data Networks shall be type-accepted or approved by the NTC. Radio equipment with an effective radiated power not exceeding ____ mW, and no external antenna are considered indoor equipment devices.

a. 100

b. 150

c. 200

d. 250

Solution:

### Complete List of Communications Engineering Exams: ECE Pre-Board

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