# Communications Engineering Mastery Test 17: ECE Pre-Board

(Last Updated On: April 2, 2021) This is 100 items Practice Examinations set 17 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 17

Choose the letter of the best answer in each questions.

1. A method of comparing two audio systems by switching inputs so the same recording is heard in rapid succession over one system and then the other.

a. AB test

c. system test

d. end test

Solution:

2. An AM receiver is tuned to broadcast station at 600 kHz. Calculate the image rejection in dB assuming that the input filter consists of one tuned circuit with a Q of 40.

a. 19.28 dB

b. 39.65 dB

c. 38.57 dB

d. 19.83 dB

Solution:

3. A sonic frequency lying above audio frequencies, ranging usually above 20 kHz.

a. voice frequency

b. mid-range frequency

c. ultrasonic frequency

d. light frequency

Solution:

4. What principle is used by a carbon type microphone?

a. variable capacitance

b. variable resistance

c. variable inductance

d. piezoelectric effect

Solution:

5. The ratio in decibels of the incident power to the reflected power on a transmission line.

a. return loss

b. reflection loss

c. buffer loss

d. clutter loss

Solution:

6. A ray that propagates through a fiber by total internal reflection and passing through the optical axis of the fiber.

a. light ray

b. visual ray

c. reflected ray

d. meridional ray

Solution:

7. Electromagnetic frequencies in the range of 33-40 GHz (0.909 to 0.750 centimeter wavelengths).

a. Ku band

b. Ka band

c. L band

d. S band

Solution:

8. An organization consisting of representatives from national standards bodies from different countries, responsible for development standards to facilitate international trade and services.

a. ISO

b. ANSI

c. OSI

d. ITU

Solution:

9. Also known as IEEE 1394, a scalable, flexible, and low-cost serial digital interlace that connects consumer electronic devices such as video cameras, digital camera, etc. with personal computers.

a. Fire hazard

b. Fire wire

c. Fire wall

d. Fixed wire

Solution:

10. A computer hardware and/or software that acts as a buffer between an internal network and the Internet to provide security against unauthorized access

a. casing

b. buffer

c. security code

d. firewall

Solution:

11. A unit of luminance. It is equal to the uniform luminance of an emitting or reflecting light at a rate of one lumen per square centimeter.

a. lambert

b. lux

c. lumens

d. phons

Solution:

12. The protocol used for transmitting e-mail on the Internet

a. SIMM

b. SMTP

c. SPX

d. RJ-II

Solution:

13. A figure of merit used to measure the dependence of the signal output of a photo detector on the input radiant power

a. Responsitivity

b. resolution

c. quality factor

d. precision

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 bandwidth efficiency of the scheme.

a. 5.4167 bits/cycle

b. 1.35 bits/cycle

c. 5.4167 x 1010 bits/cycle

d. 270.833 kbits/cycle

Solution:

15. In radio wave propagation, what is the lowest layer of the ionosphere whose intensity is greatest at noon, when maximum solar radiation is absorbed by the upper atmosphere.

a. ozone layer

b. stratosphere

c. troposphere

d. D layer

Solution:

16. Frequency of operation of a low-power wireless technology (Bluetooth) that provides a connectivity standard for network devices.

a. 2.4 GHz

b. 4.2 GHz

c. 3.4 GHz

d. 4.3 GHz

Solution:

17. A fiber has an index of refraction of 1.6 for the core and 1.4 for the cladding. Calculate the critical angle.

a.  29°

b. 30°

c. 60°

d. 61°

Solution:

18. What is the effective earth’s radius when Ns = 300?

a. 8500 km

b. 9320 km

c. 5600 km

d. 4850 km

Solution:

19. It refers to IEEE 802.11 network

a. Wi-Fi

b. WWW

c. WAN

d. LAN

Solution:

20. In electronic navigation, the Omega system uses time sharing so that all stations can use the same frequencies. It can cover the whole world, has a lesser bandwidth, and has a small widening of lanes giving good hyperbolic Lines. What is the frequency band used by Omega?

a. 100 kHz

b. 10 to 13 kHz

c. 70 to 130 kHz

d. 2 MHz

Solution:

21. A component that samples the microwave signal traveling in one direction down a transmission line.

a. directional coupler

b. combiner

c. isolator

d. circulator

Solution:

22. What is the major disadvantage of a klystron?

a. low efficiency

b. narrow bandwidth

c. low gain

d. high noise

Solution:

23. A phase-locked loop has a VCO with a free-running frequency of 14 MHz. As the frequency of the reference input is gradually raised from zero, the loop locks at 12 MHz and comes out of lock again at 18 MHz. Calculate the lock range.

a. 4 MHz

b. 2 MHz

c. 12 MHz

d. 8 MHz

Solution:

24. A single telephone signal is fitted into a frequency band from 0 Hz to __________.

a. 3,400 Hz

b. 4000 Hz

c. 3000 Hz

d. 4,100 Hz

Solution:

25. What carrier-to-noise ratio is required for microwave relay systems?

a. 5-10 dB

b. 10-15 dB

c. 20-25 dB

d. 10-20 dB

Solution:

26. 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. 62.5%

b. 37.5%

c. 39.1%

d. 60.9%

Solution:

27. Which of the following is the most difficult for a radar to measure accurately?

a. angle

b. velocity

c. range

d. b and c

Solution:

28. A metal foil launched from a target to create false radar target.

a. decoy

b. chaff

c. missile

d. stealth

Solution:

29. What is the frequency range of cellular telephone?

a. 860-949 MHz

b. 806-949 MHz

c. 608-948 MHz

d. 860-849 MHz

Solution:

30. A deceptive jamming technique where the jamming signal is given a false Doppler shift so that the radar thinks the target velocity is different than it really is.

a. Home-on jammer

b. Velocity-gate pull-off

c. Inverse-gate pull-off

d. Range-gate pull-in

Solution:

31. It pertains to sound which also corresponds to color in light.

a. hue

b. pitch

c. intensity

d. chrominance

Solution:

32. This is the ability of sound to inhibit the perception of another sound.

a. overlapping

b. interruption

d. interference

Solution:

33. An standard protocol used to connect after packet switching network

a. x.75

b. x.25

c. x.76

d. x.74

Solution:

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

a. red

b. blue

c. black

d. green

Solution:

35. A microwave system has a reliability of 99.99%, compute for the amount of outage in minutes.

a. 53 min.

b. 58 min.

c. 68 min.

d. 98 min.

Solution:

36. It pertains to the change of the crystal oscillator frequency by loading.

a. pushing

b. swaying

c. drifting

d. pulling

Solution:

37. Audio frequency response is confined to

a. 300-3400 Hz

b. 300-3000 Hz

c. 300-4000 Hz

d. either a or b

Solution:

38. Determine the cut-off wavelength of a fiber with a 5 micrometer diameter core. The core and the cladding indices of refraction are 1.6 and 1.4 respectively.

a. 5.059 mm

b. 6.059 mm

c. 3.059 mm

d. 4.059 mm

Solution:

39. The transmitter power output in single sideband operation is expressed in terms of

a. watts

b. dBm

c. dB

d. PEP

Solution:

40. Flicker noise in radio communications is also referred to as ________ noise.

a. pink noise

b. white noise

c. thermal noise

d. agitation noise

Solution:

41. Suppose that the transmitter and receiver towers have equal height. How high would they have to be to communicate over a distance of 34 km?

a. 23.5 m

b. 28.47 m

c. 17 m

d. 8.47 m

Solution:

42. What is the peak power of a radar pulse if the width is 1.0 microsecond, PRR is 900 and the average plate power input is 45 watts?

a. 50 kW

b. 60 kW

c. 45 kW

d. 62.5 kW

Solution:

43. Gain of a folded dipole above an isotropic antenna

a. 1.74 dB

b. 1.64 dB

c. 2.14 dB

d. 3.64 dB

Solution:

44. In a fiber optic system, the core of PCS fiber is ________.

a. mica

b. paper

c. plastic

d. glass

Solution:

45. Determine the dB gain of a receiving antenna which delivers a microvolt signal to a transmission line over that of an antenna that delivers a 2 microvolt signal under identical circumstances.

a. -6

b. -3

c. 6

d. 3

Solution:

46.The 1.55 µm “window” is not yet in use with fiber optic systems because

a. the attenuation is higher than at 0.85 µm

b. the attenuation is higher than at 1.3 µm

c. suitable laser devices have not yet been developed

d. it does not lend itself to wavelength multiplexing

Solution:

47. A ferrite is

a. a nonconductor with magnetic properties

b. an intermetallic compound with particularly good conductivity

c. an insulator which heavily attenuates magnetic fields

d. a microwave semiconductor invented by Faraday

Solution:

48. IEEE standard for local area networks (LAN) covering OSI layers 3 to 7.

a. 802.3

b. 802.4

c. 802.2

d. 802.1

Solution:

49. A particular amplifier is designed to be a frequency doubler. If the input signal frequency is 15.4 MHz, a circuit in the output will be tuned to

a. 7.7 MHz

b. 15.4 MHz

c. 30.8 MHz

d. 61.6 MHz

Solution:

50. R3E modulation is sometimes used to

a. allow the receiver to have a frequency synthesizer

b. simplify the frequency stability problem in reception

c. reduce the power that must be transmitted

d. reduce the bandwidth required for transmission

Solution:

51. How many degrees is the phase difference between the I and Q color signal carrier in colored TV sets?

a. 180

b. 270

c. 90

d. 45

Solution:

52. What are the typical transmitter- receiver spacing for microwave relay?

a. 10-20 miles

b. 10-30 miles

c. 5-50 miles

d. 10-50 miles

Solution:

53. Indicate which of the following statements about the advantages of the phase discriminator over the slope detector is false:

a. Much easier alignment

b. Better linearity

c. Greater limiting

d. Fewer tuned circuits

Solution:

54. What limits the transmitter-receiver spacing for a microwave relay?

a. gain of antenna

b. curvature of the earth

c. frequency assigned

d. antenna sites

Solution:

55. A GPS satellite has how many orbit period in hours?

a. 24

b. 12

c. 18

d. 36

Solution:

56. An AM transmitter supplies a 10 kW of carrier power to a 50 ohm load. It operates at a carrier frequency of 1.2 MHz and is 85% modulated by a 3 MHz sine wave. Calculate the RMS voltage of the signal.

a. 825 W

b. 262.61 V

c. 1166.7 V

d. 825 V

Solution:

57. The hue of the color sync burst phase

a. red

b. blue

c. magenta

d. yellow-green

Solution:

58. It is known as the unit of pitch.

a. sone

b. phon

c. mel

d. dB

Solution:

59. What is the typical value of vidicon dark current?

a. 3 mA

b. 0.2 μA

c. 2 μA

d. 0.5 μA

Solution:

60. For a transmission line with incident voltage equal to 8 volts and reflected voltage equal to 1 volt, calculate the standing wave ratio.

a. 0.36

b. 1.115

c. 1.29

d. 1.544

Solution:

61. How many voice channels are there in a DS-2 Digital Signal Hierarchy for TDM signals?

a. 69

b. 105

c. 45

d. 96

Solution:

62. In measuring the intensity of acoustical signals, the logarithmic unit decibel (dB) is used. The threshold of hearing in dB-SPL is ________.

a. one

b. 10

c. zero

d. 100

Solution:

63. In an OSI model, BISYNC protocol belongs to what layer?

b. physical layer

c.       network layer

d. transport layer

Solution:

64. According to the Philippine Electronics Code, what is the maximum permissible accumulated dose of a 68-year old person?

a. 200 rems

b. 230 rems

c. 250 rems

d. 277 rems

Solution:

65. A component containing ferrite materials that allows microwave signals to pass in one direction through the component, but absorbs microwave signals passing in the other directions.

a. combiner

b. isolator

c. coupler

d. puller

Solution:

66. In electronic radio navigation, the ADF is a navigational aid that is used for automatic determination of relative bearing to a transmitting radio station or Non-Directional Beacon (NDB). It is also used for reception of weather information and other broadcast programs. The frequency of operation of the Automatic Direction Finder is

a. 1030 to 1090 MHz

b. 108 to 112 MHz

c. 16 to 24 kHz, 2 MHz, 75 MHz

d. 190 to 1860 kHz

Solution:

67. The frequency change of an electronically tuned oscillator at a specified time after it has reached its desired frequency.

a. freq. deviation

b. post-tuning drift

c. freq. pulling

d. freq. pushing

Solution:

68. For reasonably efficient operation of a transistor amplifier, what should be the load resistance be with 12 volts at the collector and 5 watts power output?

a. 100.3 ohms

b. 14.4 ohms

c. 10.3 ohms

d. 144 ohms

Solution:

69. What is the major disadvantage of Traveling Wave Tubes (TWTs)?

a. low efficiency

b. high cost

c. low gain

d. high noise

Solution:

70. What is the advantage of cable communication systems compared with a broadcast system?

a. higher gain

b. higher capacity

c. lesser noise

d. low cost

Solution:

71. A radar that directs its beam into a given area of space to determine accurately the angular location of a target.

Solution:

72. What position accuracy can be obtained with the GPS?

a. within 5 m

b. within 4 m

c. within 10 m

d. within 2 m

Solution:

73. A networking device that allows connection between two dissimilar computer networks.

a. gateway

b. handshaking

c. splitter

d. divider

Solution:

74. A type of noise generated by the thermal motion of electrons in a medium at a temperature above absolute zero.

a. Gaussian noise

b. flicker noise

c. pink noise

d. black noise

Solution:

75. What is the index of refraction of a certain medium if the velocity of propagation of a radio wave in this medium is 1.527 x 108 m/s?

a. 0.509

b. 0.631

c. 0.713

d. 1.965

Solution:

76. The dominant mode of propagation is preferred with rectangular waveguides because (indicate false statement)

a. it leads to the smallest waveguide dimensions

b. the resulting impedance can be matched directly to coaxial lines

c. it is easier to excite than the other modes

d. propagation of it without any spurious geberation can be ensured

Solution:

77. Calculate for the color subcarrier frequency for TV channel 9.

a. 196.25 MHz

b. 196.83 MHz

c. 187.25 MHz

d. 190.83 MHz

Solution:

78. A condition when an incoming call meets an outgoing call causing a blockage.

a. glitch

b. lock

c. glare

d. crunch

Solution:

79. V-numbers less than what value indicate single mode fiber operation.

a. 3.453

b. 2.405

c. 5.426

d. 2.507

Solution:

80. If the color oscillator does not operate, the result will be

a. no picture

b. No color

c. incorrect hues

d. No color sync

Solution:

81. It minimizes side and blockage radiations from a microwave dish.

b. shroud

c. vertex plate

d. dehydrator

Solution:

82. If the antenna current increases 3.4 times, the radiated power will increase to _______.

a. 18.5%

b. 15.33%

c. 11.56%

d. 12.825%

Solution:

83. The signal to noise ratio for satisfactorily Telephone Communication Service.

a. 40 dB

b. 50 dB

c. 45 dB

d. 35 dB

Solution:

84. A protocol for interconnecting digital programmable instruments (DPI).

a. IEEE 488

b. IEEE 802

c. IEEE 394

d. IEEE 801

Solution:

85. The probability of a telephone call being blocked and receiving a network busy signal on the telephone circuit.

a. reliability

b. availability

d. Erlang measurement

Solution:

86. A type of RF modulation technique in which the frequency of an analog signal is varied in accordance with the variations in the amplitude of a digital signal.

a. PAM

b. FSK

c. FM

d. PDM

Solution:

87. What is the effective radiated power of a repeater with 450 W transmitting power output, 4 dB feedline loss, 6 dB duplexer loss, and 7 dB circulator and feedline loss and antenna gain of 25 dB?

a. 2893.31 W

b. 2523.83 W

c. 2839.31 W

d. 2425.38 W

Solution:

88. A rectangular waveguide has a width of 1.2 in and a height of 0.7 in. The waveguide will pass all signals above ___ GHz.

a. 4 GHz

b. 8.44 GHz

c.  10 GHz

d. 4.92 GHZ

Solution:

89. In microwave communications systems, for a carrier frequency of 6 GHz and a distance of 40 km, determine the free-space path loss in dB.

a. 80 dB

b. 84.2 dB

c. 140 dB

d. 144.2 dB

Solution:

90. In a microwave communications system, if the minimum carrier-to-noise (C/N) requirement for a receiver with a 10 MHz bandwidth is 22 dB, the minimum receive carrier power is

a. -82 dB

b. 76 dBm

c. 84 dB

d. -82 dBm

Solution:

91. A rectangular waveguide used for microwave transmission has a width of 1.4 inches and a height of 0.8 inches. All signals above ____ GHz will be passed by the waveguide.

a. 4.3 GHz

b. 2 GHz

c. 4.2 GHz

d. 5 GHz

Solution:

92. A pyramidal horn has an aperture (opening) of 58 mm in the E plane and 78 mm in the H plane. It operates at 15 GHz. Calculate the gain in dBi.

a. 19.29

b. 24.14

c. 15.8

d. 19.31

Solution:

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

a. 120 dBSPL

b. 115.56 dBSPL

c. 41.58 dBSPL

d. 57.78 dBSPL

Solution:

94. A tuned circuit that dissipates energy taken from another circuit.

a. absorption circuit

b. phantom circuit

c. LC circuit

d. tank circuit

Solution:

95. What is the increase in sound pressure level if the pressure is doubled?

a. increases by 6 dB

b. increases by 3 dB

c. decreases by 6 dB

d. decreases by 3 dB

Solution:

96.  Find the characteristic impedance of polyethylene, which has a dielectric constant of 2.4.

a. 163.9 ohms

b. 377 ohms

c. 243 ohms

d. 250 ohms

Solution:

97. Calculate the electric field intensity in millivolts per meter at 30 kW from a 5 km source.

a. 190 mV/m

b. 95.49 uV/m

c. 0.189 W/m

d. 13.416 V/m

Solution:

98. Determine the critical frequency value of an HF signal if its maximum usable frequency is 7050.50 kHz at 35 degrees incidence.

a. 4936.8 kHz

b. 5775 kHz

c. 4044 kHz

d. 4908.75 kHz

Solution:

99. A radio wave moves from air (er = 1) to glass (er = 7.8). Its angle of incidence is 20 degrees. What is the angle of refraction?

a. 7 degrees

b. 29 degrees

c. 10.3 degrees

d. 72.79 degrees

Solution:

100. Determine the refractive index of an ionospheric layer with 1.567 x 106 free electrons per cu m. The frequency of the radio wave is 32 kHz.

a. 0.999

b. 0.936

c. 0.956

d. 0.987