University of Pangasinan - ECE 111005619

1)The bandwidth in depends on the number of significant sidebands.

1. FCM
2. QAM
3. Delta Modulation
4. Frequency Modulation

2. A carrier wave is amplitude modulated by two sine waves of different frequencies with modulation indices of 0.3 and

0.4. What is the overall modulation index?

a) 0.1

b) 0.5

c) 0.2

d) 0.7

3. What is the ratio of maximum deviation allowed to the modulating frequency

1. The ratio of the audio modulating frequency to the center carrier frequency
2. The ratio of the maximum carrier frequency deviation to the highest audio   modulation frequency
3. The ratio of the highest audio modulating frequency to the average audio

being used called?

4.For        percent modulating frequency

1. Percent Modulation
2. Modulation Index
3. Modulation Sideband
4. Deviation ratio

5.(Nov 1997) In the designation of bandwidth and emission, what letter in the symbol represents a double- sideband of modulation? a) C

2. A
3. B
4. H

6. What is the main function of a balanced modulator?

1. Produce balanced modulation of a carrier wave
2. Limit noise picked by a receiver
3. Produce 100% modulation
4. Suppress carrier signal in order to create a SSB or DSB

7. What     is      the     major advantage of FM over AM?

1. Less noise
2. Simple circuits
3. No interference
4. High frequency

8.A method of generating SSB signal; that utilizes only one balanced modulator circuit.

1. Phase-Shift method
2. Weaver method
3. Third method
4. Filter method

9. modulation in AM, the modulation envelope has a peak value double the unmodulated carrier level.

a) 66.67

b) 50

c) 100

d) 83.3

10. In AM, maximum desirable output of a transmitter is obtained when its modulation is %.

a) less than 100

b) 100

3. 50
4. greater than 100

11. What pattern of modulation must used when neutralizing an operating transmitter?

a) 50%

b) 10 %

c) 80%

d) 100% or over

12. The PM signal produces by an FM circuit is called

1. Direct PM
2. Indirect FM
3. Direct FM
4. Indirect PM

13. What is an application for vestigial         sideband transmission?

1. TV Broadcast
2. Telephony
3. AM Broadcast
4. FDM

14. The modulation index of an AM wave is changes from 0 to 1. The transmitter power is?

1. Increased by 50%
2. Doubled
3. Unchanged
4. Halved

15. What is the carrier power transmitted on a 75-Ω antenna if mf=2 and Vc (unmodulated) is 2 kVpk?

1. 1.29 kW
2. 12.9 kW
3. 9 kW
4. 10 kW

16.A SSB transmitter drives

121 V peak into a 50-Ω antenna. What is the PEP?

1. 292 W
2. 121 W
3. 73 W
4. 146W

17.A 1500-kHz carrier and 2 kHz intelligence signal are combined in anon-liner device. What component is present at the output?

1. 1492 kHz
2. 1502 kHz
3. all of the above

1500 kHz

19.The modulated       carrier power in FM

1. Decreases with modulating signal power
2. All of the above
3. Increases with modulating signal power
4. Is      independent     of modulating signal power

20.(Apr 1998) How does a SSB transmitter output power normally expressed?

1. Peak power
2. Average power
3. In term of peak-to-peak power
4. In term of peak envelope power

21.(Nov 1998) In radio regulation. The first symbol in the designation of radio emission is .

1. Type of modulation of the main carrier
2. Bandwidth
3. Type of information to be transmitted
4. Nature of signal(s)

22.A   2-kW  RF carrier is sinusoidally modulated 100%

. Haw much power is in one sideband?

1. 500 W
2. 125 W

c) 2000 W

d) 250 W

23. In what classes are SSB linear amplifiers operated?

1. C or D
2. D
3. B or C
4. A or AB

24. What produces splatter in an AM transmission?

1. overmodulation
2. Clipping
3. Flickering
4. Harmonics

25. An    indirect  method  of generating FM is

1. Varactor diode modulator
2. Reactance     transistor modulator
3. Armstrong modulator
4. Reactance tube modulator

26. What is the power saving when the carrier is suppressed in a regular AM signal modulated to an index of 100%?

a) 66.7 %

b) 16.7%

c) 33.3%

d) 100%

27. What is the result of overmodulation of an FM emission?

1. Higher power
2. Excessive     bandwidth distortion
3. distortion
4. Lower frequency

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

1. Less modulating power is required
2. The transmitted power is mote useful
3. Lower    bandwidth    is required
4. Better noise immunity is provided

29. What type of device can be used in balanced modulators?

1. AF, IF
2. RF, IF
3. AF, RF
4. AF, PF

30. An AM signal displayed on an oscilloscope has a maximum span of 5 V and a minimum of 1 V. What is the modulation index?

 a) 67%

b) 120%

c) 20%

d) 80%

31.(Nov 1997) Operating method in which the transmission is made alternately in each direction of a telecommunication channel.

1. Simplex operation
2. Semi-duplex operation
3. Duplex operation
4. Half duplex operation

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

1. The gain of the amplifier must be high
2. The   selectivity   of the receiver must be good.
3. There   must   be   three detectors.
4. The receiver needs to reinsert the missing carrier.

33.(Mar 1996) If the percentage of modulation of an AM amplifier is 88% and the modulation signal is 1 volt, the carrier has an amplitude of .

1. 0.88 volt
2. 1.88 volts
3. 1.14 volts
4. 0.12 volt

34.In SSB transmission, which sideband can be eliminated?

1. Lower only
2. Either
3. Upper only
4. Depends upon the use

35.(Apr 1998) A form of single sideband emission where the degree of carrier suppression enables the carrier to be reconstituted and be used for demodulation.

1. Reduced carrier single sideband emission
2. Double sideband emission
3. Half     carrier    single sideband emission
4. Full carrier single sideband emission

36.(Nov 1996) What is the type of emission used by the standard AM radio broadcast?

1. D
2. F
3. C
4. A

37.(Apr 1998) If a transmitter supplies 8 kW to the antenna when it is unmodulated, determine the total radiated power when modulated at 30%. a) 5 kW

2. 15 kW
3. 8.36 kW
4. 20 kW

38.(Nov 1997) Modulation in which the modulated wave is always present.

1. Log-periodic modulation
2. Continues modulation
3. Carrier modulation
4. Front-end

39.The     power     in     FM as the modulation index increases. a) Increases

2. Fluctuates
3. Remain constant
4. Decreases

40.(Apr 1997) Modulation means a) varying of some parameters of a carrier such as its amplitude to transmit information

2. transmit pulse in DC form on a copper wire
3. utilization of a single transmission channels to carry multiple signals
4. varying of information

41.(Nov 1998) Refers to the first symbol in an emission designation with an amplitude modulated main carrier represented by letter A.

1. Double   sideband    full carrier
2. Independent sideband
3. Double sideband
4. Single         sideband suppressed carrier

42.A system uses a deviation of 100 kHz and a modulating frequency of 15 kHz. What is the approximate bandwidth?

1. 215 kHz
2. 230 kHz
3. 115 kHz
4. 200 kHz

43.The rms antenna current for an AM transmitter increases by 15% over the unmodulated value when sinusoidal modulation is applied. Find the depth of modulation.

a) 0.6

b) 0.75

c) 0.8

d) .05

44.(Mar 1996) What is the primary advantage of DSBSC in AM?

1. It is simpler to transmit and receive than the standard AM
2. No transmitter power is wasted in the carrier
3. All of these
4. Reduce bandwidth over standard AM

45.If a 7-A carrier is modulated 100% by a sinusoidal tone, how much does the antenna current increase?

a) 66.7%

b) 22.5%

c) 33.3%

d) 44.8%

46.(Nov 1997) A single sideband emission in which the degree of carrier suppression enables the carrier to be reconstituted and to be used for demodulation.

1. Half     carrier    single sideband emission
2. Standard single sideband emission
3. Full carrier single band emission
4. Reduce carrier single sideband emission

47. What is the percent modulation of a signal in the FM broadcast band at 92 MHz with 20 kHz frequency deviation?

a) 27%

b) 72%

c) 12%

d) 60%

48. FM      has      a      major disadvantage of                       .

1. High voltage
2. Greater bandwidth
3. Low efficiency
4. Greater coverage

49. What is another term meaning     “downward modulation”?

1. Positive Carrier Shift
2. Harmonic Modulation
3. Negative Carrier Shift
4. Distortion Modulation

50. Which of the following is not an advantage of vestigial sideband transmission?

1. Reduces         power requirements
2. Reduces    transmission bandwidth
3. Easy to detect the carrier
4. Simple receiver circuitry

51. What formula determines sideband power in AM emissions?

1. Pc(m2/2)
2. Pc(m2/3)
3. Pc(m2/4)
4. Pc(m2/5)

52. In            communications systems,                      demodulation

           .

1. Is       opposite       of modulation
2. Removes sidebands
3. Is    performed  at    the transmitting station
4. Rectifies modulated signal

53. Which of the following is not a major difference between FM and AM receivers?

1. IF frequency
2. AGC
3. deemphasis
4. Limiter

54.(Nov 1996) Which symbol indicates that only one sideband is transmitted?

1. H3E
2. B8E
3. A3E
4. C3F

55.In AM, increasing the amplitude of the modulating signal, the amount of power in the information part of the transmitted   signal    is relative to the power used for the carrier.

1. Constant
2. Decreased
3. Varying
4. Increased

56.(Mar 1996) Three audio waves with 100, 200 and 300 volts amplitude respectively, simultaneously modulate a 450 volts carrier. What is the total percent of modulation of the Am wave?

a) 115.5%

b) 69%

c) 83%

d) 50%

57. What is the greatest possible modulation value without distortion?

a) 50%

b) 99.9%

c) 100%

d) 66.67%

58. What is the power saving in J3E system at 100% modulation?

a) 66.67%

b) 33.3%

c) 100%

d) 83.3%

59. What happens in standard AM transmission when no modulating signal is being transmitted?

1. There are no sidebands.
2. There are two carriers
3. There     are     several sidebands.
4. There is no signal.

60.(Nov 1998) What is the first symbol of radio signal emission having an amplitude modulated main carrier, double sideband? a) C

2. H
3. B
4. A

61. Compute the modulation index of an FM signal with a carrier swing of 10 kHz when the modulating signal is 5 kHz.

1. 4
2. 1

c) 0.5

d) 2

62. In what type of transmitters is balanced modulators used?

1. SSB
2. A3E
3. F3E
4. PM

63. What do you call a heterodyne     frequency changer?

1. Mixer
2. Modulator
3. Frequency synthesizer
4. Frequency translator

64.(Nov     1997)     An     AM

transmitter is rated 100 W at 100% modulation. How much power is required for the carrier?

a) 100 W

b) 33.33 W

c) 66.66 W

d) 83.33 W

65. What is the major requirement of the oscillators used in an SSB receiver?

1. Selectivity
2. Goof feedback
3. High frequency
4. stability

66. In FM, what determines bandwidth?

1. Modulation phase
2. Carrier power
3. Carrier frequency
4. Modulation index

67. What is the bandwidth of a narrowband FM signal generates by a 2 kHz audio signal a 110-MHz FM carrier?

1. 4 kHz
2. 1 kHz
3. 2 kHz
4. 5 kHz

68.(Nov 1998) In modulation technique, which of the following is referred to audible pitch?

1. Frequency
2. Harmonic
3. Width
4. Amplitude

69. To what feature of the modulating tone is FM deviation proportional?

1. Frequency
2. Amplitude
3. Harmonics
4. Phase

70. In Frequency Modulation

           .

1. The amplitude of the carrier according to the amplitude of the modulating signal
2. The frequency of carrier varies according to the frequency of the modulating signal
3. The frequency of carrier varies according to the amplitude       of         the modulating signal
4. The frequency of carrier varies according to the phase of the modulating signal

71. In a transmitted AM wave, state where the information is contained?

1. Carrier
2. Sidebands
3. Modulating signal
4. Envelope

72. An 88-MHz carrier is modulated by an audio tone that caused a frequency deviation of 15 kHz. What is the carrier swing of this FM signal?

1. 30 kHz
2. 60 kHz
3. 45 kHz
4. 15 kHz

73.A system has 150 kHz of bandwidth available for a 10- kHz modulating signal. What is the approximate deviation?

1. 75 kHz
2. 65 kHz
3. 70 kHz
4. 100 kHz

74. When the modulating frequency is halved, the modulation index is doubled and the modulating voltage remains constant. The type of modulation is

1. AM
2. PCM
3. FM
4. PM

75. For an AM signal modulated to a depth of 100% by a pure tone, the power is the power of unmodulated carrier.

1. 3 / 2 times
2. less than
3. twice as
4. Same as

76. What is the shape of a trapezoidal pattern at 100% modulation?

1. Circle
2. Square
3. Rectangle
4. Triangle

77. The total power content of an AM signal is 600 W. What is the percentage modulation if each sideband contains 100 W?

a) 33.3%

b) 66.7%

c) 100%

d) 83.3%

78. Which of the following is an advantage of PM over FM?

1. One amplifier is required
2. Requires    a    simpler transmitter
3. Requires    a     complex circuitry
4. A    need    for    several modulators

79. The antenna current of an AM transmitter is 6.2 A when unmodulated and rises to 6.7 A when modulated. What is the %m?

a) 42.8%

b) 67%

c) 57.9%

d) 51%

80.(Mar 1996) In the phase shift method, how many circuits must be balanced?

1. None of these
2. 4
3. 1
4. 2

81.In a 5-kW AM transmitter high-level modulation is used. What is the value of the audio signal power needed for 100 percent modulation?

1. 5 kW
2. 15 kW
3. 50 kW
4. 2.5 kW

82.(Nov 1997) The third symbol in the designation of radio emission under the IYU rules refers to

1. bandwidth
2. type of information to be transmitted
3. type of modulation of the main carrier
4. nature             of signal(s)modulating the main carrier

83. Which of the following is not a continuous wave modulation?

1. AM
2. PM
3. PCM
4. FM

84. Determine   the     power saving in percent when the carrier is suppressed in an AM signal modulated to 80% a) 75.8%

b) 100%

c) 66.7%

d) 80%

85.A radio transmitter is rated as having a frequency accuracy of ±0.2 parts per million. What is the maximum frequency error at 150 MHz?

1. ±7.5 Hz
2. ±20 Hz
3. ±30 Hz
4. ±150 Hz

86. An FM signal with modulation index m is applied to a frequency tripler. The modulation index at the output is .

1. 0
2. 3m
3. m / 2
4. m

87. For an FM transmitter, the initial carrier frequency is 8 MHz with a frequency deviation of 1 kHz. If the total frequency multiplication of the transmitter is 12, determine the final; frequency deviation.

1. 120 kHz
2. 1 kHz
3. 12 kHz
4. 8 MHz

88. What factor(s) determine the modulation index of an FM signal?

1. Amplitude of the carrier
2. c and d are true
3. Frequency deviation
4. Frequency     of      the modulation signal

89. An AM transmission of 1000 W is fully modulated. Calculate            the       power transmitted as a SSB signal. a) 1000 W

2. 333 W
3. 667 W
4. 167 W

90. What will the normal AM receiver detect from an unmodulated RF AC wave?

1. Nothing
2. AF signal
3. Carrier
4. noise

91. The rms antenna current of a radio transmitter is 10 A when unmodulated, rising to

12 A when the carrier is sinusoidally modulated. What is the modulation factor?

a) 1

b) 0.83

c) 0.67

d) 0.94

92.(Mar 1996) The letter- number designation B8E is a form of modulation also known as .

1. Pilot-carrier system
2. Lincompex
3. Independent sideband emission
4. Vestigial      sideband transmission