MCQ in Electronics - Modulation

BSECE Board Examination Reviewer in Communications Engineering - Modulation

1.The bandwidth in _____ depends on the number of significant sidebands. a) FCM b) QAM c) Delta Modulation d) Frequency Modulation 2.What is the ratio of maximum deviation allowed to the modulating frequency being used called? a) Percent Modulation b) Modulation Index c) Modulation Sideband d) Deviation ratio 3.(Nov 1997) In the designation of bandwidth and emission, what letter in the symbol represents a doublesideband of modulation? a) C b) A c) B d) H 4.What is the main function of a balanced modulator? a) Produce balanced modulation of a carrier wave b) Limit noise picked by a receiver c) Produce 100% modulation d) Suppress carrier signal in order to create a SSB or DSB 5.What is the major advantage of FM over AM? a) Less noise b) Simple circuits c) No interference d) High frequency 6.A method of generating SSB signal; that utilizes only one balanced modulator circuit. a) Phase-Shift method b) Weaver method c) Third method d) Filter method

7.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 8.For _____ percent 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 9.In AM, maximum desirable output of a transmitter is obtained when its modulation is _____%. a) less than 100 b) 100 c) 50 d) greater than 100 10.What pattern of modulation must used when neutralizing an operating transmitter? a) 50% b) 10 % c) 80% d) 100% or over 11.The PM signal produces by an FM circuit is called a) Direct PM b) Indirect FM c) Direct FM d) Indirect PM

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 modulation frequency c) The ratio of the highest audio modulating frequency to the average audio modulating frequency d) The ratio of the carrier center frequency to the audio modulating frequency 13.What is an application for vestigial sideband transmission? a) TV Broadcast b) Telephony c) AM Broadcast d) FDM 14.The modulation index of an AM wave is changes from 0 to 1. The transmitter power is? a) Increased by 50% b) Doubled c) Unchanged d) Halved 15.What is the carrier power transmitted on a 75- Ω 75-Ω antenna if mf=2 and Vc (unmodulated) is 2 kVpk? a) 1.29 kW b) 12.9 kW c) 9 kW d) 10 kW 16.A SSB transmitter drives 121 V peak into a 50-Ω 50-Ω antenna. What is the PEP? a) 292 W b) 121 W c) 73 W d) 146W

12.(Nov 1998) What is meant by the term deviation ratio?

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

17.A 1500-kHz carrier and 2 kHz intelligence signal are combined in anon-liner device. What component is present at the output? a) 1492 kHz b) 1502 kHz c) all of the above d) 1500 kHz 18.(Mar 1996) What is the difference between phase and frequency modulation? a) Os too great to make two systems compatible b) Is purely theoretical because they are the same in practice c) Lies in poorer audio response of phase modulation d) Lies in the different definitions of the modulation index 19.The modulated carrier power in FM a) Decreases with modulating signal power b) All of the above c) Increases with modulating signal power d) Is independent of modulating signal power 20.(Apr 1998) How does a SSB transmitter output power normally expressed? a) Peak power b) Average power c) In term of peak-to-peak power d) In term of peak envelope power 21.(Nov 1998) In radio regulation. The first symbol in the designation of radio emission is _____. a) Type of modulation of the main carrier b) Bandwidth c) Type of information to be transmitted d) Nature of signal(s)

22.A 2-kW RF carrier is sinusoidally modulated 100% . Haw much power is in one sideband? a) 500 W b) 125 W c) 2000 W d) 250 W 23.In what classes are SSB linear amplifiers operated? a) C or D b) D c) B or C d) A or AB 24.What produces splatter in an AM transmission? a) overmodulation b) Clipping c) Flickering d) Harmonics 25.An indirect method of generating FM is a) Varactor diode modulator b) Reactance transistor modulator c) Armstrong modulator d) 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? a) Higher power b) Excessive bandwidth distortion c) distortion d) Lower frequency

28.Which of the following is not an advantage of FM over  AM? a) Less modulating power is required b) The transmitted power is mote useful c) Lower bandwidth is required d) Better noise immunity is provided 29.What type of device can be used in balanced modulators? a) AF, IF b) RF, IF c) AF, RF d) 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. a) Simplex operation b) Semi-duplex operation c) Duplex operation d) Half duplex operation 32.What is the main problem in receiving a suppressed carrier transmission or a single sideband transmission? a) The gain of the amplifier must be high b) The selectivity of the receiver must be good. c) There must be three detectors. d) The receiver needs to reinsert the missing carrier.

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

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 _____. a) 0.88 volt b) 1.88 volts c) 1.14 volts d) 0.12 volt 34.In SSB transmission, which sideband can be eliminated? a) Lower only b) Either c) Upper only d) 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. a) Reduced carrier single sideband emission b) Double sideband emission c) Half carrier single sideband emission d) Full carrier single sideband emission 36.(Nov 1996) What is the type of emission used by the standard AM radio broadcast? a) D b) F c) C d) 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 b) 15 kW c) 8.36 kW d) 20 kW

38.(Nov 1997) Modulation in which the modulated wave is always present. a) Log-periodic modulation b) Continues modulation c) Carrier modulation d) Front-end 39.The power in FM _____ as the modulation index increases. a) Increases b) Fluctuates c) Remain constant d) Decreases 40.(Apr 1997) Modulation means a) varying of some parameters of a carrier such as its amplitude to transmit information b) transmit pulse in DC form on a copper wire c) utilization of a single transmission channels to carry multiple signals d) 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. a) Double sideband full carrier b) Independent sideband c) Double sideband d) 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? a) 215 kHz b) 230 kHz c) 115 kHz d) 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? a) It is simpler to transmit and receive than the standard AM b) No transmitter power is wasted in the carrier c) All of these d) 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. a) Half carrier single sideband emission b) Standard single sideband emission c) Full carrier single band emission d) Reduce carrier single sideband emission

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

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 _____. a) High voltage b) Greater bandwidth c) Low efficiency d) Greater coverage 49.What is another term meaning “downward modulation”? a) Positive Carrier Shift b) Harmonic Modulation c) Negative Carrier Shift d) Distortion Modulation 50.Which of the following is not an advantage of vestigial sideband transmission? a) Reduces power requirements b) Reduces transmission bandwidth c) Easy to detect the carrier d) Simple receiver circuitry 51.What formula determines sideband power in AM emissions? a) Pc(m2/2) b) Pc(m2/3) c) Pc(m2/4) d) Pc(m2/5) 52.In communications systems, demodulation  ______. a) Is opposite of modulation b) Removes sidebands c) Is performed at the transmitting station d) Rectifies modulated signal

53.Which of the following is not a major difference between FM and AM receivers? a) IF frequency b) AGC c) deemphasis d) Limiter 54.(Nov 1996) Which symbol indicates that only one sideband is transmitted? a) H3E b) B8E c) A3E d) 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. a) Constant b) Decreased c) Varying d) 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? a) There are no sidebands. b) There are two carriers c) There are several sidebands. d) 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 b) H c) B d) A 61.Compute the modulation index of an FM signal with a carrier swing of 10 kHz when the modulating signal is 5 kHz. a) 4 b) 1 c) 0.5 d) 2 62.In what type of transmitters is balanced modulators used? a) SSB b) A3E c) F3E d) PM 63.What do you call a heterodyne frequency changer? a) Mixer  b) Modulator c) Frequency synthesizer d) Frequency translator

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

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? a) Selectivity b) Goof feedback c) High frequency d) stability 66.In FM, what determines bandwidth? a) Modulation phase b) Carrier power c) Carrier frequency d) Modulation index 67.What is the bandwidth of a narrowband FM signal generates by a 2 kHz audio signal a 110-MHz FM carrier? a) 4 kHz b) 1 kHz c) 2 kHz d) 5 kHz 68.(Nov 1998) In modulation technique, which of the following is referred to audible pitch? a) Frequency b) Harmonic c) Width d) Amplitude 69.To what feature of the modulating tone is FM deviation proportional? a) Frequency b) Amplitude c) Harmonics d) Phase

70.In Frequency Modulation  ______. a) The amplitude of the carrier according to the amplitude of the modulating signal b) The frequency of carrier varies according to the frequency of the modulating signal c) The frequency of carrier varies according to the amplitude of the modulating signal d) 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? a) Carrier b) Sidebands c) Modulating signal d) 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? a) 30 kHz b) 60 kHz c) 45 kHz d) 15 kHz 73.A system has 150 kHz of bandwidth available for a 10kHz modulating signal. What is the approximate deviation? a) 75 kHz b) 65 kHz c) 70 kHz d) 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 a) AM b) PCM c) FM d) PM 75.For an AM signal modulated to a depth of 100% by a pure tone, the power is _____ the power of unmodulated carrier. a) 3 / 2 times b) less than c) twice as d) Same as 76.(Nov 1998) A third symbol emission which represent television. (0 correct answers) a) F b) A c) D d) C

77.What is the shape of a trapezoidal pattern at 100% modulation? a) Circle b) Square c) Rectangle d) Triangle 78.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%

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

79.Which of the following is an advantage of PM over FM? a) One amplifier is required b) Requires a simpler transmitter c) Requires a complex circuitry d) A need for several modulators 80.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% 81.(Mar 1996) In the phase shift method, how many circuits must be balanced? a) None of these b) 4 c) 1 d) 2 82.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? a) 5 kW b) 15 kW c) 50 kW d) 2.5 kW 83.(Nov 1997) The third symbol in the designation of radio emission under the IYU rules refers to a) bandwidth b) type of information to be transmitted c) type of modulation of the main carrier d) nature of signal(s)modulating the main carrier

84.Which of the following is not a continuous wave modulation? a) AM b) PM c) PCM d) FM 85.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% 86.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? a) ±7.5 Hz b) ±20 Hz c) ±30 Hz d) ±150 Hz 87.An FM signal with modulation index m is applied to a frequency tripler. The modulation index at the output is _____. a) 0 b) 3m c) m / 2 d) m 88.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. a) 120 kHz b) 1 kHz c) 12 kHz d) 8 MHz

89.What factor(s) determine the modulation index of an FM signal? a) Amplitude of the carrier b) c and d are true c) Frequency deviation d) Frequency of the modulation signal 90.An AM transmission of 1000 W is fully modulated. Calculate the power transmitted as a SSB signal. a) 1000 W b) 333 W c) 667 W d) 167 W 91.What will the normal AM receiver detect from an unmodulated RF AC wave? a) Nothing b) AF signal c) Carrier d) noise 92.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 93.(Mar 1996) The letternumber designation B8E is a form of modulation also known as _____. a) Pilot-carrier system b) Lincompex c) Independent sideband emission d) Vestigial sideband transmission

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

94.For an FM signal in the 88-108-MHz broadcast band with a frequency deviation of 15 kHz, determine the percent modulation. a) 20% b) 60% c) 40% d) 80%

100.(Nov 1997) A good example of a pilot tone system used in commercial frequency modulation stations. a) Frequency modulation b) Stereo multiplexing c) Time division d) FDM

105.In FM for a given frequency deviation, the modulation index varies  _____ with the modulating frequency. a) Independently b) Inversely c) Directly d) Equally

95.What are the le7tternumber designations of carrier and one SB? a) A3E b) F3E c) H3E d) J3E

101.The circuit used for producing a double sideband suppressed carrier type of  AM signal is called _____. a) AGC b) Balances modulator c) Mixer d) PLL

106.What is the maximum power output of a CB A3E emission? a) 4 W b) 10 kW c) 10 W d) 3 kW

96.FM system is superior to  AM because a) It produces more rock music b) It has wider bandwidth c) It is at VHR band d) It eliminates most of amplitude variation noise 97.Calculate the modulating frequency that causes an FM signal to have a bandwidth of 50 kHz when its frequency deviation is 15 kHz. a) 50 kHz b) 40 kHz c) 20 kHz d) 10 kHz 98.During 100% modulation, what percentage of the average output power is in the sidebands? a) 100% b) 16.67% c) 66.67% d) 33.3% 99.The total transmitted power for an AM signal is 1200 W at 100% modulation. What is the power for each sideband? a) 1200 W b) 100 W c) 200 W d) 1000 W

102.If an FM transmitter has two doublers and one tripler, what is the carrier swing when the oscillator deviates 2 kHz? a) 24 kHz b) 2 kHz c) 48 kHz d) 36 kHz 103.In FM, what produces the sidebands? a) Carrier and its harmonics b) RF signal c) Carrier signal d) Modulating signal 104.In Phase Modulation (PM), the modulation index represents ______. a) The ratio of the modulation amplifier to the carrier amplitude b) The maximum phase shift c) The maximum frequency deviation d) The total number of sidebands

107.(Nov 1996) The output of a balanced modulator is  _____. a) LSB and USB b) USB c) Carrier d) LSB 108.The purpose of the balances modulator circuits is to eliminate the _____. a) Distortion b) Sidebands c) Noise d) Carrier 109.(Apr 1998) Refers to an emission designation for facsimile. a) A3C and F3C b) R3E and A3E c) J3E and F4E d) A3J and A4E 110.Which produces greater interference, overmodulated positive or negative peaks? a) Negative b) neither c) Positive d) either

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

111.(Apr 1997) Which transmit only sideband? a) H3E b) 3AJ c) A3E d) 11BE 112.What is the main feature of DSB transmission? a) Narrow bandwidth b) High reliability c) High voltage d) Carrier is suppressed 113.A 100-V carrier is amplitude modulated by a 1kHz sine wave. What is the side-frequency amplitude when m=0.75? a) 75 V b) 18.75 V c) 100 V d) 37.5 V 114.An SSB contains 30 kW. The power content of the carrier is _____ kW. a) 30 b) 0 c) 20 d) 10 115.What stage in an AM transmitter creates its own sine wave? a) Buffer b) Modulator c) Oscillator d) Amplifier 116.(Nov 1996) frequency and modulation utilizes modulation. a) AM and Fm b) Phase c) angle d) Digital

Both phase _____

117.The major difference between FM and PM a) Lies in the poorer audio response of phase modulation index b) All of the above c) Lies in the different definition of modulation index d) Is too great to make the two system compatible 118.(Apr 1998) The final power amplifier in an FM y=transmitter usually operates class _____. a) B b) C c) A d) AB 119.What percent of the radiated power is in the sidebands with 50% sinusoidal modulation (AM)? a) 16.67% b) 33% c) 11% d) 20% 120.What determine the bandwidth of a transmitted  AM signal? a) The lowest modulation amplitude b) The highest frequency component of the modulating signal c) The lowest frequency component of the intelligence d) The maximum modulation amplitude 121.(Nov 1998) The third symbol radio emission which represent telephone transmission including sound broadcasting. a) F b) C c) E d) W

122.What is the letter-number designation for an FM facsimile? a) F3C b) A3E c) C3C d) F3E 123.An unmodulated carrier is 300 VP-P. Calculate %m when its maximum p-p value reaches 400 V. a) 100% b) 33.3% c) 66.67% d) 83.3% 124.What is the percent modulation of an AM wave that has a power content of 12 kW in each sideband when modulated by a single tone? a) 30% b) 66% c) 82% d) 75% 125.(Nov 1997) The first symbol in the designation of radio emission under the ITU rules refers to a) bandwidth b) type of modulation of the main carrier c) nature of signal(s) modulating the main carrier d) type of information to be transmitted 126.What constitutes the input to an AM transmitter? a) Mixer and amplifier b) Mixer and local oscillator c) Buffer and IF amplifier d) RF oscillator and/or audio amplifier 127.When a carrier is frequency-modulated, what is developed on both sides carrier? a) Carrier b) Envelope c) Noise d) sidebands

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

128.If the 500-Hz modulation of a 1-MHz carrier has 3rd harmonic distortion, what is the emission bandwidth? a) 3 kHz b) 1 kHz c) 1500 Hz d) 1 MHz 129.(Apr 1997) 100% modulation inn AM means a corresponding increase in total power by _____. a) 50% b) 100% c) 25% d) 75% 130.A modulation technique commonly used for low-cost digitization of voice signals. a) A3 b) F3 c) A5C d) A0 131.For a 75-MHz FM carrier modulated by 5-kHZ audio tone that causes a frequency deviation of 15 kHz, determine the FM signal bandwidth. a) 200 kHz b) 100 kHz c) 80 kHz d) 40 kHz 132.(Mar 1996) In AM, the carrier carries _____ intelligence. a) No b) Distorted c) Same d) Difference 133.(Nov 1998) In amplitude modulation technique the unmodulated carrier is referred as having _____. a) 50% modulated b) over modulated c) 0% modulation d) 100% modulation

134.Modulating two waves of the same frequency but with  _____. a) 90° b) 180° c) 45° d) 360° 135.For an unmodulated carrier of 1000V and a modulated peak value of 1800 V, what is the modulation index? a) 0.7 b) 0.8 c) 0.9 d) 0.5 136.What factor determines the modulation index of an FM transmission? a) Carrier frequency b) Carrier phase c) Modulating signal frequency d) Carrier amplitude 137.(Mar 1996) Which of the following pulse modulation systems is analog? a) PCM b) Differential PCM c) Delta d) PWM 138.With _____, the modulation envelope is an expression of the amplitude and frequency of the modulation signal. a) AM b) FM c) PCM d) PM 139.(Apr 1998) emission C3F? a) Television b) Facsimile c) RTTY d) Modulated CW

What

is

140.An FM signal has a frequency deviation of 2000 Hz caused by modulating signal of 500 Hz. What is the modulation index? a) 2 b) 8 c) 5 d) 4 141.(Apr 1998) Which of the following refers to a double side band full carrier? a) A3E b) A3J c) F3 d) R3A 142.What is the maximum power that can be contained in the sideband without distortion? a) 50% b) 25% c) 66.67% d) 16.67% 143.What is the amount of carrier swing necessary to produce an 80% modulation for the audio portion of the TV band? a) 20 kHz b) 25 kHz c) 50 kHz d) 40 kHz 144.A DSB-SC system must suppress the carrier by 50 dB from its original value of 10 W. To what value must the carrier be reduced? a) 0.1 W b) 0.001 W c) 0.0001 W d) 0.01W 145.What is the following is not a product of overmodulation? a) Image b) Spurious signal c) Buckshot d) Splatter

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BSECE Board Examination Reviewer in Communications Engineering - Modulation

146.(Nov 1996) Which determines the number of sideband components in FM? a) Modulation frequency b) Modulation index c) Carrier frequency d) All of these 147.For an FM signal a) The total number of sidebands depends on the modulation frequency the carrier frequency b) The carrier frequency cannot disappear c) The carrier frequency disappears when the modulation index is large d) The amplitude of any sideband depends on the modulation index

ARVIN

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