MCQs in Modulation Part XIX

This is the Multiples Choice Questions Part 19 of the Series in Modulation as one of the Communications Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies, Communications Books, Journals and other Communications References.

Online Questions and Answers Topic Outline

• MCQs in Amplitude Modulation
• MCQs in Phase Modulation
• MCQs in Sound Pressure Level
• MCQs in Frequency Modulation
• MCQs in Pulse Modulation

MCQs in Modulation Series

Following is the list of multiple choice questions in this brand new series:

Modulation MCQs

PART 1: MCQs from Number 1 – 50                        Answer key: PART I

PART 2: MCQs from Number 51 – 100                   Answer key: PART II

PART 3: MCQs from Number 101 – 150                 Answer key: PART III

PART 4: MCQs from Number 151 – 200                 Answer key: PART IV

PART 5: MCQs from Number 201 – 250                 Answer key: PART V

PART 6: MCQs from Number 251 – 300                 Answer key: PART VI

PART 7: MCQs from Number 301 – 350                 Answer key: PART VII

PART 8: MCQs from Number 351 – 400                 Answer key: PART VIII

PART 9: MCQs from Number 401 – 450                 Answer key: PART IX

SEE: More Questions and Answers in Modulation

PART 19: MCQs from Number 901 – 950                 Answer key: PART XIX

Continue Practice Exam Test Questions Part XIX of the Series

901. The principal circuit in the popular 1496/1596 IC balanced modulator is a

• a. Differential amplifier
• b. Rectifier
• c. Bridge
• d. Constant current source

902. The most commonly used filter in SSB generators uses

• a. LC network
• b. Mechanical resonators
• c. Crystals
• d. RC networks and op amps

903. The equivalent circuit of a quartz crystal is a

• a. Series resonant circuit
• b. Parallel resonant circuit
• c. Neither a nor b
• d. Both a and b

904. A crystal lattice filter has crystal frequencies of 27.5 and 27.502 MHz. The bandwidth is approximately

• a. 2 kHz
• b. 3kHz
• c. 27.501 MHz
• d. 55.502 MHz

905. An SSB generator has a sideband filter centered at 3.0 MHz. The modulating signal is 3 kHz. To produce both upper and lower sidebands, the following carrier frequencies must be produced:

• a. 2.7 and 3.3 MHz
• b. 3.3 and 3.6 MHz
• c. 2997 and 3003 kHz
• d. 3000 and 3003 kHz

906. In the phasing method of SSB generation, one sideband is canceled due to

• a. Phase shift
• b. Sharp selectivity
• c. Carrier suppression
• d. Phase inversion

907. A balanced modulator used to demodulate a SSB signal is called a(n)

• a. Transporter
• b. Product detector
• c. Converter
• d. Modulator

908. Frequency translation is done with a circuit called a

• a. Summer
• b. Multiplier
• c. Filter
• d. Mixer

909. The inputs to a mixer are f_o and f_m. In down conversion, which of the following mixer output signals is selected?

• a. F_o
• b. F_m
• c. F_o – f_m
• d. F_o + f_m

910. Mixing for frequency conversion is the same as

• a. Rectification
• b. AM
• c. Linear summing
• d. Filtering

911. Which of the following can be used as a mixer?

• a. Balanced modulator
• b. FET
• c. Diode modulator
• d. All the above

912. The desired output from a mixer is usually selected with a

• a. Phase-shift circuit
• b. Crystal filter
• c. Resonant circuit
• d. Transformer

913. The amount of frequency deviation from the carrier center frequency in an FM transmitter is proportional to what characteristic of the modulating signal?

• a. Amplitude
• b. Phase
• c. Angle
• d. Duty Cycle

914. Both FM and PM are types of what kind of modulation?

• a. Amplitude
• b. Phase
• c. Angle
• d. Duty Cycle

915. If the amplitude of the modulating signal decreases, the carrier deviation

• a. Increases
• b. Decreases
• c. Remains constant
• d. Both b and c

916. In PM, a frequency shift occurs while what characteristic of the modulating signal is changing?

• a. Shape
• b. Phase
• c. Frequency
• d. Amplitude

917. Maximum frequency deviation of a PM signal occurs at

• a. Zero crossing points
• b. Peak positive amplitude
• c. Peak negative amplitude
• d. Peak positive or negative amplitudes

918. A 100-MHz carrier is deviated 50 KHz by a 4 kHz signal. The modulation index is

• a. 5
• b. 8
• c. 12.5
• d. 40

919. The maximum deviation of an FM carrier is 2 kHz by a maximum modulating signal of 400 Hz. The deviation ratio is

• a. 0.2
• b. 5
• c. 8
• d. 40

920. According the Nyquist theorem, the sampling rate that can be used in a PCM system is _____ the highest audio frequency

• a. Once
• b. Eight times
• c. Twice
• d. Thrice

921. SSB transmission requires only _______ of the bandwidth for a DSBFC

• a. ¼
• b. 2/3
• c. ½
• d. ¾

922. Which of the following pulse modulation systems is analog?

• a. Delta
• b. Differential PCM
• c. PWM
• d. PCM

923. Which of the following is not a major benefit of FM over AM?

• a. Greater efficiency
• b. Noise immunity
• c. Capture Effect
• d. Lower Complexity and Cost

924. The primary disadvantage of FM is it

• a. Higher cost and complexity
• b. Excessive use of spectrum space
• c. Noise susceptibility
• d. Lower efficiency

925. The phenomenon of a strong FM signal dominating weaker signal on a common frequency is referred to as the

• a. Capture effect
• b. Blot out
• c. Quieting factor
• d. Dominating syndrome

926. If the plate supply voltage for a plate-modulated class C amplifier is E, the maximum plate-cathode voltage could be almost as high as

• a. 4E
• b. 3E
• c. 2E
• d. E

927. In a low-level AM system, amplifiers following the modulated stage must be

• a. Linear devices
• b. Harmonic devices
• c. Class C amplifiers
• d. Nonlinear devices

928. If the carrier of a 100 percent modulated AM wave is suppressed, the percentage power saving will be

• a. 50
• b. 150
• c. 100
• d. 66.66

929. Leak-type bias is used in a plate-modulated class C amplifier to

• a. Prevent tuned circuit damping
• b. Prevent excessive grid current
• c. Prevent overmodulation
• d. Increase the bandwidth

930. The output stage of a television transmitter is most likely to be a

• a. Plate-modulated class C amplifier
• b. Grid-modulated class C amplifier
• c. Screen-modulated class C amplifier
• d. Grid-modulated class A amplifier

931. The modulation index of an AM wave is changed from 0 to 1. The transmitted power is

• a. Unchanged
• b. Halved
• c. Doubled
• d. Increased by 50 percent

932. One of the advantages of base modulation over collector modulation of a transistor class C amplifier is

• a. The lower modulating power required
• b. Higher power output per transistor
• c. Better efficiency
• d. Better linearity

933. A carrier simultaneously modulated by two sine waves with modulation indices of 0.3 and 0.4; the total modulation index

• a. 1
• b. 0.5
• c. 0.7
• d.  Cannot be calculated unless the phase relations are known

934. In the stabilized reactance modulator AFC system,

• a. The discriminator must have a fast time constant to prevent demodulation
• b. The higher the discriminator frequency, the better the oscillator frequency stability
• c. The discriminator frequency must not be too low, or the system will fail
• d. Phase modulation is converted into FM by the equalizer circuit

935. In the spectrum of a frequency of a frequency-modulated wave

• a. The carrier frequency disappears when the modulation index is large
• b. The amplitude of any sideband depends on the modulation index
• c. The total number of sidebands depends on the modulation index
• d. The carrier frequency cannot disappear

936. The difference between phase and frequency modulation

• a. Is purely theoretical because they are the same in practice
• b. Is too great to make the two systems compatible
• c. Lies in the poorer audio response of phase modulation
• d. Lies in the different definitions of the modulation index

937. Indicate the false statement regarding the Armstrong modulation system.

• a. The system is basically phase, not frequency, modulation
• b. AFC is not needed, as a crystal oscillator is used
• c. Frequency multiplication must be used
• d. Equalization is unnecessary

938. An FM signal with a modulation index m_f is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of

• a. m_f/3
• b. m_f
• c. 3 m_f
• d. _9mf

939. An FM signal with a deviation δ is passed through a mixer, and has its frequency reduced fivefold. The deviation in the output of the mixer is

• a. 5 δ
• b. δ
• c. δ/5
• d. Indeterminate

940. A pre-emphasis circuit provides extra noise immunity by

• a. Boosting the bass frequencies
• b. Amplifying the higher audio frequencies
• c. Pre-amplifying the whole audio band
• d. Converting the phase modulation to FM

941. Since noise phase modulates the FM wave, as the noise sideband frequency approaches the carrier frequency, the noise amplitude

• a. Remains constant
• b. Decreased
• c. Increased
• d. Equalized

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

• a. Amplitude modulation
• b. Phase modulation
• c. Frequency modulation
• d. Any of the three

943. Indicate which one of the following is not an advantage of FM over AM

• a. Better noise immunity is provided
• b. Lower bandwidth is required
• c. The transmitted power is more useful
• d. Less modulating power is required

944. One of the following is an indirect way of generating FM. This is the

• a. Reactance FET modulator
• b. Varactor diode modulator
• c. Armstrong modulator
• d. Reactance bipolar transistor modulator

945. Indicate the false statement regarding the advantages of SSB over double-sideband, full-carrier AM.

• a. More channel space is available
• b. Transmitter circuits must be more stable, giving better reception
• c. The signal is more noise resistance
• d. Much less power is required for the same signal strength

946. When the modulation index of an AM wave is doubled, the antenna current is also doubled. The AM system being used is

• a. A3H
• b. A5C
• c. A3J
• d. A3

947. Indicate which of the following advantages of the phase cancellation method of obtaining SSB over the filter method is false

• a. Switching from one sideband to the other is simpler
• b. It is possible to generate SSB at any frequency
• c. SSB with lower audio frequencies present can be generated
• d. There are more balanced modulators; therefore the carrier is suppressed better

948. The most commonly used filter in SSB generation are

• a. Mechanical
• b. RC
• c. LC
• d. Low- pass

949. Indicate in which one of the following only one sideband is transmitter

• a. A3H
• b. A3
• c. A3B
• d. A5C

950. A3A 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.

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