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# MCQ in Modulation Part 19 | ECE Board Exam

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.

#### MCQ Topic Outline included in ECE Board Exam Syllabi

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

#### Continue Practice Exam Test Questions Part 19 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

Solution:

902. The most commonly used filter in SSB generators uses

a. LC network

b. Mechanical resonators

c. Crystals

d. RC networks and op amps

Solution:

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

Solution:

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

a. 2 kHz

b. 3 kHz

c. 27.501 MHz

d. 55.502 MHz

Solution:

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

Solution:

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

Solution:

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

a. Transporter

b. Product detector

c. Converter

d. Modulator

Solution:

908. Frequency translation is done with a circuit called a

a. Summer

b. Multiplier

c. Filter

d. Mixer

Solution:

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

a. Fo

b. Fm

c. Fo โ fm

d. Fo + fm

Solution:

910. Mixing for frequency conversion is the same as

a. Rectification

b. AM

c. Linear summing

d. Filtering

Solution:

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

a. Balanced modulator

b. FET

c. Diode modulator

d. All the above

Solution:

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

a. Phase-shift circuit

b. Crystal filter

c. Resonant circuit

d. Transformer

Solution:

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

Solution:

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

a. Amplitude

b. Phase

c. Angle

d. Duty Cycle

Solution:

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

a. Increases

b. Decreases

c. Remains constant

d. Both b and c

Solution:

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

a. Shape

b. Phase

c. Frequency

d. Amplitude

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

a. ยผ

b. 2/3

c. ยฝ

d. ยพ

Solution:

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

a. Delta

b. Differential PCM

c. PWM

d. PCM

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

a. mf/3

b. mf

c. 3 mf

d. 9mf

Solution:

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

a. 5 ฮด

b. ฮด

c. ฮด/5

d. Indeterminate

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

948. The most commonly used filter in SSB generation are

a. Mechanical

b. RC

c. LC

d. Low- pass

Solution:

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

a. A3H

b. A3

c. A3B

d. A5C

Solution:

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.

Solution:

#### Questions and Answers in Modulation Series

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

MCQ in Modulation
PART 1: MCQ from Number 1 โ 50                        Answer key: PART 1
PART 2: MCQ from Number 51 โ 100                   Answer key: PART 2
PART 3: MCQ from Number 101 โ 150                 Answer key: PART 3
PART 4: MCQ from Number 151 โ 200                 Answer key: PART 4
PART 5: MCQ from Number 201 โ 250                 Answer key: PART 5
PART 6: MCQ from Number 251 โ 300                 Answer key: PART 6
PART 7: MCQ from Number 301 โ 350                 Answer key: PART 7
PART 8: MCQ from Number 351 โ 400                 Answer key: PART 8
PART 9: MCQ from Number 401 โ 450                 Answer key: PART 9
PART 10: MCQ from Number 451 โ 500                 Answer key: PART 10

### Complete List of MCQ in Communications Engineering per topic

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