# MCQ in Modulation Part 14 | ECE Board Exam

(Last Updated On: April 18, 2020) This is the Multiples Choice Questions Part 14 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 14 of the Series

651. He developed the first successful FM radio system

a. B.E.Alpine

b. N.S. Kapany

c. E.H. Armstrong

d. A.C.S. Van Heel

Solution:

652. Results whenever the phase angle of sinusoidal wave is varied with respect to time

a. angle modulation

b. digital modulation

c. amplitude modulation

d. pulse modulation

Solution:

653. In the spectrum of a frequency -modulated wave

a. the carrier frequency disappears with a large modulation index

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:

654.What is the frequency swing of an FM broadcast transmitter when modulated 60%

a. 60 kHz

b. 45 kHz

c. 30 kHz

d. 25 kHz

Solution:

655. Varying the frequency of a constant -amplitude carrier directly proportional to the amplitude to the modulating signal at a rate equal to the frequency of the modulating signal

a. amplitude modulation

b. angle modulation

c. phase modulation

d. frequency modulation

Solution:

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

a. amplitude

b. frequency

c. phase

d. shape

Solution:

657. It is a modulation where the angle of a wave carrier is varied from its reference value

a. amplitude modulation

b. angle modulation

c. analog modulation

d. digital modulation

Solution:

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

a. amplitude

b. phase

c. angle

d. duty cycle

Solution:

659. Varying the phase of a constant amplitude carrier displacement proportional to the amplitude of the modulating signal at a rate equal to the frequency of the modulating signal.

a. amplitude modulation

b. angle modulation

c. phase modulation

d. frequency modulation

Solution:

660. 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 responses of phase modulation

d. lies in the different definitions of the modulation index

Solution:

661. The relative angular displacement of the carrier phase in radians with respect to the reference phase is called __________.

a. phase deviation

b. carrier deviation

c. frequency deviation

d. information deviation

Solution:

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

a. increases

b. decreases

c. remains constant

d. goes to zero

Solution:

663. On an FM signal, maximum deviation occurs at what point on the modulating signal?

a. zero-crossing points

b. peak positive amplitudes

c. peak negative amplitude

d. both peak positive and negative amplitudes

Solution:

664. The amount of oscillator frequency increase and decrease around the carrier frequency is called _________.

a. frequency deviation

b. phase shift

c. intelligence frequency

d. baseband

Solution:

665. The relative displacement of the carrier frequency in hertz in respect to its unmodulated value is called _____________.

a. frequency deviation

b. phase deviation

c. information deviation

d. carrier deviation

Solution:

666. 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:

667. It is the instantaneous change in phase of the carrier at a given instant of time and indicates how much phase of the carrier is changing with respect to its reference phase.

a. instantaneous frequency

b. instantaneous frequency deviation

c. instantaneous phase

d. instantaneous phase deviation

Solution:

668. Calculate the amount of frequency deviation caused by a limited noise spike that still cause an undesired phase shift of 35 degrees when the input frequency is 5 kHz.

a. 2.40 kHz

b. 3.05 kHz

c. 1.29 kHz

d. 4.45 kHz

Solution:

669. Which of the following determines the rate of carrier deviation?

a. intelligence frequency

b. frequency deviation

c. carrier frequency

Solution:

670. It is the precise phase of the carrier at a given instant of time

a. instantaneous phase deviation

b. instantaneous phase

c. instantaneous frequency deviation

d. instantaneous frequency

Solution:

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

a. shape

b. phase

c. frequency

d. amplitude

Solution:

672. In FM, it is a device that in which amplitude variations are derived in response to frequency or phase variations

a. detector

b. discriminator

c. demodulator

Solution:

673. Maximum frequency deviation of a PM signal occurs at

a. zero-crossing points

b. peak positive amplitudes

c. peak negative amplitude

d. peak positive and negative amplitude

Solution:

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

a. remains constant

b. is decreased

c. is increased

d. is equalized

Solution:

675. It is the instantaneous change in frequency of the carrier and is defined as the first time derivative of the phase deviation

a. instantaneous frequency

b. instantaneous frequency deviation

c. instantaneous phase

d. instantaneous phase deviation

Solution:

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

a. remains constant

b. is decreased

c. is increased

d. is equalized

Solution:

677. It is the precise frequency of the carrier at a given instant of time is defined as the first time derivative of the instantaneous phase.

a. instantaneous frequency

b. instantaneous frequency deviation

c. instantaneous phase

d. instantaneous phase deviation

Solution:

678. It is the output-versus-input transfer functions for modulators which give the relationship between the output parameter changes in respect to specified changes in the input signal.

a. frequency deviation

b. deviation sensitivity

c. transconductance curve

d. phase deviation

Solution:

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

a. amplitude modulation

b. phase modulation

c. frequency modulation

d. any of the above

Solution:

680. In PM, carrier frequency deviation is not proportional to:

a. modulating signal amplitude

b. carrier amplitude and frequency

c. modulating signal frequency

d. modulator phase shift

Solution:

681. To compensate for increases in carrier frequency deviation with an increase in modulating signal frequency, what circuit is used between the modulating signal and phase modulator?

a. low-pass filter

b. high-pass filter

c. phase shifter

d. bandpass filter

Solution:

682. Indicate which one of the following is not an advantage of PM 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:

683. With phase modulation, the maximum frequency deviation occurs during what value of the modulating signal?

a. positive peak value

b. rms value

c. negative peak value

d. zero crossings

Solution:

684. With frequency modulation, maximum frequency deviation occurs _____ of the modulation signal.

a. positive peak value

b. both positive and negative peak value

c. negative peak value

d. zero crossings

Solution:

685. What was the first broadcast FM system called?

a. Arc transmitter

b. MOPA

c. Armstrong

d. crystal

Solution:

686. With phase modulation, peak phase deviation is called _________.

a. modulation index

b. frequency deviation

c. phase deviation

d. instantaneous phase

Solution:

687. The FM produced by PM is called

a. FM

b. PM

c. indirect FM

d. indirect PM

Solution:

a. local oscillator operates below the signal frequency

b. mixer input must be tuned to the signal frequency

c. local oscillator frequency is normally double the OF

d. RF amplifier normally works at 455kHz above the carrier frequency

Solution:

689. If the amplitude of the modulating signal applied to a phase modulator is constant, the output signal will be

a. zero

b. the carrier frequency

c. above the carrier frequency

d. below the carrier frequency

Solution:

a. squelch

b. variable sensitivity

c. variable selectivity

d. double conversion

Solution:

691. The peak-to-peak frequency deviation is sometimes called __________.

a. phase deviation

b. peak phase deviation

c. carrier swing

d. instantaneous frequency

Solution:

692. A 100MHz carrier is deviated 50 kHz by 4kHz signal. The modulation index is

a. 5

b. 8

c. 12.5

d. 20

Solution:

693. With angle modulation, it is defined as the ratio of the frequency deviation actually produced to the maximum frequency deviation allowed by law stated in percent form.

a. modulation index

b. percent modulation

c. frequency deviation

d. phase deviation

Solution:

694. In a broadcast FM system, the input S/N = 4. Calculate the worst case S/N at the output if the receiver’s internal noise effect is negligible.

a. 19.8:1

b. 21.6:1

c. 23:1

d. 15:1

Solution:

695. It is a circuit in which the carrier is varied in such a way that its instantaneous phase is proportional to the modulating signal.

a. frequency modulators

b. amplitude modulators

c. phase modulators

d. mixers

Solution:

696. In a ratio detector

a. the linearity is worse than in a phase discriminator

b. stabilization against signal strength variations is provided

c. the output is twice that obtainable from the similar phase discriminator

d. the circuit is the same as in a discriminator, except that the diodes are reversed

Solution:

697. 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:

698. The unmodulated carrier is a single-frequency sinusoid commonly called _________.

a. unrest frequency

b. rest frequency

c. frequency-modulated frequency

d. carrier frequency

Solution:

699. It is a circuit in which the carrier is varied in such a way that its instantaneous phase is proportional to the integral of the modulating signal

a. phase modulator

b. phase deviator

c. amplitude deviator

d. frequency modulator

Solution:

700. The typical squelch circuit

a. cuts off an audio amplifier when the carrier is absent

b. eliminates the RF interference when the signal is weak

c. cuts off an IF amplifier when the AGC is maximum

d. cuts off an IF amplifier when the AGC is minimum

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

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

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