# MCQs in Modulation Part XV

Compiled MCQs in Modulation Part 15 of the series as one topic in Electronic System and Technologies (Communications Engineering) in the ECE Board Exam.

This is the Multiples Choice Questions Part 15 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
PART 15: MCQs from Number 701 – 750                 Answer key: PART XV

### Continue Practice Exam Test Questions Part XV of the Series

701. Frequency modulators are also known as _________.

• a. phase deviators
• b. frequency deviators
• c. phase modulators
• d. amplitude deviators

702. A 70 kHz carrier has a frequency deviation of 4 kHz with a 1000 Hz signal. What is the bandwidth of the FM signal?

• a. 4 kHz
• b. 7kHz
• c. 10 kHz
• d. 28 kHz

703. The controlled oscillator synthesizer is sometimes preferred to the direct one because

• a. it is simpler piece of equipment
• b. its frequency stability is better
• c. it does not require crystal oscillators
• d. it is relatively free of spurious frequencies

704. A system with a differentiator followed by an FM modulator is called

• a. PM modulator
• b. FM modulator
• c. PM demodulator
• d. FM demodulator

705. The image frequency of a superheterodyne receiver

• a. is created within the receiver itself
• b. is due to insufficient adjacent channel rejection
• c. is not rejected by the IF tuned circuits
• d. is independent of the frequency to which the receiver is tuned

706. A system with FM demodulator followed by an integrator

• a. PM modulator
• b. PM demodulator
• c. FM modulator
• d. FM demodulator

707. A system with an integrator followed by a PM modulator

• a. PM modulator
• b. FM modulator
• c. PM demodulator
• d. FM demodulator

708. An FM transmitter has a maximum deviation of 12 kHz and a maximum modulating frequency of 12 kHz. The bandwidth by Carson's rule is

• a. 24 kHz
• b. 33.6 kHz
• c. 38.8 kHz
• d. 48 kHz

709. A system with PM demodulator followed by a differentiator

• a. PM modulator
• b. FM modulator
• c. PM demodulator
• d. FM demodulator

710. A receiver has poor IF selectivity. It will therefore also have poor

• a. blocking
• b. double-spotting
• c. diversity reception
• d. sensitivity

711. Three point tracking is achieved with

• a. variable selectivity
• c. double spotting
• d. double conversion

712. He mathematically proved that for a given modulating signal frequency a frequency-modulated wave cannot be accommodated in a narrower bandwidth than an amplitude modulated wave.

• a. R.C. Alpine
• b. E.H. Armstrong
• c. J.R. Carson
• d. J.J. Thomson

713. The maximum allowed deviation of the FM sound signal in TV is 25 kHz. If the actual deviation is 18 kHz, the percent modulation is

• a. 43 percent
• b. 72 percent
• c. 96 percent
• d. 139 percent

714. The local oscillator of a broadcast receiver is tuned to a frequency higher than the incoming frequency

• a. to help the image frequency rejection
• b. to permit easier tracking
• c. because otherwise an intermediate frequency could not be produced
• d. to allow adequate frequency coverage without switching

715. 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

716. Low-index FM systems are also known as __________.

• a. wideband FM
• b. narrowband FM
• c. commercial FM
• d. medium FM

717. For high-index signal, a method of determining the bandwidth is called ________ approach

• a. quasi-stationary
• b. quasi-movement
• c. quasi-deviation
• d. any of these

718. When a receiver has a good blocking performance, this means that

• a. it does not suffer from double-spotting
• b. its image frequency rejection is poor
• c. it is unaffected by AGC derived from a nearby transmission
• d. its detector suffers from burnout

719. He established a general rule to estimate the bandwidth for all angle-modulated system regardless of the modulation index.

• a. R.C. Alpine
• b. E.H. Armstrong
• c. J.R. Carson
• d. J.J. Thomson

720. An AM receiver uses a diode detector for demodulation. This enables it satisfactorily to receive

• a. single-sideband, suppressed carrier
• b. single-sideband, reduced carrier
• c. independent sideband
• d. single-sideband, full carrier

721. The primary disadvantage of FM is its

• a. higher cost and complexity
• b. excessive use of spectrum space
• c. noise susceptibility
• d. lower efficiency

722. A rule that approximates the bandwidth necessary to transmit an angle-modulated wave as twice the sum of the peak frequency deviation and the highest modulating frequency.

• a. Carson's rule
• b. Shannon's rule
• c. Hartley's law
• d. Hartley-Shannon law

723. It is the worst case modulation index and is equal to the maximum peak frequency deviation divided by the maximum modulating signal frequency

• a. peak phase deviation
• b. frequency deviation
• c. deviation ratio
• d. signal to noise ratio

724. The receiver circuit that rids FM noise is the

• a. modulator
• b. demodulator
• c. limiter
• d. low-pass filter

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

• a. capture effect
• b. blot out
• c. quieting factor
• d. domination syndrome

726. The highest side frequencies form one channel are allowed to spill over into adjacent channels producing an interference known as _________.

• a. co-channel interference
• c. splatter
• d. overmodulation

727. A pre-emphasis is usually a ________.

• a. high-pass filter
• b. band-stop filter
• c. low-pass filter
• d. bandpass filter

728. Frequency modulation transmitters are more efficient because their power is increased by what type of amplifier?

• a. class A
• b. class B
• c. class C
• d. all of the above

729. Noise interferes mainly with modulating signals that are

• a. sinusoidal
• b. non-sinusoidal
• c. low frequencies
• d. high frequencies

730. A de-emphasis is usually a _________.

• a. high pass filter
• b. band-stop filter
• c. low-pass filter
• d. bandpass filter

731. A pre-emphasis is a __________.

• a. integrator
• b. differentiator
• c. either integrator or differentiator
• d. neither integrator or differentiator

732. A de-emphasis is a _____________.

• a. integrator
• b. differentiator
• c. either integrator or differentiator
• d. neither integrator or differentiator

733. Pre-emphasis circuit boost what modulating frequencies before modulation?

• a. high frequencies
• b. mid-range frequencies
• c. low frequencies
• d. all of the above

734. The primary disadvantage of direct PM

• a. relatively unstable LC oscillators must be used to produce carrier frequency which prohibits using crystal oscillators
• b. relatively high frequency deviations and modulation indices are easily obtained due to the fact that the oscillators are inherently unstable.
• c. crystal oscillators are inherently stable and therefore more difficult for them to achieve high phase deviations and modulation indices
• d. carrier oscillator is isolated form the actual modulator circuit and therefore can be stable source.

735. It is an angle modulation in which the frequency of the carrier is deviated by the modulating signal

• a. direct PM
• b. PM
• c. indirect FM
• d. any of these

736. One of the following is a method of performing frequency up conversion

• a. heterodyning
• b. amplification
• c. modulation
• d. none of these

737. A pre-emphasis circuit is a

• a. low-pass filter
• b. high-pass filter
• c. phase shifter
• d. bandpass filter

738. Pre emphasis is compensated for the receiver by a

• a. phase inverter
• b. bandpass filter
• c. high-pass filter
• d. low-pass filter

739. A circuit that compares the frequency of the non-crystal carrier oscillator to a crystal reference oscillator and then produces a correction voltage proportional to the difference between the two frequencies

• a. AFC
• b. squelch circuit
• c. AGC
• d. heterodyning circuit

740. A frequency selective device whose output voltage is proportional to the difference between the input frequency and its resonant frequency

• a. modulator
• b. squelch circuit
• c. frequency discriminator
• d. FM transmitters

741. Allows FM receiver to differentiate between two signals received with the same frequency but different amplitudes

• a. flywheel effect
• b. amplitude limiting
• c. noise immunity
• d. capture effect

742. If an FM transmitter employs one doubler, one tripler, and one quadrupler, what is the carrier frequency swing when the oscillator frequency swing is 2 kHz?

• a. 24 kHz
• b. 48 kHz
• c. 14 kHz
• d. 12 kHz

743. The cut-off frequency of pre-emphasis and de-emphasis circuits is

• a. 1 kHz
• b. 2.122 kHz
• c. 5 kHz
• d. 75 kHz

744. Which of the following is not a disadvantage of angle modulation?

• a. wide bandwidth
• b. complex
• c. high cost
• d. less noise

745. In FM receivers, which of the following rejects the image frequency?

• a. preselector
• b. detector
• c. IF amplifier
• d. mixer

746. In FM receivers, which of the following provides most gain and selectivity of the receiver?

• a. detector
• b. RF amplifier
• c. local oscillator
• d. IF amplifier

747. Another name for Voltage Variable Capacitor is

• a. PIN diode
• b. varactor diode
• c. snap diode
• d. hot carrier diode

748. The depletion region in a junction diode forms what part of a capacitor?

• a. plates
• c. package
• d. dielectric

749. Which of the following removes the information from the modulated wave in FM receivers?

• a. amplifiers
• b. mixer
• c. speakers
• d. discriminator

750. The final IF amplifier in FM receivers is sometimes called ___________.

• a. tuned amplifier
• b. limiter
• c. passband filter
• d. any of these

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