MCQs in Modulation Part XVI

(Last Updated On: September 10, 2019)

MCQs in Modulation - Part XVI

This is the Multiples Choice Questions Part 16 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 16: MCQs from Number 751 – 800                 Answer key: PART XVI

Continue Practice Exam Test Questions Part XVI of the Series

751. _________ are frequency-dependent circuits designed to produce an output voltage that is proportional to the instantaneous frequency at its output

  • a. PM receivers
  • b. PM demodulators
  • c. FM demodulators
  • d. FM receivers

752. Increasing the reverse bias on a varactor diode will it cause its capacitance to

  • a. decrease
  • b. increase
  • c. remains the same
  • d. drop to zero

753. The capacitance of a varactor diode is in what general range?

  • a. pF
  • b. nF
  • c. uF
  • d. F

754. Which of the following is the simplest form of tuned-circuit frequency discriminator?

  • a. Foster-Seeley discriminator
  • b. Ratio detector
  • c. slope detector
  • d. PLL detector

755. It is simply two single-ended slope detectors connected in parallel and fed 180 degrees out phase.

  • a. Foster-Seeley discriminator
  • b. quadrature detector
  • c. balanced slope generator
  • d. PLL detector

756. The frequency change in crystal oscillator produced by a varactor diode is

  • a. zero
  • b. small
  • c. medium
  • d. large

757. A phase modulator varies the phase shift of the

  • a. carrier
  • b. modulating signal
  • c. modulating voltage
  • d. sideband frequency

758. Which of the following tuned-circuit frequency discriminator is relatively immune to amplitude variations in its input signal?

  • a. ratio detector
  • b. slope detector
  • c. balanced slope detector
  • d. quadrature detector

759. In FM demodulators, it is also called coincidence detector

  • a. quadrature demodulator
  • b. PLL demodulator
  • c. Foster-Seely discriminator
  • d. ratio detector

760. The widest phase variation is obtained with ________.

  • a. RC low-pass filter
  • b. RC high-pass filter
  • c. LR low-pass filter
  • d. LC resonant circuit

761. An FM receiver provides 100dB of voltage gain prior to the limiter. Calculate the receiver’s sensitivity if the limiter’s quieting for an FM receiver is 300 mV?

  • a. 4.5 uV
  • b. 3.0 uV
  • c. 2.1 uV
  • d. 1.3 uV

762. The small frequency change produced by a phase modulator can be increased by using ___________.

  • a. amplifier
  • b. mixer
  • c. frequency multiplier
  • d. frequency divider

763. In FM receiver, limiters produce a constant-amplitude output of all signals above a prescribed minimum input level called _________.

  • a. threshold voltage
  • b. capture level
  • c. quieting level
  • d. any of these

764. The inherent ability of FM to diminish the effects of interfering signals is called _______.

  • a. capture effect
  • b. noise suppression
  • c. adjacent channel rejection
  • d. non of these

765. A crystal oscillator whose frequency can be changed by an input voltage is called _______.

  • a. VCO
  • b. VXO
  • c. VFO
  • d. VHF

766. Which oscillators are preferred for carrier generators because of their good frequency stability?

  • a. LC
  • b. RC
  • c. LR
  • d. crystal

767. Which of the following frequency demodulators requires an input limiter?

  • a. Foster-Seely discriminator
  • b. Pulse-averaging discriminator
  • c. quadrature detector
  • d. PLL

768. Provides a slight automatic control over the local oscillator circuit and compensates for its drift that would otherwise cause a station to become detuned.

  • a. AGC
  • b. AFC
  • c. VVC
  • d. VCO

769. ________ of an FM receiver is the maximum dB difference signal strength between two received signals necessary for the capture effect to suppress the weaker signal.

  • a. capture effect
  • b. capture gain
  • c. capture ratio
  • d. capture loss

770. When two limiter stages are used, there is called ___________.

  • a. double limiting
  • b. two-time limiting
  • c. reserve limiting
  • d. ratio limiting

771. Which discriminator averages pulses in a low-pass filter?

  • a. ratio detector
  • b. PLL
  • c. quadrature detector
  • d. pulse-averaging discriminator

772. Which of the frequency demodulator is considered the best overall?

  • a. ratio detector
  • b. PLL
  • c. quadrature
  • d. pulse-averaging discriminator

773. One of the prominent advantage of FM over PM is

  • a. FM requires frequency multipliers to increase the modulation index and frequency deviation to useful levels
  • b. the voltage controlled oscillators of FM can be directly modulated and produce outputs with high frequency deviations and high modulation
  • c. the modulation index of FM is independent of the modulating signal frequency
  • d. FM offers better signal-to-noise performance than PM

774. What special speaker is used for low frequency?

  • a. baffle
  • b. base
  • c. tweeter
  • d. woofer

775. Each speaker assembly at the receiver reproduces exactly the same information

  • a. monophonic
  • b. multiphonic
  • c. stereophonic
  • d. any of these

776. In a pulse averaging discriminator, the pulse are produced by a(n)

  • a. astable multivibrator
  • b. zero-crossing detector
  • c. one-shot
  • d. low-pass filter

777. A reactance modulator looks like a capacitance of 35pF in parallel with the oscillator-tuned circuit whose inductance is 50 uH and capacitance is 40 pF. What is the center frequency of the oscillator prior to FM?

  • a. 1.43 MHz
  • b. 2.6 MHz
  • c. 3.56 MHz
  • d. 3.8 MHz

778. The frequency of an SCA channel subcarrier is _______.

  • a. 38 kHz
  • b. 15 kHz
  • c. 67 kHz
  • d. 53 kHz

779. The L-R stereo channel in FM broadcasting is between

  • a. 50 Hz to 15 kHz
  • b. 60 kHz to 74 kHz
  • c. 23 kHz to 53 kHz
  • d. 20 Hz to 20 kHz

780. An FM demodulator that uses a differential amplifier and tuned circuits to convert frequency variations into voltage variations is the

  • a. quadrature detector
  • b. Foster-Seeley discriminator
  • c. differential peak detector
  • d. phase-locked loop

781. The output amplitude of the phase detector in a quadrature detector is proportional to

  • a. pulse width
  • b. pulse frequency
  • c. input amplitude
  • d. the phase shift value at center

782. The output to a PLL is 2MHz. In order for the PLL to be locked. The VCO output must be

  • a. 0 MHz
  • b. 1 MHz
  • c. 2 MHz
  • d. 4 MHz

783. With stereo transmission, the maximum frequency deviation is

  • a. 75 kHz
  • b. 15 kHz
  • c. 25 kHz
  • d. 3 kHz

784. The L + R stereo channel occupies _________.

  • a. 50 Hz to 15 kHz
  • b. 60 kHz to 74 kHz
  • c. 23 kHz to 53 kHz
  • d. 20 Hz to 20 kHz

785. The band of frequencies over which a PLL will acquire or recognize an input signal is called the

  • a. circuit bandwidth
  • b. capture range
  • c. band of acceptance
  • d. lock range

786. The three primary frequency bands are allocated by FCC for two-way FM radio communications except:

  • a. 132 MHz to 174 MHz
  • b. 450 MHz to 470 MHz
  • c. 806 MHz to 947 MHz
  • d. 1026 MHz to 1035 MHz

787. The maximum frequency deviation for two-way transmitters is typically

  • a. 25 kHz
  • b. 5 kHz
  • c. 75 kHz
  • d. 3 kHz

788. Decreasing the input frequency to be locked PLL will cause the VCO output to

  • a. decrease
  • b. increase
  • c. remains constant
  • d. jump to the free-running frequency

789. The range of frequencies over which a PLL will track input signal variations is known as the

  • a. circuit bandwidth
  • b. capture range
  • c. band of acceptance
  • d. lock range

790. The maximum modulating signal frequency for two-way transmitter is typically

  • a. 3 kHz
  • b. 5 kHz
  • c. 15 kHz
  • d. 75 kHz

791. Over a narrow range of frequencies, the PLL acts like a

  • a. low-pass filter
  • b. bandpass filter
  • c. tunable oscillator
  • d. frequency modulator

792. The output of a PLL frequency demodulator is taken from the

  • a. low-pass filter
  • b. VCO
  • c. phase detector
  • d. none of these

793. The primary advantage of FM over AM

  • a. capture effect
  • b. noise immunity
  • c. FM can use class C amplifiers
  • d. FM is more efficient

794. The usual cutoff frequency of pre-emphasis and de-emphasis in broadcast FM?

  • a. 50 Hz
  • b. 75 Hz
  • c. 2122 Hz
  • d. 3183 Hz

795. The maximum deviation for narrowband FM?

  • a. 2500
  • b. 5
  • c. 1.67
  • d. 75

796. Which of the following is best frequency demodulator in use?

  • a. Foster-Seeley discriminator
  • b. ratio detector
  • c. slope detector
  • d. PLL

797. The range of frequencies over which the PLL will capture an input signal is known as ________.

  • a. lock range
  • b. capture range
  • c. bandwidth
  • d. sidebands

798. Type of FM demodulator that is widely used in TV audio demodulators

  • a. ratio detector
  • b. quadrature detector
  • c. PLL
  • d. pulse-averaging discriminator

799. A variation of Foster-Seeley discriminator widely used in older TV receiver designs

  • a. ratio detector
  • b. PLL
  • c. quadrature detector
  • d. crosby modulator

800. The range of frequencies over which a PLL will track an input is called

  • a. lock range
  • b. capture range
  • c. track range
  • d. driving range

Complete List of MCQs in Communications Engineering per topic

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