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# MCQ in Modulation Part 16 | ECE Board Exam

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.

#### 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 16 of the Series

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

b. PM demodulators

c. FM demodulators

Solution:

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

Solution:

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

a. pF

b. nF

c. uF

d. F

Solution:

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

Solution:

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

a. Foster-Seeley discriminator

c. balanced slope generator

d. PLL detector

Solution:

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

a. zero

b. small

c. medium

d. large

Solution:

757. A phase modulator varies the phase shift of the

a. carrier

b. modulating signal

c. modulating voltage

d. sideband frequency

Solution:

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

Solution:

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

b. PLL demodulator

c. Foster-Seely discriminator

d. ratio detector

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

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

a. capture effect

b. noise suppression

d. non of these

Solution:

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

a. VCO

b. VXO

c. VFO

d. VHF

Solution:

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

a. LC

b. RC

c. LR

d. crystal

Solution:

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

a. Foster-Seely discriminator

b. Pulse-averaging discriminator

d. PLL

Solution:

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

Solution:

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

Solution:

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

a. double limiting

b. two-time limiting

c. reserve limiting

d. ratio limiting

Solution:

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

a. ratio detector

b. PLL

d. pulse-averaging discriminator

Solution:

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

a. ratio detector

b. PLL

d. pulse-averaging discriminator

Solution:

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

Solution:

774. What special speaker is used for low frequency?

a. baffle

b. base

c. tweeter

d. woofer

Solution:

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

a. monophonic

b. multiphonic

c. stereophonic

d. any of these

Solution:

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

Solution:

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

Solution:

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

a. 38 kHz

b. 15 kHz

c. 67 kHz

d. 53 kHz

Solution:

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

Solution:

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

b. Foster-Seeley discriminator

c. differential peak detector

d. phase-locked loop

Solution:

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

Solution:

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

Solution:

783. With stereo transmission, the maximum frequency deviation is

a. 75 kHz

b. 15 kHz

c. 25 kHz

d. 3 kHz

Solution:

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

Solution:

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

Solution:

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

Solution:

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

a. 25 kHz

b. 5 kHz

c. 75 kHz

d. 3 kHz

Solution:

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

a. decrease

b. increase

c. remains constant

Solution:

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

Solution:

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

a. 3 kHz

b. 5 kHz

c. 15 kHz

d. 75 kHz

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

795. The maximum deviation for narrowband FM?

a. 2500

b. 5

c. 1.67

d. 75

Solution:

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

a. Foster-Seeley discriminator

b. ratio detector

c. slope detector

d. PLL

Solution:

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

Solution:

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

a. ratio detector

c. PLL

d. pulse-averaging discriminator

Solution:

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

a. ratio detector

b. PLL

d. crosby modulator

Solution:

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

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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