MCQs in Modulation Part XVIII

This is the Multiples Choice Questions Part 18 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

SEE: More Questions and Answers in Modulation

PART 18: MCQs from Number 851 – 900                 Answer key: PART XVIII

Continue Practice Exam Test Questions Part XVIII of the Series

851. Having an information signal change some characteristic of a carrier signal is called

• a. Multiplexing
• b. Modulation
• c. Duplexing
• d. Linear mixing

852. Which of the following is not true about AM?

• a. The carrier amplitude varies.
• b. The carrier frequency remains constant.
• c. The carrier frequency changes.
• d. The information signal amplitude changes the carrier amplitude.

853. The opposite of modulation is

• a. Reverse modulation
• b. Downward modulation
• c. Unmodulation
• d. Demodulation

854. The circuit used to produce modulation is called

• a. Modulator
• b. Demodulator
• c. Variable gain amplifier
• d. Multiplexer

855. A modulator circuit performs what mathematical operation on its two inputs?

• a. Addition
• b. Multiplication
• c. Division
• d. Square root

856. The ratio of the peak modulating signal voltage to the peak carrier voltage is referred to as

• a. The voltage ratio
• b. Decibels
• c. The modulation index
• d. The mix factor

857. If m is greater than 1, what happens?

• a. Normal operation
• b. Carrier drops to zero
• c. Carrier frequency shifts
• d. Information signal is distorted

858. For ideal AM, which of the following is true?

• a. m = 0
• b. m = 1
• c. m < 1
• d. m > 1

859. The outline of the peaks of a carrier has the shape of the modulating signal and is called the

• a. Trace
• b. Waveshape
• c. Envelope
• d. Carrier variation

860. Overmodulation occurs when

• a. V_m > V_c
• b. V_m < V_c
• c. V_m = V_c
• d. V_m = V_c = 0

861. The values of V_max and V_min as read from an AM wave on oscilloscope are 2.8 and 0.3. the percentage of modulation is

• a. 10.7 %
• b. 41.4 %
• c. 80.6 %
• d. 93.3 %

862. The new signals produced by modulation are called

• a. Spurious emissions
• b. Harmonics
• c. Intermodulation products
• d. Sidebands

863. A carrier of 880 kHz is modulated by a 3.5 kHz sine wave. The LSB and USB are, respectively,

• a. 873 and 887 kHz
• b. 876.5 and 883.5 kHz
• c. 883.5 and 876.5 kH
• d. 887 and 873 kHz

864. A display of signal amplitude versus frequency is called the

• a. Time domain
• b. Frequency Spectrum
• c. Amplitude Spectrum
• d. Frequency Domain

865. Most of the power in an AM signal is in the

• a. Carrier
• b. Upper sideband
• c. Lower sideband
• d. Modulating signal

866. An AM signal has a carrier power of 5 W. the percentage of modulation is 80% the total sideband power is

• a. 0.8 W
• b. 1.6 W
• c. 2.5 W
• d. 4.0 W

867. For 100 % modulation, what percentage of power is in each sideband?

• a. 25 %
• b. 33.3 %
• c. 50 %
• d. 100 %

868. An AM transmitter has a percentage of modulation of 88. The carrier power is 440 W. The power is 440 W. The power in one sideband is

• a. 85 W
• b. 110 W
• c. 170 W
• d. 610 W

869. An AM transmitter antenna current is measured with no modulation and found to be 2.6 amperes. With modulation, the current rises to 2.9 amperes. The percentage of modulation is

• a. 35 %
• b. 70 %
• c. 42 %
• d. 89 %

870. What is the carrier power in the problem above if the antenna resistance is 75 ohms?

• a. 195 W
• b. 631 W
• c. 507 W
• d. 792 W

871. In an AM signal, the transmitted information is contained within the

• a. Carrier
• b. Modulating signal
• c. Sidebands
• d. Envelope

872. An AM signal without the carrier is called a(n)

• a. SSB
• b. Vestigial sideband
• c. FM signal
• d. DSB

873. What is the minimum AM signal needed to transmit information?

• a. Carrier plus sidebands
• b. Carrier only
• c. One sideband
• d. Both sideband

874. The main advantage of SSB over standard AM or DSB is

• a. Less spectrum space is used
• b. Simpler equipment is used
• c. Less power is consumed
• d. A higher modulation percentage

875. In SSB, which sideband is the best to use?

• a. Upper
• b. Lower
• c. Neither
• d. Depends upon the use

876. The typical audio modulating frequency range used in radio and telephone communication is

• a. 50 Hz to 5 kHz
• b. 50 Hz to 15 kHz
• c. 100Hz to 10kHz
• d. 300 Hz to 3 kHz

877. An AM signal with a maximum modulating signal frequency of 4.5 kHz has a total bandwidth of

• a. 4.5 kHz
• b. 6.75 kHz
• c. 9 kHz
• d. 18 kHz

878. The modulation system used for telegraphy is

• a. Frequency-shift keying
• b. Two-tone modulation
• c. Pulse-code modulation
• d. Single-tone modulation

879. The process of translating a signal, with or without modulation, to a higher or lower frequency for processing is called

• a. Frequency multiplication
• b. Frequency division
• c. Frequency shift
• d. Frequency conversion

880. Frequency translation is carried out by a circuit called a

• a. Translator
• b. Convertor
• c. Balanced modulator
• d. Local oscillator

881. An input signal of 1.8 MHz is mixed with a local oscillator of 5 MHz. A filter selects the difference signal. The output is

• a. 1.8 MHz
• b. 3.2 MHz
• c. 5 MHz
• d. 6.8 MHz

882. One type of pulse communications system uses pulse that appear as a group, and which vary in number according to the loudness of the voice. This type of pulse modulation is called

• a. Pulse duration modulation
• b. Pulse amplitude modulation
• c. Pulse code modulation
• d. Pulse position modulation

883. An SSB transmitter produces a 400-V peak to peak signal across a 52-Ω antenna load. The PEP output is

• a. 192.2 W
• b. 384.5 W
• c. 769.2 W
• d. 3077 W

884. The output power of an SSB transmitter is usually expressed in terms of

• a. Average power
• b. RMS power
• c. Peak-to-peak power
• d. Peak envelope power

885. The letter-number designation B8E is a form of modulation also known as

• a. Pilot-carrier system
• b. Independent sideband emission
• c. Lincomlex
• d. Vestigal sideband transmission

886. Amplitude modulation is the same as

• a. Linear mixing
• b. Analog multiplication
• c. Signal summation
• d. Inductor

887. In a diode modulator, the negative half of the AM wave is supplied by a(n)

• a. Tuned circuit
• b. Transformer
• c. Capacitor
• d. Inductor

888. Amplitude modulation can be produced by

• a. Having the carrier vary a resistance
• b. Having the modulating signal vary a capacitance
• c. Varying the carrier frequency
• d. Varying the gain of an amplifier

889. Amplitude modulators that vary the carrier amplitude with the modulating signal by passing it through an attenuator work on the principle of

• a. Rectification
• b. Resonance
• c. Variable resistance
• d. Absorption

890. The component used to produce AM at very high frequencies is a

• a. Varactor
• b. Thermistor
• c. Cavity resonator
• d. PIN diode

891. Amplitude modulation generated at a very low voltage or power amplitude is known as

• a. High-level modulation
• b. Low-level modulation
• c. Collector modulation
• d. Minimum modulation

892. A collector modulator has a supply voltage of 48 V. The peak-to-peak amplitude of the modulating signal for 100 percent modulation is

• a. 24 V
• b. 48 V
• c. 96 V
• d. 120 V

893. A collector modulated transmitter has a supply voltage of 24 V and collector current of 0.5 A. The modulator power for 100 percent modulation is

• a. 6 W
• b. 12 W
• c. 18 W
• d. 24 W

894. The circuit that recovers the original modulating information from an AM signal is known as a

• a. Modulator
• b. Demodulator
• c. Mixer
• d. Crystal set

895. The most commonly used amplitude demodulator is the

• a. Diode mixer
• b. Balanced modulator
• c. Envelope detector
• d. Crystal filter

896. A circuit that generates the upper and lower sidebands but no carrier is called a(n)

• a. Amplitude modulator
• b. Diode detector
• c. Class C amplifier
• d. Balanced modulator

897. The inputs to a balance modulator are 1 MHz and a carrier of 1.5 MHz. The outputs are

• a. 500 kHz
• b. 2.5 MHz
• c. 1.5 MHz
• d. Both a and b

898. A widely used balanced modulator is called the

• a. Diode bridge circuit
• b. Full-wave bridge rectifier
• c. Lattice Modulator
• d. Balanced bridge modulator

899. In a diode ring modulator, the diodes act like

• a. Variable resistors
• b. Switches
• c. Rectifiers
• d. Variable capacitors

900. The output of a balanced modulator is

• a. AM
• b. FM
• c. SSB
• d. DSB

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