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Communications MCQ Set 1

1. Which is the dominant mode for a rectangular waveguide?
a) TE 01
b) TM 01
c) TE 10
d) TM 10

View Answer

Answer: c [Reason:] Rectangular waveguides are earliest form of transmission lines. It supports TM and TE mode, but it not supports TEM mode. A rectangular waveguide can’t propagate below some certain frequency. The dominant mode for it is TE 10 mode.

2. EIRP stands for _________
a) Effective Isotropic Radiated Power
b) Effective Isotropic Reflected Power
c) Effective Isotropic Refracted Power
d) Effective Internal Radiated Power

View Answer

Answer: a [Reason:] ERIP stands for Effective Isotropic Radiated Power. It is basically the output power when a signal is concentrated into a smaller area with the help of antenna.

3. Characteristic impedance of a cable depends only on the resistance per foot of the wire used.
a) True
b) False

View Answer

Answer: b [Reason:] The characteristic impedance of a cable depends on the inductance per foot and the capacitance per foot.

4. When calculating the maximum number of users, limiting factor in FDM is ___________
a) bandwidth of each signal
b) type of each signal
c) type of media signal
d) length of the channel

View Answer

Answer: a [Reason:] When calculating the maximum users in frequency division multiplexing, the bandwidth of each transmitting signal must be observed very carefully and thus it is also the limiting factor in FDM.

5. The minimum channel Bandwidth is used by which modulation technique?
a) VSB
b) SSB
c) DSB-SC
d) FM

View Answer

Answer: b [Reason:] A signal has two sidebands which are exactly the mirror images of each other. So we can remove one side band which further reduces its bandwidth.

6. CDMA stands for Carrier Division Multiple Access.
a) True
b) False

View Answer

Answer: b [Reason:] CDMA stands for Code Division Multiple Access. It refers to any protocol that is used in second generation and third generation wireless communication.

7. QPSK symbol contains ________
a) a byte
b) 4 bits
c) a dibit
d) 8 bits

View Answer

Answer: c [Reason:] In QPSK, only two bits are transmitted per symbol. It represents 00, 01, 10, 11.

8. What is the full form of ATM?
a) Asynchronous Transfer Mode
b) Asynchronous Transmission Mode
c) Asynchronous Transfer Model
d) Automatic Transfer Mode

View Answer

Answer: a [Reason:] ATM stands for Asynchronous Transfer Mode. It uses asynchronous time division multiplexing and encodes data into small but fixes size packets.

9. Who invented the Ethernet?
a) IBM
b) Xerox
c) Intel
d) Panasonic

View Answer

Answer: b [Reason:] Ethernet is a computer technology mostly used in LANs. Ethernet was invented by Xerox.

10. MAN stands for ________
a) Manchester Access Network
b) Metropolitan Area Network
c) Multiple Area Network
d) Multiple Access Network

View Answer

Answer: b [Reason:] MAN stands for Metropolitan Area Network. It interconnects computers that are under a fixed geographic area larger than that covered by LAN but smaller than the area covered by WAN.

Communications MCQ Set 2

1. Demodulation is done in ________
a) Transmitter
b) Radio Receiver
c) Receiving antenna
d) Transducer

View Answer

Answer: b [Reason:] Demodulation means extracting the original signal from a carrier wave. The extraction of original signal is generally used with radio receiver.

2. What is Fidelity?
a) Equally amplifies all the signal frequencies at receiver
b) Ability of receiver to select wanted signal from various incoming signal
c) Minimum magnitude of input signal required to produced a specified output
d) Process of varying one or more properties of carrier signal

View Answer

Answer: a [Reason:] Fidelity is the ability of amplifier to reproduce input signal without any distortion. The ability of receiver to select wanted signal from various incoming signal is called Selectivity while sensitivity is the minimum magnitude of input signal required to produced a specified output. And the process of varying one or more properties of carrier signal is called modulation.

3. In a receiver, noise is usually developed at ________
a) Audio stage
b) Receiving antenna
c) RF stage
d) IF stage

View Answer

Answer: c [Reason:] Ability of radio receiver to pick up required level of radio signals will enable it to operate more effectively. All the methods that are used to make receiver more sensitive use the fact that the limiting factor of the sensitivity is not the level of amplification available, but the levels of noise that are present within the radio receiver or outside.

4. Which oscillator is used as a local oscillator in radio receiver?
a) Wien-bridge
b) Hartley
c) Crystal
d) Phase Shift

View Answer

Answer: b [Reason:] In Hartley oscillator, the oscillation frequency is determined by a tuned circuit. It generally consists of capacitors and inductors i.e. an LC oscillator. Generally used as a local oscillator in radio receiver.

5. Process of recovering information signal from received carrier is known as ________
a) Sensitivity
b) Selectivity
c) Detection
d) Multiplexing

View Answer

Answer: c [Reason:] Detection means extracting information Contained in a modulated carrier wave while minimum magnitude of input signal required to produced a specified output is Sensitivity. Ability of receiver to select wanted signal from various incoming signal is called Selectivity and Multiplexing means sending multiple signals over a communication link at the same time in the form of a single complex signal.

6. What is the use of varacter diode in radio receiver?
a) Demodulation
b) Mixing
c) Multiplexing
d) Tuning

View Answer

Answer: d [Reason:] Varacter diode is a tuning diode having variable capacitance, they are operated in reverse bias. Therefore there is no flow of current in it.

7. What is the function of radio receiver?
a) to detect and amplify information signal from the carrier
b) to transmit message
c) to process the electrical signal from different aspects
d) to convert one form of energy into other

View Answer

Answer: a [Reason:] Channel is a medium through which a message is transmitted. Transmitter is used process the electrical signal from different aspects. Transducer is used to convert one form of energy into another form and the role of receiver is to detect and amplify information signal from the carrier.

8. Figure of merit is ________
a) Ratio of output signal to noise ratio to input signal to noise ratio
b) Ratio of input signal to noise ratio to output signal to noise ratio
c) Ratio of output signal to input signal to a system
d) Ratio of input signal to output signal to a system

View Answer

Answer: a [Reason:] Figure of merit is a numerical quantity based on characteristic of system that represents a measure of efficiency or effectiveness. It is defined as the ratio of output signal to noise ratio to input signal to noise ratio.

9. Superheterodyne principle provides selectivity at ________
a) RF stage
b) IF stage
c) Before RF stage
d) Audio

View Answer

Answer: b [Reason:] A superheterodyne receiver works as normal radio receiver. It uses frequency mixing to convert received signal to a fixed intermediate frequency (IF) which can be processed more conveniently than original carrier frequency.

10. A heterodyne frequency changer is ________
a) Mixer
b) Demodulator
c) Modulator
d) Fidelity

View Answer

Answer: a [Reason:] A mixer is a nonlinear electrical circuit that creates new frequencies from two signals applied to it. Mixers are widely used to shift signals from one to other frequency range, which is known as heterodyning process.

Communications MCQ Set 3

1. Luminance is measured in ________
a) Foot-candles
b) IRE units
c) Lumins
d) NTSC units

View Answer

Answer: b [Reason:] Luminance refers to brightness. It is a photometric measure of luminous intensity per unit area of light travelling in a given direction. It is measured in IRE units.

2. The maximum luminance level is called ________
a) max white
b) peak white
c) all white
d) width to power

View Answer

Answer: b [Reason:] Luminance refers to brightness. It is a photometric measure of luminous intensity per unit area of light travelling in a given direction. It is measured in IRE units. The maximum luminance level is called peak white.

3. Which term is used for defining high and low points of a satellite’s orbit?
a) perigee and apogee
b) apogee and perigee
c) uplink and downlink
d) downlink and uplink

View Answer

Answer: b [Reason:] Apogee and Perigee are respectively the terms used for defining high and low points of a satellite’s orbit.

4. What is the power order of power level for an earth station to transmit to a satellite?
a) 104 watts
b) 103 watts
c) 100 watts
d) 101 watts

View Answer

Answer: b [Reason:] The standard power level of an earth station to transmit to a satellite is of the order of 103 Watts.

5. What is the full form of DBS?
a) direct broadcast satellite
b) decibels of signal
c) down beam signal
d) direct broadcast system

View Answer

Answer: a [Reason:] DBS stands for direct broadcast satellite. In Direct Broadcast Satellite subscribers receives signal directly from geostationary satellite.

6. RCC stands for __________
a) Radio Common Carrier
b) Radio Communication Carrier
c) Radio Cellular Carrier
d) Radio Cell Carrier

View Answer

Answer: a [Reason:] RCC stands for Radio Common Carrier. It was introduced in 60’s. Like a radio it can also transmit voice communication through a push to talk system. But it used a public telephone network and has its own telephone number.

7. Current PCs are referred as __________
a) first-generation
b) second-generation
c) third-generation
d) digital-generation

View Answer

Answer: b [Reason:] Current PCs in today’s time are referred as second generation.

8. ISM stands for _________
a) IEEE Standard Message
b) Industrial, Scientific and Messaging
c) Industrial, Scientific and Medical
d) IEEE Secure Message

View Answer

Answer: c [Reason:] ISM stands for Industrial, Scientific and Medical. In it some radio frequencies are only used for Industrial, Scientific and Medical purposes not for telecommunications purpose.

9. Push pull amplifier is a class B amplifier.
a) True
b) False

View Answer

Answer: a [Reason:] Push pull amplifier uses a pair of active devices that alternately supply current to a connected load and also absorb current from a connected load. It is a class B amplifier.

10. Bluetooth uses ________
a) CDMA
b) Frequency hopping
c) QPSK
d) QAM

View Answer

Answer: b [Reason:] Bluetooth is a wireless technology. It is used for exchanging data over short distances. It usually uses frequency hopping.

Communications MCQ Set 4

1. For a periodic function, the spectral density and auto-correlation functions are ________
a) Laplace transform pair
b) Fourier transform pair
c) Gauss transform pair
d) Hartley transform pair

View Answer

Answer: b [Reason:] Fourier transform breaks a function into an alternate representation, characterized by sine and cosines. If a function is periodic, the spectral density and auto-correlation functions are Fourier transform pair.

2. Spectral density express________
a) Average voltage
b) Average power in a waveform as a function of frequency
c) Average current
d) Average impedance

View Answer

Answer: b [Reason:] Power Spectral Density (PSD) of any signal describes the power present in signal as a function of frequency.

3. What is the role of channel in communication system?
a) acts as a medium to send message signals to its medium
b) converts one form of signal to other
c) allows mixing of signals
d) helps to extract original signal from incoming signal

View Answer

Answer: a [Reason:] Channel acts as a medium to transmit message signal to its medium. Noise gets involved in signal in channel only. Transducer converts one form of energy to other form.

4. For a Gaussian process, auto correction also implies _________
a) Statistical dependance
b) Statistical independence
c) Statistical distribution
d) Ergodic process

View Answer

Answer: b [Reason:] For a Gaussian process, auto correction implies statistical independence. It is basically a stochastic process.

5. What will be the value of modulation if we want maximum undistorted transmitted power?
a) 0
b) 1
c) 0.2
d) 0.7

View Answer

Answer: b [Reason:] For getting maximum undistorted power in any modulated system, then modulation index of that system should be 1.

6. Agreement between communication devices are called ________
a) Transmission medium
b) Transistor
c) Protocol
d) Data

View Answer

Answer: c [Reason:] Protocol allows two or more entities of communication system to transmit information. Transmission medium is the path through which information travels.

7. For providing two or more voice circuits on the same carrier, we can use _________
a) SSB
b) ISB systems
c) DSB-SC
d) SSB with pilot carrier

View Answer

Answer: b [Reason:] ISB systems used provide same carrier to two or more voice circuits.

8. The output stage of television transmitters is most likely to be a __________
a) Grid modulated class C amplifier
b) Grid modulated class A amplifier
c) Plate modulated class C amplifier
d) Plate modulated class A amplifier

View Answer

Answer: a [Reason:] The output stage of television transmitters are basically class C amplifiers. It is grid modulated.

9. Modulation is used to separate differing transmission.
a) True
b) False

View Answer

Answer: a [Reason:] Modulation is the property of varying one or more properties of a periodic waveform. It is used for separating different transmission.

10. A function f(x) is odd, when?
a) f(x) = -f(x)
b) f(x) = f(-x)
c) f(x) = -f(x)f(-x)
d) f(x) = f(x)f(-x)

View Answer

Answer: a [Reason:] A function f(x) is said to be odd, when f(x) is equal to -f(-x). For an even function f(x) must be equal to f(-x).

Communications MCQ Set 5

1. What do you understand by the term SSB?
a) Suppressed Side Band
b) Single Side Band
c) Suppressed Single Band
d) Single Suppressed Band

View Answer

Answer: b [Reason:] SSB stands for Single Side band. It is used to reduce bandwidth of the signal.

2. SSB is a standard form for radio communication.
a) True
b) False

View Answer

Answer: a [Reason:] Single Side Band can also be seen as a standard form for radio communication. In Single Side Band, carrier wave is suppressed by about 50dB.

3. Ribbon microphone has a bidirectional feature.
a) True
b) False

View Answer

Answer: a [Reason:] It is correct statement that a ribbon microphone has bidirectional feature. Other microphones such as carbon, condenser etc does not have a bidirectional feature.

4. Antenna can only be used as a transmitter.
a) True
b) False

View Answer

Answer: b [Reason:] All antennas can be used as transmitter and receiver both. Antenna transmits or receives electromagnetic waves only.

5. TM is a pseudo analog modulation.
a) True
b) False

View Answer

Answer: a [Reason:] TM is a pseudo analog modulation. In TM carrier also carries a phase variable.

6. What is the full form of PPM?
a) pulse-position modulation
b) position-pulse modulation
c) pulse-pulse modulation
d) position-position modulation

View Answer

Answer: a [Reason:] PPM is used for both analog and digital signals. It is mostly used for optical communication such as optic fiber.

7. CVSDM stands for continuously variable slope delta modulation.
a) True
b) False

View Answer

Answer: a [Reason:] CVSDM stands for continuously variable slope delta modulation. It can also be seen as delta modulation having variable step size.

8. If the target is changing continuously, then the best scanning system for correct tracking is _________
a) monopulse
b) conical
c) lobe switching
d) sequential

View Answer

Answer: a [Reason:] If the targeting area is changing continuously then it is better to use monopulse scanning system for accurate tracking.

9. In NBFM, the modulation index is close to __________
a) 1
b) 100
c) 50
d) infinite

View Answer

Answer: a [Reason:] In NBFM, the modulation index is close to unity. NBFM stands for Narrow Band Frequency Modulation.

10. NBFM stands for Narrow Band Frequency Modulation.
a) True
b) False

View Answer

Answer: a [Reason:] It is a correct statement that NBFM stands for Narrow Band Frequency Modulation. In NBFM, the modulation index is close to unity.