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## Communications MCQ Set 1

1. A duplex arrangement use separate frequencies for transmission.
a) True
b) False

Answer: a [Reason:] Duplex arrangement means a cordless telephone that uses separate frequencies for transmission in base and portable units.

2. VSB modulation is used in televisions because it avoids phase distortion at low frequencies.
a) True
b) False

Answer: b [Reason:] VSB modulation is generally preferred for televisions because it reduces the required bandwidth to half.

3. A cordless telephone that uses separate frequencies for transmission in base and portable units is called _________
a) half duplex
b) duplex
c) either duplex or half duplex
d) neither duplex or half duplex

Answer: b [Reason:] A duplex arrangement is a cordless telephone that uses separate frequencies for transmission in base and portable units.

4. Which polarization is used to reduce depolarization effect on received waves?
a) Circular polarization
b) Linear polarization
c) Atomic polarization
d) dipolar polarization

Answer: a [Reason:] In circular polarization at each point the electric field of electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate. It is used to reduce depolarization effect on received waves.

5. Thermal noise, shot noise and transit time noise is part of internal noise in communication.
a) True
b) False

Answer: a [Reason:] Internal noise in communication is the noise that gets generated within the receiver or communication system. It may be put into the following categories: thermal noise, shot noise, transit time noise.

6. Circular polarization involves critical alignment between transmitting and receiving antenna.
a) True
b) False

Answer: b [Reason:] In circular polarization at each point the electric field of electromagnetic wave has a constant magnitude but its direction changes as it rotates with time at a steady rate. It is used to reduce depolarization effect on received waves. It does not involve alignment between transmitting and receiving antenna.

7. It is only the reflected color that decided the color of an object.
a) True
b) False

Answer: b [Reason:] Color of any object is decided by the reflected color for opaque object and wavelength transmitted through it for transparent object.

8. What do you understand by the term “carrier” in modulation?
a) voltage to be transmitted
b) resultant wave
c) voltage for which amplitude, phase or frequency can be varied
d) voltage for which amplitude, phase or frequency remains constant

Answer: c [Reason:] Carrier wave is used as a carrier for modulating the waves. Its amplitude, phase and frequency can be varied.

9. Carrier wave in modulation is a resultant wave.
a) True
b) False

Answer: b [Reason:] Carrier wave is basically a voltage whose parameters such as amplitude, frequency and phase can be for modulation.

10. For a low level AM system, amplifier modulated stage must have _________
a) harmonic devices
b) linear devices
c) non-linear devices
d) class A amplifiers

Answer: b [Reason:] A low level AM is the one where the modulation is applied to low power stage of the transmitter. The drawback of this approach is that linear amplification is required for RF stages.

## Communications MCQ Set 2

1. Quantization error occurs in ________
a) Time Division Multiplexing
b) Frequency Division Multiplexing
c) Pulse Code Modulation
d) Pulse Width Modulation

Answer: c [Reason:] The difference between an input value and its quantized value is called quantization error or we can also see it as that when an analog number is not converted into an exact digital number. It takes place in pulse code modulation (PCM).

2. If power transmitted is 90kW, what is the field at a distance of 45km?
a) 2
b) 1
c) 0.036
d) 0.01

3. Find the number of pulses, if the number of quantization level is 32 in PCM?
a) 3
b) 6
c) 4
d) 5

Answer: d [Reason:] 2n = 32, so n = 5.

4. Which transistor amplifier is most commonly used?
a) Common Base
b) Common Emitter
c) Common Collector
d) None of these

Answer: b [Reason:] Common Emitter is most widely used because it has high power gain and voltage gain. Moreover it also provides maximum transconductance for a given load.

5. A device uses a 8 bit word then the maximum number of words it can transmit is ________
a) 64
b) 256
c) 1024
d) 512

Answer: b [Reason:] Number of words it can transmit is 28 = 256.

6. Peak voltage of a carrier is 8kV, each sideband has an amplitude of 800V. Find its modulation index?
a) 2.8
b) 0.9
c) 0.2
d) 0.8

Answer: c [Reason:] (mVc)/2 = 800. By substituting values, we have mX8000/2 = 800. So, m = 0.2.

7. What do you understand by the term Cross talk?
a) generation of closely lying sidebands
b) a method of increasing bandwidth
c) a method of decreasing bandwidth by converting DSB-SC signal to SSB-SC
d) disturbance caused in nearby circuit due to transmitted signal

Answer: d [Reason:] Disturbances caused in nearby circuit due to some reasons are called cross talk. It is generally caused by undesired coupling.

8. AM waves is represented by Et cos ⁡ωc t. What does Et denotes?
a) envelope
b) carrier signal
c) modulating signal
d) amplitude

Answer: a [Reason:] AM wave is represented by (A + xt) cos⁡ωc t or Et cos⁡ωc t, where xt is modulating signal, A is amplitude and Et is amplitude of AM wave.

9. Wireless communication takes place through ________
a) EM waves
b) Wires
c) Optical Fibres
d) Magnetic waves

Answer: a [Reason:] Wireless communication takes place through electromagnetic waves. Waves are transmitted through antenna.

10. Which modulation technique uses minimum bandwidth?
a) DSB-SC
b) SSB-SC
c) FM
d) VSB

Answer: b [Reason:] SSB uses least bandwidth since it has only one sideband whereas DSB-SC has two sidebands which increases its bandwidth.

## Communications MCQ Set 3

1. A hub _________
a) are more common in token passing circuits
b) cannot be used in an Ethernet type network
c) sends incoming packets out to specific ports
d) sends incoming packets out to all other terminals connected to it

Answer: d [Reason:] Hubs are devices which are commonly used to connect segments of a LAN. Its role is to send incoming packets out to all other terminals connected to it.

2. A switch _________
a) are more common in token passing circuits
b) cannot be used in an Ethernet type network
c) sends incoming packets out to specific ports
d) sends incoming packets out to all other terminals connected to it

Answer: c [Reason:] A switch connects different devices together on a computer network by using packet switching to receive, process and forward data to the destination device.

3. What is the advantage of using a switch instead of a hub?
a) it is cheaper when used in large networks
b) it is helpful in placing outputs in an ordered way
c) it is reduces the number of collisions
d) it is faster when used in large networks

Answer: c [Reason:] Hubs are devices which are commonly used to connect segments of a LAN. Its role is to send incoming packets out to all other terminals connected to it. But a switch is used frequently instead of a hub it is reduces the chances of collisions.

4. Broadband LANs are provided by cable TV companies for Internet access.
a) True
b) False

Answer: a [Reason:] The term broadband refers to high speed Internet access. It is generally provided by cable TV companies.

5. Why we use record locking in networks?
a) to store records secure
b) to prevent one user from reading a record that another user is writing
c) to prevent multiple users from looking at a document simultaneously
d) to make network simpler

Answer: b [Reason:] In networks, record locking is used to prevent the interference of one user in others work, it prevents the user from reading a record that another user is writing.

6. Carrier wave carries information.
a) True
b) False

Answer: b [Reason:] It is a high frequency electro-magnetic wave. A carrier wave does not have any information. It is modulated with an input signal for the purpose of conveying information.

7. Which software is used to run a client-server network?
a) UNIX
c) Windows
d) Centos

8. For 100% amplitude modulation, the power in upper sideband when carrier power is to be 100W?
a) 100W
b) 75W
c) 25W
d) 50W

Answer: c [Reason:] Modulation index, m = 100% = 1. Power in sidebands is (Pc x m24) . By substituting the values, we have (100 x 14) which is equal to 25W.

9. A “thin” client is a ________
a) PC with no disk drives
b) “dumb” terminal
c) Node that rarely sends data
d) Node which is active for short period of time

Answer: a [Reason:] A thin client is a dumb terminal. Dumb terminal is simply an output device that accepts data from CPU.

10. IP stands for ________
a) Internet Protocol
b) Internet Process
c) Interconnected Protocol
d) Interconnected Process

Answer: a [Reason:] IP stands for Internet Protocol. IP is the principal communication protocol suite for relaying datagrams across network boundaries.

## Communications MCQ Set 4

1. Which band is used by Bluetooth in mobiles?
a) VHF band
b) UHF band
c) ISM band
d) Infrared band

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

2. BSS stands for ________
a) Basic service Set
b) Basic service System
c) Bluetooth service Set
d) Bluetooth service System

Answer: a [Reason:] BBS stands for Basic service Set. It is a term used to describe collection of stations ehich may communicate with each other within an 802.11 network.

3. What do you understand by the term CAPCODE?
a) an encryption scheme
c) an error-detection scheme
d) a digital modulation scheme

4. The “forward” PCs channel is ________
a) from the base to mobile
b) from the mobile to base
c) from mobile to mobile
d) from base to base

Answer: a [Reason:] If the PCs channel is forwarded then it means that signal goes from the base to the mobile.

5. Among all amplifiers, Common Collector has highest power gain.
a) True
b) False

Answer: b [Reason:] It is common emitter who has highest power gain. Common emitter has a very high voltage gain and also has good amount of current, so its power gain is high.

6. Find the carrier frequency if the inductance and capacitance are 30μH and 10nF respectively?
a) 244KHz
b) 523KHz
c) 290KHZ
d) 300KHz

7. What is the full form of MSC?
a) Mobile Service Cellular
b) Mobile Switching Center
c) Mobile Switching Cellular
d) Mobile Service Centar

Answer: b [Reason:] MSC stands for Mobile Switching Center. It is a 2G core network element which controls the network switching subsystem elements.

8. LNA stands for __________
a) low noise amplifier
b) low noise amplitude
c) low narrow amplifier
d) low narrow amplitude

Answer: a [Reason:] LNA stands for low noise amplifier. It is used to amplify possibly weak signals such as those as received by antenna.

9. The “payload” in a communication satellite consists of _________
a) solar cells
b) batteries
c) transponders
d) transducers

Answer: c [Reason:] Transponders works as the payload in any communication. It uses for receiving a radio signal and then automatically transmits a different signal.

10. What is the height of the geosynchronous orbit above the equator?
a) 3,578km
b) 35,780km
c) 357,800km
d) depends on satellite velocity

Answer: b [Reason:] The height of the geosynchronous orbit above the equator is approximated as 35,780 km.

## Communications MCQ Set 5

1. What is the effect on the transmitted power, if the modulation index changes from 0.8 to 1?
a) 0.1364
b) 0.239
c) 0.5
d) 0.3333

Answer: a [Reason:] The total power in an AM is given by, PT = PC (1+m22) . When modulation index, m = 0.8 PT = PC (1+0.822)=1.32Pc and when modulation index, m=1 PT=PC (1+122)=1.5PC. So increase in power =

2. Analog signal may be converted into digital signal by ________
a) Filtering
b) Mixing
c) Sampling
d) Quantization

Answer: c [Reason:] Conversion of analog signal into digital signal converts a continuous time signal in the form of digits. The conversion is done with the help of sampling technique.

3. Radio waves travel through ________
a) Water
b) Wires
c) Optical fiber cable
d) Electromagnetic waves

Answer: d [Reason:] Radio communication or wireless communication takes place through electromagnetic waves. The message is transmitted through open space via electromagnetic waves or radio waves.

4. USB (Upper Side Band) is the band of frequencies _________
a) below carrier frequency
b) includes the carrier frequency
c) that lies in AM spectrum
d) that lies in PM spectrum

Answer: c [Reason:] Upper Side Band is the band of frequencies above the carrier frequency that lies in AM spectrum. It is a part of shifted spectrum obtained after amplitude modulation.

5. PDM is generated by ________
a) combination of two series amplifiers
b) Monostable multivibrator
c) Astable multivibrator
d) Schmitt trigger

Answer: b [Reason:] Monostable multivibrators are used to generate a single output pulse of a particular width. Its output can be high or low for an external applying pulse. PDM (Pulse Density Modulation) is used to represent an analog signal with the help of a binary signal.

6. Which of the following is AM demodulation techniques?
a) Square law demodulator and Envelope detector
b) Square law demodulator and PLL detector
c) PLL detector and Envelope detector
d) PLL detector

Answer: a [Reason:] AM signals are detected or demodulated using Square law demodulator and Envelope detector. The demodulator extracts the information from the received AM signal.

7. Vestigial side band signals are detected by ________
a) Balanced modulator
b) Schmitt trigger
c) Square law modulator
d) Synchronous Detection

Answer: d [Reason:] Vestigial side band signals are detected by Synchronous detection or coherent detection technique. The distortion in a VSB signal may be reduced by reducing the modulation index and increasing the width of VSB.

8. Find lower frequency component in AM wave, given that highest frequency component is 900KHz and bandwidth is 12KHz?
a) 832KHz
b) 600KHz
c) 868KHz
d) 888KHz

Answer: d [Reason:] Highest frequency component is 900KHz and bandwidth is 12KHz. So lower frequency component is 900 – 12 = 888KHz.

9. What is the function of frequency mixer in super heterodyne receiver?
a) Multiplication of incoming signal and the locally generated carrier
b) Addition of incoming signal and the locally generated carrier
c) Amplification
d) Filtering