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Communications MCQ Set 1

1. Which layer is used for detection of bad frames in wide area network?
a) frame layer
b) link layer
c) error-check layer
d) complex layer

View Answer

Answer: b [Reason:] Wide area network covers a long geographical area and thus it also has least connected devices. Link layer is used in WAN for detection of bad frames.

2. MAU stands for __________
a) Multiple Access Unit
b) Multi-station Access Unit
c) Multiple Auxiliary Unit
d) Multi-station Access Unit

View Answer

Answer: b [Reason:] MAU stands for Multi-station Access Unit. It is a hub that connects a group of computers to a token ring LAN.

3. Packet switching is based on ________
a) switched circuits
b) un-switched circuits
c) store-and-forward
d) real time delivery

View Answer

Answer: c [Reason:] It is a method of grouping data transmitted into packets. It works on the algorithm of store and forward.

4. AM spectrum consists of ________
a) Carrier frequency
b) Upper sideband
c) Lower sideband
d) Carrier frequency with both upper and lower sideband

View Answer

Answer: d [Reason:] Spectrum of Am wave consists of a carrier with two sidebands. It is found that if carrier frequency is 5KHz then the two sidebands produced by it is 5KHz away from the carrier.

5. TEM stands for Transmitted Electromagnetic wave.
a) True
b) False

View Answer

Answer: b [Reason:] TEM stands for Transverse Electromagnetic wave. Since both electric and magnetic field are transverse to the direction of wave propagation.

6. What is the reason of attenuation in free space?
a) decrease in energy per square meter due to expansion
b) decrease in energy per square meter due to absorption
c) losses in upper atmosphere due to expansion
d) losses in upper atmosphere due to absorption

View Answer

Answer: a [Reason:] In free space, the basic reason of attenuation is the decrease in energy per square meter. It generally happens due to expansion.

7. What is the range of UHF?
a) below the microwave range
b) above the microwave range
c) same as the microwave range
d) inside the microwave range

View Answer

Answer: a [Reason:] Ultra high frequency is the ITU designation for radio frequencies that lies under 300MHz to 3 GHz i.e. its range is below the microwave range.

8. Striplines and microstrips are used to __________
a) couple sections of waveguide
b) couple waveguides to antennas
c) couple components on a circuit board
d) arrange waves in an order

View Answer

Answer: c [Reason:] The main use of Striplines and microstrips in any circuit is to couple components on a circuit board.

9. What is the another term used for a single microwave link?
a) section
b) hop
c) jump
d) skip

View Answer

Answer: b [Reason:] Microwave link is a communication system that uses a beam of radio waves in the microwave frequency range. Hop is also used in places of single microwave link.

10. In digital microwave systems, additional repeaters increase the ________
a) reliability
b) noise level
c) jitter
d) sensitivity

View Answer

Answer: c [Reason:] In telecommunication, jitter can be seen as a deviation from true periodicity of a presumably periodic signal. Higher level of jitter are more likely to occur on either slow or heavily congested link. In any circuit, adding additional repeaters finally increase the jitter only.

Communications MCQ Set 2

1. For Amplitude Modulation, Emitter modulator ________
a) Operates in class C mode
b) Has a low efficiency
c) Output power is high
d) Operates in class B mode

View Answer

Answer: b [Reason:] Emitter Modulator operates in class A region. It has a very low efficiency. The output power is low so for modulation at high level, it is not suitable.

2. MAU stands for __________
a) Multiple Access Unit
b) Multi-station Access Unit
c) Multiple Auxiliary Unit
d) Multi-station Access Unit

View Answer

Answer: b [Reason:] MAU stands for Multi-station Access Unit. It acts as a hub that connects a group of computers to a token ring local area network.

3. Packet switching is based on ________
a) switched circuits
b) un-switched circuits
c) store-and-forward
d) real time delivery

View Answer

Answer: c [Reason:] Packet switching is a method of grouping data transmitted over a network into packets. It is based on store and forward algorithm.

4. What is used for setting up a virtual circuit?
a) frame
b) network
c) link
d) user

View Answer

Answer: b [Reason:] For creation of any virtual circuit, a network is must required.

5. Which modulation is used in high frequency radio-teletype systems?
a) QAM
b) SSB
c) PSK
d) FSK

View Answer

Answer: d [Reason:] Frequency Shift Keying is a type of frequency modulation. In it data is transmitted through discrete frequency changes of a carrier signal. It is highly used in frequency radio-teletype systems.

6. When we use TDMA instead of TDM?
a) when signals come from different sources
b) when all the signals come from same source
c) when all the signals contain the same information
d) when there is RF communication

View Answer

Answer: a [Reason:] If all the signals comes from different types of sources, then it is better to use TDMA instead of TDM.

7. The effect of frequency on the resistance of a wire is called ________
a) skin effect
b) I2R loss
c) ohmic effect
d) threshold effect

View Answer

Answer: a [Reason:] Skin effect becomes more and more apparent as frequency increases. It is the effect of frequencies on the resistance of a wire.

8. The electric and magnetic field of a radio wave are perpendicular to each other.
a) True
b) False

View Answer

Answer: a [Reason:] The statement is correct that both fields are perpendicular to each other. They are also perpendicular to the direction of propagation.

9. Which polarization is possible for an electromagnetic wave?
a) vertical
b) circular
c) horizontal
d) can be vertical or horizontal or circular

View Answer

Answer: d [Reason:] In electromagnetic waves, both electric and magnetic fields are present. Due to which it can be vertically polarized or horizontally or circularly polarized.

10. On which factor dominant mode of a waveguide depends?
a) shape
b) power
c) point of signal injection
d) bandwidth

View Answer

Answer: a [Reason:] A waveguide is something that guides waves, such as electromagnetic wave or sound with minimum loss of energy. The dominant mode of a waveguide depends on the shape of the waveguide.

Communications MCQ Set 3

1. Flyback switched mode is used in television because it can supply many voltage outputs.
a) True
b) False

View Answer

Answer: b [Reason:] Flyback switched mode is used in television because it does not require filter choke. It is also cheap as compare to others.

2. What will be the effect on power if the modulation index of a frequency modulated signal is increased?
a) increases
b) decreases
c) remains constant
d) first increases and then decreases

View Answer

Answer: c [Reason:] In frequency modulation, power remains constant. So if we increase the modulation index then also it does not affect power, it will remains constant.

3. The equation 20sin⁡(108 t + 3 sin⁡ 109 t) represents which modulation?
a) AM
b) PCM
c) PM
d) FM

View Answer

Answer: d [Reason:] On comparing with the general equation of each modulation, we found that it represents Frequency modulation.

4. Monopole antenna is a type of travelling wave antenna.
a) True
b) False

View Answer

Answer: b [Reason:] Monopole antenna is a type of wire antenna. Travelling wave antenna consists helical antenna, spiral antenna.

5. In which modulation, frequency of carrier signal is varied with the amplitude of modulating signal?
a) FM
b) AM
c) PM
d) VSB

View Answer

Answer: a [Reason:] In Frequency Modulation the frequency of carrier is varied with the instantaneous amplitude of modulating signal.

6. In Phase Modulation the phase of carrier signal is varied.
a) True
b) False

View Answer

Answer: a [Reason:] In phase modulation the phase shift of carrier is varied with the instantaneous amplitude of modulating signal.

7. Power spectral density of thermal noise remains uniform upto frequency ___________
a) 1015 HZ
b) 105 HZ
c) 102 HZ
d) 1013 HZ

View Answer

Answer: d [Reason:] Power spectral density of thermal or white noise gets affected when the frequency becomes greater than 1013 Hz.

8. Carrier frequency remains constant in cell communication.
a) True
b) False

View Answer

Answer: b [Reason:] In cell communication carrier frequency does not remains constant. The carrier frequency get changes continuously.

9. Waves of which frequency can penetrate the atmosphere?
a) higher than 10 MHz
b) higher than 20 MHz
c) higher than 30 MHz
d) higher than 100 MHz

View Answer

Answer: c [Reason:] Any wave having frequency greater than 30 MHz can penetrate the atmosphere. The waves having frequency less than it cannot penetrate the atmosphere.

10. Armstrong modulator can only generate FM signal.
a) True
b) False

View Answer

Answer: b [Reason:] Armstrong Modulator can also generate PM along with FM. So the statement is incorrect.

Communications MCQ Set 4

1. The time taken by the charge carrier to cross from the emitter to the collector is called ________
a) miller time
b) transit time
c) charge time
d) base time

View Answer

Answer: b [Reason:] Transit time is that time which is taken by the charge carriers to move from emitter to collector.

2. The person who sent the first radio signal across the atlantic ocean was ________
a) Marconi
b) Maxwell
c) Hertz
d) Bell

View Answer

Answer: a [Reason:] Marconi is the first person who sent the first radio signal across the atlantic ocean. It was Maxwell who originated the theory of radio waves. After some years, it was Hertz who applied Maxwell theories to the production and reception of waves.

3. What is the use of bypass capacitor?
a) to remove RF from non-RF circuits
b) to couple RF around an amplifier
c) to neutralize amplifiers
d) to reduce the miller effect

View Answer

Answer: a [Reason:] A bypass capacitor is generally used to dampen the AC or noise present at all frequencies. In communication, it is used to remove RF from non-RF circuits.

4. The ability to change the operating frequency rapidly without a lot of retuning is called ________
a) Agility
b) VFO
c) Expansion
d) Spread-spectrum

View Answer

Answer: a [Reason:] Agility is the process of changing operating frequency rapidly without a lot of returning.

5. A resonant circuit is used in narrowband RF amplifiers.
a) True
b) False

View Answer

Answer: a [Reason:] The quality factor Q, of a resonant circuit is a measure of quality of resonant circuit. We can also say that it tells about “goodness” of resonant circuit. A higher value for Q means a more narrow bandwidth, which we want in many application.

6. What is the full form of ALC?
a) Amplitude Level Control
b) Automatic Level Control
c) Accurate Level Control
d) Amplitude Limiter Control

View Answer

Answer: b [Reason:] ALC stands for Automatic Level Control. It is a technology which is used for automatic control of output power.

7. In high level amplitude modulation, power in the sidebands comes from _________
a) Modulating amplifier
b) RF amplifier
c) Driver stage
d) Carrier

View Answer

Answer: a [Reason:] In amplitude modulated system, amplitude of carrier is varied in proportion with the wave being transmitted. For high level amplitude modulation, modulating amplifiers is used to give power to sideband.

8. To generate a SSB signal ________
a) Full carrier AM is required
b) DSB-SC is required
c) Quadrature signal is required
d) High frequency signal is needed

View Answer

Answer: b [Reason:] Single side band uses only one of its sideband among two sidebands. The two sidebands carries exactly the same information and thus removing a sideband does not have any effect on our signal. Due to the removal of one sideband total bandwidth required also decreases which makes it more efficient than others. For its generation, a high frequency signal is needed.

9. Which statement is true about direct FM modulator?
a) it integrates the modulating signal
b) it differentiates the modulating signal
c) varies the frequency of carrier oscillator
d) varies the phase of carrier oscillator

View Answer

Answer: c [Reason:] Frequency modulated system can be produced either by direct ways or indirect ways. Armstrong method comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator.

10. Which statement is true about indirect FM modulator?
a) it integrates the modulating signal
b) it differentiates the modulating signal
c) varies the frequency of carrier oscillator
d) varies the phase of carrier oscillator

View Answer

Answer: d [Reason:] Frequency modulated system can be produced either by direct ways or indirect ways. Armstrong method comes under indirect method. Direct FM modulator is generally used to vary the frequency of carrier oscillator while indirect FM modulator varies the phase of carrier oscillator.

Communications MCQ Set 5

1. What is the expected modulation index in case of wide band FM?
a) less than 1
b) 1
c) 12
d) more than 1

View Answer

Answer: d [Reason:] For producing Narrow band frequency modulation, modulation index should be less than 1. For wideband frequency modulation, modulation index should be greater than 1.

2. What is the expected modulation index in case of narrow band FM?
a) less than 1
b) 1
c) 12
d) more than 1

View Answer

Answer: a [Reason:] For producing Narrow band frequency modulation, modulation index should be less than 1. For wideband frequency modulation, modulation index should be greater than 1.

3. Which of the following statement is true about pulse position modulation system?
a) pulses have constant width but varying amplitude
b) pulses have constant amplitudes and constant widths
c) pulses have constant amplitude but varying widths
d) pulses have varying width and varying amplitude

View Answer

Answer: b [Reason:] In pulse modulation, message information is encoded in the amplitude of series of signal pulse. In pulse modulation, pulses have both constant amplitude and widths.

4. IF stage is a receiver exploys ________
a) impedance coupling
b) capacitive coupling
c) single tuned transformer coupling
d) double tuned transformer coupling

View Answer

Answer: d [Reason:] A frequency to which a carrier wave is shifted as an intermediate step is known as Intermediate Frequency. It exploys double tuned transformer coupling.

5. A 1000 KHz carrier is modulated with 300 Hz, 8000 Hz and 2 KHz waves. Determine the frequencies whose chances of occurring in output is least?
a) 1000 KHz
b) 1002 KHz
c) 998 KHz
d) 999.2 KHz

View Answer

Answer: a [Reason:] Frequencies present in output are of the form fc ± fm, fc ± 2fm, fc ± 3fm.

6. In higher power AM transmission, modulation is done at _________
a) Buffer stage
b) IF stage
c) Oscillator stage
d) RF power stage

View Answer

Answer: d [Reason:] RF power amplifier converts a low power radio frequency signal to high power. Modulation is done at RF power stage for high power AM transmission.

7. If modulation index of an AM was in changed from 0 to 1, then transmitted power ________
a) increases by 100%
b) increases by 50%
c) increases by 75%
d) remains unaffected

View Answer

Answer: b [Reason:] Modulation index tells us that by how much amount the modulated carrier signal varies around its unmodulated level. If modulation index changes to 1 from 0, its P_t increases by 50%.

8. ________ microphones works on piezoelectric effect?
a) Crystal
b) Carbon
c) Moving coil
d) Condenser

View Answer

Answer: a [Reason:] Piezoelectric effect is the generation of electric charge in response to applied mechanical stress. Crystal microphones works on it only.

9. In PCM system, output S/N increases ________
a) linearly with width
b) exponentially with bandwidth
c) inversely with bandwidth
d) linearly with bandwidth

View Answer

Answer: b [Reason:] Pulse code modulation (PCM) is a digital form of communication. If we calculate the ratio of signal to noise ratio for different bandwidth then we observe that it increases exponentially with it.

10. Companding is used in PCM transmitters to overcome quantizing noise in PCM.
a) True
b) False

View Answer

Answer: b [Reason:] It decreases the number of bits required to record the strongest signal. Companding also improves signal to noise ratio.

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