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Communications MCQ Set 1

1. Which of the following is an indirect way of generating frequency modulated signals?
a) Armstrong modulator
b) Varacter diode modulator
c) Reactance FET modulator
d) Reactance bipolar transistor modulator

View Answer

Answer: a [Reason:] The indirect way of generating frequency modulated signals was first proposed by Armstrong. A frequency modulator so designed is named as Armstrong modulator.

2. Which of the following determines carrier deviation in frequency modulation?
a) modulating voltage
b) frequency
c) amplitude
d) either frequency or amplitude

View Answer

Answer: a [Reason:] In frequency modulation, frequency of carrier varies with the modulating voltage. In frequency modulation, it is modulating voltage that is responsible for deviation of carrier.

3. Balance modulator is used to produce __________
a) DSB
b) VSB
c) AM
d) SSB

View Answer

Answer: a [Reason:] A balance modulator mixes audio signal and radio frequency carrier, but suppresses the carrier, leaving only sidebands. Double side band is usually produced by balance modulator.

4. Full AM signal is preferred over SSB in broadcasting purpose because ________
a) generation of full AM is easier
b) detection of full AM is simpler
c) requires large bandwidth
d) for both detection and generation of full AM

View Answer

Answer: b [Reason:] SSB is preferred because of its low bandwidth. It reduces its bandwidth by removing one of two bands since both bands are exactly same and carries same information. But full amplitude modulation is sometimes preferred over it because in it detection of full AM is simpler.

5. Which among the following is not necessarily the advantage of SSB over AM?
a) required bandwidth for SSB is low
b) less power handled
c) complex circuit
d) simple circuit

View Answer

Answer: d [Reason:] SSB is preferred because of its low bandwidth. It reduces its bandwidth by removing one of two bands since both bands are exactly same and carries same information. It has many more advantage over AM but it has not simple circuit.

6. Which filter is used to get back the original signal from sampled signal?
a) low pass filter
b) high pass filter
c) band pass filter
d) band reject filter

View Answer

Answer: a [Reason:] Sampling is the conversion of continuous-time signal to discrete-time signal. Now to get back the original signal we have to use low pass filter.

7. Carson’s rule is used to ________
a) calculate Bandwidth of FM signal
b) calculate SNR
c) calculate Modulation index
d) calculate Figure of merit

View Answer

Answer: a [Reason:] According to Carson’s rule, the required bandwidth is twice the sum of the maximum frequency deviation and the maximum modulating signal frequency or B = 2(fd +fm)Hz.

8. FM signals can be generated by using ________
a) Varacter diode
b) Laser diode
c) Backward diode
d) Gunn diode

View Answer

Answer: a [Reason:] Varacter diode or tuning diode that has a variable capacitance. It is operated as reverse-biased and therefore no current flows. It is mainly used for generation of FM signals only.

9. Granular noise occurs in Delta Modulation, when ____________
a) pulse rate decreases
b) pulse amplitude decreases
c) modulating signal increases
d) modulating signal remains constant

View Answer

Answer: d [Reason:] Delta modulation is used for transmission of voice information where quality is not the primarily importance. Its drawback is it has two noises namely slope overload and granular noise. So for getting rid from these noises we use ADM (Adaptive Delta Modulation).

10. DM stands for ________
a) Density Modulation
b) Delta Modulation
c) Doubling Modulation
d) Delta Medium

View Answer

Answer: b [Reason:] DM stands for Delta Modulation. Delta modulation is used for transmission of voice information where quality is not the primarily importance.

Communications MCQ Set 2

1. If we compared to the USB, the power in the LSB is ________
a) different
b) twice of USB
c) same
d) half of USB

View Answer

Answer: c [Reason:] The two bands i.e. upper sideband and lower sideband generally contains same information. They also has same power.

2. What will be the effect on power in amplitude modulated system if we increase the modulation index?
a) remains same
b) becomes twice
c) increases
d) decreases

View Answer

Answer: a [Reason:] If we increase or decrease modulation index, it not affects our power. So if we increase the modulation index our power remains same.

3. What is the modulation index for getting maximum power in amplitude modulated system?
a) 1
b) 12
c) 0.3
d) 0.8

View Answer

Answer: a [Reason:] For getting maximum power, it is required to set the maximum and minimum voltage of wave such that we get modulation index equal to unity.

4. How can we derive FM from PM?
a) by integrating the modulating signal before applying to the PM oscillator
b) by integrating signal out of the PM oscillator
c) by differentiating the modulating signal before applying to the PM oscillator
d) by differentiating signal out of the PM oscillator

View Answer

Answer: a [Reason:] Frequency modulation can be derived from phase modulated system, if we integrate our modulating signal. But this integration must be done before applying our wave to PM oscillator.

5. How an AM radio station increase its signal-to-noise ratio?
a) by increasing its modulation index
b) by decreasing its modulation index
c) by maintaining a constant modulation index
d) by increasing the frequency

View Answer

Answer: a [Reason:] Signal to noise ratio is the ratio of signal power to the noise power. It is often described in decibels. It is directly proportional with modulation index and thus it increases with modulation index.

6. FM bandwidth can be approximated by ________
a) Carson’s rule
b) Armstrong’s rule
c) Bessel’s rule
d) Pythagoras rule

View Answer

Answer: a [Reason:] Carson’s rule is made to calculate bandwidth of a frequency modulated system. According to Carson’s rule Bandwidth, B = 2(∆f + fm).

7. Which effect is observed when FM reception deteriorates abruptly due to noise?
a) Threshold effect
b) Capture effect
c) Noise effect
d) Limit effect

View Answer

Answer: a [Reason:] Threshold effect has low output signal to noise ratio. It contains large noise as compared to input signal to envelope detector. In threshold effect, detection of message signal is difficult.

8. FM stereo _________
a) is implemented using an SCA signal
b) has a higher signal to noise ratio than mono FM
c) is not compatible with mono FM
d) uses DSBSC AM modulation

View Answer

Answer: d [Reason:] A stereo FM contains three major sections :- monomode, stereo mode and section common to both mono and stereo mode. The stereo section is much complicated than others. It uses DSB AM modulation for its process.

9. Signal to noise ratio of a frequency modulated system is better than amplitude modulated system.
a) True
b) False

View Answer

Answer: a [Reason:] Signal to noise ratio is the ratio of signal power to the noise power. It is often described in decibels. It is directly proportional with modulation index and thus it increases with modulation index. It is better for frequency modulated systems.

10. What will be the effect on power if the distance between the sidebands and center frequency increases?
a) power decreases
b) power increases
c) power remains same
d) power becomes twice of its previous value

View Answer

Answer: a [Reason:] If the distance between the central frequency and sidebands increases, the effective power decreases.

Communications MCQ Set 3

1. When two or more signals share a common channel, it is called ________
a) sub-channeling
b) channeling
c) switching
d) multiplexing

View Answer

Answer: d [Reason:] Multiplexing is a method by which multiple analog or digital signals are combined. In multiplexing many signals are combined into one signal over a shared medium.

2. One of the reason of distortion is shift in phase relationships between baseband frequencies.
a) True
b) False

View Answer

Answer: a [Reason:] If we shift the phase relationships between baseband frequencies, it will ultimately results in distortion.

3. Miller effect can cause an amplifier to oscillate.
a) True
b) False

View Answer

Answer: a [Reason:] Miller effect is responsible for the increase in equivalent input capacitance of an inverting voltage amplifier. The increase equivalent input capacitance is given by, CM = C(1 + AV).

4. How can we successfully avoid Miller effect?
a) using a common-base amplifier
b) using a common-emitter amplifier
c) by increasing the Q factor
d) by decreasing the Q factor

View Answer

Answer: a [Reason:] Miller effect is responsible for the increase in equivalent input capacitance of an inverting voltage amplifier. The increase equivalent input capacitance is given by, CM = C(1 + AV). Miller effect can be avoided by using a common-base amplifier.

5. What is the two basic specification of a receiver?
a) sensitivity and selectivity
b) superious response and tracking
c) signal and noise
d) number of convertors and number of IFs

View Answer

Answer: a [Reason:] Sensitivity and selectivity are the two key specifications for any receiver, which is used for the purpose in communication.

6. Who invented the superheterodyne receivers?
a) Hertz
b) Armstrong
c) Foster
d) Seeley

View Answer

Answer: b [Reason:] Superheterodyne uses frequency mixing to convert a received signal to a fixed IF. This IF can be processed more easily than the original carrier frequency. IT was invented by Armstrong.

7. Skin effect refers ________
a) the increase of wire resistance with frequency
b) the decrease of wire resistance with frequency
c) the uniform nature of wire resistance with frequency
d) the way radio signals travel across a flat surface

View Answer

Answer: a [Reason:] Skin effect becomes more and more apparent as frequency increases. It refers to the increase of wire resistance with frequency.

8. What is the full form of AFC?
a) Amplitude to frequency conversion
b) Automatic frequency conversion
c) Automatic frequency control
d) Audio frequency control

View Answer

Answer: c [Reason:] AFC stands for Automatic frequency control. It is a method to automatically keep a resonant circuit tuned to frequency of an incoming radio signal.

9. The frequency of local oscillator ________
a) is above the RF frequency
b) is below the RF frequency
c) can be either below or above the RF frequency
d) is fixed typically at 450KHz

View Answer

Answer: c [Reason:] The frequency of local oscillator is not fixed. It can be below or above the RF frequency.

10. Phase distortion is important in ________
a) voice communication systems
b) color video receivers
c) monochrome video receivers
d) radio reception

View Answer

Answer: b [Reason:] Phase distortion is change in the shape of waveform. It occurs when filter’s phase response is not linear over the frequency range of interest. It is important in color video receivers.

Communications MCQ Set 4

1. What is the full form of DTMF?
a) Dual-Tone Multi frequency
b) Digital Telephony Multiple Frequency
c) Dual-Tone Master Frequency
d) Digital Tone Multiple Frequency

View Answer

Answer: a [Reason:] DTMF is an in-band telecommunication signal. It uses the voice-frequency band over telephone lines. It was developed by Bell Systems in United States.

2. If we see practically, parallel data transmission is sent ________
a) usually over long distances
b) over short distances only
c) usually over a coaxial cable
d) over any distance

View Answer

Answer: b [Reason:] In serial transmission, bits are transmitted one at a time over a single channel. In parallel transmission bits are sent simultaneously over their own individual channel. It sent data over short distances only.

3. Who invented the five-level teletype code?
a) Teletype company
b) Morkum company
c) Western Union
d) Emile Baudot

View Answer

Answer: d [Reason:] Emile Baudot invented the five-level teletype code. Each character in alphabet is represented by a series of five bits.

4. What is the full form of LATA?
a) Local Access Telephone Area
b) Local Area Telephone Access
c) Local Access and Transport Area
d) Local Area Transport Access

View Answer

Answer: c [Reason:] LATA is term in the U.S. for a geographical area covered by one or more local telephone companies. It is legally referred to as local exchange carriers.

5. The transmitter and receiver are frame-by-frame synchronized using the data bits in asynchronous transmission.
a) True
b) False

View Answer

Answer: b [Reason:] In Asynchronous transmission, transmitter and receiver are synchronized frame-by-frame using the start and stop bits, not by data bits.

6. Why synchronous transmission is more preferred?
a) it has no start and stop bits
b) it is cheaper than asynchronous
c) it is easier to implement
d) less complex

View Answer

Answer: a [Reason:] In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient.

7. In frequency modulation, there is a large increase in noise and hence decrease in the signal to noise ratio.
a) True
b) False

View Answer

Answer: b [Reason:] In frequency modulation, there is a large decrease in noise and hence increase in the signal to noise ratio.

8. The output of a battery eliminator is closed to ________
a) 70V DC
b) 70V AC
c) 6V AC
d) 6V DC
Answer: d

View Answer

Explanation: Battery eliminator is used to deliver electrical power without the need for multiple batteries. Its output power is approximately 6V.

9. Which statement is true about HDLC?
a) it is an IBM product
b) it is a bit-oriented protocol
c) it is identical to SDLC
d) it is non-identical to SDLC

View Answer

Answer: b [Reason:] HDLC is a high-level data link control. It is a bit-oriented protocol. HDLC is group of rules for transmitting data between network points.

10. What is the use of ARQ?
a) correct bit errors
b) put data in a temporary buffer
c) correct synchronization problems
d) make data bits simpler

View Answer

Answer: a [Reason:] ARQ is an error control method. It is used for data transmission that uses acknowledgements and inputs to achieve reliable data transmission.

Communications MCQ Set 5

1. Baseband compression produces ________
a) a small range of frequencies from low to high
b) a small range of different phases
c) a small number of signals
d) a small range of amplitude

View Answer

Answer: d [Reason:] A signal compression method in a wireless network provides efficient transfer of compressed signal samples over serial data links in the system. Baseband compression produces a small range of amplitude.

2. Automatic Level Control (ALC) is used to keep the modulation index close to 100%.
a) True
b) False

View Answer

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

3. A signal that ________ must have linear power amplifier.
a) is complex
b) has variable frequency
c) is linear
d) has variable amplitude

View Answer

Answer: d [Reason:] If any signal has variable amplitude then its amplifier must be linear.

4. Transmitters are designed usually to derive a load impedance of ________
a) 50 ohms resistive
b) 150 ohms resistive
c) 250 ohms resistive
d) 500 ohms resistive

View Answer

Answer: a [Reason:] Transmitter is an electronic device that produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. Transmitters are usually designed to derive a load impedance of 50 ohms resistive.

5. What we called a resistor if a transmitter is connected to a resistor instead of an antenna?
a) a test load
b) a temporary load
c) a dummy load
d) a heavy load

View Answer

Answer: c [Reason:] If a transmitter is connected to resistor not antenna than it is called dummy load.

6. A class D amplifiers is very efficient than other amplifiers.
a) True
b) False

View Answer

Answer: a [Reason:] Class D amplifier is also known as switching amplifier. It is operate as electronic switches, and not electric gain device which is commonly used in most amplifiers.

7. The carrier is suppressed in ________
a) a mixer
b) a frequency multiplier
c) a transducer
d) a balance modulator

View Answer

Answer: d [Reason:] A balance modulator is the one which mixes the audio and carrier of radio frequency. Balance modulator suppresses the carrier and leaves only sidebands.

8. What is the full form of AFC?
a) Amplitude to frequency conversion
b) Automatic frequency conversion
c) Automatic frequency control
d) Audio frequency control

View Answer

Answer: c [Reason:] AFC stands for Automatic frequency control. It is a method to automatically keep a resonant circuit tuned to frequency of an incoming radio signal.

9. Mixing is used in communication to ________
a) raise the carrier frequency
b) lower the carrier frequency
c) to altered the deviation
d) to change the carrier frequency to any required value

View Answer

Answer: d [Reason:] Mixing is used to change the frequency of carrier. The frequency can be changed to any required value in communication.

10. On which factor the bandwidth required for a modulated carrier depends?
a) baseband frequency range
b) signal to noise ratio
c) carrier frequency
d) amplitude of carrier frequency

View Answer

Answer: a [Reason:] Bandwidth can be seen as a range of frequencies within a band, that is used for transmitting a signal. A signal bandwidth is depend on amplitude of carrier frequency.

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