Communication Systems MCQs Aeronautical Engineering)

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What does the term ‘modulation’ refer to in communication systems?
A) The process of encoding data into signals
B) The process of decoding signals into data
C) The process of amplifying signals
D) The process of filtering signals
Answer: A) The process of encoding data into signals
2. Which modulation technique varies the amplitude of the carrier signal?
A) Frequency Modulation (FM)
B) Amplitude Modulation (AM)
C) Phase Modulation (PM)
D) Pulse Width Modulation (PWM)
Answer: B) Amplitude Modulation (AM)
3. In communication systems, what does ‘signal-to-noise ratio’ (SNR) measure?
A) The ratio of the signal power to the noise power
B) The ratio of the noise power to the signal power
C) The strength of the noise in a signal
D) The strength of the signal in a noise
Answer: A) The ratio of the signal power to the noise power
4. Which modulation technique is used to vary the frequency of the carrier signal?
A) Amplitude Modulation (AM)
B) Frequency Modulation (FM)
C) Phase Modulation (PM)
D) Pulse Code Modulation (PCM)
Answer: B) Frequency Modulation (FM)
5. What is ‘bandwidth’ in the context of communication systems?
A) The range of frequencies over which a signal is transmitted
B) The power of the transmitted signal
C) The time duration of the signal
D) The rate of data transmission
Answer: A) The range of frequencies over which a signal is transmitted
6. Which device is used to convert analog signals into digital signals?
A) Digital-to-Analog Converter (DAC)
B) Analog-to-Digital Converter (ADC)
C) Amplifier
D) Filter
Answer: B) Analog-to-Digital Converter (ADC)
7. What is the primary function of a ‘demodulator’ in a communication system?
A) To amplify the received signal
B) To convert the modulated signal back into its original form
C) To filter out unwanted noise
D) To encode data for transmission
Answer: B) To convert the modulated signal back into its original form
8. In digital communication, what is ‘bit rate’?
A) The number of bits transmitted per second
B) The frequency range of the signal
C) The time duration of each bit
D) The power of the transmitted signal
Answer: A) The number of bits transmitted per second
9. Which type of modulation involves varying the phase of the carrier signal?
A) Amplitude Modulation (AM)
B) Frequency Modulation (FM)
C) Phase Modulation (PM)
D) Pulse Code Modulation (PCM)
Answer: C) Phase Modulation (PM)
10. In a communication system, what does ‘noise’ refer to?
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– A) Unwanted signals that interfere with the desired signal
– B) The signal strength of the carrier
– C) The modulation index of the signal
– D) The bandwidth of the signal
– **Answer:** A) Unwanted signals that interfere with the desired signal
11. What is the purpose of ‘frequency hopping’ in communication systems?
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– A) To spread the signal over a wide frequency band to avoid interference
– B) To increase the data transmission rate
– C) To enhance the signal-to-noise ratio
– D) To reduce the signal bandwidth
– **Answer:** A) To spread the signal over a wide frequency band to avoid interference
12. Which modulation technique is typically used in FM radio broadcasting?
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– A) Amplitude Modulation (AM)
– B) Frequency Modulation (FM)
– C) Phase Modulation (PM)
– D) Pulse Code Modulation (PCM)
– **Answer:** B) Frequency Modulation (FM)
13. In digital communication, what does ‘sampling’ refer to?
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– A) The process of converting an analog signal into discrete digital values
– B) The process of amplifying the signal
– C) The process of filtering out noise
– D) The process of encoding data
– **Answer:** A) The process of converting an analog signal into discrete digital values
14. Which modulation technique is known for its robustness against signal degradation?
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– A) Amplitude Modulation (AM)
– B) Frequency Modulation (FM)
– C) Phase Modulation (PM)
– D) Pulse Code Modulation (PCM)
– **Answer:** B) Frequency Modulation (FM)
15. What does the term ‘channel capacity’ refer to in communication systems?
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– A) The maximum data rate that can be transmitted through a communication channel
– B) The minimum bandwidth required for data transmission
– C) The power of the signal in the channel
– D) The range of frequencies used in the channel
– **Answer:** A) The maximum data rate that can be transmitted through a communication channel
16. What is ‘quantization’ in digital signal processing?
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– A) The process of mapping a continuous range of values into a finite range of discrete values
– B) The process of amplifying the signal
– C) The process of filtering out noise
– D) The process of encoding data
– **Answer:** A) The process of mapping a continuous range of values into a finite range of discrete values
17. In communication systems, what is the ‘modulation index’?
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– A) A measure of the extent of modulation applied to the carrier signal
– B) The frequency of the carrier signal
– C) The bandwidth of the modulated signal
– D) The signal-to-noise ratio
– **Answer:** A) A measure of the extent of modulation applied to the carrier signal
18. Which modulation technique is commonly used in television broadcasting?
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– A) Amplitude Modulation (AM)
– B) Frequency Modulation (FM)
– C) Phase Modulation (PM)
– D) Pulse Width Modulation (PWM)
– **Answer:** B) Frequency Modulation (FM)
19. What is the primary function of a ‘repeater’ in communication systems?
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– A) To amplify and retransmit the signal to extend its range
– B) To encode data for transmission
– C) To convert digital signals to analog signals
– D) To filter out unwanted frequencies
– **Answer:** A) To amplify and retransmit the signal to extend its range
20. What does ‘spread spectrum’ technique achieve in communication systems?
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– A) It spreads the signal over a wide frequency band to minimize interference and improve security
– B) It reduces the signal bandwidth for efficient transmission
– C) It increases the amplitude of the signal
– D) It simplifies the modulation process
– **Answer:** A) It spreads the signal over a wide frequency band to minimize interference and improve security
21. In communication systems, what is ‘bit error rate’ (BER)?
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– A) The number of errors in a transmitted data stream per unit of time
– B) The total number of bits transmitted
– C) The ratio of signal power to noise power
– D) The time required to transmit a single bit
– **Answer:** A) The number of errors in a transmitted data stream per unit of time
22. Which technique is used to reduce the effects of noise in a communication system?
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– A) Error Correction Coding
– B) Frequency Modulation
– C) Amplitude Modulation
– D) Pulse Code Modulation
– **Answer:** A) Error Correction Coding
23. What does ‘carrier frequency’ refer to in modulation?
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– A) The frequency of the unmodulated signal used to carry information
– B) The frequency of the modulated signal
– C) The frequency range of the modulated signal
– D) The frequency of the noise in the system
– **Answer:** A) The frequency of the unmodulated signal used to carry information
24. Which modulation technique involves encoding data into pulses of varying width?
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– A) Pulse Code Modulation (PCM)
– B) Pulse Width Modulation (PWM)
– C) Amplitude Modulation (AM)
– D) Frequency Modulation (FM)
– **Answer:** B) Pulse Width Modulation (PWM)
25. What is the ‘Nyquist theorem’ related to in communication systems?
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– A) The minimum sampling rate required to accurately represent a signal
– B) The maximum bandwidth required for a signal
– C) The modulation index of a signal
– D) The signal-to-noise ratio
– **Answer:** A) The minimum sampling rate required to accurately represent a signal
26. Which technique is used to combine multiple signals into one signal over a shared medium?
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– A) Multiplexing
– B) Demodulation
– C) Modulation
– D) Amplification
– **Answer:** A) Multiplexing
27. What does ‘bit stuffing’ achieve in communication systems?
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– A) It ensures synchronization by adding extra bits to a data stream
– B) It encodes data into a signal
– C) It amplifies the signal
– D) It filters out noise
– **Answer:** A) It ensures synchronization by adding extra bits to a data stream
28. In communication systems, what is ‘Doppler shift’?
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– A) The change in frequency of a signal due to relative motion between the transmitter and receiver
– B) The change in amplitude of a signal due to interference
– C) The change in phase of a signal due to modulation
– D) The change in bandwidth of a signal due to noise
– **Answer:** A) The change in frequency of a signal due to relative motion between the transmitter and receiver
29. Which modulation technique is most resistant to noise and interference?
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– A) Amplitude Modulation (AM)
– B) Frequency Modulation (FM)
– C) Phase Modulation (PM)
– D) Pulse Code Modulation (PCM)
– **Answer:** B) Frequency Modulation (FM)
30. What is ‘Error Detection’ in communication systems?
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– A) Techniques used to identify errors in transmitted data
– B) Techniques used to correct errors in transmitted data
– C) Techniques used to encrypt transmitted data
– D) Techniques used to amplify transmitted data
– **Answer:** A) Techniques used to identify errors in transmitted data
31. In communication systems, what does ‘demodulation’ refer to?
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– A) The process of recovering the original signal from the modulated carrier
– B) The process of encoding data into a carrier signal
– C) The process of amplifying the carrier signal
– D) The process of converting digital signals into analog signals
– **Answer:** A) The process of recovering the original signal from the modulated carrier
32. What is the primary purpose of ‘forward error correction’ (FEC)?
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– A) To correct errors in data transmission without the need for retransmission
– B) To detect errors in data transmission
– C) To encrypt data for secure transmission
– D) To modulate the carrier signal
– **Answer:** A) To correct errors in data transmission without the need for retransmission
33. What does ‘time division multiplexing’ (TDM) accomplish?
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– A) It divides the time into slots and allocates each slot to a different signal
– B) It divides the frequency spectrum into multiple channels
– C) It modulates the signal to reduce noise
– D) It amplifies the signal to extend range
– **Answer:** A) It divides the time into slots and allocates each slot to a different signal
34. Which type of filter is commonly used to eliminate high-frequency noise in communication systems?
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– A) Low-pass filter
– B) High-pass filter
– C) Band-pass filter
– D) Band-stop filter
– **Answer:** A) Low-pass filter
35. What is ‘symbol rate’ in digital communication?
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– A) The rate at which symbols are transmitted per second
– B) The number of bits per symbol
– C) The bandwidth of the signal
– D) The frequency of the carrier signal
– **Answer:** A) The rate at which symbols are transmitted per second
36. What is ‘pulse shaping’ in communication systems?
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– A) The process of modifying the shape of the transmitted pulse to reduce interference and improve performance
– B) The process of amplifying the signal
– C) The process of encoding data into pulses
– D) The process of filtering out noise
– **Answer:** A) The process of modifying the shape of the transmitted pulse to reduce interference and improve performance
37. In communication systems, what is the purpose of ‘spread spectrum’ techniques?
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– A) To spread the signal over a wide frequency band to improve security and reduce interference
– B) To compress the signal for efficient transmission
– C) To increase the data rate of the signal
– D) To amplify the signal
– **Answer:** A) To spread the signal over a wide frequency band to improve security and reduce interference
38. Which modulation technique is characterized by varying the width of the pulses?
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– A) Pulse Width Modulation (PWM)
– B) Frequency Modulation (FM)
– C) Amplitude Modulation (AM)
– D) Phase Modulation (PM)
– **Answer:** A) Pulse Width Modulation (PWM)
39. What does ‘co-channel interference’ refer to in communication systems?
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– A) Interference caused by signals operating on the same frequency channel
– B) Interference caused by signals operating on different frequency channels
– C) Interference caused by noise in the system
– D) Interference caused by multipath propagation
– **Answer:** A) Interference caused by signals operating on the same frequency channel
40. What is the primary advantage of ‘frequency division multiplexing’ (FDM)?
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– A) It allows multiple signals to be transmitted simultaneously over the same channel by using different frequency bands
– B) It divides the signal into different time slots for transmission
– C) It increases the bandwidth of the signal
– D) It amplifies the signal to extend its range
– **Answer:** A) It allows multiple signals to be transmitted simultaneously over the same channel by using different frequency bands
41. What is ‘adaptive modulation’?
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– A) A technique that adjusts the modulation scheme based on the quality of the communication channel
– B) A technique that amplifies the signal for better performance
– C) A technique that encodes data into signals
– D) A technique that filters out unwanted frequencies
– **Answer:** A) A technique that adjusts the modulation scheme based on the quality of the communication channel
42. Which modulation technique is used in digital cellular systems?
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– A) Quadrature Amplitude Modulation (QAM)
– B) Frequency Modulation (FM)
– C) Amplitude Modulation (AM)
– D) Pulse Code Modulation (PCM)
– **Answer:** A) Quadrature Amplitude Modulation (QAM)
43. What does ‘multipath propagation’ refer to in communication systems?
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– A) The phenomenon where a signal arrives at the receiver by multiple paths due to reflection, diffraction, and scattering
– B) The process of encoding data into signals
– C) The process of amplifying the signal
– D) The process of filtering out noise
– **Answer:** A) The phenomenon where a signal arrives at the receiver by multiple paths due to reflection, diffraction, and scattering
44. Which modulation technique is commonly used for high-definition television (HDTV) broadcasting?
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– A) Quadrature Amplitude Modulation (QAM)
– B) Frequency Modulation (FM)
– C) Phase Modulation (PM)
– D) Pulse Width Modulation (PWM)
– **Answer:** A) Quadrature Amplitude Modulation (QAM)
45. What is the function of a ‘mixer’ in communication systems?
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– A) To combine two signals to produce new frequencies
– B) To amplify the received signal
– C) To filter out unwanted noise
– D) To encode data for transmission
– **Answer:** A) To combine two signals to produce new frequencies
46. In communication systems, what is ‘error correction’ used for?
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– A) To identify and correct errors in transmitted data
– B) To detect errors in transmitted data
– C) To encode data for transmission
– D) To modulate the carrier signal
– **Answer:** A) To identify and correct errors in transmitted data
47. What is ‘frequency division duplexing’ (FDD)?
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– A) A technique where different frequency bands are used for transmission and reception
– B) A technique where time slots are used for transmission and reception
– C) A technique where multiple signals are combined into one signal
– D) A technique where the signal is spread over a wide frequency band
– **Answer:** A) A technique where different frequency bands are used for transmission and reception
48. What is ‘phase shift keying’ (PSK)?
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– A) A modulation technique where data is encoded by varying the phase of the carrier signal
– B) A modulation technique where data is encoded by varying the frequency of the carrier signal
– C) A modulation technique where data is encoded by varying the amplitude of the carrier signal
– D) A modulation technique where data is encoded by varying the width of pulses
– **Answer:** A) A modulation technique where data is encoded by varying the phase of the carrier signal
49. What is ‘carrier frequency’?
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– A) The frequency of the signal that carries the information
– B) The frequency of the modulating signal
– C) The frequency of the noise in the system
– D) The frequency of the signal after demodulation
– **Answer:** A) The frequency of the signal that carries the information
50. In digital communication, what does ‘symbol’ represent?
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– A) A unit of data that represents a group of bits
– B) A unit of analog signal
– C) A unit of noise in the system
– D) A unit of frequency in the signal
– **Answer:** A) A unit of data that represents a group of bits

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