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Digital Communications MCQs set-12
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1. Entropy calculation returns
Random variable
Deterministic number
Random number
None of the mentioned
2. Entropy of N random variables is the _____ of the entropy of individual random variable.
Sum
Product
Sum of squares
Average
3. Average energy per bit is given by
average energy symbol/log2 M
average energy symbol * log2 M
log2 M/ Average energy symbol
none of the mentioned
4. Which FSK has no phase discontinuity?
Continuous FSK
Discrete FSK
Uniform FSK
None of the mentioned
5. FSK reception is
Phase Coherent
Phase non coherent
Phase Coherent & non coherent
None of the mentioned
6. FSK reception uses
Correlation receiver
PLL
Correlation receiver & PLL
None of the mentioned
7. In non coherent reception _____ is measured.
Phase
Energy
Power
None of the mentioned
8. Every frequency has ____ orthogonal functions.
One
Two
Four
Six
9. If we correlate the received signal with any one of the two orthogonal function, the obtained inner product will be
In phase
Quadrature
Zero
Cannot be determined
10. If we correlate the received signal with both orthogonal function the inner product will be
In phase
Quadrature
In phase and quadrature
Unity
11. Simulation is used to determine
Bit error rate
Symbol error rate
Bit error
Symbol error
12. Matched filter is a _____ technique.
Modulation
Demodulation
Modulation & Demodulation
None of the mentioned
13. Which is called as on-off keying?
Amplitude shift keying
Uni-polar PAM
Amplitude shift keying & Uni-polar PAM
None of the mentioned
14. QAM uses ______ as the dimensions.
In phase
Quadrature
In phase & Quadrature
None of the mentioned
15. Which system uses QAM?
Digital microwave relay
Dial up modem
Digital microwave relay & Dial up modem
None of the mentioned
16. In phase lock which parameter is synchronized
Frequency
Phase
Frequency & Phase
None of the mentioned
17. Coherent modulation requires ____ level of synchronization.
One
Two
Three
None of the mentioned
18. Non coherent system requires
Phase synchronization
Frequency synchronization
Phase & Frequency synchronization
None of the mentioned
19. For block codes _____ is necessary.
Phase synchronization
Frequency synchronization
Frame synchronization
None of the mentioned
20. The synchronization necessary for BPSK is
Frequency tracking
Bit timing
Phase tracking
All of the mentioned
21. Transmitter synchronization implies
One way communication
Two way communication
One & Two way communication
None of the mentioned
22. As the synchronization levels increases, cost
Decreases
Increases
Remains the same
None of the mentioned
23. Synchronization is used in system which has
Non coherent modulation techniques
Many users accessing
Non coherent modulation techniques & Many users accessing
None of the mentioned
24. Which method has fast acquisition and can work without return link?
Open loop method
Closed loop method
Open & Closed loop method
None of the mentioned
25. Which method has two way link?
Open loop method
Closed loop method
Open & Closed loop method
None of the mentioned
26. Which method requires external authority and is inflexible?
Open loop method
Closed loop method
Open & Closed loop method
None of the mentioned
27. Which method needs precorrect time?
Open loop method
Closed loop method
Open & Closed loop method
None of the mentioned
28. In open loop method, the time reference error __________ with respect to time.
Increases exponentially
Decreases exponentially
Increases quadratically
Decreases quadratically
29. When a terminal is able to utilize the measurements made on the return link it is called as
Open loop method
Closed loop method
Quasi close loop method
None of the mentioned
30. Which reduces the effective distance between signals in signal space?
Time error
Frequency offset
Time error & Frequency offset
None of the mentioned
31. The system which has ______ signal to noise ratio can tolerate larger timing error.
Large
Small
Large & Small
None of the mentioned
32. Phase locked loops consists of
Phase detectors
Loop filter
Voltage controlled oscillator
All of the mentioned
33. In VCO the output frequency is a linear function of its input
Frequency
Voltage
Time period
None of the mentioned
34. PLL designs have
First order loop
Second order loop
Higher order loop
None of the mentioned
35. A cycle slip occurs when the magnitude of the original phase error exceeds
Î radians
2Ï€ radians
Ï€/2 radians
Ï€2 radians
36. When phase noise and phase jitter is doubled, the phase variance increases by
Two times
Four times
0.5 times
8 times
37. Acquisition is a ______ operation.
Linear
Non linear
Linear & Non linear
None of the mentioned
38. To avoid the loop to be driven to lock, the sweep rate should be
Smaller
Larger
It does not depend on it
None of the mentioned
39. Which method is more accurate?
Closed loop synchronizer
Open loop synchronizer
Closed & Open loop synchronizer
None of the mentioned
40. What is the function of the edge detector?
Differentiation
Rectification
Differentiation & Rectification
None of the mentioned
41. Continuous phase modulation has
More bandwidth efficiency
More smoothness
More bandwidth efficiency & smoothness
None of the mentioned
42. CPM has
Narrower bandwidth
Wider bandwidth
More bandwidth requirement
None of the mentioned
43. The number of filters in CPM receiver structure is
LM
ML
M/L
None of the mentioned
44. In which modulation schemes, the spreading of spectrum occurs?
Frequency modulation
Amplitude modulation
Frequency & Amplitude modulation
None of the mentioned
45. Gaussian noise has _____ power spread _____ over all frequencies.
Zero, uniformly
Zero, non uniformly
Infinite, uniformly
Infinite, non uniformly
46. Jamming is caused by
Multipath
Natural phenomena
Multipath & Natural phenomena
None of the mentioned
47. Which system makes the detection difficult for all users other than the intended users?
Low probability of intercept
Low probability of detection
Low probability of intercept & detection
None of the mentioned
48. The radio meter consists of
Low pass filter
High pass filter
Band pass filter
Band reject filter
49. Spread spectrum signals are used for
Ranging
Determination of position
Ranging & Determination of position
None of the mentioned
50. Uncertainty in the delay measurement is _________ to the bandwidth of signal pulse.
Directly proportional
Inversely proportional
Not related
None of the mentioned
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