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Digital Communications MCQs set-5
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1. Some of the M-ary waveforms are
PAM
PPM
PDM
All of the mentioned
2. Which method should be implemented for reducing bandwidth?
Multilevel codes
Multilevel signalling
PAM
PDM
3. In M-ary PPM waveform, modulation is effected by
Delaying
Advancing
Delaying & Advancing
None of the mentioned
4. For both PPM and PDM _______ is kept constant.
Amplitude
Time period
Frequency
Number of levels
5. The method in which small amount of controlled ISI is introduced into the data stream rather than trying to eliminate it completely is called as
Correlative coding
Duobinary signalling
Partial response signalling
All of the mentioned
6. From digital filter we will get the output pulse as the _______ of the current and the previous pulse.
Summation
Difference
Product
Ratio
7. In duobinary signalling method, for M-ary transmission, the number of output obtained is
2M
2M+1
2M-1
M2
8. The method using which the error propagation in dubinary signalling can be avoided is
Filtering
Precoding
Postcoding
None of the mentioned
9. In precoding technique, the binary sequence is _____ with the previous precoded bit.
And-ed
Or-ed
EXOR-ed
Added
10. The duobinary filter, He (f) is called as
Sine filter
Cosine filter
Raised cosine filter
None of the mentioned
11. The method which has greater bandwidth efficiency is called as
Duobinary signalling
Polybinary signalling
Correlative coding
All of the mentioned
12. In polybinary signalling method the present bit of binary sequence is algebraically added with ______ number of previous bits.
j
2j
j+2
j-2
13. The primary advantage of this method is
redistribution of spectral density
to favor low frequencies
redistribution of spectral density & to favor low frequencies
none of the mentioned
14. Source encoding procedure does
Sampling
Quantization
Compression
All of the mentioned
15. Which signals are function of time?
Random signal
Deterministic signal
Random & Deterministic signal
None of the mentioned
16. Auto-correlation function is a
Even function
Odd function
Even & Odd function
None of the mentioned
17. Shot noise occurs in
Transistors
Valves
Transistors & Valves
None of the mentioned
18. Source coding reduces
Redundancy
Average bit rate
Redundancy & Average bit rate
None of the mentioned
19. Delay element in delta modulation acts as
First order predictor
Second order predictor
Third order predictor
Fourth order predictor
20. Non uniform quantization includes
Compression
Expansion
Compression & Expansion
None of the mentioned
21. The quantization will be finer when
Smaller the number of discrete amplitudes
Larger the number of discrete amplitudes
Does not depend on amplitudes
None of the mentioned
22. Different cases of sampling include
Ideal impulse sampling
Flat-topped sampling
Sampling with rectangular pulses
All of the mentioned
23. Transmitted pulse becomes distorted due to
Ideal transmission characteristic
Non ideal transmission characteristic
All of the mentioned
None of the mentioned
24. In which mixing is easier?
Analog signal
Digital signal
Analog & Digital signal
None of the mentioned
25. Which filter does not have sharp output?
Linear phase filter
Delayed symmetric filter
Linear phase & Delayed symmetric filter
None of the mentioned
26. Using ARMA filter
Sampling can be done in real time
Gives sharp output
All of the mentioned
None of the mentioned
27. To avoid aliasing
Reduce the bandwidth
Cut out high frequency
Reduce the bandwidth & Cut out high frequency
None of the mentioned
28. Which requires interpolation filtering?
Up-sampler
D to A converter
Up-sampler & D to A converter
None of the mentioned
29. A to D conversion process uses
Sampler
Quantizer
Sampler & Quantizer
None of the mentioned
30. Reconstruction filter is difficult to implement in hardware.
True
False
31. Which process requires low pass filter?
Up-sampling
Down-sampling
Up-sampling & Down-sampling
None of the mentioned
32. Decreasing the data rate is called as
Aliasing
Down sampling
Up sampling
None of the mentioned
33. Original signal came to be retraced from sampled version using
Low pass filtering
High pass filtering
Low & High pass filtering
None of the mentioned
34. The signal can be reconstructed
At Nyquist rate
Above Nyquist rate
At & above the Nyquist rate
None of the mentioned
35. Which device is needed for the reconstruction of signal?
Low pass filter
Equalizer
Low pass filter & Equalizer
None of the mentioned
36. The term heterodyning refers to
Frequency conversion
Frequency mixing
Frequency conversion & mixing
None of the mentioned
37. The causes for error performance degradation in communication systems are
Interference
Electrical noise
Effect of filtering
All of the mentioned
38. Thermal noise in the communication system due to thermal electrons
Can be eliminated
Cannot be eliminated
Can be avoided upto some extent
None of the mentioned
39. White noise has _______ power spectral density.
Constant
Variable
Constant & Variable
None of the mentioned
40. Which are called as hard decisions?
Estimates of message symbol with error correcting codes
Estimates of message symbol without error correcting codes
All of the mentioned
None of the mentioned
41. The filter which is used to recover the pulse with less ISI is called as
Matched filter
Correlator
Matched filter & Correlator
None of the mentioned
42. The composite equalizing filter is the combination of
Receiving and equalizing filter
Transmitting and equalizing filter
Amplifier and equalizing filter
None of the mentioned
43. The sample from the demodulation process consists of sample which is _______ to energy of the received symbol and _____ to noise.
Directly and inversely proportional
Inversely and directly proportional
Both directly proportional
Both inversely proportional
44. The average noise power of white noise is
0
Infinity
1
None of the mentioned
45. The channel may be affected by
Thermal noise
Interference from other signals
Thermal noise & Interference from other signals
None of the mentioned
46. Channels display multi-path due to
Scattering
Time delayed reflections
Diffraction
All of the mentioned
47. The method in which the tail of one pulse smears into adjacent symbol interval is called as
Intersymbol interference
Interbit interference
Interchannel interference
None of the mentioned
48. If each pulse of the sequence to be detected is in _____ shape, the pulse can be detected without ISI.
Sine
Cosine
Sinc
None of the mentioned
49. What is symbol rate packing?
Maximum possible symbol transmission rate
Maximum possible symbol receiving rate
Maximum bandwidth
Maximum ISI value allowed
50. A nyquist pulse is the one which can be represented by _____ shaped pulse multiplied by another time function.
Sine
Cosine
Sinc
None of the mentioned
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