1. TECHNICAL QUIZ-I
EC6501 DIGITAL COMMUNICATION YEAR-III SEM-V

2. 1. What is the first Communication system used?
Telephony
Telegraphy
Analog Transmission system
None of the above

3. 2) Which does not belong to analog pulse modulation?
Pulse Amplitude modulation
Pulse Position modulation
C)Pulse Width modulation
D)Pulse Code modulation

4. 3) Which of the given communication medium offers very high speed?
Microwave
Optical
WLAN
Coaxial

5. 4) What is the interval between frequencies at which spectrum, Gx(f) dropped 3dB below the peak value is called as?
Null-null bandwidth
Fractional power containment bandwidth
Half power bandwidth
Absolute bandwidth

6. 5) What is the width of the main spectral lobe, where most of the signal power contained is called as?
Null-null bandwidth
Fractional power containment bandwidth
C) Half power bandwidth
D)Absolute bandwidth

7. 6) Which Bandwidth is infinite for all the realizable waveforms?
Null-null bandwidth
Fractional power containment bandwidth
C) Half power bandwidth
D)Absolute bandwidth

8. 7) What is Symbol or Baud rate?
Bits per second
Bytes per second
C) Symbols per second
D) none of the above

9. 8) What is the Bandwidth of the
8) What is the Bandwidth of the digital signal , (given Rs , the symbol rate)?
B = RS / 2
B = 2RS
C) B = RS * T0
D) B = RS / T0

10. 9) What is the carrier and message signal in an analog Pulse Communication system?
Carrier = Pulse, Message = Pulse
Carrier = analog, Message = Pulse
C) Carrier =analog, Message = Pulse
D)Carrier = Pulse, Message = analog

11. 10) Which modulation varies the amplitude of the carrier wave in accordance with that of the message signal?
Pulse modulation
Amplitude modulation
C) Frequency modulation
D)Angle modulation

12. 11) What is the Unit of Bit error rate?
bit / sec
B) byte/sec
symbols/sec
no unit

13. 12) What is the property to which the Additive noise channel is related with?
Gaussian probability distribution
additive noise
Uniform Spectral density
all the above

14. 13) What is the other name for AWGN Noise channel model ?
Linear filter channel
Linear time variant channel
C)Additive noise channel
D)None of the above

15. 14) Which is called the figure of merit of the digital communication?
Spectral density
Power efficiency
Spectral efficiency
BER

16. 15) What is GSOP?
Gram Schmidt Orthogonalisation Principle
General Schmidt Orthogonalisation Principle
Gram Schmidt Orthogonalisation Procedure
Gram Schmidt Orthogonalisation Problem

17. 16) What is obtained from GSOP?
Basis set
Dimension of the signal space
Basis functions
signal space

18. 17) Which channel requires Repeater?
Free Space broadcast
Wireless LAN
Coaxial Cable
None

19. 18) Which modulation is affected by the Aperture effect?
PAM
PPM
PWM
PCM

20. 19) What is the value of the inner product for orthonormal basis functions? a)one B) zero C)twice their value D)square of the value

21. 20) Which block coverts analog signal into digital signal?
Formatter
Encoder
Sampler
Quantiser

22. 21. Which is the first process performed in analog to digital conversion? A)one B) zero C)twice their value D)square of the value

23. 22. What is the Nyquist interval ?
A)2W samples per sec
B) 1/2W samples per sec
C)1/2W seconds
D)2W seconds

24. 23. Which Sampling is used for reconstructing a waveform on real time basis? A)Flat top sampling B)Impulse sampling C) Natural sampling D)None of the above

25. 25) What is the condition to avoid anti-aliasing, given Fs and Fm are sampling & modulating frequency? A) Fs < 2Fm B) Fs > 2Fm C) Fs = 2Fm D)Fm > 2Fs

26. What is the discrete representation of the message signal is called as?
A)Sampling
B)Quantization
C)Encoding
D)Formatting

27. 27. What is the spacing between two adjacent representation levels
27. What is the spacing between two adjacent representation levels ? A)Step size B)Quantum size C)Reconstruction level D)Both A & B

28. 28) Which Quantizer has maximum quantization error ?
Midtread
B) Midriser
C) Biased
D) None of the above

29. 29) What is the Crest factor. A)Rms Value / Peak Value B)Rms Value
29) What is the Crest factor? A)Rms Value / Peak Value B)Rms Value * Peak Value C) Peak value / Rms Value D)2* peak value

30. 30) What is the process of Compression and expansion in PCM is called as?
Uniform Quantisation
B) Non-uniform quantization
C) Companding
D) Tappered quantizing levels

31. 31. Which is not a temporal waveform coding?
A)DM
B) DPCM
C)LPC
D)PCM

32. 31) Which Noise affects a PCM system?
Aliasing noise
B)Channel noise
C) Quantisation noise
D)All

33. 33) Which of them does not belong to source coding
33) Which of them does not belong to source coding? A)DPCM B)DM C)ADM D) PCM

34. 34) What is the sampling rate value for Delta Modulation?
2 * Nyquist rate
B) 3 * Nyquist rate
C)4 * Nyquist rate
D) none of the above

35. 35) What is the Reason for Slope overload distortion ?
Step size is too large
B)Step size is too small
C)Both
D)None

36. 36) Which coding performs a spectral channelization by a bank of narrow filters?
Sub band coding
B) Adaptive Sub band coding
C)Adaptive Transform coding
D)Model based coding

37. 37) Which coding is a powerful speech analysis technique to estimate the basic speech parameters?
Sub band coding
B) Adaptive Sub band coding
C)Linear Predictive coding
D)Model based coding

38. 38) What is the difference between the input signal m(t) and the output quantized signal mq(t) is called as?
quantisation
B)quantization noise
C)quantization error
D)both B & C

39. 39) What is the SNR of a PCM system with L representation levels?

40. 39) What is meant by binary frequency shift keying (BFSK)
39) What is meant by binary frequency shift keying (BFSK)? a) Shifting two frequencies to key a microphone b) Using two distinctly different frequencies to represent digital 0s and 1s c) Shifting digital information at a binary frequency d) Half of quadrature shift keying

41. 40) Which of the following item affects the bit error rate (BER) of a received signal? a)  Oscillator phase noise b)  Baseband filtering c)  Carrier suppression d)  All the above

42. 41) What frequency is allowed by the Federal Communications Commission (FCC) for each FM station?
A) 20 KHz
B) 100 KHz
C) 200 KHz
D) 300Khz

43. 42)Which modulation allows the amplitude of the carrier signal to be varied to represent data, with both frequency and phase remaining constant?
A) ASK
B) PSK
C) FSK
D) QAM

44. 43)What frequency is allowed by the Federal Communications Commission for each AM station?
5 KHz
B) 10 KHz
C) 20 KHz
D) 200KHz

45. 44) How many carrier frequencies are used in BFSK?2 1 3

46. 45) How many carrier frequencies are used in BASK?

47. 46) What Conversion happens in AM and FM?
digital-to-digital
digital-to-analog
analog-to-analog
analog-to-digital

48. 47) What Conversion happens in ASK, PSK, FSK, and QAM ?
A) digital-to-digital
B) digital-to-analog
C) analog-to-analog
D) analog-to-digital

49. 48) Which transmission allows the carrier signal to be modulated so that its amplitude varies with the changing amplitudes of the modulating signal? AM PM FM DM

50. 49) Which transmission allows the phase of the carrier signal to be modulated to follow the
changing voltage level (amplitude) of themodulating signal?
A) AM
B) PM
C) FM
D) DM

51. 50) Which modulation allows the frequency of the carrier signal to be varied to represent data, with both peak amplitude and phase remaining constant?
A) ASK
B) PSK
C) FSK
D) QAM