analog and digital communication systems

Analog and Digital Communication Systems Tick the best possible choice.1.Hilbert Transform .. -900 and .. +900 phase shift to all positive and negative frequency components of a signal.a) adds, adds b) adds, subtracts

c) subtracts, addsd) subtracts, subtracts

2.Cross correlation between a signal and its Hilbert Transform is ..a) 0b) 1

c) < 1d) > 1

3.Modulation causes ..a) Reduction in antenna heightb) Ease for multiplexing

c) Long distance communicationd) All of them

4.DSB AM signal consists of a) Carrier componentb) USB

c) LSBd) All of them

5.Message signal can be recovered for the AM wave if the Modulation index is.a) < 1b) >1

c) = 1d) Both a and c

6.The maximum efficiency in DSB AM system is equal to a) 11b) 22

c) 33d) 44

7.DSB AM is commonly used due to .a) Simplicityb) Low cost

c) Both a and bd) Not a and b

8.The bandwidth requirement of DSB AM system is equal to .. that of message signal.a) One time ofb) Twice of

c) Greater than 2 times ofd) Both b and c

9.Non linear device are used to in DSB AM system.a) Generate b) Detect


10.The bandwidth requirement of DSB SC system is equal to .. that of message signal.a) One time ofb) Twice of


11.Power requirement of DSB AM is .. that of DSB SC systems.a) Less thanb) Greater than

c) Equal tod) Cant say

12.The bandwidth requirement of SSB system is equal to .. that of message signal.a) One time ofb) Twice of


13.The number of carrier is .. in ISB modulation.a) Oneb) Two

c) Threed) Four

14.The number of carrier is .. in QAM modulation.a) Oneb) Two

c) Threed) Four

15.The proper condition to recover message using envelop detector in AM system is .a) fm 1/(RC) fcd) fm >> 1/(RC) >> fc

16.Pilot carrier is used in demodulation.a) Synchronousb) Asynchronous


17.PLL can be used for in FM system.a) Modulationb) Demodulation


18.In superheterodyne AM receiver, the frequency of IF signal is around KHz.a) 445b) 450

c) 455d) 460

19.Sum of the squares of the all the Bessel function coefficients is a) < 1b) > 1

c) = 1d) Cant say

20.Bandwidth requirement in a FM system is . Ideally.a) BW = fmb) BW > fm

c) BW < fmd) Infinite

21.Bandwidth requirement in a FM system is . In real cases.a) BW =n fmb) BW =2n fm

c) BW = 3n fmd) Infinite

22.The value of n is chosen in FM system such that it contains . percentage of total power.a) At least 90b) At least 95

c) At least 98d) 100

23.In NBFM, the modulation index is .a) > 1

c) = 1d) None of them

24.In WBFM, the modulation index is .a) > 1

c) = 1d) None of them

25.The change in frequency is converted into change in voltage or current is called a) Discriminatorb) Differentiation


26.The effect of noise is significant at .frequencies in commercial FM radio system.a) Lowerb) Higher

c) Alld) All of them

27.The bandwidth occupied by stereo FM system is . KHz.a) 65b) 70

c) 75d) 85

28.Range of frequency occupied by L+R signal in stereo FM system is .. KHz.a) 0 15b) 16 30

c) 23 38d) 38 53

29.Range of frequency occupied by L-R signal in stereo FM system is .. KHz.a) 0 15b) 23 53

c) 23 38d) 38 53

30.Frequency of pilot carrier occupied in stereo FM system is .. KHz.a) 15b) 19

c) 38d) 53

31.The range of frequency of voice is .a) 0 4 KHzb) 300 4000 Hz

c) 300 3400 Hzd) 0 3100 Hz

32.In telephony, .. Hz is used as the guard band.a) 600b) 900

c) 500d) 800

33.One pre group consists of .. voice channels in telephony.a) 1b) 2

c) 3d) 4

34. One channel group consists of .. pre - groups channels in telephony.a) 1b) 2

c) 3d) 4

35.One super group consists of .. channel groups channels in telephony.a) 5b) 6

c) 3d) 4

36.One master group consists of .. super groups channels in telephony.a) 10b) 9

c) 12d) 11

37.One super master group consists of .. master groups channels in telephony.a) 5b) 6

c) 3d) 4

38.psdf of white noise is .. over entire range of frequency of interest.a) Constantb) Changing

c) both a and bd) not a and b

39.Sounds waves travel as ..a) longitudinal wavesb) transverse waves

c) both a and bd) either of a or b

40.The audio frequency range is .a) 5 1000 Hzb) 50 Hz 20 KHz

c) 16 Hz 20 KHzd) 0 Hz 20 KHz

41.Radio broadcasts are generally a) AM b) FM

c) Either of a or bd) None of a and b

42.Video signals are transmitted through . a) AMb) FM


43.Pre emphasis circuits are used .. modulator in FM system.a) Beforeb) After


44.De emphasis circuits are used .. demodulator in FM system.a) Beforeb) After


45.Pre emphasis circuits are .. filters.a) Low passb) High pass

c) Band passd) Band stop

46.De emphasis circuits are .. filters.a) Low passb) High pass

c) Band passd) Band stop

47.A carrier is modulated by two modulating waves with modulation indices of 0.6 and 0.8. the overall modulation index is a) 1b) 0.7

c) 0.2d) 1.4

48.FM broadcast is used in a) VHF rangeb) UHF range

c) MF ranged) Both a and b

50.When modulation index in AM is increased from 0.5 to 1, the transmitted powera) Remains the sameb) Increased by 25%

c) Increased by 33.3%d) Increased by 50%

51.The sequence of symbols is converted into binary sequence by .a) Source encoderb) Source decoder

c) Channel encoderd) Both a and c

52.If the symbol rate is 10 symbols/sec and 5 bit of codeword is used then the data rate is a) 10 bits/secb) 5 bits/sec

c) 15 bits/secd) 50 bits/sec

53.Channel encoder adds some extra bits to the output of source encoder to ..a) Detect errorb) Correct error

c) Both a and bd) None of a and b

54.The channel has frequency bandwidth.a) Finiteb) Infinite

c) Depends on noised) None

55.The unwanted change in waveform of signal at output is termed as ..a) Noiseb) Distortion

c) Interferenced) All of them

56... distortion causes scaling in amplitude and phase shift.a) Linearb) Non linear


57.IM stands for ..a) Interference magnitudeb) Inter modulation

c) Independent modulationd) Intermediate modulation

58.Contamination of the received signal by some other extraneous is called .a) Noiseb) Distortion

c) Interferenced) All of them

59.ISI stands for .a) Inter symbol interferenceb) Intermediate symbol interference

c) Independent Symbol Interferenced) None of them

60.The division of a branch current at a junction causes .a) Shot noiseb) Partition noise

c) Thermal noised) All of them

61.The noise produced due to anode current in vacuum tubes is ..a) Shot noiseb) Partition noise

c) Thermal noised) All of them

62.Analog to digital conversion consists of ..a) Samplingb) Quantization

c) Codingd) All of them

63.Nyquist criterion for sampling is ..a) Fs > fx b) Fs > 2 fx

c) Fs < fx d) All of them

64.The number of quantization levels is in uniform quantization if 5 bits of coding is used.a) 5b) 10

c) 32d) 31

65.The quantization error in uniform quantization is where is step size.a) = /2

c) = /2d) =

66.The average power of quantization noise in uniform quantization is where is step size.a) = 2/10b) = 2/11

c) = 2/12d) = 2/13

67.The SQNR is improved by .. dB for each extra bit added in coding foe uniform quantization.a) 4b) 5

c) 6d) 7

68.PCM stands for a) Phase Code Modulationb) Pulse Code Modulation

c) Pulse Coding Modulationd) None of them

69.The step size is increased if the probability of occurrence of symbol in non uniform quantization.a) Increasesb) Remains constant

c) Decreasesd) Both a and c

70.Compression of signal is done . sampling in non uniform quantization in PCM.a) Beforeb) After

c) Duringd) Both a and b

71.Expansion of signal is done . Digital to analog conversion in non uniform quantization in PCM.a) Beforeb) After

c) Duringd) Both a and b

72.Synchronization is used in multiplexing.a) TDMb) FDM


73.The T1 frame in TDM PCM telephone system consists of .a) 100 bitsb) 125 bits

c) 150 bitsd) 175 bits

74.The T1 frame in TDM PCM telephone system spans for .a) 190 secb) 191 sec

c) 192 secd) 193 sec

75.The signalling rate at the output of T1 multiplexer in TDM PCM telephone system is Mbps.a) 1.544b) 1.644

c) 1.444d) 5.544


c) 4.312d) 7.312


c) 44.736d) 45.736

78.The signalling rate at the output of T4 multiplexer in TDM PCM telephone system is Mbps.a) 274b) 275

c) 276d) 277

79.The signalling rate at the output of T5 multiplexer in TDM PCM telephone system is Mbps.a) 460b) 560

c) 660d) 670

80.The unit of information content of a message is a) natsb) bits

c) decitd) all of them

81.The information content of a message increases if its probability a) increasesb) decrease

c) remains constantd) both a and b

82.The information content of a message may be ..a) positiveb) negative

c) either of a or bd) neither of a and b

83.The information content of a message is if its probability is 1.a) 1b) 0

c) 0.5d) None

84.If two binary digits occur with equal probability the information content in each digit is .a) 0 bitb) 1 bit

c) 2 bit d) bit

85.The value of entropy is the maximum when all symbols have probabilities.a) Unequalb) Equal

c) Increasing orderd) Decreasing order

86.The data rate of M-ary signalling is times faster than that in binary system under same conditions.a) log10 M b) loge M

c) log2 M d) all of them

87.The best time to sample is the instance when the eye opening is a) minimumb) maximum

c) half a wayd) closed

88.The maximum bandwidth efficiency is of the modulation scheme.a) DSB - AM b) DSB SC

c) SSBd) VSB

89.The power consumed by .modulation scheme is the least.a) DSB - AM b) FM

c) SSBd) VSB

90.The power consumed by .modulation scheme is the maximum.a) DSB - AM b) FM

c) SSBd) VSB

91.Parity method is used to errors in digital communication.a) Detectb) Correct


92.Parity method can detect error if errors occur at . number of positions.a) Evenb) Odd

c) All d) None

93.In codes, the message bits are followed by the check bits.a) Blockb) Convolution


94.In codes, the message bits and the check bits are interleaved.a) Blockb) Convolution


95.PAM stands for .a) Phase Angle Modulationb) Pulse Angle Modulation

c) Pulse Amplitude Modulationd) Phase Amplitude Modulation

96.The number of non zero components in a codeword is called a) Minimum Distanceb) Hamming Distance

c) Hamming Weightd) Minimum Weight

97.The Hamming Weight for the codeword 00110111 is ..a) 3b) 5

c) 8d) 2

98.The Hamming Distance between the codeword {010 and 111} is .a) 3b) 5

c) 8d) 2

99.A linear block code with minimum distance dmin can correct upto . Errors in each codeword.a) dmin/2b) dmin

c) (dmin 1)/2d) dmin

100.For detecting n or less error bits, it is necessary and sufficient that Hamming Distance must be ..a) > (n + 1)b) < (n+1)

c) >= (n +1)d) (2n + 1)b) < (2n+1)

c) >= (2n +1)d) = (m+n+1), m>nb) >= (m+n+1), n>m

c) nd) m

103.The signal to noise ratio in a hi fi system should be at least . dB.a) 25b) 50

c) 75d) 100

104.The non linear distortion in a hi fi system should be less than . %.a) 10b) 5

c) 2d) 1

105.The dynamic range in a hi fi system should be at least . dB.a) 150b) 120

c) 80d) 40

106.FSK is used mostly in ..a) Telegraphyb) Telephony

c) Satellite communicationd) Radio communication

107.If the transmission bandwidth is doubled in FM, SNR is .a) Doubledb) Raised by 4 times

c) Decreased by 4 timesd) halved

108.If there are M messages and each message has a probability p = 1/m, the entropy is .a) 0b) 1

c) log2 Md) M log2 M

109.If a source of information generates message at a rate of r message per second and H is entropy, the information rate is a) H/rb) 1/rH

c) rHd) r/H

110.As per Shannon Hartley theorem, a noiseless Gaussian channel has .a) Zero capacityb) Infinite capacity

c) Small capacityd) None of them

Note: - Do read electrical representation of binary signals as NRZ, Polar, frequency ranges of different waves and so on.

analog and digital communication systems

Documents