1. If the Nyquist's rate of a signal x(t) is fo, the Nyquists rate of its integral is [01D01] a. fo

b. fo/2 c. 2fo d. fo/4 2. In 8-PSK system, adjacent phasors differ by an angle given by( in degrees) [01D02] a. n/4

b. _/8 c. _/2 d. _/ 6 3. Band Width efficiency of a Digital Modulation Method is [01M01] a. (Minimum Band width )/ (Transmission Bit Rate) b. (Power required)/( Minimum Band width) c. (Transmission Bit rate)/(Minimum Band width)

d. (Power Saved during transmission)/(Minimum Band width) 4. In DPSK, the two possible signal sets are [01M02] a. out of phase by 1800 b. orthogonal over 0 le t le Tb c. orthogonal over D:\dc-90\digitalcommunication\05310403101M02CX1.gif

d. are of different energy 5. The minimum band width required to multiplex 12 different message signals each of band width 10KHz is [01M03] a. 60KHz b. 120KHz

c. 180KHz d. 160KHz 6. Which of the following is the feature of a Digital communication System? [01S01] a. Less Band width requirement than Analog Communication system b. More affected by channel Noise c. Inaccurate than the Analog Communication system

d. Less transmitted power 7. The Auto-correlation function of White Noise is [01S02] a. Impulse function

b. Constant c. Sampling function d. Step function 8. Under equal band width requirement, [01S03] a. sampling rate in Delta Modulation is more than that of PCM

b. sampling rate in Delta Modulation is less than that of PCM c. sampling rate in Delta Modulation is same as that of PCM d. Data rate in PCM is more than that of Delta Modulation 9. The minimum band width required for a BPSK signal is equal to [01S04] a. bit rate

b. twice the bit rate c. half of the bit rate d. one fourth of bit rate 10. Which of the following is correct? [01S05] a. Non-coherent reception of PSK results in more probability of error than coherent reception. b. Coherent reception of PSK results in more probability of error than Non-coherent reception c. Orthogonal FSK is of less probability of error than Non-Orthogonal FSK d. QPSK system is of less probability of error than BPSK system 11. A Band pass signal has a spectral range extending from 20KHz to 82KHz.Which of the following sampling rates will allow the recovery of the above signal from its sampled version? [02D01] a. 82KHz b. 90KHz c. 165KHz d. 160KHz 12. A Delta Modulation system operates with a sample rate 'fs' and a fixed step size S. If the input for the system is the base band signal m(t) = Dt , for t>0, then to avoid slope over loading, step size should be [02D02] a. greater than 8.fs b. less than 8/fs c. greater than D/fs d. less than 8.fs 13. The signal f(t)=0.5.Cos104t is instantaneously sampled and is recovered from its Samples using a rectangular LPF. The minimum filter band width required for reconstruction is [02M01] a. 10Hz b. 5Hz c. 20Hz d. 2.5Hz 14. Three Base band signals band limited to 5KHz ,6KHz, and 7KHz are being time division multiplexed. At the de -multiplexing end, cross talk occurs if the channel band width is [02M02] a. greater than 18KHz b. less than 18KHz c. less than 14KHz d. greater than 14 KHz 15. A 1KHz sinusoidal signal is ideally sampled at 1500 samples/sec and the sampled signal is passed through an ideal LPF with cut off frequency of 800Hz.Which of the following will be output of the LPF? [02M03] a. 700KHz b. 500KHz

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22. For an input of X(t) = u(-t) - u(-t-3T), the impulse response of the corresponding [03D02] a. u(t-3T) - u(t-6T) b. u(t) - u(t+3T) c. u(t+3T) - u(t+6T) d. u(t+3T) - u(t) .

23. The Nyquist interval for the signal x(t) =[ (Sin504t)/(4t) ] + [(Sin1004t)/(4t)]2 is [03M01] a. 100/_ sec b. _/200 sec c. n/100 sec

d. 200/_ 24. ASCII code uses 128 characters which are binary encoded. If the source generates 100 Kilo characters per second, the data rate required to transmit the output of the [03M02] a. D:\dc-90\digitalcommunication\05310403103M02AX1.gif b.D:\dc90\digitalcommunication\05310403103M02BX1.gif c.D:\dc-

90\digitalcommunication\05310403103M02CX1.gif d.D:\dc90\digitalcommunication\05310403103M02DX1.gif 25. A communication system is transmitting information in the form of either +V volts rectangular pulse or -V volts rectangular pulse,each of duration 1msec.The minimum sampling rate required to reconstruct above signals from their sampled versions is [03M03] a. 1KHz b. 2KHz

c. 3KHz d. 4KHz 26. Three Base band signals, band limited to 6KHz,7KHz,and 8KHz are time division multiplexed using a channel of Band width of 3KHz.Then, at the demultiplexing [03S01] a. Signals can not be reconstructed b. Cross talk will be there c. Signals should be over sampled d. Cross talk will not be there

27. In Non-Coherent demodulation, the receiver [03S02] a. relies on carrier phase b. relies on the carrier amplitude

c. makes an error with less probability d. uses a carrier recovery circuit 28. BPSK and QPSK systems are [03S03] a. of Same band width b. using same carrier recovery circuit for demodulation c. of same bit error probability

d. of same symbol duration 29. A signal X(t)=5.Cos(1504t-60) is sampled at 200Hz.The fundamental period of the

c. 800KHz d. 600KHz 16. Companding results in [02S01] a. More S/N ratio at higher amplitudes of the base band signal b. More S/N ratio at lower amplitudes of the base band signal c. Uniform S/N ratio through out the base band signal d. Better S/N ratio at lower frequencies 17. The maximum output S/N ratio obtainable using a Matched filter is [02S02] a. D:\dc-90\d igitalcommunication\ 05310403102S02AX1.gif b. D:\dc-90 \digitalcommunication\053 10403102S02BX1.gif c.D:\dc-90\d igitalcommunication\0531040310 2S02CX1.gif d. D:\dc-90\d igitalcommunication\0531040310 2S02DX1.gif 18. A uniform quantizer is having a step size of .05 volts. This quantizer suffers from a maximum quantization error of [02S03] a. 0.1V b. 0.025 V c. 0.2 V d. 0.05 V 19. A signal is sampled at 8KHz and is quantized using 8-bit uniform quantizer. Assuming Tone Modulation, which of the following is correct for a PCM signal? [02S04] a. Bit rate = 32Kbps b. Bit rate = 64Kbps c. Bit rate = 16Kbps d. Bit rate = 8Kbps 20. In the output of a Delta Modulation speech encoder, the consecutive pulses are of opposite polarity during the time interval t=2 sec to t= 4 sec .This indicates that, during this interval [02S05] a. i/p to the modulator is essentially a constant b. Modulator is going through slope over loading c. Speech signal is being sampled at NyquistJs rate d. quantization error is more 21. A Binary communication system transmits equally likely 1's and 0's.A received '1' produces a voltage of 1V in the presence of Zero mean Gaussian noise with unit y variance. A received '0' produces zero volts in the presence of same above noise. If the received signal is above the threshold, the decision is in favour of 1.The probability with which a transmitted 1 is received as 0 is [03D01] a. Q(-0.5) b. Q(1) c. Q(-1) d. Q(0.5)

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sampled sequence is [03S04]

a. 1/200

b. 2/200

c. 4

d. 8

30. Among the digital Modulation systems QPSK,8-

PSK, BFSK,DPSK, the system with

lowest bit error probability is [03S05]

a. 8-PSK

b. BFSK

c. DPSK

d. QPSK

31. Two signals defined as S1(t)=A/3 for 0 D:\dc-90

\d igitalcomm

unication\053

10403104D0

1QX1.gif

T

= 0 else where

and S2(t) = B/2 for 0 D:\dc-90

\d igitalcomm

unication\053

10403104D0

1QX2.gif

T/2

= - B/2 for T/2 D:\dc-90

\d igitalcomm

unication\053

10403104D0

1QX3.gif

T

are applied as the input for a matched filter. For the

same noise power, if both the

above signals are to have the same maximum S/N at

the filter's output, A and B

should be related as [04D01]

a. B=1.5A

b. A=1.5B

c. A=B

d. A=B/3

32. The base band signal m(t)=6.Sin24t is transmitted

using Delta Modulation whose

Sampling rate is 3 times the Nyquist rate for the input

signal. The step size used is

10mV.If Bis the bandwidth required for the modulated

signal,then it is proportional to

[04D02]

a. 6bps

b. 12bps

c. 18bps

d. 3bps

33. If Eb, the energy per bit of a Binary signal is 106

and the White noise PSD eta /2=105,

then, the maximum output S/N in dB is [04M01]

a. 13

b. 1

c. 20

d. 10

34. A binary communication system is transmitting

data at a rate of 10Kbps using RZ

Signaling.The minimum channel Band width required for the above system is [04M02] a. 10KHz b. 5KHz c. 20KHz d. 15KHz 35. The Nyquist's rate for the signal x(t)= 1+Cos(20004t) + Sin(40004t) is [04M03] a. 4KHz b. 2KHz c. 6KHz d. 8KHz 36. Which of the following FSK system transmitting data at a rate of fb bps with fH and fL being the highest and lowest frequencies being transmitted is an orthogonal FSK system? [04S01]

a. D:\dc-90\digitalcommunication\05310403104S01AX1.gif =5fb b. D:\dc-90\digitalcommunication\05310403104S01BX1.gif c. D:\dc-90\digitalcommunication\05310403104S01CX1.gif d. D:\dc-90\digitalcommunication\05310403104S01DX1.gif 37. If is the energy contained in a bit duration , the distance between the closest points in the constellation diagram of QPSK system is [04S02] a. b. 2 D:\dc -90 \digit alco mmu nicati on\ c. D:\dc -90 \digit alco mmu nicati on\ /2 d. D:\dc-90 \d igitalcomm unication\053 10403104S02 DX1.gif 38. The phase angles of the possible outcomes of an 8-PSK system are obtained as [04S03] a. (2m+1)4/8 where 'm' is an integer b. 2m_/8 where 'm' is an integer c. (m+1)_/8 where 'm' is an integer d. (m+2)_/8 where 'm' is an integer

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48. Which of the following statements is correct? [05S03] a. A Band Pass signal requires less minimum sampling rate than a low pass signal

b. Digital transmission of a signal is more accurate than Analog transmission c. A Band pass signal is also a Band limited signal d. QPSK system is advantageous because of its less bit error probability than BPSK 49. The equiavalent number of q-levels in Delta Modulation system are [05S04] a. 4 b. 2

c. 8 d. 16 50. If is the band width efficiency and 'D' is the carrier synchronization, then for a BPSK system [05S05] a. =0.5 and 8 is required. b. =1 and D is required

c. =0.5 and 8 is not required d. =1 and 8 is not required 51. In a digital TDM system,24 voice signals are multiplexed, each signal being sampled at a rate of 8Ksamples/sec, and 256 q-levels are used. Each frame has one synch. Bit added.The bit rate of the system is [06D01] a. 1544Mbps b. 1544Kbps

c. 15.44Kbps d. 15.44Mbps 52. If the transmission probabilities of a '1' and '0' are and respectively and if the transition probability is 1/8 in a binary communication system, the average probability of error is [06D02] a. 1/8

b. c. d. 53. A communication channel band limited to 15KHz is available for a PCM system, Which is implementing a sampling rate of 8KHz.The maximum permissible sampling rate for the above system causing no channel band width wastage is [06M01] a. 10KHz

b. 18KHz c. 15KHz d. 8KHz 54. A binary communication system is transmitting data at a rate of 10Kbps using NRZ signaling. The minimum channel Band width required for the above system is [06M02] a. 10KHz

b. 5KHz c. 20KHz d. 15KHz 55. A binary data communication system is transmitting information using the following signaling scheme: S1(t)=2V for 0PtP2sec and S2(t)=0 for 0PtP2 sec. The threshold

39. If X(t) is a signal with Nyquist's rate F0, then the Nyquists rate for the derivative of X(t) is [04S04] a. 2F0 b. F0 c. F0/2 d. F0/4 40. If X(t) is a band limited signal with Nyquist`s rate of F0, then X(t).CosW0t is [04S05] a. Band pass signal b. Band limited signal c. of Nyquist's rate 2F0 d. of band width Fo/2. 41. The minimum sampling rate required for the signal x(t)= Cos54t + 10.Cos104t is [05D01] a. 10 Hz b. 5Hz c. 20Hz d. 30Hz 42. The Nyquist's interval for the signal x(t)= [(Sin3t)/(t)].[(Sint)/(t)] is' [05D02] a. n/4 sec b. _/2 sec c. _/8 sec d. _/6 sec 43. In a PCM system, under Tone Modulation, if the code word length is increased from 12 to 13 bits, the corresponding S/Nq improves by a factor of [05M01] a. 6 b. 4 c. 8 d. 10 44. The minimum pass band width in Hz required for the reconstruction filter to get back the signal x(t)=Cos10W0t+Cos11W0t+Cos12W0t from its sampled version is [05M02] a. 12f0 b. 6f0 c. 5.5f0 d. 5f0 45. For a baseband signal with a band limiting frequency of 500Hz, which of the following is the maximum sampling period that can be used for its sampling? [05M03] a. 1 msec b. 2 msec c. 3 msec d. 4 msec 46. The Band width efficiency of 8-PSK system is [05S01] a. 2 b. 3 c. 4 d. 5 47. The advantage of Manchester encoding is [05S02] a. less band width requirement b. less bit energy required for transmission c. less probability of error d. less bit duration

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used by the decision making device in the intended

receiver for this system is [06M03]

a. 4V

b. 8V

c. 2V

d. 1V

56. Which of the following signaling schemes is a

differential coding scheme? [06S01]

a. Unipolar

b. NRZ-L

c. NRZ-I

d. RZ

57. The impulse response of the filter matched to the

input signal x(t)=u(t)-u(t-T) is

[06S02]

a. x(t)

b. x(-t)

c. x(2t)

d. 2.x(t)

58. Which of the following is equal to '1'? [06S03]

a. area enclosed by the impulse function 2.D(t)

b. Q(x)+Q(-x)

c. erfc(x) at x = E

d. Bit error Probability in ASK system

59. For same bit error probability , the signal energy in

BPSK and Non-Orthogonal FSK

signals differ by [06S04]

a. 4dB

b. 2dB

c. 5dB

d. 1dB

60. The Band width efficiency of 16 QAM system is

[06S05]

a. 1

b. 2

c. 3

d. 4

61. X(t) and Y(t) are two low pass signals band limited

to D:\dc-

90\digitalcommunication\05310403107D01QX1.gif Hz

respectively. The

product X(t).Y(t) is sampled using a sampling signal

with sampling period T. Then,

D:\dc-90

\d igitalcom

mun ication

\05310403

107D01QQ

is( in sec) [07D01]

a.

D:\dc-

90\digitalcommunication\05310403107D01AX1.gif

b.

D:\dc-90

\d igitalcommunication\05310403107D01BX1.g

if

c.

D:\dc-

90\digitalcommunication\05310403107D01CX1.gif

d.

D:\dc-90\digitalcommunication\05310403107D01DX1.gif . 62. If the maximum permissible error in the sampling amplitude of the signal 5.Cos2004 t is 0.5 % of its peak, then the lowest possible data word length required to encode the signal is [07D02] a. 5 b. 6 c. 7 d. 8 63. A system with its frequency response = 0 for 2KHzP fP 4KHz can not be realized according to [07G01] a. Causality of a system b. Paley-Wiener criterion c. Schwartz's inequality d. Nyquist's pulse shaping criterion 64. If X = D:\dc-90 \digitalcommunication\05310 403107M01QX1.gif in the expression for the bit error probability in coherent BPSK, then with an imperfect carrier phase synchronization of 600 , then X will be [07M01] a. 0.8 times the original b. 0.5 times the original c. 0.7 times the original d. remaining unaltered 65. A real signal X(t) is determined from its samples taken at a minimum rate of Ws=10004.Then, the value of W for which X(W) is guaranteed to be zero is [07M02] a. W>500n b. W>1000_ c. W<500_ d. W=500_ 66. If a low pass signal X(t) is sampled using the sampling signal with pertid 'T', then the magnitude response of the reconstruction filter used for the recovery of X(t) from its sampled version should be [07M03] a. D:\dc-90\digitalcommunication\05310403107M03AX1.gif b. D:\dc-90\digitalcommunication\05310403107M03BX1.gif c. D:\dc-90\digitalcommunication\05310403107M03CX1.gif d. D:\dc-90\digitalcommunication\05310403107M03DX1.gif 67. An FSK system transmitting the data at a rate of Fb is having its highest and lowest transmission frequencies as FH=10.Fb and FL=6Fb. This FSK system is [07S01] a. Non-Orthogonal BFSK b. orthogonal 4-FSK c. Orthogonal BFSK

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b. Compressing the base band signal in its peak to peak excursion c. increasing S/Nq at higher amplitudes of the base band signal d. making the data word length equal to 1 bit. 71. If X(t) is a signal with Nyquist's rate 2Fo, the Nyquist's rate of X(t).Cos2Wot is [08D01] a. 6.Fo b. 4.Fo c. 2.Fo d. 8.Fo 72. For the Band pass signal X(t)= Cos404t + 2.Cos504t, which of the following is the minimum sampling frequency? [08D02] a. 10Hz b. 40Hz c. 50Hz d. 20Hz 73. The value of the integral D : \ d c - 9 0 \ D:\dc-90\digitalcommunication\05310403108M01QX2.gif [08M01] a. 1 b. _ c. 2 d. 2 _ 74. Noise with uniform PSD of N w/Hz is passed through a filter with transfer function H(w)= 2.exp(-jwtd) followed by an ideal LPF with pass band over (0,B).The output Noise power in watts is [08M02] a. 2NB b. 4NB c. 8NB d. 16NB 75. The Nyquist's rate of sampling of an analog signal S(t) for alias free reconstruction is 5000samples/sec.For a signal x(t) = [S(t)]2 ,the corresponding sampling rate in samples/sec is [08M03] a. 2500 b. 7500 c. 10000 d. 12000 76. A digitally Modulated carrier in QPSK system is [08S01] a. Energy Signal b. Power signal c. both energy and power signal d. neither energy nor power signal

d. Non-orthogonal 4-FSK 68. If D1 and D2 are the distances between the two closest points in the constellation diagrams of BPSK and BFSK systems, then, in terms of bit energy Eb, [07S02] a. = = D:\dc-90 \d igitalcomm unication\053 10403107S03 AX3.gif b. = =2 D:\dc -90 \digit alco mmu nicati on\ c. = D:\dc-90 \d igitalcomm unication\053 10403107S03 CX2.gif and =2 D:\dc -90 \digit alco mmu nicati on\ d. = 2 D:\dc -90 \digit alco mmu nicati on\ and = D:\dc-90 \d igitalcomm

unication\053 10403107S03 DX4.gif 69. If Fb is the bit rate, then the Baud rate in BPSK and QPSK are respectively [07S03] a. D:\dc-90 \d igitalcommunication\05 310403107S04AX1.gif b. D:\dc-90 \digitalcommunication\0531040 3107S04BX1.gif c. D:\dc-90 \digitalcommuni cation\0531040 3107S04CX1.gif d. D:\dc-90 \digitalcommunication\0531040 3107S04DX1.gif 70. DPCM involves [07S04] a. increasing S/Nq at lower amplitudes of the base band signal

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77. The probability density function of uniform noise extending from -1.5 v to +1.5 v is [08S02] a. 1/3

b. 1/6 c. 2/3 d. 3/2 78. A modulation scheme with a densely packed constellation diagram is [08S03] a. more energy efficient b. with more probability of error

c. more power efficient d. with less probability of error 79. Which of the following is numerically small? [08S04] a. (1/2).erfc(0.5) b. (1/2) erfc(0.05) c. (1/2).erfc(10)

d. (1/2).erfc(0.25) 80. In a digital communication system , the relation between the carrier frequency Wc and the bit duration Tb is [08S05] a. Wc.=n/Tb

b. Wc.Tb = 1/n c. Wc/Tb=n d. Tb/Wc=n 81. One thousand signals each having a 5KHz band width are sampled at the Nyquist's rate and then Time division multiplexed.The time separation between the adjacent samples of different base band signals should be [09D01] a. 0.1 μsec

b. 0.1 msec c. 1μsec d. 10μsec 82. The signal f(t)=Cos54t + 2.Cos104t is instantaneously sampled using a sampling signal S(t) of period of 0.1sec and the height of each impulse in S(t) is 5v.The height of the sample in the sampled signal at t = 0.1 sec is [09D02] a. - 10v

b. - 2.5v c. 7.5v d. 2v 83. The maximum allowable sampling interval for the signal X(t) = 2.Cos54t + 0.5.Cos104t is [09D03] a. 0.1 sec b. 0.2 sec

c. 0.3 sec d. 0.4 sec 84. If the data word length in a Tone modulated PCM system changes from 12 bits to 16 bits, the change is S/Nq is by a factor of [09M01] a. 16 b. 128 c. 256

d. 64 85. The signal D:\dc-90

\d igitalcommu nication\05310 403109M02QX 1.gif with X = 2Wo[t - (1/8fo)] becomes zero at 't'= [09M02] a. 3/8fo b. 4/8fo c. 6/8fo d. 10/8fo 86. Granular Noise in Delta Modulation system can be reduced by [09S01] a. using a square law device b. increasing the step size c. decreasing the step size d. adjusting the rate of rise of the base band signal 87. The error rate in DPSK system is more than that of PSK system , due to [09S02] a. differential encoding in DPSK system b. the orthogonality of the two possible signal sets in DPSK system c. the absence of Carrier recovery circuit in the demodulation of DPSK signal d. more band width occupied by DPSK signal 88. The sampling theorem gives a condition for [09S03] a. band limiting frequency of the base band signal b. period of the sampling signal c. Lower frequency limit for the base band signal d. magnitude of the sampling signal 89. The period of the signal x(t) = Cos54t + 0.5.Cos104t is [09S04] a. 0.1 sec b. 0.4 sec c. 0.2 sec d. 0.3 sec 90. Which of the following systems are not physically realizable as per Paley-Wiener criterion? [09S05] a. H(f)= 2 for D:\dc- 90 \digitalc ommuni cation\0 531040 3109S 2KHz b. H(f)= 0 for 2KHz P f P 5KHz c. H(f)= 2. for f 0 d. H(w)= 3. for w 0 91. A signal X(t) = 2.Cos8004t + Cos14004t is sampled by using a Sampling signal defined as S(t) with a period of 1msec and is defined in one period as S(t)= 1 for - 1/6 msec D:\dc-90 \d igitalcomm unication\053 10403110D0 1QX1.gif +1/6 msec =0 else where.

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continuous sequence of zeros is eliminated? [10S03] a. Uni polar b. NRZ-L c. NRZ-I d. AMI 99. A Matched filter [10S04] a. minimizes the output S/N b. reduces the transmission energy requirement c. minimizes the probability of error d. is unique for all signaling representations 100. The energy of the two possible signals in a BPSK system is [10S05] a. b. A2Tb c. A2Tb d. ATb 101. The Nyquist's interval for the signal X(t) = [(Sin504 t)/( pi t)]2 is [11D01] a. 0.1sec b. 0.01sec c. 0.0001sec d. 1sec 102. The minimum symbol rate of a PCM system transmitting an analog signal band limited to 2KHz , with the number of Q-levels 64 is [11D02] a. 24Kbps b. 28Kbps c. 20Kbps d. 32Kbps 103. A signal extending over -4v to +4v is quantized into 8 levels. The maximum possible quantization error obtainable is [11M01] a. 0.5v b. 1v c. 0.25v d. 1.25v 104. The minimum step size required to avoid slope overloading in a Delta Modulation system transmitting a sinusoidal signal of amplitude 20V and frequency 500Hz using a sampling rate of 25,000 samples/sec is [11M02] a. 2.5V b. 5V c. 7.5V d. 8V 105. The minimum symbol rate of a PCM system transmitting an analog signal band limited to 2KHz , with the number of Q-levels 64 is [11M03] a. 24Kbps b. 28Kbps c. 20Kbps d. 32Kbps 106. The output of a Delta Modulation system is [11S01] a. difference between m(t) and its approximated version b. digitized difference between m(t) and its approximated version

Which of the following is the frequency component present in the sampled signal? [10D01] a. 2.6KHz b. 1KHz c. 800Hz d. 1.8KHz 92. A random variable X with uniform density in the interval 0 to 1 is quantized as Given: if 0 D:\dc-90 \d igitalcommunication\0 5310403110D02QX1.g if0.3, Xq=0; if 0.3 D:\dc-90 \d igitalcommunication\0 5310403110D02QX2.g if1, Xq=0.7, where Xq is the quantized value of X. The Mean square value of Quantization Noise in the range 0 D:\dc-90 \d igitalcommunication\0 5310403110D02QX3.g if0.3 is [10D02] a. 0.009 b. 0.039 c. 0.198 d. 0.159 93. For a signal s(t) = U(t) - U(t-2), the maximum output S/N for the corresponding Matched filter is [10M01] a. 4/n b. 2/K c. 1/K d. 2K 94. If the product of Step size and sampling frequency of a Delta Modulation System is 25120, which of the following rates of rise of the base band signal Will result in slope over loading? [10M02] a. 15079.6 b. 37699.11 c. 18849.55 d. 16945.22 95. The Nyquist's rate of a signal S(t) is 5000Hz. Then, the Nyquist's interval for the signal S2(t) is [10M03] a. 1msec b. 0.01msec c. 0.1 msec d. 1μsec 96. The selection D:\dc-90\digitalcommunication\05310403110S01QX1.gif , in FSK system is to [10S01] a. optimize the band width requirement. b. reduce the probability of error. c. make the signal more energy efficient. d. use the matched filter during demodulation 97. The advantage of Offset QPSK is [10S02] a. amplitude variations are less pronounced b. band width occupied is less c. less transmitted power d. probability of error is less 98. In which of the following signaling formats, the synchronization problem due to

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c. digitized polarity of difference between m(t) and its approximated version

d. digitized version of m(t). 107. For the digital data 1,0 represented as +V volts and - V volts respectively, which of the following can act as a Matched filter? [11S02] a. Differentiator b. Integrator

c. Sampling Circuit d. Bit synchronizer 108. Which of the following is the desirable feature of a line code? [11S03] a. Zero PSD at zero frequency

b. Non-zero PSD at zero frequency c. same voltage level for continuous sequence of 1's d. same voltage level for continuous sequence of 0's 109. The dependency of S/Nq ratio on the channel band width in a PCM system is given as [11S04] a. S/Nq= (3/2). D:\dc-90

\d igitalcommunication \05310403111S 04AX1 .gif b. S/Nq= (3/2). D:\dc-90 \d igitalcomm unication\053 10403111S04 BX1.gif c. S/Nq= (3/2). D : \ d c d. S/Nq= (3/2). D:\dc-90 \d igitalcommunication \05310403111S 04DX 1.gif 110. .Non-coherent detection of FSK signal results in [11S05] a. more band width occupancy b. more probability of error

c. energy efficiency than BPSK d. less probability of error 111. A band pass signal has a spectral range extending from 40KHz and 102KHz.Which of the following sampling rates will allow the recovery of the above signal from its sampled version? [12D01] a. 102KHz b. 124KHz c. 130KHz d. 205KHz

112. A sinusoidal sognal with peak to peak amplitude of 1.536volts is quantized into 128 levels using uniform quantization .The resulting quantization noise power is [12D02] a. 0.786 v b. 48 μv2 c. 12μv2

d. 3.072 v

113. The signal f(t) = 2.Cos1004t is instantaneously sampled .The minimum filter Band width required for the reconstruction filter to recover f(t) from its sampled version is [12M01] a. 100Hz b. 50Hz c. 200Hz d. 25Hz 114. The maximum output S/N ratio of the filter matched to the signal 2[U(t) - U(t- 2)] is [12M02] a. 16/n b. 8/K c. 4/K d. 2/K 115. If the bit energy of a binary signal is 106 and PSD of white noise is U/2 = 105 , then So/No for Matched filter is [12M03] a. 26dB b. 10dB c. 20dB d. 15dB 116. The Bit error probability of an Integrate and Dump receiver is given as (1/2).erfc(0.2).The same can be expressed as [12S01] a. Q( D:\dc-90 \d igitalcommunication\0531040311 2S01AX1.gif ) b. (1/2). Q( D:\dc-90 \d igitalcommunication\0531040311 2S01BX1.gif ) c. 2.Q( D:\dc-90 \d igitalcommunication\0531040311 2S01CX1.gif ) d. Q( D:\dc- 90 \digitalc ommuni cation\0 531040 3112S ) 117. Delta Modulation system is [12S02] a. having more data word length than PCM system b. referred to as 1 bit PCM c. having more sampling rate than PCM system, under equal band width requirement d. same as DPCM. 118. RZ signaling and Manchester encoding schemes are having [12S03] a. level transitions at t =Tb/2 b. same bit error probability c. synchronization problem due to continuous sequence of 0's only d. synchronization problem due to continuous sequence of 1's only 119. Baud rate for a BFSK system is [12S04] a. half of the bit rate b. twice the bit rate

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128. If Fs number of samples are to be transmitted, using W number of bits per sample, using a digital communication system, the minimum bandwidth required (in Hz) is [13S03] a. M2.Fs b. Fs.M c. Fs.y/2 d. M.Fs2 129. The possible signal sets in which of the following systems are orthogonal? [13S04] a. PSK over (0,Tb) b. FSK over (0,2Tb) c. DPSK over (0,2Tb) d. QPSK over (0,Tb) 130. Band width efficiency is 3 in [13S05] a. 8-PSK and 8-QAM b. QPSK and 8-PSK c. BQAM and 16PSK d. 8-QAM and 4-PSK 131. A 1mw video signal having a band width of 100MHz is transmitted to a receiver through a cable which is having 40dB loss. If the channel noise PSD is 10 w/Hz, S/N ratio at the receiver input is [14D01] a. 40dB b. 50dB c. 60dB d. 70dB 132. Noise with uniform PSD of D:\dc- 90 \digital comm unicati on\0 w/Hz is passed through a system with impulse response h(t) = exp( - 2 ).The dc component of the PSD of the noise at the output of the system is [14D02] a. D:\dc- 90 \digital comm unicati on\0 w/Hz b. 0.25x D:\dc- 90 \digital comm unicati on\0 w/Hz c. 0.5x D:\dc- 90 \digital comm unicati on\0 w/Hz

c. same as the bit rate

d. one fourth the bit rate

120. Minimum band width required for unipolar

signaling format of digital data is

[12S05]

a. half of the bit rate

b. equal to the bit rate

c. twice the bit rate

d. four times the bit rate

121. A base band signal X(t) is a ramp over (S,+S). Its

Mean square value is [13D01]

a. S2/12

b. S2/3

c. S2/4

d. 2.S2/3

122. The impulse response of a filter matched to the

signal X(t)= U(t)+U(t-1) - 2.U(t-

2) is [13D02]

a. U(t)+U(t-1) 2.U(t-2)

b. 2.U(t) U(t-1) U(t-2)

c. U(t)+2.U(t-1) 2.U(t-2)

d. U(t) 2U(t-1) 2.U(t-2)

123. A signal is sampled at 8KHz and is quantized

using 8-bit uniform quantizer.

Assuming tone modulation, the S/Nq (in dB) is

[13M01]

a. 25.8

b. 39.8

c. 55.8

d. 49.8

124. The noise in a communication channel is

considered to be Gaussian random

variable with mean=1 and variance = 3.The area

enclosed by its pdf curve over (0,V)

is [13M02]

a. 1

b. 2

c.

d. E

125. The minimum data rate of a TDM system

multiplexing three analog signals

having band widths 1200Hz,600Hz,600Hz and using

12 bits to encode each sample is

[13M03]

a. 28.8Kbps

b. 57.6Kbps

c. 14.4Kbps

d. 7.2Kbps

126. The inacuuracy in a digital communication is due

to [13S01]

a. channel noise

b. data word length

c. more sampling rate

d. rounding off process before transmission

127. The signaling format used for electrical

representation of digital data preferably

should have [13S02]

a. more duration per bit

b. more rectangular pulses in one bit duration

c. zero dc PSD

d. non-zero dc PSD

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d. The impulse response of a matched filter is same as the input signal 140. If erfc(x)= 0.02, then erf(x) is equal to [14S05] a. - 0.02 b. 0.98

c. 0.02 d. 1 141. The Nyquist;s band width of a Binary PCM system sampling at a rate of 8000samples/sec and using 40 quantization levels is [15D01] a. 24KHz

b. 16KHz c. 8KHz d. 20KHz 142. For the base band signal X(t) = 3.Cos5004t,the number of bits required to achieve an S/Nq of 40dB is [15D02] a. 4 b. 5 c. 6 d. 7

143. A Uniform quantizer is having a step size of Y.The output of that quantizer x(t) added with a constant 'c' is applied to another similar quantizer whose output is y(t).The minimum value of 'c' for which x(t)Zy(t) is [15M01] a. O b. ▲/2

c. O2/12 d. 2O 144. The Band width of a signal input to a PCM system is restricted to 4KHz.The input varies from - 3.8v to +3.8v.If the step size used is 0.06v, the number of Q-levels into which the signal is divided is [15M02] a. 135 b. 127

c. 150 d. 175 145. Five telemetry signals, each of B.W. 1KHz are to be multiplexed.If the Sampling rate of the multiplexing system is 20 % above the Nyquist's rate, the data rate of the multiplexing system ( in samples/sec) is [15M03] a. 10Kbps b. 12Kbps

c. 22Kbps d. 20Kbps 146. Granular Noise in Delta Modulation system can be reduced by [15S01] a. increasing the step size b. increasing the slope of the base band signal c. reducing the step size

d. reducing the slope of the base band signal 147. The similarity between analog and digital modulation methods is [15S02] a. base band signal format is same b. carrier is same

c. modulated carriers are energy signal d. modulated carriers are power signals

d. 2x D:\dc- 90 \digital comm unicati on\0 w/Hz 133. If the received signal at the input of a detector in a digital communication system can take any value between - 1v to +1v with equal probability, its Mean square value is [14M01] a. zero b. c. 1/3 d. 134. A BPSK system is transmitting data at a rate of 1Mbps.The minimum B.W and the Baud rate of the above system is [14M02] a. 1MHz,1Mbps b. 0.5MHz, 1Mbps c. 0.5MHz,0.5Mbps d. 1MHz, 0.5Mbps 135. Zero mean , white Gaussian noise is passed through an Ideal LPF with pass band extending from - 5KHz to +5KHz. The output is zero at time t = [14M03] a. 0.15sec b. 0.2sec c. 0.35 sec d. 0.55sec 136. The impulse response of a filter matched to the input signal S(t) over 0 P t PT is [14S01] a. S(t - T) b. S( - T- t) c. S(T - t ) d. S(t + T) 137. Digital data '1' is expressed using S1(t) =U(t) - U(t-T) and '0' is represented using S2(t) = - [ U(t)-U(t-T)].Which of the following can act a Matched filter for the above signals? [14S02] a. RC LPF with very small time constant b. RC HPF with very large time constant c. RC LPF with very large time constant d. RC HPF with very small time constant 138. The Nyquist's band width of a PCM system with data rate of 100Mbps is [14S03] a. 100MHz b. 200MHz c. 50MHz d. 150MHz 139. Which of the following statements is correct? [14S04] a. Matched filter is a unique system that can be used for any signaling format. b. Impulse response of a Matched filter is zero for t< 0. c. The output S/N of a Matched filter is independent of i/p signal energy

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d. 0.125/Fo 156. Adjacent phasors in M-ary PSK system differ in Phase by [16S01] a. _/M b. 2n/M c. M_ d. 2M_ 157. A digitally modulated carrier [16S02] a. extends over one symbol duration b. extends over t = - E to t = E c. has finite power d. has infinite energy 158. In a QPSK system, [16S03] a. symbol error probability and bit error probability are same b. bit error probability is more than that of BPSK system c. symbol error probability is twice of that of bit error probability d. band width requirement is more that of BPSK signal 159. Non-Coherent detection of FSK signal [16S04] a. makes use of envelope detector b. makes use of phase information of the carrier c. makes use of local carrier d. results in better noise performance than Coherent detection 160. Which of the following is the disadvantage of a Digital communication system? [16S05] a. poor noise performance b. detection is complex c. redundancy d. error probability is large. 161. An FSK system is transmitting a signal 2.Cos(24x10000)t for a '1' and the signal 2.Cos(24x2000)t for a '0' over a duration of 0 P t P 1μsec and zero else where. The optimum band width occupied by the FSK signal is [17D01] a. 1MHz b. 2MHz c. 3MHz d. 4MHz 162. In a certain telemetry system, there are four analog signals of band widths 3.6KHz, 1.5KHz,1.5KHz,1.5KHz respectively. With minimum sampling rate for the multiplexing system, the frame length( in samples) can be [17D02] a. 4 b. 5 c. 6 d. 7 163. The step size used in uniform quantization of a signal 3.Cos5004t which is to be transmitted using 10 bit PCM is [17M01] a. 0.0058v b. 170.6v c. 0.003v d. 341.3v

148. If P(t) = U(t) - U(t-2), the impulse response of the corresponding Matched filter is [15S03] a. P(t) b. P(- t) c. - P(t) d. P( - 2t). 149. Which of the following can be used as a Predictor in a DPCM transmitter? [15S04] a. Equalizer b. Tapped Delay Line Filter c. Scrambler d. Quantizer 150. A Binary channel with bit rate 36Kbps is available for PCM voice transmission. the maximum data rate of the PCM system can be [15S05] a. 18Kbps b. 72Kbps c. 36Kbps d. 35Kbps 151. If X(t) is a band limited signal with Nyquist's rate of Wo, then X(t).CosWot is [16D01] a. band limited signal band limited to Wo b. band pass signal with pass band from 0.5Wo to 1.5Wo c. band limited signal band limited to 1.5Wo d. band pass signal with pass band from Wo to 1.5Wo 152. If an ideal LPF with cut off frequency of 500Hz is used to recover a band limited base band Signal from its sampled version, the maximum allowed separation between adjacent samples of the signal is [16D02] a. 1μsec b. 1msec c. 0.1μsec d. 0.1msec 153. In multiplexing 24 voice signals, if the sampling rate of multiplexing system is 8Kilo samples/sec, the adjacent samples of the same signal and different signals in the multiplexed signal are separated by [16M01] a. 100μsec,5.2μsec b. 125μsec, 5.2μsec c. 125μsec,0.192μsec d. 100μsec,0.192μsec 154. The impulse response of the filter matched to the signal 2.U(t) - U(t -1) - U(t - 2) is [16M02] a. U(t) + U(t - 1) - 2.U(t-2) b. 2.U(t) - U(t -1) - U(t - 2) c. U(t) - U(t -1) - U(t - 2) d. 2.U(t) + U(t -1) - U(t - 2) 155. The Nyquist's interval for a signal X(t) is 1/Fo.The Nyquist's interval for X2(t) is [16M03] a. 1/Fo b. 0.5/Fo c. 0.25/Fo

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0.5CosWot, 2Cos2Wot, Cos4Wot , so that each signal is sampled at the same sampling rate is ( in rev/sec) [18D02] a. 4fo b. 8fo

c. 6fo d. 2fo 173. One thousand signals ,each having a 5KHz band width are to be time division Multiplexed. The Nyquist's rate for the multiplexing system is [18M01] a. 0.2sec b. 0.1msec

c. 1sec d. 0.1μsec 174. The maximum separation between the adjacent samples of the signal Cos54t + 0.5 Cos104t is [18M02] a. 0.1sec b. 0.2sec

c. 0.15sec d. 0.3sec 175. The seperation between the the q-levels Q1 and Q3 for the signal with peak=20v, quantized into 256 levels is [18M03] a. 0.156v b. 0.078v c. 0.312v

d. 0.234v 176. The area enclosed by the density function of Gaussian Noise with mean=2 and variance of 5 is [18S01] a. 2.5 b. 1

c. 3 d. 2 177. A finite duration signal is [18S02] a. power signal b. a non-band limited signal

c. band limited signal d. periodic signal 178. A quantizer is a [18S03] a. linear system with memory b. non-linear system with memory c. Linear system with memory d. non-Linear system without memory

179. A repeater in the transmission of 1's and 0's is [18S04] a. an amplifier b. a reconstruction device

c. an attenuator d. an equalizer 180. Under same band width requirement, the ratio of quantization Noise power in PCM to Delta Modulation system is [18S05] a.

b. 4 c. d. 2 181. The sampling rate of an analog signal S(t) for alias free sampling is

164. The Nyquist's interval for the signal X(t)= [(Sin304t)/(4t)] + {[(Sin3004t)/(4t)]}2 is [17M02] a. 150/_ sec b. n/300 sec c. 300/_ sec d. _/150sec 165. For a digital communication system, the bit error probability is given as 0.5.erfc(x). The mathematics involved with the system resulted that erf(x) = 0.98.The bit error probability of the system is [17M03] a. 0.51 b. 0.49 c. 0.01 d. 0.04 166. The 6-dB rule in PCM(in dB) ,using μ-Law companding for μ=255, in terms of data Word length W is [17S01] a. 1.76 + 6.02M b. 6.02+1.76M c. 6.02y - 10.1 d. 6.02 M + 10.1 167. Which of the following is a Causal system? [17S02] a. Ideal LPF b. Matched filter c. Ideal BPF d. System with transfer function H(f) = 0 for 20KHz Q f Q 40KHz 168. A Matched filter [17S03] a. maximizes output S/N ratio and increases the bit error probability b. minimizes output S/N ratio and increases the bit error probability c. minimizes output S/N ratio and decreases the bit error probability d. maximizes output S/N ratio and decreases the bit error probability 169. The advantage of NRZ signaling is [17S04] a. zero DC PSD b. less band width requirement c. more energy d. less bit duration 170. quantization error is independent of [17S05] a. base band signal amplitude b. sampling rate c. number of q-levels d. Step size 171. The response of a channel for a sample as an input is given as r(t) = [(2.Wo.Io)/4].[(Sin(x))/x] where x = 2.Wo.(t- 0.25/fo). The response of the channel is zero for t= [18D01] a. 0.5/fo b. 3/4fo c. 3/8fo d. 5/8fo 172. The revolution rate of the commutator required to multiplex the signals CosWot,

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a. delaying its impulse response by t = V

b. using active components which are capable of

providing gain

c. cascading two band pass filters

d. advancing its impulse response by t = E

190. Nyquist's interval indicates [19S05]

a. The separation between the adjacent samples of

the sampled signal Ans.d

b. period of the sampling signal

c. period of the base band signal

d. Maximum separation between the adjacent

samples of the sampled signal

191. A digital communication system transmits a '1'

and a '0' with probabilities

D:\dc-90

\d igitalcommunication\05310403120D01QX

1.gif respectively. If the transition probability is , the

average probability of error

is [20D01]

a. 0.25

b. 0.5

c. 0.55

d. 0.75

192. For an input of S(t) = A[U(t) - U(t-1)], the peak

value and the duration of the

output of the filter matched to S(t) are [20D02]

a. AT2 and (0,2)sec

b. A2T and (0,1)sec

c. AT2 and (0,2)sec

d. A2T and (0,2)sec

193. Noise with uniform PSD 'K' w/Hz is passed

through a filter with impulse

response h(t) = K.](t-td). The PSD of the output of the

filter in w/Hz is [20M01]

a. K2

b. K

c. k3

d. K.D

194. A bipolar signal is +A volts or -2A volts

rectangular pulse during the interval

(0,T).Assuming the signals are transmitted with equal

likelihood, the Threshold used

by the detector in Integrate and Dump receiver is

[20M02]

a. 0 volts

b. - AT/2

c. AT/2

d. AT

195. Digital Information '1' is represented by S1(t) =

A.Cos2?Fot and '0' is

represented by S2(t) = 0 for an interval of (0,T). For

the transmitted signal energy to

be A2T/2, where 'n' is an integer. [20M03]

a. Fo = n.T

b. F0 = T/n

c. F0 = n/T

d. Fo ± T = n.

196. The advantage of DPCM over Delta Modulation

is [20S01]

a. Prediction is used

b. Less data word length

5000samples/sec. The maximum separation between the adjacent samples of X(t) = Sn(t) in sec. is [19D01] a. 1/2500.n b. 1/5000.n c. 1/10000.n d. 1/1000n 182. The maximum sampling rate for the signal X(t)= 5 { (Sin ,2 , pi .1000t)/( pi t) } 3+7 { (Sin ,2 , pi .1000t)/( pi t) } 2 in samples/sec is [19D02] a. 2000 b. 4000 c. 6000 d. 8000 183. A discrete-time amplifier uses a sampling interval T=25μsec.The highest frequency of the base band signal that can be processed by this amplifier with no aliasing is [19M01] a. 40KHz b. 20KHz c. 60KHz d. 80KHz 184. A signal X(t) = 3.Sin(2004t-300) is instantaneously sampled at 400Hz.The resulting sampled sequence is periodic with a period of [19M02] a. 4 sec b. 2 sec c. 1/400 sec d. 0.002sec 185. The impulse response of the filter matched to the signal S(t) = - U(t) +2.U(t-1) - U(t-2) is [19M03] a. U(t) - 2.U(t-1) + U(t-2) b. - U(t) - 2.U(t-1) + U(t-2) c. - U(t) - 2.U(t-1) - U(t-2) d. U(t) -2.U(t-1) - U(t-2) 186. Cross talk in communication channel is due to [19S01] a. Noise in the channel b. repeaters in the channel c. limited band width of the channel d. nonlinearity of the channel 187. To avoid aliasing, the minimum number of samples/cycle that a sinusoidal signal should have is [19S02] a. 2 b. 4 c. 6 d. 8 188. Aliasing can be eliminated by [19S03] a. increasing the highest frequency of the base band signal b. making the base band signal band limited c. attenuating the low frequency components of the signal d. making the signal a non-band limited signal 189. An Ideal LPF can be made physically realizable by [19S04]

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c. quantization noise power is less

d. Tapped delay line filter is used 197. To sample a given signal, band limited to 10 Hz, the maximum permitted sample width so as to enable the recovery of the base band signal is [20S02] a. 0.05sec b. 0.1sec

c. 0.01 sec d. 0 05sec 198. The probability of error of a digital communication system expressed in terms of erfc(x) [20S03] a. is independent of x b. decreases as x decreases c. increases as x increases d. decreases as x increases

199. Matched filter gives an impulse response which is [20S04] a. zero for t>0 b. zero for t = 0 c. zero for t<0

d. zero for t ?0 200. Orthogonal PSK means [20S05] a. DPSK system

b. Offset-QPSK system c. Non-Offset QPSK system d. 8-PSK system

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