signals : 1. Signals with finite energy are called as _______ signals. [ ]

(a) Energy signals (b) power signals (c) periodic signals (d) deterministic signals 2. A System is defined as y(n)=x(-n). This system is a_________ [ ]

(a) time-variant (b) time-invariant (c) Dynamic (d) None of these.

3. The sinc(x) is defined as ________ [ ] (a) Sin(x)/x (b) Cos(x)/x (c) Sin (π x)/x (d) None

4. The value of integral ∫ 𝛿𝛿(𝑡𝑡)𝑐𝑐𝑐𝑐𝑐𝑐𝑡𝑡 𝑑𝑑𝑡𝑡∞−∞ is equal to ________ [ ]

(a) Zero (b) One (c) Infinity (d) Undefined

5. A system is said to be causal if the system output at any time depends only on the values of____ [ ] (a) Present input. (b) The future input. (c) The present and past input. (d) The past output.

6. A system is said to be linear if it satisfies______________________ [ ] (a)Homogeneity property. (b) Additive property (c) Only (a). (d) Both (a) and (b).

7. The Fourier transform of a voltage signal x(t) is X(f). The unit of X(f) is_____________ [ ] (a) volt (b) volt-sec (c) volt/sec (d) volt2

8. The impulse response of a system is ( ) ( )nh n a u n= The condition for the system to be BIBO stable is__ [ ] (a) a is real and positive. (b) a is real and negative (c) a > 1. (d) a < 1.

9. The response of a linear, time-invariant discrete-time system to a unit step input u(n) is the unit impulse δ(n). The system response to a ramp input nu(n) would be_______________ [ ] (a) u(n) (b) u(n-1) (c) nδ(n) (d) δ(n-1)

10. If f(t) is periodic function and it possess even symmetry, then its Fourier series contains__________ [ ] (a) Only Cosine terms (b) Only Sine terms (c) Both Cosine and Sine terms (d) None 11. Fourier Transform of Signum function is ______________ [ ] (a) 𝐹𝐹𝐹𝐹[𝑐𝑐𝑠𝑠𝑠𝑠(𝑡𝑡)] = −2𝑗𝑗

𝜔𝜔 (b) 𝐹𝐹𝐹𝐹[𝑐𝑐𝑠𝑠𝑠𝑠(𝑡𝑡)] = −2𝑗𝑗 (c) 𝐹𝐹𝐹𝐹[𝑐𝑐𝑠𝑠𝑠𝑠(𝑡𝑡)] = 1

𝜔𝜔 (d) None

12. Fourier Transform of Impulse function is_________ [ ] (a) Infinity (b) Zero (c) One (d) None 13. If a rectangular pulse is passed through a ideal Low pass filter, then its response is a ________ [ ] (a)Triangular function (b) Trapezoidal function (c) Sampling function (d) none 14. The units for Power spectral density is ___________ [ ] (a) Joules/Hz (b) Joules. Hz (c) Watts/Hz (d) None 15. The function f1(t)*f2(t) is given by ____________ [ ] (a) τττ

αdtff )()( 21 −∫

∞

− (b) ττ

αdtf )(2 −∫

∞

− (c) τ

ττ

αd

tff

∫∞

− − )()(

2

1 (d) None

16. An LTI system is causal if and only if its impulse response is _______for negative values of n. [ ] (a) Infinite (b) Unity (c) Finite (d) Zero 17. The inverse Fourier transform of δ (f) is_________________ [ ]

(a) u(t) (b) 1 (c) δ(t) (d) 𝑒𝑒𝑗𝑗2𝑡𝑡𝑡𝑡𝑡𝑡

18. Two discrete time systems with impulse responses h1(n) = δ(n -1) and h2(n) = δ(n– 2) are connected in

cascade. The overall impulse response of the cascaded system is________________ [ ] (a) δ[n - 1] + δ[n - 2] (b) δ[n - 4] (c) δ[n - 3] (d) δ[n - 1] δ[n - 2]

19. The auto correlation of a Rectangular Pulse is a __________ [ ] (a) Square function (b) Signum function (c) Triangular function (d) Gate function

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20. The ROC of a LTI stable system contains____________________ [ ] (a) Poles (b) unit circle (c) impulse (d) ramp 21. The following technique is used to convert the continuous time signal into discrete time signal is ____ [ ] (a) Ideal sampling (b) Natural sampling (c) Flat-top sampling (d) All 22. Laplace transform of e-at u(t) is ________ (a>0) [ ] (a) 1/(S-a) (b) 1/(s+a) (c) (S+a) (d) (s-a) 23. Laplace Transform of -t f(t) is _________ [ ] (a) dF(s)/ds (b) F(s) (c) F (2s) (d) None 24. Two sequences x1 (n) and x2 (n) are related by x2 (n) = x1 (- n), In the z- domain, their ROC’s are_____ [ ]

(a) The same (b) Reciprocal of each other. (c) Negative of each other. (d) Complements of each other.

25. The auto-correlation function of a rectangular pulse of duration T is__________ [ ] (a) a rectangular pulse of duration T. (b) a rectangular pulse of duration 2T. (c) a triangular pulse of duration T. (d) a triangular pulse of duration2T.

26. The average power (Pg) and energy (Eg) of the signal g(t) shown in figure are [ ] (a) Pg = 25, Eg = 150 (b) Pg = 0, Eg = 150 (c) Pg = 25, Eg = 3 (d) Pg = 25, Eg = 50

27. A band limited signal is sampled at the Nyquist rate. The signal can be recovered by passing the samples

through_______ [ ] (a) an RC filter (b) an envelope detector (c) a PLL (d) an ideal low-pass filter with appropriate bandwidth

28. If a signal f(t) has energy E, the energy of the signal f(2t) is equal to______________________ [ ] (a) E (b) 2E (c) E/2 (d) 4E

29. A band pass signal extends from 1 KHz to 2 KHz. The minimum sampling frequency needed to retain all information in the sampled signal is_________ [ ] (a) 1 KHz. (b) 2 KHz (c) 3 KHz. (d) 4 KHz.

30. If a function f (t)u(t) is shifted to right side by t0, then the function can be expressed as_____________ [ ]

(a) f (t − t0)u(t) (b) f( t) u (t- t0) (c) f (t − t0)u(t − t0) (d) f (t + t0)u(t + t0) 31. Match List I (Type of signal) with List II (property of Fourier transform) and select the correct answer using

the codes given below the lists: List I List II A. Real and even symmetric 1. Imaginary and even symmetric B. Real and odd symmetric 2. Real and even symmetric C. Imaginary and even symmetric 3. Real odd symmetric D. Imaginary and odd symmetric 4. Imaginary and odd symmetric

Codes: A B C D matched with_____________________ [ ] (a) 1 4 2 3 (b) 2 4 1 3 (c) 1 3 2 4 (d) 2 3 1 4

32. A signal x(t) = 5 cos 400πt is sampled at a rate 300 samples/s. The resulting samples are passed through an ideal LPF of cut-off frequency 150 Hz. Which of the following will be contained in the output of the LPF? __________ [ ] (a) 100 Hz (b) 100 Hz, 150 Hz (c) 50 Hz, 100 Hz (d) 50 Hz, 100 Hz, 150 Hz

33. Z-transform of a signal an x(n) is ______________ [ ]

(a) X[a] (b) X[Z.a] (c) X[Z/a] (d) None of these 34. Z-transform of a signal u (n) is ________ [ ] (a) 1/(1-Z-1) (b) 1/(1-Z) (c) (1-Z) (d) None of these 35. The ROC of Z -transform of unit-step sequence u(n), is____________________ [ ]

(a) Entire z -plane (b) z < 1 (c) z > 1 (d) none of these 36. The ROC of Z-transform does not contain any__________ [ ]

(a) Poles (b) 1’s (c) zeros (d) none of these 37. The differentiation of a unit step signal is, _____________________ [ ]

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(a) an impulse signal (b) a ramp signal (c) an exponential signal (d) a parabolic signal

38. Undersampling of the DFT of sequence x(n) of length –L occurs if we choose DFT length N as___ [ ] (a) N<L (b) N=L (c) N>L (d) N=2L

39. Which of the following statement is true for the twiddle factor 𝑤𝑤𝑁𝑁 = 𝑒𝑒−𝑗𝑗2𝑡𝑡/𝑁𝑁_______________ [ ] (a) Periodic, &symmetric (b) aperiodic &symmetric (c) aperiodic & asymmetric (d) periodic &asymmetric.

40. Zero padding to a time domain sequence improves_____________ [ ] (a) Power of the signal (b) resolution of the spectrum (c) ISI (d) none of these

41. 𝑊𝑊82 = ____________ [ ]

(a) j (b) 𝑗𝑗2 (c) -j (d) 1√2− 𝑗𝑗

√2

42. Assume x(n) and h(n) are two finite duration sequences both of length N with DFT s X(k) and H(k) respectively. If Y(k)=X(k)H(k) the y(n) is computed with _________________ [ ] (a) Linear convolution of x(n)and h(n) (b) circular convolution of x(n)and h(n) (c) Multiplication of x(n)and h(n) (d) correlation of x(n) and h(n)

43. For a sequence x(n)={1, 2, -3 , 0, 1, -1, 4, 2} ,the N-DFT points X(0), X(4) respectively are_________ [ ] (a) 6, 0 (b) 6, 6 (c) 0, 0 (d) 6, 2

44. 256-DFT consists ______________number of frequency samples in the spectrum. [ ] (a) 128 (b) 512 (c) 256 (d) 2256

45. DTFT of a sequence is ____________________ [ ] (a)Discrete periodic with N (b) discrete aperiodic (c) continuous and periodic with 2π (d) continuous aperiodic

46. DFT of a sequence gives_______________ [ ] (a) Always imaginary spectrum (b) continuous and discrete (c) continuous spectrum (d) discrete spectrum

47. If x(n) and h(n) are sequences of lengths L , N respectively, then what are the resultant sequences lengths respectively, if they are linearly convolved and circularly convolved____________ [ ] (a) L+M-1, max(L,M) (b) max(L,M) , L+M (c) min(L,M) , L+M-1 (d) L+M-1, min(L,M) Communications:::

48. Which of the following method is used to generate amplitude modulated signal?__________ [ ] (a) Indirect method (b) Square-law modulator (c) Hartley oscillator (d) none 49. Double Side Band suppressed carrier (DSB-SC) modulated signal contains______ [ ] (a) Two Lower Side bands (b) One lower sideband and one upper side band

(c) Two upper side bands (d) none 50. Which of the following modulation scheme requires the minimum transmitted power and minimum channel

bandwidth? ____ [ ] (a)VSB (b) DSB-SC (c) SSB (d) AM

51. According to Carson’s Rule, the bandwidth of frequency modulated (FM) signal is _________ [ ] (a) BT=2(Δf+fm) (b) BT=2Δf (c) BT= fm /Δf (d) None {BT= Transmission bandwidth, Δf=frequency device, fm= message signal frequency} 52. Limiter is not required in following FM demodulator._____________ [ ]

(a) Foster-Seelay Discriminator (b) Balanced modulator (c) Ratio Detector (d) None 53. In DSB-SC system, the figure of merit is ____________ [ ] (a) 0 (b) ∞ (c) 1 (d) None 54. In AM transmitter, the Broad cast frequency range is _________ [ ] (a) 550 -1650 KHz (b) 300-3000MHz (c) 30-300MHz (d) None 55. The Pulse width modulation (PWM) is defined as ___________ [ ] (a) Amplitude of the carrier pulse changing. (b) Position of the Carrier pulse (c) Width of the carrier pulse changing (d) none 56. An AM signal and a narrowband FM signal with identical carriers, modulating signals and modulation indices

of 0.1 are added. The resultant signal can be closely approximated by ____________ [ ] (a) Broadband FM (b) SSB with carrier (c) DSB-SC (d) SSB without carrier

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57. For a message signal 𝑚𝑚(𝑡𝑡) = cos (2𝜋𝜋𝑓𝑓𝑚𝑚𝑡𝑡) and carrier of frequency fc, SSB signal represented by____ [ ] (a) cos(2𝜋𝜋𝑓𝑓𝑚𝑚𝑡𝑡) cos (2𝜋𝜋𝑓𝑓𝑐𝑐𝑡𝑡) (b) cos (2𝜋𝜋𝑓𝑓𝑐𝑐𝑡𝑡) (c) cos (2𝜋𝜋(𝑓𝑓𝑐𝑐 + 𝑓𝑓𝑚𝑚)𝑡𝑡) (d) [1 + cos(2𝜋𝜋𝑓𝑓𝑚𝑚𝑡𝑡)] cos (2𝜋𝜋𝑓𝑓𝑐𝑐𝑡𝑡) 58. Pre-emphasis and De-emphasis are used in ______ [ ] (a)FM transmitter, FM receiver respectively (b) FM receiver, FM transmitter respectively

(c) Both used in FM transmitter (d) both used in FM receiver

59. A super-heterodyne radio receiver with an intermediate frequency of 455 KHz is tuned to a station operating at 1200KHz.The associated image frequency is __________KHz. [ ]

(a) 2855 (b) 2110 (c) 745 (d) 1655 60. Armstrong’s method is used to generate a _________signal [ ] (a) AM (b) DSB-SC (c) NBFM (d) WBFM 61. Choose the correct one from among the alternatives A, B, C, D after matching an item in Group 1 with the most

appropriate item in Group2._______ Group 1 Group 2 [ ] P- Ring modulator 1- Clock recovery Q -VCO 2- Demodulation of FM R- Foster-Seely discriminator 3- Frequency conversion S -Mixer 4- Summing the two inputs

5 -Generation of FM 6- Generation of DSB-SC

(a) P – 1 Q – 3 R – 2 S – 4 (b) P – 6 Q – 5 R – 2 S – 3 (c) P – 6 Q – 1 R – 3 S – 2 (d) P – 5 Q – 6 R – 1 S – 3 62. In FM modulation, when the modulation index increases, transmitted power is_______ [ ]

(a) Constant (b) increased (c) decreased (d) none of these 63. Sound signals in TV are____________ [ ]

(a) Amplitude modulated (b) dc modulated (c) frequency modulated (d) a and c 64. The maximum power in AM, when modulation index is____________ [ ]

(a) 0 (b) 0.5 (c) 0.7 (d) 1 65. FM signal is less affected by_______________________________ [ ]

(a) Loss (b) temperature (c) frequency (d) noise 66. In frequency modulation, frequency is____________________________ [ ]

(a) Constant (b) zero (c) variable (d) one 67. Modulating signal has______________ [ ]

(a) low frequency (b)low modulation (c) high frequency (d)none of these. 68. Technique that allows the simultaneous transmission of multiple signals across a single data link.____ [ ]

(a) Demodulating (b) Multiplexing (c) Compressing (d) None 69. The amplitude modulated wave form 𝐴𝐴𝑐𝑐[1 + 𝑘𝑘𝑎𝑎𝑚𝑚(𝑡𝑡) ]𝑐𝑐𝑐𝑐𝑐𝑐𝜔𝜔𝑐𝑐𝑡𝑡 is fed to an ideal envelope detector. The maximum

magnitude of 𝑘𝑘𝑎𝑎𝑚𝑚(𝑡𝑡) is less than 1.Which of the following could be the detector output? [ ] (a) 𝐴𝐴𝑐𝑐m(t) (b)𝐴𝐴𝑐𝑐2[1 + 𝑘𝑘𝑎𝑎𝑚𝑚(𝑡𝑡)]2 (c) 𝐴𝐴𝑐𝑐[1 + 𝑘𝑘𝑎𝑎𝑚𝑚(𝑡𝑡)] (d) 𝐴𝐴𝑐𝑐[1 + 𝑘𝑘𝑎𝑎𝑚𝑚(𝑡𝑡)]2

70. A 3500 Hz audio tone amplitude modulates an 800 kHz carrier resulting in 85% modulated signal. The highest frequency that

appears in the spectra of the modulated signal is____________ [ ] (a) 3500Hz (b) 796500Hz (c) 800000Hz (d) 803500Hz

71. A 96 KHz bandwidth is required to accommodate eight AM broadcasts simultaneously. The maximum

modulating frequency of each station must be limit___________ [ ] (a) 12 kHz (b) 10 kHz (c) 8 kHz (d) 6 kHz

72. Average power of an angle modulated signal x(t) = 6cos[2πx106t+2sin(8000πt) +4cos(8000pt)] V. is____ [ ]

(a) 10W (b) 18W (c) 20W (d) 28W

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73. The Hilbert transform of 𝑐𝑐𝑐𝑐𝑐𝑐𝜔𝜔1𝑡𝑡 + 𝑐𝑐𝑠𝑠𝑠𝑠𝜔𝜔2𝑡𝑡 is ______________________ [ ]

(a) sinω1 t − cosω2 t (b) sinω1 t + cosω2 t (c) cosω1 t − sinω2 t (d) sinω1 t + sinω2 t

74. Find the correct match between group-1 and group -2. __________ [ ]

P -[1 + 𝑘𝑘𝑚𝑚(𝑡𝑡)]𝐴𝐴𝑐𝑐𝑠𝑠𝑠𝑠(𝜔𝜔𝑐𝑐𝑡𝑡) W – Phase modulation Q - 𝑘𝑘𝑚𝑚(𝑡𝑡)𝐴𝐴𝑐𝑐𝑠𝑠𝑠𝑠(𝜔𝜔𝑐𝑐𝑡𝑡) X – Frequency modulation R - 𝐴𝐴𝑐𝑐𝑠𝑠𝑠𝑠(𝜔𝜔𝑐𝑐𝑡𝑡 + 𝑘𝑘𝑚𝑚(𝑡𝑡)) Y – Amplitude modulation S - 𝐴𝐴𝑐𝑐𝑠𝑠𝑠𝑠{𝜔𝜔𝑐𝑐𝑡𝑡 + ∫ 𝑚𝑚(𝜏𝜏𝑡𝑡

−∞ )𝑑𝑑𝜏𝜏} Z – DSB-SC modulation (a) P - Z Q - Y R – X S - W (b) P – W Q – X R – Y S – Z

(c) P - X Q – W R – Z S - Y (d) P – Y Q – Z R – W S – X 75. The Column-I lists the attributes and the Column-II lists the modulation systems. Match the attribute to the

modulation system that best meets it__________ [ ] Column-I Column-II P- Power efficient transmission of signals 1- Conventional AM Q- Most bandwidth efficient transmission of voice signals 2- FM R- Simplest receiver structure 3 -VSB S- Bandwidth efficient transmission of signals with Significant dc component 4 -SSB-SC

(a) P-4; Q-2; R-1; S-3 (b) P-2; Q-4; R-1; S-3 (c) P-3; Q-2; R-1; S-4 (d) P-2; Q-4; R-3; S-1 76. A device with input x(t) and output y(t) is characterized by 𝑦𝑦(𝑡𝑡) = 𝑥𝑥2(𝑡𝑡). An FM signal with frequency

deviation of 90 kHz and modulating signal bandwidth of 5 kHz is applied to this device. The bandwidth of the output signal is___________ [ ] (a) 370 kHz (b) 190 kHz (c) 380 kHz (d) 95 kHz

77. The image channel selectivity of super heterodyne receiver depends upon_________________ [ ]

(a) IF amplifiers only (b) RF & IF amplifiers only (c) Preselector, RF &IF amplifiers (d) Preselector ,&RF amplifiers

78. Companding is used in PCM to____________ (a) Reduce B.W (b) Reduce power (c) Increase S/N ratio (d) Get almost uniform S/N ratio

79. The main advantage of DM over PCM is _________________ [ ] (a) Less bandwidth (b) Less power (c) Better S/N ratio (d) Simple Circuitry

80. Which of the following gives minimum probability of error__________ [ ]

(a) ASK (b) FSK (c) PSK (d) DPSK 81. Entropy gives____________ [ ]

(a) Amount of information (b) Rate of information (c) Measure of uncertainty (d) Probability of message 82. Channel capacity, if B=4 KHz, SNR =20db.__________ [ ] (a) 2.663kbps (b) 0.2663kbps (c) 26.63kbps (d) 2663kbps 83. Slope overload distortion occurs in _________modulation system [ ] (a) Delta modulation (b) PAM (c) PCM (d) FSK 84. Convolutional codes are easily generated with a ________ [ ] (a) Shift Register (b) Cyclic codes (c) Tree (d) Trellis 85. Non uniform Quantization is used in______________ system [ ]

(a) PCM (b) DPCM (c) DM (d) ADM 86. The bit rate of QPSK communication system is 34Mbps, Baud rate of the system is_____ [ ]

(a) 68Mbps (b) 34Mbps (c) 17Mbps (d) None of these 87. ________system is more affected by noise [ ]

(a) PSK (b) ASK (c) FSK (d) DPSK 88. The cascade combination of a compressor and an expander, is called ________ [ ]

(a) modem (b) Limitter (c) companding (d) ISI

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89. Aperture effect in flat-top sampling of PAM signal generation is reduced by using_______ [ ] (a) predictor (b) Integrator (c) comparator (d) equalizer

90. Which of the following pulse modulation scheme is analog_____________ [ ]

(a) PCM (b) PWM (c) DM (d) DPCM 91. For a bit-rate of 8 Kbps, the best possible values of the transmitted frequencies in a coherent binary FSK

system are________ [ ] (a) 16 KHz and 20 KHz (b) 20 KHz and 32 KHz (c) 20 KHz and 40 KHz (d) 32 KHz and 40 KHz

92. For a BPSK Scheme bit error probability is given by____________ [ ]

(a) 𝑝𝑝𝑒𝑒 = 12𝑒𝑒𝑒𝑒𝑓𝑓𝑐𝑐�𝐸𝐸𝑏𝑏

𝑁𝑁𝑜𝑜 (b) �𝐸𝐸𝑏𝑏

𝑁𝑁𝑜𝑜 (c) 2𝑒𝑒𝑒𝑒𝑓𝑓𝑐𝑐�𝐸𝐸𝑏𝑏

𝑁𝑁𝑜𝑜 (d) None of these

93. Nyquist sampling rate of a signal given by 𝑥𝑥(𝑡𝑡) = cos(4000𝑡𝑡𝑡𝑡)cos (1000𝑡𝑡𝑡𝑡)

2𝑡𝑡 __________ [ ]

(a) 4000Hz (b) 1000Hz (c) 3000Hz (d) 5000Hz 94. Eye diagrams used to measure the ______________parameter of a digital communication system [ ]

(a) ISI (b) jitter (c) both (a) and (b) (d) power

95. Match Group 1 with Group 2 ____________ [ ] 1. FM P. Slope overload 2. DM Q. µ-law 3. PSK R. Envelope detector 4. PCM S. Capture effect

T. Hilbert transform U. Matched filter

(a) 1 – T 2 – P 3 – U 4 - S (b) 1 – S 2 – U 3 – P 4 – T (c) 1 – S 2 – P 3 – U 4 - Q (d) 1 – U 2 – R 3 – S 4 – Q 96.Noise with double-sided power spectral density of K over all frequencies is passed through a RC low pass filter with 3dB

cut-off frequency of fc. The noise power at the filter output is______________ [ ] (a) K (b) Kfc (c) Kπfc (d) ∞

97. In a PCM system with uniform quantization, increasing the number of bits from 8 to 9 will reduce the quantization noise power by factor of______________________ [ ] (a) 9 (b) 8 (c) 4 (d) 2

98. Match the following group-1 with group-2 ____________ [ ] 1. Envelop detector P-TDM 2. Quadrature null effect Q-SSB-SC 3. Voice signal transmission R-PCM 4. Quantization noise S-AM 5. Slope overload distortion T-slope detector 6. Under sampling U-DM V-DSB-SC W-aliasing effect (a)1-S 2-V 3-Q 4-R 5-U 6-W (b) 1-S 2-Q 3- 4-U 5-R 6-W (c) 1-S 2-V 3-P 4-U 5-T 6-W (d) 1-S 2-Q 3-V 4-R 5-T 6-P 99. Four independent messages have bandwidths of 100 Hz, 200 Hz and 400 Hz, respectively. Each is sampled at the

Nyquist rate, and the samples are time division multiplexed and transmitted. The transmitted sample rate is ______[ ] (a)1600 Hz (b) 800 Hz (c) 400 Hz (d) 200 Hz

100. QAM uses different ……… in order to transmit multiple bits in one signal change. [ ]

(a) Frequencies (b) pulses (c) bit-rates (d) amplitude-phase

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