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GATE 2004 : Electronics And Communication Engineering

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For more files visit www.educationobserver.com/forum Q.1 Q.30 Carry One Mark Each 1. Consider the network graph shown in figure. Which one of the following is NOT a tree of this graph? (a) (c) 2. (b) (d) The equivalent inductance measured between the terminals 1 and 2 for the circuit shown in figure, is M 1 L2 L1 2 (a) L 1 + L2 + M 3. (b) L 1 + L2 - M (c) L 1 + L2 + 2M The circuit shown in Fig.Q.3, with R = 1 1 ,L = H, C = 3F has input voltage W 3 4 v (t ) = sin2t. The resulting current i(t) is (a) 5 sin (2t + 53.1o ) (b) 5 sin (2t - 53.1o ) (c) 25 sin (2t + 53.1o ) (d) 25 sin (2t - 53.1o ) i(t) v(t) R (d) L 1 + L2 - 2M L C For more files visit www.educationobserver.com/forum 4. For the circuit shown in Fig.Q.4, the time constant RC = 1ms. The input voltage 2 sin103 t. The output voltage v0 (t ) is equal to is v i (t ) = R 103 t - 45o ) (a) sin ( 103 t + 45o ) (b) sin ( 10 t - 53 (c) sin ( 3 o V1(t) V0(t) C ) 103 t + 53o ) (d) sin ( 5. For the R-L circuit shown in Fig.Q.5, the input voltage v i (t ) = u (t ). The current i(t) is 1H i(t) vi(t) 2 (a) i(t) (b) i(t) 0.5 1 0.31 0.63 2 (c) t(sec) i(t) t(sec) i(t) (d) 0.5 1 0.31 0.63 1/2 6. 1/2 2 t(sec) t(sec) The impurity commonly used for realizing the base region of a silicon n-p-n transistor is (a) Gallium (b) Indium (c) Boron (d) Phosphorus For more files visit www.educationobserver.com/forum 7. If for a silicon n-p-n transistor, the base-to-emitter voltage (VBE) is 0.7V and the collector-to-base voltage (VCB) is 0.2V, then the transistor is operating in the (a) normal active mode (c) inverse active mode 8. (b) saturation mode (d) cutoff mode Consider the following statements S1 and S2. S1: The of a bipolar transistor reduces if the base width is increased. S2: The of a bipolar transistor increases if the doping concentration in the base in increased Which one of the following is correct? (a) S1 is FALSE and S2 is TRUE (c) both S1 and S2 are FALSE 9. (b) both S1 and S2 are TRUE (d) S1 is TRUE and S2 is FALSE An ideal op-amp is an ideal (a) voltage controlled current source (c) current controlled current source 10. (b) voltage controlled voltage source (d) current controlled voltage source Voltage series feedback (also called series shunt feedback) results in (a) increase in both input and output impedances (b) decrease in both input and output impedances (c) increase in input impedance and decrease in output impedance (d) decrease in input impedance and increase in output impedance 11. The circuit in Figure is a R - R + Vin C Vout C (a) low-pass filter (b) high-pass filter (c) band-pass filter (d) band-reject filter For more files visit www.educationobserver.com/forum 12. Assuming VCesat=0.2V and = 50, the minimum base current (IB) required to drive the transistor in Fig.Q.12 to saturation is 3V (a) 56 A IC (b) 140 mA 1k IB (c) 60 A (d) 3 mA 13. A master slave flip-flop has the characteristic that (a) change in the input immediately reflected in the output (b) change in the output occurs when the state of the master is affected (c) change in the output occurs when the state of the slave is affected (d) both the master and the slave states are affected at the same time 14. The range of signed decimal numbers that can be represented by 6-bite 1 s complement number is (a) -31 to +31 15. (c) -64 to +63 (d) -32 to +31 A digital system is required to amplify a binary-encoded audio signal. The user should be able to control the gain of the amplifier from a minimum to a maximum in 100 increments. The minimum number of bits required to encode, in straight binary is (a) 8 16. (b) -63 to +64 (b) 6 (c) 5 (d) 7 Choose the correct one from among the alternatives A,B,C,D after matching an item from Group 1 with the most appropriate item in Group 2. Group 1 Group 2 P. Shift register 1. Frequency division Q. Counter 2. Addressing in memory chips R. Decoder 3. Serial to parallel data conversion (a) P 3 Q 2 R - 1 (b) P 3 Q 1 R - 2 (c) P 2 Q 1 R 3 (d) P 1 Q 2 R - 2 For more files visit www.educationobserver.com/forum 17. Figure shows the internal schematic of a TTL AND-OR-Invert (AOI) gate. For the inputs shown in Figure, the output Y is (a) 0 A B (b) 1 Y (c) AB Inputs are floating (d) AB 18. Vout Figure is the voltage transfer characteristic of (a) an NMOS inverter with enhancement mode transistor as load (b) an NMOS inverter with depletion mode transistor as load (c) A CMOS inverter (d) A BJT inverter Vin 0 19. The impulse response h[n] of a linear time-invariant system is given by h [n]= u [n + 3]+ u [n - 2]- 2u [n - 7] where u[n] is the unit step sequence. The above system is (a) stable but not causal (c) causal but unstable 20. (b) stable and causal (d) unstable and not causal The distribution function fx (x ) of a random variable X is shown in Fig.Q.20. the probability that X = 1 is Fx(x) 1.0 0.55 0.25 -2 (a) zero (b) 0.25 0 1 3 (c) 0.55 x (d) 0.30 For more files visit www.educationobserver.com/forum 21. The z-transfrom of a system is H (z ) = z z - 0.2 If the ROC is z < 0.2, then the impulse response of the system is (a) n (0.2) u [n ] (b) n - n - 1] u[ n (c) - (0.2) u [n] 22. n (0.2) - n - 1] (d) - (0.2) u [ The Fourier transform of a conjugate symmetric function is always (a) imaginary (c) real 23. (b) conjugate anti-symmetric (d) conjugate symmetric The gain G (s)H (z ) = margin 2( 1 + z) s2 for system with open-loop transfer function , is (a) 24. the Given the G (s)H (z ) = (b) 0 (c) 1 (d) - K , the point of intersection of the asymptotes s (s + 1)(s + 3) of the root loci with the real axis is (a) -4 25. 8 6 (d) 4 (b) 12 (c) 16 (d) 8 An AM signal is detected using an envelope detector. The carrier frequency and modulating signal frequency are 1 MHz and 2 KHz respectively. An appropriate value for the time constant of the envelope detector is (a) 500 sec 27. (c) -1.33 In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to quantization noise ratio improves by the factor (a) 26. (b) 1.33 (b) 20 sec (c) 0.2 sec (d) 1 sec An AM signal and a narrow-band FM signal with identical carriers, modulating signals and modulation indices of 0.1 are added together. The resultant signal can be closely approximated by (a) broadband FM (b) SSB with carrier (c) DSB-SC (d) SSB without carrier For more files visit www.educationobserver.com/forum 28. In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 t t2. This indicates that during this interval (a) the input to the modulator is essentially constant (b) the modulator is going through slope overload (c) the accumulator is in saturation (d) the speech signal is being sampled at the Nyquist rate 29. The phase velocity of an electromagnetic wave propagating in a hallow metallic rectangular waveguide in the TE10 mode is (a) equal to its group velocity (b) less than the velocity of light in free space (c) equal to the velocity of light in free space (d) greater than the velocity of light in free space 30. Consider a lossless antenna with a directive gain of +6db. If 1mW of power is fed to it the total power radiated by the antenna will be (a) 4mW (b) 1mW (c) 7mW (d) 1 mW 4 Q.31 Q.90 Carry Two Marks Each 31. For the lattice circuit shown in Fig. Q.31, Za = j2W and Z b = 2W. The values of z the open circuit impedance parameters Z = 11 z 21 1 - j 1 + j (a) 1 + j 1 + j Zb 1 1 - j 1 + j (b) j j 1 + 1 3 Za 1 + j 1 + j (c) 1 - j 1 - j 1 + j - 1 + j (d) - 1- j 1- j z12 are z22 Za 2 4 Zb For more files visit www.educationobserver.com/forum 32. The circuit shown in Fig.Q.32 has initial current iL (0and an initial voltage Vc (0- )= )= 1A through the inductor - 1V across the capacitor. For input v(t) = u(t), the Laplace transform of the current i(t) for t 0 is 1H 1 + i(t) + 1F v(t) - - (a) 33. (b) s+ 2 s + s+ 1 2 (c) s- 2 s + s+ 1 2 (d) s- 2 s + s- 1 2 Consider the Bode magnitude plot shown in Fig.33. The transfer function H(s) is (a) (b) (c) (d) 34. s s + s+ 1 2 (s + 10) (s + 1)(s + 100) 20log|H(j )| 0 -20dB/decade 10 (s + 10) (s + 1)(s + 100) -20 102 (s + 1) (s + 10)(s + 100) 103 (s + 100) (s + 1)(s + 10) 1 The transfer function H (s) = H (s) = V0 (s) Vi (s) 10 100 of an R-L-C circuit is given by 106 s2 + 20s + 106 the Quality factor (Q-factor) of this circuit is (a) 25 35. (b) 50 (c) 100 (d) 5000 For the circuit shown in Fig.Q.35, the initial conditions are zero. Its transfer V (s) function H (s) = c is Vi (s) 10mH 10k (a) 1 s + 106 s + 106 2 103 (c) 2 s + 103 s + 106 (b) 106 s + 103 s + 106 2 106 (d) 2 s + 106 s + 106 Vi(t) 100 F Vc(t) For more files visit www.educationobserver.com/forum 36. A system described by the following differential equation d 2y dy + 3 + 2y = x (t ) is initially at rest. For input x(t) = 2u(t), the output y(t) is dt dt 2 (a) (c) 37. (1 - 2e- t + e- 2t )u (t ) (0.5 + e- t + 1.5e- 2t )u (t ) (b) (1 + 2e (d) (0.5 + 2e - t - e- 2t )u (t ) - t + 2e- 2t )u (t ) Consider the following statements S1and S2 S1: At the resonant frequency the impedance of a series R-L-C circuit is zero. S2: In a parallel G-L-C circuit, increasing the conductance G results in increase in its Q factor. Which one of the following is correct? (a) S1 is FALSE and S2 is TRUE (c) S1 is TRUE and S2 is FALSE 38. (b) both S1 and S2 are TRUE (d) both S1 and S2 are FALSE In an abrupt p-n junction, the doping concentrations on the p-side and n-side are N A = 9 1016 / cm3 and ND = 1 1016 / cm3 respectively. The p-n junction is reverse biased and the total depletion width is 3 m. The depletion width on the p-side is (a) 2.7 m 39. (d) 0.75 m (b) 1 1016 / cm3 (c) 2.5 1015 / cm3 (d) 2 1015 / cm3 Consider an abrupt p-junction. Let Vbi be the built-in potential of this junction and VR be the applied reverse bias. If the junction capacitance (C1) is 1 pF for Vbi + VR = 1V, then for Vbi + VR = 4V, Cj will be (a) 4 pF 41. (c) 2.25 m The resistivity of a uniformly doped n-type silicon sample is 0.5 -cm. If the electron mobility ( n) is 1250 cm2/V-sec and the charge of an electron is 1.6 10-19 Coulomb, the donor impurity concentration (ND) in the sample is (a) 2 1016 / cm3 40. (b) 0.3 m (b) 2 pF (c) 0.25 pF (d) 0.5 pF Consider the following statements S1 and S2. S1: The threshold voltage (VT) of a MOS capacitor decreases with increase in gate oxide thickness S2: The threshold voltage (VT) of a MOS capacitor decreases with increase in substrate doping concentration. Which one of the following is correct? (a) S1 is FALSE and S2 is TRUE (b) both S1 and S2 are TRUE (c) S1 is TRUE and S2 is FALSE (d) both S1 and S2 are FALSE For more files visit www.educationobserver.com/forum 42. The drain of an n-channel MOSFET is shorted to the gate so that VGS = VDS. The threshold voltage (VT) of MOSFET is 1V. If the drain current (ID) is 1 mA for VGS = 2V, then for VGS = 3V, ID is (a) 2 mA 43. (d) 4 mA (b) 0.886 eV (c) 0.854 eV (d) 0.706 eV The neutral base width of a bipolar transistor, biased in the active region, is 0.5 m. the maximum electron concentration and the diffusion constant in the base are 1014/cm3 and Dn = 25 cm2/sec respectively. Assuming negligible recombination I the base, the collector current density is (the electron charge is 1.6 10-19 coulomb) (a) 800 A/cm2 45. (c) 9 mA The longest wavelength that can be absorbed by silicon, which has the bandgap of 1.12eV, is 1.1 m. If the longest wavelength that can be absorbed by another material is 0.87 m, then the bandgap of this material is (a) 1.416 eV 44. (b) 3 mA (b) 8 A/cm2 (c) 200 A/cm2 (d) 2 A/cm2 Assuming that the of the transistor is extremely large and VBE = 0.7V, Ic and VCE in the circuit shown in Figure, are 5V IC 4k 1k 2.2k + VCE 300 (a) IC = 1mA, VCE = 4.7V (c) IC = 1mA, VCE = 2.5V 46. (b) IC = 0.5mA, VCE = 3.75V (d) IC = 0.5mA, VCE = 3.9V A bipolar transistor is operating in the active region with a collector current of 1mA. Assuming that the of the transistor is 100 and the thermal voltage (VT) is 25 mV, the transconductance (gm) and the input resistance (r ) of the transistor in the common emitter configuration, are (a) gm = 25mA / V and rp = 15.625k W (b) gm = 40mA / V and rp = 4.0kW (c) gm = 25mA / V and rp = 2.5k W (d) gm = 40mA / V and rp = 2.5kW For more files visit www.educationobserver.com/forum 47. The value of C required for sinusoidal oscillations of frequency 1kHz in the circuit 2.1k of Fig.Q.47 is 1k (a) 1 mF 2p L (b) 2pmF (c) 1 2p 6 + L Vout C mF 1k (d) 2p 6mF L C 1k 48. In the op-amp circuit given in Fig.Q.48, the load current IL is (a) (b) 49. R1 R1 Vs ns R2 (c) (d) ns R2 + ns RL C R2 ns RL R2 iL RL In the voltage regulator shown in Fig.Q.49, the load current can vary from 100mA to 500mA. Assuming that the Zener diode is ideal (i.e., the Zener knee current is negligibly small and Zener resistance is zero in the breakdown region), the value of R is R (a) 7 + (b) 70 (c) 70 W 3 12V 5V Variable load 100 to 500 mA - (d) 14 50. In a full-wave rectifier using two ideal diodes, Vdc and Vm are the dc and peak values of the voltage respectively across a resistive load. If PIV is the peak inverse voltage of the diode, then the appropriate relationships for this rectifier are (a) Vdc = Vm , PIV = 2Vm p (b) Vdc = 2 Vm , PIV = 2Vm p For more files visit www.educationobserver.com/forum (c) Vdc = 2 51. Vm , PIV = Vm p Vm , PIV = Vm p The minimum number of 2 to 1 multiplexers required to realize a 4 to 1 mutliplexer is (a) 1 52. (d) Vdc = (b) 2 (c) 3 (d) 4 The Boolean expression AC + BC is equivalent to (a) AC + BC + AC (c) AC + BC + BC + ABC 53. (b) BC + AC + BC + AC B (d) ABC + ABC + ABC + ABC 11001, 1001 and 111001 correspond to the 2 s complement representation of which one of the following sets of number? (a) 25, 9 and 57 respectively (c) -7, -7 and 7 respectively 54. (b) -6, -6 and 6 respectively (d) -25, -9 and 57 respectively The 8255 Programmable Peripheral Interface is used as described below. I. An A/D converter is interfaced to a microprocessor through an 8255. the conversion is initiated by a signal from the 8255 on Port C. A signal on Port C causes data to be strobed into Port A. II. Two computers exchange data using a pair of 8255s. Port A works as a bidirectional data port supported by appropriate handshaking signals. The appropriate modes of operation of the 8255 for I and II would be (a) Mode 0 for I and Mode 1 for II (c) Mode 2 for I and Mode 0 for II 55. (b) Mode 1 for I and Mode 0 for II (d) Mode 2 for I and Mode 1 for II The number of memory cycles required to execute the following 8085 instructions I. LDA 3000H II. LXI D, FOF 1H Would be (a) 2 for I and 2 for II (b) 4 for I and 3 for II (c) 3 for I and 3 for II (d) 3 for I and 4 for II For more files visit www.educationobserver.com/forum 56. In the modulo-6 ripple counter shown in Figure, the output of the 2-input gate is used to clear the J-K flip-flops. 1 C J B J A J Clock input C K B K A K 2-input gate The 2-input gate is: (a) a NAND gate 57. (b) a NOR gate (c) an OR gate (d) an AND gate Consider the sequence of 8085 instructions given below. LXI H, 9258 MOV A, M, CMA, MOV M, A Which one of the following is performed by this sequence? (a) contents of location 9258 are moved to the accumulator (b) contents of location 9258 are compared with the contents of the accumulator (c) contents of location 8529 are complemented and stored in location 8529 (d) contents of location 5892 are complemented and stored in location 5892 58. A Boolean function f of two variables x and y is defined as follows: f(0,0) = f(0,1) = f(1,1)=1; f(1,0) = 0 Assuming complements of x and y are not available, a minimum cost solution for realizing f using only 2-input NOR gates and 2-input OR gates (each having unit cost) would have a total cost of (a) 1 unit 59. (b) 4 unit (c) 3 unit (d) 2 unit It is desired to multiply the numbers 0AH by 0BH and store the result in the accumulator. The numbers are available in registers B and C respectively. A part of the 8085 program for this purpose is given below: MVI A, 00H Loop; - - - - - - - - - - For more files visit www.educationobserver.com/forum .. HLT END The sequence of instruction to the complete the program would be (a) JNZ LOOP, ADD B, DCR C (b) ADD B, JNZ LOOP, DCR C (c) DCR C, JNZ LOOP, ADD B (d) ADD B, DCR C, JNZ LOOP 60. A 1 kHz sinusoidal signal is ideally sampled at 1500 samples/sec and the sampled signal is passed through an ideal low-pass filter with cut-off frequency 800 Hz. The output signal has the frequency (a) zero Hz 61. (b) 0.75 kHz (c) 0.5 kHz (d) 0.25 kHz A rectangular pulse train s(t) as shown in Fig.Q.61 is convolved with the signal cos2 (4 p 103 t ). the convolved signal will be a s(t) (a) DC 1 (b) 12 kHz sinusoid (c) 8 kHz sinusoid (d) 14 kHz sinusoid t 0.1 msec 62. 0 Consider the sequence x [n]= - 4 - j5 1 + j2 4 The conjugate anti-symmetric part of the sequence is (a) [ -4 j2.5 4 j2.5] (b) [ j2.5 1 j2.5] (c) [ j5 j2 0] (d) [ -4 63. j2 1 4] A casual LTI system is described by the difference equation 2y [n]= a y [n - 2]- 2 x [n]+ b x [n - 1] the system is stable only if (a) a = 2, (c) 64. b < 2 a < 2, any value of b (b) a > 2, b > 2 (d) b < 2, any value of a 1 is excited with 10u(t). s+ 2 The time at which the output reaches 99% of its steady state value is A causal system having the transfer function H (s) = For more files visit www.educationobserver.com/forum (a) 2.7 sec 65. (b) 2.5 sec (c) 2.4 sec (d) 2.1 sec The impulse response h[n] of a linear time invariant system is given as - 2 2 n = 1, - 1 h [n]= 4 2 n = 2, - 2 0, otherwise If the input to the above system is the sequence e (a) 4 2e 66. jp n 4 (b) 4 2e - jp n 4 jp n 4 (c) 4e , then the output is jp n 4 (d) - 4e jp n 4 Let x(t) and y(t) (with Fourier transforms X(f) and Y(f) respectively) be related as x(t) shown in Figure. y(t) 1 -2 0 -2 t 2 -1 0 t -1 Then Y(f) is (a) - 67. 1 f X e 2 2 j 2p f (b) - f j 2p f (c) - X e 2 f (d) - X e 2 j 2p f A system has poles at 0.01 Hz, 1 Hz and 80 Hz; zeros at 5 Hz, 100 Hz and 200 Hz. The approximate phase of the system response at 20 Hz is (a) -90 68. 1 f j 2p f X e 2 2 (b) 0 (c) 90 (d) -180 Consider the signal flow graph shown in Figure. The gain x1 a b x2 e (a) 1 - (be + cf + dg) abc x3 c f x4 d x5 is x1 x5 g (b) bedg 1 - (be + cf + dg) For more files visit www.educationobserver.com/forum (c) 69. abcd 1 - (be + cf + dg) + bedg (d) 1 - (be + cf + dg) + bedg abcd - 2 2 , then sin At is If A = 1 - 3 (a) 1 sin (- 4t ) + 2 sin (- t ) - 2 sin (- 4t ) + 2 sin (- t ) 3 - sin (- 4t ) + sin (- t ) 2 sin (- 4t ) + sin (- t ) sin (- 2t ) sin (2t ) (b) sin t sin 3 t ( ) ( ) (c) (d) 70. 1 sin (4t ) + 2 sin (t ) 2 sin (- 4t ) + 2 sin (- t ) 3 2 sin (4t ) + sin (t ) - sin (- 4t ) + sin (t ) 1 cos (- t ) + 2 cos (t ) - 2 cos (- 4t ) + 2 sin (- t ) 3 - cos (- 4t ) + sin (- t ) - 2 cos (- 4t ) + cos (- t ) The open G (s) = (a) 71. loop K transfer s (s2 + s + 2)(s + 3) 21 > K> 0 44 function of a unity feedback system . The range of K for which the system is stable is (b) 13 > K > 0 (c) 21 < K< 4 (d) - 6 < K < For the polynomial P (s) = s5 + s 4 + 2s3 + 2s2 + 3s + 15, the number of roots which lie in the right half of the s-plane is (a) 4 72. (b) 2 (c) 3 (d) 1 The state variable equations of a system are: 1. x1 = - 3x1 - x2 + u 2. x2 = 2 x1 y = x1 + u the system is (a) controllable but not observable (b) observable but not controllable (c) neither controllable nor observable 73. is (d) controllable and observable 1 0 , the state transition matrix e At is given by Given A = 0 1 0 (a) - t e e- t 0 et (b) 0 0 et e- t (c) 0 0 e- t 0 (d) t e et 0 For more files visit www.educationobserver.com/forum 74. Consider the signal x(t) shown in Fig.Q.74. Let h(t) denote the impulse response of the filter matched to x(t), with h(t) being non-zero only in the interval 0 to 4 sec. The slop of h(t) in the interval 3 < t < sec is x(t) 1 sec- 1 (a) 2 (b) - 1 sec- 1 (c) - 1 sec- 1 2 1 (d) 1 sec- 1 t(sec) 1 4 3 2 -1 75. A 1mW video signal having a bandwidth of 100 MHz is transmitted to a receiver through a cable that has 40 dB loss. If the effective one-sided noise spectral density at the receiver is 10-20 Watt/Hz, then the signal to noise ratio at the receiver is (a) 50 db 76. (b) 30 db (c) 40 db (d) 60 db A 100 MHz carrier of 1 V amplitude and a 1 MHz modulating signal of 1 V amplitude are fed to a balanced modulator. The output of the modulator is passed through an ideal high-pass filter with cut-off frequency of 100 MHz. The output of the filter is added with 100 MHz signals of 1 V amplitude and 90 phase shift as shown in Fig.Q.76. The envelope of the resultant signal is (a) constant (b) (c) 5 - sin (2p 106 t ) 4 (d) 77. 1 + sin (2p 106 t ) 5 + cos (2p 106 t ) 4 1MHz, 1V Balanced Modulator HPF 100MHz + + 100MHz, 1V 100MHz, 1V.90 Two sinusoidal signals of same amplitude and frequencies 10 kHz and 10.1 kHz are added together. The combined signal is given to an ideal frequency detector. The output of the detector is (a) 0.1 kHz sinusoid (b) 20.1 kHz sinusoid (c) a linear function of time (d) a constant For more files visit www.educationobserver.com/forum 78. Consider a binary digital communication system with equally likely 0 s and 1 s. When binary 0 is transmitted the voltage at the detector input can lie between the level s-0.25V and +0.25V with equal probability: when binary 1 is transmitted, the voltage at the detector can have any value between 0 and 1 V with equal probability. If the detector has a threshold of 2.0V (i.e., if the received signal is greater than 0.2 V, the bit is taken as 1), the average bit error probability is (a) 0.15 79. (b) 0.2 (c) 0.05 (d) 0.5 A random variable X with uniform density in the interval 0 to 1 is quantized as follows: If 0 X 0.3, xq = 0 If 0.3 < X 1, xq= 0.7 Where xqis the quantized value of X The root-mean square value of the quantization noise is (a) 0.573 (b) 0.198 (c) 2.205 (d) 0.266 80. Group 1 Group 2 1. FM P. Slope overload 2. DM Q. -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 (c) 1 S 2 P 3 U 4 - Q 81. (b) 1 S 2 U 3 P 4 - T (d) 1 U 2 R 3 S 4 - Q Three analog signals, having bandwidths 1200 Hz, 600 Hz and 600 Hz, are sampled at their respective Nyquist rates, encoded with 12 bit words, and time division multiplexed. The bit rate for the multiplexed signal is (a) 115.2 kbps (b) 28.8 kbps (c) 57.6 kbps (d) 38.4 kbps For more files visit www.educationobserver.com/forum 82. Consider a system shown in Fig.Q.82. Let X(f) and Y(f) denote the Fourier transforms of x(t) and y(t) respectively. The ideal HPF has the cutoff frequency 10 kHz. x(t) Balanced Modulator ~ HPF 10MHz Balanced Modulator 10KHz ~ y(t) 13KHz X(f) -3 f(kHz) 1 -1 3 The positive frequencies where Y(f) has spectral peaks are (a) 1 kHz and 24 kHz (c) 1 kHz and 14 kHz 83. (b) 2 kHz and 24 kHz (d) 2 kHz and 14 kHz A parallel plate air-filled capacitor has plate area of 10-4 m2 and plate separation of 10-3 m. It is connected to a 0.5 V, 3.6 GHz source. The magnitude of the 1 displacement current is = p 10- 9 F / m o 36 (a) 10 mA 84. (b) 100 mA (c) 10 A (d) 1.59 mA A source produces binary data at the rate of 10 kbps. The binary symbols are represented as shown in Figure. Binary 1 Binary 0 1V t(msec) 0 0.1 0 0.1 t(msec) -1V The source output is transmitted using two modulation schemes, namely Binary PSK (BPSK) and Quadrature PSK (QPSK). Let B1 and B2 be the bandwidth For more files visit www.educationobserver.com/forum requirements of BPSK and QPSK respectively. Assuming that the bandwidth of the above rectangular pulses is 10 kHz, B1 and B2 are (a) B1 = 20 kHz, B2= 20 kHz (c) B1 = 20 kHz, B2= 10 kHz 85. (b) B1 = 10 kHz, B2= 20 kHz (d) B1 = 10 kHz, B2= 10 kHz Consider a 300 quarter-wave long (at 1 GHz) transmission line as shown in Figure. It is connected to a 10V, 50 sources at one end and is left open circuited at the other end. The magnitude of the voltage at the open circuit end of the line is Z0=300 10V, 50 Source /4 (a) 10 V 86. (b) 5 V (c) 60 V (d) 60 V 7 In a microwave test bench, why is the microwave signal amplitude modulated at 1 kHz (a) To increase the sensitivity of measurement (b) To transmit the signal to a far-off place (c) To study amplitude modulation (d) Because crystal detector fails at microwave frequencies. 87. u r x + ja y )e jkz If E = (a jwt ur k y + ja x )e jkz (a and H = wm jwt , the time averaged Poynting vector is (a) null vector 88. k a (b) z wm 2k a (c) z wm k a (d) z 2wm Consider an impedance Z = R + jX marked with point P in an impedance Smith chart as shown in Fig.Q.88. The movement from point P along a constant resistance circle in the clockwise direction by an angle 45 is equivalent to r=0.5 x=0 x=-0.5 (a) adding an inductance in series with Z (b) adding a capacitance in series with Z x=-1 P For more files visit www.educationobserver.com/forum (c) adding an inductance in shunt across Z (d) adding a capacitance in shunt across Z 89. A plane electromagnetic wave propagating in free space in incident normally on a large slab of loss-less, non-magnetic, dielectric material with > 0. Maxima and minima are observed when the electric field is measured in front of the slab. The maximum electric field is found to be 5 times the minimum field. The intrinsic impedance of the medium should be (a) 120 90. (b) 60 (c) 600 (d) 24 A lossless transmission line is terminated in a load which reflects a part of the incident power. The measured VSWR is 2. the percentage of the power that is reflected back is (a) 57.73 (b) 33.33 (c) 0.11 (d) 11.11

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