## ELECTRONICS AND TELECOMMUNICATION- PAGE 1

1. Consider the following statements for a metal oxide semiconductor field effect transistor (MOSFET):

P: As channel length reduces, OFF-state current increases.

Q: As channel length reduces, output resistance increases.

R: As channel length reduces, threshold voltage remains constant.

S: As channel length reduces, ON current increases.

Which of the above statements are INCORRECT?

(A) P and Q (B) P and S (C) Q and R (D) R and S

Ans: C

2. Match the inferences X, Y, and Z, about a system, to the corresponding properties of the elements of first column in Routh’s Table of the system characteristic equation.

X: The system is stable …

Y: The system is unstable …

Z: The test breaks down …

P: … when all elements are positive

Q: … when any one element is zero

R: … when there is a change in sign of coefficients

(A) X→P, Y→Q, Z→R (B) X→Q, Y→P, Z→R

(C) X→R, Y→Q, Z→P (D) X→P, Y→R, Z→Q

Ans: D

3. A closed-loop control system is stable if the Nyquist plot of the corresponding open-loop transfer function

(A) encircles the s-plane point (−1 + j0) in the counterclockwise direction as many times as the number of right-half s-plane poles.

(B) encircles the s-plane point (0 − j1) in the clockwise direction as many times as the number of right-half s-plane poles.

(C) encircles the s-plane point (−1 + j0) in the counterclockwise direction as many times as the number of left-half s-plane poles.

(D) encircles the s-plane point (−1 + j0) in the counterclockwise direction as many times as the number of right-half s-plane zeros.

Ans: A

4. In an 8085 system, a PUSH operation requires more clock cycles than a POP operation. Which one of the following options is the correct reason for this?

(A) For POP, the data transceivers remain in the same direction as for instruction fetch (memory to processor), whereas for PUSH their direction has to be reversed.

(B) Memory write operations are slower than memory read operations in an 8085 based system.

(C) The stack pointer needs to be pre-decremented before writing registers in a PUSH, whereas a POP operation uses the address already in the stack pointer.

(D) Order of registers has to be interchanged for a PUSH operation, whereas POP uses their natural order.

Ans: C

P: As channel length reduces, OFF-state current increases.

Q: As channel length reduces, output resistance increases.

R: As channel length reduces, threshold voltage remains constant.

S: As channel length reduces, ON current increases.

Which of the above statements are INCORRECT?

(A) P and Q (B) P and S (C) Q and R (D) R and S

Ans: C

2. Match the inferences X, Y, and Z, about a system, to the corresponding properties of the elements of first column in Routh’s Table of the system characteristic equation.

X: The system is stable …

Y: The system is unstable …

Z: The test breaks down …

P: … when all elements are positive

Q: … when any one element is zero

R: … when there is a change in sign of coefficients

(A) X→P, Y→Q, Z→R (B) X→Q, Y→P, Z→R

(C) X→R, Y→Q, Z→P (D) X→P, Y→R, Z→Q

Ans: D

3. A closed-loop control system is stable if the Nyquist plot of the corresponding open-loop transfer function

(A) encircles the s-plane point (−1 + j0) in the counterclockwise direction as many times as the number of right-half s-plane poles.

(B) encircles the s-plane point (0 − j1) in the clockwise direction as many times as the number of right-half s-plane poles.

(C) encircles the s-plane point (−1 + j0) in the counterclockwise direction as many times as the number of left-half s-plane poles.

(D) encircles the s-plane point (−1 + j0) in the counterclockwise direction as many times as the number of right-half s-plane zeros.

Ans: A

4. In an 8085 system, a PUSH operation requires more clock cycles than a POP operation. Which one of the following options is the correct reason for this?

(A) For POP, the data transceivers remain in the same direction as for instruction fetch (memory to processor), whereas for PUSH their direction has to be reversed.

(B) Memory write operations are slower than memory read operations in an 8085 based system.

(C) The stack pointer needs to be pre-decremented before writing registers in a PUSH, whereas a POP operation uses the address already in the stack pointer.

(D) Order of registers has to be interchanged for a PUSH operation, whereas POP uses their natural order.

Ans: C

5. The Ebers-Moll model of a BJT is valid

(A) only in active mode

(B) only in active and saturation modes

(C) only in active and cut-off modes

(D) in active, saturation and cut-off modes

Ans: D

6. Which one of the following statements is correct about an ac-coupled common-emitter amplifier operating in the mid-band region?

(A) The device parasitic capacitances behave like open circuits, whereas coupling and bypass capacitances behave like short circuits.

(B) The device parasitic capacitances, coupling capacitances and bypass capacitances behave like open circuits.

(C) The device parasitic capacitances, coupling capacitances and bypass capacitances behave like short circuits.

(D) The device parasitic capacitances behave like short circuits, whereas coupling and bypass capacitances behave like open circuits.

Ans: A

(A) only in active mode

(B) only in active and saturation modes

(C) only in active and cut-off modes

(D) in active, saturation and cut-off modes

Ans: D

6. Which one of the following statements is correct about an ac-coupled common-emitter amplifier operating in the mid-band region?

(A) The device parasitic capacitances behave like open circuits, whereas coupling and bypass capacitances behave like short circuits.

(B) The device parasitic capacitances, coupling capacitances and bypass capacitances behave like open circuits.

(C) The device parasitic capacitances, coupling capacitances and bypass capacitances behave like short circuits.

(D) The device parasitic capacitances behave like short circuits, whereas coupling and bypass capacitances behave like open circuits.

Ans: A

7. In an 8085 microprocessor, the contents of the accumulator and the carry flag are A7 (in hex) and 0, respectively. If the instruction RLC is executed, then the contents of the accumulator (in hex) and the carry flag, respectively, will be

(A) 4E and 0 (B) 4E and 1

(C) 4F and 0 (D) 4F and 1

Ans: D

8. The minimum number of 2-input NAND gates required to implement a 2-input XOR gate is

(A) 4

(B) 5

(C) 6

(D) 7

Ans: A

9. If a right-handed circularly polarized wave is incident normally on a plane perfect conductor, then the reflected wave will be

(A) right-handed circularly polarized

(B) left-handed circularly polarized

(C) elliptically polarized with a tilt angle of 45 degree

(D) horizontally polarized

Ans: B

10. An intrinsic semiconductor at absolute zero temperature:

1) has only a few holes and few electrons. 2) has very large number of holes and electrons

3) behaves like a good conductor 4) behaves like a good insulator

Ans: 4

11. In a P-N diode, with the increase of reverse bias, the current :-

1) increase 2) decrease 3) remains constant 4) may increase or decrease depending upon doping

Ans: 3

12. Transistor is usually encapsulated in

1) graphite powder 2) enamel paint 3) epoxy resin 4) Any of these

Ans: 3

13. The JFET can operate in

1) depletion mode only 2) enhancement mode only

3) either depletion or enhancement mode at a time 4) both depletion or enhancement modes simultaneously

Ans: 1

14. The output current versus input voltage transfer characteristic of an n-channel JFET is such that there is

1) zero current flow at zero input voltage bias 2) current flow only when a positive input threshold voltage is crossed.

3) current flow only when a negative input cut-off voltage bias is crossed. 4) no cut-off input voltage

Ans: 3

15. An SCR triggered by a current pulse through its gate can be turned off by

1) giving another pulse of the same polarity to the gate 2) by giving pulse to the cathode

3) by giving pulse to the anode 4) by reversing the polarity of anode and cathode voltage

Ans: 4

16. An operational amplifier is a

1) high gain CE amplifier 2) cascaded CE amplifier 3) high gain direct coupled amplifier 4) high gain CB amplifier

Ans: 3

17. Gain of an Op Amp inverting amplifier with an input of 0.25 V and output of 17.5 V is

1) 4.375 2) 17.75 3) 17.25 4) 70

Ans: 4

18. MOS transistor

1) has only one p-n junction

2) conduct when sufficient voltage is applied to gate electrode

3) has only two electrodes

4) has gate electrode in direct contact with the silicon

Ans: 2

19. Which one of the following circuits is most suitable as an oscillator at a frequency of 100 Hz?

1) Hartley oscillator 2) Colpitts oscillator

3) Crystal oscillator 4) Twin-T oscillator

Ans: 4

20. Which one of the following sets of circuits can be obtained by using a 555 timer ?

1) Pulse modulator and amplitude demodulator

2) Pulse modulator and astable multivibrator

3) Amplifier demodulator and a.c. to d.c. converter

4) a.c. to d.c. converter and astable multivibrator

Ans: 2

21. The common mode error voltage in a DVM can be eliminated by using at its input

1) a differential amplifier 2) a wide band amplifier 3) a tuned amplifier 4) a low pass filter

Ans: 1

22. An OR gate may be imagined as

1) switches connected in series 2) switches connected in parallel

3) MOS transistors connected in series 4) None of these

Ans: 2

23. Which of the following logic gates dissipates minimum power

1) RTL 2) TTL 3) MOS 4) ECL

Ans: 3

24. The fan out TTL logic gate is about

1) 5 2) 10 3) 20 4) 50

Ans: 2

25. Consider the following statements regarding registers and latches:

1. Registers are made of edge triggered FFs, whereas latches are made from level-triggered FFs.

2. Registers are temporary storage devices whereas latches are not.

3. A latch employs cross-coupled feedback connections.

4. A register stores a binary word whereas a latch does not.

Which of the statements given above are correct

1) 1 and 2

2) 1 and 3

3) 2 and 3

4) 3 and 4

Ans: 2

26. The output voltage of a 5-bit DAC that has a digital input of 11010 (Assuming 0 = 0V and 1 = +10V) is

1) 3.4375V

2) 6.0V

3) 8.125V

4) 9.6875V

Ans: 3

27. The essential blocks of a phase lock loop (PLL) are phase detector, amplifier,

1) high-pass filter and crystal controlled oscillator 2) low-pass filter and crystal controlled oscillator

3) high-pass filter and voltage controlled oscillator 4) low-pass filter and voltage controlled oscillator

Ans: 4

28. In the 8421 BCD code the decimal number 125 is written as

1) 1111101 2) 7 D 3) 00010010 0101 4) None of these

Ans: 3

29. Consider the following instructions of 8085 µP

1. MOV M, A

2. ADD C

3. MVI A, FF

4. CMP M

Which of these cause change in the status of flag (s) ?

1) 1 and 2 2) 1, 2 and 3 3) 3 and 4 4) 2 and 4

Ans: 4

30. Energy needed to move 4 coulombs of charge is 4 joules. The potential difference is

1) 2 Volt 2) 1 Volt 3) 0.1 Volt 4) 0.2 Volt

Ans: 2

31. The first and the last critical frequency of an RC-driving point impedance function must respectively be

1) a zero and 2 pole 2) a pole and a pole 3) a zero and a zero 4) a pole and a zero

Ans: 4

32. In a linear system, several sources acting simultaneously produce an effect which is sum of the separate effects caused by individual sources at a time. This is

1) Reciprocity theorem 2) Superposition theorem 3) Millman theorem 4) Norton’s theorem

Ans: 2

33. The function of the reference electrode in a pH meter is to

1) produce a constant voltage 2) provide temperature compensation 3) provide a constant current 4) measure average pH value

Ans: 1

34. A popular method of increasing the range of an ac instrument is use of

1) shunt 2) multiplier 3) ac potentiometer 4) instrument transformer

Ans: 4

35. A dc voltage of 1V is applied to the X-plates of a CRO and an ac voltage 2 sin 100 t is applied to the Y plates. The resulting display on the CRO screen will be a

1) vertical straight line 2) horizontal straight line 3) sine wave 4) slant line

Ans: 1

36. The most light sensitive transducer for conversion of light into electrical power is the

1) Photodiode 2) solar cell 3) Photoconductive cell 4) photovoltaic cell

Ans: 1

37. Rochelle salt is a crystalline material used in producing

1) velocity transducer 2) photoelectric transducer 3) piezoelectric transducer 4) differential transformer transducer

Ans: 3

38. The gauge factor of the material of strain gauge is such that the resistance changes from 1000 ohms to 1009 ohms when subjected to a strain of 0.0015. The Poisson’s ratio for the material of the gauge wire is

1) 1.75

2) 2

3) 2.5

4) 6

Ans: 3

39. Consider the following statements in connection with the null or balance condition in a bridge circuit

1. It is always independent of the magnitude of the source voltage or its impedance.

2. It is independent of the sensitivity of the detector or its impedance.

3. It is unchanged if the impedances of one set of adjacent arms are interchanged.

4. It is unchanged if the source and the detector are interchanged. Which of these statements are correct ?

1) 1, 2 and 3 2) 1, 2 and 4 3) 2, 3 and 4 4) 1, 3 and 4

Ans: 2

40. In a linear network, when the a.c. input is doubled, the a.c. output becomes

1) two times 2) four times 3) half 4) one-fourth.

Ans: 1

41. Consider the following statements regarding a moving coil instruments :

1. The sensitivity of a moving coil voltmeter is specified in terms of ohms per volt.

2. A higher range moving coil voltmeter has higher sensitivity.

3. A higher current moving coil instrument has higher sensitivity.

4. Higher sensitivity meters give more reliable results.

Which of these statements are correct ?

1) 1, 2 and 3 2) 1, 3 and 4 3) 1, 2 and 4 4) 2, 3 and 4

Ans: 2

42. In a series RLC circuit at resonance with Q₀ = 10 and with applied voltage of 100 mV at resonance frequency, voltage across capacitor is 1) 100 mV 2) 1 Volt 3) 10 mV 4) 10 Volt

Ans: 2

43. Network function 4s/(s+1)(s+3) has

1) one zero and two poles 2) one zero and one pole

3) two zeroes and one pole 4) one zero and no pole

Ans: 1

44. Two coils have self-inductance of 0.09 H and 0.01 H and a mutual inductance of 0.015 H. The coefficient of coupling between the coils is 1) 0.06 2) 0.5 3) 1.0 4) 0.05

Ans: 2

45. The depth of penetration of wave in a lossy dielectric increases with increasing

1) conductivity 2) permeability 3) wavelength 4) permittivity

Ans: 3

46. The normalized frequency of a step index fibre is 28 at 1300 nm wavelength. What is the total number (approx) of guided modes that can be supported by the fibre

1) 50

2) 200

3) 400

4) 800

Ans: 3

47. For producing circularly polarized beams in microwave communication field, the type of antenna ideally suited is

1) helical antenna

2) parabolic disc with circular aperture

3) pyramidal horn with symmetrical beam shapes in E and H plane

4) circular loop antenna

Ans: 1

48. If the initial conditions in a system are zero, it means that system is

1) working with zero reference input 2) working but does not store energy

3) at rest and has no energy stored in any of its parts 4) at rest but stores energy

Ans: 3

49. The region of convergence of the z-transform of a unit step function is

1) |z| >1

2) |z| <1

3) (Real part of z) >0

4) (Real part of z) <0

Ans: 1

50. The system response of a system can be best tested with

1) unit impulse input signal 2) ramp input signal

3) sinusoidal input signal 4) exponentially decaying input signal

Ans: 1

(A) 4E and 0 (B) 4E and 1

(C) 4F and 0 (D) 4F and 1

Ans: D

8. The minimum number of 2-input NAND gates required to implement a 2-input XOR gate is

(A) 4

(B) 5

(C) 6

(D) 7

Ans: A

9. If a right-handed circularly polarized wave is incident normally on a plane perfect conductor, then the reflected wave will be

(A) right-handed circularly polarized

(B) left-handed circularly polarized

(C) elliptically polarized with a tilt angle of 45 degree

(D) horizontally polarized

Ans: B

10. An intrinsic semiconductor at absolute zero temperature:

1) has only a few holes and few electrons. 2) has very large number of holes and electrons

3) behaves like a good conductor 4) behaves like a good insulator

Ans: 4

11. In a P-N diode, with the increase of reverse bias, the current :-

1) increase 2) decrease 3) remains constant 4) may increase or decrease depending upon doping

Ans: 3

12. Transistor is usually encapsulated in

1) graphite powder 2) enamel paint 3) epoxy resin 4) Any of these

Ans: 3

13. The JFET can operate in

1) depletion mode only 2) enhancement mode only

3) either depletion or enhancement mode at a time 4) both depletion or enhancement modes simultaneously

Ans: 1

14. The output current versus input voltage transfer characteristic of an n-channel JFET is such that there is

1) zero current flow at zero input voltage bias 2) current flow only when a positive input threshold voltage is crossed.

3) current flow only when a negative input cut-off voltage bias is crossed. 4) no cut-off input voltage

Ans: 3

15. An SCR triggered by a current pulse through its gate can be turned off by

1) giving another pulse of the same polarity to the gate 2) by giving pulse to the cathode

3) by giving pulse to the anode 4) by reversing the polarity of anode and cathode voltage

Ans: 4

16. An operational amplifier is a

1) high gain CE amplifier 2) cascaded CE amplifier 3) high gain direct coupled amplifier 4) high gain CB amplifier

Ans: 3

17. Gain of an Op Amp inverting amplifier with an input of 0.25 V and output of 17.5 V is

1) 4.375 2) 17.75 3) 17.25 4) 70

Ans: 4

18. MOS transistor

1) has only one p-n junction

2) conduct when sufficient voltage is applied to gate electrode

3) has only two electrodes

4) has gate electrode in direct contact with the silicon

Ans: 2

19. Which one of the following circuits is most suitable as an oscillator at a frequency of 100 Hz?

1) Hartley oscillator 2) Colpitts oscillator

3) Crystal oscillator 4) Twin-T oscillator

Ans: 4

20. Which one of the following sets of circuits can be obtained by using a 555 timer ?

1) Pulse modulator and amplitude demodulator

2) Pulse modulator and astable multivibrator

3) Amplifier demodulator and a.c. to d.c. converter

4) a.c. to d.c. converter and astable multivibrator

Ans: 2

21. The common mode error voltage in a DVM can be eliminated by using at its input

1) a differential amplifier 2) a wide band amplifier 3) a tuned amplifier 4) a low pass filter

Ans: 1

22. An OR gate may be imagined as

1) switches connected in series 2) switches connected in parallel

3) MOS transistors connected in series 4) None of these

Ans: 2

23. Which of the following logic gates dissipates minimum power

1) RTL 2) TTL 3) MOS 4) ECL

Ans: 3

24. The fan out TTL logic gate is about

1) 5 2) 10 3) 20 4) 50

Ans: 2

25. Consider the following statements regarding registers and latches:

1. Registers are made of edge triggered FFs, whereas latches are made from level-triggered FFs.

2. Registers are temporary storage devices whereas latches are not.

3. A latch employs cross-coupled feedback connections.

4. A register stores a binary word whereas a latch does not.

Which of the statements given above are correct

1) 1 and 2

2) 1 and 3

3) 2 and 3

4) 3 and 4

Ans: 2

26. The output voltage of a 5-bit DAC that has a digital input of 11010 (Assuming 0 = 0V and 1 = +10V) is

1) 3.4375V

2) 6.0V

3) 8.125V

4) 9.6875V

Ans: 3

27. The essential blocks of a phase lock loop (PLL) are phase detector, amplifier,

1) high-pass filter and crystal controlled oscillator 2) low-pass filter and crystal controlled oscillator

3) high-pass filter and voltage controlled oscillator 4) low-pass filter and voltage controlled oscillator

Ans: 4

28. In the 8421 BCD code the decimal number 125 is written as

1) 1111101 2) 7 D 3) 00010010 0101 4) None of these

Ans: 3

29. Consider the following instructions of 8085 µP

1. MOV M, A

2. ADD C

3. MVI A, FF

4. CMP M

Which of these cause change in the status of flag (s) ?

1) 1 and 2 2) 1, 2 and 3 3) 3 and 4 4) 2 and 4

Ans: 4

30. Energy needed to move 4 coulombs of charge is 4 joules. The potential difference is

1) 2 Volt 2) 1 Volt 3) 0.1 Volt 4) 0.2 Volt

Ans: 2

31. The first and the last critical frequency of an RC-driving point impedance function must respectively be

1) a zero and 2 pole 2) a pole and a pole 3) a zero and a zero 4) a pole and a zero

Ans: 4

32. In a linear system, several sources acting simultaneously produce an effect which is sum of the separate effects caused by individual sources at a time. This is

1) Reciprocity theorem 2) Superposition theorem 3) Millman theorem 4) Norton’s theorem

Ans: 2

33. The function of the reference electrode in a pH meter is to

1) produce a constant voltage 2) provide temperature compensation 3) provide a constant current 4) measure average pH value

Ans: 1

34. A popular method of increasing the range of an ac instrument is use of

1) shunt 2) multiplier 3) ac potentiometer 4) instrument transformer

Ans: 4

35. A dc voltage of 1V is applied to the X-plates of a CRO and an ac voltage 2 sin 100 t is applied to the Y plates. The resulting display on the CRO screen will be a

1) vertical straight line 2) horizontal straight line 3) sine wave 4) slant line

Ans: 1

36. The most light sensitive transducer for conversion of light into electrical power is the

1) Photodiode 2) solar cell 3) Photoconductive cell 4) photovoltaic cell

Ans: 1

37. Rochelle salt is a crystalline material used in producing

1) velocity transducer 2) photoelectric transducer 3) piezoelectric transducer 4) differential transformer transducer

Ans: 3

38. The gauge factor of the material of strain gauge is such that the resistance changes from 1000 ohms to 1009 ohms when subjected to a strain of 0.0015. The Poisson’s ratio for the material of the gauge wire is

1) 1.75

2) 2

3) 2.5

4) 6

Ans: 3

39. Consider the following statements in connection with the null or balance condition in a bridge circuit

1. It is always independent of the magnitude of the source voltage or its impedance.

2. It is independent of the sensitivity of the detector or its impedance.

3. It is unchanged if the impedances of one set of adjacent arms are interchanged.

4. It is unchanged if the source and the detector are interchanged. Which of these statements are correct ?

1) 1, 2 and 3 2) 1, 2 and 4 3) 2, 3 and 4 4) 1, 3 and 4

Ans: 2

40. In a linear network, when the a.c. input is doubled, the a.c. output becomes

1) two times 2) four times 3) half 4) one-fourth.

Ans: 1

41. Consider the following statements regarding a moving coil instruments :

1. The sensitivity of a moving coil voltmeter is specified in terms of ohms per volt.

2. A higher range moving coil voltmeter has higher sensitivity.

3. A higher current moving coil instrument has higher sensitivity.

4. Higher sensitivity meters give more reliable results.

Which of these statements are correct ?

1) 1, 2 and 3 2) 1, 3 and 4 3) 1, 2 and 4 4) 2, 3 and 4

Ans: 2

42. In a series RLC circuit at resonance with Q₀ = 10 and with applied voltage of 100 mV at resonance frequency, voltage across capacitor is 1) 100 mV 2) 1 Volt 3) 10 mV 4) 10 Volt

Ans: 2

43. Network function 4s/(s+1)(s+3) has

1) one zero and two poles 2) one zero and one pole

3) two zeroes and one pole 4) one zero and no pole

Ans: 1

44. Two coils have self-inductance of 0.09 H and 0.01 H and a mutual inductance of 0.015 H. The coefficient of coupling between the coils is 1) 0.06 2) 0.5 3) 1.0 4) 0.05

Ans: 2

45. The depth of penetration of wave in a lossy dielectric increases with increasing

1) conductivity 2) permeability 3) wavelength 4) permittivity

Ans: 3

46. The normalized frequency of a step index fibre is 28 at 1300 nm wavelength. What is the total number (approx) of guided modes that can be supported by the fibre

1) 50

2) 200

3) 400

4) 800

Ans: 3

47. For producing circularly polarized beams in microwave communication field, the type of antenna ideally suited is

1) helical antenna

2) parabolic disc with circular aperture

3) pyramidal horn with symmetrical beam shapes in E and H plane

4) circular loop antenna

Ans: 1

48. If the initial conditions in a system are zero, it means that system is

1) working with zero reference input 2) working but does not store energy

3) at rest and has no energy stored in any of its parts 4) at rest but stores energy

Ans: 3

49. The region of convergence of the z-transform of a unit step function is

1) |z| >1

2) |z| <1

3) (Real part of z) >0

4) (Real part of z) <0

Ans: 1

50. The system response of a system can be best tested with

1) unit impulse input signal 2) ramp input signal

3) sinusoidal input signal 4) exponentially decaying input signal

Ans: 1

51. In a feedback system, feedback factor of 0.1 is used with forward gain of 10. The sensitivity of the system with respect to the feedback element is

1) -0.5

2) 0.5

3) -0.9

4) 0.9

Ans: 1

52. In a cellular communications system, path loss between transmitter and receiver is due to

1) scattering from building, trees, vehicles, and other structures only.

2) scattering from building, trees, vehicles, and other structures and due to reflections from ground only

3) scattering from building, trees, vehicles, and other structures and due to reflections from ground along with reflections from ionosphere only.

4) scattering from building, trees, vehicles, and other structures and due to reflections from ground along with reflections from ionosphere along with loss due to surface wave phenomenon.

Ans: 2

53. Match List I with List II and select the correct answer using the codes given below the list :

List I

A. Television

B. Radio

C. Radar

D. Data communication

List II

1. Either AM or FM used

2. Both AM and FM are used

3. PCM is used

4. Digital system

1) A(4) B(3) C (1) D (2)

2) A(2) B(1) C (3) D (4)

3) A(4) B(1) C (3) D (2)

4) A(2) B(3) C (1) D (4)

Ans: 4

54. For 10-bit PCM system, the signal to quantization noise ratio is 62dB. If the number of bits are increased by 2, then the signal to quantization noise ratio will

1) increase by 6dB 2) increase by 12 dB 3) decrease by 6dB 4) decrease by 12 dB

Ans: 2

55. A 8 kHz communication channel has an SNR of 30 dB. If the channel bandwidth is doubled, keeping the signal power constant, the SNR for the modified channel will be

1) 27 dB 2) 30 dB 3) 33 dB 4) 60 dB

Ans: 1

56. What is the SNR improvement with FSK over ASK in most types of noise environment ?

1) 200 to 300 dB 2) 3 to 4 dB 3) 10 to 12 dB 4) 0 dB

Ans: 2

57. The frequency range 30MHz - 300MHz is:

1) medium frequency 2) very high frequency 3) super high frequency 4) Infrared frequency

Ans: 2

58. Which of the following pulse modulation is analog ?

1) PCM 2) Differential PCM 3) PWM 4) Delta

Ans: 3

59. Random satellite moves in

1) random paths 2) polar orbits 3) geostationary orbits 4) equatorial plane

Ans: 2

60. Which one of the following statements is correct ? In a ratio detector,

1) linearity is worse than that of a phase discriminator.

2) Stabilization is provided against signal strength variations

3) The output is twice of that obtainable form a similar phase discriminator

4) The circuit is same as that in a discriminator, except that the diode connections are reversed

Ans: 2

61. Heterodyne principle is used in

1) Transmitter 2) Receiver 3) Oscillator 4) Power amplifier

Ans: 2

62. For an AM wave, the maximum voltage was found to be 10 V and the minimum voltage was found to be 5V. The modulation index of the wave would be

1) 0.33 2) 0.52 3) 0.40 4) 0.1

Ans: 1

63. The FM telemetry as compared with AM telemetry requires a channel that is

1) equal to that of AM telemetry

2) smaller than what is required for AM telemetry

3) 100 times of that required for AM telemetry

4) 10 times of that required for AM telemetry

Ans: 4

64. For small value of gain k, the root must be

1) at origin 2) at infinity 3) far away from the poles of the loops transfer functions 4) near the poles of the transfer function

Ans: 4

65. If a system is critically damped and gain is increased, the system 1) becomes overdamped 2) becomes underdamped 3) becomes oscillatory 4) remains critically underdamped

Ans: 2

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