### BEL Placement-Paper Whole-Testpaper Latest (2012-2013)-30 Oct 2012

**BELPlacement paper with answers|BEL Previously asked Questtions with answers|**

**BEL Written Test** **Questions**

ROUND 1

1. Transition capacitance Ct of a Varicap diode with Knee voltage Vt, reverse voltage Vr and K, the constant based on semiconductor material and the construction technique & N dependent on type of junction is given by

a. 1 / K (Vt + Vr)N/2

b. 1 / K (Vt + Vr)N

c. K / (Vt + Vr)N

d. K / (Vt + Vr)1/N

Answer : c

2. Ct = K / (Vt + Vr)N where Vt Knee voltage, Vr reverse voltage, K manufacturing dependent constant and N dependent on type of junction, for alloy junction the value of N is

a. 1/3

b. 2/3

c. 1/2

d. 1/4

Answer : c

3. The distortion less output characteristic of a network means

a. Constant amplitude and linear phase shift over frequency

b. Linear phase shift and amplitude need not be constant

c. Any amplitude and phase

d. None of these

Answer : a

4. Single sideband means suppressed

a. Carrier

b. Carrier and one side band

c. One side band

d. None of these

Answer : b

5. In an amplitude modulated signal, lower side band frequency is equal to (if the carrier frequency is fc and modulation frequency is fm)

a. fm + fc

b. fc – fm

c. fm r fc

d. fc / fm

Answer : b

6. The noise figure of a receiver is a measure of:

1. Excess noise generated

2. Bandwidth of the receiver

3. Gain of the receiver

4. Operating frequency

Answer :1

7. The ratio receiver is:

1. Direct detection type

2. Super regenerative type

3. Super heterodyne type

4. None of these

Answer : 3

8. In an amplitude modulation system, the modulation index is dependent upon:

1. Modulating frequency only

2. Carrier amplitude only

3. Modulating signal amplitude only

4. Modulating and carrier amplitudes only

Answer : 2

9. Image rejection mixer is generally used:

1. To reject the unwanted signal

2. To improve signal amplitude

3. To improve noise figure

4. To improve conversion loss

Answer : 3

10. The value of a resistor creating thermal noise is doubled. The noise power generated is therefore:

1. Halved

2. Quadrapuled

3. Doubled

4. Unchanged

Answer : 2

11. Ct = K / (Vt + Vr)N where Vt Knee voltage, Vr reverse voltage, K manufacturing dependent constant and N dependent on type of junction, for diffused junction the value of N is

a. 1/3

b. 2/3

c. 1/2

d. 1/4

Answer : a

12. In JFET, the drain current Id is given by (Idss drain – source saturation current Vgs – Gate – source voltage, Vp the pinch off voltage)

a. Idss[1 – Vp/Vgs]

b. Idss(1 – Vgs/Vp)2

c. Idss[1 – Vgs/Vp)

d. Idss(1 – Vgs/Vp)3/2

Answer : b

13. The shadow mask in colour tube is used to

a. Reduce X-Ray emission

b. Ensure each beam hits its own dots

c. Increase screen brightness

d. Provide degaussing for the screen

Answer : b

14. Indicate which of the following signal is not transmitted in colour TV

a. Y

b. Q

c. R

d. I

Answer : c

15. Another name for horizontal retrace in TV receiver is the

a. Ringing

b. Burst

c. Damper

d. Fly back

Answer : d

16. Another name for the colour sync in the colour TV system

a. Ringing

b. Burst

c. Damper

d. Fly back

Answer : b

17. The HV anode supply for a picture tube of a TV receiver is generated in the

a. Mains transformer

b. Vertical output stage

c. Horizontal output stage

d. Horizontal oscillator

Answer : c

18. The output of vertical amplifier is

a. Direct current

b. Amplified vertical sync pulse

c. A saw tooth voltage

d. A saw tooth current

Answer : d

19. In a transistor if Alpha = 0.98, current gain is equal to

a. 29

b. 59

c. 69

d. 49

Answer : d

20. The active region in the common emitter configuration means

a. Both collector and emitter junction is reverse biased

b. The collector junction is forward biased and emitter junction

c. The collector junction is reverse biased and emitter junction is forwared biased

d. Both collector & emitter junction are forward biased

Answer : c

21. The saturation region in the common emitter configuration means that

a. Both collector & emitter junction are reverse biased

b. The collector junction is forward biased and emitter junction

c. The collector junction is reverse biased and emitter junction is forwared biased

d. Both collector & emitter junction are forward biased

Answer : d

22. The % of Red, Green & Blue in 100% White Y is given by

a. 30%, 59%, 11%

b. 50%, 30%, 11%

c. 30%, 11%, 50%

d. 33.3%, 33.5%, 38.3%

Answer : a

23. Equalizing pulse width, if H is the Horizontal sync rate

a. 0.64 H

b. 0.07 H

c. 0.04 H

d. 0.16 H

Answer : c

24. In a simple RC network the bandwidth is equal to

a. 1/2 p RC

b. RC / 2

c. 2 C / p R

d. 2 p / RC

Answer : a

25. The time constant of a RC network is given by

a. RC

b. C/R

c. R/C

d. None of these

Answer : d

26. First zero crossing of pulse frequency spectrum occurs at if d is the pulse width, T is the pulse repetition rate

a. 1/d

b. d/T

c. T/d

d. T

Answer : a

27. Indicated the false statement:

1. HF mixer are generally noisier than HF amplifier

2. Impulse noise voltage is independent of bandwidth

3. Thermal noise is independent of the frequency at which it is measured

4. Industrial noise is usually of the impulse type

Answer : 2

28. If the carrier of a 100 percent modulated AM wave is suppressed the percentage power saving will be:

a. 50

b. 70

c. 100

d. 66.6

Answer : d

29. A balanced modulator produces:

1. The carrier and Two side bands

2. The carrier and one side band

3. Two side bands alone

4. Carrier and a number of side bands

Answer : 3

30. The frequency deviation in FM system is proportional to:

1. Modulating frequency

2. Carrier amplitude

3. Modulating signal amplitude

4. None of these

Answer : 3

31. In FM, the total transmitted power is:

1. Dependent on modulating signal amplitude

2. Dependent on modulating frequency

3. Dependent on modulating index

4. Independent of the above

Answer : 4

32. A quarter wave line when short circuited at the far end behaves like

1. Pure inductor

2. Pure capacitor

3. Parallel tuned circuit

4. Series tuned circuit

Answer : 3

33. The stub line used to match transmission line with a given load impedance is generally

1. Another open circuited line

2. Another short circuited line

3. Quarter wave transmission line

4. Half wave transmission line

Answer : 2

34. The smith chart generally covers a distance of

1. Quarter wavelength

2. Half wavelength

3. One wavelength

4. Twice the wavelength

Answer : 2

35. The component generally used to sample a portion of the energy transmitted in a line is

1. Isolator

2. Circulator

3. Directional coupler

4. None of these

Answer : 3

36. The return loss in a transmission line is a measure of

1. Loss of the line

2. Standing wave ratio

3. Characteristic impedance of the line

4. None of these

Answer : 2

37. The antenna can be considered as

1. Matching the source and free space

2. Matching the source to the line

3. Matching the line and free space

4. None of these

Answer : 3

38. The free space impedance is approximately equal to

1. 177 W

2. 277 W

3. 377 W

4. 50 W

Answer : 3

39. The polarization refers to

1. The physical orientation of the radiated wave

2. The directional of propagation of the wave

3. Direction perpendicular to the propagation of the wave

4. None of these

Answer : 3

40. If u & e are the permeability and permittivity respectively the characteristic impedance of the medium is given by

a. ue

b. Öu/e

c. Öe/u

d. Öeu

Answer : 2

41. The power density at distance ‘r’ from an isotropic radiator with transmitted power P is:

1. P/r2

2. P/2 p r2

3. P/4 p r2

4. None of these

` Answer : 3

42. The carrier in an FM system disappears for the lowest modulation index of:

a. 0.5

b. 1.0

c. 2.4

d. 3.5

Answer : c

43. The difference between phase and frequency modulation:

1. Is purely theoretical because they are the same in practice

2. Is too great to make the two systems compatible

3. Lies in the poorer audio response of phase modulation

4. Lies in the different definition of the modulation index

Answer : 4

44. The overall noise figure of two cascaded amplifiers is equal to

1. The algebraic sum of the two

2. The sum of the squares of the two

3. The square root of the product of the two

4. None of these

Answer : 4

45. The noise power output of an amplifier is equal to:

1. KTo BFG

2. KTo FG

3. KTo F/G

4. KTo / FG

Answer : 1

46. The effective noise temperature of an amplifier is equal to

1. (F + 1) To

2. FTo

3. (F – 1) To

4. None of these

Answer : 3

47. The noise figure of an amplifier depends upon

1. Its bandwidth

2. Its gain

3. Its operating frequency

4. None of these

Answer : 4

48. The velocity of electromagnetic wave in a coaxial cable is

1. Equal to the velocity in free space

2. Less than the velocity in free space

3. Greater than the velocity in free space

4. None of these

Answer : 2

49. The standing wave ratio [SWR] in a transmission line:

1. Is proportional to the load impedance

2. Is dependent on the source impedance

3. Is a mis-match between the load and line

4. Is a measure of its power handling capability

Answer : 3

50. The standing wave ratio (SWR) is unity in a transmission line if

1. The load impedance is equal to the characteristic impedance of the line

2. The load impedance is twice that of the characteristic impedance

3. The load impedance is half of the characteristic impedance of the line

4. None of these

Answer : 1

51. The standing wave voltage node along a line repeats at the rate of if L is the wave length

a. L/4

b.L/2

c.L

d.2L

Answer : 2

52. FM modulation becomes equivalent to AM modulation if

1. FM index is greater than 1

2. FM index is equal to 1

3. FM index is very much less than 1

4. FM index less than or equal to 1

Answer : 3

53. S/N improvement of FM over AM, B is the FM modulation index

a. 3B2

b.B

c.2B

d.B/2

Answer : a

54. Picture transmission in TV employs

1. Suppressed carrier modulation

2. Vestigial side band

3. Single side band

4. None of these

Answer : 2

55. Sound transmission in TV employ

1. Amplitude modulation

2. Phase modulation

3. Frequency modulation

4. Pulse amplitude modulation

Answer : 3

56. One of the following is an indirect way of generating FM this is the:

1. Reactance FET modulator

2. Varacter divide modulator

3. Amstrong modulator

4. Reactance bipole transistor modulator

Answer : 3

57. The modulation index of AM wave is changed from 0 to 1. The transmitted power is

1. Un-changed

2. Halved

3. Doubled

4. Increased by 50%

Answer : 4

58. The isotropic antenna is represented by

1. Dipole antenna

2. Rhombic antenna

3. Yagi uda antenna

4. No such antenna exists in practice

Answer : 4

59. The gain of parabolic reflector antenna is proportional to

1. The diameter of the reflector

2. Square of the diameter of the reflector

3. Aperture area of the feed

4. None of these

Answer : 2

60. The parabolic reflector antenna are generally used to

1. Provide high gain

2. Provide pencil beam

3. Increase bandwidth of operation

4. None of these

Answer : 2

61. Cassegrain feed is used with a parabolic reflector to

1. Increase gain of the system

2. Increase the bandwidth of the system

3. Reduce the size of the main reflector

4. Allow the feed to be placed at a convenient point

Answer : 4

62. A helical antenna is used for satellite tracking because of its

1. Circular polarization

2. Maneuverability

3. Broad bandwidth

4. Good front – to – back ratio

Answer : 1

63. The discone antenna is

1. A useful direction finding antenna

2. Used as a radar receiving antenna

3. Circularly polarized like other circular antenna

4. Useful as a VHF receiving antenna

Answer : 4

64. Waveguides are used mainly for microwave signals because

1. They depend on straight line propagation which applies to microwaves only

2. Losses would be too heavy at lower frequencies

3. There are no generators powerful enough to excite them at lower frequencies

4. They would be too bulky at lower frequencies

Answer : 4

65. The wavelength in a waveguide

1. Is greater than in free space

2. Depends only on the waveguide dimensions and the free-space wavelength

3. Less than the free space wavelength

4. Equal to the free space wavelength

Answer : 1

66. The dominant mode of propagation is preferres with rectangular waveguide because(indicate false statement)

1. It leads to the smallest waveguide dimensions

2. The resulting impedance can be matched directly to coaxial lines

3. It is easier to excite than the other modes

4. Propagation of it without any spurious generation can be ensured

Answer : 2

67. The velocity of propagation (group velocity) in a waveguide is

1. Less than the free space velocity

2. Greater than the free space velocity

3. Equal to be free space velocity

4. None of these

Answer : 1

68. A wave can propagate in a waveguide if its cut off wavelength is

1. Greater than the free space wavelength

2. Less than the free space wavelength

3. Equal to be free space wavelength

4. None of these

Answer :3

69. The dominant mode in a rectangular waveguide is

a. TE11

b. TE10

c.TE20

d.TM11

Answer : 2

70. The characteristic wave impedance of a waveguide

1. Depends on the mode of propagation

2. Does not depend on the mode of propagation

3. Is same as the free space impedance

4. None of these

Answer : 1

71. A choke flange may be used to couple two waveguides

1. To help in the alignment of the waveguides

2. Because it is simpler than any other joint

3. To compensate the discontinuities at the joint

4. To increase the bandwidth of the system

Answer : 2

72. Frequencies in the UHF range is normally propagated by means of

1. Ground waves

2. Sky waves

3. Surface waves

4. Space waves

Answer : 4

73. As electromagnetic waves travel in free space, only one of the following can happen to them

1. Absorption

2. Attenuation

3. Reflection

4. Refraction

Answer : 2

74. High frequency waves are

1. Absorbed by the F2 layer

2. Reflected by the D layer

3. Affected by the solar cycle

4. Capable of use for long distance communications on the moon

Answer : 3

75. Indicate which one of following terms applies to troposcatter propagation

1. SIDS

2. Fading

3. Fraday rotation

4. Atmospheric storms

Answer : 2

76. When microwave signals follow the curvature of the earth, this in known as

1. Faraday effect

2. Ducting

3. Ionospheric reflection

4. Tropospheric scattering

Answer : 2

77. An ungrounded antenna near the ground:

1. Is unlikely to need an earth mat

2. Acts as a single antenna of twice the height

3. Must be horizontally polarized

4. Acts as an antenna array

Answer : 4

78. One of the following consists of non-resonant antenna:

1. The folded dipole

2. The rhombic antenna

3. The end fire array

4. The broad side array

Answer : 2

79. Balun is:

1. A circuit element to connect balance line to unbalanced antenna or line:

2. A circuit element to connect balance line to balanced line

3. A circuit element to connect unbalance line to unbalanced line

4. None of these

Answer : 1

80. The slotted line is used to measure:

1. Standing wave ratio

2. Load impedance

3. Source impedance

4. None of these

Answer : 1

81. In amplitude modulation Ec ( 1 + m Sin Wmt) Sin Wot, each side band amplitude will be:

1. Ecm/2

2. Ecm

3. Ec/m

4. 2Ec/m

Answer : 1

82. The dominant mode in a circular waveguide is

a. TE01

b.TE11

c.TM01

d.TM11

Answer : 3

83. A ferrite is

1. A non-conductor with magnetic properties

2. An inter metallic compound with particularly good conductivity

3. An insulator which heavily attenuates magnetic fields

4. A microwave semiconductor invented by farady

Answer : 1

84. The maximum power that may be handled by a ferrite component is limited by the

1. Curie temperature

2. Saturation magnetization

3. Line width

4. Gyro magnetic resonance

Answer : 1

85. The isolator is

1. Bidirectional

2. Unidirectional

3. Used to tap the power in a waveguide transmission line

4. Used for None of these of the above

Answer : 2

86. Isolator is generally used:

1. To protect the high power transmitter

2. To protect receiver

3. To protect the antenna

4. To avoid arcing in waveguides

Answer : 1

87. A TR tube is used

1. To protect the high power transmitter

2. To protect receiver

3. To avoid arcing in waveguides

4. For None of these of the above

Answer : 2

88. Rieke diagrams are used to select best operating conditions for

1. TWT amplifier

2. Klystron oscillator

3. Magnetron oscillator

4. Cross field amplifiers

Answer : 3

89. The gain bandwidth product of a microwave transistor FT, is the frequency at which the

1. Alpha of the transistor falls by 3 dB

2. Beta of the transistor falls by 3 dB

3. Beta of the transistor falls to unity

4. Power gain of the transistor falls to unity

Answer : 1

90. The cavity magnetron uses strapping to

1. Prevent mode jumping

2. Prevent cathode-back heating

3. Ensure bunching

4. Improve the phase-focussing effect

Answer : 4

91. The transferred – electron bulk effect occurs in

1. Germanium

2. Gallium arsenide

3. Silicon

4. Metal semiconductor junction

Answer : 2

92. One of the following is not used as a microwave mixer or detector

1. Crystal diode

2. Schottky – barrier diode

3. Backward diode

4. PIN diode

Answer : 4

93. SAW devices may be used as:

1. transmission media like stripline

2. filters

3. UHF amplifiers

4. Oscillators at millimeter frequencies

Answer : 2

94. Surface acoustic waves propagate in:

1. Gallium arsenide

2. Indium phosphide

3. Stripline

4. Quartz crystal

Answer : 4

95. A parametric amplifier has an input and output frequency of 2.25 GHz, and is pumped at 4.5 GHz is a

1. Traveling wave amplifier

2. Degenerate amplifier

3. Lower-side band up converter

4. Upper-side band up converter

Answer : 2

96. The negative resistance in a tunnel diode

1. Is maximum at the peak point of the characteristic

2. Is available between the peak and valley points

3. Is maximum at the valley point

4. May be improved by the reverse bias

Answer : 2

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