Communication Systems MCQ Electrical Engineering

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About Communication Systems

Following are some of the multiple choice questions on the Communication Systems with answers that will help the students in developing their knowledge.

Communication Systems MCQ

1. Circular polarization

  • Is useful in reducing depolarization effect on received wave
  • Involves critical alignment of transmitting and receiving antenna
  • Is useful in discrimination between reception of adjacent beams
  • None of the above

2. PAM stands for

  • Pulse Analogue Modulation
  • Phase Analogue Modulation
  • Pulse Amplitude Modulation
  • Phase Amplitude Modulation

3. VSB modulation is preferred in TV because

  • It reduces the bandwidth requirement to half
  • It avoids phase distortion at low frequencies
  • It results in better reception
  • None of the above

4. For attenuation of high frequencies we should use

  • Shunt capacitance
  • Series capacitance
  • Inductance
  • Resistance

5. A woofer should be fed from the input through a

  • Low pass filter
  • High pass filter
  • Band pass filter
  • Band stop filter

6. DVD uses

  • Laser beam for both recording and playback
  • Laser beam for recording and video head for playback
  • Video head for recording and laser beam for playback
  • None of the above

7. In Pulse Code Modulation system

  • Large bandwidth is required
  • Quantising noise can be overcome by companding
  • Quantising noise can be reduced by decreasing the number of standard levels
  • Suffers from the disadvantage of its incompatibly with TDM

8. A modem is classified as low speed if data rate handled is

  • Upto 100 bps
  • Upto 250 bps
  • Upto 400 bps
  • Upto 600 bps

9. The main function of a balanced modulator is to

  • Produce balanced modulation of a carrier wave
  • Produce 100% modulation
  • Suppress carrier signal in order to create a single-sideband or double sideband
  • Limit noise picked by a receiver

10. A cordless telephone using separate frequencies for transmission in base and portable units is known as

  • Duplex arrangement
  • Half duplex arrangement
  • Either A or B
  • Neither A nor B

11. Which of the following does not cause losses in optical fibre cables?

  • Stepped index operation
  • Impurities
  • Microbending
  • Attenuation in glass

12. A buffer amplifier is

  • A double-tuned amplifier
  • A high gain amplifier
  • A cathode follower stage
  • None of the above

13. Commercial Frequency deviation of FM is

  • 70 kHz
  • 75 kHz
  • 80 kHz
  • 65 kHz

14. If output power of a radio receiver is doubled, its volume is increased by __________ dB.

  • 2
  • 3
  • 1
  • -3

15. Which of the following is used to generate PDM?

  • Free running multi-vibrator
  • Monostable multi-vibrator
  • JK flip-flop
  • Schmitt trigger

16. When the length of antenna is a whole wavelength

  • The radiation at right angles is zero
  • The radiation at right angles is maximum
  • The radiation is zero in all directions
  • The radiation is maximum in all directions

17. Which of the following is a digital modulation technique?

  • PCM
  • PSK
  • DM
  • All

18. For telegraphy the most commonly used modulation system is

  • FSK
  • Two tone modulation
  • PCM
  • Single tone modulation

19. The disadvantage of FM over AM is that

  • High output power is needed
  • High modulating power is needed
  • Noise is very high for high frequency
  • Large bandwidth is required

20. A telephone channel requires a bandwidth of about

  • 1 kHz
  • 3 kHz
  • 10 kHz
  • 50 kHz

21. Which of the following is an indirect way of generating FM?

  • Armstrong modulator
  • Varactor diode modulator
  • Reactance FET modulator
  • Reactance bipolar transistor

22. One of the advantages of base modulation over collector modulation of a transistor class C amplifier is

  • Improved efficiency
  • Better linearity
  • High power output per transistor
  • The lower modulating power requirement

23. The maximum power output of a standard A earth station over the total band allocated to satellite communication is about

  • 0.5 kW
  • 8 kW
  • 20 kW
  • 50 kW

24. As per Shannon-Hartley theorem, a noise less Gaussian channel has

  • Zero capacity
  • Infinite capacity
  • Small capacity
  • None of the above

25. An audio signal (say from 50 Hz to 10000 Hz) is frequency translated by a carrier having a frequency of 106 Hz. The values of initial (without frequency translation) and final (after frequency translation) fractional change in frequency from one band edge to the other are

  • 200 and 1.01
  • 200 and 10.01
  • 200 and 100.1
  • 200 and 200

26. Skip distance depends on time of day and angle of incidence.

  • True
  • False

27. In practical commercial FM system, channel bandwidth is

  • 150 kHz
  • 100 kHz
  • 88 MHz
  • 108 MHz

28. If sampling is done at the rate of 10 kHz. The bandwidth required is

  • 35 kHz
  • 70 kHz
  • 10 kHz
  • 1280 kHz

29. In EM waves, polarization

  • Is always vertical in an isotropic medium
  • Is caused by reflection
  • Is due to transverse nature of waves
  • Results from longitudinal nature of waves

30. It is found that a ship to ship communication suffers from fading. This can be avoided by using

  • Space diversity
  • Frequency diversity
  • Broad band antenna
  • Directional antenna

31. An FM radio receiver which is tuned to a 91.6 MHz broadcast station may receive an image frequency of __________ MHz.

  • 102.3
  • 113
  • 70.2
  • 80.9

32. In case of low level amplitude modulation system, the amplifiers following the modulated stage must be

  • Class C amplifiers
  • Linear devices
  • Non-linear devices
  • Harmonic devices

33. For a low level AM system, the amplifiers modulated stage must be

  • Linear devices
  • Harmonic devices
  • Class C amplifiers
  • Non-linear devices

34. A three stage telephone switching structure is to have 128 input and 128 output terminals. There are 16 first stage and 16 third stage matrices. To avoid blocking the number of intermediate paths required is

  • 16
  • 15
  • 8
  • 1

35. A zero mean white Gaussian noise is passed through an ideal low pass filter of bandwidth 10 kHz. The output of the samples so obtained would be

  • Correlated
  • Statistically independent
  • Uncorrelated
  • Orthogonal

36. Under ordinary circumstances, impulse noise can be reduced in

  • FM only
  • AM only
  • Both AM and FM
  • None of the above

37. In a FM receiver, amplitude limiter

  • Amplifiers low frequency signals
  • Reduces the amplitude of signals
  • Eliminates any change in amplitude of received FM signals
  • None of the above

38. Assertion (A): In FM the frequency of the carrier is varied by the modulating voltageReason (R): FM and PM are two forms of angle modulation.

  • Both A and R are correct and R is correct explanation of A
  • Both A and R are correct but R is not correct explanation of A
  • A is correct but R is wrong
  • A is wrong but R is correct

39. Full duplex operation permits transmission in both directions at the same time.

  • True
  • False

40. In case of frequency modulation, modulating voltage remains constant if the modulating frequency is lowered, then

  • Amplitude of distant sidebands decreases
  • Amplitude of distant sidebands increases
  • Amplitude of distant sidebands remains constant
  • Amplitude of distant sidebands first increases, then decreases

41. The modulation index of an FM is changed from 0 to 1. How does the transmitted power change?

  • Gets halved
  • Gets doubled
  • Gets increased by 50 percent
  • Remains unchanged

42. For a given carrier wave, maximum undistorted power is transmitted when value of modulation is

  • 1
  • 0.8
  • 0.5
  • 0

43. In TV systems, equalising pulses are sent during

  • Horizontal blanking
  • Vertical blanking
  • Serrations
  • Horizontal retrace

44. For a plate-modulated class C amplifier the plate supply voltage is E. The maximum plate cathode voltage could be almost high as

  • 2E
  • 3E
  • 4E
  • 6E

45. In Modulation, “carrier” is

  • Resultant wave
  • Speech voltage to be transmitted
  • Voltage with constant frequency, phase or amplitude
  • Voltage for which frequency, phase or amplitude is varied

46. If in a broadcasting studio, a 1000 kHz carrier is modulated by an audio signal of frequency range 100-5000 kHz, the width of channel is __________ kHz.

  • 5
  • 4.9
  • 995
  • 10

47. Which one of the following is analog?

  • PCM
  • PWM
  • Delta modulation
  • Differential PCM

48. For AM receivers the standard IF frequency is

  • 106 kHz
  • 455 kHz
  • 1.07 MHz
  • 10.7 MHz

49. FM transmitting and receiving equipment as compared to AM equipment is

  • Costly
  • Cheaper
  • Almost equally costly
  • None of the above

50. Leak type bias is used in plate modulated class C amplifier to

  • Increase the bandwidth
  • Prevent over modulation
  • Prevent excessive grid current
  • Prevent tuned circuit damping

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