COMMUNICATION SYSTEMS Questions :-

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

A. duplex arrangement
B. half duplex arrangement
C. either (a) or (b)
D. neither (a) nor (b)

Answer: Option A

2. For attenuation of high frequencies we should use

A. shunt capacitance
B. series capacitance
C. inductance
D. resistance

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Answer: Option A

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

A. upto 100 bps
B. upto 250 bps
C. upto 400 bps
D. upto 600 bps

Answer: Option D

4. VSB modulation is preferred in TV because

A. it reduces the bandwidth requirement to half
B. it avoids phase distortion at low frequencies
C. it results in better reception
D. none of the above

Answer: Option A

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

A. low pass filter
B. high pass filter
C. band pass filter
D. band stop filter

Answer: Option A

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

A. Armstrong modulator
B. Varactor diode modulator
C. Reactance FET modulator
D. Reactance bipolar transistor

Answer: Option A

7. When the length of antenna is a whole wavelength

A. the radiation at right angles is zero
B. the radiation at right angles is maximum
C. the radiation is zero in all directions
D. the radiation is maximum in all directions

Answer: Option A

8. Circular polarization

A. is useful in reducing depolarization effect on received wave
B. involves critical alignment of transmitting and receiving antenna
C. is useful in discrimination between reception of adjacent beams
D. none of the above

Answer: Option A

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

A. 102.3
B. 113
C. 70.2
D. 80.9

Answer: Option B

10. For telegraphy the most commonly used modulation system is

A. FSK
B. two tone modulation
C. PCM
D. single tone modulation

Answer: Option A

11. Commercial Frequency deviation of FM is

A. 70 kHz
B. 75 kHz
C. 80 kHz
D. 65 kHz

Answer: Option B

12. The colour of an object is decided by

A. the reflected colour
B. the wavelength transmitted through it
C. reflected colour for opaque object and wavelength transmitted through it for transparent objects
D. none of the above

Answer: Option C

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13. In Pulse Code Modulation system

A. large bandwidth is required
B. quantising noise can be overcome by companding
C. quantising noise can be reduced by decreasing the number of standard levels
D. suffers from the disadvantage of its incompatibly with TDM

Answer: Option A

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

A. 2 B. 3
C. 1 D. -3

Answer: Option B

15. Which of the following statements is correct?

A. Convex lens has positive focal power and concave lens have negative focal power
B. Convex lens has negative focal power and concave lens have positive focal power
C. All lens have positive focal power
D. All lens have negative focal power

Answer: Option A

16. In Modulation, “carrier” is

A. resultant wave
B. speech voltage to be transmitted
C. voltage with constant frequency, phase or amplitude
D. voltage for which frequency, phase or amplitude is varied

Answer: Option D

17. To eliminate ghosts in the picture

A. use a longer transmission line
B. connect a booster
C. change the antenna orientation of location
D. twist the transmission line

Answer: Option C

18. The frequency range of 300 kHz to 3000 kHz is known as

A. low frequency
B. medium frequency
C. high frequency
D. very high frequency

Answer: Option B

19. Which of the following does not cause losses in optical fiber cables?

A. Stepped index operation
B. Impurities
C. Micro bending
D. Attenuation in glass

Answer: Option A

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

A. linear devices
B. harmonic devices
C. class C amplifiers
D. non-linear devices

Answer: Option A

21. Assertion (A): In FM the frequency of the carrier is varied by the modulating voltage

Reason (R): FM and PM are two forms of angle modulation.

A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

Answer: Option B

22. A telephone channel requires a bandwidth of about

A. 1 kHz
B. 3 kHz
C. 10 kHz
D. 50 kHz

Answer: Option B

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

A. 1
B. 0.8
C. 0.5
D. 0

Answer: Option A

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

A. zero capacity
B. infinite capacity
C. small capacity
D. none of the above

Answer: Option B

25. DVD uses

A. Laser beam for both recording and playback
B. Laser beam for recording and video head for playback
C. Video head for recording and laser beam for playback
D. None of the above

Answer: Option A

26. Fourier analysis indicate that a square wave can be represented as

A. a fundamental sine wave and odd harmonics
B. a fundamental sine wave and even harmonics
C. a fundamental sine wave and harmonics
D. fundamental and subharmonic sine waves

Answer: Option A

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

A. costly
B. cheaper
C. almost equally costly
D. none of the above

Answer: Option A

28. 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

A. 200 and 1.01
B. 200 and 10.01
C. 200 and 100.1
D. 200 and 200

Answer: Option A

29. 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.

A. 5
B. 4.9
C. 995
D. 10

Answer: Option D

30. Which one of the following is analog?

A. PCM
B. PWM
C. Delta modulation
D. Differential PCM

Answer: Option B

31. The disadvantage of FM over AM is that

A. high output power is needed
B. high modulating power is needed
C. noise is very high for high frequency
D. large bandwidth is required

Answer: Option D

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

A. PCM
B. PSK
C. DM
D. All

Answer: Option B

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

A. Free running multi-vibrator
B. Monostable multi-vibrator
C. JK flip-flop
D. Schmitt trigger

Answer: Option B

34. SSB can be generated by

A. filter method
B. phase cancellation method
C. good attenuation characteristics
D. all of the above

Answer: Option D

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

A. correlated
B. statistically independent
C. uncorrelated
D. orthogonal

Answer: Option B

36. What is the purpose of peak clipper circuits in radio transmitters?

A. To prevent over modulation
B. To reduce bandwidth
C. To increase bandwidth
D. To regulate oscillator I/P voltage

Answer: Option A

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

A. class C amplifiers
B. linear devices
C. non-linear devices
D. harmonic devices

Answer: Option B

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

A. FM only
B. AM only
C. both AM and FM
D. none of the above

Answer: Option A

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

A. amplitude of distant sidebands decreases
B. amplitude of distant sidebands increases
C. amplitude of distant sidebands remains constant
D. amplitude of distant sidebands first increases, then decreases

Answer: Option B

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

A. 35 kHz
B. 70 kHz
C. 10 kHz
D. 1280 kHz

Answer: Option A

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

A. space diversity
B. frequency diversity
C. broad band antenna
D. directional antenna

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Answer: Option B

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

Communication Systems In Organizations Affect

A. True
B. False

Answer: Option A

43. In practical commercial FM system, channel bandwidth is

A. 150 kHz
B. 100 kHz
C. 88 MHz
D. 108 MHz

Answer: Option A

44. In EM waves, polarization

A. is always vertical in an isotropic medium
B. is caused by reflection
C. is due to transverse nature of waves
D. results from longitudinal nature of waves

Answer: Option C

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

A. 0.5 kW
B. 8 kW
C. 20 kW
D. 50 kW

Answer: Option A

46. PAM stands for

A. Pulse Analogue Modulation
B. Phase Analogue Modulation
C. Pulse Amplitude Modulation
D. Phase Amplitude Modulation

Answer: Option C

47. The characteristic impedance of a twin wire feeder used for TV signals is about

A. 1000 ohm
B. 500 ohm
C. 300 ohm
D. 100 ohm

Answer: Option C

48. In a FM receiver, amplitude limiter

A. amplifiers low frequency signals
B. reduces the amplitude of signals
C. eliminates any change in amplitude of received FM signals
D. none of the above

Answer: Option C

49. A buffer amplifier is

A. a double-tuned amplifier
B. a high gain D.C. amplifier
C. a cathode follower stage
D. none of the above

Answer: Option B

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

A. increase the bandwidth
B. prevent over modulation
C. prevent excessive grid current
D. prevent tuned circuit damping

Answer: Option C

51. The direction of rotation of a CD is

A. clockwise
B. anticlockwise
C. clockwise or anticlockwise depending on frequency of data stored
D. mostly anticlockwise but some times clockwise

Answer: Option B

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

A. improved efficiency
B. better linearity
C. high power output per transistor
D. the lower modulating power requirement

Answer: Option D

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

A. True
B. False

Answer: Option A

54. In a TV receiver antenna the length of reflector rod

A. is the same as that of dipole
B. is less than that of dipole
C. is more than that of dipole
D. may be equal, more or less than that of dipole

Answer: Option C

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

A. Gets halved
B. Gets doubled
C. Gets increased by 50 percent
D. Remains unchanged

Answer: Option C

56. For AM receivers the standard IF frequency is

A. 106 kHz
B. 455 kHz
C. 1.07 MHz
D. 10.7 MHz

Answer: Option B

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

A. 2E
B. 3E
C. 4E
D. 6E

Answer: Option C

58. In TV systems, equalizing pulses are sent during

A. horizontal blanking
B. vertical blanking
C. serrations
D. horizontal retrace

Answer: Option A

59. 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

A. 16
B. 15
C. 8
D. 1

Answer: Option B

60. The main function of a balanced modulator is to

A. produce balanced modulation of a carrier wave
B. produce 100% modulation
C. suppress carrier signal in order to create a single-sideband or double sideband
D. limit noise picked by a receiver

Answer: Option B

COMMUNICATION SYSTEMS Questions and Answers pdf free download ::

A “hello how are you” from one person, from one location, needs to be conveyed effectively and, clearly without noise to another person in another location. A picture sent to someone far away should be received without any distortion. A file transferred from one location to another location should be received without errors. Communication engineering is a process by which, connection (link) is established between two points, for information exchange maximizing customer delight. The main examples of the communication system include telephone, telegraph, mobile, Edison telegraph, computer and TV cable. The sources of this system can be divided into electric otherwise non-electric. These are the sources of an input or message signal. The sources include audio files like mp3, mp4, MKV, and GIFs (graphic image files), human voice, e-mail messages, TV picture, and electromagnetic radiation.

What is a Telecommunication System?

Telecommunication implies communication between two points, separated by a distance. “Tele” means “at a distance”. It takes into account that something may be and will be lost in the process; hence the term ‘telecommunication’ includes all kinds of distances and all kinds of techniques such as radio, telegraphy, television, telephony, data communication, and computer networking.

We can define telecommunication as, communicating information such as data, text, pictures, voice, audio, video, feelings, thoughts over a long distance. The medium for such signal transmission can be thro electrical wire or cable (also known as “copper”), optical fiber or ether etc. If the communication is through the free-space by means of electromagnetic waves, then it is called wireless.

The Internet is the largest example of a typical data communication network. Few other forms of Telecom networks can be Corporate and academic wide-area networks (WANs). Different technologies have evolved, to bring out newer applications. Broadband and mobile Communications have instantly become popular. Some of the technologies in vogue are

• Digital Telephone networks
• WiMAX, WIFI, BLUETOOTH
• Police wireless (Walkie talkie)
• GSM / CDMA / UMTS / LTE / Wireless LAN
• Facebook, Twitter, Linked In, WhatsApp

Distance does not matter anymore. Communication has to happen anytime, anywhere, at any place, through any medium, at any speed, through any device.

Basic Elements of Communication System

The basic elements of a communication system are shown in the elementary block diagram.

Objectives

Communication Systems Engineering

The objectives of a communication system include Minimum bandwidth, Maximum quality (Signal to Ratio), Minimum Bit Error Rate (BER), Maximum speed, Economy, Reliability, Mobility.

Messages

The message can be voice, music, Data, Video, Temperature, Light, Pressure etc

Input Transducer

The input can be in any energy form (temperature, pressure, light) but for transmission purposes, this needs to be converted to electrical energy. Transducer does this.

Modulator

Translates the input signal to a higher frequency spectrum and also modulates (camouflages) the signal to combat noise (Amplitude Modulation, Freq Modulation, Phase Modulation, PCM, Delta Modulation, ASK, FSK, PSK, QPSK, QAM, GMSK, etc). The output can be analog or digital (thro A/D converters).

Transmitter

It converts information into a signal that is suitable for transmission over a medium. Transmitter increases the power of the signal thro power amplifiers and also provides interfaces to match the transmission medium, such as an antenna interface, fiber interface and so on.

Antenna

If it is wireless communication, antenna propagates (radiates) the signal through the air (atmosphere)

Channel

A channel in a communication system just refers to the medium through which an electrical signal travels. These media are classified into two types such as guided as well as unguided. Guided media can be directed from a source in the direction of the receiver by using connecting cables. In OFC-optical fiber communication, an optical fiber is a medium. Additional guided media may comprise telephone wire, coaxial cable, and twisted pairs, etc.

The second type of media namely unguided media that refers to a communication channel which forms space among the source as well as the receiver. In RF communication, the medium is space which is called air. It is the only thing among the source & receiver whereas in further cases such as sonar, the medium is generally water since sound waves tour powerfully through assured liquid media. The two types of Medias are measured unguided for the reason that there are no connecting wires between the source as well as the receiver.

Noise

Noise is the challenge for communication engineers. It is random and unpredictable in nature. Noise is the undesirable electric energy that enters the communication system and interferes with the desired signal.

• Noise is produced at the transmitter, channel and also at the receiver. Everywhere.
• It can be man-made and natural.
• Natural noise: Lightning, Solar radiation, Thermal
• Man-made: Welding, Sparking, Motors, Car ignition, Tube lights, Electronic fan regulators etc

Receiver

• Receives the signal (desired) with noise (undesired).
• Recovers the original signal in spite of the noise.
• Consists of amplifiers, filters, mixers, oscillators, demodulators, transducers.
• The receiver consists of a similar sequence of block diagrams.
• Whatever was done in the transmitter will be undone in the receiver.
• For example, modulation in TX will be matched by Demodulation in RX, A to D in TX will be undone by D to A in the receiver and so on.

Application Areas of Communication System

There are several types of communications which are used in different fields. The application areas of communication system mainly include the following.

A strategic communications system is applicable for straight support of strategic forces. It is designed to meet up the necessities of changing strategic conditions as well as environmental conditions. It gives protectable communications like data, voice, video, between the mobile users to make possible. Generally, requires very short fitting times, typically on the hours of order, in order to gather the necessities of common replacement.

An Emergency communication system is normally based on the computer that is mainly used for the two-way communication of urgent situation of sending messages between two persons & groups of persons. The main intention of these systems to combine the cross-communication of messages among is different communication technologies.

An ACD or Automatic call distributor is one kind of communication system that routinely assigns, queues, as well as unites callers in the direction of handlers. Main applications of this system involved in customer service, placing an order by telephone, otherwise management services.

A VCCS or Voice Communication Control System is basically an automatic call distributor with characteristics that make to utilize in dangerous situations.

Thus, this is all about the basic elements of the communication system, and the key components of this system mainly include sources, input transducers, transmitter, communication channel receiver, and the output transducer. Here is a question for you, what are the different types of communication systems?