JEE Main & Advanced Physics Communication System / संचार तंत्र Question Bank

done Critical Thinking Total Questions - 14

• question_answer1)
  A sky wave with a frequency 55 MHz is incident on D-region of earth's atmosphere at 45o. The angle of refraction is (electron density for D-region is 400 electron/cm3) [Haryana PMT 2003]
  A)
             60° done clear
  B)
             45° done clear
  C)
             30° done clear
  D)
             15° done clear
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• question_answer2)
  In a diode AM-detector, the output circuit consist of R = 1kW and C = 10 pF. A carrier signal of 100 kHz is to be detected. Is it good
  A)
             Yes  done clear
  B)
             No done clear
  C)
             Information is not sufficient done clear
  D)
             None of these done clear
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• question_answer3)
  Consider an optical communication system operating at l~800 nm. Suppose, only 1% of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of 8 kHz
  A)
             4.8 ´ 108                                  done clear
  B)
             48 done clear
  C)
             6.2 ´ 108                                  done clear
  D)
             4.8 ´ 105 done clear
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• question_answer4)
  A photodetector is made from a semiconductor In 0.53Ga 0.47As with Eg = 0.73 eV. What is the maximum wavelength, which it can detect
  A)
             1000 nm                                  done clear
  B)
             1703 nm done clear
  C)
             500 nm                                    done clear
  D)
             173 nm done clear
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• question_answer5)
  A transmitter supplies 9 kW to the aerial when unmodulated. The power radiated when modulated to 40% is
  A)
             5 kW                                         done clear
  B)
             9.72 kW done clear
  C)
             10 kW                                       done clear
  D)
             12 kW done clear
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• question_answer6)
  The antenna current of an AM transmitter is 8 A when only carrier is sent but increases to 8.96 A when the carrier is sinusoidally modulated. The percentage modulation is
  A)
             50%                                           done clear
  B)
             60% done clear
  C)
             65%                                           done clear
  D)
             71% done clear
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• question_answer7)
  The total power content of an AM wave is 1500 W. For 100% modulation, the power transmitted by the carrier is
  A)
             500 W                                       done clear
  B)
             700 W done clear
  C)
             750 W                                       done clear
  D)
             1000 W done clear
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• question_answer8)
  The total power content of an AM wave is 900 W. For 100% modulation, the power transmitted by each side band is 
  A)
             50 W                                         done clear
  B)
             100 W done clear
  C)
             150 W                                       done clear
  D)
             200 W done clear
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• question_answer9)
  The modulation index of an FM carrier having a carrier swing of 200 kHz and a modulating signal 10 kHz is
  A)
             5     done clear
  B)
             10 done clear
  C)
             20   done clear
  D)
             25 done clear
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• question_answer10)
  A 500 Hz modulating voltage fed into an FM generator produces a frequency deviation of 2.25 kHz. If amplitude of the voltage is kept constant but frequency is raised to 6 kHz then the new deviation will be 
  A)
             4.5 kHz                                     done clear
  B)
             54 kHz done clear
  C)
             27 kHz                                      done clear
  D)
             15 kHz done clear
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• question_answer11)
  The audio signal used to modulate 60 sin (2p ´ 106 t) is \[15\sin 300\pi t.\]The depth of modulation is 
  A)
             50%                                           done clear
  B)
             40% done clear
  C)
             25%                                           done clear
  D)
             15% done clear
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• question_answer12)
  The bit rate for a signal, which has a sampling rate of 8 kHz and where 16 quantisation levels have been used is
  A)
             32000 bits/sec                       done clear
  B)
             16000 bits/sec done clear
  C)
             64000 bits/sec                       done clear
  D)
             72000 bits/sec done clear
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• question_answer13)
  An amplitude modulated wave is modulated to 50%. What is the saving in power if carrier as well as one of the side bands are suppressed
  A)
             70%                                           done clear
  B)
             65.4% done clear
  C)
             94.4%                                       done clear
  D)
             25.5% done clear
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• question_answer14)
  In AM, the centpercent modulation is achieved when
  A)
             Carrier amplitude = signal amplitude done clear
  B)
             Carrier amplitude ¹  signal amplitude done clear
  C)
             Carrier frequency = signal frequency done clear
  D)
             Carrier frequency ¹ signal frequency done clear
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