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

done Self Evaluation Test - Communication System Total Questions - 100

• question_answer1)
  Which mode of communication is not employed for the transmission of T.V. signals?
  A)
  Ground wave propagation done clear
  B)
  sky wave propagation done clear
  C)
  space wave propagation done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer2)
  Audio signal cannot be transmitted because
  A)
  the signal has more noise f Thinking done clear
  B)
  the signal cannot be amplified for distance communication done clear
  C)
  the transmitting antenna length is very small to design done clear
  D)
  the transmitting antenna length is very large and impracticable done clear
  View Solution play_arrow

• question_answer3)
  An antenna is a device
  A)
  that converts electromagnetic energy into radio frequency signal done clear
  B)
  that converts radio frequency signal into electromagnetic energy done clear
  C)
  that converts guided electromagnetic waves into free space electromagnetic waves and vice-versa done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer4)
  Modulation is the process of superposing
  A)
  low frequency audio signal on high frequency waves done clear
  B)
  low frequency radio signal on low frequency audio waves done clear
  C)
  high frequency audio signal on low frequency radio waves done clear
  D)
  low frequency audio signal on low frequency radio waves done clear
  View Solution play_arrow

• question_answer5)
  The maximum peak to peak voltage of an AM wire is \[24\text{ }mV\] and the minimum peak to peak voltage is \[8\text{ }mV\]. The modulation factor in percentage is
  A)
  \[10%\] done clear
  B)
  \[20%\] done clear
  C)
  \[25%\] done clear
  D)
  \[50%\] done clear
  View Solution play_arrow

• question_answer6)
  A laser beam is used for carrying out surgery because it       
  A)
           is highly monochromatic done clear
  B)
    is highly coherent done clear
  C)
  is highly directional done clear
  D)
  can be sharply focused done clear
  View Solution play_arrow

• question_answer7)
  Which of the following frequencies will be suitable for beyond-the horizon communication using sky waves?
  A)
  \[10\text{ }kHz\] done clear
  B)
  \[10\text{ M}Hz\] done clear
  C)
  \[\text{1 G}Hz\] done clear
  D)
  \[\text{1000 G}Hz\] done clear
  View Solution play_arrow

• question_answer8)
  The sky wave propagation is suitable for radio- waves of frequency
  A)
  upto \[2\,MHz\] done clear
  B)
  from \[2\,MHz\] to \[20\,MHz\] done clear
  C)
  from \[2\,MHz\] to \[30\,MHz\] done clear
  D)
  from \[2\,MHz\] to \[50\,MHz\] done clear
  View Solution play_arrow

• question_answer9)
  The maximum range \[{{d}_{\max }},\] of radar is
  A)
  proportional to the cube root of the peak transmitted power done clear
  B)
  proportional to the fourth root of the peak transmitted power done clear
  C)
  proportional to the square root of the peak transmitted power done clear
  D)
  Not related to the peak transmitted power at all done clear
  View Solution play_arrow

• question_answer10)
  Frequencies in the UHF range normally propagate by means of-
  A)
  Ground waves done clear
  B)
  Sky waves. done clear
  C)
  Surface waves done clear
  D)
  Space waves done clear
  View Solution play_arrow

• question_answer11)
  A T.V. tower has a height 150 m. What is the population density around the T.V. tower if the total population covered is 50 lakh? The radius of earth is \[6.4\times {{10}^{6}}m\].       
  A)
  \[800\,k{{m}^{-2}}\] done clear
  B)
  \[829\,k{{m}^{-2}}\] done clear
  C)
  \[82.6\,k{{m}^{-2}}\] done clear
  D)
  \[826.6\,k{{m}^{-2}}\] done clear
  View Solution play_arrow

• question_answer12)
  What will be the image frequency of an FM radio receiver that is tuned to \[98.6\text{ }MHz\] broadcast station?
  A)
  \[111.8\,MHz\] done clear
  B)
  \[108\,MHz\] done clear
  C)
  \[121.6\,MHz\] done clear
  D)
  \[132\,MHz\] done clear
  View Solution play_arrow

• question_answer13)
  The temperature of earth's atmosphere increases with height in
  A)
  troposphere done clear
  B)
  stratosphere and ionosphere done clear
  C)
  mesosphere and tonosphere done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer14)
  Critical frequency \[{{v}_{c}}\] for the ionosphere is -
  A)
  \[{{v}_{c}}=9.{{N}_{\max }}\] done clear
  B)
                     \[{{v}_{c}}=9\sqrt{{{N}_{\max }}}\] done clear
  C)
  \[{{v}_{c}}=6.IN\max \] done clear
  D)
         \[{{v}_{c}}=6.{{N}_{max}}\] done clear
  View Solution play_arrow

• question_answer15)
  The phenomenon by which light travels in an optical fibres is
  A)
  Reflection done clear
  B)
                                 Refraction done clear
  C)
  Total internal reflection done clear
  D)
         Transmission done clear
  View Solution play_arrow

• question_answer16)
  The attenuation in optical fibre is mainly due to
  A)
  absorption done clear
  B)
  scattering done clear
  C)
  neither absorption nor scattering done clear
  D)
  both (a) and (b) done clear
  View Solution play_arrow

• question_answer17)
  The fundamental radio antenna is a metal rod which has a length equal to
  A)
  \[\lambda \] in free space at the frequency of operation done clear
  B)
  \[\lambda /2\] in free space at the frequency of operation done clear
  C)
  \[\lambda /4\] in free space at the frequency of operation done clear
  D)
  \[3\lambda /4\] in free space at the frequency of operation done clear
  View Solution play_arrow

• question_answer18)
  Long range radio transmission is possible when the radio waves are reflected from the ionosphere. For this to happen the frequency of the radio waves must be in the range:
  A)
  \[80-150\,MHz\] done clear
  B)
  \[8-25MHz\] done clear
  C)
  \[1-3\,MHz\] done clear
  D)
  \[150-1500\,kHz\] done clear
  View Solution play_arrow

• question_answer19)
  The TV telecast is to cover a radius of \[120\text{ }km\] (given the radius of the Earth\[=6400\text{ }km\]), the height of the transmitting antenna is
  A)
  \[1280\,m\] done clear
  B)
  \[1125\,m\] done clear
  C)
  \[1560\,m\]        done clear
  D)
         \[79\text{ }m\] done clear
  View Solution play_arrow

• question_answer20)
  The radio waves of frequency \[300\text{ }MHz\] to \[3000\text{ }MHz\] belong to
  A)
  high frequency band done clear
  B)
  very high frequency band done clear
  C)
  ultra high frequency band done clear
  D)
  super high frequency band done clear
  View Solution play_arrow

• question_answer21)
  Electromagnetic waves with frequencies greater than the critical frequency of ionosphere cannot be used for communication using sky wave propagation because:    
  A)
      the refractive index of the ionosphere becomes very high for \[f>{{f}_{c}}\] done clear
  B)
  the refractive index of the ionosphere becomes very low for \[f>{{f}_{c}}\] done clear
  C)
  the refractive index of the ionosphere very high for \[f<{{f}_{c}}\] done clear
  D)
  none of the above done clear
  View Solution play_arrow

• question_answer22)
  In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frquency will be
  A)
  \[50\,cycles/s\] done clear
  B)
  \[100\,cycles/s\] done clear
  C)
  \[500\,cycles/s\] done clear
  D)
  \[50,000\,cycles/s\] done clear
  View Solution play_arrow

• question_answer23)
  Long distance short-wave radio broadcasting uses
  A)
  ground wave done clear
  B)
  ionospheric wave done clear
  C)
  direct wave done clear
  D)
  sky wave done clear
  View Solution play_arrow

• question_answer24)
  What is the modulation index of an over modulated wave
  A)
  \[1\] done clear
  B)
  Zero done clear
  C)
  \[<\,1\] done clear
  D)
  \[>\,1\] done clear
  View Solution play_arrow

• question_answer25)
  Which of the following statements is correct?
  A)
  Short waves are completely absorbed by ionosphere. done clear
  B)
  Radio   waves   are   unpolarised electromagnetic waves. done clear
  C)
  Optical interference between fibres is zero. done clear
  D)
  Shorter the wavelength, the smaller is the velocity of wave propagation. done clear
  View Solution play_arrow

• question_answer26)
  Broadcasting antennas are generally
  A)
  omnidirectional type done clear
  B)
  vertical type done clear
  C)
  horizontal type  done clear
  D)
  None of these done clear
  View Solution play_arrow

• question_answer27)
  Which range of frequencies is suitable for sky wave propagation?
  A)
  \[1\,kHz\] to \[500\,kHz\]  done clear
  B)
  \[1\,MHz\] to \[2\,MHz\] done clear
  C)
  \[2\,MHz\] to \[20\,MHz\] done clear
  D)
  Above \[30\,MHz\] done clear
  View Solution play_arrow

• question_answer28)
  In earth's atmosphere, for \[{{F}_{2}}\] -layer, the virtual height and critical frequency in night time are
  A)
   \[210\,km\] and \[5\text{ }MHz\] done clear
  B)
         \[250\,km\] and \[6\,MHz\] done clear
  C)
  \[280\text{ }km\] and \[7\text{ }MHz\] done clear
  D)
  \[350\,km\] and \[6\,MHz\] done clear
  View Solution play_arrow

• question_answer29)
  In ground or surface wave propagation, the loss of power in a signal wave is due to
  A)
  induced charges in earth which travel in ground along with the wave, resulting the alternating currents in the earth's surface done clear
  B)
  interference of waves done clear
  C)
  superposition of waves done clear
  D)
  high frequency of signal wave. done clear
  View Solution play_arrow

• question_answer30)
  A transducer used at the transmitting end, serves the purpose of converting
  A)
  electrical signal to sound form done clear
  B)
  sound signal to electrical form done clear
  C)
  electrical signal to magnetic form done clear
  D)
  sound signal to magnetic form done clear
  View Solution play_arrow

• question_answer31)
  In which frequency range, space waves are normally propagated
  A)
  HF done clear
  B)
  VHF done clear
  C)
  UHF done clear
  D)
  SHF done clear
  View Solution play_arrow

• question_answer32)
  In an optical fibre, the diameter of the core is nearly
  A)
  \[{{10}^{-2}}m\] done clear
  B)
  \[{{10}^{-4}}m\] done clear
  C)
  \[{{10}^{-8}}m\] done clear
  D)
  \[{{10}^{-10}}m\] done clear
  View Solution play_arrow

• question_answer33)
  Communication satellite is used when the distance of transmission is greater than -
  A)
  \[100\,km\] done clear
  B)
  \[500\,km\] done clear
  C)
  \[10\,km\] done clear
  D)
  \[1000\,km\] done clear
  View Solution play_arrow

• question_answer34)
  The electron density of a layer of ionosphere at a height \[150\text{ }km\] from the earth's surface is \[9\times {{10}^{9}}\,per\,{{m}^{3}}.\]For the sky transmission from this layer up to a range of \[250\text{ }km,\]The critical frequency of the layer is
  A)
  \[2\,Hz\] done clear
  B)
  \[2.7\,Hz\] done clear
  C)
  \[2.78\,Hz\] done clear
  D)
  \[2.7\,MHz\] done clear
  View Solution play_arrow

• question_answer35)
  What should be the maximum acceptance angle at the aircore interface of an optical fibre if \[{{n}_{1}}\]and \[{{n}_{2}}\] are the refractive indices of the core and the cladding, respectively?
  A)
  \[{{\sin }^{-1}}({{n}_{2}}/{{n}_{1}})\] done clear
  B)
  \[{{\sin }^{-1}}\sqrt{n_{1}^{2}-n_{2}^{2}}\] done clear
  C)
  \[\left[ {{\tan }^{-1}}\frac{{{n}_{2}}}{{{n}_{1}}} \right]\] done clear
  D)
  \[\left[ {{\tan }^{-1}}\frac{{{n}_{1}}}{{{n}_{2}}} \right]\] done clear
  View Solution play_arrow

• question_answer36)
  Space wave propagation is useful for -
  A)
  low frequency waves and large distances done clear
  B)
  low frequency waves and small distances done clear
  C)
  high frequency waves done clear
  D)
  ultra-high frequency waves done clear
  View Solution play_arrow

• question_answer37)
  Which one of the following is used in line-transmission -
  A)
  coaxial cable done clear
  B)
         optical fibre cable done clear
  C)
  twisted pair        done clear
  D)
  all the above done clear
  View Solution play_arrow

• question_answer38)
  A TV tower has a height of\[100m\]. By how much the height of tower be increased to triple its coverage range?
  A)
  \[800\text{ }m\] done clear
  B)
  \[700\text{ }m\] done clear
  C)
  \[600\text{ }m\] done clear
  D)
  \[500\text{ }m\] done clear
  View Solution play_arrow

• question_answer39)
  In a radio receiver, noise is generally developed at-
  A)
  IF stage done clear
  B)
  audio stage done clear
  C)
  RF stage done clear
  D)
  receiving antenna done clear
  View Solution play_arrow

• question_answer40)
  Range of frequencies allotted for commercial FM radio broadcast is -
  A)
  \[88\]to\[108\text{ }MHz\] done clear
  B)
  \[88\] to \[108\text{ }kHz\] done clear
  C)
  \[8\]to\[88\text{ }MHz\] done clear
  D)
  \[88\] to \[108\text{ }GHz\] done clear
  View Solution play_arrow

• question_answer41)
  A super heterodyne receiver is designed to receive transmitted signals between 5 and\[10\text{ }MHz\]. The tuning range of the local oscillate for IF frequency \[600\text{ }kHz\] for high-side tuning would be      
  A)
                     \[4.6\] to\[9.6\text{ }MHz\] done clear
  B)
  \[5.6\] to \[10.6\text{ }MHz\] done clear
  C)
  \[4.6\] to\[10.6\text{ }MHz\] done clear
  D)
  \[5.6\] to \[9.6\text{ }MHz\] done clear
  View Solution play_arrow

• question_answer42)
  For television broadcasting, the frequency employed is normally -
  A)
  \[30-300\text{ }MHz\] done clear
  B)
  \[3-30\text{ }MHz\] done clear
  C)
  \[30-300\text{ }KHz\] done clear
  D)
  \[30-300\text{ }Hz\] done clear
  View Solution play_arrow

• question_answer43)
  If the heights of transmitting and the receiving antennas are each equal to h, the maximum line- of-sight distance between them is (R is the radius of earth)
  A)
  \[\sqrt{2Rh}\] done clear
  B)
  \[\sqrt{4Rh}\] done clear
  C)
  \[\sqrt{6Rh}\] done clear
  D)
  \[\sqrt{8Rh}\] done clear
  View Solution play_arrow

• question_answer44)
  A signal of peak voltage \[5\text{ }V\] at \[10\text{ }kHz\] is modulated using a carrier wave of peak voltage \[10\text{ }V\] at\[2\text{ }MHz\]. The side band frequencies are
  A)
  \[2010kHz,1990kHz\] done clear
  B)
        \[2000kHz,\text{ }1990kHz\] done clear
  C)
  \[2010kHz,\text{ }2000\text{ }kHz\] done clear
  D)
  \[2100kHz,\text{ }1900kHz\] done clear
  View Solution play_arrow

• question_answer45)
  If the maximum amplitude of an amplitude modulated wave is \[25\text{ }V\] and the minimum amplitude is \[5\text{ }V,\] the modulation index is:
  A)
  \[\frac{1}{5}\] done clear
  B)
  \[\frac{1}{3}\] done clear
  C)
  \[\frac{3}{2}\] done clear
  D)
         \[\frac{2}{3}\] done clear
  View Solution play_arrow

• question_answer46)
  The electromagnetic waves of frequency \[2\text{ }MHz\] to \[30\text{ }MHz\] are used
  A)
  in ground wave propagation done clear
  B)
  in sky wave propagation done clear
  C)
  in microwave propagation done clear
  D)
  in satellite communication done clear
  View Solution play_arrow

• question_answer47)
  100% modulation in FM means ,
  A)
  actual frequency deviation > maximum allowed frequency deviation done clear
  B)
  actual frequency deviation = maximum allowed frequency deviation done clear
  C)
  actual frequency deviation > maximum allowed frequency deviation done clear
  D)
  actual frequency deviation < maximum allowed frequency deviation done clear
  View Solution play_arrow

• question_answer48)
  The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 893 A when the carrier is sent, but it increases to 893 A when the carrier is modulated by a single sine wave. Find the percentage modulation.
  A)
  \[60.1%\] done clear
  B)
  \[70.1%\] done clear
  C)
  \[80.1%\] done clear
  D)
  \[50.1%\] done clear
  View Solution play_arrow

• question_answer49)
  When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is
  A)
  0 rad done clear
  B)
  \[(3\pi /2)\]rad done clear
  C)
  \[(\pi /2)\]rad done clear
  D)
  \[\pi \,rad\] done clear
  View Solution play_arrow

• question_answer50)
  The rms value of a carrier voltage is 100 volts. Compute its rms value when it has been amplitude modulated by a sinusoidal audio voltage to a depth of 30%.             
  A)
  \[94\,V\] done clear
  B)
  \[104.5\,V\] done clear
  C)
  \[114.4\,V\] done clear
  D)
  \[124\,V\] done clear
  View Solution play_arrow

• question_answer51)
  A carrier frequency of \[1\text{ }MHz\] and peak value of \[10\text{ }V\] is amplitude modulated with a signal frequency of \[10\text{ }kHz\] with peak value of\[0.5\text{ }V\]. Then, the modulation index and the side band frequencies respectively are  
  A)
   \[0.05\]and\[1\pm 0.010\text{ }MHz\] done clear
  B)
  \[0.5\]and \[1\pm 0.010\text{ }MHz\] done clear
  C)
  \[0.5\]and \[1\pm 0.005\text{ }MHz\] done clear
  D)
  \[0.05\]and \[1\pm 0.005\text{ }MHz\] done clear
  View Solution play_arrow

• question_answer52)
  The wrong statement is
  A)
  Electromagnetic waves with frequencies more than the critical frequency of ionosphere cannot be used for communication using sky wave propagation. done clear
  B)
  The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency. done clear
  C)
  Diode lasers are used as optical sources in optical communication. done clear
  D)
  Diode lasers consume more energy. done clear
  View Solution play_arrow

• question_answer53)
  A sinusoidal carrier voltage of frequency \[10\text{ }MHz\] and amplitude 200 volts is amplitude modulated by a sinusoidal voltage of frequency \[10\text{ }kHz\]producing \[40%\]modulation. Calculate the frequency of upper and lower sidebands.
  A)
  \[10010kHz,9990\text{ }kHz\] done clear
  B)
  \[1010kHz,990kHz\] done clear
  C)
  \[10100\text{ }Hz,9990\text{ }Hz\] done clear
  D)
  \[1010MHz,990MHz\] done clear
  View Solution play_arrow

• question_answer54)
  The most useful transmission for low frequency and small distance is through -
  A)
  sky waves done clear
  B)
  ground waves done clear
  C)
  surface waves done clear
  D)
  space waves done clear
  View Solution play_arrow

• question_answer55)
  A \[1000\text{ }kHz\] carrier is simultaneously modulated with \[300\text{ }Hz,\] \[800\text{ }Hz\] and \[2\text{ }kHz\] audio waves. The frequencies present in the output is
  A)
  \[999.7\text{ }kHz,\text{ }100.3\text{ }kHz,\text{ }999.2\text{ }kHz\] done clear
  B)
  \[1000.8\text{ }kHz,\text{ }998\text{ }kHz,\text{ }1002\text{ }kHz\] done clear
  C)
  \[1002.8\text{ }kHz,\text{ }996\text{ }kHz,\text{ }1106\text{ }kHz\] done clear
  D)
  both (a) and (b) done clear
  View Solution play_arrow

• question_answer56)
  The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to -
  A)
  \[{{h}^{1/2}}\] done clear
  B)
  h     done clear
  C)
  \[{{h}^{3/2}}\] done clear
  D)
  \[{{h}^{2}}\] done clear
  View Solution play_arrow

• question_answer57)
  For good demodulation of AM signal of carrier frequency/, the value of RC should be
  A)
  \[RC=\frac{1}{f}\] done clear
  B)
  \[RC<\frac{1}{f}\] done clear
  C)
  \[RC\ge \frac{1}{f}\] done clear
  D)
   \[RC>>\frac{1}{f}\] done clear
  View Solution play_arrow

• question_answer58)
  An audio frequency of \[10\text{ }kHz\] is transmitted by SSB after AM with carrier waves of frequency\[1\,MHz\]. The frequency of current in output load is
  A)
  \[1010\,kHz\] or \[990\,kHz\] done clear
  B)
    \[1010\,MHz\] or \[1010\,MHz\] done clear
  C)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       \[110\text{ }kHz\] or \[990\text{ }kHz\] done clear
  D)
  \[110\text{ }MHz\] or \[990\text{ }MHz\] done clear
  View Solution play_arrow

• question_answer59)
  At maximum modulation (i.e. \[m=1\]), the power in each sideband is......... of that of carrier.
  A)
  \[25%\] done clear
  B)
  \[50%\] done clear
  C)
  \[40%\] done clear
  D)
  \[60%\] done clear
  View Solution play_arrow

• question_answer60)
  In an FM system a \[7\text{ }kHz\] signal modulates \[108\,MHz\]carrier so that frequency deviation is\[50\,kHz\]. The carrier swing is
  A)
  \[7.1\] done clear
  B)
  \[2.8\]    done clear
  C)
  \[5.8\] done clear
  D)
  \[3.2\] done clear
  View Solution play_arrow

• question_answer61)
  An FM signal has a resting frequency of \[105\text{ }MHz\] and highest frequency of \[105.03\text{ }MHz\] when modulated by a signal of frequency \[5\text{ }kHz.\]The carrier swing is
  A)
  \[25\,kHz\] done clear
  B)
  \[54\,kHz\] done clear
  C)
  \[60\,kHz\] done clear
  D)
  \[75\,kHz\] done clear
  View Solution play_arrow

• question_answer62)
  A detector circuit must -
  A)
  rectify the signal done clear
  B)
  deliver an audio output signal done clear
  C)
  perform the above two functions done clear
  D)
  None of the above done clear
  View Solution play_arrow

• question_answer63)
  An oscillator is producing FM waves of frequency \[2\text{ }kHz\] with a variation of\[10\text{ }kHz\]. What is the modulating index?
  A)
  5 done clear
  B)
  4     done clear
  C)
  3 done clear
  D)
  2 done clear
  View Solution play_arrow

• question_answer64)
  An AM- signal is given as \[{{x}_{AM}}(t)=100\,[p(t)+0.5\,g(t)]\,\,\cos \,{{\omega }_{c}}t\] in interval \[0\le t\le 1.\]. One set of possible values of the modulating signal and modulation index would be   
  A)
                \[t,\,\,0.5\] done clear
  B)
  \[t,\,\,1.0\] done clear
  C)
  \[t,\,\,1.5\] done clear
  D)
  \[{{t}^{2}},\,\,2.0\] done clear
  View Solution play_arrow

• question_answer65)
  In frequency modulated wave:
  A)
  frequency varies with time done clear
  B)
  amplitude varies with time done clear
  C)
  both frequency and amplitude vary with time done clear
  D)
  both frequency and amplitude are constant done clear
  View Solution play_arrow

• question_answer66)
  In light modulation, which characteristic of the carrier light wave is varied?
  A)
  Amplitude done clear
  B)
  Frequency done clear
  C)
  Phase done clear
  D)
  Intensity done clear
  View Solution play_arrow

• question_answer67)
  An FM radio station operating at \[630\text{ }kHz\] is permitted to broadcast audio frequencies up to\[\text{6 }kHz\]. The band pass filter in its modulation circuit can retain the frequencies
  A)
  \[636\,kHz,\text{ }630\,kHz\] done clear
  B)
  \[12\,kHz,\text{ }6\,kHz\] done clear
  C)
  \[1260\,kHz,6\,kHz\] done clear
  D)
  \[1260kHz,\text{ }630kHz\] done clear
  View Solution play_arrow

• question_answer68)
  What is the band width in amplitude modulation?
  A)
  Equal to signal frequency done clear
  B)
  Two times the signal frequency done clear
  C)
  Half the signal frequency done clear
  D)
  One fourth the signal frequency done clear
  View Solution play_arrow

• question_answer69)
  A \[10\text{ }kW\] carrier is sinusoidally modulated by two carriers corresponding to a modulation index of 30% and 40% respectively then total power radiated by the modulator is
  A)
  \[10.25\,kW\] done clear
  B)
  \[11.25\,kW\] done clear
  C)
  \[12.75\,kW\] done clear
  D)
  \[17\,kW\] done clear
  View Solution play_arrow

• question_answer70)
  As the modulation level is increased, the carrier power -
  A)
  is increased done clear
  B)
  is decreased done clear
  C)
  remains the same done clear
  D)
  None of the above done clear
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• question_answer71)
  A device with input \[x(t)\] and output \[y(t)\] is characterized by: \[y(t)={{x}^{2}}(t)\]. An FM signal with frequency deviation of \[90\text{ }kHz\] and modulating signal bandwidth of \[5\text{ }kHz\] is applied to this device. The bandwidth of the output signal is   
  A)
    \[370\,kHz\] done clear
  B)
  \[190\,kHz\] done clear
  C)
  \[380\,kHz\] done clear
  D)
  \[95\,kHz\] done clear
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• question_answer72)
  12 signals each band limited to \[5\text{ }kHz\] are to be transmitted by frequency-division multiplexer. If AM-SSB modulation guard band of \[\text{1 }kHz\] is used then the bandwidth of multiplexed signal is
  A)
  \[\text{101 }kHz\] done clear
  B)
  \[\text{99 }kHz\] done clear
  C)
  \[\text{84 }kHz\] done clear
  D)
  \[\text{71 }kHz\] done clear
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• question_answer73)
  If level of modulation is increased........power is increased.
  A)
  carrier done clear
  B)
  sideband done clear
  C)
  carrier as well as sideband done clear
  D)
  none of the above done clear
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• question_answer74)
  Determine the modulation index and carrier swing of an FM carrier having a frequency deviation of \[25\text{ }kHz\] and a modulating signal of\[5\text{ }kHz\].
  A)
  \[7,\,\,70\,kHz\] done clear
  B)
  \[8,\,\,80\,kHz\] done clear
  C)
  \[5,\,\,50\,kHz\] done clear
  D)
  \[10,\,\,100\,kHz\] done clear
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• question_answer75)
  A radio station has two channels. One is AM at \[1020\text{ }kHz\] and the other FM at\[89.5\text{ }MHz\]. For good results you will use
  A)
  longer antenna for the AM channel and shorter for the FM done clear
  B)
  shorter antenna for the AM channel and longer for the FM done clear
  C)
  same length antenna will work for both done clear
  D)
  information given is not enough to say which one to use for which done clear
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• question_answer76)
  Band width is dependent on -
  A)
  the frequency of carrier done clear
  B)
  the frequency of modulated signal done clear
  C)
  the thickness of the cable done clear
  D)
  the resistance of the circuit. done clear
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• question_answer77)
  An audio signal represented as \[25\,\sin \,2\pi (2000\,t)\]amplitude modulated by a carrier wave: \[60\,\sin \,2\pi (100\,,\,000)t\]. The modulation index of the modulated signal is   
  A)
          \[25%\] done clear
  B)
  \[41.6%\] done clear
  C)
  \[50%\] done clear
  D)
  \[75%\] done clear
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• question_answer78)
  If a carrier wave c(t) = A \[\sin {{\omega }_{c}}t\] is amplitude modulated by a modulator signal \[m(t)=A\,\sin {{\omega }_{m}}t\]then the equation of modulated signal \[[{{C}_{m}}(t)]\]and its modulation index are respectively
  A)
  \[{{C}_{m}}(t)=A(1+\sin {{\omega }_{m}}t)\,\sin {{\omega }_{c}}t\] and 2 done clear
  B)
  \[{{C}_{m}}(t)=A(1+\sin {{\omega }_{m}}t)\,\sin {{\omega }_{m}}t\] and 1 done clear
  C)
  \[{{C}_{m}}(t)=A(1+\sin {{\omega }_{m}}t)\,\sin {{\omega }_{c}}t\] and 1 done clear
  D)
  \[{{C}_{m}}(t)=A(1+\sin {{\omega }_{c}}t)\,\sin {{\omega }_{m}}t\] and 2 done clear
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• question_answer79)
  When the modulating frequency is doubled, the modulation index is halved and the modulating voltage remains constant. The modulation system is
  A)
  Amplitude modulation done clear
  B)
  Phase modulation done clear
  C)
  Frequency modulation done clear
  D)
  All of the above done clear
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• question_answer80)
  Pre-emphasis in FM system is done to
  A)
  compress modulating signal done clear
  B)
  expand modulating signal done clear
  C)
  amplify lower frequency component of the modulating signal done clear
  D)
  amplify higher frequency component of the modulating signal done clear
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• question_answer81)
  A broadcast radio transmitter radiates \[12\text{ }kW\]when percentage of modulation is 50%, then the unmodulated carrier power is
  A)
  \[5.67\,kW\] done clear
  B)
  \[7.15\,kW\] done clear
  C)
  \[9.6\text{ }kW\] done clear
  D)
  \[12\text{ }kW\] done clear
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• question_answer82)
  AM is used for broadcasting because
  A)
  it is more noise immune than other modulation systems done clear
  B)
  it requires less transmitting power compared with other systems done clear
  C)
  its use avoids receiver complexity done clear
  D)
  no other modulation system can provide the necessary bandwidth faithful transmission. done clear
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• question_answer83)
  The frequency deviation in a FM transmission is\[18.75\text{ }KHz\]. If it broadcasts in \[88-108\text{ }MHz\] band, then the percent modulation is
  A)
  \[10%\] done clear
  B)
  \[25%\] done clear
  C)
  \[50%\] done clear
  D)
  \[75%\] done clear
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• question_answer84)
  A transmitter radiates \[10\text{ }kW\] of power with the carrier unmodulated and \[11.8\text{ }kW\] with the carrier sinusoidally modulated. The modulation factor is
  A)
  \[56%\] done clear
  B)
                     \[60%\] done clear
  C)
  \[72%\] done clear
  D)
         \[84%\] done clear
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• question_answer85)
  A modulated signal \[{{C}_{m}}(t)\] has the form \[{{C}_{m}}(t)=30\]\[\sin 300\pi t+10(\cos 200\pi t-\cos 400\pi t)\]. The carrier frequency \[{{f}_{c}},\] the modulating frequency (message frequency) \[{{f}_{\omega }}\] and the modulation index \[\mu \] are respectively given by :     
  A)
  \[{{f}_{c}}=200\,Hz;\,{{f}_{w}}=50\,Hz;\,\,\mu =\frac{1}{2}\] done clear
  B)
  \[{{f}_{c}}=150\,Hz;\,{{f}_{w}}=50\,Hz;\,\,\mu =\frac{2}{3}\] done clear
  C)
  \[{{f}_{c}}=150\,Hz;\,{{f}_{w}}=30\,Hz;\,\,\mu =\frac{1}{3}\] done clear
  D)
  \[{{f}_{c}}=200\,Hz;\,{{f}_{w}}=30\,Hz;\,\,\mu =\frac{1}{2}\] done clear
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• question_answer86)
  The T.V. transmission tower in Delhi has a height of\[240\text{ }m\]. The distance upto which the broadcast can be received. (Radius of earth is \[6.4\times {{10}^{6}}m\])
  A)
  \[60\,km\] done clear
  B)
                     \[100\,km\] done clear
  C)
  \[50\,km\] done clear
  D)
                     \[55\,km\] done clear
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• question_answer87)
  An audio signal consists of two distinct sounds: one a human speech signal in the frequency band of \[200\text{ }Hz\] to \[2700\text{ }Hz,\] while the other is a high frequency music signal in the frequency band of \[10200\text{ }Hz\] to \[15200\text{ }Hz\]. The ratio of the AM signal bandwidth required to send both the signals together to the AM signal bandwidth required to send just the human speech is:
  A)
  \[2\] done clear
  B)
  \[5\]      done clear
  C)
  \[6\] done clear
  D)
  \[3\] done clear
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• question_answer88)
  A signal of \[5\text{ }kHz\] frequency modulates a carrier of frequency \[1\text{ }MHz\] and peak voltage \[25\,V\]. If the amplitude at the side bands of the amplitude modulated signal is \[5V,\] then the modulation index is:
  A)
  \[0.8\] done clear
  B)
  \[0.6\]     done clear
  C)
  \[0.5\] done clear
  D)
  \[0.4\] done clear
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• question_answer89)
  Television signals on earth cannot be received at distances greater than 100 km from the transmission station. The reason behind this is that
  A)
  the receiver antenna is unable to detect the signal at a disance greater than 100 km done clear
  B)
  the TV programme consists of both audio and video signals done clear
  C)
  the TV signals are less powerful than radio signals done clear
  D)
  the surface of earth is curved like a sphere done clear
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• question_answer90)
  A carrier frequency of \[10\,kV\] at \[1\text{ }MHz\] is amplitude modulated by a \[1\text{ }kHz\] signal of \[6\text{ }kV\] peak voltage. When the modulation pattern is observed on a calibrated CRO, the voltage indicated by the CRO will be
  A)
  \[16\] done clear
  B)
  \[32\] done clear
  C)
  \[864\] done clear
  D)
  \[84\] done clear
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• question_answer91)
  Determine the modulation index and carrier swing of an FM carrier having a frequency deviation of \[56\text{ }kHz\] and a modulating signal of\[8\text{ }kHz\].
  A)
  \[9,\,\,580\,kHz\] done clear
  B)
  \[3,\,101\,kHz\] done clear
  C)
  \[7,112\,kHz\] done clear
  D)
  \[8,\,\,80\,kHz\] done clear
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• question_answer92)
  Given the electric field of a complete amplitude modulated wave as \[\vec{E}=\hat{i}{{E}_{C}}\left( 1+\frac{{{E}_{m}}}{{{E}_{C}}}\cos {{\omega }_{m}}t \right)\,\cos {{\omega }_{C}}t.\] Where the subscript c stands for the carrier wave and m for the modulating signal. The frequencies present in the modulated wave are
  A)
  \[{{\omega }_{C}}\] and \[\sqrt{\omega _{C}^{2}+\omega _{m}^{2}}\] done clear
  B)
  \[{{\omega }_{C}},\,{{\omega }_{C}}+{{\omega }_{m}}\] and \[{{\omega }_{C}}-{{\omega }_{m}}\] done clear
  C)
  \[{{\omega }_{C}}\] and  \[{{\omega }_{m}}\] done clear
  D)
  \[{{\omega }_{C}}\] and \[\sqrt{{{\omega }_{C}}{{\omega }_{m}}}\] done clear
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• question_answer93)
  In optical communication system operating at \[1200\text{ }nm,\] only \[2%\] of the source frequency is available for TV transmission having a bandwidth of \[5\text{ }MHz\]. What is the number of TV channels that can be transmitted?
  A)
  1 million done clear
  B)
  50 million done clear
  C)
  1 thousand done clear
  D)
  50 thousand done clear
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• question_answer94)
  The velocity of all radio waves in free space is \[3\times {{10}^{8}}m/s.\] What the frequency of a radio wave of wavelength is \[150\,m\].
  A)
  \[5\,MHz\] done clear
  B)
  \[2\,MHz\] done clear
  C)
  \[0.5\,MHz\] done clear
  D)
  \[0\,MHz\] done clear
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• question_answer95)
  Maximum usable frequency (MUF) in F-region layer is x, when the critical frequency is \[60\text{ }MHz\]and the angle of incidence is \[70{}^\circ \]. Then calculate x.
  A)
  \[122\,MHz\] done clear
  B)
  \[216\,Hz\] done clear
  C)
  \[175\,MHz\] done clear
  D)
  \[75\text{ }Hz\] done clear
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• question_answer96)
  If \[{{E}_{c}}=20\,\sin \,{{10}^{5}}\pi t\] and \[{{E}_{m}}=10\,\sin \,400\,\pi t\] are carrier and modulating signals, the modulation index is:
  A)
  \[56\,%\] done clear
  B)
  \[30\,%\] done clear
  C)
  \[50\,%\] done clear
  D)
  \[48\,%\] done clear
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• question_answer97)
  The area of the region covered by the TV broadcast by a TV tower of 100 m height is (Radius of the earth \[=6.4\times {{10}^{6}}m\]).
  A)
  \[1.28\pi \times {{10}^{3}}k{{m}^{2}}\] done clear
  B)
  \[2\pi \times {{10}^{4}}k{{m}^{2}}\] done clear
  C)
  \[3.1\times {{10}^{4}}k{{m}^{2}}\] done clear
  D)
  \[6\pi \times {{10}^{4}}k{{m}^{2}}\] done clear
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• question_answer98)
  Determine the modulation index \[({{m}_{f}})\] and carrier swing (S) of an FM carrier having a frequency deviation of \[25\text{ }kHz\] and a modulating signal of\[5\text{ }kHz\].
  A)
  \[{{m}_{f}}=3\]  done clear
  B)
                                 \[{{m}_{f}}=5\] done clear
  C)
  \[S=80\,kHz\]      done clear
  D)
         \[S=60\,kHz\] done clear
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• question_answer99)
  Calculate the power developed by an amplitude modulated wave in a load resistance of \[100\,\Omega ,\] if the peak voltage of carrier wave is \[100\text{ }V\] and modulation index is \[0.4\].
  A)
  50 watt done clear
  B)
  54 watt done clear
  C)
  104 watt done clear
  D)
  4 watt done clear
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• question_answer100)
  The maximum range for the tropospheric transmission of radio wave of wavelength 3m using the transmitting antenna and receiving antenna of heights \[100\,m\] and \[60\,m\] respectively is
  A)
  \[8\,m\] done clear
  B)
  \[800\,m\] done clear
  C)
  \[8\,km\] done clear
  D)
         \[80\,km\] done clear
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