21. If a time function contains highest components of whz, then it can be completely determined by specifying its ordinates at a series of points spaced every—
    

1. 1. 1	sec or less
      w

   
   
   

   2. 1	sec or less
      2w

   
   
   

   3. 1	sec
      w

      
      

   
   
   

   4. None of these

   
   
   

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   NA

   Correct Option: B

   NA

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22. The basic restriction on the reconstruction of a sampled signal is—
    

1. 1. The sampling must be in the form of impulse train
      

   
   
   

   2. The signal must be passed through low pass filter
      

   
   
   

   3. Both and
      

   
   
   

   4. None of these

   
   
   

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   NA

   Correct Option: C

   NA

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23. An FM signal with a deviation δ is passed through a mixer, and has its frequency reduced fivefold. The deviation in the output of the mixer is—
    

1. 1. 5δ
      

   
   
   

   2. Indeterminate
      

   
   
   

   3. δ

      5

      
      

   
   
   

   4. δ

   
   
   

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   NA

   Correct Option: D

   NA

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24. A pre-emphasis circuit provides extra noise immunity by—
    

1. 1. Boosting the bass frequencies
      

   
   
   

   2. Amplifying the higher audio frequencies
      

   
   
   

   3. Preamplifying the whole audio band
      

   
   
   

   4. Converting the phase modulation to FM

   
   
   

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   A pre-emphasis circuit provides extra noise immunity by amplifying the higher audio frequencies.

   Correct Option: B

   A pre-emphasis circuit provides extra noise immunity by amplifying the higher audio frequencies.

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25. Since noise phase-modulates the FM wave, as the noise sideband frequency approaches the carrier frequency, the noise amplitude—
    

1. 1. Remains constant
      

   
   
   

   2. Is decreased
      

   
   
   

   3. Is increased
      

   
   
   

   4. Is equalized

   
   
   

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   NA

   Correct Option: B

   NA

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