136. Armstrong modulator generates—

1. 1. AM signals
      
      

   
   
   

   2. FM signals
      

   
   
   

   3. PM signals
      

   
   
   

   4. None of these

   
   
   

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   Correct Option: B

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137. The most commonly employed system of communication for commercial radio broadcast in india is—
     

1. 1. FM
      

   
   
   

   2. PCM
      

   
   
   

   3. PM
      

   
   
   

   4. AM

   
   
   

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   Correct Option: D

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138. A de-emphasis circuit is used—
     

1. 1. prior to demodulation

   
   
   

   2. after demodulation

   
   
   

   3. to de-emphasise the magnitude of low frequency components.

   
   
   

   4. to boost the magnitude of high frequency.

   
   
   

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   Correct Option: B

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139. The pre-emphasis circuit is used—

1. 1. after modulation.

   
   
   

   2. prior to modulation.

   
   
   

   3. to increase or emphasise the amplitude of low frequency components of the signal.

   
   
   

   4. None of these.

   
   
   

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   Correct Option: B

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140. In the spectrum of a frequency modulated wave—

1. 1. the number of significant sideband depends upon modulation index

   
   
   

   2. carrier frequency cannot disappear.

   
   
   

   3. carrier frequency vanishes when modulation index is large.

   
   
   

   4. None of these.

   
   
   

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   Correct Option: A

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