136. The function δ(2n) is equal to—

1. 1. δ(n)

   
   
   

   2. 	1	δ(n)
      	2

   
   
   

   3. 2δ(n)

   
   
   

   4. 2δ		n
      		2

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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137. An energy signal has F(ω) = 8. Its energy density spectrum will be—

1. 1. 64

   
   
   

   2. 16

   
   
   

   3. 32

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   As we know that energy density spectrum
   

   =		∞	|F(ω)|2dω
   		– ∞

   
   = 8²
   = 64

   Correct Option: A

   As we know that energy density spectrum
   

   =		∞	|F(ω)|2dω
   		– ∞

   
   = 8²
   = 64

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138. Two function f₁(t) and f₂(t) with cross correlation of 5 has a average power of 2 and 5 respectively the power of f₁(t) + f₂(t) is—

1. 1. 17

   
   
   

   2. 3

   
   
   

   3. 12

   
   
   

   4. √39

   
   
   

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1. View Hint View Answer Discuss in Forum

   Given
   P₁ = 2 [Power of function f₁(t)]
   P₂ = 5 [Power of function f ₂(t)]
   R_{1, 2} (τ) = 5
   Now, average power,
   P_{1, 2} = P₁ + P₂ + 2R_{1, 2} (τ)
   = 2 + 5 + 2 × 5
   = 17
   Hence, alternative (A) is the correct choice.

   Correct Option: A

   Given
   P₁ = 2 [Power of function f₁(t)]
   P₂ = 5 [Power of function f ₂(t)]
   R_{1, 2} (τ) = 5
   Now, average power,
   P_{1, 2} = P₁ + P₂ + 2R_{1, 2} (τ)
   = 2 + 5 + 2 × 5
   = 17
   Hence, alternative (A) is the correct choice.

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139. A causal LTI system is described by the difference equation—
     2y[n] = αy[n – 2] – 2x[n] + βx[n – 1]
     The system is stable only if—

1. 1. [α] = 2, |β| < 2

   
   
   

   2. |α| = 2, |β| < 2

   
   
   

   3. |α| = 2, | any value of β

   
   
   

   4. |β| > 2, any value of α

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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140. The impulse response h[n] of a linear time invariant system is given as
     

     h[n] =		– 2√2 , n = 2 – 1
     		4√2 , n = 2 – 1
     		0, otherwise

     
     If input to the above system is the sequence e^jπn/4, then the output is—

1. 1. 4√2 e^jπn/4

   
   
   

   2. 4√2 e^{– jπn/4}

   
   
   

   3. 4e^jπn/4

   
   
   

   4. – 4e^jπn/4

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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