26. A signal x (t) = 100 cos (2π × 10³) t is ideally sample with sampling period of 50 μ sec and then passed through an ideal low-pass filter with cut-off frequency of 15 kHz.
    Which of the following frequencies is/are present at the filter output?

1. 1. 12 kHz only
      

   
   
   

   2. 8 kHz only
      

   
   
   

   3. 12 kHz and 9 kHz
      

   
   
   

   4. 12 kHz and 8 kHz

   
   
   

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1. View Hint View Answer Discuss in Forum

   Given x(t) = 100 cos (24π × 10³t)
   Hence f_m = 12 kHz
   

   fs =	1	=	1
   	T		50 × 10−6

   
   

   =	1000 × 103	= 20 kHz
   	50

   
   given that the cut-off frequency of a LPF is 15 kHz. Therefore, the frequencies passed through LPF are f_m and f_s – f_m i.e., 12 kHz and 8 kHz, since given that LPF cut-off frequency 15 kHz.
   Hence alternative (D) is the correct choice.

   Correct Option: D

   Given x(t) = 100 cos (24π × 10³t)
   Hence f_m = 12 kHz
   

   fs =	1	=	1
   	T		50 × 10−6

   
   

   =	1000 × 103	= 20 kHz
   	50

   
   given that the cut-off frequency of a LPF is 15 kHz. Therefore, the frequencies passed through LPF are f_m and f_s – f_m i.e., 12 kHz and 8 kHz, since given that LPF cut-off frequency 15 kHz.
   Hence alternative (D) is the correct choice.

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27. The frequency generated by each decade in a direct frequency synthesizer is much higher than the frequency shown; this is done to—
    

1. 1. Reduce the spurious frequency problem
      

   
   
   

   2. Increase the frequency stability of the synthesizer
      

   
   
   

   3. Reduce the number of decades
      

   
   
   

   4. Reduce the number of crystals required

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: A

   NA

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28. Indicate the false statement. Noting that no carrier is transmitted with J3E, we see that—
    

1. 1. The receiver cannot use a phase comparator for AFC
      

   
   
   

   2. Adjacent-channel rejection is more difficult
      

   
   
   

   3. Production of AGC is a rather complicated process
      

   
   
   

   4. The transmission is not compatible with A3E

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: B

   NA

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29. One of the following cannot be used to demodulate SSB—
    

1. 1. Product detector
      

   
   
   

   2. Diode balanced modulator
      

   
   
   

   3. Bipolar transistor balanced modulator
      

   
   
   

   4. Complete phase-shift generator

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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30. A low ratio of the ac to the dc load impedance of a diode detector results in—
    

1. 1. Diagonal clipping
      

   
   
   

   2. Poor AGC operation
      

   
   
   

   3. Negative-peak clipping
      

   
   
   

   4. Poor AF response

   
   
   

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1. View Hint View Answer Discuss in Forum

   A low ratio of the ac to the dc load impedance of a diode detector results in negative-peak clipping.

   Correct Option: C

   A low ratio of the ac to the dc load impedance of a diode detector results in negative-peak clipping.

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