51. The most commonly used system of modulation for telegraphy is—

1. 1. on-off keying.
      

   
   
   

   2. frequency shift keying
      

   
   
   

   3. pulse code modulation
      

   
   
   

   4. differentiating the PPM signals.

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Refer synopsis

   Correct Option: A

   Refer synopsis

---

52. Armstrong modulator generates—

1. 1. AM signals
      
      

   
   
   

   2. FM signals
      

   
   
   

   3. PM signals
      

   
   
   

   4. None of these

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Refer synopsis

   Correct Option: B

   Refer synopsis

---

---

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

1. 1. FM
      

   
   
   

   2. PCM
      

   
   
   

   3. PM
      

   
   
   

   4. AM

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Refer synopsis

   Correct Option: D

   Refer synopsis

---

54. 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.

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Refer synopsis

   Correct Option: B

   Refer synopsis

---

---

55. 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.

   
   
   

---

1. View Hint View Answer Discuss in Forum

   Refer synopsis

   Correct Option: B

   Refer synopsis

---