Code: DE - 12                                                   Subject: COMMUNICATION ENGINEERING

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                         (2x10)

a. The bandwidth of speech signal used for AM broadcasting is

(A)  5 KHz.                                         (B)  20 KHz.

(C)   3.1 KHz.                                     (D)  None of above.

b. UHF range of frequencies extends from

(A)  3 MHz to 30 MHz.                     (B)  300 MHz to 3 GHz.

(C)  3 GHz to 30 GHz.                        (D)  None.

             c.   The wavelength for a signal of frequency 100 KHz is  

(A) 300 Km.                                      (B)  3 Km.

(C)  30 m.                                           (D)  None.

             d.   The temperature of resistor creating thermal noise is doubled.  The noise power generated is 

(A)  Halved.                                       (B)  Doubled.

(C)  Quadrupled.                                (D)  Unchanged.   

             e.   If amplitude of the carrier wave is 100V and is modulated to 50%, the amplitude of the sidebands will be 

(A) 50 V.                                           (B)  12.5 V.

(C)  25 V.                                           (D)  0.5 V.

             f.    Antenna commonly used for microwave links are

(A) Loop antenna.                              (B)  Parabolic antenna.

(C)  Yagi-Uda antenna.                       (D)  Rhombic antenna.

             g.   The geo-stationary satellite is located above earth at about

(A) 36000 Km.                                  (B)  9600 Km.

(C)  6400 Km.                                    (D)  None.

             h.   Which colour TV system is used in India

(A) NTSC.                                         (B)  SECAM.

(C)  PAL-D.                                       (D) None.

             i.    The magnitude of reflection co-efficient on a transmission line lies in the range

(A) 0 to 1.                                          (B) 0 to 100.

(C) 1 to .                                         (D) 0 to .

             j.    Which scanning is used in TV

(A)  Progressive.                                 (B)  Interlaced.

(C)  A & B.                                         (D)  None.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   What is noise?  Explain various sources of noise.                                                (8)

             b.   Two resistors of 5  and 20  are at .  Find the thermal noise power and voltage for a 10 kHz bandwidth

(i) for each resistor.

(ii) for their series combination.                                                        (8)

Q.3     a.   What is amplitude modulation?  Derive an expression for amplitude modulated wave.                      (8)

             b.   An AM transmitter with an unmodulated carrier power is  modulated simultaneously by three modulating signals with , find

(i) Effective modulation index.

(ii) Upper and lower sideband power.

(iii) Total transmitted power.                                                                        (8)

Q.4     a.   State advantages & disadvantages of SSB transmission.                                      (8)

b.   Explain working of ratio detector using a circuit diagram.                                     (8)

Q.5     a.   What is pulse width modulation?  Explain briefly.                                                (8)

     b.   Draw and explain block diagram of PLL.                                                            (8)

  Q.6     a. What is a forward error correcting code? How do such codes function? Explain with an example.                                                              (8)

             b.   Explain waveguide excitation.                                                                             (8)

Q.7     a.   Explain how ionosphere is formed?  Discuss different layers and their importance.               (8)

b.   Explain following terms for antenna

(i)   Directive gain.                               (ii)   Resistance.

                   (iii) Bandwidth.                                    (iv)  Beam width.                                    (8)

Q.8     a.   What are the different types of linkages used in satellite communication?              (8)

             b.   Explain propagation of light through optical fibre.                                                (8)

Q.9     a.   Write short note on FDM.                                                                                  (8)

b.   Describe the operation of Horn antenna.                                                             (8)