AMIETE – ET (OLD SCHEME)

 

Code: AE15                                                      Subject: COMMUNICATION ENGINEERING

Flowchart: Alternate Process: DECEMBER 2009Time: 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 the best alternative in the following:                                   (2x10)

          

a.   Noise figure of a receiver is 1.6.  Its equivalent noise temperature will be

 

(A)    464 K                                          (B)  174 K

(C)  160 K                                           (D)  0.16 K

           

  1. A broadcast radio transmitter radiates 10 kilowatt, when the modulation percentage is 60.  The carrier power will be 

 

(A) 8.47 kilowatt.                                 (B) 6 kilowatt. 

(C) 600 kilowatt.                                  (D) 3.65 kilowatt.

 

  1. The FM wave is represented by the voltage equation .  The maximum deviation of the FM wave will be    

 

(A) 60 Hz                                             (B) 1250 Hz

(C)                                       (D) 995 Hz

 

  1. A signal f(t) is band-limited to 4 KHz.  The Nyquist rate for sampling of the signal  is given by       

 

            (A) 28 KHz                                          (B) 8 KHz                   

(C) 24 KHz                                          (D) 12 KHz

 

  1. The channel capacity of a Gaussian channel of infinite band width is given by (where S is the signal power and is the PSD of white noise)

 

            (A)                                      (B)           

(C)                        (D)

 

  1. For a (n, k) Block code, the generator matrix dimension is given by 

 

            (A)                                              (B)         

(C)                                              (D)

 

  1. For a continuous wave RADAR with transmit frequency of 5 GHz, the Doppler frequency seen by a stationary radar when the target radial velocity is                 100 Km/hour is    

 

            (A) 413 Hz                                           (B)  463.5 Hz  

(C) 927 Hz                                           (D) 500 Hz

 

h.   The pulse duration in a pulsed RADAR is sec.  The range resolution in this case is no better than

 

(A) 150 m                                            (B)  3 Km       

(C) 1.5 Km                                          (D)  300 m

 

       i.     The value of is (where  is the Bessel function of nth order and first kind)      

 

(A)     1                                                (B) 

             (C)                                                  (D)  0

 

      j.     The Hilbert transform of a signal f(t) is given by  

 

(A)                            (B) 

             (C)                             (D)

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

 

Q 2.     a.  Explain the working of Ring Modulator in detail.                                                            (8)

 

             b.  For tone modulation, determine the upper limit of RC time constant in an envelope detector.            (8)

 

Q 3.     a.  An angle-modulated signal with carrier frequency  rad/s is described by the equation  

(i)                  Find the frequency deviation .

(ii)                Find the deviation ratio .

(iii)               Find the phase deviation .

(iv)              Estimate the bandwidth of .                                                            (8)

 

             b.  Derive an expression for WBFM signal starting from first principle.  Also draw its spectrum for modulation index .                                                                                                              (8)

 

Q 4.     a.  Signals  and  are applied as the inputs of an ideal low-pass filters  and

 
 

 

 

 

 

 

 

 

 

 

 

 


                  The output  and  of these filters as shown in Fig.1 are multiplied to obtain the signal .  Find the Nyquist rate of  and .                              (10)

 

             b.  Explain the difference between Natural sampling and Flat-top sampling.                         (6)

 

  Q5.     a.  A zero-memory source emits messages  and  with probabilities 0.8 and 0.2 respectively.  Find the Huffman binary code for this source as well as for its second order extension.  Determine the code efficiencies in each case.                                                                                                                 (8)

 

             b.  For a (6, 3) code the generator matrix  is

                  .

                  The receiver receives .  Determine the corresponding data word if the channel is Binary symmetric channel and the maximum-likelihood decision is used.                                    (8)

       

  Q6.     a.  Derive the radar range equation and discuss the factors influencing maximum range.        (8)

 

             b.  Draw block diagram of a monochrome television receiver and explain its working.          (8)

                                                                                                                                                          

  Q7.     a.  Explain shot noise, thermal noise and white noise.                                                          (6)

 

             b.  Determine and plot the pdf of envelope of narrow band noise.                                        (6)

 

             c.  A receiver connected to an antenna whose resistance is  has an equivalent noise resistance of .  Calculate the receiver’s noise figure in dB and its equivalent noise temperature.                   (4)

 

  Q8.     a.  Explain the companding in a PCM system.  Also derive an expression for signal to quantization noise ratio in a PCM system.                                                                                                      (8)

 

             b.  Write a short note on FM stereophonic broadcasting.                                                    (8)

       

  Q9.          Write a short notes on:

 

(i)                  Relationship between Bandwidth and SNR for a communication system.                 (8)

(ii)                Need of modulation in a Radio transmission.                                                      (4)

(iii)               Slope overload distortion in DM system.                                                           (4)