AMIETE – ET (OLD SCHEME)

 

Code: AE15                                                      Subject: COMMUNICATION ENGINEERING

Flowchart: Alternate Process: JUNE 2010Time: 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:                                  (210)

 

      a.     The autocorrelation function of white noise is

 

(A)    Gaussian                                      (B)  Constant

(C)  Sinusoidal                          (D)  A delta function

           

  1. The channel capacity under the Additive White-Gaussian noise environment for a discrete memoryless channel with bandwidth of 4 MHz and SNR of 31 is 

 

(A) 20 Mbps                                        (B) 40 Mbps   

(C) 124 Mbps                                      (D) 10 Mbps.

 

  1. An image uses 512512 picture elements. Each of the picture elements can take any of the 8 distinguishable intensity levels. The maximum Entropy in the above image will be

 

(A) 262144 bits                                    (B) 784332 bits

(C) 32768 bits                                      (D) 64000 bits

 

  1. Aperture effect distortion is related with            

 

            (A) Ideal Impulse-train sampling            (B) Natural sampling

(C) Flat-top sampling                            (D) Pulse-width Modulation

 

  1. In a block code, for correcting t errors, the Hamming distance, dmin, should satisfy:

 

            (A) t dmin                                          (B) dmin   t dmin +2

            (C) 2t+1dmin 2t+2                         (D) 2tdmin2t+1

 

  1. The Ring Modulator is used for the  generation of

 

            (A) SSB-SC signal                               (B) DSB-SC signal      

(C) FM signal                                       (D) AM signal

 

 

 

  1. In a stereophonic FM broadcasting system, the  pilot carrier frequency is     

 

            (A) 15 kHz                                           (B)  75  kHz    

(C) 10.7  MHz                                     (D) 19 kHz

 

h.   The COHO in MTI radar operates at the  

 

(A) intermediate frequency                    (B)  transmitted frequency

(C) received frequency             (D)  pulse repetition frequency

 

       i.     Equalizing pulses in TV are sent during      

 

(A)   Horizontal blanking                       (B)  Vertical blanking

             (C)  the serrations                                (D)  the horizontal retrace

 

      j.     An FM signal with a modulation index mf  is passed through a frequency tripler. The wave in the output of tripler will have a modulation index of

 

(A)    mf / 3                                          (B)  mf / 9

             (C)   mf                                               (D) 3 mf

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

 

Q 2.     a.  Derive an expression for the Equivalent noise resistance at the input of the first stage in a two-stage Amplifier.                                                                                                                                    (8)

 

             b.  Find the mathematical expression for representation of narrowband noise.                      (8)

 

Q 3.     a.  Make a block diagram of phase-shift method of SSB generation to generate the Upper Side Band and write the mathematical expression for a USB-SSB signal. Assume modulating signal is m(t).    (8)

 

             b.  Calculate the percentage power saving when the carrier and one of the  sidebands are  suppressed in an AM wave modulated to a depth of (a) 100% (b) 50%.                                                         (8)

 

Q 4.     a.  What will happen if a PM signal is received by an FM receiver and vice-versa? Also describe the need of pre-emphasis and de-emphasis in an FM system.                                                           (8)

            

             b.  Describe the working of a basic reactance modulator for the generation of FM signal. Determine the value of the capacitor reactance obtainable from a reactance FET whose gm is 12 milli-Siemens. Assume that the gate-to-source resistance is one-ninth of the reactance of the gate-to-drain capacitor and that the frequency is 5 MHz.                                                                                                                         (8)

 

Q5.       a. Derive the expression for the signal-to-quantization noise ratio in a

                 PCM system.                                                                                                                 (8)

 

                 

 

             b.  Describe the working of a Delta-Modulator and derive the condition to avoid the    slope-overload error for sinusoid of amplitude A and frequency f.                                                                                         (8)

 

  Q6.     a. There are 8 possible messages m1 to m8 with probabilities as given        below:

 

                       Message          m1       m2       m3       m4       m5       m6       m7       m8

                       Probability     1/2       1/8      1/8      1/16    1/16    1/16     1/32    1/32

 

                       Generate a code for these messages using Shannon-Fano Algorithm.                         (8)

 

             b.  Describe the Hamming Code in brief.                                                                            (8)

                                                                                                                                                          

  Q7.     a.  Describe the operation of a CW Doppler radar. Can we use a CW radar for range measurement? Discuss.                                                                                                                           (8)

 

             b.  Write a short note on phased array radar.                                                                      (8)

 

  Q8.     a.  Make a composite TV video waveform at the end of an odd field and explain it.                  (8)

                                                        

             b.  Write a note on colour transmission and reception in a TV system.                                 (8)

       

  Q9.          Write short notes on:

 

(i)                  Spectrum and bandwidth of FM signal.                                                                 

(ii)                Adaptive delta-Modulation.                                                                                  

(iii)               Channel capacity of a Gaussion channel.

(iv)              Recovery of original signal from the samples                                                 (44)