DipIETE – ET (OLD SCHEME)

 

Code: DE07                                           Subject: NETWORKS AND TRANSMISSION LINES

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:                                  (210)

       

             a.  An RLC circuit has a resonance frequency of 120 kHz and Q- factor of 120. Its bandwidth will be

 

                  (A) 1 Hz                                               (B) 1 kHz

                  (C) 100 kHz                                         (D) 120 kHz

 

             b.  Which of the following theorem enables a number of voltage (or current)

                  source to be combined directly into a single voltage (or current source).

 

                  (A) Compensation theorem                   (B)  Reciprocity  theorem

                  (C) Superposition  theorem                   (D) Milliman’s theorem

 

             c.  The  reflection  co-efficient of the simplest standing wave is

 

                  (A) 0                                                    (B)  1

                  (C) –1                                                  (D) infinity

 

             d.  A transmission line  of characteristic impedance 75 ohms is to be connected to  a load of impedance ( 150+j0) W using a quarter wavelength transformer. The required characteristic impedance of the transformer for the perfect matching would be

 

                  (A) 420 W                                            (B) 315 W 

                  (C) 276 W                                            (D) 106 W

 

             e.  In a series resonance circuit at resonance

 

                  (A)                                       (B)   

                  (C) L2C2 =1                                     (D) L2C2 =1

 

             f.   A two-port network is reciprocal or bilateral provided

 

                  (A) Z11 =  Z22                                       (B) Z11 =  Z12

                  (C) Z12 =  Z21                                       (D) Z21 =  Z22

 

             g.  A function is given by H(s)=  it will have zero at

                                                 

                  (A) infinity                                            (B) anywhere  on the s-plane

                  (C) on the imaginary axis                       (D) on the origin

 

       

             h.  Laplace transform of  a function f(t)  is given by

 

                  (A)                                     (B)

                  (C)                                  (D)

 

             i.   If the characteristic impedance is 314 ohms and cut off frequency is 1000 Hz. Which of the following design is correct, for a low pass prototype filter.

   

                  (A) L=10 mH, C=10 mF                      (B) L=50 mH, C=20 mF

                  (C) L=100 mH, C=1.015 mF               (D) L=500 mH,C=1mF

 

             j.   If P1 and   P2    are the input and output powers, the attenuation in dB of the network is given by

 

                  (A) P1/ P2                                             (B) log10 P1/ P2

                  (C) 10 log10 P1/ P2                                (D) 20 log10 P1/ P2

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

 

  Q.2     a.   Write short note on Unilateral and Distributed elements.                                      (4)

                  

             b.   A resistance R and  5mF capacitor are connected in series across a 100 V d.c supply. Calculate the value of R such that the voltage across the capacitor becomes 50 V in 5 sec, after the circuit is switched on.                                                           (6)

 

c.   Two capacitors A and B have capacitance of 100 mF and   50 mF respectively.

 

                   (i )  A and B  are connected in series and fed from 240 V d.c source. Find           VA and VB and total energy stored.


(ii)  A and B  are connected in parallel  across a  240 V d.c source. Find         energy   stored.                                                                  (6)

 

 

Q.3      a.   Draw  an asymmetrical  T- Network  whose series impedances are                   

                  Z1 = 400W,  Z2 =  800W, and shunt impedance is   Z3 = 1200W. Find

 

(i)     The image impedance of the network.

(ii)  What should be the value of terminating impedance to obtain                 impedance matching?                                                                  (8)

 

            b.   Explain the concept of Voltage Standing Wave Ratio (VSWR). What are the uses of half wave  in transmission lines?                                (2+4+2)

                             

  Q.4     a.   Find the inverse Laplace transform of

 

                   (i)

                   (ii)                                                                                   (4+4)

 


             b.   The response of a circuit to a unit impulse is . Find the response for an input v(t)=e-2t using convolution.                                                                                                                         (8)

            

Q.5    a.    A two port network is terminated by a load impedance ZL at port 2. Find driving point impedance at port1 in terms of                                               (8)

 

(i) Z parameters    (ii)  Y parameters   (iii)  ABCD parameters

 

             b.   Obtain the expression for the steady state response of circuit containing resistor R, inductor L and capacitor C.  The voltage applied to the circuit is .                                                (8)

                  

Q.6      a.    In the network shown below. Find

 

 (i) The value of resistance RL which should be connected

           across ab so that maximum power  will be delivered to it.

     (ii)  Maximum power

                   (iii)  Total power delivered by the source.                                                           (8)

Text Box:
 

b.      State Superposition theorem. Apply this theorem to find the voltage

                            VAB in the circuit shown below:-                                                                (8)

 

Text Box:

 

 

 

 

                                                                                                                                                                                                                                                                                            (iii)  When RL is adjusted for maximum power transfer, what percentage of power delivered by 360 V source reaches RL.                               (8)

 

       

 

 

 

 

  Q.7     a.   What are the properties of series resonance circuit. Show that the condition for resonance in a parallel RLC circuit is same to that of a series RLC circuit.                                                                      (2+6)

 

             b.   Find the resonance frequency of a series RLC circuit where R= 2.5W,       L= 25mH and C= 50mF. Evaluate Q factor also.                         (8)

 

  Q.8     a.   A transmission Line with characteristic impedance of 300 W is terminated in a purely resistive load. It is found by measurement that the minimum value of voltage upon it is 5mV and maximum voltage is 7.5mV. what is the value of the load resistance.                                                               (8)

 

             b.   Explain the Types of distortions in a transmission line. Derive the   condition for minimum distortion.                                                                       (4+4)

                                                                             

  Q.9     a.     For a symmetrical T attenuator, if the ratio of input to output power is 5.2 and      

                      load impedance is 300 W. Calculate:-

 

                   (i)   Series and shunt arm impedance.                                                                               (ii)  The attenuation in dB                                                                                             (8)

 

             b    Classify  filters  and draw  attenuation versus frequency  characteristics of all  filters.            (8)