DipIETE – ET (NEW SCHEME)   –   Code: DE57

Subject: NETWORKS AND TRANSMISSION LINES

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 the best alternative in the following:                                  (210)

a. An ideal voltage source has

(A) Zero internal resistance                   (B)  Infinite internal resistance

(C) Low internal resistance                   (D) All of above

             b. The Laplace transform of shifted unit step function f(t) = u(t-a) is given by: 

(A) (B)

                  (C) (D) None of above.

             c.  Thevenin’s theorem is valid for network containing only

(A) Linear elements                              (B) Non linear elements

(C) Reactive elements                           (D) None of above.

             d.  A network function is given by H(s) = . It would have a zero at:

(A) Real axis of s plane                         (B) At infinity

(C) Imaginary axis of s plane                 (D) At origin

             e.  In z-parameter representation if Z₂₁ = Z₁₂ then the network is:

(A) Bi lateral                                         (B) Symmetrical

(C) Balanced                                        (D) Inverse.                                                          

             f.   Higher the Q of series circuit,

(A) sharper its resonance                      (B) greater its bandwidth

(C) broader its resonated curve             (D) narrower its passband

              g.   In a R-L-C circuit the impedance is given by:

(A) Z = R-X_L+X_C (B) Z = R+X_L-X_C

(C) (D)

h.   Propagation constant in a lossless line is given by:

(A) L/C                                                (B) LC

(C) (D)

             i.   VSWR on short circuited lossless line is given by:

(A) Zero                                               (B) Infinity

(C) Unity                                              (D) None of above

             j.   Attenuators have

(A) gain and phase constant                  (B) attenuation constant

(C) gain only                                         (D) attenuation and phase constant

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

  Q.2     a.   What are different types of energy sources. Describe each briefly.                       (8)

             b.   Calculate the equivalent resistance of a given  network (Fig.2(b)) connected with a load of 100  and a supply voltage of 25 volts. Also find out the load current.                                                    (8)

  Q.3     a.   State and prove convolution theorem.   (8)

b.   Derive an expression for Laplace transform of unit impulse function.                    (8)

Q.4     a.   State superposition and maximum power transfer theorem.                                  (8)

             b.   Find out the current through the terminal resistance 1  at A and B using Thevenin’s theorem (Fig. 4(b))                                                               (8)

  Q.5     a.   Derive the relationship between the resonance frequency f_n and half power frequencies f₁ and f₂ in series resonant circuit.                                   (8)

             b.   A tank circuit is supplied by a current source having internal resistance as      50 k. If the constituents of the tank circuit are a 50 nF capacitor and a coil of resistance 30  and inductance 25 mH, find the frequency of resonance and Q factor.                                                                 (8)

Q.6     a.   What are different types of distortions in a transmission line? Discuss each briefly.               (8)

              b.   A telephone line has the following primary constant per km loop, R = 20 ,

                   L = 10 mH, C = 0.1 F and G = 10 mho. Find its characteristic impedance

                   at angular frequency of 5  10³ radians/sec.                                                       (8)

Q.7     a.   A transmission line with a characteristics impedance of 300  is terminated in purely resistive load. The minimum value of voltage is 5 V and maximum voltage is 7.5 V. What is the value of the load resistance?                                                            (8)

             b.   What is meant by impedance matching in transmission lines? Discuss briefly different impedance matching elements used.                                     (8)

  Q.8     a.   Design an L-attenuator to operate into a resistance of 500  and to provide an attenuation of 15 dB.                                                                   (8)

             b.   Design a constant K high pass filter having f_c = 4 kHz and design impedance R_o = 600  ( section).                                                                  (8)

Q.9     a.   Derive the expression for ABCD parameters in terms of Y parameters.               (8)

             b.   Check the stability of the following polynomial by applying Routh-Hurwitz criterion.

                           P(s) = s⁴+2s³+4s²+12s+10                                                                        (8)