SECTION-A
I . Determine the transmission matrix for the circuit shown and explain why open circuit impedance parameters can not be defined for this circuit. 12

<img src=".E:anuradhaCIVILS 2012CIVILS MAIN 2012images180-1a.jpg">


Using duality property show that the Fourier transform of <img src=".E:anuradhaCIVILS 2012CIVILS MAIN 2012images180-1a.jpg"> is equal to er where is the unit step.

A continuous time signal is given by
A cos (8000 1tt) cos (2000 1tt) 12
The signal is sampled with a sample period of 3x10--4 seconds. Can we recover the signal from the sampled version using an appropriate low pass filter 12
A lossless transmission line having a length of I00 metre is terminated by a resistive load of 200 ohms. It is fed by a generator of voltage volts and has impedance 100 ohms. If characteristic impedance of the line is 300 ohms, calculate the transmission loss and return loss in decibels. 12
Assuming ideal op-amps, determine the expression for the input impedance of the given circuit and a simple passive equivalent of the circuit looking into terminal

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-1e.jpg">

2. Show that there can be no value of RL in the circuit given in Fig. that will make it resonant. 20

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-2a.jpg">

A system consists of two blocks connected in cascade. The first block has impulse response h1 2u(t). The second block is shown below

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-2b.jpg">

Find the impulse response of the overall system using the relation
hi • hzCt). 20

Determine the output current of the Widlar current source; given that ± V ± 15 volts,
lc0 l0-14 amp., p 200, VT 25 mV. 20

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-2b.jpg">

3. Find Y and Z parameters for the following circuit

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-3a.jpg">

State Tellegen's theorem for network analysis. 20
A particular lossless material has µ 4 and E 9. A IO MHz uniform plane wave is propagating in the ay direction with Ex0 400 Vim and E E 0 at P(0·6, 0·6, 0·6) at t 60 ns.
Determine
<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-3b1.jpg">



20
Figure shows a sinusoidal oscillator. By an appropriate analysis, determine the condition of oscillation and frequency of oscillation in terms of circuit elements assuming ideal op-amps.

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-3c.jpg">

4. The block diagram of a discrete time LTI system is given below

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-4a.jpg">

Determine the transfer function 20
A 50 ohm lossless line connects a matched signal of 100 kHz to a load of 100 ohm. Load power is 1OO mW. Estimate
Voltage reflection coefficient of load.
VSWR of the load.
(iii)Position of first Vmin and Vmax
(iv)Impedance at Vmin and Vmax and values of Vmax and Vmin.

Define the terms Attenuation loss, Reflection loss, Transmission loss, Return loss and Insertion loss. 20

Explain the operation of the given circuit by sketching relevant waveforms assuming
that positive and negative saturation levels of output voltage of the op-amp comparator are V sat1 and V sat2 respectively and are not equal. Determine an expression for the frequency of the generated output voltage.

<img src="E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-4c.jpg">

SECTION-B
5. Show how a D flip-flop can be converted to SR flip-flop.
Convert decimal 65,535 to its hexadecimal and binary.
12
12
A 2-pole full pitch concentrated coil of n turns is placed in the stator of an electric machine in two slots diagonally opposite to each other. A permanent magnet 2-pole rotor is rotating at N rpm producing a flux per pole with its flux density sinusoidally varying in space in the airgap. At time t 0 rotor field axis is in line with the stator coil axis. Write an expression for the flux linking the stator coil as a function of time. Derive from this expression the r.m.s. value of the voltage induced in the stator coil. Draw the waveform of flux linkage and voltage generated. Write expression for frequency of voltage in terms of speed. 12
Draw the simplified circuit diagram for a voltage step-up DC-converter and show that when duty cycle is zero, the output of DC-converter is equal to source voltage whereas DC voltage is infinity if the duty cycle is unity. 12
Evaluate whether the following function given by expression

<img src=".E:anuradhaCIVILS 2012CIVILS MAIN 2012images/188-5e.jpg">

is a probability density function (PDF). 12

6. Indicate how many flip-flops are required to construct each of the following counters
mod-3
mod 6
mod-9. 20
Two winding 10 kVA, 500/50 V transformer is converted to an auto-transformer to obtain the rating of
550/50
500/550 and
500/450 V.
Compute the kVA rating of auto transformer for the above connections, VA transferred
conductivity and magnetically. 20
Consider a superhet receiver with fLo fe fIF, f1F 455 kHz, fc 2 MHz.
The RF amplifier is preceded by a first order RLC band pass filter with f0 2 MHz and B 0·5 MHz. Assume the IF-BPF is nearly ideal and mixer has unity gain. What is the minimum spurious frequency input rejection ratio in dB

If the above receiver has a LO with a second harmonic whose voltage level is half that of the fundamental component, determine what input frequencies will be accepted and at what power level in dB as compared to the correct input. 20
7. What would be the binary address for a memory system having a capacity of 1024 bits. For the above memory system, what is the decimal address for the binary address 10ll001lO1? What is the address in hexadecimal 20
Explain with diagram the soft starting of induction motor to start from zero speed to rated speed. Briefly compare with a star-delta starter used for the same purpose.
A 3-phase, 4-pole 50 Hz induction motor is controlled by a variable frequency inverter that maintains the ratio of voltage to frequency across the motor constant. Torque-speed curve in stable region is a straight line. It has a maximum torque of 2 p.u. and slip speed at maximum torque at all frequency is constant at 150 rpm. Draw a family of Torque speed characteristics (on a graph paper) at 10, 20, 30, 40 50 Hz with usual assumptions. It is driving a load whose torque is directly proportional to speed giving rated torque at 50 Hz. Graphically calculate speeds at all the above frequencies. 20
In an FM system, when the audio frequency is 500 Hz and AF voltage is 2·4 the deviation is 4·8 kHz. If the AF voltage is now increased to 7·2 what is the new deviation If the AF voltage is raised to 1O V while AF is dropped to 200 Hz, what is the deviation Evaluate modulation index in each case.
lf cos 200 1tt, determine AM transmission bandwidth BT and average transmitted power ST for the AM modulated signal assuming A c 1O and µ (modulation index) 0·6.
What will be the values of BT and ST in the case of DSB transmission 20
8. A d.c. shunt motor is driving a constant torque load. If the voltage across the motor is halved explain how the armature current and speed would be changed. 20
A 11 kV dc source having internal resistance of 1 ohm supplies 600 A to a 5 kV, 3 phase, 6-pulse 50 Hz inverter. Compute the

reactive power absorbed by the inverter,
effective value of the ac line current,
the required firing angle,
dc voltage generated by the inverter, and
dc current carried by each SCR.
12
0
20
A commercial FM radio station alternates between music and talk show/call in formats. The broadcasted CD music is band limited to 15 kHz based on convention.
Assuming D (deviation ratio)= 5 is used for both music and voice, what percentage of the available transmission bandwidth is used during the talk show if we take W 5 kHz for voice signals
An AM system with envelope detection has 30 dB under full load tone modulation condition with W 8 kHz. If all bandwidths are increased accordingly, while other parameters are held fixed, what is the largest usable value of W 20
14
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