Questiom of TELECOMMUNICATION SYSTEMS (sem-5) -2009

                               TELECOMMUNICATON SYSTEM
                             CS/B.tech(ECE)SEM-5/EC-501/209-10
1. Choose the correct Alternative.
 (1) In modem uploading data rates always less then downloading data rates because
   (i) SNR (20db)is very low in communication channel.
   (ii) quantisation noise limits the channel data rates
   (iii) during uploading extra control bits are added with the data
   (iv) none of these.
 (2) the voice signal BW is 4 KHz and the Nyquist sampling rate is 8 KHz and time multiplexed space swiching 30 channel is to be multiplexed. the TS is
   (i) 4.16 micro sec (ii) 8.33 micro sec. (iii)125 micro sec (iv) none of these
 (3) MTTR means
   (i) Mean time to repair (ii) Maximum time to repair
   (ii) Most time to repair (iv) mean time to represent.
 (4) Blocking probability is
    (i) call congestion (ii) time congestion (iii) both (i) and (ii). (iv)none of these
 (5) GOS in india is
   (i)0.002 (ii) 0.02 (iii) 0.2 (iv) 2.
  (6) ISDN B-channel carries data and service at
    (i) 16 kbps (ii) 32 kbps (iii) 64 kbps (iv) 1.544 Mbps
 (7) Loudspeaker is an end instrument of
   (i)transmitter side (ii) receiver side (iii) both (iv) none of these
 (8) CHILL is a
    (i) CCITT language (ii) IEEE language (iii) IEE language (iv) ANSI language.
 (9) Attenuation can be reduced in subscriber loop by using
   (i) higher diameter in copper wire (ii) series of inductance in line
   (iii) lower diameter in copper wire (iv) serise of capacitance in line.
 (10) SDL stands for
    (i) software description language (ii) specification derived language
    (iii) specification description language (iv) sofeware derive language.
(11) A subscriber makes 3 calls of 3 mints , 4 mints, and 2 mints duaration in one hour period Calculate the subscriber traffic in Erlangs.
   (i)0.15 E (ii) 0.2E (iii)0.5E (iv) 0.7 E
 (12) In a  Strowger system the high value of CCI indicates
   (i) good design (ii) poor design (iii) no impact on design (d) none of these
                       GROUP - B
 Answer any three
 2 (a) What do you mean by point to point communication ?
   (b) Explain the disadvantages of this system
   (c) If the number of node in point to point communication is 770 , find out the total number of links required for total connevtivity.
3. (a) Show the GOS =  p b  , explain the meaning of the symbol.
   (b) Over a 20 minute observation interval, 40 subscribers initiate calls. Total duration of the calls is 4800 sec . calculate the load offered to the network by the sescribers and the average subscriber traffic.
4. What is call completion rate (CCR) ? 10000 subscribers are connected to an exchange , if the exchange is designed to achieve a CCR of 0.8 when the busy hour calling rate is 4.8 , calculate BHCA of the exchange.
5. What is BORSCHT function ? Why is this important in electronics exchange.
6. How many type of transmission medi are used in telecommunication ? What are the advantages of twisted pair cable over parallel wire cable ? what is step index fiber and graded index fiber?
                    GROUP -C
Answer any there
7 (a) assuming simultaneously forward and backward wave propagation in a transmission line. Derive the follwing general equation for the line,
    V=V1cos hrd +I1Z0sinhrd,
    I= I1coshrd+I1/Z0 sinhrd,
   Where V and I are the voltage and current respectively at a distance from a load end of the transmission line having characteristic independence Z0 and propagation constant r. the load end voltage and current V1 and I1respectively.
 (b) A loseless line has a characteristics impedance of 75 ohm and is terminated in a load of 300 ohms . find out the reflection cofficient and VSWR in the line.
  (c) explain the principle of DTMF dialing.
8. (a) what ia ISDN? Explain the transmission channel in ISDN?
   (b) what are the drawbacks of ISDN? how does B-ISDN overcome from this?
  (C) Write function grouping and reference point in ISDN.
9. (a) Explain centralized SPC and different modes of it.
(b) Explain distributed SPC and explain the different types of leve processing in it.
 (c) In the load sharing configuration of centralised SPC MTBF =2000 hours and MTTR =4 hours calculate the unavailability for single and dual processor system.
(d) Explain time division space switching.
10. What is DTE and DCE? Explain how data communication takes place between DTE and DCE using RS @#@C serial interface. why is conventional telephone modem down stream data rate 56 kbps? A telephone line has a bandwidth of 3000 Hz and SNR is 34 Db calculate the data rate of this line.
11. Write short notes on any three of the following.
(A) Packet switching
(b) ISDN systems interface.
 (c) Difference between circiut switch , packet swith and message swith
(d) Modems and standards
(e) facsimile transmission.

Microelectronic & optoelectronic quastion of 2007 ,4th sem ECE ,WBUT

Microelectronic and optoelectronic 2007 ,wbut 4th semester
GROUP-B
2. Derive the one dimensional continuity equation for minority carriers in generation recombination process, under low injection condition.Gn, GP, Rn and Rp are generation and recombination rates for electron/hole.
3. What is population inversion in laser? What is external quantum efficiency in a semiconductor laser? What is the optical feedback and oscillation by which the amplified coherent emission is obtained?
4. An n-type semiconductor at thermal equilibrium(T=300K) has a linear variation in doping concentration given by Nd(x)=1016-1919x, 0≤x≤1µm.Determine induced electric field. (volt equivalent temperature at room temperature =0.02V)
5. Discuss the principle of operation of vertical power BJT.
6. With energy band diagram describe schottky junction barrier formation . Describe its operation under external bias.
GROUP-C
7. (a) What is SCR? point out its major uses.
(b0 By using two transistor analog, briefly describe the operation of two terminal scr.
(c) Is it possible to observe the purpose of SCR by connecting two transistors? Explain.
(d) How does the presence of third terminal control the I-V response of SCR? Explain with system diagram.
8. (a) Sketch the ideal energy band diagram of a metal-semiconductor junction in which Фm<фs. Explin why this is an ohmic contact.
(b) Discuss how 2D-electorn gas is formed ain semiconductor heterojuction.
(c) the schottky barrier of a Si schottky junction is фBN=0.59v,the effective Richardson is A=111A/K2-cm2 and the crosssection area is a=10-4cm2
for T=100k, calculate
(i) Ideal reverse saturation current
(ii) The diode current for V (applied)=0.30V.
9. (a) Illustrate the basic process flow in micromanaging? What do you mean by optical lithography?
(b) What do you mean by plasma etching?
(c) Explain one non-lithographic microfabrication technology.
10. (a) What is the advantage of optical fibre over the copper wire system ?
(b) What is the difference between step index and graded index fibres?
(c) Distinguish between non-radiative and radiative recombination processes in a semiconductor .Express the internal quantum efficiency in terms of the life times of the process.
(d) Asilican optical fiber has a core refractive index of 1.5 and the cladding refractive index of 1.450 . calculate
(i) the critical angle for the core cladding interface.
(ii) the acceptance angle in air for fiber .
(iii) the nimerical aperture (NA) of the fiber.
11. Write short note on any three of the following
(a) Solar cell
(b) semiconductor laser
(c) Insulated bipolar junction transistor
(d) P-I-N photodiode
(e) O.E.I.C.

WBUT question of Analog communication 2007

2007
ANALOG COMMUNICATION
GROUP-B
2 (A) Define amplitude modulation and modulation index. Use a sketch of sinusoidally modulated AM waveform to help to explain the definition.
(b) Derive the expression between the output power of an AM transmitter and the depth of modulation.
3. What is angle modulation ? Justify that frequency modulation is an angle modulation.
4. drive the expression of single to noise ratio of DSB-SC system.
5.(A)What do you mean by FDM? when it is used?
(b) What is Carson's rile?
6. The equation for an FM wave is
S(t)=10sin(5.7×108t + 5sin12×103t)
Calculate:
(a) carrier frequency
(b) modulating frquency
(c) frequency deviation
(d) modulation index
(e) power dissipated in 100 ohm
GROUP-C
7.(a) What is the concept behind NBFM ? Drive its equation.
(b) Explain how FM can be generated using VCO.
(c) Discuss about the roles of pre-emphasis and de-emphasis circuit in FM
broadcasting.
8.(a) Draw the block diagram for generation and detection of PCM system.
(b) What is quantization? Find signal to quantization noise ratio for PCM system.
(c) A signal is sampled at Nyquist rate of 8 kHz and is quantized using 8 bit uniform quantizer. Assuming SNRq for a sinusoidal signal, calculate bit rate, SNRq and BW.
9 (a) State and prove parseval's power theorem.
(b) Describe with a block diagram the principle of operation of a square low modulator generating DSB-SC.
(c) Explain the advantages and disadvantages of modulation.
10 (a) Draw the block diagram of a superheterodyne receiver and explain its working principle .
(b) Explain the operation of balanced modulator.
11 Write short notes on any three of the following :
(a) Entropy and its properties
(b) QCM
(c) termal noise
(d) power spectral density function
(e) pulse coded modulation

Question of WBUT Analog circuit of 2008 4th sem ECE

hi my friends form 3rd june B.TECH exam of WBUT is start ,so i going to post the Question paper of 2008 of ECE 4th sem .i try to post the question paper before exam.so today i am posting the question of anlog circuit of 4th sem because the frist exam is analog circuit on 4th june.
the Question is as follows(objective question are not given)
QUESTION of 2008
GROUP-B
2. Draw and explain half wave rectifier.
3. compare between class A,class B,and class AB amplifier.
4. what is the advantages and disadvantages of feedback in amplifier?What are the type of feedback required for (i) voltage amplifier (ii) current amplifier?
5. Draw and explain the operation of Hartley oscillator.
6. What is clipper?with help of circuit diagram and wave forms,describe the operation of a positive and negative clipper.
GROUP-C
7 (a) Draw and explain briefly the circuit of single stage current series feedback amplifier . Mention effect of negative feedback on gain and bandwidth.(b) Write down the barkhausen criterion for sinusoidal oscillation.Obtain expression for output frequency and condition to sustain oscillation of a RC phase shift oscillator.
(c) What are the advantages of differential amplifier?
8 (a) a numerical problem form op-amp.
(b) Write down the criteria of good instrumentation amplifier. Draw the circuit of an instrumentation amplifier using a transducer bridge and explain its operation.
(C) Realize multiplier using logarithmic amplifier. Mention application of analog multiplier.
9 (a) Draw the circuit and explain voltage to current converter (Grounded load) .
(B)Explain the Op-Amp integrator circuit .
(c) What is voltage follower ?
10. (a) what is function of voltage regulator ?
(b) Give and explain the important parts of series regulated power supply using discrete component.
(c) Draw the function diagram of 723 regulator.
11.Write short notes on any three of the follwing.
(A) Push pull amplifier
(B) Wein bridge oscillator
(C) Bridge rectifier
(D) clamping circuit
(e) Logarithmic amplifier.
this is question of 2008
bast of luck for sem.

ouestion for WBUT upcoming exam 4th sem ECE

Analog Electronics & Circuits
EC-401
Time:3 Hours TotalMarks-70

Group-A

Answer any ten questions 10 x 1= 10

1.i) In a full wave rectifier if the input frequency is 50 Hz then frequency at the output of the filter is
(a) 50 Hz (b)75 Hz (c) 75 Hz (d) 0 Hz

ii) To obtain high input and output impedance the type of the feedback amplifier is (a)Voltage series (b) Current series (c) Voltage shunt (d) Current shunt

iii) An OP-AMP has gain bandwidth product of 1 MHz and a voltage gain of 20 dB .Then the -3dB bandwidth of the OP-AMP will be
(a) 50 kHz (b) 100 kHz (c) 1000/17 (d) 1000/7.07

iv) Wide range of high purity sine wave can be generated by
(a) RC-phase shift oscillator (b) Crystal oscillator (c) Wein bridge oscillator d) Hartley oscillator

v) The slew rate of an OP-AMP is 0.5V/μs.The maximum frequency of a sinusoidal input of 2Vrms that can be handled without excessive distortion is
(a) 3 kHz (b) 30 kHz (c) 200 kHz (d) 2 MHz

vi) In order to generate a square waveform from a sinusoidal input signal the choice of the circuit is
(a) Schmitt trigger (b) Clipper and amplifier (c) Monostable Multivibrator (d) Both a and c

vii) An increase in the ambient temperature means that maximum power rating of the transistor
(a) will increase (b) will decrease (c) may increase or decrease (d) may increase or remain the same.

viii) The threshold voltage of an n channel enhancement mode MOSFET is 0.5 ,when the device is biased at a gate voltage of 3V,pinch of will be occur at a drain voltage of
(a) 1.5 V (b) 2.5 V (c) 3.5 V (d) 4.5 V

ix) Stability factor (S) for a fixed bias circuit is given by
(a) 1+β (b) 1-β (c) 1/β (d) β-1

x) For maximum unclipped output from a CE amplifier , the Q point should be
(a) at the centre of the DC load line.(b) at the centre of the AC load line (c) at the centre of the collector current (d)none of these.

xi) A CB amplifier has re =6 ohm, RL =600 ohm and α= 0.98.Voltage gain is
(a) 100 (b) 588 (c) 98 (d) 6

xii) For high frequency response of a transistor amplifier suitable model to use is
(a) Lattice network (b) Hybrid-π (c) T-network (d) Kelvin network


xiii) The period of oscillation of a symmetrical multivibrator depends upon the discharging time constant and is roughly given by
(a) T=1.4RC (b) T=RC/14 (c) T=1.4 √(RC) (d) T= √(1.4) RC

Group-B

Answer any three questions 3 x 5= 15

2. a) Define the term thermal resistance for a power transistor.
b) A Ge transistor has thermal resistance of its junction as 0.33oC/mW and the ambient temperature is 28 oC.Calculate : (i) maximum power dissipation that can be allowed without heat sink, and (ii) ) maximum power dissipation that can be allowed if a heat sink is used,which reduces the thermal resistance of the transistor to 0.09 oC/mW.
2+3=5
3.Draw the Ebers-Moll model of an npn transistor and find out the expression of the transistor terminal currents.
2+3=5
4.An amplifier has a gain A= 60 dB and output impedance of 12 K. It is required to reduce the output impedance to 500 ohm. Calculate the negative feedback required.
5
5.Find out the expression of the stability factor for a voltage divider biased amplifier.
5
6.a)What will be the shape of the output for the following circuit














b) Find out the expression of ripple factor for a half wave rectifier.
2+3=5


Group-C


Answer any three questions 3 x 15= 45

7.a) What are the differences between voltage and power amplifiers ? Why heat sink is used ?
b) Find out the expression of collector efficiency of a class-A amplifier.
c) An crystal has equivalent series inductance L= 3 H and series capacitance C=0.05 Pf and mounting capacitance Cm=10 pF. Calculate the series and parallel resonant frequencies for the crystal.
(4+2)+4+5=15
8.a)Draw a circuit of differential amplifier with an active load connection.
b)What are the advantages of differential amplifier ?
c)Find out the transconductance of the above amplifier.
d) Explain with diagram the operating principle of 555 timer. 3+2+4+6=15
9. a) Draw the circuit of an instrumentation amplifier and find out the expression of Vo.
b) What will be the transfer function of the following circuit. What type of filter it is ?

c) What are the applications of tuned amplifiers ?(2+4)(6+1)+2=15
10.a)Draw the I-V characteristics of a CE configuration transistor
b) What do you mean by early-effect.
c) Show that a transistor can be used as an inverter.
d) Analyze the transistor amplifier (shown below in the figure)using small signal equivalent circuit. Given β = 100.
2+1+4+8=15
11. Write short notes on any of the three from the following given below:
3x5=15
a) Photodiode
b) Wein bridge oscillator.
c) Bistable multivibrator.
d) Enhancement type MOSFET.
e) Schmitt trigger.
i am not able to post the corresponding figure of some question.
this is a question set for upcoming exam of WBUT .

analog circuit question

short note 2005
1.logarithimic amp..,,2.freqency 2 voltage converter,,,3.voltage controlled osci llator..4.level shifting ckts…
2004
1.cross over distortion….2.constant current source…3.switched mode power supply….4.v-i…&i—v converters….
2003
1.bias compensation…2.precision rectifier…
2008
Push pull amp,,,wien bridge oscillator,,,bridge rectifier,,,clamping ckt,,,transistor can act as a switch,,,
Operational amp…differential amp..
2003….draw d differential amp ckt diagram using BJT & obtain d expression 4 its differential voltage gain???
Wat is d significance of CMRR in differential amp???enlist d charectiristic of an ideal op amp??draw d block diagram showing different stages of an op amp????virtual grnd??logarithimic amp/???
2004
Obtain d expression 4…1.short ckt current gain..2. fT(T suffix) 4 a CE amp using hybrid I-I(pie ) model??
D following low parameters r known 4 a given transistor at room temp & at Ic(c suff)=10 mA & Vce =10V hie =500ohm : hoe=4 x 10^-5;hfe=100;hre=10^-4
(cont)At same operating pt fT=50Mhz Cob=3pF.compute d value of all hybrid I-I (pie) parameters…
3.wat r d criteria of good instrumentation amp????draw d ckt dia of instrumentation amo using a transducer bridge..explain its operation,,,,
2005
3.wat r d disereble properties of an ideal OPAMP????explain d operation of basic differential amp????
Describe d steps 4 building of ins amp 4m d basic diff amp????
4.draw d ckt dia of a voltage 2 cur converter & explain its operation?????
2005….8.a. wat is Miller Effect???b.when it is a factor 2 take into consideration???c.wat effect does it have on high frequency gain??
b.Draw d current Mirror ckt& explain it’s operation??c.Why Willson current source is better than d current mirror ckt????
7.a. wat r d merits of SMPS over regulated power supply????b.with d help of neat ckt dia briefly explain d operation of a SMPS????c..Numerical transistor shunt regulator…
1.a .Draw & explain in ckt which uses a diode 2 compensate 4 changes i>in VBE ii>in ICO..
Explain d conseqense of Early Effect (base width modulation)….
2.a. wat is non linear distortion????why does such distortion occur in amp????
b.explain why even harmonies r not present in a push –pull amp…c.a single turn transistor amp used 2 ampfy modulate RF carrierof 600KHz& band width of 10khz.d ckt has a total o/p rest of 20kohm…Cal d value of inductance & capacitance of a tuned ckt????

WBUT question of EM Theory

2004

1. (a) the unit of electrical flux density is

(b) A transmission line of length λ/4 shorted at far end behavers like

(c) Impedance inversion may be obtained with a

(d) A transmission line is terminated by a pure capacitor, the VSWR in the line is

(e) UHF radio wave propagate as

(f) The radiation resistance of an antenna is the

(g) The standard reference antenna for the directive gain is the

(h) The pointing vector gives the

(i) Which of the following layers persists at night?

(j) For satellite communication, the frequency, should be

2. (a) Wright the Maxwell’s equation for time varying electromagnetic field, when the medium is homogenous, source free, lossless, isotropic and linear. Explain the properties of the parameters of the medium.

(b) Electric field component of a propagating electromagnetic wave in free space are gives as

W_x=E_z=0 and E_y=E_ocos(wt-B_z)

Determine the field components of the magnetic field.

3. (a) Define and explain the line parameters of a transmission line. Indicate the units of these parameters.

(b) Derive the expression of input voltage and input current in term of output voltage and output current and the relative parameters of line.

4. (a) Explain what is meant by retarded vector potentials ? Derive the expression for far field components of electrical and magnetic fields due to a current element ID1.

(b) Explain the terms: Gain; Effective aperture; Radiation resistance of an antenna.

5. (a) Assuming flat earth, derive the expression of the electrical field received by a antenna from a transmitting antenna radiating a signal of P watt a UHF . Assuming also that the earth is a good conducer and height of the antenna (h₁ andh₂) are significantly less than their distanced.

(b) Wright a short note on duct propagation.

6. (A) derive the expression of input impedance Z in of a lossless transmission line in terms of relevant parameters, when the line is terminated in a load impedance Z_L .

(b) Give s neat sketch of variation of Z in as a function of the electric length of the line, when the line is terminated in a (a) short circuit and(b) open circuit, Discuss the significance of the plots .

7. (a) Explain the inconsistency present in the Ampere’s law. How the law is modified by Maxwell? Explain.

(b) Establish the expression of the frequency at which the conduction current equals to displacement current within an unbound medium. Find the frequency for a medium having σ=5.0 S/m and Є_r=1.

WBUT question of EM theory 2005

2005

1. Define the following terms connected with sky wave propagation: Virtual height, critical frequency, skip distance and Fading.

2. Write the definition of (i) Isotropic antenna, (ii) Beam width. Show that the directive of an elemental antenna is 1.5.

3. Explain the effect of ground on the propagation characteristics of radio wave in the medium and shout wave bands.

4. Why did Maxwell introduce the concept of displacement current? Explain how the vector potential equation was subsequently modified by this concept.

5. What is meant by Magnetic vector potential? How is circularly polarized EM-wave produced?

6. Given E=A_y[10cos(10⁶t-B_y)], at a point in air ,find H and the pointing vector at that point.

7. State Faraday’s laws of electromagnetic induction and express the same in differential form as used in Maxwell’s electromagnetic field equation.

8. Starting form Maxwell’s field equation in their differential form, prove that the pointing vector gives the power flow per unit area of cross section, at a point in the medium of propagation.

9. Calculate the amplitudes of the reflected and refracted waves in terms of the incident wave amplitude assuming plane monochromatic waves incident normally on the boundary surface between two dielectrics.

10. Starting from the expressions of electrical and magnetic fields due to a short dipole, derive an expression of its radiation resistance.

11. Derive the expression for radiation resistance of elemental dipole antenna.

12. Starting with Maxwell’s equation derive the equation.

∆²E=ЄH∂²E/∂²t +ЄH∂²E/∂²t

For a linear, homogeneous isotropic medium characterized by Є, σ and μ where the symbols have their usual meaning.

13. Show that the ratio of the electrical magnetic magnetic field of a uniform plane wave is a constant depending upon the medium and that the electrical and magnetic fields are perpendicular to each other.

14. A long cylinder of radius a and length L carries a uniform magnetization M parallel to its axis .the cylindrical magnet passes at constant velocity V through a circular ring of slightly larger diameter. Graph the emf induced in the ring as a function of time giving reason thereof.

15. Explain what are meant by

(i) Surface wave

(ii) Ground wave

WBUT question of EM theory of 4th sem

2006
Group-B
2(a). What do you mean by self inductance?
(B). A 3 cm long solenoid carries a current of 400mA. IF the solenoid is to produce a magnetic flux density of 5 mWb/m², how many turns of wire are needed?
3 (a) State Ampere's circuit law.
(b) A hollow conducting cylinder has inner radius a and outer radius b and carries current I along the positive Z-direction .Find H everywhere.
4(a) States Faraday's law. From the fundamental principle establish the relation

∆×B= -∂B/∂t

5. What do u you mean by effective height of an antenna? Calculate it for linear and sinusoidal distribution of current.

6. what do you mean by skin effect? Calculate the skin depth for radio waves of wavelength 3 m (in free space) in copper, the electrical conductivity of which is 6×10⁷ s/m.

Group C

7(a) Write the maxwell’s equation for time varying electromagnetic fields, when the medium is homogeneous, source free, loss less, isotropic and linear. Explain the properties of the parameters of the medium.

(b) Explain the inconsistency present in the Ampere’s law. How is the low modified by Maxwell?

8(a) Derive the expression of input impedance, Z_in of a lossless transmission line in terms of relevant parameters, when the line is terminated in load impedance, Z_L.

(b) Give a neat sketch of variation of Z_in as a function of electrical length of the line, when the line is terminated in a (i) short circuit and (ii) open circuit. Discuss the significance of the plots.

9(a) Explain the mechanism for tropospheric scatter propagation.

(b) What is radio horizon?

(c) Derive the expression for critical frequency for sky wave propagation.

10(a) Explain the formation of standing wave pattern on transmission line.

(b) Deduce the relation between the reflection co-efficient and VSWR.

(c) A 70Ω lossless line has S=1.6 an θ_k=300⁰. If the line is 0.6λ long, obtain

(i) K, Z_{L, ,} Z_in (ii) the distance of the first minimum voltage fro

11 Find the relationship between the effective aperature and directivity of an antenna. Show that the effective aperture for isotropic antenna is 0.079 λ². Derive an expression for the Friis formula in communication system.

m the load.