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

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.