ies practice papaer

28A/11, Ground Floor- Jia Sarai New Delhi 16 Ph.: 09811382221, 011-32662945 www.panaceainstitute.org.in 1

DO NOT OPEN THIS TEST BOOKLET UNTIL YOU ARE ASKED TO DO SO

Test Booklet Series

TEST BOOKLET

Electronics & Communication Paper

Topic Test Signal & Communication

Time Allowed: One Hour

Maximum Marks: 100

INSTRUCTIONS

1. IMMEDIATELY AFTER THE COMMENCEMENT OF THE EXAMINATION YOU SHOULD

CHECK THAT THIS TEST BOOKLET DOES NOT HAVE ANY UNPRINTED OR TORN OR

MISSING PAGES OR ITEMS ETC. IF SO, GET IT REPLACED BY A COMPLETE TEST

BOOKLET.

2. ENCODE CLEARLY THE TEST BOOKLET SERIES A, B, C, OR D AS THE CASE MAY BE IN

THE APPROPRIATE PLACE IN THE ANSWER SHEET.

3. You have to enter your Roll Number on the

Test Booklet in the Box provided alongside.

DO NOT write anything else on the Test Booklet.

4. This Test Booklet contains 60 items (questions). Each item comprises four responses (answers). You

will select the response which you want to mark on the Answer Sheet. In case you feel that there is

more than one correct response, mark the response which you consider the best. In any case, choose

ONLY ONE response for each item.

5. You have to mark all you responses ONLY on the separate Answer Sheet provided. See directions in

the Answer Sheet.

6. All items carry equal marks.

7. Before you proceed to mark in the Answer Sheet the response to various items in the Test Booklet,

you have to fill in some particulars in the Answer Sheet as per instructions sent to you with your

Admission Certificate.

8. After you have completed filling in all your responses on the Answer Sheet and the examination has

concluded, you should hand over to the Invigilator only the Answer Sheet. You are permitted to take

away with you the Test Booklet.

9. Sheets for rough work are appended in the Test Booklet at the end.

10. Penalty for wrong answers:

THERE WILL BE PENALTY FOR WRONG ANSWERS MARKED BY A CANDIDATE IN THE

OBJECTIVE TYPE QUESTION PAPERS.

(i) There are four alternatives for the answer to every question. For each question for which a wrong answer has been given by the candidate, one-third (0.33) of the marks assigned to that

question will be deducted as penalty.

(ii) If a candidate gives more than one answer, it will be treated as a wrong answer even if one of the given answers happens to be correct and there will be same penalty as above to that

question.

(iii) If a question is left blank, i.e., no answer is given by the candidate, there will be no penalty for that question

DO NOT OPEN THIS TEST BOOKLET UNTIL YOU ARE ASKED TO DO SO


Q.1. The following below equations describe discrete time systems, which of the following statement is

not correct? (where u(k) is the input and y(k) is the output)

(A) y k 2 ky k 1 y k u k is Linear Time-varying System

(B) 2y k 2 ky k 1 y k u k is Non linear Time-varying system

(C) y k 2 3y k 1 2y k u k is Linear Time Varying System

(D) 2y k 2 y k 1 y k u k is Non Linear Time invariant system

Q.2. Which of the following statements are correct?

1. Time constant of a 1st order system is reciprocal of position of pole

2. The natural response of system is calculated for input x (t) value equal to zero

3. The time constant of the system dx(t)

x(t) f (t)dt

is 1 sec

(A) 1 & 2 (B) 2 & 3 (C) 1 & 3 (D) 1, 2 & 3

Q.3. Which of the following statements are correct?

1. Forced response is same as Zero-state Response

2. Natural response is same as Zero-input response

3. The forced response of the system dy(t)

2y(t) x(t)dt

when input x(t) k is k/2

(A) 1 & 2 (B) 2 & 3 (C) 1 & 3 (D) 1, 2 & 3

Q.4. If continuous time signal x(t) is written as j3t 4 jtx(t) e 4je 4cos wt then its R.M.S value will be:

(A) 3 (B) 4 (C) 2.445 (D) 5

Q.5. Which of the following statement is not correct?

(A) t

y(t)x(t)

is a Linear system

(B) n

k n

y[n] k.x[k]

is a Linear Time Variant system

(C) 2y[n] x [n] is an example of causal system

(D) 2y[n] x[ n ] is Linear system

Q.6. If input-output relationship of system is given as

2t

y(t) x(t)dt

then system is:

(A) Linear Time Invariant and Unstable

(B) Linear Causal Unstable &Time invariant

(C) Linear Non Causal, Unstable& Time Variant

(D) Linear Time Invariant and stable

Q.7. If Periodic signal n n 1

x[n] cos cos9 7 7

has period N then its value will be

(A) 32 (B) 126 (C) 252 (D) Non-Periodic


Q.8. If h (t) represents response of a linear system then which of the following statements is not correct?

(A) For a stable system impulse response of system decreases exponentially

(B) If the system is time variant then the response of the system to an input of (t T) is h(t T) for

all values of constant T

(C) If the system is static or Non dynamic then h(t) is of the form A (t) where the constant A

depends upon system

(D) If the system is causal then h(t)=0 for t 2 (B) n < - 8 and n >- 2 (C) n < - 9 and n > -2 (D) n < - 9 and n > -3

Q.13. If the input x(t) is delayed by 3 sec and the impulse response h(t) is advanced by 5 sec then the

output of the system y(t) is given by:

(A) y(t-3) (B) y(t+3) (C) y(t+2) (D) y(t-2)

Q.14. What is the derivative of signal x(t) equals to sgn(t)

(A) (t) (B) 2 (t) (C) 2 (t) (D) Not defined

Q.15. Which of the followings statements are true about Fourier series?

1. All periodic signals can be represented by Fourier series

2. It expresses the given periodic waveform as combination of D.C component, sine and cosine

waveforms of different harmonic frequencies

3. Both amplitude and phase spectra of Fourier series are discrete in nature

4. Amplitude spectra of F.S is continuous while phase spectra of F.S is discrete in nature.

(A) 1, 2 & 3 (B) 1, 2 & 4 (C) Only 1 & 2 (D) 1, 2, 3 & 4


0 T nT-nT -T

1

O-1

T

T/2

t

Q.16. Match List-I (Nature of periodic functions) with List-II (Properties of spectrum Function) and select

the correct answer using the codes given below the lists:

List-I List-II

(Nature of periodic functions) (Properties of spectrum function)

A. impulse train 1. Only even harmonics are present

B. Full-wave rectified sine 2. Impulse train with strength 1/T

Function

C. 2 4

sin .cos .6 6

t t 3. 3 3 1 1

1 1 1 1; ; ;

4 4 4 4C C C C

j j j j

D. 4. Only odd harmonics are present

5. Both even and odd harmonics are present.

Codes:

A B C D

A. 5 2 3 4 B. 2 1 4 3

C. 5 2 4 3 D. 2 1 3 4

Q.17. Which of the following statement is not correct.

(A) Fourier representation of continuous and periodic signal is discrete and aperiodic

(B) Fourier representation of continuous and aperiodic signal is continuous and aperiodic

(C) Fourier representation of Discrete and periodic signal is discrete and periodic

(D) Fourier representation of Discrete and aperiodic signal is continuous and aperiodic

Q.18. If a function f(t) has Fourier-transform F(w) then what is the value of jwtF(t)e dt

(A) 1

f (w)2

(B) 1

f ( w)2

(C) 2 f (w) (D) 2 f ( w)

Q.19. If signal x(t) is an even function then the value of its Fourier transform will be:

0 0

(A)2 x(t)cos wt dt (B)2 x(t)sin wt dt

0 0

(C)2j x(t)cos wt dt (D) 2j x(t)sin wt dt

Q.20. The Fourier transform of u(t) is :

(A) 1

j (B) j (C)

1

(1 )j (D)

1( )

j

Q.21. Which of the following statements are true about Fourier Transform?

1. Fourier transform of a conjugate symmetric function is always real

2. Fourier transform of a conjugate anti-symmetric function is always imaginary


3. For any real sequence magnitude spectrum of Fourier transform is even and phase spectrum is odd

(A) 1 & 2 only (B) 2 & 3 only (C) 1 & 3 only (D) 1, 2 & 3 only

Q.22. Consider the function 1 2H(jw) H (w) jH (w) where 1H (w) is an odd function and 2H (w) is an

even function. The inverse Fourier transform of H (jw) is:

(A) Real and odd function (B) Complex function

(C) Purely Imaginary function (D) Purely imaginary and odd function

Q.23. A voltage signal v(t) has the following Fourier transform :

| | 1

( )0 | | 1

j te forV j

for

The power that would be dissipated in a 1 resistor fed from V(t) is :

(A) 0 W (B) 1 W (C) 1

W

(D) 1

2W

Q.24. The impulse response of a single pole system would approach a Non zero constant as time

approaches towards infinity if and only if the pole is located in the S-plane:

(A) On the negative real axis (B) at the origin

(C)On the positive real axis (D) On the imaginary axis

Q.25. Which of the following statement is not correct about Laplace Transform values?

(A) Laplace transform of function (t) is unity.

(B) Laplace transform of unit doublet function is s

(C) Laplace transform of unit step function u(t) is 1/s

(D) Laplace transform of function tu(t) is 2/s2

Q.26. Let 3( ) ( ) & ( ) ( )t tx t e u t h t e u t Then what is the value of ( ) ( ) ( )y t x t h t as t

(A) 0 (B) 1 (C) 2 (D)

Q.27. Which of the following statements are correct about R.O.C of Laplace transform?

1. If x(t) is two sided function then ROC will consists of a strip in s-plane

2. If x(t) is a finite duration signal then ROC will be entire s-plane

3. If signal x(t) has ROC value equal to R then ROC of x(at) will be R/a

4. If signal x(t) has ROC value equal to R then ROC of x(-t) will be R

(A) 1, 2 & 3 (B) 2, 3 & 4 (C) 1, 3 & 4 (D) 1, 2, 3 & 4

Q.28. Z & Laplace Transform are related by formula:

( ) ( ) ( ) ( ) ln sT sTA z e B z e C z sT D s z

Q.29. For the given system x[n]= [n] and y[n] is related to x[n] by the equation 1

y n y n 1 x n2

then what is the value y[2]?

(A) 1/2 (B) 1/4 (C) 2 (D) 4


Q.30. Match List-I {x(n)]} with List-II {x(z)]} and select the correct answer using the code given below

the lists :

List-I {x(n)]} List-II {x(z)]}

A. n u(n) 1. 1

1 2, :| | | |

(1 )

zROC z

z

B. n u( n 1) 2. 1

1, :| | | |

(1 )ROC z

z

C. nn u(n 1) 3. 1

1, :| | | |

(1 )ROC z

z

D. nn u(n). 4. 1

1 2, :| | | | .

(1 )

zROC z

z

Codes: A B C D A B C D

(A) 2 4 3 1 (B) 1 3 4 2

(C) 1 4 3 2 (D) 2 3 4 1

Q.31. Which of the following statement is not true about Auto Correlation Function (ACF?)

(A) ACF has even symmetry

(B) ACF has maximum value at origin and this is equal to mean square value of signal

(C) ACF of the signal 2

( ) cos cos2

Ax t A wt is wt

(D) ACF of the signal 2

( ) s sin2

Ax t A inwt is wt

Q.32. Which of the following is not a property of Power Spectral Density (P.S.D) function?

(A) PSD of a real sequence is real, even and nonzero

(B) PSD of a real sequence is real, odd and nonzero

(C) PSD of a white noise is constant

(D) ACF and PSD are Fourier transform pairs to each other

Q.33. If E represents the expectation of a Random variable X then the variance of random variable 5X

will be:

2 2 2 2 2 2( ) 5 [ ] ( ) 25 [ ] ( ) 25{ [ ] [ ]} ( ) 5{ [ ] [ ]} A E X B E X C E X E X D E X E X

Q. 34. Total power saving when carrier and one of the side bands are suppressed in an AM wave modulated

to a depth of 50%:

(A) 66.67% (B) 94.44% (C) 83.33% (D) 100%

Q.35. Which of the following statement is not correct about envelop detector (Detection method of AM)

(A) It is an asynchronous detection method which used only diode, capacitor &resistor

(B) If RC time constant is low then there will be large amount of ripple and fluctuation at the output

(C) If RC time constant is high then there will be negative clipping or diagonal clipping at the output

(D) Output of envelop detector has only message signal without any DC component

Q.36. A single tone amplitude modulated signal at a modulation depth of 100% transmits a total power of

15 W then power in carrier component is:

(A) 5W (B) 10W (C) 12 W (D) 15W


Q.37. A 1 MHz sinusoidal carrier is amplitude modulated by a symmetrical square wave of period 100

micro sec then which of the following frequencies will be present at the output signal:

1. 1010 KHZ 2. 990 KHZ 3. 1020 KHZ 4.1030 KHZ

(A) 1, 2 & 3 only (B) 1, 2 & 4 only (C) 1, 3 & 4 only (D) 1, 2, 3 & 4


(A) A frequency modulated signal is produced when a modulating signal m(t) is integrated and

applied to a phase modulator

(B) For sinusoidally modulated FM carrier it is possible that for particular values of the modulation

index all the power lies in side frequencies and no power in the carrier

(C) When carrier to noise ratio is high an increase in transmission bandwidth decreases the figure of

merit of an FM system

(D) A phase modulator signal is produced when a modulating signal m(t) is differentiated and

applied to a frequency modulator

Q.39. The modulated carrier average power in an FM system is equal to the:

(A) Modulating signal power

(B) Unmodulated carrier power

(C) Difference between modulating signal power and unmodulated carrier power

(D) Sum of modulating signal power and unmodulated carrier power

Q.40. Which of the following statements are correct about FM?

1. Ideal value of bandwidth is infinite because FM spectrum consists of a carrier and infinite

number of side band components.

2. FM has better noise immunity in compare to AM due to Threshold effect in FM

3. It is impossible to differentiate between PM and FM by seeing modulated signal of PM&FM

(A) 1 & 2 only (B) 2 & 3 only (C) 1 & 3 only (D) 1, 2 & 3

Q.41. A composite signal is expressed as Xc (t) = Ac cos c t- Am cos (c- m)t +Am cos (c+m) t. Which

of the followings statements are true?

1. It is equation of NBFM signal

2. Bandwidth of this signal is 2wm same as in case of AM

3. Either envelop detector or discriminator method can be employed to retrieve the sinusoidal

component at m from xc (t)?

(A) 1 & 2 (B) 2 & 3 (C) 1 & 3 (D) 1, 2 & 3

Q.42. A carrier wave of frequency 100 MHz is frequency modulated by a sinusoidal wave of amplitude of

20 Volt and frequency 100 KHz. If frequency sensitivity of modulator is 25KHz/volt then the

bandwidth of FM signal is :

(A) 2.1 KHz (B) 2.1MHz (C) 1.2 KHz (D) 1.2MHz

Q.43. In case of FM if message signal frequency is halved and signal amplitude is doubled then the peak

frequency deviation and peak phase deviation will become respectively:

(A) doubled and doubled (B) doubled and becomes 4 times

(C) doubled and remains unchanged (D) becomes 4 time and doubled


Q.44. If Frequency modulated signal with 0

( ) cos ( )

t

FM c c fX t A t k m t dt

is applied to an Ideal

envelop detector then output at envelop detector will be :

(A) 0 (B) Ac (C) m(t) (D) m(t)+ D.C signal

Q.45. Which of the following statement is not correct about RF amplifier in case of Super Hetro dyne

receiver (SHR)?

(A) Image channel rejection in SHR comes from RF amplifier only

(B) RF amplifier is also known as Pre-selector

(C) RF amplifier is compulsory in both AM and FM receiver

(D) RF amplifier is generally a Class-A amplifier

Q.46. Match the following:

List-1 List-2

A. Simplest receiver 1. SSB

B. Quadrature Null effect 2. AM

C. Voice transmission 3. DSB

D. Direct method 4. FM

Codes: A B C D A B C D

(A) 1 2 3 4 (B) 2 1 3 4

(C) 2 3 1 4 (D) 1 3 2 4

Q.47. A super Hetro-dyne receiver is to operate in frequency range of (550-1650) KHz with the

intermediate frequency of 450KHz.If receiver is tuned to 700 KHz then what is the value of Image

frequency in KHz.

(A) 1600KHz (B) 1150 KHz (C) 2100KHz (D) 1000KHz

Q.48. An image uses 256x256 picture elements, each of the picture elements can take any of the 8

distinguishable intensity levels. Then maximum entropy of the above image will be

(A) 196,608 bits (B) 524288 bits (C) 2048 bits (D) 768 bits

Q.49. A source produces 26 symbols with equal probability then what is the average value of information

produced by this source?

(A) 4 bits/symbols (B) 6 bits/symbols (C) 8 bits/symbols (D) between 4 and 6 bits/symbols

Q.50. The number of bits per sample of a PCM system depends upon the:

(A) Sampler type (B) quantizer type

(C) Number of levels of quantizer (D) Sampling rate

Q.51. Which one of the following signal pairs can represent a BPSK signal?

c c(A) Acos2 f t &Asin 2 f t

c c(B) Acos2 f t & Asin 2 f t

c c(C) Acos2 f t & Acos2 f t

c c(D) Acos2 f t &2Asin 2 f t

Q.52. QPSK system is superior to BPSK system because:

(A) Its bandwidth is higher than that of BPSK

(B) Interchannel interference in QPSK system is less that in BPSK system

(C) Bandwidth of QPSK is half of bandwidth of BPSK system

(D) In QPSK system inter symbol interference is improved


s(t)

4

20

Q.53. In Time division multiple access system a traffic system on the receiver side must receive the traffic

burst addressed to it .For this

(A) Transmitting frame acquisition is required

(B) Proper synchronization of the timing of transmit frame is required

(C) Frame efficiency should be higher

(D) Synchronization is necessary to overcome the perturbation of satellite

Q.54. What is the impulse response of filter matched to signal s(t).

(A) s(t4) (B) s(t)

(C) s(t1) (D) s(t2)

Q.55. Which of the following has maximum probability of error?

(A) ASK (B) BPSK (C) BFSK (D) MSK

Q.56. Consider the following statements comparing Delta Modulation with PCM system:

Delta Modulation requires:

(A) Higher sampling rate, higher bandwidth and less hardware

(B) Higher sampling rate, lower bandwidth and less hardware

(C) Lower sampling rate, higher bandwidth and more hardware

(D) Lower sampling rate, lower bandwidth and less hardware

Q.57. The frequencies used in satellite communication are generally in the range of 1 to 10 GHz because:

1. Antenna size are small at these frequencies

2. These frequencies can penetrate through ionosphere and will not reflect from ionosphere

3. Helical antenna can be used at these frequencies

(A) 1 & 2 (B) 2 & 3 (C) 1 & 3 (D) 1, 2 & 3


(A) A geo-stationary satellite is located at about 35000Km from earth and can cover one side of the

earth

(B) Geosynchronous satellite remains stationary relative to earth antennas

(C) Time period of both geosynchronous and geostationary is 24 hrs

(D) Three geosynchronous satellite can cover 100% global coverage including polar region

Q.59. Optical fiber having Numerical Aperture (N.A) in the range of 0.15 to 0.4.Fibers having higher N.A

values generally exhibit:

(A) Reduced losses (B) High bandwidth

(C) Reduced losses and low band width (D) Greater losses and low band width

Q.60. The possible dispersion in case of single mode fiber are:

1. Waveguide dispersion 2. Material dispersion 3.polarization mode dispersion

(A) 1 & 2 (B) 2 & 3 (C) 1 & 3 (D) 1, 2 & 3


Engineering Service Examination -2013

SI No.

Electronics&Telecommunication Engineering

PAPER-Signal&Communication

(Conventional)

Time allotted: 90 Minute Maximum marks: 100

INSTRUCTIONS

Candidates should attempt Question No. 1 which is compulsory and remaining FOUR from questions taking

two each from section-A and Section-B. The number of marks carried by each question is indicated at the

end of the question. Answers must be written only in English. Assume suitable data if found necessary and

indicate the same clearly. Values of the following constants may be used wherever necessary:

Electronic charge = 1.6 109 Coulomb

Free space permeability = 4 107 Henry /m.

Free space permittivity = 91

1036

Farad/m.

Velocity of light in free space = 3 108 m/ sec.

Boltzmann constant = 1.38 1023

joule /K.

Planck constant = 6.626 1034

joule-sec.

Important: Candidates are to note that all parts and sub parts of a question are to be attempted

continuously in answer book. That is all parts and sub parts of a question being attempted must be

completed before attempting the next question.

Any page left blank in answer book must be clearly struck out. Answers that follow pages left blank

may not be given credit.


0

2t

x(t)

+1

-1

x(t)2

1

2 1 0 1 2t

Q.1 (a) Consider the sequence x[n] = [- 4 j5, 1 + j2, 4] then calculate conjugate anti-symmetric part &

conjugate symmetric part of the sequence? (2.5+2.5)

Q.1 (b) If wave form is given only for 1 period then Fourier series representation of periodic signal x (t) will

be. (5)

Q.1(c) The input and output of a causal LTI system is related by the differential equation

2

2

( ) ( )6 8 ( ) 2 ( )

d y t dy ty t x t

dt dt

then find the impulse response of the system. (5)

Q.1 (d) Let ( ) ( ) ( )g t x t x t where denotes convolution and x(t)=u(t)-u(t-1) with u(t) being the unit

step function then what is the impulse response of the filter matched to signal

( ) ( ) ( 2) ( )s t g t t g t (5)

Q. 1(e) How Frequency modulation may be obtained from a phase modulator with proper diagram (5)

Q.1 (f) State sampling theorem with the help of instantaneous sampling (5)

Q.1 (g) If pulse rate in Delta Modulation is 56000 per-sec if input message signal is

5cos (2 1000 t) + 2 cos(2 2000 t) volt where t is in sec then what is minimum value of step

size which will avoid slope over load distortion. (5)

Q.1 (h) An Si Fiber has N.A equals to 0.173 and supports 400 modes at a wavelength of 1.3 micrometer

What is the value of its core area? (5)

SECTION-A

Q.2 (a) with mathematical expressions, define the properties stability, memory less system and causality

of a LTI system. (10)

(b) For a LTI system impulse response is ( ) ( )th t e u t the condition for stability is? (5)

Q. 3. (a) Determine the Fourier transform of the signal shown in the following fig. (10)

(b) Calculate Fourier Transform of signal 2

1( )

1x t

t

(5)


Q. (4) Determine the response of the system 5 1

( ) ( 1) ( 2) ( )6 6

y n y n y n x n to the input signal

when input 1

( ) ( ) ( 1).3

x n n n (15)

SECTION-B

Q. (5) (a) with the help of block diagram explain working of Super-heterodyne receiver and why frequency

of Local oscillator is always higher than signal frequency? What is double spotting in case of SHR?(10)

(b) A super heterodyne receiver is to operate in the frequency range 550 kHz-1650 kHz, with the

intermediate frequency of 450 kHz. Let R = max

min

C

C denote the required capacitance ratio of the local

oscillator If the receiver is tuned to 700 kHz then what is the value of R? (5)

Q.6 (a) A signal is band limited to 3.6 KHz and three other signals are band limited to 1.2 KHz each. These

signals are to be transmitted by means of Time Division Multiplexing (TDM).If each signal is sampled at its

Nyquist rate setup a scheme to achieve this multiplexing and also specify the speed of commutator in

samples per second. (10)

(b) Show that speed of T1 system is 1.54 Mbps (5)

Q.7 (a) The carrier frequency of an Uplink is 6 GHz. The transmitting earth station EIRP is 80dBW.If

satellite receiver G/T is -8dB/oK and the transmission losses are 0.6dB.Calculate the CNR at the satellite

receiver input for an earth station to satellite distance of 35860Km. (10)

(b) The system noise temperature at the input of the LNA of a satellite receiver station operating in the

C-band is 450 K.If the diameter of the receiver antenna (parabolic reflector) is 30 m, compute the

earth station figure of merit.(5)


SECTION-B

ies practice papaer

Documents