--l

Ple:rse rvrite y't'ttr Roll No. intrriecliatetr

IVth Semester (8. Tech) ECE

Paper Cocle (ETEC - 20S)

Time:1%Flrs.

SECOND _ TERIVI EXANIINATIONREGUT,AR STUDEI{T

Rolr No.:iJ + [r (We

Anri! ?3C6

Sub. CS&C-r

lV{ ax i tnunt l\''1.', l'-, : ] INote : r\ttslllll! an.v three q tlesti o n s. Ouest

q{ttl An angle * modtrlated signal is given oy xit) = 5 ct'rs [2 rt ( 106)t

l/ Crr you ideptil-v q'lerher x(t) is Plr4 or an Flr4 signal. .lgsti{,r'.

(ii)-J)ctermine t|e instanraneotti: iiecptenci' in I'17. {br the sigr-ral.

'/ X(t):cos 200 tt t cos (5 sin 2 P t ) +

Sin 200 11 t sin (5 sin 2 n t)(iii) Sketch the instantaneoLrs fiequency - time cLrrve for a 100 - MHz carrier rvave fiequency

modulateci by I _' KHz sL1liare rvave that has zero dc cottrponetrt and peak-to-peak voltage of 20

V. The frequency' deviation constant is 9 KH2/V. (2)

(iv) State clearly the diff'erence benveen moduiation inciex and cieviation ratio (2)

(v) Explain why de-emphasis is used in FM reception. What is the function of I're-enrphasis in

FM transrnitter? (2)

,/+\

e2 (a) A siven angle - nrodulated signal has maximum fi'equency' cleviatillp pt-{p fol an

input sinusoid of unit amplitude and frequency of ,120_H<. Determin:^*:-::q,:ired freqrtencl'

-.,ltipli"ution factor 'n' to produce a maximrrm tiedueFG deviation of 2Q l(Hz \!]en the input1 i .' r'

nlit amoliitude and a flrequdncy o240 H ancle modLrlation trsed is

)PM (2) FM {)

+ 0.2 cos 200 n tl(l)

, (:)

(b) Explain in detail the generation of (i) PAM (ii) PWM (iii) PPM (6)

(s)Q3 (a) An angle -modulated

X(t)= 10 cos [2 P1

(l) Considering x (t) as a

( 2) Considering x (t) as a

(b) Describe in detail direct method

conversion.

signal is described by(t061t + 0.1 sin 110'r tt tJ

PM signal with Kp: 10, find m (0.

FM sigrial with K;: 10 g, find m(t).

Q3

OA J (a)Amodulatingsignal 5cos2n(15xl0lt),anglemodulatesacarrierAcosw.t.-(>-- iij einA the modulation index and the bandwidth for (a) the FM System, (b) the PM System.

iliy o.t"t.nine the change in the bandwidth and the modulation index for both FM and PM. iffm is reduced to 5 KHTAssume Kp: Kf : 1 5 KHIN ' (5)

e4 (b) What is the difference between Natural Sampling and Flat-top Sampling in Pulse

Modulation . Draw the spectrum of a Flat - top sampled signal tbr

of generating Narrow Band FM to wide Band Flvl(s)

(i) Impulse SamPled Signal

Please write your Roll No. immediately

SECOND - TERM EXAM'TNATIONIVth Semester(B.Tech) ECE March. 2009

Paper Code (ETEC -208) Sub. CS&C -ITime : | %Ihs Maximum Marks : 30

Note: Attempt any three questions. Question No. 1 is compulsory. All questions caffy

equal marks.

Q I (dwhat are the advantages of Pulse modulation over continuous wave modulation.

@B"plain.mu-ltlton*F}4 waves by giving an example.

Ic)pdfine the lollowiirg terms:(i).Instantaneous frequency of FM.

1-ii) Instantaneous phase of PM '

-4"{f Using Carson's rule, prove that bandwidth of FM is consteint for audio signals./ k) pina the permissibie range in maxirnum modulation index for Commercial FM which-iit 20 Hzto 15 KHz rnoduliting frequencies . *T

5 V.V\"* (2 x 5 )

,, 1Q2(A/Explain w.hy de-emphasis is used in Flr{ reception. What is the function of pre'

.gnfphasis in an FM transmitter? (4)

, , t6iA,3 KHzsimrsoiclal signal of 5V pr:ak is used to phase moclulate a camier, the phase,

^-\/. devratron constant being hadN. Determine the practical barrdwidth required for the

modulatedsignal. t f,..j\? l)nr,,1vn

\ (2)

/' rv'l frrncfin." n""tr" the exnression fttr 'rusoidal FMfiU"tngBessel functions, derive the expression fol avcrage porver in sit ()

Q3 (a) By giving an example, describe briefly the block diagram of practical method o1

generating WBFN{ signal using Armstrong method'

(b) Draw and explain the follou'ing circuits

(5)

-{fPwu nrodulator

$ifPPnA mociulator (5i\-'r'

Q4(a) A carrier voitage 10 Cos8nl061i:i angie moduiated by a rnodulating signal

5 Cos30n103t(i) Determine the bandvridth of FM, Kl': 15 KHzA/'(ii) Assuming the same l:andwrdth , find Ko per phase modulation.

(iii) Determine the chaiige in the banclwidth for fi'equency' and phase rnodulation if the

modulating signal becontes 5 Cos10a1{)3t (5)

(b) Draw the block diagr:am of phase locked loop (PLL) IfM demoduiator. Explain the

function of each block. (5)

CLASS TrsT ilCOMMUNICATION SYSTEM & CIRCUITS-I

ETEC_208

4tn sEMESTER EcEREGULAR

Time:90 Minutes

Nqz:

ts)(2)

(3)

Max. Marks:30

Note: Question [tlo' 1 is compulsory and attempt any two questions from question filo. 2,g & 4.

tttttwhat are the differences between narrowband FM & wideband FM? ?-'{b) what is modulation index ml of FM which is being broadcasted in g8-10g MHZ band if the carrierSwing is 128 KHz? 't2'-.'"{ c) How FM can be generated using phase modurator. Exprain the concept? . 2*(d) what are the differences between natural sampling & Flat top sampling? Expiain advantages offlat top sampling over naturalsampling?

!fu) What is noise Triangle? How is it formed? 2

7-

9((a)ExplainFosterseeleyDemodulatorindetails. Alsoexplainadvantages&disadvantagesof FosterSeeley Demodulator^(b) what are the differences between Foster seeley Detector & Ratio Detector?

a 3F( State & prove sampling theorem.(b) What is aliasing effect and how can it be removed?( c) Find Nyquist rate & Nyguist interval for signal x(f) = 112n{cos 4000nt x cos Lg00nt)

9((a) Explain PAM, PPM & pwM Modurators & Demodurators in detairs.representation of pWM & ppM.

Also explain the spectral

{10)

Plcasc u'ritc' your Rol l No. i rtrtn"'tl iatel l'

I'r Scmester (8. Tcch) ECE

Paper ('odc (ETEC - 208)

'l'inrc: I l" llrs.

Itcrlirrlttattcc ol"i'lt l: r,-'cci ver

*41ful t''' supc{,rf .11 SUpCrltctrttdvl(: rCCClyqr \\'hilt lS lll, iitl OI tllg.,'llxcl-llllt-tiiil\\'hat is Qualitr lactor? R1'gi'irlg itr; '::tulrple. e'i',laitr lrori

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Rt,ll No.

Fr RST - TEni l'! E.UMINATIA\RIicLrL,tfBEIgplM

Februan'2008

Sub. ('S&C-l

Maxilrrtunt Marks: 30

l'tltc l,'f ixcr arr.l 'r lr),.)it c l'l'c.t:r tl

NllUjUtltffl-@g1if'g l.is cornpulsor'-r'..!ll quesliory21:v.ggttal ntarks

Qt.,"rfii'trat il thc rnlue of IIr ir Alr,1 'l'rartsttti'.,iiirl. r\ll\'\\'t'rr.se itl (?)

t-/

(2)(l)

Q2

tMl:rnllirt rvlrv thc Qrraliti t.ri'strut'ld itl ,'l"t'['r'tttsttti:;:ri()l: l:i i](\r)l')

W1';\n igtrplitirtlc-rrrorltrliitr'tl urttplil',c-r prt;,;:lcs lllroulf,ut tlf' l(l(r \\ all l{j(J'1li,

nt(r.irllaiion. 'l'hc intcrnal ltrss i:; 20 s'.

,trfl'i'ttt is thc' ttttrltocitrlltcd t:airier p''''i''r'l(2)*fif \\'hal is th.' .;idctratril ptrit'cr.'

(.) I)crive an esprcssiol li'rr N'loclulaticr index of A'vl tvirvcr ntQdtrlitted b;,'scvcral

Sinusoidal signals'? (3)

ifflDeriye thc.'i:prcssion firr generittion.cf l)SB-S(' s'ave, tisittg Balanced

" j,in,.t,,tni.tr' ( {)

' i'c,l;-r* iq,,isroi. c::.-r;'o1''-)- ij'tnet'i-ft*ill'trilq;ri-i;ii'i: 'iri i '.'ili;':' i:sii':;jti:"ii\"' i,i,rd rlrc p,rrr.cr,lclsirr :;i''c..'lrtlnl-pfuroisc voltrgc rl'^thc tcrrrtinlr's,{irrtrlcri bv

jiJ-Scricsct,rirl.,irrltiorr tii) Pardfrift ccrnrlrinatto;t of tltese i'i'si:;tor,s. (3)

",lj'

r*vf \\'lrrtt is .*iilglt., sirle I'lrrrri (t'S*llt ntorf$4rf iort'." L)isC'.t.s.i tltc trclr (llrti.ltlcs illl'-l/'

.lis;.rcllnrrrnlcs trl'SSll rirotlrrlltion orrbr DSII-SC' artcl '\\4 tttotlttl;rtion (-l)

-(*,ifl)re1, tlrr: lllttc:k cli;ruruutt ol'a srrp,-:ilfdii'rlcit'tlc t't'u -'i\',"'l' rtl'l(l ,l\plll;iltlrc firnctiqn of'c:aclt [:lock.

':( c ) \\'l'at ni"r.' il:c tlrllr','1.'rrcl:s cr!''l

q)'{ \\'r'itc slrtrrt notis'tir',.,tliii';,tirIhrrvitrr-'.:'

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ntttl5it:'rc'rltclt't-.tl"rter'1'1'(ji\'(:r'l (2)

00)

:::i+_:Il:i

isi,i

.06.o.tPt

+ a 2(a) Describe the relation

depth of modulation, and Plotto maximum.

Please write your Roll No. immediately Roll No.

FIRST _ TERM EXAMINATION

IVth Semester(B.Tech) ECE Feb' 2009

Paper Code (ETEC -208) Sub' CS&C -lTime : I YzHrs Maximum Marks : 30

Note: Attempt any three questions. Question No' I is compulsory' All questions caffy

equal marks.

, 97 (gfExplain the significance of intermediate frequency in AM transmission'

"',6fi explain what is the need for frequency translation'

_Anistinguistr linear modulation from exponential modulaticn. Give examples of each'

- glWttut are the advantages of TRF receiver?(e) A bandwidth of 10 MHz is to be considered for the transmission of AM signatr. lf the

ffi.ri audio frequency used to modulate the carrier do not exceed 5 KHz, how many

stations could be troudcust within this band simultaneously wi.thout interfering with one

anorner. (2 x 5)

between the output power of an AM transmitter and the

it as a graph for values of the modulation index from zero(4)

-{61Define sienal-to-noise ratio and noise figure of a receiver' {2)

,-ffi;;;i;; th;;pression for addition of noise due to severalqmplifiers (4)u,_)/'-

Q 3 (a). The signals Vr(t): ?- coso'(i) + cos 2co1(t)

Vz(t):2 cosarz (t) + cos 2aY(l)

are muitiplied. plot the resultant amplitude*frequency characteristic assuming that

,rrrZ*'r, but is not a hatmonic of cl1 ' R'epeat for ro2 :2o1 (5)

e3(b) Detine and describe independent-sideband transrnission. Is pilot carrier used in

this transmission. Give some examples in which pilot carrier is ttsed for transmission' (5)

Qa(a).A DSB modulated signal q(t) :A m(t) cos 2n f"t is multiplied with a local carrier

c(t) : cos( r.o.t + 0) ancl the output is passed tlrough a LPF rvith a bandwidth equal to the

bandwidth of the message miO . ti ttre power of the message signal m(t) is Pm 'determine I

(i) The power of the modulated :rignal'

(iD The power of the modulated signal at the output of the LPF. (5)

Q4(b) A carrier wave of a frequency of 20 KHz is amplitude modulated by a modulating

signal f(t): cos 2n,03t+ cos intOit. Fincl the expression for the corresponding SSB-SC* (s)signal.

norrxo. 6TQol t8r*FIRST TERM EXAMINATION, FEBRUARY 2O1O

B. Tech IV Semester ECECommunication Systems & Circuit I (ETEC 208)

Max. Marks;30 Time: 90 minutes

REGULARQuestion No. I is compulsory & attempt any two questions from Q.No.2,3 & 4.

Q.No.1 (a) What are the characteristics of lpry_N"oi;e

Arypl{191. Also give any tw"o

t ]-:'i'=?i; g: ,ri.r-- applications of LNA. . . YY ','l; ,i {. .u . e)

' l.

", -ft\ wr'ut are the difterences b.,H.n';;;"'.t%oouiu,ion'& high tevel\vmodulation scheme? (2)

(c) What is the importance of selecting optimum value of time constant in envelope

detection?

What is Quadrature Amplitude Modulation?

(2)

(2)(d)

(e) Which modulation scheme is used for transmission of TV signals & why? (2)

Q.No.2 (a) Draw the block diagram of superhetrodyne receiver & explain it along with the

various parameters of this receiver? (8)

For a broadcast superhetrodyne receiver having no RF amplifier, loaded quality

factor of antenna coupling circuit is I00. Find the image frequency & its rejection

ratio at an incoming frequency of 100 KHz. (2)

'lQ.No.3 (a) Drive the generalequation of SSB. Explain the phase shift method of generation of

SSB. (5)

(b) An SSB Transmission contains 10KW. This transmission is to be replaced by

standard amplitude modulated signal with the same power content. Determine the

power content of carrier and each side band when percentage of modulation is 60%

(5)

Q.No. 4(a) What is Noise temperature? Whatare the adv4ntages of finding Noise

tempJ-fatu-re? (3)

(b) What is White Noise? Draw the Power Spectrum of White Noise. (3)

(c) Find the Noise Figure of three stage cascaded Amplifier with each stage having

power gain of l0 dB and Noise Figure of 5 dB. (4)