COMMUNICATION ENGINEERING 2 MARKS

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ECC6666551 1 CCOOMMMMUUNNIICCAATTIIOON N EENNGGIINNEEEERRIINNGG 3 3 0 0 0 0 33 1

1.. AANNAALLOOGG CCOOMMMMUUNNIICCAATTIIOONN 99 AM

AM

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Frequency spectrumFrequency spectrum

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vector representationvector representation

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 power relat power relationsions

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generation of AMgeneration of AM

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DSB, DSB/SC, SSB, VSB AM Transmitter  !eceiver" FM an# $M

DSB, DSB/SC, SSB, VSB AM Transmitter  !eceiver" FM an# $M

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frequency spectrumfrequency spectrum

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 power  power relations relations % % &BFM &BFM   'BFM, 'BFM, (eneration (eneration of of FM FM an# an# DM, DM, Amstrong Amstrong met)o# met)o#  !eactance mo#ulations %

!eactance mo#ulations % FM  $M frequency*FM  $M frequency* +*

+* DDIIGGIITTAALL CCOOMMMMUUNNIICCAATTIIOONN 99 $ulse mo#ulations

$ulse mo#ulations

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concepts of sampling an# sampling t)eormes, $AM, $'M, $$M,concepts of sampling an# sampling t)eormes, $AM, $'M, $$M, $TM, quantiation an# co#ing % DCM, DM, slope overloa# error* ADM, D$CM, --.  $TM, quantiation an# co#ing % DCM, DM, slope overloa# error* ADM, D$CM, --.  systems

systems

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AS., FS., $S., BS., $S., AM, MS., (MS., applications of DataAS., FS., $S., BS., $S., AM, MS., (MS., applications of Data communication*

communication* 0*

0* SOURCE SOURCE CODES, CODES, LINE LINE CODES CODES & & ERROR ERROR CONTROL CONTROL (Qualitati(Qualitati! ! "#l$% "#l$% 99 $rimary communication

$rimary communication

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entropy, properties, BSC, B1C, source co#ing % S)aum, Fao,entropy, properties, BSC, B1C, source co#ing % S)aum, Fao, 2uffman co#ing % noiseless co#ing )eorem, B'

2uffman co#ing % noiseless co#ing )eorem, B'

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S&! tra#e off co#es% &!3, !3, AM4,S&! tra#e off co#es% &!3, !3, AM4, 2DB$, AB, MBnB co#es % 1fficiency of transmissions, error control co#es an# 2DB$, AB, MBnB co#es % 1fficiency of transmissions, error control co#es an# applications% convoluti

applications% convolutions  ons  5loc6 co#es*5loc6 co#es* 7*

7* MMUULLTTIILLE E AACCCCEESSS S TTEECC''NNIIQQUUEESS 99 SSMA tec)niques % FDMA, TDMA, CDMA, SDMA application in wire an# wireless SSMA tec)niques % FDMA, TDMA, CDMA, SDMA application in wire an# wireless communicatio

communication % A#vantages 8n % A#vantages 8merits9 %merits9 % :*

:* SATELLITE, OTICAL I)ERSATELLITE, OTICAL I)ER

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OO**EERRLLIINNEE, , SSCCAADDAA 99 -r5its

-r5its % t% types of ypes of satellites satellites % frequency us% frequency use# lin6 e# lin6 esta5lis)ment, MA tec)niques esta5lis)ment, MA tec)niques use# inuse# in satellite communication, eart) station" aperture actuators use# in satellite

satellite communication, eart) station" aperture actuators use# in satellite

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4ntelsat an#4ntelsat an# 4nsat% fi5ers

4nsat% fi5ers

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types% sources, #etectors use#, #igital filters, optical lin6% power line carrier types% sources, #etectors use#, #igital filters, optical lin6% power line carrier  communicatio

communications% ns% SCADASCADA

TE+T )OOS TE+T )OOS

TOTAL - 5 ERIODS TOTAL - 5 ERIODS ;

;

.T aub &

.T aub & Schiling “Principles of

Schiling “Principles of commu

communication systems” T ata McGraw hill

nication systems” T ata McGraw hill

2!

2!

2." .#as “Principles of $igital

/ MARS QUESTIONS AND ANS*ERS / MARS QUESTIONS AND ANS*ERS

UNIT I UNIT I ANALOG

ANALOG COMMUNICATCOMMUNICATIONION 1.

1. D!i#! aD!i#! a2litu! 2litu! M"ulatM"ulati"#.i"#.

Amplitu#e Mo#ulation is t)e process of c)anging t)e amplitu#e of a relatively )ig) Amplitu#e Mo#ulation is t)e process of c)anging t)e amplitu#e of a relatively )ig) frequency carrier signal

frequency carrier signal in proportioin proportion wit) n wit) t)e instantaneous t)e instantaneous value of value of t)e t)e mo#ulatingmo#ulating signal*

signal* +*

+* D!i#! M"ulati"# i#!4 a# 2!!#t "ulati"# " a# AM 7a!.D!i#! M"ulati"# i#!4 a# 2!!#t "ulati"# " a# AM 7a!. Mo#ulation in#e< is a term

Mo#ulation in#e< is a term use# to #escri5e t)e amount of amplitu#e c)ange presentuse# to #escri5e t)e amount of amplitu#e c)ange present in an AM waveform *4t is also calle# as coefficient of mo#ulation* Mat)ematically in an AM waveform *4t is also calle# as coefficient of mo#ulation* Mat)ematically mo#ulation in#e< is

mo#ulation in#e< is m = 1m/ 1c

m = 1m/ 1c

')ere m = Mo#ulation coefficient ')ere m = Mo#ulation coefficient 1m = $ea6 c)ange in

1m = $ea6 c)ange in t)e amplitu#e of t)e output waveform voltage*t)e amplitu#e of t)e output waveform voltage* 1c = $ea6 amplitu#e of t)e

1c = $ea6 amplitu#e of t)e unmo#ulatunmo#ulate# carrier voltage*e# carrier voltage*

$ercent mo#ulation gives t)e percentage c)ange in t)e amplitu#e of t)e output wave w)en $ercent mo#ulation gives t)e percentage c)ange in t)e amplitu#e of t)e output wave w)en t)e carrier is ac

t)e carrier is acte# on 5y a mo#ulating signal*te# on 5y a mo#ulating signal* 0*

0* D!i#! L"7 l!!l D!i#! L"7 l!!l M"ulati"#.M"ulati"#.

4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e 4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e final stage of t)e

final stage of t)e transmitter* transmitter* For low level AM mo#ulator class A amplifier is use#*For low level AM mo#ulator class A amplifier is use#* 7*

7* D!i#! 'i8 l!!l M"ulati"#.D!i#! 'i8 l!!l M"ulati"#.

4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final 4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage w)ere t)e carrier signal is at its ma<imum amplitu#e* For )ig) level mo#ulator class stage w)ere t)e carrier signal is at its ma<imum amplitu#e* For )ig) level mo#ulator class C amplifier is use#*

C amplifier is use#* :*

:* *at i: t! aa#ta8! " l"7 l!!l "ulati"#;*at i: t! aa#ta8! " l"7 l!!l "ulati"#; An a#vantage of

An a#vantage of low level low level mo#ulatiomo#ulation is n is t)at less t)at less mo#ulating signal mo#ulating signal power ispower is require# to ac)ieve a

require# to ac)ieve a )ig) percentage of mo#ulation)ig) percentage of mo#ulation** >*

>* Di:ti#8ui: <!t7!!# l"7 l!!l a# i8 l!!l "ulati"#.Di:ti#8ui: <!t7!!# l"7 l!!l a# i8 l!!l "ulati"#.

4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e 4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e final stage of t)e transmitter*4t requires less power to ac)ieve a )ig) percentage of  final stage of t)e transmitter*4t requires less power to ac)ieve a )ig) percentage of  mo#ulation*

mo#ulation*

4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage 4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage w)ere t)e carrier signal is at its ma<imum amplitu#e an# t)us ,requires a muc) )ig)er  w)ere t)e carrier signal is at its ma<imum amplitu#e an# t)us ,requires a muc) )ig)er  amplitu#e mo#ulatin

amplitu#e mo#ulating signal to g signal to ac)ieve a ac)ieve a reasona5le percent mo#ulation*reasona5le percent mo#ulation* ?*

/ MARS QUESTIONS AND ANS*ERS / MARS QUESTIONS AND ANS*ERS

UNIT I UNIT I ANALOG

ANALOG COMMUNICATCOMMUNICATIONION 1.

1. D!i#! aD!i#! a2litu! 2litu! M"ulatM"ulati"#.i"#.

Amplitu#e Mo#ulation is t)e process of c)anging t)e amplitu#e of a relatively )ig) Amplitu#e Mo#ulation is t)e process of c)anging t)e amplitu#e of a relatively )ig) frequency carrier signal

frequency carrier signal in proportioin proportion wit) n wit) t)e instantaneous t)e instantaneous value of value of t)e t)e mo#ulatingmo#ulating signal*

signal* +*

+* D!i#! M"ulati"# i#!4 a# 2!!#t "ulati"# " a# AM 7a!.D!i#! M"ulati"# i#!4 a# 2!!#t "ulati"# " a# AM 7a!. Mo#ulation in#e< is a term

Mo#ulation in#e< is a term use# to #escri5e t)e amount of amplitu#e c)ange presentuse# to #escri5e t)e amount of amplitu#e c)ange present in an AM waveform *4t is also calle# as coefficient of mo#ulation* Mat)ematically in an AM waveform *4t is also calle# as coefficient of mo#ulation* Mat)ematically mo#ulation in#e< is

mo#ulation in#e< is m = 1m/ 1c

m = 1m/ 1c

')ere m = Mo#ulation coefficient ')ere m = Mo#ulation coefficient 1m = $ea6 c)ange in

1m = $ea6 c)ange in t)e amplitu#e of t)e output waveform voltage*t)e amplitu#e of t)e output waveform voltage* 1c = $ea6 amplitu#e of t)e

1c = $ea6 amplitu#e of t)e unmo#ulatunmo#ulate# carrier voltage*e# carrier voltage*

$ercent mo#ulation gives t)e percentage c)ange in t)e amplitu#e of t)e output wave w)en $ercent mo#ulation gives t)e percentage c)ange in t)e amplitu#e of t)e output wave w)en t)e carrier is ac

t)e carrier is acte# on 5y a mo#ulating signal*te# on 5y a mo#ulating signal* 0*

0* D!i#! L"7 l!!l D!i#! L"7 l!!l M"ulati"#.M"ulati"#.

4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e 4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e final stage of t)e

final stage of t)e transmitter* transmitter* For low level AM mo#ulator class A amplifier is use#*For low level AM mo#ulator class A amplifier is use#* 7*

7* D!i#! 'i8 l!!l M"ulati"#.D!i#! 'i8 l!!l M"ulati"#.

4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final 4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage w)ere t)e carrier signal is at its ma<imum amplitu#e* For )ig) level mo#ulator class stage w)ere t)e carrier signal is at its ma<imum amplitu#e* For )ig) level mo#ulator class C amplifier is use#*

C amplifier is use#* :*

:* *at i: t! aa#ta8! " l"7 l!!l "ulati"#;*at i: t! aa#ta8! " l"7 l!!l "ulati"#; An a#vantage of

An a#vantage of low level low level mo#ulatiomo#ulation is n is t)at less t)at less mo#ulating signal mo#ulating signal power ispower is require# to ac)ieve a

require# to ac)ieve a )ig) percentage of mo#ulation)ig) percentage of mo#ulation** >*

>* Di:ti#8ui: <!t7!!# l"7 l!!l a# i8 l!!l "ulati"#.Di:ti#8ui: <!t7!!# l"7 l!!l a# i8 l!!l "ulati"#.

4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e 4n low level mo#ulation, mo#ulation ta6es place prior to t)e output element of t)e final stage of t)e transmitter*4t requires less power to ac)ieve a )ig) percentage of  final stage of t)e transmitter*4t requires less power to ac)ieve a )ig) percentage of  mo#ulation*

mo#ulation*

4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage 4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage w)ere t)e carrier signal is at its ma<imum amplitu#e an# t)us ,requires a muc) )ig)er  w)ere t)e carrier signal is at its ma<imum amplitu#e an# t)us ,requires a muc) )ig)er  amplitu#e mo#ulatin

amplitu#e mo#ulating signal to g signal to ac)ieve a ac)ieve a reasona5le percent mo#ulation*reasona5le percent mo#ulation* ?*

An image frequency is any frequency ot)er t)an t)e selecte# ra#io frequency carrier  An image frequency is any frequency ot)er t)an t)e selecte# ra#io frequency carrier  t)at ,if allowe# to enter a receiver an# mi< wit) t)e local oscillator ,will pro#uce a cross t)at ,if allowe# to enter a receiver an# mi< wit) t)e local oscillator ,will pro#uce a cross  pro#uct frequency t)

D!i#! L"al O:illat" ta>i#8.

Trac6ing is t)e a5ility of t)e local oscillator in a receiver to oscillate eit)er a5ove or   5elow t)e selecte# ra#io frequency carrier 5y an amount equal to t)e interme#iate

frequency t)roug)out t)e entire ra#io frequency 5an#* 9. D!i#! 'i8 :i! i#?!ti"# ta>i#8.

4n )ig) si#e in@ection trac6ing , t)e local oscillator s)oul# trac6 a5ove t)e incoming !F carrier 5y a fi<e# frequency equal to f!F f4F *

;* D!i#! L"7 :i! i#?!ti"# ta>i#8*

4n low si#e in@ection trac6ing ,t)e local oscillator s)oul# trac6 5elow t)e !F carrier   5y a fi<e# frequency equal to f!F f4F *

;;* D!i#! ta>i#8 !".'"7 it i: !u!.

T)e #ifference 5etween t)e actual local oscillator frequency an# t)e #esire# frequency is calle# trac6ing error*4t is re#uce# 5y a tec)nique calle# t)ree point trac6ing* ;+* D!i#! ia8! !=u!#$ !?!ti"# ati".

T)e image frequency re@ection ratio is t)e measure of t)e a5ility of preselector to re@ect t)e image frequency* Mat)ematically ,4F!! is

4F!! =8;+r+9;/+

')ere r= 8fim/f!F98f!F/fim9 ;0* D!i#! '!t!"$#i#8.

2etero#yne means to mi< two frequencies toget)er in a nonlinear #evice or to translate one frequency to anot)er using nonlinear mi<ing*

;7* *at a! t! i:aa#ta8!: " "#!#ti"#al ("% "u<l! :i! <a# ull ai! :$:t!;

4n conventional AM ,carrier power constitutes two t)ir#s or more of t)e total transmotte# power*T)is is a ma@or #raw5ac6 5ecause t)e carrier contains no information "t)e si#e5an#s contain t)e information * Secon# ,conventional AM systems utilie twice as muc) 5an#wi#t) as nee#e# wit) single si#e5an# systems*

;:* D!i#! Si#8l! :i!<a# :u22!::! ai! AM.

AM Single si#e5an# suppresse# carrier is a form of amplitu#e mo#ulation in w)ic) t)e carrier is totally suppresse# an# one of t)e si#e5an#s remove#*

;>* D!i#! AM @!:ti8ial :i!<a#. .

AM vestigial si#e5an# is a form of amplitu#e mo#ulation in w)ic) t)e carrier an# one complete si#e5an# are transmitte#,5ut only part of t)e secon# si#e5an# is transmitte#*

;?* *at a! t! aa#ta8!: " :i#8l! :i!<a# ta#:i::i"#; T)e a#vantages of SSBSC are

;* $ower conservation% &ormally ,wit) single si#e 5an# transmission ,only one si#e5an# is transmitte# an# t)e carrier is suppresse#* So less power is require# to pro#uce essentially t)e same quality signal*

+*Ban#wi#t) conservation% Single si#e5an# transmission requires )alf as muc) 5an#wi#t) as conventional AM #ou5le si#e 5an# transmission*

0* &oise re#uction% Because a single si#e 5an# system utilies )alf as muc)  5an#wi#t) as conventional AM,t)e t)ermal noise power is re#uce# to )alf t)at of a #ou5le

si#e 5an# system*

;* *at a! t! i:aa#ta8!: " :i#8l! :i! <a# ta#:i::i"#;

;*Comple< receivers% Single si#e 5an# systems require more comple< an# e<pensive receivers t)an conventional AM transmission *

+* Tuning Difficulties% Single si#e 5an# receivers require more comple< an# precise tuning t)an conventional AM receivers*

;E* D!i#! i!t !=u!#$ "ulati"#.

4n #irect frequency mo#ulation , frequency of a constant amplitu#e carrier signal is #irectly proportional to t)e amplitu#e of t)e mo#ulating signal at a rate equal to t)e frequency of t)e mo#ulating signal*

+* D!i#! i#i!t !=u!#$ M"ulati"#.

4n in#irect frequency mo#ulation ,p)ase of a constant amplitu#e carrier #irectly  proportional to t)e amplitu#e of t)e mo#ulating signal at a rate equal to t)e frequency of t)e

mo#ulating signal*

+;* D!i#! i#:ta#ta#!"u: !=u!#$ !iati"#.

T)e instantaneous frequency #eviation is t)e instantaneous c)ange in t)e frequency of t)e carrier an# is #efine# as t)e first #erivative of t)e instantaneous p)ase #eviation* ++* D!i#! !=u!#$ !iati"#.

Frequency #eviation is t)e c)ange in frequency t)at occurs in t)e carrier w)en it is acte# on 5y a mo#ulating signal frequency* Frequency #eviation is typically given as a pea6  frequency s)ift in 2ert8Do9*T)e pea6 to pea6 frequency #eviation 8+Df9 is sometimes calle# carrier swing*T)e pea6 frequency #eviation is simply t)e pro#uct of t)e #eviation sensitivity an# t)e pea6 mo#ulating signal voltage an# is e<presse# mat)ematically as Df=.; Vm 2

+0* Stat! Ca:"# ul!.

Carson rule states t)at t)e 5an#wi#t) require# to transmit an angle mo#ulate# wave as twice t)e sum of t)e pea6 frequency #eviation an# t)e )ig)est mo#ulating signal

fre-uency. Mathematically carsons rule is

B=+8Df fm9 2*

. D!i#! D!iati"# ati".

Deviation ratio is t)e worst case mo#ulation in#e< an# is equal to t)e ma<imum  pea6 frequency #eviation #ivi#e# 5y t)e ma<imum mo#ulating signal frequency*

Mat)ematically ,t)e #eviation ratio is D!= Df 8ma<9 fm8ma<9

/5. *at i: ulti2l!4i#8;

Multiple<ing is t)e transmission of information from one or more source to one or  more #estination over t)e same transmission me#iam*

UNIT II

DIGITAL COMMUNICATION 31. D!i#! ta#:i::i"# li#!.

A transmission line is a metallic con#uctor system t)at is use# to transfer electrical energy from one point to anot)er* A transmission line is two or more con#uctors separate#  5y an insulator, suc) as a pair of wires or a system of wire pairs*

0+* D!i#! <ala#! ta#:i::i"# li#!.

4n 5alance# transmission line, 5ot) con#uctors carry current" one con#uctor carries t)e signal an# t)e ot)er is t)e return* T)is type of transmission is calle# #ifferential or   5alance# signal transmission*

00* D!i#! u#<ala#! ta#:i::i"# li#!.

4n un5alance# transmission line, one wire is at groun# potential w)ere as t)e ot)er  wire is at signal potential* T)is type of transmission is calle# single en#e# or un5alance# signal transmission*

07* D!i#! O2!# 7i! ta#:i::i"# li#!.

An open wire transmission line is a two wire parallel con#uctor* 4t consists simply of two parallel wires, closely space# an# separate# 5y air* &oncon#uctive spacers are  place# at perio#ic intervals for support an# to 6eep t)e #ielectric 5etween t)e con#uctors

constant* T)e #ielectric is simply t)e air 5etween an# aroun# t)e two con#uctors in w)ic) t)e T1M wave propagates*

0:* *at a! t! aa#ta8!: " "2!# 7i! ta#:i::i"# li#!; a* Simple in construction

 5* !a#iation losses are )ig)

c* 4t is suscepti5le to noise pic6ups* 0>* D!i#! t7i:t! 2ai a<l!.

are ca5le# into cores* T)e cores are covere# wit) various types of s)eat)s neig)5oring pairs are twiste# wit) #ifferent pitc) to re#uce interference 5etween pairs #ue to mutual con#uction*

B. D!i#! :i!l! a<l! ta#:i::i"# li#!.

4n s)iel#e# ca5le transmission line, parallel two wire transmission lines are enclose# in a metallic con#uctive metal 5rai# to re#uce t)e ra#iation losses an# interference* T)e metal 5rai# is connecte# to groun# acts as s)iel#* T)e 5rai# also prevents signal ra#iation from reac)ing t)e con#uctors*

0* D!i#! "#!#ti ta#:i::i"# li#!.

Coa<ial or concentric con#uctors are use# for )ig) frequency applications to re#uce losses an# to isolate transmission pat)s* T)e 5asic coa<ial ca5le consists of a center  con#uctor surroun#e# 5y a concentric con#uctor* At )ig) frequencies, t)e coa<ial outer  con#uctor provi#es e<cellent s)iel#ing against e<ternal interference*

0E* D!:i<! t! !l!tial a# 2$:ial 2"2!ti!: " a ta#:i::i"# li#!.

T)e electrical properties of a transmission line are wire con#uctivity an# insulator  #ielectric constant* T)e p)ysical properties are wire #iameter an# con#uctor spacing*

7* Li:t a# !:i<! t! "u 2ia$ "#:ta#t: " a ta#:i::i"# li#!.

T)e primary constants of a transmission line are series #c resistance, series in#uctance, s)unt capacitance, an# s)unt con#uctance* T)e primary constants are uniformly #istri5ute# t)roug) out t)e lengt) of t)e line an# t)erefore are commonly calle# #istri5ute#  parameters*

7;* Li:t t! :!"#a$ "#:ta#t: " a ta#:i::i"# li#!. Secon#ary constants of a transmission line are   C)aracteristic impe#ance*

  $ropagation constant

7+* D!i#! aat!i:ti i2!a#! " a ta#:i::i"# li#!.

C)aracteristic impe#ance is #efine# as t)e impe#ance seen loo6ing into an infinitely long line or t)e impe#ance seen loo6ing into a finite lengt) of line t)at is terminate# in a  purely resistive loa# equal to t)e c)aracteristic impe#ance of t)e line* 4t is also calle# as

surge impe#ance*

70* D!i#! 2"2a8ati"# "#:ta#t.

$ropagation constant is use# to e<press t)e attenuation 8signal loss9 an# t)e p)ase s)ift per unit lengt) of a transmission line* 4t is also calle# as propagation coefficient*

77* D!i#! !l"it$ at" " a ta#:i::i"# li#!.

Velocity factor 8sometimes calle# velocity constant 9 is #efine# as t)e ratio of t)e actual velocity of propagation t)roug) free space* Mat)ematically t)e velocity factor is Vf=vp/c

')ere vf= velocity factor

Vp=actual velocity of propagation

5. Li:t a# !:i<! i! t$2!: " ta#:i::i"# li#! l"::!:.

Transmission line losses are con#uctor loss, ra#iation loss, #ielectric )eating loss, coupling loss, an# corona*

7>* D!:i<! a# i#i!#t 7a!, !l!t! 7a!.

An or#inary transmission line is 5i#irectional" power can propagate equally well in  5ot) #irections* Voltage t)at propagates from t)e source towar# t)e loa# is calle# inci#ent voltage, an# t)e voltage t)at propagates from t)e loa# towar# t)e source is calle# reflecte# voltage*

7?* D!i#! !:"#a#t li#!.

A transmission line wit) no reflecte# power is calle# a flat or resonant line* 7* D!i#! #"#!:"#a#t ta#:i::i"# li#!.

A transmission line is nonresonant if it is of finite lengt) or if it is terminate# wit) a resistive loa# equal in o)mic value to t)e c)aracteristic impe#ance of t)e transmission line* 7E* D!i#! !l!ti"# "!ii!#t.

T)e reflection coefficient 8sometimes calle# t)e coefficient of reflection9 is a vector  quantity t)at represents t)e ratio of reflecte# voltage to inci#ent voltage or reflecte# current to inci#ent current *Mat)ematically ,t)e reflection coefficient is gamma,  , #efine# 5y

 =1r/1i 8or9 4r/4i

')ere =reflection coefficient 8unitless9 1i =inci#ent voltage 8volts9

1r =reflecte# voltage 8volts9 4r = reflecte# current 8amps9 4i =inci#ent current 8amps9 :* D!i#! at! li#!.

')en 3o=3H, all t)e inci#ent power is a5sor5e# 5y t)e loa# *T)is is calle# a matc)e# line*

')ere 3o=c)aracteristic impe#ance 3H= loa# impe#ance

:;* D!i#! u#at! li#!.

')en 3o  3H, some of t)e inci#ent power is a5sor5e# 5y t)e loa# an# some is returne# to t)e source* T)is is calle# an unmatc)e# or mismatc)e# line*

')ere 3o=c)aracteristic impe#ance 3H= loa# impe#ance

:+* D!i#! :ta#i#8 7a!.

4n unmatc)e# line, some of t)e inci#ent power is a5sor5e# 5y t)e loa# an# some is returne# to t)e source* So t)ere are two electromagnetic waves, traveling in opposite

rection present on t)e line at t)e same time* T)e two traveling waves setup an terference pattern 6nown as stan#ing wave*

:0* D!i#! :ta#i#8 7a! ati".

T)e stan#ing wave ratio is #efine# as t)e ratio of t)e ma<imum voltage to t)e minimum voltage 8or9 t)e ma<imum current to t)e minimum current of a stan#ing wave on a transmission line*S'! is often calle# t)e voltage stan#ing wave ratio 8VS'!9*

S'!= Vma< Vmin

:7* D!i#! 8"u# 7a! 2"2a8ati"#.

A groun# wave is an electromagnetic wave t)at travels along t)e surface of eart)* T)erefore groun# waves are sometimes calle# surface waves* (roun# waves must 5e vertically polarie#*

::* *at a! t! i:aa#ta8!: " 8"u# 7a! 2"2a8ati"#; ;* (roun# waves require relatively )ig) transmission power*

+* (roun# waves are limite# to very low, low, an# me#ium frequencies, requiring large antennas*

:>* *at a! t! aa#ta8!: " 8"u# 7a! 2"2a8ati"#;

;* (roun# waves are relatively unaffecte# 5y c)anging atmosp)eric con#itions* +* 4f t)e transmitte# power is large enoug), t)en groun# wave propagation can 5e use# to communicate 5etween any two points in t)e worl#*

:?* D!i#! :2a! 7a! 2"2a8ati"#.

Space wave propagation of electromagnetic energy inclu#es ra#iate# energy t)at

tra/els in the lower few miles of earths atmosphere. Space wa/es

inclu#e 5ot) #irect an# groun# reflecte# waves* Direct waves travel essentially in a straig)t line 5etween t)e transmit an# receive antennas* space wave propagation wit) #irect waves is commonly calle# line of sig)t transmission*

:* D!i#! :>$ 7a!:.

waves *

1lectromagnetic waves t)at are #irecte# a5ove t)e )orion level are calle# s6y

:* D!i#! itial !=u!#$.

T)e critical frequency is #efine# as t)e )ig)est frequency t)at can 5e propagate# #irectly upwar# an# still 5e returne# to eart) 5y t)e ionosp)ere*

:E* D!i#! itual !i8t.

Virtual height is the height abo/e earths surface from which a refracte$ wave appears to )ave 5een reflecte#*

#i in

>* D!i#! a4iu u:a<l! !=u!#$.

Ma<imum usa5le frequency is t)e )ig)est frequency t)at can 5e use# for s6y wave  propagation 5etween two specific po

ints on earths surface.

UNIT III

SOURCE CODES, LINE CODES & ERROR CONTROL (Qualitati! "#l$% 61. *at a! t! aa#ta8!: " i8ital ta#:i::i"#;

a* T)e a#vantage of #igital transmission over analog transmission is noise immunity* Digital pulses are less suscepti5le t)an analog signals to variations cause# 5y noise*

0#igital signals are better suite$ to processing an$ multiple1ing than

analog

signals*

0#igital transmission systems are more noise resistant than the analog

transmission systems*

0#igita

l systems are 5etter suite# to evaluate error performance* >+* *at a! t! i:aa#ta8!: " i8ital ta#:i::i"#;

  T)e transmission of #igitally enco#e# analog signals requires significantly more  5an#wi#t) t)an simply transmitting t)e original analog signal*

  Analog signal must 5e converte# to #igital co#es prior to transmission an# converte# 5ac6  to analog form at t)e receiver, t)us necessitating a##itional enco#ing an# #eco#ing circuitry*

>0* D!i#! 2ul:! "! "ulati"#.

4n pulse co#e mo#ulation, analog signal is sample# an# converte# to fi<e# lengt), serial 5inary num5er for transmission* T)e 5inary num5er varies accor#ing to t)e amplitu#e of t)e analog signal*

>7* *at i: t! 2u2":! " t! :a2l! a# "l iuit;

T)e sample an# )ol# circuit perio#ically samples t)e analog input signal an# converts t)ose samples to a multilevel $AM signal*

>:* *at i: t! N$=ui:t :a2li#8 at!;

 &yquist sampling rate states t)at, t)e minimum sampling rate is equal to twice t)e )ig)est au#io input frequency*

>>* D!i#! a# :tat! t! au:!: " "l "! i:t"ti"#.

T)e minimum sampling rate8fs9 is equal to twice t)e )ig)est au#io input frequency8fa9*4f fs is less t)an two times fa ,#istortion will result* T)e #istortion is Calle# aliasing or fol# over #istortion* T)e si#e frequencies from one )armonic fol# over into t)e si#e5an# of anot)er 

)armonic* T)e frequency t)at fol#s over is an alias of t)e input signal )ence ,t)e

names “aliasing” or “fol$ o/er $istortion” .

4f t)e magnitu#e of sample e<cee#s t)e )ig)est quantiation interval, overloa# #istortion occurs*

. D!i#! =ua#tiati"#.

uantiation is a process of appro<imation or roun#ing off* Assigning $CM co#es to a5solute magnitu#es is calle# quantiing*

>E* D!i#! $#ai a#8!.

Dynamic range is t)e ratio of t)e largest possi5le magnitu#e to t)e smallest possi5le magnitu#e* Mat)ematically, #ynamic range is

D!= Vma< Vmin

?* D!i#! "i#8 !ii!#$.

Co#ing efficiency is t)e ratio of t)e minimum num5er of 5its require# to ac)ieve a certain #ynamic range to t)e actual num5er of $CM 5its use#* Mat)ematically, co#ing efficiency is

Co#ing efficiency= Minimum num5er of 5its 8inclu#ing sign 5it9 G ; Actual num5er of 5its8inclu#ing sign 5it9

?;* D!i#! "2a#i#8.

Compan#ing is t)e process of compressing, t)en e<pan#ing* 'it) compan#e# systems, t)e )ig)er amplitu#e analog signals are compresse# prior to transmission, t)en e<pan#e# at t)e receiver*

?+* D!i#! :l"2! "!l"a. '"7 it i: !u!.

T)e slope of t)e analog signal is greater t)an t)e #elta mo#ulator can maintain, an# is calle# slope overloa#* Slope overloa# is re#uce# 5y increasing t)e cloc6 frequency an#  5y increasing t)e magnitu#e of t)e minimum step sie*

?0* D!i#! 8a#ula #"i:!.'"7 it i: !u!.

')en t)e original input signal )as relatively constant amplitu#e, t)e reconstructe# signal )as variations t)at were not present in t)e original signal* T)is is calle# granular  noise*

(ranular noise can 5e re#uce# 5y #ecreasing t)e step sie* ?7* D!i#! aa2ti! !lta "ulati"#.

A#aptive #elta mo#ulation is a #elta mo#ulation system w)ere t)e step sie of t)e AC is automatically varie# #epen#ing on t)e amplitu#e c)aracteristics of t)e analog input signal*

?:* D!i#! 2!a> !=u!#$ !iati"# " S.

$ea6 frequency #eviation 8f9 is t)e #ifference 5etween t)e carrier rest frequency an# eit)er t)e mar6 or space frequency an# eit)er t)e mar6 or space frequency*

6. D!i#! "ulati"# i#!4 " S.

T)e mo#ulation in#e< in FS. is #efine# as ) = 8f9

fa

w)ere )= FM mo#ulation in#e< calle# t)e ) factor in FS. fa = fun#amental frequency of t)e 5inary mo#ulating signal 8f9 = $ea6 frequency #eviation 8)ert9

??* D!i#! <it at!.

4n #igital mo#ulation, t)e rate of c)ange at t)e input to t)e mo#ulator is calle# t)e

 5it rate 8f59 an# )as t)e unit of 5its per secon# 85ps9* ?* D!i#! )au at!.

T)e rate of c)ange at t)e output of t)e mo#ulator is calle# 5au#* ?E* D!i#! QAM.

ua#rature amplitu#e mo#ulation is a form of #igital mo#ulation w)ere t)e #igital information is containe# in 5ot) t)e amplitu#e an# p)ase of t)e transmitte# carrier*

* *it! t! !lati"#:i2 <!t7!!# t! i#iu <a#7it !=ui! " a# S :$:t! a# t! <it at!.

T)e minimum 5an#wi#t) can 5e appro<imate# as B=+f +f5

')ere B=minimum 5an#wi#t) 8)ert9

 f=minimum pea6 frequency #eviation 8)ert9 F5=5itrate

UNIT I@

MULTILE ACCESS TEC'NIQUES 1. D!i#! ata "u#iati"# "!:.

Data communication co#es are prescri5e# 5it sequences use# for enco#ing c)aracters an# sym5ols*

+* D!i#! !" !t!ti"#.

1rror #etection is simply t)e process of monitoring t)e receive# #ata an# #etermining w)en a transmission )as occurre#*

0* D!i#! E"2l!4. B

1c)ople< is a relatively simple type of error #etection sc)eme t)at is use# almost e<clusively in #ata communications systems w)ere )uman operators are use# to enter t)e #ata manually from a 6ey5oar#*

. D!:i<! :!ial i#t!a!.

Serial interface is use# to ensure an or#erly flow of #ata 5etween t)e line control unit an# t)e mo#em*

:* D!i#! 2aall!l i#t!a!.

$arallel interfaces transfer #ata 5etween two #evices eig)t or more 5its a time* T)at is one entire #ata wor# is transmitte# at a time *$arallel transmission is sometimes referre# to as serial 5y wor# transmission*

>* *at a! t! aa#ta8!: " 2aall!l ta#:i::i"#;

T)e a#vantage of parallel transmission is #ata are transmitte# muc) faster t)an wit) serial transmission 5ecause t)ere is a transmission pat) for eac) 5it of t)e wor#* 4n parallel interface t)ere is no nee# to convert #ata from parallel to serial or vice versa*

?* *at i: t! 2u2":! " ata "!;

T)e primary purpose of #ata mo#em is to interface computers, computer networ6s, an# ot)er #igital terminal equipment to analog communication lines an# ra#io terminals* * Cla::i$ ata "!:.

Data mo#ems are generally classifie# in to sync)ronous an# async)ronous #ata mo#ems*

E* D!i#! OSI.

T)e term open system interconnection is t)e name for a set of stan#ar#s for  communications among computers* T)e primary purpose of -S4 stan#ar#s is to serve as a structural gui#eline for e<c)anging information 5etween computers, terminals an# networ6s*

E* *at a! t! aa#ta8!: " <u: t"2"l"8$;

a* T)e 5us topology is easy to un#erstan#, install, an# use for small networ6s*

 5* T)e ca5ling cost is less as t)e 5us topology requires t)e least amount of ca5le to connect t)e computers*

c* T)e 5us topology is easy to e<pan# 5y @oining two ca5les wit) a B&C 5arrel connector*

#* 4n t)e e<pansion of 5us topology repeaters are use# to 5oost t)e signal an# increase t)e #istance*

E;* *at a! t! i:aa#ta8!: " :ta t"2"l"8$;

-ne #isa#vantage of a star topology is t)at t)e networ6 is only as relia5le as t)e central no#e* ')en t)e central no#e fails, t)e entire system fails*

E+* D!:i<! LAN.

A local area networ6 is usually a privately owne# an# lin6s t)e #evices in a single office, 5uil#ing or campus of up to a few 6ilometers in sie*

3. D!i#! LAN t"2"l"8$.

T)e topology or p)ysical arc)itecture of a HA& i#entifies )ow t)e stations are interconnecte#*

E7* *at a! t! :!!# la$!: " "2!# :$:t! i#t!"##!ti"#; T)e seven layers of open system interconnection are

  $)ysical layer    Data lin6 layer    &etwor6 layer    Transport layer    Session layer    $resentation layer    Application layer  UNIT @

SATELLITE, OTICAL I)ER

–

O*ERLINE, SCADA 95. D!i#! :at!llit!.

Satellite is a celestial 5o#y t)at or5its aroun# a planet*4n aerospace terms, a satellite is a space ve)icle launc)e# 5y )umans an# or5its eart) or anot)er celestial 5o#y*

*,.State eplers first law.

 eplers first law states that a satellite will orbit a

primary bo$y following

an elliptical pat)*

*!.State eplers secon$ law.

 eplers secon$ law states that for e-ual time inter/als of time a satellite will sweep out equal areas in t)e or5ital plane, focuse# at t)e 5ary center*

+. State eplers thir$ law.

T)e t)ir# law states t)at t)e square of t)e perio#ic time of or5it is proportional to t)e cu5e of t)e mean #istance 5etween t)e primary an# t)e satellite*

EE* D!i#! "<ital :at!llit!.

-r5ital satellites are also calle# as nonsync)ronous satellite*&onsync)ronous satellites rotate aroun# eart) in an elliptical or circular pattern* 4n a circular or5it, t)e spee# or rotation is constant )owever in elliptical or5its t)e spee# #epen#s on t)e )eig)t t)e satellite is a5ove t)e eart)*

;* D!i#! 2"8a! "<it.

'f the satellite is orbiting in the same $irection as earths rotation an$ at an angular velocity greater t)an t)at of eart), t)e or5it is calle# a  progra#e 8or9 posigra#e or5it*

01. D!i#! !t"8a! "<it.

'f the satellite is orbiting in the opposite $irection as the earths rotation or in t)e same #irection wit) an angular velocity less t)an t)at of eart), t)e or5it is calle# a retrogra#e or5it*

;+* D!i#! G!" :$#"#"u: :at!llit!.

(eo sync)ronous or geo stationary satellites are t)ose t)at or5it in a circular pattern wit) an angular velocity equal to t)at of 1rat)* (eosync)ronous satellites )ave an or5ital time of appro<imately +7 )ours, t)e same as eart)" t)us geosync)ronous satellites appear to  5e stationary as t)ey remain in a fi<e# position in respect to a given point on eart)*

;0* D!i#! a2"8!! a# 2!i8!!.

T)e point in an or5it w)ic) is locate# fart)est from t)e eart) is calle# apogee* T)e point in an or5it w)ic) is locate# closest to eart) is calle# perigee*

;7* D!i#! a#8l! " i#li#ati"#.

 T he angle of inclination is the angle between the earths e-uatorial plane an# t)e or5ital plane of a satellite measure# countercloc6wise at t)e point in t)e or5it w)ere it crosses t)e equatorial plane traveling from sout) to nort)*

;:* D!i#! D!!#i#8 #"!.

T)e point w)ere a polar or incline# or5it crosses t)e equatorial plane traveling from sout) to nort)* T)is point is calle# #escen#ing no#e*

;>* D!i#! a:!#i#8 #"!.

T)e point w)ere a polar or incline# or5it crosses t)e equatorial plane traveling from nort) to sout) is calle# ascen#ing no#e*

;?* D!i#! li#! " #"!:.

T)e line @oining t)e ascen#ing an# #escen#ing no#es t)roug) t)e center of eart) is calle# line of no#es*

;* D!i#! a#8l! " !l!ati"#.

Angle of elevation is t)e vertical angle forme# 5etween t)e #irection of travel of an electromagnetic wave ra#iate# from an eart) station antenna pointing #irectly towar# a satellite an# t)e )oriontal plane*

;E* D!i#! Aiut a#8l!.

Aimut) is t)e )oriontal angular #istance from a reference #irection, eit)er t)e sout)ern or nort)ern most point of t)e )orion*

;;* *at a! t! aa#ta8!: " "2tial i<! "u#iati"#;   (reater information capacity

4mmunity to static interference 1nvironmental immunity

  Safety   Security

;;;* D!i#! a i<! "2ti :$:t!.

An optical communications system is an electronic communication system t)at uses lig)t as t)e carrier of information* -ptical fi5er communication systems use glass or plastic fi5ers to contain lig)t waves an# gui#e t)em in a manner similar to t)e way electromagnetic waves are gui#e# t)roug) a wavegui#e*

;;+* D!i#! !ati! i#!4.

T)e refractive in#e< is #efine# as t)e as t)e ratio of t)e velocity of propagation of  lig)t ray in free space to t)e velocity of propagation of a lig)t ray in a given material*

Mat)ematically, t)e refractive in#e< is n = c/ 

w)ere c = spee# of lig)t in free space   = spee# of lig)t in a given material

;;0* D!i#! itial a#8l!.

Critical angle is #efine# as t)e minimum angle of inci#ence at w)ic) a lig)t ray may stri6e t)e interface of two me#ia an# result in an angle of refraction of EIor greater*

;;7* D!i#! :i#8l! "! a# ulti "! 2"2a8ati"#.

4f t)ere is only one pat) for lig)t to ta6e #own t)e ca5le, it is calle# single mo#e* 4f t)ere is more t)an one pat) ,it is calle# multimo#e*

;;:* D!i#! a!2ta#! a#8l!.

4t #efines t)e ma<imum angle in w)ic) e<ternal lig)t rays may stri6e t)e air/fi5er  interface an# still propagate #own t)e fi5er wit) a response t)at is no greater t)an ; #B  5elow t)e ma<imum value*

;;>* D!i#! #u!ial a2!tu!.

 &umerical aperture is mat)ematically #efine# as t)e sine of t)e ma<imum angle a lig)t ray entering t)e fi5er can )ave in respect to t)e a<is of t)e fi5er an# still propagate #own t)e ca5le 5y internal reflection*

;;?* D!i#! "al i:2!:i"#.

Mo#al #ispersion or pulse sprea#ing is cause# 5y t)e #ifference in t)e propagation times of lig)t rays t)at ta6e #ifferent pat)s #own a fi5er* Mo#al #ispersion can occur only   

in multimo#e fi5ers*4t can 5e re#uce# 5y using single mo#e step in#e< fi5ers an# gra#e# in#e< fi5ers*

1. *at a! t! aa#ta8!: " !t!"?u#ti"# LED:;

a* T)e increase in current #ensity generates a more 5rilliant lig)t spot* 5* T)e smaller emitting area ma6es it easier to couple its emitte# lig)t into fi5er*

c* T)e small effective area )as a smaller capacitance, w)ic) allows t)e planar  )etero@unction H1D to 5e use# at )ig)er spee#s*

119. *at a! t! i:aa#ta8!: " i#?!ti"# la:! i"!;

  4HDs are typically on t)e or#er of ; times more e<pensive t)an H1Ds

  Because 4HDs operate at )ig)er powers, t)ey typically )ave a muc) s)orter life time t)an H1Ds*

  4HDs are more temperature #epen#ent t)an H1Ds* 16 a> Qu!:ti"#: 1. E42lai# i# !tail a<"ut :u2! !t!"$#! !!i!.

2etero#yne means to mi< two frequencies toget)er in a nonlinear #evice or to translate one frequency to anot)er using nonlinear mi<ing* T)ere are five sections to a super)etero#yne receiver* T)ey are !F section,t)e mi<er/converter section,t)e 4F section,t)e au#io #etector section, an# t)e amplifier section*

R

:!ti"#-T)e !F section consists of preselector an# an amplifier stage*:!ti"#-T)e primary purpose of t)e preselector is to provi#e enoug) initial 5an#limiting to prevent a specific unwante# ra#io frequency,calle# t)e image frequency*

An image frequency is any frequency ot)er t)an t)e selecte# ra#io frequency carrier t)at ,if  allowe# to enter a receiver an# mi< wit) t)e local oscillator ,will pro#uce a cross pro#uct frequency t)at is equal to t)e interme#iate frequency*

Mi4! "#!t!

:!ti"#-T)e mi<er stage is a nonlinear #evice an# its purpose is to convert ra#io frequencies to interme#iate frequencies*

I

:!ti"#-T)e 4F section consists of a series of 4F amplifiers an# 5an#pass filters an# is often calle# t)e 4F strip* T)e receiver gain an# selectivity is ac)ieve# in 4F section*

D!t!t"

S!ti"#-T)e purpose of t)e #etector section is to convert t)e 4F signals 5ac6 to t)e original source information*

Aui" A2lii!

:!ti"#-T)e au#io section comprises several casca#e# au#io amplifiers an# one or more spea6ers* +* E42lai# i# !tail a<"ut AM "ulat" iuit:.

T)e location in a transmitter w)ere mo#ulation occurs #etermines w)et)er t)e circuit is a low level or a )ig) level transmitter* 4n low level mo#ulation, mo#ulation ta6es  place prior to t)e output element of t)e final stage of t)e transmitter* For low level AM

mo#ulator class A amplifier is use#* 4n )ig) level mo#ulators, t)e mo#ulation ta6es place in t)e final element of t)e final stage w)ere t)e carrier signal is at its ma<imum amplitu#e* For )ig)

level mo#ulator class C amplifier is use#* An a#vantage of low level mo#ulation is t)at less mo#ulating signal power is require# to ac)ieve a )ig) percentage of mo#ulation*

E42lai# i# !tail a<"ut M "ulat":.

FM mo#ulators are classifie# into two types*T)ey are ;*Direct FM mo#ulators

+*4n#irect FM mo#ulators Di!t M

"ulat"-4n #irect frequency mo#ulation, frequency of a constant amplitu#e carrier signal is #irectly proportional to t)e amplitu#e of t)e mo#ulating signal at a rate equal to t)e frequency of t)e mo#ulating signal* T)ere are t)ree common met)o#s for pro#ucing #irect frequency mo#ulation% Varactor #io#e mo#ulators, FM reactance mo#ulators, an# linear  integrate# circuit #irect FM mo#ulators*

I#i!t M

"ulat"-4n in#irect frequency mo#ulation ,p)ase of a constant amplitu#e carrier #irectly  proportional to t)e amplitu#e of t)e mo#ulating signal at a rate equal to t)e frequency of t)e

mo#ulating signal*

7* E42lai# i# !tail a<"ut M !"ulat":.

FM #emo#ulators are frequency #epen#ent circuits #esigne# to pro#uce an output voltage t)at is proportional to t)e instantaneous frequency*Several circuits are use# for  #emo#ulating FM signals*T)e most common are t)e slope #etector, foster seeley #iscriminator, an# ratio #etector are forms of tune# circuit frequency #iscriminators*

:* E42lai# i# !tail a<"ut AM 2!a> !t!t".

T)e function of an AM #etector is to #emo#ulate t)e AM signal an# recover or  repro#uce t)e original source information*T)e recovere# signal s)oul# contain t)e same frequencies as t)e original information signal an# )ave t)e same relative amplitu#e c)aracteristics*

>* E42lai# i# !tail a<"ut 2ul:! "! "ulati"#.

4n pulse co#e mo#ulation, analog signal is sample# an# converte# to fi<e# lengt), serial 5inary num5er for transmission* T)e 5inary num5er varies accor#ing to t)e amplitu#e of t)e analog signal*

?* E42lai# i# !tail a<"ut )S. Stat! !it: a# !!it: " )S.

4n 5inary p)ase s)ift 6eying, two output p)ases are possi5le for a single carrier  frequency* -ne output p)ase represents logic ; an# t)e ot)er logic * B$S. transmitter% * E42lai# i# !tail a<"ut QS.

$S. is an Mary enco#ing sc)eme w)ere M=7*'it) $S. four output p)ases are  possi5le for a single carrier frequency* Two 5its are cloc6e# into t)e 5it splitter* After 5ot)

 5its )ave 5een serially inputte#, t)ey are simultaneously parallel outputte# * -ne 5it is #irecte# to t)e 4 c)annel an# t)e ot)er to t)e  c)annel *T)e 4 5it mo#ulates a carrier t)at is in p)ase wit) t)e reference oscillator an# t)e  5it mo#ulates a carrier t)at is EI out of   p)ase or in qua#rature wit) t)e reference carrier*

E42lai# i# !tail a<"ut S.

Frequency s)ift 6eying is a form of constant amplitu#e angle mo#ulation similar to conventional frequency mo#ulation e<cept t)at t)e mo#ulating signal is a 5inary signal t)at varies 5etween two #iscrete voltage levels rat)er t)an a continuously c)anging analog waveform*

;* E42lai# i# !tail a<"ut  2a:! S.

1ig)t p)ase $S. is an Mary enco#ing tec)nique w)ere M=*'it) an  $S.  mo#ulator ,t)ere are eig)t possi5le output p)ases *To enco#e eig)t #ifferent p)ases ,t)e incoming 5its are consi#ere# in groups of t)ree 5its ,calle# tri5its*

;;* E42lai# i# !tail a<"ut 8!":$#"#"u: :at!llit!. Stat! it: aa#ta8!: a# i:aa#ta8!:.

(eo sync)ronous or geo stationary satellites are t)ose t)at or5it in a circular pattern wit) an angular velocity equal to t)at of 1rat)* (eosync)ronous satellites, )ave an or5ital time of appro<imately +7 )ours,t)e same as eart)" t)us geosync)ronous satellites appear to  5e stationary as t)ey remain in a fi<e# position in respect to a given point on eart)*

;+* )i!l$ !:i<! t! "2!ati"# " a li8t !itti#8 i"!.

Hig)t emitting #io#e is a pn @unction #io#e, usually ma#e from a semicon#uctor  material suc) as aluminum gallium arseni#e or gallium arseni#e p)osp)i#e*H1Ds emit lig)t  5y spontaneous emission

–

lig)t is emitte# as a result of t)e recom5ination of electrons an# )oles* ')en forwar# 5iase#, minority carriers are in@ecte# across t)e pn @unction* -nce across t)e @unction, t)ese minority carriers recom5ine wit) ma@ority carriers an# give up energy in t)e form of lig)t*

;0* )i!l$ !:i<! t! "2!ati"# " a# i#?!ti"# la:! i"!.

T)e in@ection laser #io#e is similar to H1D* 4n fact, 5elow a certain t)res)ol# current, an 4HD acts similarly to an H1D* A5ove t)e t)res)ol# current, an 4HD oscillates" lasing occurs*

T)e #isa#vantages of in@ection laser #io#e are

  4HDs are typically on t)e or#er of ; times more e<pensive t)an H1Ds   Because 4HDs operate at )ig)er powers, t)ey typically )ave a muc) s)orter

life time t)an H1Ds*

  4HDs are more temperature #epen#ent t)an H1Ds*

;7* *at a! t! i!!#t t$2!: " ata "u#iati"# "!:; E42lai# i# !tail. T)e #ifferent types of #ata communication co#es are

i* ASC44 Co#e

ii* 1BCD4C Co#e iii* Bar Co#es

;:* E42lai# i# !tail a<"ut :!ial a# 2aall!l i#t!a!. 9.

Serial interface is use# to ensure an or#erly flow of #ata 5etween t)e line control unit an# t)e mo#em* $arallel interfaces transfer #ata 5etween two #evices eig)t or more 5its a time* T)at is one entire #ata wor# is transmitte# at a time *$arallel transmission is

metimes referre# to as serial 5y wor# transmission* T)e a#vantage of parallel ansmission is #ata are transmitte# muc) faster t)an wit) serial transmission 5ecause t)ere is a transmission pat) for eac) 5it oft)e wor#* 4n parallel interface t)ere is no nee# to convert #ata from parallel to serial or vice versa*

;>* E42lai# i# !tail a<"ut Data "!:.

T)e primary purpose of #ata mo#em is to interface computers, computer networ6s, an# ot)er #igital terminal equipment to analog communication lines an# ra#io terminals* Data mo#ems are generally classifie# in to sync)ronous an# async)ronous #ata mo#ems* A:$#"#"u:

M"!:-Async)ronous mo#ems are use# primarily for low spee# #ata circuits* 4t use AS. or FS.* S$#"#"u: ata

"!:-Sync)ronous #ata mo#ems are use# for me#ium an# )ig) spee# #ata transmission an# use eit)er $S. or AM mo#ulation*

;?* E42lai# i# !tail a<"ut ISDN.

T)e 4ntegrate# Services Digital &etwor6 is a propose# networ6 to provi#e voice, #ata, vi#eo, an# facsimile information wit)in t)e same networ6* 4SD& arc)itecture%

T)ere are t)ree 5asic types of c)annels availa5le wit) 4SD&*T)ey are B c)annel% >7.5ps

D c)annel% ;> or >7 .5ps

2 c)annel% 07,;:0>, or ;E+ .5ps ;* E42lai# i# !tail a<"ut LAN.

A local area networ6 is usually a privately owne# an# lin6s t)e #evices in a single office, 5uil#ing or campus of up to a few 6ilometers in sie*

LAN

t"2"l"8i!:-T)e topology or p)ysical arc)itecture of a HA& i#entifies )ow t)e stations are interconnecte#*

T)e #ifferent types of topologies are   Star topology

  Bus topology !ing topology ;E* E42lai# i# !tail a<"ut OSI.

T)e term open system interconnection is t)e name for a set of stan#ar#s for  communications among computers* T)e primary purpose of -S4 stan#ar#s is to serve as a structural gui#eline for e<c)anging information 5etween computers, terminals an# networ6s*

T)e seven layers of open system interconnection are   $)ysical layer 

  Data lin6 layer    &etwor6 layer    Transport layer 

  Session layer    $resentation layer    Application layer