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Principles of Communication

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  PRINCIPLE OF COMMUNICATIONS Principles of Communication Communication is the process of transmission of signals from place to place It in!ol!es !arious steps inclu ing# reception# processing# propagation# recei!ing an interpreting From the time of sen ing a  person thousan s of $ilometers to this perio communication has e!elope  In e!er% &al$ of life communication pla%s an important role A !ancement of technolog% an the nee for 'uic$ transmission of signals has impro!e the fiel of communication Basic Elements of a Communication System (Transmitter# channel an a recei!er form )asic elements of a communication s%stem From the transmitter signal is sent an the recei!er recei!es the signal The me ia responsi)le for carr%ing the infromation  )et&een the transmitter an recei!er is calle channel Transmitter an recei!er are trans ucers &hich con!ert signal from one form to another# so that carr%ing# processing or recei!ing the information  )ecomes easier Design :  The follo&ing factors arc to )e $ept in min &hile the communication s%stem is )eing esigne *i+ Form of con!e%ing the information#*ii+ Use of information )% transmitter#*iii+ Fee ing the channel &ith information appropriatel%# *i!+ Effect of channel on information#*!+ Metho of presenting the information )% the recei!er an *!i+ ,ifference if an% )et&een the srcinal an the recei!e signal What Signal Means? Signal means the information to )e communicate in the electrical form Signal is classifie into t&o forms *i+ Analog Signal - Continuous signal ha!ing multiple le!els )ut confine )et&een a ma.imum an minimum !alue *ii+ Digital Signal - A iscontinuous signal ha!ing onl% t&o clearl% efine le!els or !alues Sinusoi al Signal /0 A sin* ω t+ or / 0 Acos* ω t+ is the simplest form The range of    fre'uencies f 0 * ω 12 π +3ranges from 2456to 24$56 *7an -&i th+ for au io signals,igital signals are to ha!e efine !alues put in co e form &hich is interprete )% the electronic e!ices un er use Analog signals can )e ma e igital an !ice-!ersa 7% sampling the analog signal# 'uanti6ing an then co ing# it is easier to con!ert For con!ersion it is necessar% to o sampling more fre'uentl% as the signal Nyanist Theorem ( Sampling of the analog signal shoul )e one at the rate e'ual to atleast t&ice the ma.imum fre'uenc% present ,igital co ing is one )% )inar% igits 848 an 9:8 to mean a)sence 1 OFF an present 1ON respecti!el% MODUAT!ON an DE#MODUAT!ON: Mo ulation is the process of changing the characteristic of soun energ% li$e Amplitu e# Fre'uenc% or phase# so that effecti!e transmission can ta$e place Au io signal in the fre'uenc% range of 2456 to 24$56 cannot tra!el to large istances So a high fre'uenc% carrier &a!e is use to carr% *he au io signal The characteristic of &a!e is change )% super-imposing the signal *au io+ on the carrier &a!e Since the energ% transmitte is a mo ulate one# there is a nee to e-mo ulate the signal )efore one can e-co e itMo ulation is a necessit% )ecause( *i+ Lo& fre'uenc% signals ie out in small istances in air me ia*ii+ At lo& fre'uencies# ra iation is not possi)le ue to poor efficienc%*iii+ The length of antenna to )e use epen s on the &a!elength an so is large at lo& fre'uencies $a%   Am&litu e Mo ulation: Mo ulation   Factor* cgrce of mo ulation 1Mo ulation in e.+It is efine as the ratio of change of amplitu e of carrier &a!e to the amplitu e of au io signalMo ulation factor 0 Amplitu e change of Carrier &a!e1 Amplitu e of Au io Signalm a   etermines the strength an 'ualit% of the transmitte signalAmplitu e mo ulation of t&o &a!es f  c  an fs# results in t&o si e-)an fre'uencies (f  c   ;f  s + an *f  c -f  s + calle as upper an lo&er si e )an s The )an &i th re'uire k)v AM is t&ice the fre'uenc% of the mo ulating signal The amplitu e of the un-mo ulate carrier &a!e is ma e proportional to the instantaneous strength of the mo ulating signal as a result of amplitu e mo ulation Nois% reception# lo& efficienc%# small operating range an lac$ of 'ualit% are some limitations of amplitu e mo ulation $'%   (re)uency Mo ulation ( <hen the fre'uenc% of carrier &a!e is change in ###############################################################################################################################*CC  = Opposite >opichan Ar%a Mahila college College roa # A)ohar# Cell ?@::BDD::  PRINCIPLE OF COMMUNICATIONSreference to the fre'uenc% of signal# it is calle fre'uenc% mo ulation Mo ulation factor is efine as the ratio of the ma.imum change in fre'uenc% * δ + of carrier to the fre'uenc% of mo ulating signal (f  m  ) *ie+ m r   0 δ 1f  m FM signal gi!es noiseless# high fi elit% reception &ith higher efficienc% FM is ha!ing some limitations namel%# *i+Re'uirement for &i er )an *ii+ Comple. mo ulation an e-mo ulation techni'ues *iii+ Range of reception is !er% small Limite to line of sight istance $c%   *hase Mo ulation: The phase of the carrier &a!e is altere in accor ance &ith the mo ulating signal ,e!iation in phase is irectl% proportional to the amplitu e of the mo ulating signal an is in epen ent of fre'uenc% $ %   *ulse Mo ulation ( Mo ulation of a ra io fre'uenc% carrier )% the use of short pulses is calle pulse mo ulation It is )ase on sampling of the information signal at perio ic inter!als at a)out t&ice the ma.imum fre'uenc% or a)out D444 times per secon  There arc !arious s%stems in pulse mo ulation namel% *i+ Pulse-amplitu e Mo ulation *PAM+ *ii+ Pulse-position Mo ulation *PPM+ *iii+ Pulse- uration Mo ulation *P,M+ *i!+ Pulse-co e Mo ulation *PCM+ MODUATO+ an DE#MODUATO+ MODEM ( An electronic e!ice &hich mo ulates EM <a!e at the transmitter an emo ulates the incoming signal at the recei!er It ta$es signal from a iput e!ice an con!erts it into a analog signal )efore transmission In the other    en *recei!er+# the carrier &a!e is emo ulate )% the Mo em Mo ems iffer in#*i+Spee of transmission*ii+ Mo ulation metho *iii+ 7an -&i th of operation ANTENNA ( An antenna is a length of a con uctor &hich con!erts signal In a transmitting antenna# the electrical energ% is con!erte into EM <a!e# &hile in a recei!ing antenna EM <a!es are con!erte to electrical signals The length of the antenna is to ha!e resonance at the fre'uenc% of operationAntenna length 0 elocit% of EM<a!e1 Fre'uenc% of Signal,ipole Antenna -Omni- irectional antenna ,ish-t%pe Antenna - ,irectional antenna In ish-t%pe antenna# the iple is place at the focus of para)olic or spherical ish# to collect EM<a!es Such   antennas are use in Ra ars an satellite communication (A, $(acsimile Telegra&hy% ( FAG repro uces a   ocument at a   istant place The   srcinal ocument is con!erte into transmitta)le co es at the transmitting en # an con!erte )ac$ at the recei!ing en  Optical scanner# co er# eco er an a printer form part of a FAG Satellite Communication ( Micro&a!e communication cannot go )e%on the line of sight Atmosphere cannot reflect )ac$ energies )e%on the ra io-fre'uenc% range So satellite communication is importantA space craft in an or)it aroun the earth# fitte &ith all transmitting an recei!ing e!ices transfers signalfrom a place to e!er% point on the surface of earth The communication satellites are place in an or)it calle 8geo-stationar%8 or)it or 8par$ing or)it8 at a height of BH#444 $m a)o!e the surface of earth A -antages *i+ Large area co!erage *ii+ er% relia)le *iii+ Cost effecti!eness Disa -antages *i+Not useful for securit% information *ii+ Cost of placing satellites is !er% high# *iii+Not man% satellites can )e place in geo-stationar% or)it +emote Sensing : The techni'ue of collecting all information a)out e!er% o)ect# at large istances &ithout touching ph%sicall% is calle remote sensing e.ploring in-accessi)le areas an unco!uning the natural resources an istur)ances is one through this techni'ue using satellites Remote sensing satellites are place in Sun-s%nchronous or)its passes o!er a particular area of earth at the same focal timeor at the same time as the SUN is at the same place Remote sensing satellites are use in#*i+ In entif%ing the sources an e.tent of pollution# *ii+ <aste-lan mapping *iii+ >roun -&ater sur!e% *i!+ ,rought assesment *!+ <eather monitoring *!i+ Fin ing potential fishing 6ones *!ii+ Sur!e% of natural forests *!iii+ Sp%ing-mo!ement of troops or nuclear tests ine Communication ( Point-to-point communication using a gui e me ium is calle Mine communication8 Telephone an telegraph lines are e.amples for line communication The transmission character epen s on *i+ Me ium nature an *ii+ Nature of the signalT&iste pair# Co-a.ial Ca)les an Optical fi)res are some gui e me ia use  ###############################################################################################################################*CC  = Opposite >opichan Ar%a Mahila college College roa # A)ohar# Cell ?@::BDD:2  PRINCIPLE OF COMMUNICATIONS T.iste *air ( T&o insulate copper &ires arrange in spiral pattern to re uce electro-magnetic interference is a t&iste pair 7oth analog an igital signals are transporte as mo ulate signal Loss of energ% comes ue to *i+ 5eating of &ire *ii+ Ra iation loss at higher fre'uencies *iii+ Increase in the resistance Co#a/ial Ca'le ( Consists of a hollo& outer c%lin rical con uctor surroun ing a co-a.ial single inner con uctor Inner con uctor is of copper an the outer con uctor is either a soli or )rai e mesh of fine &ires# ma e of ielectric Teflon an pol%eth%lene As the fre'uenc% of operation increases# the ielectric )ecomes more an more con ucting an lea s to ielectric loss Comparati!el% the% ha!e re uce attenuation an so repeater stations ma% )e place at a)out 24 $m an  )an -&i th is also large <ith igital signals# the )an -&i th can )e impro!e  O&tical Communication using O&tical (i'res: A light )eam is use as a carrier &a!e It carries the information at a much faster rate than ra io-&a!es an micro-&a!es Optical fi)res arc isigne for transmission since# *i+ Light is su)ecte to much a)sorption in free space *ii+ Large interference ta$es  place It &or$s on the principle of total internal reflection The esign of optical fi)re is such that repeate internal reflection ta$es place to carr% information e!en through )en s an corners An optical fi)re consists of a glass core surroun e )% a large glass cla ing protecte )% a coating The refracti!e in e. of cla ing is less than that of the core for total internal reflection to ta$e place A -antages of O&tical (i're Communication *i+ Thousan s of information are carrie )% thin glass fi)res *ii+ Temperature an magnetic fiel oes not affect the fi)re communication *i!+ Jamming of information is a!oi e *!+ Rate of communication is impro!e *!+ Noise free communication O&tical ight Source: Light source use in communication *optical+ must ha!e some special characters ( *i+ Shoul )e small an can )e easil% couple to fi)res# *ii+ Shoul )e monochromatic of appropriate &a!elength# *iii+ Rapi s&itching )et&een states 948 an Tin igital form is re'uire  LE, - Light Emitting ,io e an LASER - Light Amplification )% Stimulate Emission of Ra iation are commonl% use as optical sources *rinci&le of ASE+  Normall% the electrons in !arious atoms remain in the groun state &hich is highl% sta)le 7% pro!i ing energ% the% are e.cite an the population in higher unsta)le or)it is attaine  This  process of in!erting the population is calle polulation in!ersion Population in!ersion is one )% sho&ering energ% in the form of light ra iations So the process is calle optical pumping The steps in!ol!e in the LAS IN> action is (- A)sorption of optical energ% →  Spontaeous emission of electron to metasta)le state →  Stimulate emission of esire fre'uenc% ,epen ing on the acti!e me ia use LASERs are of ifferent t%pes namel% *i+ Ru)% Laser*ii+ >as lasers *5e an Ne gas+*iii+ Semi con uctor Lasers *>a As+# A&&lications of ASE+ *i+ Communication*ii+ Measurement of istance*iii+ 7loo less $nife in the fiel of me icine *i!+ Cutting an &el ing of metals*!+ <eapons for estruction ight Emitting Dio e ( <hen for&ar )ias is applie to a pn-unction# holes an electrons are inecte into the other si e of the unction recom)ination of electrons an holes ta$e place This lea s to the emission of photon - light The intensit% of emitte light is proportional to the for&ar current con ucte  )% the unction that controls the num)er of holes an electrons crossing to recom)ine !m&ortant as&ects of O&tical (i'res $i% Numerical A&erture :  ,epen s irectl% on the iameter of thecore of optical fi)re It is e'ual to sine of the critical angle of inci ence *ie+ sin i c  0 √ * µ 2: - µ 22 + &here µ :   an µ 2   are the refracti!e in e. of the core an cla ing respecti!el%# *ii+ Attenuation ( Means po&er loss or loss of information strength >eneral &a!elength range is :B to : µ m *iii+ Dis&ersion ( 7roa ening of pulses happen ue to ispersion ,ue to this efection of in i!i ual  pulses )ecome ifficult# there )% re ucing the istance an spee of transmission ###############################################################################################################################*CC  = Opposite >opichan Ar%a Mahila college College roa # A)ohar# Cell ?@::BDD:B
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