Radio and Television Systems

7/24/2019 Radio and Television Systems

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Radio and Television Systems

ABOUT THIS CHAPTER

In the last chapter the basic concepts of the familiar telephone system erecovered! An e"#ally familiar system that is ta$en almost as m#ch for %ranted

as the telephone system is radio and television! &ost people are never very farfrom a radio or television' and many ho#rs per day are spent bein% entertainedor informed by one or the other of these systems! Since television incl#desradio(type information in its so#nd portion' and since both depend onbroadcastin% information over an electroma%netic radiation transmission lin$'an analysis of the basic concepts of television ill also serve to cover thef#ndamentals of radio!

Th#s' this chapter ill emphasi)e the techni"#es and applications of televisionsystems' and at the same time' vario#s disc#ssions ill indicate ho thesetechni"#es apply to radio broadcastin%! The *rst most basic concept of#nderstandin% television systems is the techni"#e for transmittin% pict#res

electronically!HO+ ARE I&A,ES TRA-S&ITTE. E/ECTRO-ICA//01

The components re"#ired to broadcast pict#res from a television camera to atelevision receiver and display them on a T2 pict#re t#be are shon in 3i%#re 4(5! The p#rpose of the camera is to convert the optical information 6re7ectedli%ht aves8 of the ima%e into correspondin% electrical si%nals! The microphoneconverts any so#nd associated ith the ima%e' s#ch as speech or m#sic' intocorrespondin% si%nals! These si%nals m#st be mod#lated onto a hi%h(fre"#encycarrier and ampli*ed #ntil they are poerf#l eno#%h to ca#se electroma%neticradiation at the level desired from the broadcastin% antenna! The ran%e and

direction of s#ch radiation depends on the poer of the transmitter' thefre"#ency of the carrier' and the desi%n of the antenna! These factors eredisc#ssed in some detail in the chapter on the comm#nications spectr#m! If thereceiver is properly located ithin ran%e of the transmitter' it ill detect theradiation as a c#rrent 7o in its antenna! At the receiver' this si%nal level isincreased ith a hi%h(fre"#ency ampli*er' demod#lated' and processed toprod#ce the ori%inal so#nd in a spea$er and the ori%inal ima%e on a pict#ret#be! It is this processin%' both at the camera and at the television receiver'that m#st be #nderstood if the operation of a television system is to be#nderstood! As shon in 3i%#re 4(5! the transmission lin$ many times is bycable rather than electroma%netic radiation! This in no ay chan%es the system

concepts!Commentary9 The basic elements of a television system incl#de a camera andmicrophone to convert ima%es and so#nd into electrical si%nals' a transmitterto broadcast the si%nals' a receiver to recover the si%nals' and a pict#re t#beand spea$er to reprod#ce the ima%es and so#nd!


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Figure 7-1 Basic Elements of TV system

Camera Ima%e to Electrical Si%nals

3i%#re 4(: ill#strates ho a television camera converts an optical ima%e into acorrespondin% electrical si%nal! In this case' the ima%e is that of the letter H!/enses in the front of the camera foc#s this ima%e on the face of the camerat#be' hich is abo#t an inch in diameter! Enclosed in a vac##m inside this t#beis a photosensitive material coverin% the inside of its face' a sharply foc#sedbeam of electrons that scans across a tar%et in the pattern shon' and somemeans for detectin% c#rrent variations in the electron beam as it scans across

the tar%et! +hen li%ht hits the face of the t#be and the photosensitive material'electrons are emitted' b#t hen the face is dar$ no electrons are emitted! Theemitted electrons ca#se a copy of the ima%e to appear on the tar%et s#rface!Hoever' no the ima%e is de*ned by the amo#nt of positive char%e instead ofne%ative char%e A hi%h positive char%e for hi%h intensity li%ht; a lo positivechar%e for lo intensity or nearly dar$ conditions

Commentary9 A television camera contains a t#be hose face is coated ithli%ht sensitive material! Ima%es foc#sed on this area are reprod#ced on a tar%et


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s#rface ithin the t#be here they ca#se c#rrent variations in an electronbeam that scans the tar%et

Figure 7-2 Conversion of optical image to electrical Signals

The Scan Pattern

As the electron beam is ca#sed to scan the tar%et from left(to(ri%ht across thet#be for one hori)ontal line' it is moved sloly don vertically in a contin#o#smanner ca#sin% it also to scan toard the bottom of the t#be!

As the beam scans' a re7ected beam is collected and detected thro#%h aresistor shon in 3i%#re 4(:! The re7ected beam ill contain the same n#mber

of electrons as the ori%inal scannin% beam if there is no positive char%e on thetar%et s#rface! If there is a positive char%e the re7ected beam ill have lesselectrons 6less c#rrent8 beca#se some electrons combine to ne#trali)e thepositive char%e! Therefore the c#rrent in the re7ected beam ill be inverselyproportional to the li%ht intensity of the ima%e that is foc#sed on the camerat#be! The c#rrent variations prod#ce the volta%e variations of 3i%#re 4(!5 at theo#tp#t of the television camera t#be!


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As shon in 3i%#re 4(


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.#rin% 7ybac$ the volta%e is made even more positive than the level thatcorresponds to blac$ in the ima%e! 3inally' hen the hori)ontal scan line coversthe hori)ontal mar$ of the letter H the o#tp#t volta%e ill be at the blac$ levelfor the entire idth of the letter as shon in *%#re 4(the dar$er the ima%e' thehi%her the volta%e! .#rin% the ?7ybac$@ intervals beteen line scans' thevolta%e is set to its ma=im#m positive level!

The scan contin#es #ntil it reaches the bottom of the face of the t#be! As ares#lt' the entire to(dimensional ima%e is converted into a lon% contin#o#selectrical si%nal ith time containin% as many 7ybac$ p#lses as there are

hori)ontal lines scanned in the to(dimensional *eld! Beteen to of the7ybac$ p#lses' the hite(to(blac$ variations in the ima%e ill be converted tocorrespondin% volta%e variations 6lo to hi%h8 at the o#tp#t of the t#be! The7ybac$ p#lses tell the receiver pict#re t#be electronics hen to ca#se thebeam to 7ybac$ to the left side and hen to start a ne line!

The electrical si%nal 6called the video si%nal8 beteen the 7ybac$ p#lses tellsthe receiver hat variations of hite and blac$ to prod#ce on a %iven hori)ontalline of the re%enerated pict#re! The electronic circ#its in the camera t#be6transmitter8 and the pict#re t#be 6receiver8 m#st ca#se the electron beam toscan in the desired pattern and m#st be synchroni)ed to%ether!

Commentary9 To acc#rately reprod#ce the pict#re' the scannin% circ#its in thecamera and receiver m#st be synchroni)ed! Special si%nals are transmittedalon% ith video si%nal for this p#rpose!

SCA--I-, THE RECEI2ER PICTURE TUBE

The pattern that is scanned is ill#strated on the television receiver pict#re t#bein 3i%#re 4(! The video si%nal mod#lates the intensity of the electron beam!+hen the li%ht intensity is bri%ht at the camera' the beam ill ca#se a bri%htspot on the pict#re t#be at the same location! A chan%in% c#rrent in thede7ection coils prod#ces a ma%netic *eld hich ca#ses the beam to scan theline traces that correspond to the scan pattern at the T2 camera! This is called

the raster! The electron stream %enerated by the electron %#n is foc#sed into abeam to prod#ce a *ne spot on the pict#re t#be face! The pict#re t#be facecontains a li%ht emittin% phosphor hich emits li%ht in proportion to theintensity of the electron beam c#rrent! The beam intensity is proportional tothe video si%nal volta%e applied beteen the control %rid and the cathode ofthe t#be!


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Commentary9 The face of the pict#re t#be in a television receiver has a li%ht(emittin% phosphor coatin% that is scanned by an electron beam movin% in stepith the beam of the transmittin% T2 camera! The incomin% video si%nal variesthe beam intensity to reprod#ce the ori%inal ima%e!

Reprod#cin% a Character

The si%nal patterns of 3i%#re 4(!


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vertical de7ection volta%es re"#ired to ca#se the beam to scan the re"#iredpattern are indicated in 3i%#re 4(Db and Dc! There are several important detailsindicated by these si%nals! 3irst of all' as mentioned previo#sly' there are nomany levels of %ray in the pict#re video si%nal beteen blac$ and hite levels!As the pict#re information chan%es' these levels vary contin#o#sly! Second'small p#lses are shon on top of the 7ybac$ 6blan$in%8 p#lses! These aresynchroni)ation p#lses to ma$e s#re the receiver hori)ontal and verticalde7ection si%nals 63i%#re 4 Db and Dc8 are synchroni)ed ith those at thetransmitter

Commentary9 In the volta%e ran%e beteen ma=im#m 6blac$8 and minim#m6hite8' the video si%nal can prod#ce any shade of %ray!

Figure 7-% Vi#eo an# &e'ection signals in television systems


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Hori)ontal and 2ertical Scan 3re"#encies

The fre"#ency of the hori)ontal de7ection si%nal and the 7ybac$ p#lses is5D'4D cycles per second to provide a spacin% beteen correspondin% portionsof the 7ybac$ or hori)ontal de7ection si%nals of F


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Figure 7-( nterlace# Scan )attern for television pictures

Interlaced Scan Pattern

The solid lines sho the scan pattern startin% at A for the *rst *eld of thepict#re' hich ends at the bottom of the pict#re area 6B8 one( half ay across

the pict#re idth 6recall the vertical and hori)ontal si%nal relationships of 3i%#re4(D8! Th#s' there are :F: 5G: lines per vertical trace or *eld! As the verticalretrace occ#rs' the hori)ontal de7ection si%nal contin#es an even n#mber ofde7ection periods so that the *rst line of the second *eld of the pict#re startsat point C! This *eld scan pattern contin#es' oset from the *rst *eld scanpattern so that an interlaced scan pattern occ#rs from *eld to *eld! This %ivesthe eect of seein% the same pict#re F times a second' hich eectivelyavoids any 7ic$er in the pict#re! This type of scannin% is called interlacedscannin% ith to interlaced *elds of :F: 5G: lines each per frame! There areF *elds per second and


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The D:D lines per frame provides a pict#re resol#tion of abo#t

All of the disc#ssion th#s far has ass#med a blac$(and(hite 6monochrome8television system! In order to transmit and reprod#ce color pict#res' severalelements m#st be added to the system!

Comentary9 The resol#tion of the pict#re reprod#ced on a television screendepends on the bandidth of the video si%nal and the receiver itself! Thehi%her the bandidth' the %reater the n#mber of pict#re elements that can beindivid#ally controlled in each screen line!


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Figure 7-7 )attern to &etermine resolution of TV

HO+ ARE CO/OR PICTURES PRO2I.E. E/ECTRO-ICA//01

In order to transmit the information contained in a color pict#re' the pict#re

content m#st be bro$en don into its primary colors! In color television theprimary colors chosen are red! %reen' and bl#e' since appropriate combinationsof these components ill prod#ce anv color! To identify the content of each ofthese primary colors in the pict#re' the television camera consists of threeseparate t#bes or electron %#ns ( one for each of the three colors 6see 3i%#re 4(M! The li%ht from the scene vieed by the camera is passed thro#%h red! %reen'and bl#e *lters and scanned by three separate electron beams!


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Comentary9 A color television camera brea$s a pict#re don into three primary(color ima%es ith red! %reen' and bl#e *lters! The three ima%es are scannedith three separate electron beams!

Figure 7-* Transmitting Color images

/#minance and Chrominance

The si%nals for each color are combined by an electronic matri= circ#it toprod#ce to si%nals' called the l#minance 608 hich contains the %ray levelinformation' and the chrominance 6C8 hich contains the color information!+hen the l#minance is applied to an ordinary blac$(and(hite t#be' a normalblac$(and(hite pict#re res#lts!

Comentary9 2ideo si%nals for color television have to components9 l#minanceto control the %ray level and chrominance to control the sat#ration 6color

intensity8 and h#e 6tint8! Blac$(and( hite television sets #se only thel#minance si%nal to control their %ray level!

The transmitted si%nal contains the l#minance and chrominance si%nals! +henthe si%nal is processed by a color receiver the red! %reen and bl#e si%nals arerecovered' ampli*ed' and then mod#late the intensity of an electron beam inthe color television pict#re t#be! The face of the t#be no has three phosphorslocated in a re%#lar pattern ne=t to each other over the hole s#rface of the


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t#be ( one for red! one for %reen' and one for bl#e In the t#be' as shon in3i%#re 4(M' each of the colors has its on electron beam hich is foc#sed onthe t#be face so that it hits the color phosphor that corresponds to its color! Ashado mas$ plate is placed beteen the beams and the color phosphors sothat the red beam can hit only the red phosphor the %reen beam only the %reenphosphor' and the bl#e beam only the bl#e phosphor! The chrominanceamplit#de and phase determine the beam c#rrents for the three color beams!

The amplit#de contains the color intensity 6called color sat#ration8 and thephase contains the blend 6h#e or tint8 of color! The t#be de7ection systemmoves all three beams in #nison thro#%h the interlaced scan pattern of 3i%#re4(F! The foc#sin% electrodes for each beam provide for precise foc#s andaimin% of the individ#al beams of the three beam %ro#p! The overall res#lt isthe reprod#ction of the ori%inal color pict#re detected by the color camera!

Comentary9 Color pict#re t#bes have a separate phosphor coatin% and electronbeam for each of the three colors!


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Representin% the Color Spectr#m

It may seem impossible for a sin%le chrominance sin#soid to contain all thecolor information in a color pict#re! Hoever' if the color spectr#m is tho#%ht ofas a spectr#m of contin#o#sly varyin% h#es or colors from deep bl#e to deepred' it is easy to see ho an electrical parameter' s#ch as volta%e' c#rrent'

resistance or phase can be assi%ned val#es to represent all the colors! In colortelevision the parameter chosen is the phase of the chrominance sin#soid!Recall that it as stated previo#sly that phase is a meas#re of the position intime of a aveform compared to a reference! Comentary9 The phase of thechrominance si%nal 6its position in time compared to a reference si%nal8indicates color 6h#e8! The amplit#de of the chrominance si%nal indicates colorintensity 6sat#ration8!

Phase of a Color Si%nal

The basic idea is ill#strated in 3i%#re 4(N! 3i%#re 4(Na is a reference sine avesi%nal! It crosses the time a=is at )ero 6point A8 hen the amplit#de is )ero and

is startin% to increase to a positive ma=im#m! The aveform in 3i%#re 4(Nd issaid to be 5M o#t of phase beca#se even tho#%h its amplit#de %oes thro#%h)ero at )ero on the time a=is 6point B8' it is startin% to increase to its mostne%ative ma=im#m! It is a mirror ima%e of the aveform in 3i%#re 4(Na!Another ay of loo$in% at 3i%#re 4(Nd is that it is li$e a 3i%#re 4(Na aveformthat has moved in time position one half of a cycle don the time a=is 6Point Chas moved to the Point B position8! One f#ll cycle is


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The chrominance sine aves of 3i%#re 4(Nb' 4(Nc and 4(Nd are si%nals receivedat dierent times representin% the color of the camera si%nal! These arecontained in the pict#re si%nal and are transmitted at the same time as thel#minance si%nals! The si%nal of 3i%#re 4(Nb is in(phase 6)ero de%rees phase8ith the reference of 3i%#re 4(Na! This corresponds to a color of yello! 3i%#re4(Nc is N o#t(of(phase from the reference; it corresponds to a color beteenred and ma%enta! 3i%#re 4(Nd is a bl#e beca#se it is 5M o#t(of(phase and a5M o#t(of(phase electrical si%nal corresponds to bl#e! Th#s' by detectin% thephase of the chrominance si%nal ith respect to the color sync' the color canbe determined! Information is also contained in the ma%nit#de of thechrominance! .etectin% the ma%nit#de sets the intensity of the color!

Comentary9 A chrominance si%nal in phase ith the reference indicates yello!A chrominance si%nal N de%rees o#t of phase ith the reference indicates red!A chrominance si%nal 5M de%rees o#t of phase indicates bl#e!

Figure 7-+ "elations,ip $eteen color signal p,ase an# colorreference


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Separatin% Chrominance and /#minance

.ierent color television receivers #se the chrominance and l#minance si%nalsin dierent ays! One of the more common approaches is to provide the color


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si%nals mi=ed ith the l#minance si%nals #sin% the relationships e=pressed inthe e"#ations of 3i%#re 4(5! The l#minance si%nal is de*ned in 3i%#re 4(5 asconsistin% of


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Color Circ#itry

The ay these dierence and l#minance si%nals are #sed in a color televisioncan be #nderstood by e=aminin% the color circ#itry of a typical television! Atypical color circ#it bloc$ dia%ram is shon in 3i%#re 4(55! The video si%nalprevio#sly received and ampli*ed is fed into this %ro#p of circ#its' incl#din% the

blan$in% p#lses for hori)ontal and vertical retrace! As shon in 3i%#re 4(55' thesi%nal also incl#des the color(sync b#rst on top of the 7ybac$ p#lse' and thechrominance C sin#soid added to the l#minance 0 video si%nal! This si%nal isapplied to the l#minance lo(pass ampli*er' the chrominance bandpassampli*er' and the color b#rst bandpass ampli*er!

The to bandpass ampli*ers pass the

Comentary9 A lo(pass ampli*er in color receivers separates the l#minance

si%nal from the video si%nal! Bandpass ampli*ers separate the chrominanceand b#rst si%nals from the video si%nals!

Figure 7-11 Color circuits in a TV receiver


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.#rin% blan$in% the b#rst ampli*er is t#rned on and the chrominance ampli*eris t#rned o! In this manner the color b#rst synchroni)es the

The chrominance si%nal mod#lated ith the color oscillator sin#soid delayed byN de%rees prod#ces the R(0 si%nals! &od#latin% the chrominance si%nal ithan inverted color oscillator si%nal 65M o#t(of(phase8 %enerates B(0! The si%nalR(0 is m#ltiplied by (!D5 and the si%nal B(0 by (!5N! These are added toprod#ce ,(0! These three si%nals are applied to the %rids of the three color

%#ns! +ith the l#minance si%nal 6(08 applied to the cathode' the net repellin%volta%e each electron beam sees is the %rid volta%e min#s the cathode volta%e!As shon in 3i%#re 4(55' for the red %#n this o#ld be R(0 ( 6(08 or R! Thecorrespondin% dierence e"#ations for bl#e and %reen vary the electron beamc#rrent in proportion to the appropriate color si%nals! As the beams e=cite thephosphors' the s#m of the colors prod#ced reprod#ces the ori%inal color at theappropriate spot on the receiver pict#re t#be!


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Comentary9 The color(sync component of the video inp#t synchroni)es the

A color $iller circ#it is shon in 3i%#re 4(55! Its p#rpose is to t#rn o thechrominance bandpass ampli*er if no color sync is detected or if the color

oscillator is defective! 3or this case' the only si%nal controllin% the beams is 06for all three beams if the receiver circ#its are adQ#sted properly8 and astandard blac$(and(hite ima%e is prod#ced

Comentary9 If the video inp#t does not contain a color b#rst sync si%nal' thechrominance circ#its are t#rned o and a blac$(and(hite ima%e is displayed!

O2ERA// RECEI2ER

R3 and I3 Ampli*ers

All television receivers' hether blac$ and hite 6monochrome8 or color m#streceive the si%nal from the transmitter via an antenna' amplify it and prepare it

for display on the pict#re t#be! Conse"#ently the front end@ hi%h(fre"#ency6R38 and intermediate(fre"#eney 6I38 ampli*cation sta%es incl#din% the videodetector and the a#tomatic %ain control circ#its 6A,C8 are common types toboth receivers! An overall bloc$ dia%ram is shon in 3i%#re 4(5:! Televisioninformation can be broadcast on any of the channels shon in 3i%#re 4(5

Comentary9 R3 and I3 ampli*er sta%es are common to both color and blac$(and(hite television receivers!

Figure 7-12 Components of a color TV receiver


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The R3 ampli*er is a bandpass ampli*er that provides the initial ampli*cationat the partic#lar fre"#ency received on the antenna! It passes only the


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fre"#encies of the channel selected by the receiver t#ner or channel selectorbeca#se the bandpass is set by this sitch! The si%nal passin% thro#%h the R3ampli*er is mi=ed ith a sine ave si%nal from an oscillator! The mi=in%prod#ces a si%nal at the s#m of the R3 and oscillator fre"#ency and another atthe dierence fre"#ency beteen the to inp#t si%nals! The channel selectort#nes the oscillator at the same time as it t#nes the R3 ampli*er so that thedierence fre"#ency o#t of the mi=er is alays to F me%ahert)!

Commentary9 The R3 ampli*er ampli*es si%nals received from the T2 antennaor cable in the channel that yo# select! The R3 ampli*ers o#tp#t is mi=ed iththe o#tp#t of a variable( fre"#ency oscillator to prod#ce an intermediatefre"#ency 6I38 that is the same for every channel!

The selected channel si%nal ill be ampli*ed by the (to F( me%ahert)bandpass ampli*er called the intermediate(fre"#ency ampli*er or I3 ampli*er!I3 ampli*ers are #sed so that one hi%h(performance ampli*er section can be#sed to provide the maQority of the receiver %ain' re%ardless of the R3 channelthat has been selected! This allos the desi%ners to prod#ce a m#ch betterampli*er than o#ld be possible if the ampli*er had to provide a bandpassmatched to the channel selected! The o#tp#t of the I3 ampli*er has eno#%hsi%nal volta%e to drive the video and so#nd circ#its!

2ideo .etector and A,C

The video detector removes the (me%ahert) carrier from the amplit#demod#lated I3 si%nal! The stren%th of the o#tp#t of the detector is fed toa#tomatic %ain control circ#its 6A,C8 to maintain the %ains of the R3 and I3ampli*ers at desired levels over a fairly narro ran%e! This prevents stron%antenna si%nals from behavin% dierently from ea$ si%nals at the o#tp#t ofthe video detector! If a ea$ si%nal is received' the A,C control sets the R3 andI3 ampli*er %ains at a hi%h val#e so that a stron% video o#tp#t is available! Ifthe antenna si%nal is stron%' the A,C control sets the ampli*er %ains lo sothat the video o#tp#t is not overdriven or distorted! Th#s' the A,C controlcirc#it maintains a relatively stron% #ndistorted video detector o#tp#t that islar%ely independent of the stren%th of the antenna si%nal!

Commentary9 The video detector separates the carrier from the I3 si%nal andsends the res#ltant composite video si%nal to the so#nd' video ampli*cation'color separation' and de7ection circ#its!

So#nd Circ#its

The video detector o#tp#t is sent to fo#r dierent receiver s#bsystems9 theso#nd circ#its' the video ampli*cation and color separation circ#its containin%the l#minance and chrominance ampli*ers' and the de7ection circ#its! Thel#minance and chrominance circ#its have already been disc#ssed! 3i%#re 4(lbcontains more detail of the fre"#ency separation of the vario#s si%nals in thevideo si%nal o#t of the detector! The so#nd s#bsystem pic$s the so#nd carriero#t of the overall video si%nal by #sin% a narro bandpass ampli*er centered at!D &H)! This ampli*er reQects the pict#re information b#t passes the so#nd


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information! The so#nd carrier is a fre"#ency mod#lated si%nal hich isconverted to a#dio

Commentary9 The so#nd si%nal is pic$ed o of the video si%nal by a narrobandpass ampli*er centered at !D &H)!

3re"#encies by techni"#es previo#sly disc#ssed! A#dio ampli*ers boost thissi%nal to the level that is re"#ired by the lo#dspea$ers!

.e7ection Circ#its

The de7ection circ#its e=tract the hori)ontal and vertical synchroni)in% p#lseso the top of the 7ybac$ p#lses shon in 3i%#re 4(D! These are #sed tosynchroni)e the fre"#encies and startin% points of the hori)ontal 63i%#re 4(Db8and vertical 63i%#re 4(Dc8 de7ection si%nals prod#ced by the hori)ontal andvertical oscillators respectively! The o#tp#ts of these oscillators are ampli*edand applied to the de7ection coils to provide the proper raster scan patternthat as disc#ssed earlier! The fast retrace of the hori)ontal de7ection si%nal

shon in 3i%#re 4(Db is #sed to %enerate the hi%h volta%e re"#ired by theanode electrode of the pict#re t#be 63i%#re 4(5'8! A hi%h(fre"#ency p#lse is%enerated by the 5( microsecond hori)ontal retrace and is transformed andrecti*ed to a volta%e of 5M to :D $ilovolts of dc by the hi%h(volta%e s#pplycirc#its! This hi%h volta%e is re"#ired to accelerate the electrons to provide theproper screen bri%htness! There also is a lo(volta%e poer s#pply hichprovides poer to all the circ#its thro#%ho#t the receiver!

As mentioned earlier in the disc#ssion on fre"#ency spectr#m and resol#tion'some of the performance feat#res of television depend on the channelbandidth allotted to the television si%nal containin% the pict#re and so#ndinformation! The carrier and bandidth of these si%nals have been

standardi)ed by the broadcast ind#stry and the 3ederal Comm#nicationsCommission! /ets loo$ at the bandidth re"#irements in more detail!

Commentary9 The de7ection circ#its #se the synchroni)in% p#lses in the videosi%nal to %enerate the correct scan pat(tern in the pict#re t#be!

+HAT ARE THE BA-.+I.TH REUIRE&E-TS O3 RA.IO A-. TE/E2ISIO-1

T2 Channels

Since the bandidth of the I3 ampli*er in 3i%#re 4(5: is F &H) 6F ( 8' thenone o#ld e=pect that the television channel bandidth is F &H)! This ise=actly correct as shon in 3i%#re 4(5


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additional 5 UH3 channels e=tendin% to MN &H)' hoever these have nobeen allocated to land mobile service! If the CAT2 and the broadcast channelsare co#nted' the 3CC has provided N channels 6e=cl#din% any s#b(bandchannels that are potentially available to CAT2 belo the channel : fre"#encyband8!

Commentary9 The 3ederal Comm#nications Commission allocates speci*cchannels for television broadcastin% hich ran%e in fre"#ency from S &H) toMF &H)!

Figure 7-13 Television c,annel fre/uencies

Si%nal Bandidth of T2

The feat#re that all of these channels share is the common F &H) televisionsi%nal bandidth of f: f5 shon in 3i%#re 4(5! The pict#re carrier fre"#encyis 5!:D &H) above * 6the loer band fre"#ency8' and the so#nd broadcastcarrier is D!4D &H) above ft! -ote that the so#nd carrier is !D &H) and thechroma si%nal is

occ#pies the fre"#encies from D to F &H)' the pict#re carrier is at DD!:D&H)' the chroma si%nal is at DM!M< &H)' and the so#nd carrier is at DN!4D &H)'

Q#st :D $H) belo the #pper fre"#ency limit f: for the channel : band!

The pict#re carrier fre"#ency is amplit#de mod#lated by the pict#re andchroma information! Since the channel bandidth is c#t(o 5!:D &H) belo thisfre"#ency' only the *rst


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sin%le(side(band mod#lated! As a res#lt' the fre"#encies of the l#minance thate=tend beyond 5!:D &H) from the carrier are reprod#ced only at 5G: theamplit#de of the si%nals that *t into the 5!:D( &H) fre"#ency band! The loerfre"#encies prod#ce the %eneral feat#res of the pict#re; the #pper fre"#enciesthe pict#re sharpness and detail! The loer sideband of the amplit#demod#lated si%nal from the pict#re carrier fre"#ency don to the loer bandlimit is called the vesti%ial sideband!

Commentary9 Television channels have a bandidth of F &H)! The pict#recarrier fre"#ency is 5!:D &H) above the loer band fre"#ency! The so#ndcarrier is !D &H) above the pict#re carrier!

Figure 7-1! Ban#i#t, Features of commercial TV c,annel

So#nd Reprod#ction of 3& and T2

The so#nd information is mod#lated onto the so#nd carrier' hich is !D &H)

above the pict#re carrier' #sin% fre"#ency mod#lation ith a deviationbandidth of W:D $ilohert)! This compares ith the X4D( $ilohert) deviationavailable in 3& stations! These deviations occ#r for 5 mod#lation of a#diosi%nals! Both 3 & and television so#nd can reprod#ce a#dio fre"#encies in theD(H) to 5D($H) ran%e' tho#%h the 3& si%nals tend to be more imm#ne to noiseith their ide deviations! In addition' 3& stations tend to be m#ltiple=edstereophonic so#nd and are %enerally reprod#ced ith hi%h(*delity so#nd


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system' hile the television so#nd is monophonic and is reprod#ced ith hatis %enerally classed as a poor "#ality system!

In the f#t#re' television receivers co#ld certainly oer improved a#dio *delitythro#%h improved a#dio ampli*ers and hi%h "#ality spea$er systems! It ispossible for television stations to provide stereophonic so#nd ithin the

present F(&H) bandidth by sli%htly increasin% the bandidth available for theso#nd channel! This development' if it occ#rs at all' o#ld most li$ely occ#r*rst in non(broadcast television netor$s! Certainly the cost of componentsboth at the transmitter and receiver play an important part in this decision!

Commentary9 The pict#re carrier is amplit#de mod#lated' hile the so#ndcarrier is fre"#ency mod#lated! The typical T2 receiver' hoever' does nothave hi%h(*delity circ#its li$e those often #sed in 3& radio!

Figure 7-1% Broa#cast Television System

+HAT ARE SO&E T0PICA/ T2 A-. RA.IO -ET+ORJS1

&ost of the disc#ssion th#s far in this chapter has ass#med that the system hasbeen a commercial television broadcastin% netor$' the components of hichare shon in 3i%#re 4(5D! The st#dio is the central comm#nications center for


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s#ch a facility! It ori%inates local nes pro%rams and sportin% events! Itreceives pro%rams from national television netor$s via microave lin$s orleased telephone lines of s#Ycient bandidth to handle the television channelre"#irements!

Remote /in$s

The transmitter for radiatin% the television material %enerated at the st#dio inmost cases is not at the st#dio! The st#dio #s#ally is at some convenientb#siness location in a metropolitan area! The hi%h(poer transmitters and hi%hantenna toers need to be located in remote areas on tops of hills or otherhi%h points overloo$in% the area to be served by the broadcast! 3or this reason'the st#dio si%nals m#st be relayed to the transmittin% facility on a st#dio(to(transmitter lin$! The 3CC lists several fre"#ency bands for #se for this p#rposeas indicated in 3i%#re 4(5D! These fre"#encies are #sed to send the televisionpro%ram material' comm#nications information' and control si%nals to thetransmittin% facility! The st#dio antenna and the lin$ receivin% antenna at thetransmittin% facility m#st be ithin a line(of(si%ht path of each other!

Commentary9 Since television transmitters are #s#ally some distance from thest#dio' the 3CC reserves several fre"#ency bands for st#dio(to(transmitterlin$s!

Transmitter Separation

To broadcast 6radiate the si%nal8 a hi%h(poer transmitter feeds #p to D$iloatts to a broadcast antenna on a toer abo#t D feet hi%h! Televisionreceivers ithin a line(of(si%ht radi#s from the transmittin% antenna of :D to 4D

miles ill receive the si%nals! .#e to this ran%e' the 3CC $eeps stationsbroadcastin% on the same channel separated by a distance of at least :miles 6dependin% on hether the stations are 2H3 or UH38 so the stations illnot interfere ith each other! Stations hose channels are adQacent infre"#ency' s#ch as channel : and


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from D $H) to 5!F &H)! In this fre"#ency ran%e a hi%h(poer 6D$+8transmitted si%nal can travel lon% distances' partic#larly at ni%ht' beca#se thetransmission is not line(of( si%ht and ill bo#nce o the ionosphere!

Radio Receivers

A&(Amplit#de &od#lationThe receivers for radio si%nals are similar to the so#nd portion of the television

receiver! A typical A& band radio receiver str#ct#re is shon in 3i%#re 4(5F! Asith the T2 receiver' an oscillator and an R3 ampli*er are bein% m#ltipliedto%ether by bein% fed to a mi=er circ#it! The mi=er prod#ces the s#m anddierence fre"#encies of the to si%nals! In technical terms this is calledheterodynin%! The res#ltant si%nal' either the s#m or dierence' is the I3fre"#ency! Its detector is an A& demod#lator and it does have A,C circ#its! TheR3 ampli*er is t#ned to provide a bandpass characteristics that ill pass thesi%nal from a sin%le A& radio station to the mi=er! The oscillator fre"#ency issimilarly varied so that the dierence beteen the station fre"#ency and the

local oscillator fre"#ency ill be a DD($H) I3 fre"#ency! It is this mi=in% and I 3ampli*cation that ma$es the receiver a s#perheterodyne str#ct#re!

Commentary9 Radio Receiver circ#its are similar in operation and str#ct#re tocomparable circ#its in television receivers!

Figure 7-1( Components of super,etero#yne receiver


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The I3 ampli*er boosts only the narro ran%e of fre"#encies that the si%nal hasbeen converted to' bloc$in% any e=traneo#s si%nals or noise! The ampli*ed I3si%nal is sent to an amplit#de mod#lation detector hich %enerates the a#diosi%nal and controls the A,C circ#it in the same ay the A,C as #sed in thetelevision receiver! In the A& receiver the A,C control tends to avoid lo#db#rsts of noise from stron% stations and red#ces fadin% and other so#nd levelvariations in the a#dio si%nal! The a#dio si%nal is ampli*ed and sent to thelo#dspea$er for so#nd reprod#ction!

3&(3re"#ency &od#lation

An 3& mona#ral receiver o#ld have almost an identical str#ct#re to the bloc$dia%ram of the A& receiver of 3i%#re 4(5F e=cept that no an 3& demod#latoris #sed for the detector! The R3 and I3 fre"#encies are m#ch dierent beca#seof the hi%her fre"#encies' b#t the bloc$s perform the same basic f#nctions!


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3& Stereo Systems

3& stereo broadcasts contain to separate channels so#nd! The carrier forestereo channels is not transmitted!

The systems for broadcastin% and receivin% J& Stereo are somehat more

complicated' since to separate channels of so#nd information m#st behandled! 3or Stereo the 3& station bandidth is allocated as shon in 3i%#re 4(54! 3o#r si%nals m#st be %enerated! The *rst si%nal is a composite of so#ndinformation called / V R res#ltin% from the left channel 6/8 added to the so#ndinformation from the ri%ht channel 6R8! The third and fo#rth si%nals are thedierence beteen the / and the R so#nd information! +ithin the bandidthfrom :< $H) to D< $H) one of these is placed belo and the other above the


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the 3& detector 63i%#re 4(5M8! The simplest ay to e=tract the / V Rinformation is to send the composite si%nal thro#%h a loZ pass ampli*er that

bloc$s fre"#encies above 5D $H)! A bandpass ampli*er and phase(loc$( looploc$ onto the 5N $H) pilot si%nal' do#ble it' and provide the


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&ona#ral

Commentary9 3& mona#ral receivers #se only the / V R portion of stereosi%nals!

A mona#ral receiver o#ld simply detect the stereo / V R information anddeliver this so#nd information to a sin%le spea$er! A stereo station o#ld sendmona#ral information ith / L R so that the /(R information o#ld disappearand only / V R L :/ L :R information o#ld be received and sent to bothchannels of the stereo system!

.olby Systems

Some 3& stations provide a noise red#ction encodin% of the type #sed inmodern tape recorders! The receiver ta$es advanta%e of this encodin% tored#ce the annoyin% eects of hi%h fre"#ency noise 6often called hiss@ noise8in the reprod#ced so#nd!

The .olby system #ses circ#its in the transmitter to compress the so#ndsi%nals in certain fre"#ency ran%es prior to transmission! The receiver thene=pands the si%nals bac$ to their ori%inal dynamic ran%e!

3or e=ample in ordinary systems' si%nals varyin% from hi%h to lo level arriveat the receiver ith the lo level si%nals mas$ed o#t by noise from thetransmission! At the receiver this noticeable hiss covers #p hi%h( fre"#encycomponents of the ori%inal si%nal!

To improve the conditions' in .olby Systems the ori%inal si%nal is compressedin dynamic ran%e at the transmitter! Therefore' the transmission noise is asmaller part compared to all levels of the so#nd si%nal! At the receiver thesi%nal is e=panded and the lo levels are restored ith less noise interference!

The res#lt is a so#nd reprod#ction ith a loer or less noticeable hiss andbetter reprod#ction of hi%h(fre"#ency components of the ori%inal si%nal!

Commentary9 The .olby noise(red#ction techni"#e #sed in some 3& systemscompresses the a#dio si%nals in certain fre"#ency ran%es before transmissionto loer the initial level of noise! The receiver e=pands the si%nals to theirori%inal dynamic ran%e!

Radio .ispatch -etor$

A related system to the radio broadcast system is the radio dispatch systemshon in 3i%#re 4(5N! A central receiverGtransmitter 6transceiver8 stationprovides one(ay si%nallin% to *=ed and to portable receivers to perform thef#nction of messa%e delivery and pa%in% or beeper service! To(aytransceivers at *=ed or portable locations provide command(responseinformation for service vehicles s#ch as ta=is' emer%ency e"#ipment' or repair


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vehicles! Radio telephones in cars can also be handled by to(ay portabletransceivers! It is conceivable that handheld transceivers can be #sed to sendand receive data to and from comp#ter netor$s in the f#t#re! Certainly'amb#lances often have the capability of sendin% medical information ahead tohospitals hile enro#te to the hospital! S#ch a system is a type of datatelemetry in #se today! Stations of the type shon in 3i%#re 4(5N #se a ideran%e of fre"#encies from 5!F &H) to 5 ,H) alloted to mobile comm#nicationsby the 3CC!

Commentary9 .ispatch netor$s combine one(ay and to(ay radiotransmission in fre"#ency bands allocated by the 3CC for mobilecomm#nications!

Cable T2

Commentary9 Cable T2 companies distrib#te television pro%rammin% via cableto s#bscribers ho pay for the service!

One alternative to broadcastin% so#nd and television pro%ram material thro#%hthe air ith electroma%netic radiation is to #se cables to distrib#te thesesi%nals' Q#st as telephone lines and cables distrib#te private telephoneconversations! The cable television system of 3i%#re 4(: is an e=ample of s#chan approach! The cable television or CAT2 is a private distrib#tion netor$hich sends television and other information from a central st#dio tos#bscribers locations! The st#dio %enerates pro%rams or leases pro%rammaterial from national distrib#tors relayed to them by satellite or microavelin$s! The st#dio then sends these channels of television and so#ndbroadcastin% to the locations of the s#bscribers ho have bo#%ht theseservices! The si%nal distrib#tion is #s#ally alon% a central tr#n$ to hich feederlines are connected to s#bscriber locations! This is similar to a city ater s#pplyor other #tility distrib#tion system!


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In some systems the provision is made for comm#nications from thes#bscribers to the st#dio for service re"#ests or information re"#ests ors#bscriber pollin% or interaction ith the cable pro%rams! This is an advanta%eof the direct connected cable system! Another advanta%e is the lo(poeroperation in a noise(free environment! In addition' the cable system #s#ally canoer many channels of information all at the same time! These co#ld incl#de*rst(r#n movies' stoc$ mar$et reports' eatherGnes reports on a :(ho#rbasis' sportin% events' etc! Cable co#ld #ltimately oer access to privatecomp#ter and information netor$s' electronic %ame pools' b#r%laryprevention or safety comm#nications services' and complete home ed#cationalpac$a%es!

Figure 7-2. Ca$le TV etor4

.I,ITA/ .ISTRIBUTIO- O3 T2

Commentary9 .i%ital television si%nal processin% oers the advanta%e ofeYcient and noise(free transmission! 2ideo si%nals m#st be sampled at tice

their hi%hest fre"#ency and converted to di%ital codes!All of the systems that have been disc#ssed in this chapter have historicallybeen analo% si%nal systems! Television systems in the f#t#re may incl#de moredi%ital circ#it techni"#es d#e to the trend toard di%ital systems for telephoneand satellite comm#nications systems! +hile home T2 receivers may remainanalo% for the foreseeable f#t#re' the distrib#tion of pro%ram material fromnational so#rces to local stations may re"#ire di%ital e"#ipment! As has beendisc#ssed and ill be f#rther e=panded' di%ital transmission of s#ch si%nals


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oers the possibilities of more eYcient and more noise(free comm#nication ofthe information!

Basically' to convert a television pict#re to di%ital form re"#ires that the videosi%nal be sampled at tice its hi%hest fre"#ency and each sample converted toa PC& 6p#lse code mod#lation8 e"#ivalent! If the television si%nals contain

fre"#encies #p to !F &H) and the pict#re information re"#ires a 5(bit binarycode for acc#rate representation' then the di%ital si%nal o#ld have to be sentat a rate of !F &H) = : = 5 L N: me%abitsGsecond! This is the di%ital channelcapacity of a T telephone system channel! .i%ital si%nal compressiontechni"#es can be #sed to send a television si%nal in abo#t one(half this bitrate hich o#ld allo4 to television channels to be sent on a T line!

The more television channels that can be sent over a %iven telephone orsatellite channel' the less e=pensive the transportation@ costs for the netor$!If television is #sed to prod#ce relatively still ima%es s#ch as %raphs orpict#rephone ima%es' the bandidth re"#irements can be red#ced to less than5 &H) for a bit rate of 5 &H) = : = M bits L 5F me%abitsGsecond! This is itho#tdata compression techni"#es! Techni"#es s#ch as slo scannin% and di%italcompression co#ld allo s#ch ima%es to be sent ith only F$ bitsGsecond!S#ch transmissions o#ld be "#ite economical beca#se they can be handled bya sin%le di%ital voice channel! Hoever' it o#ld have to be a very still ima%e'

and it co#ld ta$e several seconds for the complete ima%e to be transmitted andformed on a receivin% pict#re t#be! [#st hich of these options ill *nds#Ycient commercial mar$ets remains to be seen!

Commentary9 Sendin% as many television channels as possible over a %iventelephone or satellite lin$ loers distrib#tion costs!

+HAT HA2E +E /EAR-E.1

\Television cameras convert an optical ima%e into a series of electrical si%nalsby scannin% the pict#re a line at a time ith an electron beam and convertin%each spot of the pict#re into an electrical volta%e amplit#de!

\ Television pict#re t#bes reprod#ce pict#res from electronic si%nals by #sin%the si%nals to vary the intensity of a scannin% electron beam hich in t#rnvaries the intensity of li%ht prod#ced by a phosphor on the face of the electront#be!

\ The hori)ontal and vertical scannin% of a pict#re forms the raster of thepict#re t#be!


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\ Each pict#re consists of a frame of D:D lines' ith :F:!D lines per *eld andto interlaced *elds per frame!

\ The hori)ontal scannin% fre"#ency is 5D'4D hert) and the vertical scannin%fre"#ency 6*eld repetition rate8 is F hert)!

\ The television si%nal occ#pies a bandidth of F me%ahert)!\ The color content of the pict#re is contained in the phase of a chrominancesine ave si%nal hile the blac$(and(hite content is contained in thel#minance si%nal!

+HATS -E]T1

The last to chapters have dealt ith the means of transmittin% and receivin%so#nd and pictorial information! A very important cate%ory of information in themodern electronic orld is that of data! The ne=t chapter ill concentrate ondata comm#nications and the comp#ter netor$s that #tili)e and process s#chdata!

1%51. COVE"SO TE & S)06 "TE

)ro$lem 1%5* 6a8 3or a f#ll(scale sin#soidal inp#t' hat is the ma=im#mfre"#ency that permits less than 5 /SB time(#ncertainty1 Ass#me a 5:(bitconverter ith a :D(#s conversion time' 6b8 If a sample(bold havin% an apert#re#ncertainty of D ns ere #sed ahead of the converter' hat is the ma=im#mpermissible fre"#ency for 5 /SB error d#e to time #ncertainly1 6c8 +hatminim#m samplin% rate is theoretically necessary to permit completerecovery of a si%nal havin% no components hi%her than this in fre"#ency1 6d8 Ifthe sample(hold has a D(#s ac"#isition time! hat is the ma=im#m thro#%hp#trate' #sin% the above 65:(bit8 converter1 6e8 Is the criterion of 6c8 met1

theory If the inp#t si%nal to an A.C chan%es d#rin% the conversion process'there is an #ncertainty as to the val#e of the analo% inp#t at a speci*c time>the be%innin% of conversion! Is partic#lar' if the inp#t to a s#ccessive(appro=imation converter chan%es' the di%ital o#tp#t may ta$e on any val#e in

the ran%e thro#%h hich the analo% inp#t chan%ed! In order for the time#ncertainty to be less than W5 /SB' the ma=im#m rate(of(chan%e of si%nalm#st be less than 5 /SB per conversion interval!

The ma=im#m rate(of(chan%e of a sin#soid is :pif2m' here f is a %ivenfre"#ency andM 2m' is the pea$ val#e of the sine ave 63i%! 5D(5Da8! If Tc is theconversion interval' 65D(5


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Therefore 65D(58

The sol#tion to 6a8 ill sho that this is an intolerably lo fre"#ency! If theinp#t volta%e co#ld be acc#rately sampled and retained at the precise instantdesired' and if conversion ere to ta$e

3i%! 5D(5D 6a8 Relationship beteen conversion time and sine(ave fre"#encyfor a %iven resol#tion' 6b8 Aliasin% d#e to inade"#ate samplin% rate!

place hile that inp#t val#e as in hold' there o#ld be no time #ncertainty'irrespective of the len%th of time re"#ired for conversion!

A sample(bold circ#it 63i%! 5D(5F8 contains a capacitor' a sitch' an inp#tb#er' and an o#tp#t b#er! 3or speed and acc#racy hile trac$in%' it iscon*%#red as either an RC la% circ#it or an inte%rator' connected in a feedbac$loop! .#rin% sample 6or trac$8' the loop see$s to follo the inp#t si%nal'

char%in% the capacitor as fast as it can! .#rin% hold' the sitch is open' andthe char%e remains on the capacitor' e=cept for lea$a%e' hich ca#ses a slo?droop!@ To critical


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3i%! 5D(5F Sample(bold circ#its' 6a8 3olloer' 6b8 Inte%rator' 6c8 Timin% errors!6Problem 5D!M8

dynamic parameters are ac"#isition time' hen the sitch closes' and apert#retime hen the sitch opens!

Ac"#isition time 6see 3i%! 5D( 5Fc8 is the time re"#ired for the capacitor volta%eto chan%e from the val#e that has been held to the latest si%nal val#e>toithin a re"#ired fraction of f#ll scale! Its application ill be seen in 6d8! Theapert#re time is the interval beteen the application of the hold command andthe act#al openin% of the sitch! It consists of a delay 6hich depends on thelo%ic and on the sitchin% device' typically D ns8' and an #ncertainty' d#e to

Qitter of typically D ns for %eneral(p#rpose devices!

+hen a sample(hold is #sed in an application here timin% is critical' thetimin% of the hold command can be advanced to compensate for the $noncomponent of apert#re delay! The Qitter hoever' imposes the #ltimatelimitation on timin% acc#racy! +hen a sample(hold is #sed ith as A.C' the


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timin% #ncertainty d#e to the conversion time is red#ced by the ratio of theconversion time to the apert#re Qitter! In other ords' the apert#re #ncertainty

Ta replaces the conversion delay Tc in E"! 65D(58!

If a si%nal is sampled at too slo a rate and is later reconstr#cted' distortionmay occ#r oin% to aliasin%! This is the creation of si%nals at other fre"#encies

havin% the same samplin% pattern 63i%! 5D(5Db8! To avoid aliasin%' the samplin%rate m#st be %reater than tice the hi%hest fre"#ency of interest! 3#rther' allhi%her fre"#encies m#st be *ltered o#t before samplin% 6and' at the receivin%end' after reconstit#tion8! This' in %reatly simpli*ed form' is in conse"#ence ofthe samplin% theorem!

Sol#tion 6a8 By E"! 65D(58' the ma=im#m fre"#ency is :^(5:G6pi \ :D \ 5^(F8L

6b8 By E"! 65D(58' the ma=im#m fre"#ency is :^(5:G6pi \ D 5^(N8 L 5D!D$H)!

6c8The theoretical minim#m samplin% rate' from the samplin% theorem' is : =5D!D L

CE"C &E ESTE C)T80O

En el `ltimo capt#lo se c#bren los conceptos bsicos del sistema telefnicofamiliar! Un sistema i%#almente familiar "#e se toma casi tanto por sentado"#e el sistema telefnico es la radio y la televisin! /a mayora de la %enten#nca est m#y leQos de ser #na radio o televisin' y m#chas horas por da se%astan se entretiene o informada por #no # otro de estos sistemas! .esde la


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televisin incl#ye informacin del tipo de la radio en s# porcin de sonido' yp#esto "#e ambos dependen de la dif#sin de informacin sobre #n enlace detransmisin de la radiacin electroma%ntica' #n anlisis de los conceptosbsicos de la televisin tambin servir para c#brir los f#ndamentos de laradio!

Por lo tanto' en este capt#lo se har hincapi en las tcnicas y aplicaciones delos sistemas de televisin' y' al mismo tiempo' varias disc#siones indicarcmo estas tcnicas se aplican a la radiodif#sin! El primer concepto msbsico de la comprensin de los sistemas de televisin es la tcnica para latransmisin de im%enes por va electrnica!

9Como son las im:genes transmiti#as electrnicamente;

/os componentes necesarios para transmitir im%enes de #na cmara detelevisin a #n receptor de televisin y los m#estra en #n t#bo de ima%en detelevisin se m#estran en la 3i%#ra 4(5! El propsito de la cmara es paraconvertir la informacin ptica 6ondas de l#) re7eQadas8 de la ima%en en las

correspondientes seales elctricas! El micrfono convierte c#al"#ier sonidoasociado a la ima%en' como el habla o la m`sica' en seales correspondientes!Estas seales deben ser mod#ladas sobre #na portadora de alta frec#encia yampli*can hasta "#e son lo s#*cientemente potente como para ca#sar laradiacin electroma%ntica en el nivel deseado de la antena de transmisin! /a%ama y la direccin de dicha radiacin depende de la potencia del transmisor'la frec#encia de la portadora' y el diseo de la antena! Estos factores seanali)an en detalle en el capt#lo sobre el espectro de las com#nicaciones! Si elreceptor est sit#ado correctamente dentro del alcance del transmisor'detectar la radiacin como #n 7#Qo de corriente en s# antena! En el receptor'este nivel de la seal se incrementa con #n ampli*cador de alta frec#encia'

demod#lada' y se procesa para prod#cir el sonido ori%inal en #n altavo) y laima%en ori%inal en #n t#bo de ima%en! Es este procesamiento' tanto en lacmara y en el receptor de televisin' "#e debe ser entendido si la operacinde #n sistema de televisin es para ser entendido! Como se m#estra en la3i%#ra 4(5! el enlace de transmisin m#chas veces es por cable en l#%ar de laradiacin electroma%ntica! Esto de nin%#na manera cambia los conceptos delsistema!

Comentario9 /os elementos bsicos de #n sistema de televisin incl#yen #nacmara y #n micrfono para convertir las im%enes y el sonido en sealeselctricas' #n transmisor para transmitir las seales' #n receptor pararec#perar las seales' y #n t#bo de ima%en y #n altavo) para reprod#cir las

im%enes y el sonido!

magen #e la c:mara en se


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"#e c#bre el interior de s# cara' #na enfocados a%#damente ha) de electrones"#e escanea a travs de #na diana en el patrn "#e se m#estra' y al%#nosmedios para detectar variaciones de corriente en el ha) de electrones' ya "#ee=plora a travs del obQetivo! C#ando la l#) %olpea la cara del t#bo y elmaterial fotosensible' se emiten electrones' pero c#ando el rostro est osc#rono se emiten electrones! /os electrones emitidos ca#san #na copia de laima%en "#e aparece en la s#per*cie del obQetivo! Sin embar%o' ahora laima%en se de*ne por la cantidad de car%a positiva en l#%ar de car%a ne%ativaUna alta car%a positiva para la l#) de alta intensidad; #na car%a positiva baQapara baQa intensidad o condiciones casi de noche

Comentario9 Una cmara de televisin contiene #n t#bo c#yo rostro estrec#bierto con #n material sensible a la l#)! Im%enes centradas en esta rease reprod#cen en #na s#per*cie de destino dentro del t#bo donde ca#sanvariaciones de corriente en #n ha) de electrones "#e e=plora el obQetivo

El patrn #e escaneo

A medida "#e el ha) de electrones es ca#sada para escanear el obQetivo dei)"#ierda a derecha a travs del t#bo para #na lnea hori)ontal' "#e se m#evelentamente hacia abaQo verticalmente de #na manera contin#a ca#sandotambin para escanear hacia la parte inferior del t#bo!

Como las e=ploraciones de ha)' #n ha) re7eQado se reco%e y se detecta atravs de #n resistor m#estra en la 3i%#ra 4(:! El ha) re7eQado se contiene elmismo n`mero de electrones como el ha) de e=ploracin ori%inal si no haycar%a positiva sobre la s#per*cie obQetivo! Si hay #na car%a positiva del ha)re7eQado tendr menos electrones 6menos act#ales8 debido a "#e al%#noselectrones se combinan para ne#trali)ar la car%a positiva! Por lo tanto lacorriente en el ha) re7eQado ser inversamente proporcional a la intensidad del#) de la ima%en "#e se centra en el t#bo de la cmara! /as variaciones decorriente prod#cen las variaciones de tensin de la 3i%#ra 4('5 en la salida delt#bo de cmara de televisin!

Como se m#estra en la 3i%#ra 4(e

C#ando el ha) electrnico de barrido completa #na lnea de e=ploracin'dev#elve hacia el lado i)"#ierdo de la cara del t#bo y comien)a otra lnea dee=ploracin! Este retorno se llama retorno! /a corriente de ha) se i%norad#rante 7ybac$ por"#e el voltaQe de salida se aQ#sta a s# m=imo 6osc#ridadtotal8 d#rante este tiempo de retorno 63#t#ro 4(


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e=plorando' las tres seales "#e se %eneran como informacin de lneahori)ontal en diversos p#ntos de la letra H se m#estran en la 3i%#ra 4(

Comentario9 variaciones de corriente en las variaciones de tensin prod#cto deha) de e=ploracin en la salida de la cmara osc#ra ser la ima%en detelevisin' mayor es la tensin! .#rante los intervalos 7ybac$ entree=ploraciones de lnea' la tensin est aQ#stado a s# nivel positivo m=imo!

/a e=ploracin contin`a hasta "#e alcan)a la parte inferior de la cara del t#bo!Como res#ltado' toda la ima%en bidimensional se convierte en #na sealelctrica contin#a lar%a con el tiempo "#e conten%a tantos imp#lsos deretroceso' ya "#e hay lneas hori)ontales escaneados en el campobidimensional! Entre dos de los imp#lsos de retroceso' las variaciones deblanco a ne%ro en la ima%en se convertirn a las correspondientes variacionesde voltaQe 6menor a mayor8 a la salida del t#bo! /os imp#lsos de retrocesoc#entan las im%enes receptor electrnica t#bo c#ndo hacer "#e el ha) de7ybac$ hacia el lado i)"#ierdo y el momento de iniciar #na n#eva lnea!

/a seal elctrica 6llamada la seal de vdeo8 entre los imp#lsos de retroceso ledice al receptor "# variaciones de blanco y ne%ro para prod#cir en #na lneahori)ontal dada de la ima%en re%enerada! /os circ#itos electrnicos en el t#bo cmara 6transmisor8 y el t#bo de ima%en 6receptor8 deben hacer "#e el ha) deelectrones para escanear en el patrn deseado y deben ser sincroni)ados entres!

Comentario9 Para reprod#cir con precisin la ima%en' los circ#itos dee=ploracin de la cmara y el receptor deben estar sincroni)ados! Sealesespeciales se transmiten Q#nto con la seal de vdeo para este propsito!

?0SS &E0 T8BO "ECE)TO" &E 6E

El patrn "#e se e=plora se m#estra en el t#bo de ima%en receptor detelevisin en la 3i%#ra 4(! /a seal de vdeo mod#la la intensidad del ha) deelectrones! C#ando la intensidad de la l#) es brillante en la cmara' el ha) har"#e #n p#nto brillante en el t#bo de ima%en en el mismo l#%ar! Una corrientecambiante en las bobinas de de7e=in prod#ce #n campo ma%ntico "#e hace"#e el ha) para escanear las h#ellas de lnea "#e se corresponden con elpatrn de e=ploracin en la cmara de T2! Esto se conoce como la trama! /acorriente de electrones %enerados por el can de electrones se centra en #n


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ha) para prod#cir #n b#en l#%ar en la cara del t#bo de ima%en! /a cara t#bo deima%en contiene #n fsforo emisor de l#) "#e emite l#) en proporcin a laintensidad de la corriente de ha) de electrones! /a intensidad del ha) esproporcional a la tensin de la seal de vdeo aplicada entre el reQilla de controly el ctodo del t#bo!

Comentario9 /a cara del t#bo de ima%en en #n receptor de televisin tiene #nrec#brimiento de fsforo "#e emite il#minacin "#e se di%itali)an por #n ha)de electrones en movimiento en el paso con el ha) de la cmara de transmisinde T2! /a seal de vdeo entrante vara la intensidad del ha) para reprod#cir laima%en ori%inal!

0a repro#uccin #e un persona>e

/os patrones de seal de la 3i%#ra 4(


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correspondientes de los 7ybac$ o de de7e=in hori)ontal seales de F


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de tales elementos' habra #nos 5! elementos de ima%en f#ndamentales6llamados p=eles o pels8 por c#adro! Esto se corresponde con cerca de 5:D!elementos de ima%en de la pelc#la de pelc#la de 5F mm' lo "#e si%ni*ca "#ela ima%en de televisin tiene apro=imadamente la misma resol#cin o nitide)de detalle como hara con #na pelc#la de 5F mm!

CAO &E B& V&EO

El efecto de la resol#cin hori)ontal de las lneas y el ancho de banda de vdeore"#erido p#eden IJ Kvisto mediante el e=amen de la 3i%#ra 4(4A! S#pon%a "#elos pels c#adrados son de anch#ra d! /a mayor parte del contenido de laima%en p#ede tener es c#ando todos los dems pel es ne%ro' lo "#e provoca#na seal de vdeo de la forma de la *%#ra 4(4h! Si la pel es de dimensin dcon #na separacin :d entre barras ne%ras y / G . pels por lnea' la ondac#adrada en la seal de vdeo se compone de / G p#lsos :d en D


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Comentario9 Una cmara de televisin en color rompe #na ima%en en tresim%enes a todo color principal de roQo! *ltros verde y a)#l! /as tres im%enesse escanean con tres haces de electrones separados!

0uminancia y crominancia

/as seales para cada color se combinan por #n circ#ito electrnico de matri)para prod#cir dos seales' llamada la l#minancia 608 "#e contiene lainformacin de nivel de %ris' y la crominancia 6C8 "#e contiene la informacinde color! C#ando se aplica la l#minancia a #n t#bo en blanco y ne%ro yordinario' #na ima%en en blanco y ne%ro y normal res#lta!

Comentario9 seales de vdeo para la televisin en color tienen doscomponentes9 l#minancia para controlar el nivel de %ris y crominancia paracontrolar la sat#racin 6intensidad del color8 y la tonalidad 6tinte8! Aparatos detelevisin en blanco y ne%ro slo #tili)an la seal de l#minancia para controlars# nivel de %ris!

/a seal transmitida contiene las seales de l#minancia y crominancia! C#andola seal es procesada por el receptor #n color roQo! seales verde y a)#l serec#peran' se ampli*can' y l#e%o mod#lan la intensidad de #n ha) deelectrones en el t#bo de ima%en de televisin en color! /a cara del t#bo tieneahora tres fsforos #bicados en #n patrn re%#lar Q#nto a la otra sobre toda las#per*cie del t#bo ( #no para el roQo! #no para verde' y #no para el a)#l En elt#bo' como se m#estra en la 3i%#ra 4(M' cada #no de los colores tiene s# propioha) de electrones "#e se centra en la cara del t#bo para "#e %olpea el fsforocolor "#e corresponda a s# color! Una placa de mscara de sombra se colocaentre las vi%as y los fsforos de color de modo "#e el ha) de l#) roQa p#ede%olpear slo el fsforo roQo el ha) verde slo el fsforo verde' y el ha) a)#l sloel fsforo a)#l! /a amplit#d de crominancia y la fase de determinar lascorrientes de ha) para los tres haces de color! /a amplit#d contiene laintensidad de color 6llamado sat#racin de color8 y la fase contiene la me)cla6mati) o tinte8 de color! El sistema de desviacin del t#bo m#eve las tres vi%asal #nsono a travs del patrn de e=ploracin entrela)ada de la 3i%#ra 4(F! /oselectrodos de enfo"#e para cada ha) proporcionan para #n enfo"#e preciso ycon el obQetivo de los haces individ#ales del %r#po de tres haces! El res#ltado%lobal es la reprod#ccin de la ima%en ori%inal color detectado por la cmarade color!

Comentario9 t#bos de ima%en de color tienen #n ha) separado rec#brimientode fsforo y de electrones para cada #no de los tres colores!

En representacin #el espectro #e color

P#ede parecer imposible "#e #na sola sin#soide crominancia para contenertoda la informacin de color de #na ima%en en color! Sin embar%o' si elespectro de color se considera como #n espectro de variacin contin#atonalidades o colores de a)#l prof#ndo a roQo intenso' es fcil ver cmo #nparmetro elctrico' como tensin' corriente' resistencia o fase p#ede servalores para representar asi%nado todos los colores! En la televisin en color el


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parmetro ele%ido es la fase de la sin#soide de crominancia! Recordemos "#ese a*rm anteriormente "#e fase es #na medida de la posicin en el tiempo de#na forma de onda en comparacin con #na referencia! Comentario9 /a fase dela seal de crominancia 6s# posicin en el tiempo en comparacin con #naseal de referencia8 indica el color 6mati)8! /a amplit#d de la seal decrominancia indica la intensidad del color 6sat#racin8!

Fase #e una se


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Comentario9 Una seal de crominancia en fase con la referencia indica amarillo!Una seal crominancia N %rados f#era de fase con la referencia indica roQo!Una seal de crominancia 5M %rados f#era de fase indica a)#l!

Separacin #e crominancia y luminancia

.iferentes receptores de televisin en color #tili)an las seales de crominanciay l#minancia de diferentes maneras! Uno de los enfo"#es ms com#nes es lade proporcionar las seales de color me)cladas con las seales de l#minancia#tili)ando las relaciones e=presadas en las ec#aciones de la *%#ra 4(5! /aseal de l#minancia se de*ne en la *%#ra 4(5 como "#e consiste en


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l#minancia! Por lo tanto 0 est disponible f#era del ampli*cador de paso baQo yse aplica al ctodo de los caones de electrones como 0!

Comentario9 Un ampli*cador de paso baQo en los receptores de color separa laseal de l#minancia de la seal de vdeo! Ampli*cadores de paso de bandaseparan la crominancia y seales de rfa%a de las seales de vdeo!

.#rante el ampli*cador de s#presin de rfa%a est encendido y elampli*cador de crominancia est apa%ado! .e esta manera la rfa%a de colorsincroni)a el oscilador de


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ampli*cacin' incl#yendo el detector de vdeo y los circ#itos de controla#tomtico de %anancia 6A,C8 son tipos com#nes a ambos receptores! Undia%rama %eneral de blo"#es se m#estra en la 3i%#ra 4 (5:! informacin detelevisin p#ede ser transmitido por c#al"#iera de los canales "#e se m#estranen la 3i%#ra 4(5

Comentario9 R3 y etapas de ampli*cacin son com#nes a color y en losreceptores de televisin en blanco y ne%ro!

El ampli*cador de R3 es #n ampli*cador de paso de banda "#e proporciona laampli*cacin inicial a la frec#encia partic#lar recibida en la antena! Pasa slolas frec#encias del canal seleccionado por el selector de sintoni)ador receptor ocanal debido a "#e el paso de banda se establece mediante este interr#ptor! /aseal pasa a travs del ampli*cador de R3 se me)cla con #na seal de ondasin#soidal de #n oscilador! /a me)cla prod#ce #na seal en la s#ma de lafrec#encia de R3 y el oscilador y otro en la diferencia de frec#encia entre lasdos seales de entrada! El selector de canal se sintoni)a el oscilador al mismotiempo "#e sintoni)a el ampli*cador de R3 de modo "#e la diferencia defrec#encia f#era de la me)cladora siempre es a F me%ahert)!

Comentario9 El ampli*cador de R3 ampli*ca las seales recibidas desde laantena de T2 o cable en el canal "#e seleccione! /a salida del ampli*cador deR3 se me)cla con la salida de #n oscilador de frec#encia variable para prod#cir#na frec#encia intermedia 6I38 "#e es la misma para todos los canales!

/a seal del canal seleccionado ser ampli*cada por el ampli*cador de paso debanda a F( me%ahert) llamado el ampli*cador de frec#encia intermedia I3o ampli*cador! Si se #tili)an ampli*cadores de manera "#e la seccin deampli*cador de #n alto rendimiento se p#ede #tili)ar para proporcionar lamayor parte de la %anancia del receptor' independientemente del canal de R3"#e se ha seleccionado! Esto permite a los diseadores para prod#cir #nam#cho meQor ampli*cador de lo "#e sera posible si el ampli*cador t#vo "#eproporcionar #n paso de banda adaptada a la canal seleccionado! /a salida delampli*cador de 3I tiene s#*ciente voltaQe de la seal para accionar los circ#itosde vdeo y sonido!

&etector #e v#eo y 6C

El detector de video elimina la portadora de me%ahert) de la amplit#dmod#lada SI seal! /a f#er)a de la salida del detector se alimenta a loscirc#itos de control a#tomtico de %anancia 6A,C8 para mantener lascon"#istas de la R3 y ampli*cadores en los niveles deseados en #n ran%obastante estrecho! Esto evita "#e las seales de antena f#ertes decomportarse de manera diferente a partir de seales dbiles en la salida deldetector de video! Si se recibe #na seal dbil' el control A,C aQ#sta la R3 e I3%anancias del ampli*cador en #n valor alto para "#e #na salida de vdeo f#erteest disponible! Si la seal de la antena es f#erte' el control A,C aQ#sta la%anancia del ampli*cador de baQo de manera "#e la salida de vdeo no estsobree=citado o distorsionada! Por lo tanto' el circ#ito de control A,C mantiene


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#na relativamente f#erte salida del detector de vdeo no distorsionada "#e esen %ran medida independiente de la f#er)a de la seal de la antena!

Comentario9 El detector de vdeo separa la portadora de la seal de I3 y envala seal de vdeo comp#esto res#ltante para el sonido' la ampli*cacin devdeo' separacin de colores' y los circ#itos de desviacin!

Circuitos #e soni#o

/a salida del detector de vdeo se enva a c#atro s#bsistemas receptoresdiferentes9 los circ#itos de ampli*cacin de sonido' el vdeo y circ#itos deseparacin de colores "#e contienen los ampli*cadores de l#minancia ycrominancia' y los circ#itos de desviacin! 0a se han disc#tido los circ#itos del#minancia y crominancia! 3i%#ra 4(libra contiene ms detalles de la separacinde frec#encias de las diferentes seales en la seal de salida de vdeo deldetector! El s#bsistema de sonido reco%e la portadora de sonido de la seal devdeo en %eneral mediante el #so de #n ampli*cador de paso de bandaestrecha centrado en 'D &H)! Este ampli*cador recha)a la informacin de la

ima%en' pero pasa la informacin de sonido! /a portadora de sonido es #naseal mod#lada de frec#encia "#e se convierte en a#dio

Comentario9 /a seal de sonido es sorprendido f#era de la seal de vdeo por#n ampli*cador de paso de banda estrecha centrada en 'D &H)!

/as frec#encias mediante tcnicas disc#tidas previamente! Ampli*cadores dea#dio imp#lsar esta seal para el nivel "#e se re"#iere por los altavoces!

Circuitos #e #esviacin

/os circ#itos de de7e=in e=traer los imp#lsos de sincroni)acin hori)ontales yverticales de la parte s#perior de los imp#lsos de retroceso "#e se m#estran en

la 3i%#ra 4(D! Estos se #tili)an para sincroni)ar las frec#encias y p#ntos departida de la hori)ontal 63i%#ra 4(Db8 y seales 63i%#ra 4(Dc8 de de7e=invertical prod#cidas por los osciladores hori)ontal y vertical respectivamente!/as salidas de estos osciladores se ampli*can y se aplican a las bobinas dede7e=in para proporcionar el patrn de e=ploracin de trama adec#ado "#e sedisc#ti antes! El retorno rpido de la seal de de7e=in hori)ontal m#estra enla 3i%#ra 4(Db se #tili)a para %enerar la alta tensin re"#erida por el electrodode nodo del t#bo de ima%en 63i%#ra 4(5'8! Un p#lso de alta frec#encia es%enerada por el retorno hori)ontal de 5 microse%#ndos y se transforma yrecti*cada a #na tensin de 5M a :D $ilovoltios de .C por los circ#itos dealimentacin de alta tensin! Se re"#iere esta alta tensin para acelerar los

electrones para proporcionar el brillo de la pantalla adec#ada! Tambin es #naf#ente de alimentacin de baQa tensin "#e s#ministra ener%a a todos loscirc#itos de todo el receptor!

Como se mencion anteriormente en la disc#sin sobre el espectro y laresol#cin de frec#encia' al%#nas de las caractersticas de rendimiento de latelevisin depende del ancho de banda del canal asi%nado a la seal detelevisin "#e contiene la ima%en y la informacin de sonido! El transportista yel ancho de banda de estas seales se han estandari)ado por la ind#stria de la


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radiodif#sin y de la Comisin 3ederal de Com#nicaciones! Echemos #n vista)oa los re"#isitos de ancho de banda con ms detalle!

Comentario9 /os circ#itos de de7e=in #san los p#lsos de sincroni)acin en laseal de vdeo para %enerar el patrn de lect#ra correcta en el t#bo de ima%en!

9C8?0ES SO 0OS "E8STOS &E B& #e ra#io y televisin;Canales #e television

.ado "#e el ancho de banda del ampli*cador de I3 en la *%#ra 4(5: es F &H)6F ( 8' entonces #no esperara "#e el ancho de banda del canal de televisines F &H)! Esto es e=actamente correcta como se m#estra en 3i%#ra 4(5


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mod#lada! Como res#ltado' las frec#encias de la l#minancia "#e se e=tiendenms all de 5':D &H) de la portadora se reprod#cen slo a 5G: de la amplit#dde las seales "#e se aQ#stan a la banda de frec#encia 5!:D( &H)! /asfrec#encias ms baQas prod#cen las caractersticas %enerales de la ima%en; lasfrec#encias s#periores de la nitide) de la ima%en y el detalle! /a banda lateralinferior de la seal de amplit#d mod#lada de la frec#encia portadora deima%en hasta el lmite de la banda inferior se llama la banda lateral vesti%ial!

Comentario9 /os canales de televisin tienen #n ancho de banda de F &H)! /afrec#encia portadora de ima%en es de 5':D &H) por encima de la frec#encia dela banda inferior! /a portadora de sonido es de 'D &H) por encima de laportadora de ima%en!

"epro#uccin #e soni#o #e F y TV

/a informacin de sonido es mod#lada en la portadora de sonido' "#e es 'D&H) por encima de la portadora de ima%en' #tili)ando mod#lacin defrec#encia con #n ancho de banda de desviacin de W :D $ilohercios! Esto se

compara con la desviacin 4D( X$ilohercios disponible en emisoras de 3&! Estasdesviaciones se prod#cen por 5 de mod#lacin de seales de a#dio! Tanto3& y el sonido de televisin p#eden reprod#cir frec#encias de a#dio en el D(H)a la %ama de 5D $H)' a#n"#e las seales de 3& tienden a ser ms inm#ne alr#ido con s#s amplias desviaciones! Adems' las estaciones de 3& tienden aser m#ltiple=ados sonido estereofnico y %eneralmente se reprod#cen con elsistema de sonido de alta *delidad' mientras "#e el sonido de la televisin esmonofnico y se reprod#ce con lo "#e %eneralmente se clasi*ca como #nsistema de baQa calidad!

En el f#t#ro' los receptores de televisin sin d#da podran ofrecer #na meQor*delidad de a#dio a travs de meQores ampli*cadores de a#dio y sistemas dealtavoces de alta calidad! Es posible "#e las estaciones de televisin paraproporcionar #n sonido estereofnico dentro de la presente ancho de banda deF &H) a#mentando li%eramente el ancho de banda disponible para el canal desonido! Este desarrollo' si se prod#ce en absol#to' ms probable es "#e seprod#)ca por primera ve) en las redes de los no(emisin de televisin!Ciertamente' el costo de los componentes tanto en el transmisor y el receptor

Q#e%a #n papel importante en esta decisin!

Comentario9 la portadora de ima%en es mod#lada en amplit#d' mientras "#e laportadora de sonido es mod#lada en frec#encia! El receptor normal del T2' sinembar%o' no tiene circ#itos de alta *delidad como los de #so frec#ente en la

radio 3&9C8?0ES SO 068OS TV y "a#io "E&ES TG)COS;

/a mayor parte de la disc#sin hasta ahora en este capt#lo se ha as#mido "#eel sistema ha sido #na red de dif#sin de televisin comercial' los componentesde los "#e se m#estran en la 3i%#ra 4(5D! El est#dio es el centro decom#nicaciones central para este tipo de instalaciones! Se ori%ina pro%ramasde noticias y eventos deportivos locales! Recibe los pro%ramas de las redes


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nacionales de televisin a travs de enlaces de microondas o lneas telefnicasarrendadas de ancho de banda s#*ciente para maneQar los re"#isitos de loscanales de televisin!

Enlaces a #istancia

El transmisor para irradiar el material de televisin %enerada en el est#dio enla mayora de los casos no se enc#entra en el est#dio! El est#dio por lo %enerales en al%`n l#%ar de ne%ocios cmodo en #n rea metropolitana! /ostransmisores de alta potencia y torres de alta antena deben estar #bicados en)onas remotas en las cimas de los cerros o en otros p#ntos altos con vistas a la)ona para ser servido por la dif#sin! Por esta ra)n' las seales de est#diodeben estar relacionados con la instalacin de transmisin en #n enlace deest#dio al transmisor! /a 3CC en#mera varias bandas de frec#encia para s# #sopara este *n' como se indica en la *%#ra 4!5D! Estas frec#encias se #tili)anpara enviar el material de pro%rama de televisin' la informacin de lascom#nicaciones y las seales de control a las instalaciones de transmisin! /aantena est#dio y la antena de recepcin de enlace en la instalacin detransmisin deben estar dentro de #na trayectoria de cada otra lnea de visin!

Comentario9 .esde transmisores de televisin s#elen ser cierta distancia desdeel est#dio' la 3CC se reserva varias bandas de frec#encias para enlaces(st#dio(a transmisor!

0a separacin #el transmisor

Para transmitir 6radiar la seal8 #n transmisor de alta potencia alimenta hastaD $ilovatios a #na antena de transmisin en #na torre de #nos D pies dealt#ra! Receptores de televisin dentro de #n radio de la lnea de visin de laantena de transmisin de :D a 4D millas recibirn las seales! .ebido a este

intervalo' la 3CC mantiene estaciones de radiodif#sin en el mismo canalseparados por #na distancia de al menos : millas 6dependiendo de si lasestaciones estn 2H3 o UH38 por lo "#e las estaciones no interferirn entre s!Estaciones c#yos canales son adyacentes en la frec#encia' como por eQemplo elcanal : y


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visin al i%#al "#e en la radiodif#sin de televisin! /a estacin de radio A&sera irradiar #na seal mod#lada ampli*cada en el ran%o de frec#encia de D$H) a 5'F &H)! En este ran%o de frec#encia de #na seal transmitida de altapotencia 6D $+8 p#ede viaQar lar%as distancias' sobre todo por la noche'debido a "#e la transmisin no es la vista de lnea de( y rebotar en laionosfera!

"eceptores #e ra#io

-o#ulacin #e mplitu#

/os receptores para seales de radio son similares a la porcin de sonido delreceptor de televisin! Una estr#ct#ra tpica receptor de radio A& banda sem#estra en la 3i%#ra 4(5F! Al i%#al "#e con el receptor de T2' #n oscilador y #nampli*cador de R3 se m#ltiplican entre s por ser alimentada a #n circ#itome)clador! El me)clador prod#ce las frec#encias s#ma y diferencia de las dosseales! En trminos tcnicos esto se llama heterodinacin! /a sealres#ltante' ya sea la s#ma o diferencia' es la frec#encia I3! S# detector es #n

demod#lador de A& y no tienen circ#itos A,C! El ampli*cador de R3 estsintoni)ado para proporcionar #nas caractersticas de paso de banda "#epasarn la seal desde #na `nica estacin de radio A& a la me)cladora! /afrec#encia del oscilador se vara de manera similar para "#e la diferencia entrela frec#encia de la emisora y la frec#encia del oscilador local ser #n DD $H)(I3 de frec#encia! Es esta me)cla y SI ampli*cacin "#e hace "#e el receptor de#na estr#ct#ra s#perheterodino!

Comentario9 circ#itos receptor de radio son similares en f#ncionamiento y laestr#ct#ra de los circ#itos comparables en los receptores de televisin!

El ampli*cador de I3 a#menta slo el ran%o estrecho de frec#encias "#e la

seal ha sido convertida a' blo"#eando c#al"#ier seales e=traas o r#ido! El I3ampli*cada seal se enva a #n detector de mod#lacin de amplit#d "#e%enera la seal de a#dio y controla el circ#ito A,C de la misma forma "#e elA,C se #tili) en el receptor de televisin! En el receptor A& el control A,Ctiende a evitar estallidos f#ertes de r#ido de las estaciones f#ertes y red#ce ladecoloracin y otras variaciones de nivel de sonido en la seal de a#dio! /aseal de a#dio es ampli*cada y enviada al altavo) para la reprod#ccin desonido!

F-Frecuencia o#ula#a

Un receptor de 3& monoa#ral tendra casi #na estr#ct#ra idntica a la deldia%rama de blo"#es del receptor de A& 3i%#ra 4(5F e=cepto "#e ahora #ndemod#lador de 3& se #tili)a para el detector! El R3 y frec#encias son m#ydiferentes debido a las frec#encias ms altas' pero los blo"#es reali)an lasmismas f#nciones bsicas!

Sistemas Est=reo F


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Transmisiones estreo 3& contienen dos canales independientes de sonido! Elsoporte para los canales estereo no se transmite!

/os sistemas para la transmisin y recepcin de J& estreo son #n poco mscomplicado' ya "#e dos canales independientes de informacin de sonidodeben ser maneQados! Para estreo se asi%na el ancho de banda de emisoras

de 3& como se m#estra en la 3i%#ra 4(54! C#atro seales deben ser %enerados!/a primera seal es #n comp#esto de informacin de sonido llamado / V Rres#ltante del canal i)"#ierdo 6/8 aadida a la informacin de sonido del canalderecho 6R8! /a tercera y c#arta seales son la diferencia entre la / y lainformacin de sonido R! .entro del ancho de banda de :< $H) a D< $H) #no deellos se coloca por debaQo y el otro encima de la frec#encia portadora de


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enviara informacin monoa#ral con / L R para "#e la informacin /Rdesaparecera y slo / V R L :/ L :R informacin sera recibida y enviada a losdos canales del sistema estreo!

&ol$y Sistemas

Al%#nas emisoras de 3& proporcionan #na codi*cacin de red#ccin de r#idodel tipo #tili)ado en las modernas %rabadoras! El receptor toma ventaQa de estacodi*cacin para red#cir los efectos molestos de r#ido de alta frec#encia 6amen#do llamado silbido r#ido8 en el sonido reprod#cido!

El sistema .olby #tili)a circ#itos en el transmisor para comprimir las seales desonido en ciertos ran%os de frec#encia antes de la transmisin! El receptor see=pande las seales de v#elta a s# ran%o dinmico ori%inal!

Por eQemplo' en los sistemas ordinarios' las seales "#e varan de mayor amenor nivel lle%an al receptor con las seales de baQo nivel enmascaradas porel r#ido de la transmisin! En el receptor este silbido notable c#bre hasta

componentes de alta frec#encia de la seal ori%inal!Para meQorar las condiciones' en .olby Sistemas de la seal ori%inal secomprime en el ran%o dinmico en el transmisor! Por lo tanto' el r#ido detransmisin es #na parte ms pe"#ea en comparacin con todos los nivelesde la seal de sonido! En el receptor la seal se e=pande y los niveles baQos seresta#ran con menos interferencia de r#ido! El res#ltado es #na reprod#ccinde sonido con #n siseo inferior o menos perceptible y #na meQor reprod#ccinde componentes de alta frec#encia de la seal ori%inal!

Comentario9 /a tcnica .olby de red#ccin de r#ido #tili)ado en al%#nossistemas de 3& comprime las seales de a#dio en ciertos intervalos de

frec#encia antes de la transmisin para red#cir el nivel inicial de r#ido! Elreceptor ampla las seales a s# ran%o dinmico ori%inal!

"a#io &espac,o "e#

Un sistema relacionado con el sistema de transmisin de radio es el sistema dedespacho de radio se m#estra en la 3i%#ra 4(5N! Un receptor G transmisorcentral 6transmisor(receptor8 estacin proporciona la seali)acin de #na va a*Qo y receptores porttiles para reali)ar la f#ncin de entre%a de mensaQes y depa%inacin o servicio b#scapersonas! .e dos vas transceptores en l#%ares *Qoso porttiles proporcionan informacin del comando de resp#esta para losvehc#los de servicios como ta=is' los e"#ipos de emer%encia' o reparar

vehc#los! Radiotelfonos en los coches tambin p#eden ser maneQados por lostransceptores porttiles de dos vas! Es concebible "#e transceptores porttilesse p#eden #tili)ar para enviar y recibir datos hacia y desde las redes deordenadores en el f#t#ro! Ciertamente' las amb#lancias s#elen tener lacapacidad de enviar informacin mdica por delante a los hospitales mientrascamino al hospital! Tal sistema es #n tipo de telemetra de datos en #so hoy enda! Estaciones de tipo mostrado en la 3i%#ra 4(5N #tili)an #na amplia %ama defrec#encias de 5'F &H) a 5 ,H) adQ#dicada a las com#nicaciones mviles porla 3CC!


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Comentario9 redes de .espacho se combinan en #n solo sentido y de dos vasde transmisin de radio en las bandas de frec#encias atrib#idas por la 3CCpara com#nicaciones mviles!

Televisin por ca$leComentario9 T2 cable empresas distrib#yen pro%ramas de televisin a travsdel cable a los s#scriptores "#e pa%an por el servicio!

Una alternativa a la radiodif#sin sonora y el material de pro%rama detelevisin por el aire con la radiacin electroma%ntica es #tili)ar cables paradistrib#ir estas seales' tal como las lneas telefnicas y cables distrib#irconversaciones telefnicas privadas! El sistema de televisin por cable 3i%#ra4(: es #n eQemplo de tal enfo"#e! /a televisin por cable o de televisin porcable es #na red de distrib#cin privada' "#e enva la televisin y otros datosdesde #n est#dio central para #bicaciones del s#scriptor! El est#dio %enera

pro%ramas o arrienda material del pro%rama de distrib#idores nacionalesrelacionados con ellos por enlaces satelitales o de microondas! El est#dio acontin#acin' enva estos canales de televisin y radiodif#sin sonora a las#bicaciones de los abonados "#e hayan comprado estos servicios! /adistrib#cin de la seal es por lo %eneral a lo lar%o de #n tronco central a la"#e las lneas de alimentacin estn conectadas a #bicaciones de abonado!Esto es similar a #n s#ministro de a%#a m#nicipal # otro sistema dedistrib#cin de servicios!

En al%#nos sistemas el s#ministro se ha%a para las com#nicaciones de losabonados al est#dio de las solicit#des de servicio o solicit#des de informacin ode sondeo de abonado o la interaccin con los pro%ramas de cable! Esto es #na

ventaQa del sistema de cable conectado directa! Otra ventaQa es la operacin debaQa potencia en #n entorno libre de r#idos! Adems' el sistema de cable por lo%eneral p#ede ofrecer m#chos canales de informacin' todo al mismo tiempo!Estos podran incl#ir pelc#las de estreno' informes del mercado de valores' elclima G informes de noticias sobre #na base de : horas' eventos deportivos'etc! Cable en `ltima instancia podra ofrecer acceso a redes privadas deinformtica e informacin' piscinas de Q#e%os electrnicos' prevencin de roboo servicios de com#nicaciones de se%#ridad y pa"#etes ed#cativos de casascompletas!

&istri$ucin #igital #e TV

Comentario9 Procesamiento di%ital de seales de televisin ofrece la ventaQa dela transmisin e*ciente y libre de r#ido! /as seales de vdeo deben serm#estreados al doble de la frec#encia ms alta y se convierten en cdi%osdi%itales!

Todos los sistemas "#e se han disc#tido en este capt#lo han sidohistricamente los sistemas de seales anal%icas! Sistemas de televisin en elf#t#ro p#eden incl#ir tcnicas ms di%itales del circ#ito debido a la tendenciahacia sistemas di%itales para sistemas de com#nicaciones telefnicas y va


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satlite! &ientras "#e los receptores de televisin en casa p#eden permaneceranal%ico en el f#t#ro previsible' la distrib#cin de material de pro%ramas def#entes nacionales a las estaciones locales p#ede re"#erir e"#ipo di%ital! Comose ha disc#tido y se ampliar a`n ms' la transmisin di%ital de seales conofrece las posibilidades de com#nicacin ms e*ciente y libre de r#idos de lainformacin!

Bsicamente' para convertir #na ima%en de televisin a forma di%ital re"#iere"#e la seal de vdeo se m#estrea a dos veces s# frec#encia ms alta y cadam#estra convertida a #n PC& 6mod#lacin por imp#lsos codi*cados8e"#ivalente! Si las seales de televisin contienen frec#encias de hasta 'F&H) y la informacin de ima%en re"#iere #n cdi%o binario de 5 bits para larepresentacin precisa' entonces la seal di%ital tendra "#e ser enviado a #navelocidad de 'F &H) = : = 5 L N: me%abits G se%#ndo! Esta es la capacidaddel canal di%ital de #n canal de T sistema telefnico! Tcnicas de compresinde seales di%itales p#eden #tili)arse para enviar #na seal de televisin enapro=imadamente la mitad de esta velocidad de bits "#e allo4 dos canales de

televisin "#e se enviar en #na lnea T!/os ms canales de televisin "#e se p#eden enviar en #n canal telefnico ova satlite determinado' los menos caros los costos transporte de la red! Sila televisin se #tili)a para prod#cir relativamente im%enes *Qas como %r*coso im%enes Pict#rePhone' los re"#isitos de ancho de banda p#eden red#cirse amenos de 5 &H) para #na tasa de bits de 5 &H) = : = M bits L 5F me%abits Gse%#ndo! Esto es sin tcnicas de compresin de datos! Tcnicas tales como lae=ploracin lenta y compresin di%ital podra permitir este tipo de im%enes"#e se enven con slo F$ bits G se%#ndo! Estas transmisiones seran bastanteeconmico' ya "#e p#eden ser maneQados por #n canal de vo) di%ital `nica! Sinembar%o' tendra "#e ser #na ima%en m#y "#ieto' y podra tomar varios

se%#ndos para "#e la ima%en completa a transmitirse y form en #narecepcin t#bo de ima%en! Apenas c#l de estas opciones se enc#entran losmercados comerciales s#*cientes a`n est por verse!

Comentario9 El envo de la mayor cantidad de canales de televisin como seaposible a travs de #na cone=in telefnica o por satlite determinado red#celos costos de distrib#cin!

9u= ,emos apren#i#o;

\ /as cmaras de televisin convertir #na ima%en ptica en #na serie deseales elctricas mediante la e=ploracin de la ima%en de #na lnea a la ve)

con #n ha) de electrones y la conversin de cada p#nto de la ima%en en #naamplit#d de tensin elctrica!

\ t#bos de ima%en de televisin se reprod#cen las im%enes de sealeselectrnicas mediante el #so de las seales para variar la intensidad de #n ha)electrnico de barrido "#e a s# ve) vara la intensidad de la l#) prod#cida por#n fsforo en la cara del t#bo de electrones!


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\ /a e=ploracin hori)ontal y vertical de #na ima%en forma la trama del t#bo deima%en!

\ Cada ima%en consiste en #n marco de D:D lneas' con :F:'D

Radio and Television Systems

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