Industrial Training Report - Pritesh Gupta

8/13/2019 Industrial Training Report - Pritesh Gupta

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Submitted ToDr. S. J. Basha

H.O.D.

Dept. of ECE

Industrial Training Report

On

FM Transmission and Broadcasting

SUBMI TTED TO

RAJ I V GANDHI PROUDYOGI KI VI SHWAVI DYALAYA,

BHOPALI N PARTI AL FULFI LMENT OF THE DEGREE OF BACHELOR

OF ENGI NEERI NGI N

ELECTRONI CS AND COMMUNI CATI ON ENGI NEERI NG

2013- 14

Department of Electronics and Communication

Engineering

June 2013

Submitted by

Pritesh Gupta

0820EC101071BE Final year, ECE

LNCT Indore


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Depart ment o f E l ec t ron i cs and Communi cat i on Eng i neer i ng CERTIFICATE

Thi s i s t o ce r t i f y t ha t t he p r o j ec t wor k ca r r i ed ou t and

r ecor ded i n t h i s I ndus t r i a l T r a i n i ng Repor t en t i t l ed FM

Tr ans mi s s i on and Br oadcas t i ng s ubmi t t ed i n pa r t i a l

f u l f i l l men t o f t he r equ i r emen t o f t he awar d o f t he degr ee o fBACHELOR OF ENGI NEERI NG i n E l ec t r on i cs &

Communi ca t i on a t t he Laks hmi Nar a i n Co l l ege o f

Techno l ogy , I ndor e a f f i l i a t ed t o t he Ra j i v Gandh iPr oudyog i k i V i s hwav i dya l aya , Bhopa l i s a f a i t h f u l r eco r d o f

bon a f i de p ro je c t wor k ca r r i ed ou t by PR ITESH GUP TA

( 0820EC101071) . Hence t h i s P r o j ec t Repor t i s he r e byappr oved f o r t he awar d o f t he degr ee o f Bache l o r o f

Eng i nee r i ng t o h i m .

( .. . ) ( . ..)

I n t e r na l Exami ner Ex t e r na l

Exami ner


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Depart ment o f E l ec t ron i cs and Communi cat i on Eng i neer i ng

ACKNOW LEDGEMENT

I t i s my p l eas u r e t o be i ndeb t ed t o va r i ous peop l e , who d i r ec t l y

and i nd i r ec t l y con t r i bu t ed i n t he deve l opment o f t h i s wor k and

who i n f l uenced my t h i nk i ng . I acknowl edge Manag i ng Di r ec t o rMr. Suprabhat Choks ey and Pr i nc i pa l Mr . D . Mi t r a f o r

p rov id ing th e g r ea t in f r a s t ru c tu r e o f th e co l l eg e and un i que

academi c env i r onment .I am a l s o t hankf u l and acknowl edge my g r a t i t ude t o ou r H .O .D.

Mr. S . J . Bas ha a nd f acu l t i e s f o r t he i r gu i dance and s upe r v i s i on .

The i r cons t an t s our ce o f i n s p i r a t i on and encour agement enab l ed

me t o compl e t e my d i s se r t a t i on wor k . I w i s h t o thank andacknowl edge my g r a t i t ude t o f o r h i s pe r mi s s i on and p r ov i d i ng

a l l f ac i l i t i e s f o r ca r r y i ng ou t t he t r a i n i ng .

I a l s o t hankf u l t o a l l s t a f f member s o f AI R I ndor e , Mr . R .K .Agr awal and Mr . S . Kadam t og i ve me an oppor t un i t y t o under go

voca t i ona l t r a i n i ng a t AI R I ndor e .

P r i t e s h Gup t a0820EC101071


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TABLE OF CONTENTS

Chapter Contents Page No.

I Introduction to all India Radio 1 1.1 History 1

1.2 Studio and labs intro 2

1.3 Services 2

II Description about the Industrial 3

Training 2.1 Objectives 3

2.2 Studio Centre 3

2.3 Studio Acoustic 6

2.4Acoustic Treatment 6

III Methodology Adopted 10 3.1 Optical Fiber Communication 10

3.2 Satellite Communication 12

3.3 Earthing arrangement in Broadcast station 17

IV Materials and Methods 20

20 4.1 AM Transmitters 20 4.2 FM Transmitters 23

4.3 Microphones 31

V Advantages and disadvantages 42

VI Summary and Conclusion 43

Scope of Future Work 44

References 45


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FM TRANSMISSION AND RECEPTION

Electronics and Communication Department, LNCT Indore I

List of Tables

S. No.

Description Page

1 Table 1 Satellite frequency bands allocation 13


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Electronics and Communication Department, LNCT Indore II

List of figures

S. No. Description Page

1 Fig. 2.1 Mixing and Switching board 4

2 Fig. 2.2 Master Control Room 5

3 Fig. 3.1 Optical Fiber Structure 9

4 Fig.3.2 Types Of Optical Fibers 10

5 Fig.3.3 Satellite Communication 11

6 Fig.3.4 - Flow of current through human body in a proper

earthing

15

7 Fig. 4.1 AM Transmitter 18

8 Fig. 4.2 Commercial 35 kW FM radio transmitter 19

9 Fig. 4.3 Schematic of AIR RAU center transmitter 20

10 Fig. 4.4 Frequency Modulation 21

11 Fig. 4.5 FM stereo frequency bands 22

12 Fig. 4.6 BW of FM signal 23

13 Fig. 4.7 FM transmitter 25

14 Fig. 4.8 FM Receiver 25

15 Fig. 4.9 Electro Microphone 27

16 Fig. 4.10 Ribbon Microphone 28

17 Fig. 4.11 Condenser Microphone 28

18 Fig. 4.12 Electret microphone 29

19 Fig. 4.13 Gun Microphone 29

20 Fig. 4.14 Lapel Microphone 30

21 Fig. 4.15 Contact Microphone 31

22 Fig. 4.16 Boundary Microphone 31

23 Fig. 4.17 Laser Microphone 32

24 Fig. 4.18 Wireless Microphone 33


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Electronics and Communication Department, LNCT Indore III

List of symbols used

Symbols Full form

Average absorption coefficient


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Electronics and Communication Department, LNCT Indore VI

List of Units used

Units Full form

Ohms

m Micrometers


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FM TRANSMISSION AND BROADCASTING

Electronics and Communication Department, LNCT Indore 1

CHAPTER 1

INTRODUCTION


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1.1 Introduction to All India Radio 1.1.1 History of AIR:All India Radio (AIR) , of f icial ly known s ince 1956as Akashvani i s the radio broadcas ter of India and a divis ion

of Prasar Bharat i . Es tabl ished in 1930, i t i s the s is ter service of

Prasar Bharat i ' s Doordarshan, the nat ional televis ion broadcas ter .Al l India Radio is one of the larges t radio networks in th e wor ld. I t s

headquar ters i s at the Akashvani Bhavan in New Delhi . AkashvaniBhavan houses the Drama Sect ion, the FM Sect ion and the Nat ional

Service. Doordarshan Kendra (Delhi ) of f ices are also located on thes ixth f loor at Akashvani Bhavan.

In Bri t i sh India, broadcas t ing began in July 1923 wi th programmes

by the Radio Club of Bombay and other radio clubs . According toan agreement of July 23, 1927, the pr ivate Indian Broadcas t ingCompany LTD (IBC) was author ized to operate two radio s tat ions ;

the Bombay s tat ion began on 23 July 1927, and the Calcut ta s tat ionfol lowed on 26 August 1927. On 1 March 1930, however , the

company went into l iquidat ion. The government took over thebroadcast ing faci l i t ies , beginning the Indian Sta te Broadcas t ing

Service ( ISBS) on 1 Apr i l 1930 (on an exper imental bas is for two

years , and permanent ly in May 1932) . On June 8, 1936; the ISBS

was renamed Al l India Radio.On 1 October 1939 the External Service began wi th a broadcas t

in Pushtu; i t was intended to counter radio p ropaganda f romGermany di rected to Afghanis tan, I ran and the Arab nat ions . WhenIndia became independent in 1947 the AIR network had only s ixs tat ions ( in Delhi , Bombay, Calcut ta , Madras , Lucknow, and

Tiruchi) ; the total number of radio sets at that t ime was about

275,000. On 3 October 1957 the Vividh Bharat i Service was

launched, to compete wi th Radio Ceylon. Televis ion broadcas t ingbegan in Delhi in 1959 as part of AIR, but was sp l i t off from the

radio network as Doordarshan on 1 Apr i l 1976. FM broadcas t ingbegan on 23 July 1977 in Madras , and was expanded during the

1990s .

The word "Akashvani" was coined by M. V. Gopalaswamy af terset t ing up the nat ions f i rs t pr ivate radio s tat ion in his res idence,Vi t talVihar (about 200 yards f rom AIRs current locat ion

in Mysore) in 1936. [ 5 ] Akashvani means "celes t ial announcement";

the word, of Sanskr i t or igin, i s of ten found in Hindu mythology.

When the gods wished to say something, an akashvani occurred.

Li teral ly, akash means "sky" and vani means "sound" or

message".[ 6 ] Thus, Akashvani seemed to be f i t for use by a radio

broadcaster and was later adopted as Al l India Radio 's on-ai r name

af ter independence.


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1.1.2 STUDIO & LABS INTRO: A studio is an acoust ical ly t reated compact anechoic room. I t i s

sui tably furnished and equipped wi th f lood l ight for proper l ightef fected.

A large number of microphones are used at di f ferent locat ions to

p ick up sound associated wi th program so tha t the program canbe recorded in excel len t format wi th zero d isturbances .

The microphone outputs are fed into the control room by coaxial

cables . The control room has several moni tors to view picture

p icked up by d i f ferent cameras. A moni tor i s a TV receiver thatcontains no provis ions for receiving broadcas t s ignals but

operates on a di rect input of unpopulated s ignal . A large number

of such moni tors are used to keep a check on ht contes t and

qual i ty of pictures being telecas t . In addi t ion to l ive s tudio. Video tape recording and telecomsmachine rooms are located close to the control room. In mostcases , program as enacted in the s tudio are recorded on video

tape recorder (VTR) through the control . These are later

broadcas t wi th VTR output passing through the same controlroom. Al l these rooms are interconnected by co-axial cables and

shielding wires .

1.3 SERVICES:AIR has many di f ferent services each cater ing to di f ferent

regions / languages across India. One of the most famous services ofthe AIR is the Vividh Bharat i Seva ( roughly t rans lat ing to "Mul t i -

Indian service") . Vividh Bharat i celebrated i t s Golden Jubi lee on 3

October 2007. Vividh Bharat i has the only comprehensive databaseof songs f rom the so termed "Golden Era" of Hindi f i lm music

( roughly f rom 1940s to 1980s) . This service i s the most commercialof al l and is popular in Mumbai and other ci t ies of India. Thisservice offers a wide range of programmes including news, f i lm

music, comedy shows, etc . The Vividh Bhar t i service operates on

dif ferent MW band f requencies for each ci ty as shown below. Some

programs broadcas t on the Vividh Bhart i :

Hawa-mahal - Ski t (Radio Play) based on some novels /plays . Santogen ki mehf i l - Jokes &humour


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CHAPTER 2

DESCRIPTION ABOUT THE

INDUSTRIAL TRAINING


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2.1 Objectives: To or iginate program from s tudios ei ther for l ive telecas t or for

recording on a video tape. To kni t var ious other sources of programs avai lable at the

production desk - camera output f rom s tudios, feed f rom otherKendra, outdoor , playback f rom pre recorded tape, video

graphics and characters generator etc .

Process ing/dis t r ibut ion of di f ferent sources to var ious

des t inat ions in technical areas .

Rout ing of mixed program for recording/ t ransmiss ion via master

swi tching room and Microwave to the t ransmit ter or any otherdes i red des t inat ions .

2.2 Studio Centre:Activi t ies in a recording s tudio can be divided into three majorareas such as :1. Studio f loor / Act ion area,

2. Product ion control room, and

3. Master control room/Central apparatus room,

4. Other faci l i t ies

2.2.1 Studio floor/ Action area:The s tudio f loor i s the ac tual s tage on which the ac t ions that wi l l berecorded take p lace . A s tudio f loor has the fo l lowing character i s t icsand ins ta l la t ions decora t ion:

Microphones

Light ing r igs and the associated control l ing equipment A smal l publ ic address sys tem for communicat ion

A f loor manager , who has overal l charge of the s tudio area s tage

management , and who relays t iming and other informat ion f romthe televis ion di rector .

2.2.2 Production control room:The studio control room (SCR) or product ion control room i s thep lace in studio in which the composi t ion of the outgoing program

takes place. The product ion control room is occas ional ly also cal led

a s tudio control room (SCR) or a "gal lery". Master control i s thetechnical hub of a broadcas t operat ion common among most over-

the-ai r FM/AM stat ions and FM/AM networks . Master control i s

dis t inct f rom a PCR in s tudios where the act ivi t ies such asswi tching f rom microphone to microphone are coordinated. A

transmiss ion control room (TCR) is usual ly smal ler in s ize and is a

scaled down vers ion of central cas t ing.Faci l i t ies in a PCR include: A mixer , a large control panel used to select the mul t iple-

microphone setup and other var ious sources to be recorded onair .


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Audio mixing console and other audio equipment such as ef fects

devices are used to mix the generated program voice at real t ime. Some s torage media to s tore the composed program temporar i ly. Control uni ts or remote control panels for the control of the

inner and outer environment of s tudio.

Fig. 2.1 Mixing and Switching board

2.2.3 Master control room :The master control room houses equipment that i s too noisy. I t a lso

makes sure that wire lengths and ins tal lat ion requirements are

wi thin manageable lengths .This can include:

Transmiss ion Control Room

Network Operat ions Center

I t also makes sure that coax cable and other wire lengths andins tal lat ion requirements keep wi thin manageable lengths , s ince

most high-qual i ty wir ing runs only between devices in this room.This can include the actual ci rcui t ry and connect ions between

Audio servers

Mixer (Audio Switcher) pa tch panels


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Fig. 2.2 Master Control Room

2.2.4 Other facil ities:A televis ion s tudio usual ly has other rooms wi th no technical

requirements beyond broadcas t reference moni tors and s tudio

moni tors for audio. Among them are:

One or more acoust ic rooms. A recept ion area for crew, talent , and vis i tors .

2.3 Studio Acoustic2.3.1 Introduction A broadcas t ing s tudio i s a room in s tudio complex which has been

special ly des igned and const ructed to serve the purpose ofor iginat ing broadcas t ing programs. Whenever any musician s ings

and we s i t in f ront of a performing musician to l i s ten to him, we

enjoy the program by vi r tue of the superb qual i t ies of our sensory

organs namely ears . However , when we l i s ten to the same programover the broadcas t chain at our home though domest ic receivers , the

condi t ions are ent i rely di f ferent . We as broadcas ters arecont inuously engaged in the task of ensur ing the maximum pleasure

for the l i s tener at home when the ar t i s ts are performing ins ide the

s tudios . In order to achieve our goal we must thoroughly unders tandthe character is t ic of the di f ferent components involved in the

broadcas t chain , and in this process we must preserve the orig inal

qual i ty of sound produced by the ar t i s ts ins ide the s tudio. The

science of sound is of ten cal led Acoust ics . I t would be thus

prudent to unders tand the f ield of acoust ics as applied to

broadcas t ing .


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2.4 Acoustic TreatmentGood acoust ics i s a pre- requis i te of high qual i ty broadcas t ing or

recording. Acoust ic t reatment i s provided in s tudios , control rooms,and other technical areas in order to achieve the acoust ic condi t ions

which have been found f rom exper ience to be sui table for the

var ious types of programs. In this sect ion problems and des ignaspects of internal acoust ics of a broadcas t s tudio are explained.

2.4.1 Propagation of Sound Waves Sound waves emanat ing f rom a sound source are propagated in al ldi rect ions . These sound waves are subject to ref lect ion, absorpt ion

and ref ract ion on encounter ing an obs tacle. Extent to which each ofthese phenomenon takes place depends upon the s t ructure and shape

of the obs tacle, and also on the f requency of sound waves . In close

rooms, the sound would be ref lected and re- ref lected t i l l theintens i ty weakens and i t dies down.Physical character is t ics of sound waves are thus modif ied in var ious

ways before they reach the human ear . These ref lected waves can

create echo ef fect in the room. To achieve the des i rable ef fects ofthe ref lected sound, the dimensions and shape of the room are

decided wi th due care and acoust ic t reatments are also provided on

the var ious surfaces .

2.4.2 Reverberation Time(R/T) In any enclosed room when a sound is swi tched off , i t takes a f ini telength of t ime to decay to inaudibi l i ty. The hanging-on of the

sound in a room af ter the exci t ing s ignal has been removed, i scal led reverberat ion and the t ime taken for the sound to decay toone mil l ionth of i t s ini t ial value, i .e . 60 dB, af ter the source hass topped, i s termed Reverberat ion Time(R/T) .

2.4.3 Factor Covering Reverberation TimeR/T of a room depends upon shape and s ize of room and on the total

absorpt ion offered on boundary surfaces . For a room of given

volume and surface area, the R/T can be der ived by Eyr ingsformula

Where,R/T = Reverberat ion t ime in seconds

V = Volume in cubic f t .

S = Total surface area of room in Sq. f t . = Average absorpt ion coeff icient

Average absorpt ion coeff icient ( ) i s given by


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Where,

S 1 , S 2 Snare the areas ( in sq. f t . ) of di f ferent mater ials provided,

and 1 , 2 n are the absorpt ion coeff icients of these mater ials . o f

acoust ic mater ial i s def ined as the rat io of absorbed sound to thetotal incident energy of sound. An open window absorbs /al lows to

pass al l of the sound energy s t r iking i t and reflects none. Thus i t

has o f uni ty. o f pract ical ly al l acoust ic mater ials vary wi thfrequency.

2.4.4 Effects of Reverberation on Program: Reverberat ion is the most impor tant s ingle parameter of a room. I t

inf luences the audio programs in fol lowing ways: - Volume of program increases due to reverbera t ion of sound. This i s

a desi rable fea ture , however , too much of reverbera t ion may impai rthe qual i ty of proram and, therefore , should be cont ro l led .

Reverbera t ion resul t s in pro longat ion of sound ins ide the room.This leads to blending of one sound wi th the next and produces avery p leasant cont inui ty in the f low of music . Too much of

pro longat ion, however , may create loss in in te l l ig ib i l i ty o f programdue to decrease in c lar i ty .

Reverbera t ion t ime of a room is dependent on frequency.Therefore , i t modif ies the frequency character i s t ics of the to ta l

sound f ie ld ins ide the room. High R/T a t mid and h igh frequenciesleads to increased l iveness and that a t low frequencies increases

warmth . This effec t can be used judic iously for desi rablequal i t ies .

2.4.5 Acoustic absorbers: Acoust ic absorbers are provided on the inner surfaces of the room toachieve opt imum R/T character i s t ics . Different absorbers have

di fferent absorpt ion character i s t ics . No s ingle absorber genera l lyprov ides uni form absorpt ion over the complete f requency spectrum.

Some of the commonly used absorbers are :i ) Porous Mater ia ls : Minera l wool , g lass wool , e tc . a re members of

th is c lass . These mater ia ls are very good absorber and are mosteffec t ive in mid and h igh frequencies , however , these cannot be used

wi thout some facing mater ia l . Carpets and curta ins a lso fa l l in th iscategory .

i i ) F ibrous Mater ia ls : Celo tak , insula t ion boards , perfo t i les , jo l ly-lowtone t i les e tc . fa l l in th is ca tegory . Absorpt ion of these mater ia ls

depends upon thei r sof tness . Absorpt ion eff ic iency of these mater ia lsdepends upon the t rapping and d iss ipat ion of sound energy in t inypores . Absorpt ion gets reduced if the su rface pores are f i l led with

pa in ts e tc. These mater ia l s have very poor absorpt ion on lowfrequencies . However appreciable improvement a t these frequencies i s

poss ib le by provid ing a i r-gap behind.i i i ) Panel Absorbers : Panel absorbers are th in sheets /membranes wi th

an a i r cavi ty behind.The mass of the panel and the spr inginess of theai r in the cavi ty resonant a t some part icu lar f requency. Panelabsorbers wi th 3mm teak p ly-fac ing + 50mm ai r gap + 25mm minera l


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wool resonate a t about 125Hz. This i s genera l ly used as low frequencyabsorber (LFA).

iv) Perfora ted Panel Absorbers : Perfora ted hardboard (PHB) spaced

from the wal l const i tu te a resonant type of sound absorber . Theabsorpt ion can be considerably enhanced by inser t ing asui tableporous / f ibrous damping mater ial in the a ir cavi ty . The absorp t ionpa t tern can be var ied by adjust ing the f ront and rear a ir gap from the

damping mater ia l . Absorpt ion coeff ic ient of th is absorber depends onthe percentage open area of PHBs a lso .

2.4.6 Design of Room Acoustic: Design for correct reverbera t ion t ime consis t s of es t imat ing the to ta l

absorpt ion which must be present in the s tudio . This i s ca lcula ted by

Eyrings Formula , some of the absorpt ion i s offered by windows,

doors , f looring and ar t i s t s ins ide the s tudio . For the balance

requi rement sound absorbing mater ia ls are provided on wal ls andcei l ing surfaces . Calcula t ions are genera l ly made a t s ix spotfrequencies of 125, 250, 500, 1000, 2000 and 4000 Hz. Quant i t ies of

mater ia ls of known absorpt ion coeff ic ients are se lec ted by t r ia l anderror method so that R/T requi rements are met wi th in +5% of the

opt imum R/T a t a l l these frequencies . Computer a ided design for thesame has a lso been evolved. Thereaf ter these acoust ic mater ia ls aredis t r ibuted on var ious surfaces for proper d i ffusion of sound in thestudio .


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CHAPTER 3

METHODOLOGY ADOPTED


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3.1 Optical Fiber Communication:Fiber opt ics i s being used to t ransmit televis ion, voice, and digi tal

data s ignals by l ight waves over f lexible hai r l ike threads of glassand plas t ic . I t has evolved into a sys tem of great impor tance and uses ince the

1980s .

The advantages of f iber opt ics compared to coaxial cable or twis ted

pai r cable, are endless. Mil l ions of dol lars a re being spent to putl ight wave communicat ion sys tems into operat ion, as a resul t of i t sper formance.

3.1.1 Definition:Optical Fiber Communicat ion System conver ts elect r ical s ignal into

l ight s ignal wi tch af ter pass ing through opt ical f iber cable i s

reconver ted into elect r ical s ignal by us ing opt ical Receive r3.1.2 Composition of optical fiber: Si l ica based glass or plas t ic f i laments are spun and packed into

bundles of severa l hundreds or thousands . Bundles may be put

together as rods or r ibbons and sheets .

These bundles are f lexible and can be twis ted and contor ted to

conduct l ight and images around corners

The thin glass center of the f iber where the l ight t ravels i s cal led

the Core.

The outer opt ical mater ial surrounding the core that ref lects thel ight back into the core i s cal led the cladding.

In order to protect the opt ical surface f rom mois ture and damage,i t i s coated wi th a layer of bu ffer coat ing.

Fig. 3.1 Optical Fiber Structure


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3.3.3 Operation in optical fiber system: In a f iber opt ic sys tem, there are a few major components to

per form the task of communicat ion . The Input Modulator i s needed; this modulates the incomingsignal wi th a l ight beam.

A l ight emit t ing device i s used; i t can be ei ther a l ight emit t ingdiode (LED) or a semiconductor laser diode.

A f iber opt ic cable i s used as a t ranspor tat ion medium.

A f iber opt ic sys tem conver ts an elect r ical s ignal to an inf raredl ight s ignal , and then t ransmits the s ignal onto an opt ical f iber .

An Output Modulator i s used to separate the s ignal f rom the l ight

beam.

3.3.4 Types of optical fiber:

1. Step index:This cable has index of ref ract ion for the core and the cladding. I t

causes deformat ions due to the var ious paths lengths of the l ightray. This i s cal led modal dis tor t ion. I t i s the cheapes t type of

cabl ing. Within the cladding and the core, the ref ract ive has a

speci f ic index is cons tant .2. Graded index:

In graded index f iber , rays of l ight fol low s inusoidal paths .

Al though the paths are di f ferent lengths , they al l reach the end ofthe f iber at the same t ime. Mul t imode dispers ion is el iminated and

pul se spreading is reduced. Graded Index f iber can hold the same

amount of energy as mul t imode f iber . The disadvantage is that thistakes place at on one wavelength.

Fig.3.2 Types Of Optical Fibers


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3.2 Satellite communication

3.2.1 Introduction:A satel l i te i s a radiofrequency repeater . New-generat ion satel l i tes

are regenerat ive; that i s , they have on board process ing capabi l i tymaking them more of an intel l igent uni t than a mere repeater . This

capabi l i ty enables the satel l i te to condi t ion, ampl i fy, or reformat

received upl ink data and route the data to speci f ied locat ions , or

actual ly regenerate data on board the spacecraf t as opposed tos imply act ing as a relay s tat ion between two or more ground

stat ions . I t was par t of the payload on the Space Shut t le Discovery

launched on September 12, 1993. According to NASA, i t s satel l i teweighs 3250 lb. (1477.3 kg) and measures 47.1 f t . (14.36 m) f rom

tip to t ip of the solar ar rays and 29.9 f t . (9.11 m) across the mainreceiving and t ransmit t ing antenna ref lectors , wi th a height of 15.2f t . (4.63 m) f rom the spacecraf t separat ion plane to the t ip of the

highes t antenna. The solar ar rays provide approximately 1.4

ki lowat ts . The main communicat ion antennas are a 7.2-f t (2.19-m)

receiving antenna and a 10.8-f t (3.29-m) t ransmit t ing antenna.

Fig.3.3 Satel l i te Communicat ion

In most sys tem appl icat ions , one satel l i te serves many ear th

s tat ions . With the ass is tance of ear th s tat ions , f ixed ort ranspor table, satel l i tes a reopening a new era for global satel l i te

mul t i -access channels data t ransmiss ion and broadcas t of major

news events , l ive, f rom anywhere in the wor ld. Commercial and


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operat ional needs dictate the des ign and complexi ty of satel l i te The

most common expected satel l i te at t r ibutes include the fol lowing:

Improved coverage areas and qual i ty services , and f requencyreusabi l i ty.

Compat ibi l i ty of satel l i te sys tem with other sys tems and

expandabi l i ty of current sys tem that enhances future operat ions .

High-gain, mul t iple hopping beam antenna sys tems that permit

smal ler -aper ture ear th s tat ions .

Increased capaci ty requirements that al low several G=seccommunicat ion between users .

Compet i t ive pr icing.

3.2.2 Types of Satell ites:Here are, in general , four types o f satel l i te:

Geostat ionary satel l i te (GEO) High el l ipt ical orbi t ing satel l i te (HEO)

Middle-ear th orbi t ing satel l i te (MEO)

Low-ear th-orbi t ing satel l i te (LEO)

1. Geostat ionary satel l i te (GEO): GEO stands for Geostat ionary Ear th Orbi t . This refers to satel l i testhat are placed in orbi t such that th ey remain s tat ionary relat ive to a

f ixed spot on ear th. I f a satel l i te i s placed at 35,900 km above the

ear th, i t s angular veloci ty i s equal to that of the ear th, therebycausing i t to appear to be over the same point on ear th. This al lows

for them to provide constant coverage of the area and el iminate

b lackout per iods of ordinary orbi t ing sa tel l i tes , which is good forprovid ing television broadcast ing. However the i r h igh al t i tude

causes a long delay, so two ways communicat ions , which would

need to be uploaded and then downloaded over a dis tance of 72,000km, are not of ten used wi th th is type of orbi t .

2 . High el l ipt ical orbit ing satel l i te (HEO):

An HEO satel l i te i s a special ized orbi t in which a satel l i tecont inuously swings very close to the ear th, loops out into space,

and then repeats i t s swing by the ear th. I t i s an el l ipt ical orbi t

approximately 18,000 to 35,000 km above the ear ths surface, not

necessar i ly above the equator . HEOs are des igned to give bet ter

coverage to countr ies wi th higher nor thern or southern lat i tudes .Systems can be des igned so that the apogee is ar ranged to provide

cont inuous coverage in a par t icular area. By def ini t ion, an apogee isthe highes t al t i tude point of the orbi t , that i s , the point in the orbi t

where the satel l i te i s far thes t f rom the ear th.

3. Middle-earth orbit ing satel l i te (MEO)

An MEO is a ci rcular orbi t , orbi t ing approximately 8,000 to 18,000

km above the ear ths surface, again not necessar i ly above theequator . An MEO satel l i te i s a compromise between the lower orbi ts


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and the geosynchronous orbi ts . MEO sys tem des ign involves more

delays and higher power levels than satel l i tes in the lower orbi ts .

However , i t requires fewer satel l i tes to achieve the same coverage.

4. Low-earth-orbit ing satel l i te (LEO)

LEO satel l i tes orbi t the ear th in gr ids that s t retch approximately160 to 1,600 km above the ear ths surface. These satel l i tes are

smal l , are easy to launch, and lend themselves to mass product ion

techniques . A network of LEO satel l i tes typical ly has the capaci tyto carry vas t amounts of facs imi le, elect ronic mai l , batch f i le , and

broadcast da ta a t great speed and communicate to end users through

terres t r ial l inks on ground-based s tat ions . With advances in

technology, i t wi l l not be long unt i l ut i l i ty companies are access ing

res ident ial meter readings through an LEO sys tem or t ranspor tagencies and pol ice are access ing vehicle plates , moni tor ing t raf f ic

f low, and measur ing t ruck weights through an LEO sys tem.

Communication Satell ite Frequency Bands Allocation

Band

Frequency range

(GHz) Services

VHF 0.03-0.3 Messaging

UHF 0.3-1.0 Mil i tary, navigat ionmobi le

Mobi le, audio

broadcastradiolocat ion

L 12 Mobi le navigat ion

S 24 Fixed

C 48 Mil i tary

X 812 Mil i tary

Ku 812 Fixed video broadcas t

K 1218 Fixed

Ka 1827 Fixed, audio broadcas t ,

mm waves >40 Inter Satel l i te

Table 1 Satel l i te f requency bands al locat ion

Receiving and t ransmit t ing device:

LNA (Low Noise Ampli f ier ) or LNB (Low Noise B lock)

LNA - ampl i f ies RF s ignal f rom the antenna and feeds i t intofrequency conver ter ( typical ly IF of 70/140 MHz)

LNB - ampl i f ies RF s ignal f rom the antenna and conver ts i t to an

L-band s ignal (950-2100 MHz)


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LNA is more precise and s table but more expensive than LNB (LO

stabi l i ty) .

Transmit power ampl i f iers provide ampl i f icat ion of s ignals to bet ransmit ted to the satel l i te

Transceiver takes 70/140 MHz s ignal and ampl i f ies i t to ei ther C

or Ku-band f inal f requency.

Block Up-Conver ter takes L-band s ignal and ampl i f ies i t to

ei ther C or Ku-band f inal f requency.

3.3 Earthing arrangement in broadcast station

3.3.1 Definition:

An Electrical connection to the general mass of earth to providesafe passage to fault current to enable to operate protect ive

devices and provide safety to personnel .

Or

The term Earthing means connecting the neutral point of a

supply system or Non-current carrying parts of electrical

apparatus to the general mass of earth in such a manner that at

al l t imes an immediate discharge of electrical energy takes

place without danger.

3.3.2 Objective of Earthing:

To ensure that no part of equipments , other than l ive parts ,

assume dangerous potential .

To al low sufficient current to f low safely for proper

operat ion of protect ive devices.

To suppress dangerous potential gradients on the earth

surface this may cause incorrect operat ion of control &

protect ive devices and also may cause shock or injury topersonnel .

Provide s tabil i ty of voltage, prevent excessive voltage peaks

during dis turbances and protect against l ightning surges.

3.3.3 Types of Earthing:-

Neutral Earthing:

I t deals with the earthing of system neutral to ensure

system securi ty and protect ion.


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Equipment Earthing:

I t deals with earthing of non-current carrying parts of

equipment to ensure safety to personnel and protect ion against

l ightning.

3.3.4 Danger posed to human being by electric current :

The currents , and the dangers posed to the human being, are

dependent on the voltage as well as on the electrical resis tance

of the human body (the inner body resis tance plus the skin

resis tances). The cri t ical electrical voltages with which we are

involved in our professional and private l ives are normally 220

volts , and up to 440 v olts in the case of three-phase current .

The intensi ty of the inner body resis tance is cri t ical ly

dependent on the path of the current in the body. An Average

values for the inner body resis tance along various paths taken

by the current areas fol lows:

Hand hand 1200 ohms

Hand feet 900 ohms

Hands feet 600 ohms

Thus, i f the vol tage wi th which a human being comes into contact

and the res is tance of the human body are known, the intens i ty of the

current can be eas i ly calculated. Fur ther , i f the current intens i ty canbe calculated , then the degree of danger posed to the human being

can be assessed too.


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Fig.3.4 - Flow of current through human body in a proper

earthing

The elect r ical res is t ivi ty of the ear th i .e . res is tance of the ear th to

the f low of current i s def ined assoi l res is t ivi ty Ear th res is t ivi tyvar ies f rom a few ohm-meters along some sea coas ts to many

thousands of ohm-meters in rocky, mountainous country

.Theoret ical ly, the res is tance to remote ear th of an ear th elect rodecan be calculated. This calculat ion is based on the general

res is tance formula:

R = ( r x L) / A

Where:R = res is tance to remote ear th (Ohms)

r = soi l res is t ivi ty (Ohms-cm)L = length of conduct ing path (cm)

A = cross-sect ional area of path (cm)The assumpt ion in the general formula i s that the res is t ivi ty of the

soi l i s cons tant throughout the considered area, or averaged for the

local soi l . So the target of providing good ear thing sys tem is toprovide leas t resist ance path by earth elect rode of least ear th

res is tance in a leas t res is t ivi ty soi l .


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CHAPTER 4

MATERIALS AND METHODS


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4.1 Am transmitters:

There are var ious MW AM transmit ters al l over the India. The SWtransmit ters are very few and used for most ly internat ionalbroadcas t ing purpose but soon wi l l vanish . The t ransmission bands

used for are as fol lows:

4.1.1 AM transmission bands:Long wave 200-400 kHz Medium wave 531-1602 kHz Shor t -wave

3.2-26.1 MHZ

4.1.2 Sub systems of a transmitter:1. Radio f requency select ion2. Audio f requency sect ion

3. Control and ins t rumentat ion4. Cool ing and vent i lat ion5. Power supply sys tem

6. HT supply

Power ampl i f iers :

Normal ly Class C or Class D high eff icient

Ampli f iers in both MW/SW

Employs High level plate modulat ion

Water or ai r cooled

Beam power tet rodes of Ceramic/Glass tube

Direct ly heated cathode

Screen is also modulatedAudio ci rcui ts in tube TXs: I t Consis ts of

High Pass Fi l ters

Pre ampl i f iers

Pre- correctors for non l inear i ty compensat ion

AF Drivers

Modulators - Normal ly push pul l Class B

Feed back and compensat ion ci rcui tsSW transmit ters :

Major di f ferences are Output i s balanced hence balun is used

RF ampl i f iers are wide band (3 to 26 MHz)

Final s tages are tunable in shor t t ime

Uses motor control led var iable capaci tors and inductors

VVC replaces convent ional disc capaci tors

Variable osci l lator f requency

Cool ing and vent i lat ion:

High power t ransmit ters are cooled by ai r /water

Dist i l led water of low conduct ivi ty i s used for HT s tages


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Hyper vapour- t ron and condensed vapor cool ing technique

Low pressure and High pressure fans

Heat exchangers for cool ing hot water

Output impedance:

MW Transmit ters

50 ohm (RF cable)

60 ohm (Quasi co-axial )

120 ohm

Balanced 300 Ohm

Fig. 4.1 AM Transmitter

4.2 FM Transmitter

4.2.1 Introduction:The FM transmiss ion has been developing day by day wi th theevolut ion of value added services and digi tal radio broadcas t ing.

RDS and SCA sys tems are examples of i t . AIR New Delhi uses a

sol id s tate 10 kW VHF FM transmit ter manufactured by BEL

(Bharat Elect ronics Ltd.) for mono and s tereo. The value addedservices l ike radio t raf f ic (RDS) and Subsidiary communicat ions

author i ty (SCA) are now a opt ion wi th the FM transmiss ion to meetthe needs of a broad spect rum of audiences and the emergence of

new mul t imedia forms. Fol lowing is the l i s t of BEL s FM

transmit ters i ns tal lat ion in India


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Fig. 4.2 Commercial 35 kW FM radio transmitter 4.2.2 History and development in India:The f i rs t FM broadcas t ing in India was in the year 1977 at Madras .

In the mid-ninet ies , when India f i rs t exper imented wi th pr ivate FM

broadcasts , the smal l tour ist dest ina tion of Goa was the f i f th p lacein this country of one bi l l ion where pr ivate players got FM s lots .

The other four centres were the big metro ci t ies : Delhi , Kolkata,

Mumbai and Chennai . These were fol lowed by s tat ions inBangalore, Hyderabad, Jaipur and Lucknow. Times FM (now Radio

Mirchi) began operat ions in 1993 in Ahmedabad. Unt i l 1993, Al l

India Radio or AIR, a government under taking, was the only radio

broadcaster in India . The government then took the ini t iat ive topr ivat ize the radio broadcas ting sec tor . I t sold a i r t ime b locks on i t s

FM channels in Indore, Hyderabad, Mumbai , Delhi , Kolkata, Vizag

and Goa to pr ivate operators , who developed thei r own programcontent . The Times Group operated i t s brand, Times FM, t i l l June

1998. Af ter that , the government decided not to renew contracts

given to pr ivate operators . In 2000, the government announced theauct ion of 108 FM frequencies across India

Radio Ci ty Bangalore i s India 's f i r s t pr ivate FM radio s tat ion and

was s tar ted on July 3, 2001. I t launched wi th presenters such as

Rohi t Barker , Dar ius Sunawala, JonzieKurian and Suresh Venkat .


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Fig. 4.3 Schematic of AIR RAU centre transmitter

4.2.3 Broadcast band:-

Throughout the wor ld, the broadcas t band fal l s wi thin the VHF par t

of the radio spect rum. U sual ly 87.5 to 108.0 MHz is used, or some

por t ion thereof, wi th few except ions :

In the former Soviet republ ics , and some former Eas tern

Bloc countr ies , the older 6574 MHz band is also u sed. Ass ignedfrequencies are at intervals of 30 kHz. This ban d, some t imes

refer red to a s the OIRT band, i s s lowly being phased out in manycountr ies . In those countr ies the 87.510 8.0 MHz band is refer red to

as the CCIR band. In Japan, the band 7690 MHz is used.

The f requency of an FM broad cas t s tat ion (more s t r ict ly i t s ass igned

nominal centre f requency) i s usual ly an exact mul t iple of 100 kHz

(0.1 MHz) . In most of the Americas and the Car ibbean, only oddmul t iples are used ( thus adjacent s tat ions are separated by no less

than 200 kHz) . In some par ts of Europe, Greenland and Afr ica, only


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even mul t iples are used. In I taly, mul t iples of 50 kHz (0 .05 MHz)

are used. There are other unusual and obsolete s tandards in some

countr ies , including 0.001, 0.01, 0.03, 0.074, 0.5, and 0.3 MHz

4.2.4 Modulat ion Characteris t ics:

Frequency modulat ion (FM) is a form of RF modulat ion which

conveys informat ion ov er a car r ier wave by v arying i t s f requency

(contras t this wi th ampl i tude modulat ion (AM), in which theampl i tude of the carr ier i s var ied whi le i t s f requency remains

constant ) . In analog audio appl icat ions , the ins tantaneous f requency

of the carr ier i s di rect ly propor t ional to the ins tantaneous value ofthe input s ignal . This form of modulat ion is commonly used in the

FM broadcas t band.

4.2.5 Frequency Modulation: The type of modulat ion in which the ins tantaneous f requency of the

carr ier i s var ied according to ampl i tude of modulat ing s ignal i s

cal led frequency modulat ion. Frequency modulat ion is widely usedin VHF communicat ion sys tems e.g. FM broadcas t ing, t ransmiss ion

of sound s ignal in TV, Satel l i te Communicat ion etc.

Fig. 4.4 Frequency Modulat ion

4.2.6 Pre-emphasis and de-emphasis:

Random noise has a t r iangular spect ral dis t r ibut ion in an FMsystem, wi th the ef fect that noise occurs predominant ly at the

highes t f requenc ies wi thin the baseband. This can be o ffset , to a


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l imi ted extent , by boost ing the high f requencies

before t ransmission and reducing them by a corresponding amount

in the receiver . Reducing the high f requencies in the receiver also

reduces the high-f requency noise. These processes of boost ing andthen reducing cer tain f requencies are known as pre-

emphasis and de-emphasis , respect ively.

The amount of pre-emphasis and de-emphasis used is def ined bythe t ime constant of a s imple RC f i l ter ci rcui t . In most of the wor ld

a 50 s t ime constant i s used. In Nor th America, 75 s i s used. This

appl ies to both mono and s tereo t ransmiss ions . For s tereo, pre-emphasis i s appl ied to the lef t and r ight channels before

mul t iplexing.

The amount of pre-emphasis that can be appl ied is l imi ted by thefact that many forms of contemporary music contain more high-

f requency energy than the musical s tyles which prevai led at the

b i r th of FM broadcas t ing . They cannot be pre-emphasized as much

because i t would cause excessive devia t ion of the FM carrier .Sys tems more modern than FM broadcas t ing tend to use ei ther

programme-dependent var iable pre-emphasis ; e .g . , dbx in

the BTSC TV sound sys tem or non e at al l .

4.2.7 FM stereo

The Halstead system was rejected due to lack of highfrequency stereo separation and reduction in the main

channel s ignal-to-noise ratio.

Fig. 4.5 FM stereo frequency bands


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I t i s impor tant that s tereo broadcas ts should be compat ible wi th

mono receivers . For this reason, the lef t (L) and r ight (R) channels

are algebraical ly encoded into sum (L+R) and di f ference (LR)

signals . A mono receiver wi l l use jus t the L+R s ignal so the l i s tenerwi l l hear both channels in the s ingle loudspeaker . A s tereo receiver

wi l l add the di f ference s ignal to the sum s ignal to recover the lef t

channel , and subtract the di f ference s ignal f rom the sum to recover

the r ight channel .

4.2.8 Bandwidth in FM:

In FM, the BW is based on the number of s igni f icant s idebands ,

which depends upon modulat ion index m f . In pract ice, the number

of s igni f icant s idebands is determined by acceptable dis tor t ion.These contain about 98% of the radiated power . By way of bes t

approximat ion, the Carsons Rule ( rule of thumb) gives a s imple

formula for bandwidth as

BW = 2(1+m f) fm

= 2( f + fm)

Guard band

fc-100 kHz fc-90 kHz fc fc+90 kHz fc+100 kHz

Fig. 4.6 BW of FM signal

For modulat ion index of 5 and maximum modulat ing f requency of

15 kHz, we have:

BW = 180 kHz

A guard band of 20 kHz (10 kHz on each s ide) i s provided toprevent adjacent channel inter ference. Thus the maximum

permissib le BW in FM broadcast ing is 200 kHz. For narrow band

FM (m f20) , then the BW becomes 2 f

i .e . 150 kHz. For example, i f f m = 100 Hz and f = 75 kHz.

750100

75000

m

ff

fmthen


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In this case the BW wil l be 150 kHz, but for f m = 15 kHz, BW wil l

be 180 kHz.

4.2.9 Noise Considerations in FM:FM offers the advantage of a much bet ter noise performance ascompared to AM, the reasons for which are analyzed here.

The main parameter of interes t at the input to the FM detector i s the

carr ier - to-noise rat io (C/N) . Since both the carr ier and the noiseare ampl i f ied equal ly by the var ious s tages of the receiver f rom

antenna input to the detector input , this gain can be ignored and the

input to the detector can be represented by the vol tage source E s ,which is the carr ier RMS vol tage. Also the thermal noise i s spread

over the IF bandwidth at the input to the output .

The (L+R) Main channel s ignal i s t ransmit ted as baseb and audio in

the range of 30 Hz to 15 kHz. The (LR) Sub-channel s ignal i s

modulated onto a 38 kHz double-s ideband suppressedcarr ier (DSBSC) s ignal occupying the baseband range of 23 to

53 kHz.

A 19 kHz pi lot tone, at exact ly hal f the 38 kHz sub-

carr ier f requency and wi th a p recise phase relat ionship to i t , asdef ined by the formula below, i s also generated. This i s t ransmit ted

at 810% of overal l modulat ion level and used by the rece iver to

regenerate the 38 kHz sub-carr ier wi th the correct phase. The f inal

mul t iplex s ignal f rom the s tereo generator contains the MainChannel (L+R), the pi lot tone, and the sub-channel (LR). This

composi te s ignal , a long wi th any other sub-carriers , modulates

the FM transmitter.

4.2.10 Distance covered by FM Stereo Transmitter:

The range of an FM mono t ransmiss ion is related to the t ransmit ter

RF power , the gain and radio antenna height . The FCC (USA)publishes curves tha t a id in ca lculat ion of th is maximum distance as

a funct ion of s ignal s t rength at the receiving locat ion.

For FM s tereo, the maximum dis tance covered is s igni f icant ly

reduced. Th is i s due to the presence of the 38 kHz subcarr iermodulat ion. Vigorous audio process ing improves the coverage area

of an FM s tereo s tat ion.

Consumer use of FM transmitters:

In some countr ies , smal l -scale t ransmit ters are avai lable that can

t ransmit a s ignal f rom a n audio device (usu al ly an MP3 play er or


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s imi lar ) to a s tandard FM radio receiver ; such devices range f romsmal l uni ts bui l t to car ry audio to a car radio wi th no audio- in

capabi l i ty (of ten former ly provided by spec ial adapters for audio

casset te decks , which are becoming less common on car radiodes igns) up to ful l -s ized, near-profess ional -grade broadcas t ing

sys tems that can be used to t ransmit audio throughout a proper ty.

Most such uni ts t ransmit in ful l s tereo; though some modelsdes igned for beginner hobbyis ts may not . Simi lar t ransmit ters are

of ten included in satel l i te radio receivers and some toys .

Fig. 4.7 FM Transmitter

Fig. 4.8 FM Receiver

4.3 MicrophoneA microphone (col loquial ly cal led a Mic or mike) i s an acoust ic to

elect r ic t ransducer or sensor that conver ts sound into an elect r icals ignal . In 1876 Emile Ber l iner invented th e f i rs t microphone used as

a telephone voice t ransmit ter . Microphones are used in many


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appl icat ions such as telephones , taperecorders , karaoke sys tems, hear ing aids , mot ion picture product ion,

l ive and rec orded audio engineer ing, F RS radios , megaphones , in

radio and televis ion broadcas t ing and in computers for record ingvoice, speech recogni t ion, VoIP, and for non-acoust ic purposes such

as ul t rasonic checking or knock sensors .

Most microphones today use elect romagnet ic induct ion (dynamicmicrophone) , capaci tance change ( condenser microphone) ,

p iezoelect r ic generat ion , or l ight modulat ion to produce an

elect r ical vol tage s ignal f rom mechanical vibrat ion.

The sens i t ive t ransducer element of a microphone is cal led i t selement or capsule. A complete microphone also includes a housing,

some means of br inging the s ignal f rom the element to

other equipment , and of ten an elect ronic ci rcui t to adapt the

output of the capsule to the equipment being dr iven. A wirelessmicrophone contains a radio t ransmit ter .

4.3.1 Five important characteris t ics of Microphone:

1. Frequency response2. Direct ivi ty3. Sensi t ivi ty4. Distor t ion 5. Placing of microphone

1. Frequency Response:

Frequency response refers to the way a microphone responds to

di f ferent f requencies . I t i s a character is t ic of al l microphones thatsome f requencies are greater and others are at tenuated ( reduced) .I t

depends upon: - Direct ion of ar r ival of sound and dis tance between

the source and the microphone.

2. Direct ivi ty:

Microphone has di rect ional character is t ics .

Omnidirect ional : -Pick up equal ly at al l angles .Bidirect ional : -Pick up equal ly f rom front and rear .

Unidirect ional : -microphone which pick up maximum rom front .

3. Sensi t ivi ty:

The abi l i ty to pick up weak sound and to del iver more elect r ical

Signal determines the sens i t ivi ty.

4. Distort ion:

The inabi l i ty to maintain l inear i ty, resul t ing in the addi t ion ofunwanted HARMONICs, m cal led Harmonic Dis tor t ion. The

inabi l i ty to pass the complete audio spect rum equal ly, cal led

Frequency Dis tor t ion. The inabi l i ty to handle TRANSIENTs, cal ledTrans ient Dis tor t ion. The inabi l i ty to pass al l s ignals in the same

amount of t ime, cal led Phase Dis tor t ion. 5. Placement of Microphone:


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a) As far as poss ible, microphone should be placed wi th i t s zeroaxis facing the source of sound to avoid off axis colorat ion.

b) Phasing of microphone:-Whenever two or more microphone is

used wi th thei r outputs mixed together , i t should be ensured thatthei r outputs are in phase.

c) Working dis tance: -microphone should be placed 30-45cm from

the source of sound so as to avoid proximity ef fect .

d)Talking very close to a microphone may cause sound l ike P .Hence i t should be avoided.

4.3.2 Microphone Classifications: 1. Acoust ical Class i f icat ion

2. Elect r ical Class i f icat ion

3. Polar pat tern-wise Class i f icat ion1. Acoust ical Class i f icat ion:Pressure-operated Microphone

They are depending on the output vol tage f rom a microphone andthe sound pressure on i t .

Sound Pressure i s appl ied on one s ide of the diaphragm.

Elect r ical output Sound Pressure.

Theoret ical ly Omni Direct ional .

Sensi t ivi ty at HF decreases . Examples : - Moving Coi l , Carbon, crys tal and Condenser

Microphones .

2. Pressure gradient (Veloci ty) Operated Microphones : Both s ides of diaphragm are exposed to the sound pressure.

Elect r ical Output i ns tantaneous di f ference in pressure on twosides of diaphragm

3. Combined-operat ion Microphones :

The pr inciple of pressure-operated microphones and pressure

gradient operated micro phones are combined to get maximum

sensi t ivi ty in one di rect ion and minimum sens i t ivi ty in theopposi te di rect ion.

Unidirect ional character is t ics

2. Electrical Class i f icat ion:

Elect ro dynamic Moving coi l Microphone A magnet i s moved near a coi l of wire an elect r ical current i s

generated.

Using this elect romagnet pr inciple, the dynamic microphone uses

a wire coi l and magnet to create the audio s ignal .

The diaphragm is at tached to the coi l .

Used in l ive performance where rough handl ing is common.

Examples- AKG D-202, D-222, D-900, D-770, D-190E, SM58,

SM57, SM48 etc.


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Fig. 4.9 Electro Microphone R ibbon Microphone:

I t uses a thin aluminum, Duraluminum or Nano f i lm r ibbonpl aced between the poles of a magnet to generate vol tages by

elect romagnet ic induct ion.

Very sens i t ive to shock and large sound volumes .

Very del icate

Very low impedance and hence uses in-bui l t t ransformer .

Bidi rec t ional

Fig. 4.10 Ribbon Microphone

Condenser Microphone:

I t i s a modif ied form of condenser microphone.

I t does not use external power supply.

Uses a special type of capaci tor which has a permanent vol tagebu i l t in dur ing manufacture.

The pr inciple of operat ion is that sound waves impinging on thediaphragm cause the capaci tance between the diaphragm and the

back plate to change, th is in turn induces vol tage variance on theback plate .

The output i s independent of the diaphragm surface area.


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Fig. 4.11 Condenser Microphone

Elect ret Microphone:

I t i s a modif ied form of condenser microphone.

I t does not use external power supply.

Uses a special type of capaci tor which has a permanent vol tagebu i l t in dur ing

manufacture.

Pre-ampl i f ier requires power supply.

The pr inciple of operat ion is that sound waves impinging on thediaphragm cause the capaci tance between the diaphragm and the

back plate to change, th is in turn induces vol tage variance on theback plate .

The output i s independent of the diaphragm surface area.

Light and smal l in s ize.

Excel lent qual i ty/pr ice rat io.

Fig. 4.12 Electret microphone Gun Microphone:

Highly unidi rect ional Long and rod shaped.

Good for recording s ingle voice in noisy locat ions .

Good for recording sound ef fect f rom a far dis tance.

Also used for picking up voice f rom long dis tance


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Fig. 4.13 Gun Microphone

Lapel Microphone:

The microphone is very smal l and l ight -weight and is suspendedaround the neck keeping the mike jus t below the chin.

Fig. 4.14 Lapel Microphone


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Contact Microphone: A contact microphone known as a picku p or a piezo, i s a form

of microphone des igned to sense audio vibrat ions through sol id

objects .

Size is smal l .

Unlike normal ai r microphones , contact mics are almost

completely insens i t ive to ai r

vibrat ions but t ransduce only s t ructure-borne sound.

Often used as acoust ic leakage probes , they also enjoy wideusage by noise music ar t i s ts exper iment ing wi th sound. Plain

contact microphones are pass ive and high- impedance and this cancause them to sound ' t inny' unless used wi th a matching preamp.

The most commonly avai lable contact microphone element i s

made of a thin piezoelect r ic ceramic round glued to a thin brassor al loy metal disc. This center disc i s pos i t ive whi le the brassdisc i s negat ive. I f this s i lver disc i s cracked or scorched, the

p iezo wi l l no longer funct ion a t fu l l sens i t ivi ty .

Attached wi th the sound source i t sel f .

Pickup vibrat ion puls ing through sol id.

Attach to a point so that i t should not come in the view ofcamera.

HF response is good but LF respon se is bad.

Fig. 4.15 Contact MicrophoneBoundary Microphone:

A smal l capsule microphone usual ly an elect ret , i s housed in af lat receptacle.

The di rect ivi ty i s hemispher ical at al l f requencies .

More dynamic range and clar i ty


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Fig. 4.17 - Laser Microphone

Wireless Microphone: These are ordinary microphones wi th an FM transmit ter .

Provides complete f reedom of movement .

Omnidirect ional .

Inter ference f rom outs ide source. Sui table for places where lying of microphone cable i s not

possib le .


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Fig. 4.18 Wireless Microphone

4.3.4 Applications of microphones:

Telephones

Tape Recorders Karaoke System

Hearing Aids


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CHAPTER 5

ADVANTAGES AND

DISADVANTAGES


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5.1 Advantages: This i s only means which can provide mul t i access two way

communicat ion. AIR is having a whole country Network and s tudio chains

The cos t of t ransmit t ing informat ion through satel l i te i s

independent of dis tance involved.

Satel l i te can be used for two way communicat ion or broadcas t

purpose wi th the covered area.

Good cul tural event programs are being broadcas t ing

Satel l i tes are capable of handl ing very high bandwidth. 0 I t i s

possib le to provide la rge coverage us ing sa tel l i te . For examplegeostat ionary satel l i te can cover about 42% of ear th surface

us ing global beam.

AIR is us ing Modern Technologies Broadcas t coverage of 90.81% area in country and s t i l l growing

al l over

Technical Exper t i se

AIR is proved to be useful in t ragic disas ters l ike ear thquakes ,

f lood etc.

5.2 Limitations: Some ins t ruments are very out dated in the centers .

Popular i ty AIR is decreas ing day by day because of modern

western cul ture songs and Bol lywood events . Though i t i s growing very fas t but i t i s not cover ing ful l country

a t a g lance .

Program drop out because of network l inking fai lures .

Poss ibi l i t ies of dis tor t ion in communicat ion.

Repet i t ions are monotonous .

Shor t adver t i s ing l i fe .

No durabi l i ty of message .

Less no. of audience than that of televis ion.


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CHAPTER 6SUMMARY AND CONCLUSION


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SCOPE OF FUTURE WORK


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REFERENCES


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Books referred:

Satel l i te communicat ion by Timot thy Prat t , 3r d

edi t ion, Wil ley India

Optica l

Fiber

Communicat ion,

Gerd

Keiser ,

4

t h

edit ion,

Tata

McGrawHil l Educat ion.

Journals referred: Montgomery, Henry 1959 Ampli f icat ion and High Fidel i ty in the

Greek Theater . The Class ic Journal Vol. 2.

Huurdeman, Anton (2003) . The Worldwide History ofTelecommunicat ions. John Wiley & Sons vol . 1.

Art ic le referred using World Wide Web: Various ar t icles f rom ht tp: / /en.wikipedia.org/wiki /Microphone

ht tp: / /www.s l ideshare.net /arzoosahni /elect ronic-communicat ion-ms-nupur-sr ivas tav

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Industrial Training Report - Pritesh Gupta