Design and Iimplementation of a Fm Transmitter

8/18/2019 Design and Iimplementation of a Fm Transmitter

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Design and implementation of a Fm Transmitter


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TABLE OF CONTENTS

Title pa"e

Appro al pa"eedication

Acknowled"ement

A!stract

Ta!le of content

Chapter one

Introduction

Concept of modulation and demodulation

!jecti e of the project

*i"nificance of the project.

Chapter t o

+iterature re iew

&istorical !ack"round of the project

Theories and models rele ant to the construction

*ystem component description


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Chapter three

&ardware construction and implementation

,lock dia"ram and system specification

Construction of audio frequency (Af) amplifier sta"eConstruction of radio frequency (RF) amplifier sta"e

Circuit dia"ram of FM transmitter

Circuit component analysisComponent list

Chapter four

Methodolo"y packa"in" testin" and results

Methodolo"y

-acka"in" of the systemTestin" and results

Chapter fi!eCost analysis pro!lems encounteredRecommendation and conclusion


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Cost analysis

-ro!lems encounteredRecommendation

Conclusion

References


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C"A#TER ONE


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INTROD$CTION

nformation transmission is ery ital to human life just as the early men used

sticks to produce sound which indicates the location of each other as they

wander a!out also down to the middle era when town crises come into play for

the same information propa"ation to !e transmitted from one point to another with the aid of radio communication which necessities the application of radio

transmitter and recei e.

A radio transmitter is de ice whose major function is to send information

(intelli"ence) from one point to another in most cases the information to !e

transmitted are oice music and code si"nals. &owe er the transmission of

radio si"nal is done with the aid of electrical resonance this is when the

frequency of the recei er is equal to the incomin" one from the transmitter

resonance is o!ser ed which is the totality of radio communication personally

decided to work on frequency modulation (FM) transmitter !ecause it

transmitted radio si"nal which is less distorted than other wa e !ands likeamplitude modulation and short wa e !and. The frequency on the tunin" dial

ran"es from %%M&/ to #$%M&' .


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n transmitter confi"uration a sound is fed at the microphone which is the

transducer that con erts the physical sound into the electrical si"nal which is

usually amplified !y the fist electronic circuit (audio frequency amplifier class

A) whose output is fed into a modulator which fields a frequency modulated

output fed into the final sta"e (radio frequency amplifier class C) then to theantenna which radiates the radio si"nal into the atmosphere. All these process

were !ecause audio frequency si"nal cannot !e radiated out from the antenna

directly !ecause transmission at audio frequency is not particle this is !ecause

of audio frequency si"nals.

#. They ha e reacti ely short ran"e

0. t e ery!ody started transmittin" these low frequency si"nal directly

mutual interference will render all of them ineffecti e

'. The si1e of antenna required for their would !e lar"e

Furthermore for proper understandin" of this information transmission2usin"

transmitter here !y introduce the concept of modulation and demodulation.


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CONCE#T OF %OD$LATION AND DE%OD$LATION

Modulation is technically the process of com!inin" an audio frequency si"nal

(low frequency si"nal) with a hi"h frequency oscillator. &owe er the audio

frequency si"nal which is !ein" transmitted super imposes on the carrier wa e

that transports it to the out put of the radio frequency amplifier into the antennathis audio frequency si"nal other wise known as modulatin" si"nal is !ein"

amplifier !y the radio frequency amplifier in order to o ercome air impendence

as it tra el from the transmitter to the recei er.

emodulation in the other hand is the process of separatin" or reco erin" the

si"nal (modulatin" si"nal) from the modulated earlier wa e it is the opposite of

modulation and it is performed at the recei in" end (radio recei er.)

TES OF %OD$LATION

There are three types of modulation namely amplitude modulation (AM)

frequency modulation (FM) and phase modulation (-M)

#. Amplitude modulation (AM) is the types of modulation in which the

information si"nal (audio frequency si"nal) aries the amplitude of

the earlier wa e without chan"in" it3s frequency. As the name implies


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it is only the amplitude of the earlier wa e without chan"in" it3s

frequency. As the name implies it is only the amplitude that is !ein"

aried while the frequency is kept constant as the wa e tra els

0. Frequency modulation (FM) is the type of modulation is which the

modulatin" si"nal aries the frequency of the carrier wa e here it is

only the frequency of the si"nal in frequency modulation carrier

information (intelli"ence) is carried is ariations in its frequency.

'. -hase modulation (-M) is the type of modulation that aries the

phase of the radiated wa e at the modulatin" frequency and !y an

an"le4 which is proportional to the amplitude of the modulatin" wa e

from.

OB'ECTI(E OF T"E #RO'ECT

The o!jecti e of this project is to construct an electronically operated system

known as FM transmitter capa!le of transmittin" a frequency modulated si"nal

with a littler or no distortion into the atmosphere for dissemination secondly to

aid the "radatin" student into a season research acti ities that will carry them

alon" durin" the professional practice as a scientist


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SI)NIFICANCE OF T"E #RO'ECT

The project si"nifies a lot in the electronic communication system which

telecommunication is the ital aspect which is usually demonstrated throu"h

and radio communication system the frequency modulation transmitter is

applied in a lot of instance frequency modulation is una oida!le used in FM

radio stations scattered all o er the country whose ad anta"e is paramount

compared to its counter part AM modulation frequency modulation transmitted

is equally used in a miniaturi1ed from as wireless morpheme.


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C"A#TER T*O


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Recei!erTransmitter

(COAudio Amplifier #LL

Channel

The basic Frequency Modulation communications system has:

#) Transmitter4 which isthe sub-system that takes the information signal and processesit prior to transmission. The transmitter modulates the information onto a carrier

signal and broadcasts it over the channel

0) Channel5 The medium which transports the modulated signal to the receiver. In this

project, LE will be connected to !" transmitter end. #ignals then will be picked upby the $hoto etector diode right before the !" %eceiver

') Recei er that isthe sub-system that takes in the transmitted signal from the channeland processes it to retrieve the information signal. The receiver must be able to

discriminate the signal from other signals which may use the same channel medium,amplify the signal for processing and demodulate &remove the carrier' to retrieve the

information.

Figure 1) simple drawing for FM system

Parts List


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Figure 3) An example of frequency modulation. !e top diagram s!ows t!emodulating signal superimposed on t!e carrier wa"e. !e #ottom diagram

s!ows t!e resulting frequency$modulated signal. %ef &1)

The process of modulation means to systematically use the information si"nal (what youwant to transmit) to ary some parameter of the carrier si"nal. The carrier si"nal can !e asinusoidal4 as shown a!o e4 !ut in our case the carrier si"nal will !e a square2wa e that is"enerated !y a olta"e2controlled oscillator (=C ).Design

Amplifier

n our circuit we used an amplifier in order to amplify the audio si"nal and increase theamplitude of the =C input. e chose an +M86# operational amplifier that was readilya aila!le in our la!4 and confi"ured it for use as a non2in ertin" amplifier. ur amplifierwas desi"ned to ha e "ain of 0$4 therefore if the input si"nal is #$$m= the output ofamplifier will !e 0=.(oltage Controlled Oscillator 8(CO9

A olta"e2controlled oscillator or =C is anelectronic oscillator desi"ned to !e controlledin oscillation frequency !y a olta"e input. The frequency of oscillation is aried !y the

http://en.wikipedia.org/wiki/Electronic_oscillatorhttp://en.wikipedia.org/wiki/Oscillationhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Oscillationhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Electronic_oscillator


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applied olta"e4 while in our case si"nals will !e fed into the =C to causefrequencymodulation (FM).

A olta"e2controlled oscillator (=C ) pro ides a periodic si"nal where the frequency of thesi"nal is related to the le el of an input olta"e control si"nal supplied to the =C .

e collected data to plot the olta"e2frequency characteristics of the =C of theMC#6$67,.

Figure ') "oltage$frequency c!aracteristics of t!e ( *

ue to limitation of the frequency response of the +B and photodiode4 we limited ourfrequency ran"e to a ma imum of appro imately #M&1. Therefore we chose thecharacteristics of the pink line4 which reaches #M&1 at appro imately :.9=.

For the choice of the center frequency4 we considered the capture frequency ran"e of therecei er. e !elie ed that the -++ would safely !e a!le to lock onto a frequency ran"e of'$$k&1. This meant a frequency ran"e of the =C !etween appro imately 8$$k&1 and#M&1. e chose a center frequency of %7$k&1 which corresponds to a =C input olta"eof 6.9=.

http://en.wikipedia.org/wiki/Frequency_modulationhttp://en.wikipedia.org/wiki/Frequency_modulationhttp://en.wikipedia.org/wiki/Frequency_modulationhttp://en.wikipedia.org/wiki/Frequency_modulationhttp://en.wikipedia.org/wiki/Frequency_modulation


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FM Receiver

Description

For the FM recei er our team is usin" the -hase2+ocked +oop (-++) chip which recei es anamplified si"nal from the photodiode circuit and is a!le to demodulate the si"nal. Thedemodulated si"nal is the reproduced audio si"nal.

Design

#hase loc:ed Loop

A -++ is a circuit that causes a particular system to track with another one. -++synchroni1es its output si"nal ("enerated !y oscillator (=C )) with a reference or inputsi"nal in frequency as well as phase. n the synchroni1ed4 often called locked4 state the phaseerror !etween the oscillator3s output si"nal and the reference si"nal is 1ero4 or remainconstant.

f a phase error !uilds up4 a control mechanism acts on the oscillator in such a way that the phase error is a"ain reduced to minimum. n such a control system the phase of the outputsi"nal is actually locked to the phase of the reference si"nal. This is why it is referred to as a phase locked loop.

The -++ consists of three !asic functional !locks5#) A =olta"e2Controlled scillator (=C )0) A -hase etector') A +ow -ass Filter


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Figure +) PLL diagram %ef &2)

f the phase error (error si"nal) is not 1ero4 the phase detector de elops a non1ero outputsi"nal. After some delay the loop filter would also produce the si"nal. The si"nal wouldcause the =C to chan"e its operatin" frequency in such a way that the phase error finally

anishes.

For -++4 we use the MC#6$67, chip4 which contains two phase comparators4 aolta"eDcontrolled oscillator (=C )4 and a source follower. The =C has !een already

descri!ed. For our desi"n purpose we use -hase Comparator #. -hase comparator # (ane clusi e R "ate) pro ides a di"ital error si"nal -C#out4 and maintains 9$E phase shift atthe center frequency !etween -CAin and -C,in si"nals. The followin" fi"ure shows theinside structure of the MC06$67, chip4 and input and output si"nals to the phase

comparator. (for more information please refer to Appendi )

Figure ,) PLL ircuit design and P!ase comparator &-ource M 1'/',0 datas!eet from* -emiconductor)


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-spice esi"n

F% Recei!er Circuit 8Not including photodiode circuit9

• nput si"nal from photodiode circuit recei ed at pin #6 of


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C"A#TER T"REE


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F% Transmitter Design methodolog,;

n telecommunications4 frequency modulation (FM) con eys information o er a carrier wa e !y aryin" its frequency. FM is commonly used at =&F radio

frequencies for hi"h2fidelity !roadcasts of music and speech. Throu"hout the

world4 the !roadcast !and falls within the =&F part of the radio spectrum.


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L1 Air Core Coil

Coil *pecification 2 : Turn 00 * G Bnameled Copper ireCoil +en"th $.0: nch 2 iameter $.07: nch

The desi"n details of each component are as follows./6 Condenser %IC The condenser M C is used to pick up the sound si"nals. The diaphra"minside the M C i!rates accordin" to the air pressure chan"es and "enerates AC si"nals.=aria!le resistor =R# adjusts the current throu"h the M C and thus determines thesensiti ity of M C. The condenser M C should !e directly soldered on the -C, to "etma imum sensiti ity. *lee in" the M C inside plastic tu!in" can increase its sensiti ityenormously.16 Decoupling Capacitors C# is the first decouplin" capacitor impedes the differentfrequencies of speech si"nals. C# modulates the current to the !ase of transistor. The 6.8 uFcapacitor isolates the microphone from the !ase olta"e of the transistor and only allowsalternatin" current (AC) si"nals to pass. A lar"e alue capacitor induces !ass (lowfrequencies) while a low alue one "i es tre!le (hi"h frequencies). Capacitor C0 ($.$#) actas the decouplin" capacitor. Capacitor C' across the transistor T# keeps the tank circuit

i!ratin". As lon" as the current e ists across the inductor coil +# and the Trimmercapacitor4 the tank circuit (Coil2Trimmer) will i!rate at the resonant frequency. hen thetank circuit i!rates for lon" time4 the frequency decays due to heatin". -resence of the


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capacitor C' pre ents this decay. A capacitor !etween 6 and #$ -F is necessary.06 Resistors =aria!le resistor =R# restricts the current throu"h the M C. The olta"e di ider

R# and R0 limits the !ase current of T# and R' forms the emitter current limiter. The "i enalues are necessary for the 0@ 0000A transistor.26 Transistor 0@ 0000A is the common @-@ transmitter used in "eneral purposeamplifications. t has ma imum power ratin" of $.: atts. er powerin" of 0@ 0000A can"enerate heat and destroy the de ice. *o ma imum power output should !e around #0: milliwatt. -in assi"nment of 0@ 0000 A is # Bmitter 2 0 ,ase 2 ' Collector (B,C) from the frontside (Flat side on which the num!er is printed).

.6 Inductor Coil The inductor used in the circuit is a hand made coil usin" 00 * G(*tandard ire Gau"e) enameled copper wire. The len"th4 inner diameter4 num!er of turnsetc are the important parameters to !e considered while makin" the inductor. Then only theinductor resonates in the %%2#$% !and FM frequency. For this circuit4 the coil radius wasselected as $.07 inches (outer diameter) and $.#' inner diameter. Coil can !e wound arounda screw dri er (with same diameter) to "et a : turn coil of $.0 inch lon". Remo e the coilfrom the screw dri er and use the : turn Air core coil. Remo e the enamel from the tips andsolder close to the transistor. The inductance of the coil can !e calculated usin" the formulaL < n 1 r 1 = 5r > /? @ here r is the inner radius of the coil4 is the len"th of the coil and n4num!er of turns. The resultin" alue is in Micro &enry.


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6 Trimmer capacitor A small !utton type aria!le capacitor with a alue of 00 pF can !eused to adjust the resonant frequency of the tank circuit. The aria!le capacitor and theinductor coil form the Tank circuit (+C circuit) that resonates in the %%2#$% M&1. n the tankcircuit4 the capacitor stores electrical ener"y !etween its plates while the inductor stores

ma"netic ener"y induced !y the windin"s of the coil. The resonant frequency can !ecalculated usin" the formulaf < / = 1 @ HLC < " here f is the frequency in hert14 is the coil len"th4 C is thecapacitance of trimmer in Farads4 and + is the inductance of coil in &endry.Tan: Circuit B ery FM transmitter needs an oscillator to "enerate the radio Frequency (RF)carrier wa es. The name ITankI circuit comes from the a!ility of the +C circuit to storeener"y for oscillations. The purely reacti e elements4 the C and the + simply store ener"y to !e returned to the system. n the tank (+C) circuit4 the 0@ 0000 A transistor and the feed!ack

6.8 pF capacitor are the oscillatin" components. The feed!ack si"nal makes the !ase2emittercurrent of the transistor ary at the resonant frequency. This causes the emitter2collectorcurrent to ary at the same frequency. This si"nal fed to the aerial and radiated as radiowa es.


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76 Antenna A plastic wire or Telescopic aerial can !e used as antenna. The

len"th of the antenna is ery important to transmit the si"nals in the suita!leran"e. As a rule4 the len"th of the antenna should !e J of the FM wa e len"th.

To determine the len"th of antenna4 use the followin" equation. ,y multiplyin"

the a e frequency and wa e len"th will "i e the speed of li"ht.

Speed of Light < Fre uenc, of Oscillation @ *a!elength < in ms= Sec

*a!e length < Speed of light = Fre uenc, < in meters

Antenna length < ?61. @ a!elength < in meters ,y usin" this formula it is

easy to select the antennal len"th. For the circuit mentioned a!o e4 a 0:208

inches lon" antenna is sufficient.


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Assem ling and Testing The circuit can !e assem!led on a ot type common -C, or -erf !oard. The followin" tips should !e considered while assem!lin" the circuit #. Assem!le thecomponents as close as possi!le4 especially the transistor4 trimmer and coil to pre entunwanted oscillation. 0. +ead len"th of capacitors4 resistors4 transistor should !e as small as possi!le. '. *older the M C directly on the -C, ( use the trimmed leads of the resistors toconnect M C) 6. !ser e the polarity of M C. :. Check the pins of 0@ 0000 A. The pinassi"nment is B2,2C (Bmitter ,ase Collector) from the front side (Flat side on which thenum!er is printed). 7. Coil should stand hori1ontally a!o e the Bmitter of transistor. 8. Coilshould !e closely wound."o to test After assem!lin" the circuit4 connect 9 olt !attery. A !attery operated FM

pocket radio is necessary for testin". AC powered FM players will "i e lesser performancethan the !attery powered FM recei ers due to noise. Tune the FM recei er to a K ead AirspaceL (around #$% M&1 where there is no station). -lace the FM radio 0 feet away from thetransmitter. Gently tap on the M C. f the tank circuit is properly tuned4 tappin" sound will !e heard in the radio. f no sound is heard4 sli"htly pull the coil to separate the windin"s.Adjust the shaft of the Trimmer slowly with a preset screwdri er. Check a"ain. f the soundis clear4 mo e the FM radio and assess the ran"e. Try a"ain !y adjustin" the trimmer and position of aerial of !oth transmitter and FM radio. f the sound clarity is "ood and there is

sufficient ran"e4 stick the coil with nail polish or "lue to a oid frequency chan"e. The FMtransmitter is ready to use.


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C"A#TER FO$R


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(CO chip8Transmitter Side9

Amplifier8Transmitter Side9

%C/2?2 B9

L%72/

Audio input

>5()round

5(

Result and conclusion5

Figure ) ransmitter ircuit &top "iew)

Figure 4) ransmitter ircuit ac5 "iew)

TransmitterOutput


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FM Receiver

Figure 1/) %ecei"er circuit &top "iew)

Figure 11) %ecei"er circuit ac5 "iew)Conclusion

• ncrease the input impedance of the speaker3s power amplifier sta"e to reduce thecurrent sinked !y that circuit.

• +ower the center frequency and utili1e the =C confi"ured with a less steep frequency2olta"e input cur e.

#LL Chip; %C/2?2 B9

)round>5(Recei!er unit

Recei!erInput

Recei!eroutput


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• mpro e techniques on solderin" wires. For instance4 wires soldered onto the -C !oardha e a tendency to detach if the solderin" was not sufficient.

+essons +earned From The Course

nitially4 for our FM transmitter desi"n we considered usin" some type of analo" oscillatorcircuit (i.e. usin" an R+C circuit). &owe er we learned that simply utili1in" a =C already !uilt on an C was much easier and quicker to implement.

Additionally4 in this course we learned practical desi"n and implementation issues that werenot e plicitly tau"ht in pre ious la! courses such as the effects of "round loop. Also4 sincewe worked more in2depth with AC circuits ersus pre ious courses4 we disco ered the illeffects of impedance mismatchin". This is !ecause this course required the connections ofseparately desi"ned circuits. These are issues to keep in mind when doin" future circuitdesi"ns.

References

#) http5 www.!pm2music.com *iteFiles ma"e Grafica Frequency2modulation.pn"0) http5 www.ami.ac.uk courses ami660%Nahdl u$' ima"es adNmaNim"$'."if

') www.onsemi.com pu! Collateral MC#6$67,2 .- F
http://www.bpm-music.com/SiteFiles/Image/Grafica/Frequency-modulation.pnghttp://www.ami.ac.uk/courses/ami4428_ahdl/u03/images/ad_ma_img03.gifhttp://www.onsemi.com/pub/Collateral/MC14046B-D.PDFhttp://www.bpm-music.com/SiteFiles/Image/Grafica/Frequency-modulation.pnghttp://www.ami.ac.uk/courses/ami4428_ahdl/u03/images/ad_ma_img03.gifhttp://www.onsemi.com/pub/Collateral/MC14046B-D.PDF

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Design and Iimplementation of a Fm Transmitter