Unit- 3 Transmitters and Recivers.ppt

Analog Communication

1. MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
SUBJECT NAME: ANALOG COMMUNICATIONS (PC501EC)
FACULTY NAME: Dr. M.NARESH
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2. ANALOG COMMUNICATIONS
COURSE OBJECTIVES:
1. To Analyze the Analog communication system requirements
2.To understand the Generation and Detection of various analog modulation
techniques
3.To Analyze the noise performance of analog modulation techniques
4.To understand AM and FM Receivers.
5. To Understand the Pulse modulation techniques
COURSEOUTCOMES:
CO1: Describe basic concepts of linear and non-linear modulation and
demodulation schemes
CO2: Compare analog modulation schemes in terms of modulation index,
transmission bandwidth, TX power etc.
CO3: Explaining various aspects of sampling theorem to produce various
pulse modulation schemes
CO4: Appreciate the structures of various AM and FM transmitters and
receivers and understand design parameters.
CO5: Estimate electronic noise parameters on various analog modulation
schemes.
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3. SYLLABUS
UNITI-LinearModulationschemes:Needformodulation,
conventionalAmplitudeModulation(AM).Doublesideband
suppressedcarrier(DSB–SC)modulation,Hilberttransform,
propertiesofHilberttransform.Pre-envelop.Complexenvelope
representationofbandpasssignals,In-phaseandQuadrature
componentrepresentationofbandpasssignals.Lowpass
representationofbandpasssystems.Singlesideband(SSB)
modulationandVestigial-sideband(VSB)modulation.Modulation
anddemodulationofallthemodulationschemes,COSTASloop.
UNITII-Anglemodulationschemes:FrequencyModulation(FM)
andPhasemodulation(PM),Conceptofinstantaneousphaseand
frequency.TypesofFMmodulation:NarrowbandFMandwide
bandFM.FMspectrumintermsofBesselfunctions.Directand
indirect(Armstrong's)methodsofFMgeneration.Balanced
discriminator,Foster–Seeleydiscriminator,Zerocrossingdetector
andRatiodetectorforFMdemodulation.AmplitudeLimiterinFM.
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4. UNITIV-Analogpulsemodulationschemes:Samplingof
continuoustimesignals.Samplingoflowpassandbandpasssignals.
Typesofsampling.PulseAmplitudeModulation(PAM)generation
anddemodulation.Pulsetimemodulationschemes:PWMandPPM
generationanddetection.TimeDivisionMultiplexing.
UNITIII-TransmittersandReceivers:Classificationof
transmitters.HighlevelandlowlevelAMtransmitters.FM
transmitters.PrincipleofoperationofTunedradiofrequency(TRF)
andsuperheterodynereceivers.SelectionofRFamplifier.Choiceof
Intermediatefrequency.Imagefrequencyanditsrejectionratio
Receivercharacteristics:Sensitivity,Selectivity,Fidelity,Double
spotting,AutomaticGainControl.
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UNITV-NoiseSourcesandtypes:Atmosphericnoise,Shotnoise
andthermalnoise.Noisetemperature.Noiseintwo-portnetwork:
noisefigure,equivalentnoisetemperatureandnoisebandwidth.
Noisefigureandequivalentnoisetemperatureofcascadestages.
Narrowbandnoiserepresentation.S/NratioandFigureofmerit
calculationsinAM,DSB-SC,SSBandFMsystems,Pre-Emphasisand
De-Emphasis

5. TEXT BOOKS /REFERENCES
TEXTBOOKS:
1.SimonHaykin,“CommunicationSystems,”2/e,WileyIndia,2011.,
2. B.P. Lathi, ZhiDing, “Modern Digital and Analog Communication
Systems”, 4/e, Oxford University Press, 2016
3.P.RamakrishnaRao,“AnalogCommunication,”1/e,TMH,2011.
REFERENCES:
1.Taub,Schilling,“PrinciplesofCommunicationSystems”,Tata
McGraw‐Hill,4thEdition,2013.
2.JohnG.Proakis,Masond,Salehi,“FundamentalsofCommunication
Systems”,PEA,1stEdition,2006
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6. LESSON PLAN:
UNIT III-Transmitters and Receivers
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S. No. Topic(S)
No.
of Hrs
Relevant
COs
Text Book/
Reference
Book
1.
TransmittersandReceivers:Classificationof
transmitters.HighlevelandlowlevelAM
transmitters.
2 CO4 T1,T2,T3
2.
FMtransmitters. 1 CO4 T1,T2,T3
3.
PrincipleofoperationofTunedradiofrequency
(TRF)and
2 CO4 T1,T2,T3
4.
superheterodynereceivers.SelectionofRF
amplifier.
2 CO4 T1,T2,T3
5.
Choice of Intermediate frequency. Image frequency
and its rejection ratio
1 CO4 T1,T2,T3
6.
Receiver characteristics: Sensitivity, Selectivity,
Fidelity, Double spotting, Automatic Gain Control
2 CO4 T1,T2,T3
TOTAL10

7. PRE-REQUISITES FOR THIS COURSE:
PTSP III-SEM 3-Credits
ES215EC :SS IV-SEM 3-Credits
EXTERNAL SOURCES FOR ADDITIONAL LEARNING:
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Description Proposed ActionsRelevance With POs
Relevance
With PSOs
Modulation &
Demodulation of all
Techniques including
multiplexing .
Communication Lab PO3, PO4, PO5 PSO2
CONTENT BEYOND SYLLABUS:
S. No. Topic Relevance with POs and
PSOs
1.Advanced Communication system PSO1

8. The main parts of transmitter are explained as follows :
microphone : it converts sounds into electrical signals in wires. It is the opposite of a loudspeaker.
Modulator : the audio signal is modulated into the radio frequency carrier in this modulator stage.
Frequency generator : the frequency generation stage will decide the frequency on which the
transmitter will operate.
RF power amplifier : the power amplification of the radio signal is carried out in the final stage. It
makes the signal stronger so that it can be transmitted through the channel over
long distances.
UNIT III-Transmitters and Receivers
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Basic functions of transmitter:
•Thetransmittermustgenerateasignalofcorrectfrequencyatadesiredpointinthespectrum.
•Secondlyitmustprovidesomeformofmodulationtomodulatethecarrier.
•Thirditmustprovidesufficientpoweramplificationinordertocarrythemodulatedsignaltoa
longdistance.

9. Classification of Transmitters:
1. According to the type of modulation used.
2. According to service involved.
3. According to the frequency range involved.
4. According to the power used
Classification based on transmitted frequency:
•Low frequency (lf) transmitters (30 khz-300khz)
•Mediumfrequency(mf)transmitters(300khz-3mhz)
•Highfrequency(hf)transmitters(3mhz-30mhz)
•Veryhighfrequency(VHF)transmitters(30MHZ-300MHZ)
•Ultrahighfrequency(uhf)transmitters(300mhz-3ghz)
•Microwavetransmitters(>3ghz)
3.1 Classification of transmitters
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10. Classification based on type of service involved:
1. Radio Telephony Transmitters
2. Radio telegraphy
3. TV Transmitter
4. Radar transmitters.
5. Navigational transmitters.
Classification based on type of Modulation:
1.CW Transmitters
2.AM Transmitters
3.FM Transmitters
4.SSB Transmitters
3.1 Classification of transmitters
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Classification based on power used
1. Low POWER <10KW
2. Medium POWER 10-10,000KW
3. High POWER >10,000KW

11. The RF oscillator produces the carrier signal. The RF oscillator is stabilized in order to
maintain the frequency deviation within the prescribed limit. The carrier frequency is equal to
the transmitter frequency.
Usually the transmitter operates on assigned frequencies or channels. Crystal provides the
best way to obtain the described frequency with good stability.
We cannot use the LC oscillator because they have low frequency stability.
The carrier signal from the crystal oscillator is applied to the modulator with a modulating
signal. At the output of the modulator we get the AM wave.
3.1.Low level Modulation Transmitter
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Low Level Modulation Transmitters:
Class ‘B’

12. UNIT III-Transmitters and Receivers
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The linear amplifier can be class A, AB or B type amplifiers. The linear amplifier are used in order to
avoid the wave form distortion in AM wave.
The amplitude modulated signal is then transmitted using transmitted antenna.
The transistorized modulator circuits can be used for low level modulator due to the low power which
is to be handled.
The low level transmitter does not require a large AF modulator power so its design is simplified.
Overall efficiency is much lower compared to high level modulation . This reduce to the use of less
efficient linear amplifiers.
The modulating signal is obtained from a source such as a microphone and applied to a buffer
processing unit.
The buffer is a class A amplifier which isolates the AF source from the rest of high power circuit
and amplifies it to an adequate level.
The amplified modulating signal is applied to the modulator along with the carrier. At the output
of the modulator we get the AM wave.
The AM signal is then amplified using a chain of linear amplifier to raise the power level.

13. ManyoftheAMtransmittersusethehighlevelmodulationtechnique.
Thecrystaloscillatorproducestherequiredcarriersignal.TheclassAamplifierfollowingthe
oscillatoractsasabufferwhichisolatestheoscillatorfromthehighpowercircuit.
Theoutputofthisclassaamplifierisappliedtoaclasscpoweramplifier.
Itraisesthepowerlevelofthecarriertoanintermediatelyhighvalue.
TheAFmodulatingsignalisappliedtotheaudioprocessingunitwhichprocessesthissignalas
discussedintheprevioussection.
3.1.High Level Modulation Transmitters
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High Level Modulation Transmitters:

14. CONTENTS:
3.2 Principle of operation of tuned radio frequency (TRF) and super heterodyne
receivers.
OUTCOMES:
Discuss the concept of receivers in communication system and receiver types like tuned
radio frequency receiver and super heterodyne receiver.
.
MODULE-2
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15. 3.2. Tuned Radio Frequency receiver (TRF)
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ANTENNA
coupling
Network
AM DETECTOR
RF
ampli
fier1
RF
ampli
fier2
RF
amp
lifier
3
AM POWER
AMPLIFIER
Ganged
Tuning
Receiving
Antenna
Loud
speaker
TRF receiver includes an RF stage, a detector stage , and an audio stage.
Two or three RF amplifiers are required to filter and amplify the received signal to a level
sufficient to drive the detector stage.
RF section (Receiver front end)
used to detect the signal
band limit the received RF signal
and amplifying the received RF signal.
AM detector: Demodulates the AM wave and converts it to the original information signal.
Audio section: Used to amplify the recovered signal

16. 3.3. Super Heterodyne receiver (SRH)
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ANTENNA
coupling
Network
AM
DETECTOR
RF
ampl
ifier1
AF
POWER
AMPLIFIER
Ganged
Tuning
Receiving
Antenna
Loud
speaker
Mixer
LO
IF
AMPLIFIE
R
AGC
out
AGC intAGC int
Fif Fif
Flo>Fs
fsfs
TheantennacollectstheradiosignalthetunedRFstagewithoptionalRFamplifierprovidessome
initialselectivity;itisnecessarytosuppresstheimagefrequency(seebelow),andmayalsoserveto
preventstrongout-of-passbandsignalsfromsaturatingtheinitialamplifier.
Alocaloscillatorprovidesthemixingfrequency;itisusuallyavariablefrequencyoscillatorwhichis
usedtotunethereceivertodifferentstations.thefrequencymixerdoestheactualheterodyningthat
givesthesuperheterodyneitsname;itchangestheincomingradiofrequencysignaltoahigheror
lower,fixed,intermediatefrequency(if).

17. 3.3. Super Heterodyne receiver (SRH)
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TheIFband-passfilterandamplifiersupplymostofthegainandthenarrowbandfilteringforthe
radio.thedemodulatorextractstheaudioorothermodulationfromtheifradiofrequency.the
extractedsignalisthenamplifiedbytheaudioamplifier.
Local oscillator and mixer:
Thesignalisthenfedintoacircuitwhereitismixedwithasinewavefromavariablefrequency
oscillatorknownasthelocaloscillator(LO).
Themixerusesanon-linearcomponenttoproducebothsumanddifferencebeatfrequenciessignals,
eachonecontainingthemodulationcontainedinthedesiredsignal.Theoutputofthemixermay
includetheoriginalRFsignalatfRF,thelocaloscillatorsignalatfLO,andthetwonewheterodyne
frequenciesfRF+fLOandfRF−fLO.
Themixermayinadvertentlyproduceadditionalfrequenciessuchasthird-andhigher-orderinter
modulationproducts.Ideally,theIFbandpassfilterremovesallbutthedesiredIFsignalatfIF.
TheIFsignalcontainstheoriginalmodulation(transmittedinformation)thatthereceivedradio
signalhadatfRF.

18. .
3.3. Super Hetrodyne Receiver
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Thefrequencyofthelocaloscillatorfloissetsothedesiredreceptionradiofrequencyfrf
mixestofIF
Therearetwochoicesforthelocaloscillatorfrequencybecausethedominantmixerproducts
areatfRF±FLOIfthelocaloscillatorfrequencyislessthanthedesiredreceptionfrequency,it
iscalledlow-sideinjection(fIF=fRF−fLO);ifthelocaloscillatorishigher,thenitiscalledhigh-
sideinjection(fIF=fLO−fRF).
Themixerwillprocessnotonlythedesiredinputsignalatfrf,butalsoallsignalspresentatits
inputs.Therewillbemanymixerproducts(heterodynes).Mostothersignalsproducedbythe
mixer(suchasduetostationsatnearbyfrequencies)canbefilteredoutintheIFtunedamplifier;
thatgivesthesuperheterodynereceiveritssuperiorperformance.
However,iffLOissettofRF+fIF,thenanincomingradiosignalatfLO+fIFwillalsoproducea
heterodyneatfIF;thefrequencyfLO+fIFiscalledtheimagefrequencyandmustberejectedbythe
tunedcircuitsintheRFstage.Theimagefrequencyis2fIFhigher(orlower)thanthedesired
frequencyfRFsoemployingahigherIFfrequencyfifincreasesthereceiver'simagerejection
withoutrequiringadditionalselectivityintheRFstage

19. CONTENTS:
3.3. Selection of RF amplifier. Choice of intermediate frequency. Image frequency and its
rejection ratio .
OUTCOMES:
MODULE-3
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20. 3.3. Selection of RF amplifier, Choice of IF, IRR
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RF Amplifier:
IF Amplifier:

21. Image Frequency Rejection:
The Desired signal frequency is “fs” is below the local oscillator frequency “fLO” by an amount of “fIF”
It is defined as the received signal frequency plus twice the intermediate frequency (fIF).
3.3. Selection of RF amplifier, Choice of IF, IRR
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IFsIM
fff
fff
2
2
Im

 sLoIF
IFsLo
fff
fff



Image Frequency Rejection Ration (IRR)2
22
1
1








IM
s
s
IM
f
f
f
f
Q
Q

 BW
f
Q
f
f
f
f
c
IM
s
s
IM


Where
It is defined as the ratio of the gain at the signal frequency to the gain at the image
frequency

22. CONTENTS:
3.4 Receiver characteristics: sensitivity, selectivity, fidelity, double spotting,
automatic gain control
OUTCOMES:
MODULE-
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23. 3.4 Receiver characteristics
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Receiver Characteristics:
Sensitivity
Selectivity
Fidelity
Noise Figure
Image frequency & rejection
Double spotting
Tracking and alignment
SENSITIVITY:
Abilitytoamplifyweaksignals.Minimumrfsignallevelthatcanbedetectedattheinputtothe
receiverandstillproduceausabledemodulatedinformationsignal.
Broadcastreceivers/radioreceiversshouldhavereasonablyhighsensitivitysothatitmay
havegoodresponsetothedesiredsignal.
Butshouldnothaveexcessivelyhighsensitivityotherwiseitwillpickupallundesirednoise
signals.Itisfunctionofreceivergainandmeasuresindecibels.
Sensitivity of a receiver is expressed in microvolt's of the received signal or in db below 1μv.

24. 3.4 Receiver characteristics
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Selectivity:
Selectivity of radio receiver
is its ability to Differentiate
desired signal from
unwanted signals.
It varies with receiving frequency and becomes worse when the receiving frequency is raised.
It is mainly determined by the response of the if section, mixer and rf amplifier inputs.
Selectivity decides the adjacent channel rejection of a receiver.
Selectivity is obtained by using tuned circuits, which are tuned to desired frequency. The quality
factor of these LC circuits determines the selectivity. It is given by,
Q=xl/r
For better selectivity ‘q’ should be high.

25. FIDELITY:
Fidelity is defined as –a measure of the ability of a communication system to produce an exact
replica of the original source information at the output of the receiver.
Any variations in the demodulated signal that are not in the original information signal is considered
as distortion.
Radio receiver should have high fidelity or accuracy.
Example-in an A.M. Broadcast the maximum audio frequency is 5 khzhence receiver with good
fidelity must produce entire frequency up to 5khz.
3.4 Receiver characteristics
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26. NOISE FIGURE:
Ratio of SNR of the input signal to the SNR of the output. AM broadcast receivers generally have NF
of about 5 to 10db.
It determines the smallest signal power that it can receive without making the output signal get
drowned in noise.
3.4. Receiver Characteristics
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IMAGE FREQUENCY :
Inradioreceptionusingheterodyninginthetuningprocess,anundesiredinputfrequencythatis
capableofproducingthesameintermediatefrequency(IF)thatthedesiredinputfrequency
produces.
Imagefrequency–anyfrequencyotherthantheselectedradiofrequencycarrierthatwillproduce
across-productfrequencythatisequaltotheintermediatefrequencyifallowedtoenterareceiver
andmixwiththelocaloscillator.
Itisgivenbysignalfrequencyplustwicetheintermediatefrequency
Fsi=fs+2fi

27. DOUBLE SPOTTING :
Same radio station being heard at two different points on the AM receiver dial.
The main cause of double spotting is poor front end selectivity , it can be used to
calculate IF of an unknown receiver. If IFRR is improved the DS will reduce.
3.4. Receiver Characteristics
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TRACKING & ALIGNMENT:

28. 3.4. Receiver Characteristics
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In SHR the tuning capacitors of theRF amplifier and lo are ganged together to have only one
tuning control for the receiver.
The LO frequency is tuned to pre-determined value frequency called if frequency at all times.
The process of tuning the lo to produce a predetermined frequency for each station throughout
the am band is called tracking.
To produce a fixed value always LO frequency is chosen higher than the signal frequency. The
plates of the variable capacitors of the lo section is made smaller than that of RF

29. CONTENTS:
3.5 FM transmittersand Receiver
OUTCOMES:
Discuss about FM transmitters and receiver
MODULE-
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30. 3.5. Armstrong Indirect FM Transmitter
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The principle of Armstrong method of FM signal generator is to generates a
NBFM signal indirectly by utilizing the PM techniques and the changing the
NBFM signal into a WBFM.

31. .
.
3.5. FM Super heterodyne Receiver
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It’s operates on the principle of “super heterodyning “ as the AM receiver.
FM Receiver use 88M-108M Frequency band.
In commercial FM receiver, the tuning ratio is 1.2:1 (108M/88M)
In commercial AM receiver, the tuning ratio is 3:1 (1605k/535k)
FM receiver offer improved SNR

32. FM SUPER HETERODYNE RECEIVER:
AMPLITUDELIMITER:
TheTransmittedFMsignalhasconstantAmplitude,buttheconstantamplitudeprofile
ofFMsignalchangesduetochannelnoise.
TheseunwantedamplitudevariationsinthereceivedFMsignalcauseddistortion.
FMDemodulatorreacttoamplitudevariationsaswellasfrequencychanges.
So,theseamplitudevariationsmustberemovedbeforethesignalisappliedtoFM
Demodulator.
TheAmplitudeLimiterwillremovealltheunwantedamplitudevariationsfromthe
receivedsignal.
3.5. FM Super heterodyne Receiver
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Intermediate Frequency (IF)=10.7 MHz.
It needs additional circuits like Amplitude limiter and De-emphasis ,Pre-emphasis in FM Transmitter

33. 1. Explain High level and Low level Transmitters.
2. Draw and Explain about Tuned Radio Frequency receiver.
3. Explain the operation of Super heterodyne receiver.
4. Classify the radio transmitters.
5. Write short notes on
a) intermediate amplifier
b) double spotting
c)selection of rfamplifier
d) tracking and alignment
Assignment Question
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34. Short answer questions
Questions & Answers
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S.NO QUESTION
Blooms
Taxonomy
Level
Course
Outcome
1.Classify the Radio transmitters. L2 CO4
2.Distinguish between high level and level AM transmitters.L2 CO4
3.What is the need of limiter circuit in FM receiver? L1 CO4
4.What are the receiver characteristics? L1 CO4
5.Define Image rejection ratio. L1 CO4

35. Long answer questions
Questions & Answers
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S.NO QUESTION
Blooms
Taxonomy
Level
Course
Outcome
1.Draw the Block diagram of Super-heterodyne receiver
designed to receive FM signals and explain its working.
L4 CO4
2.Explain about choice of intermediate frequency in AM
receiver.
L4 CO4
3.Draw the block diagram of high level & low level modulated
AM transmitter and explain the operation of each block.
L4 CO4
4.Explain with the block diagram the operation of AGC and
types of AGC.
L4 CO4
5.Write short notes on :
a.Double Spotting
b.Amplitude Limiter
L2 CO4

36. THE-END
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