Analog Communication Lab Manual , Prepared By Nakka. Ravi .

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Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTINDEX1. Introduction2. List of experiments3. General guidelines for conducting an experiment3.1 Simulation3.2 Hardware3.3 Do’s and Don’ts4. Experiments4.1 Amplitude modulation and demodulation4.1.1 AIM4.1.2 Theory4.1.3 MATLAB program and description4.1.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.2 DSB-SC modulation and demodulation4.2.1 AIM4.2.2 Theory4.2.3 MATLAB program and description4.2.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.3 SSB-SC modulation and Demodulation (Phase Shift method)4.3.1 AIM4.3.2 Theory4.3.3 MATLAB program and description4.3.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.4 Frequency modulation and demodulation4.4.1 AIM4.4.2 Theory4.4.3 MATLAB program and description4.4.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.5 Study of spectrum analyzer and study of AM and FM signals4.5.1 AIM4.5.2 Theory4.5.3 MATLAB program and descriptionMIST, Hyderabad – ECE DepartmentPage No.44567-1213-1617-2425-2930-32Page 1

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST4.5.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.6 Pre-emphasis and De-emphasis4.6.1 AIM4.6.2 Theory4.6.3 MATLAB program and description4.6.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.7 Time division multiplexing and de-multiplexing4.7.1 AIM4.7.2 Theory4.7.3 MATLAB program and description4.7.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.8 Frequency division multiplexing and de-multiplexing4.8.1 AIM4.8.2 Theory4.8.3 MATLAB program and description4.8.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.9 Verification of sampling theorem4.9.1 AIM4.9.2 Theory4.9.3 MATLAB program and description4.9.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.10 Pulse Amplitude modulation and demodulation4.10.1 AIM4.10.2 Theory4.10.3 MATLAB program and description4.10.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveformMIST, Hyderabad – ECE Department33-3637-4041-4748-5152-56Page 2

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST4.11 Pulse width modulation and demodulation4.11.1 AIM4.11.2 Theory4.11.3 MATLAB program and description4.11.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.12 Pulse position modulation and demodulation4.12.1 AIM4.12.2 Theory4.12.3 MATLAB program and description4.12.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.13 Frequency synthesizer4.13.1 AIM4.13.2 Theory4.13.3 MATLAB program and description4.13.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.14 AGC characteristics4.14.1 AIM4.14.2 Theory4.14.3 MATLAB program and description4.14.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveform4.15 PLL and FM demodulator4.15.1 AIM4.15.2 Theory4.15.3 MATLAB program and description4.15.4 Hardware- Apparatus- Circuit diagram- Procedure- Expected waveformMIST, Hyderabad – ECE Department57-6061-6465-6869-7374-79Page 3

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST1. IntroductionAnalog communications lab is for B.Tech III year ECE I semester. The studentslearn Analog Communications theory subject in the same semester. The lab experiments aremeant to equip the students with firm practical knowledge of the concerned subject. As listedin section-2, there are total fifteen (15) experiments in this lab which are according to JNTUHR-13 syllabus, out of which minimum 12 experiments are to be conductedGeneral procedure for conducting an experiment is described in Section – 3. Eachexperiment will first be simulated using MATLAB, a simulation software program, which thestudents have already learned in Basic Simulation lab in II year I semester. The sameexperiment will then be realized using proper hardware, as described in detail for eachexperiment in section -4.2. List of Experiments1. Amplitude modulation and demodulation2. DSB-SC modulator and detector3. SSB-SC modulator and detector4. Frequency modulation and demodulation5. Study of Spectrum Analyzer and Analysis of AM and FM Signals6. Pre-emphasis and de-emphasis7. Time division multiplexing and de-multiplexing8. Frequency division multiplexing and de-multiplexing9. Verification of sampling theorem10. Pulse amplitude modulation and demodulation11. Pulse width modulation and demodulation12. Pulse Position modulation and demodulation13. Frequency synthesizer14. AGC Characteristics15. PLL & FM demodulatorMIST, Hyderabad – ECE DepartmentPage 4

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST3.0General Guidelines for conducting an experimentEach experiment first has to be simulated using MATLAB and then be realized in hardware asdescribed in Section -4.MATLAB, short for MATrix LABoratory is a programming package specifically designed forscientific calculations and I/O. It has literally hundreds of built-in functions for a wide variety ofcomputations and many tool boxes designed for specific research disciplines, including statistics,optimization, solution of partial differential equations and data analysis.3.1SimulationEach experiment will first be simulated with MATLAB software package. The MATLABprogram code for each experiment is given in the following section. The students have to write theprograms in PC and execute them using MATLAB software and make sure that they get the expectedwaveforms as shown in this manual.The students are also advised to change certain parameters in the MATLAB program and seetheir impact on the output waveforms.3.2HardwareAfter completion of the simulation, each experiment has to be realized in hardware asdescribed for all experiments in section – 4. Out of fifteen experiments, fourteen experiments are to beconducted with the PHYSITECH lab kits along with the additional instruments as mentioned for eachexperiment in section – 4. The fifth experiment, “Study of Spectrum Analyzer and Analysis of AMand FM Signals” does not require the PHYSIITECH experiment kit.3.3Do’s and Don’tsThe students are to follow the given general Do’s and Don’ts for simulation lab.Do’s:1. Enter in to the simulation lab in time.2. Wear student identity badges round your neck before entering the lab.3. Keep silence in the lab4. Follow the instructions of the lab in-charges and lab supervisor.5. Always save your input files and results in the prescribed directory.Don’ts:1. Do not use internet or open any other programs other than MATLAB.2. Do not mishandle or rough handle the keyboard of CPU.3. Do not use pen drive or card reader without the permission of the lab in-charge.4. Do not make noise in the lab.The students are to follow the given general Do’s and Don’ts for hardware labDo’s1. Enter the hardware lab in time.2. Wear shoes/sandals in the lab.3. Wear student identity badge before entering the lab4. Follow the instructions of the lab in-charges and lab supervisor.Don’ts:1. Do not make noise in the lab.2. Do not switch the power supply until you finish all the connections.3. Do not remove connecting wires or probes when the power is ON.4. Do not mishandle the kits and instruments.5. Do not pluck the ICs or other components from the trainer kits.6. Before turning on the power, show your experimental arrangement to the lab in-charges orlab supervisor.MIST, Hyderabad – ECE DepartmentPage 5

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST4.0ExperimentsMIST, Hyderabad – ECE DepartmentPage 6

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTEXPERIMENT – 14.1Amplitude modulation and demodulation4.1.1 Aim: To study the function of Amplitude Modulation & Demodulation (undermodulation, perfect modulation & over modulation) and also to calculate the modulationindex.4.1.2 Theory:Amplitude modulation (AM) is defined as a process in which the amplitude of thecarrier wave c(t) is varied about a mean value, linearly with the base band signal m(t). AnAM wave may thus be described, in its most general form, as a function of time as follows.S(t) AC [1 Kam(t)] Cos (2 πfCt)Where KaAmplitude Sensitivity of the modulatorS(t)Modulated signalACarrier Amplitudem(t)Message SignalCThe amplitude of Kam(t) is always less than unity, that is Kam(t) 1 for all tIt ensures that the function 1 Kam(t) is always positive.When the amplitude sensitivityKa of the modulator is large enough to make Kam(t) 1 for any t, the carrier wave becomesover modulated, resulting in carrier phase reversals. Whenever the factor 1 Kam(t) crosseszero. The modulated wave then exhibits envelope distortion as shown in fig. below.The absolute maximum value of Kam(t) multiplied by 100 is referred to as the percentagemodulation.Vor percentage modulation max - VminX 100Vmax VminThe carrier frequency fc is much greater than the highest frequency component w ofthe message signal m(t), that isfC W Where W is the message bandwidth.If this condition is not satisfied, envelope cannot be visualized (and therefore detected)satisfactorily.MIST, Hyderabad – ECE DepartmentPage 7

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTPHYSITECH’S modulation and demodulation trainer has a carrier generator, whichgenerates carrier wave of 100KHz when the trainer is switched on.The blocks, carrier generator, modulator and demodulator are provided with built in supplies,no supply connections are to be given externally.m(t) 10tBASE BAND SIGNAL M(T)0-1tAM WAVE FOR K AM(T) 1 FOR ALLTs(t) 10t-1AM WAVE FOR KAM(T) 1 FOR SOME4.1.3 MATLAB Program and description:Program:A input('enter the carrier signal peak')B input('enter the baseband signal peak')f1 input('enter the baseband signal frequency')f2 input('enter the carrier signal frequency')fs input('enter the sampling frequency')t 0:0.001:1;M cos(2*pi*f1*t);N cos(2*pi*f2*t);m B/A;O A*(1 m*M).*N;O1 O;for i 1:length(t)if O1(i) 0O1(i) 0;MIST, Hyderabad – ECE DepartmentPage 8

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTendend[den, num] butter(2,2*pi*f1/fs);M1 filter(den,num,O1);M11 filter(den,num,M1);M12 filter(den,num,M11);M13 Baseband signal')subplot(5,1,2)plot(t,N)title('Carrier signal')subplot(5,1,3)plot(t,O);title('Modulated Carrier')subplot(5,1,4)plot(t,O1)title('Rectified Modulated d Signal')enter the carrier signal peakenter the baseband signal peakenter the baseband signal frequencyenter the carrier signal frequencyenter the sampling frequencyA 5B 2f1 10f2 100fs 1000Baseband ier signal0.70.80.9100.10.20.30.40.50.6Modulated Carrier0.70.80.9100.10.20.30.40.50.60.7Rectified Modulated .910.40.50.6Demodulated Signal0.4MIST, Hyderabad – ECE Department0.50.6Page 9

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST4.1.4: Hardware- Apparatus1.2.3.4.PHYSITECH’s Amplitude modulation and Demodulation trainer kit.Function GeneratorOscilloscope (DSO)Connecting wires-circuit diagram:In amplitude Modulation and demodulation trainer, the IC 8038 is used as a carrier generator.It provides 100KHz sine wave as carrier output at pin2. In modulator section series modulation isused. The first transistor works as RF amplifier and second transistor as the modulator. Thepotentiometer controls the percentage of modulation. In this circuit it is not possible to obtain 100%modulation. This is due to the RF amplifiers junction capacitance which allows RF to feed through tothe output when the transistor is normally shut off. By varying the potentiometer, percentagemodulation is changed. At certain point, the AM waveform is over modulated. This causes severedistortion of the output wave. Diode detector is used in demodulator section, to get demodulatedoutput.Amplitude modulation circuit diagramMIST, Hyderabad – ECE DepartmentPage 10

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTDemodulation circuit diagramPower supplyPower cilloscopePhysitech KitBlock diagram for Experiment-procedure1. Switch on the trainer and check the O/P of carrier generator onoscilloscope.2. Connect around 1KHz with 2 Volts A.F signal at AF I/P to the modulatorcircuit.3. Connect the carrier signal at carrier I/P of modulator circuit.4.Observe the modulator output signal at AM O/P Spring by makingnecessary changes in A.F. signal.5. Vary the modulating frequency and amplitude and observe the effects on themodulated waveform.6. The depth of modulation can be varied using the variable knob(potentiometer) provided at A.F. input.7. The percentage of modulation or modulation factor can be calculated usingthe following formulas.V% of Modulationmax-Vmin X 100VVmaxmax-V Vminminor Modulation factor Vmax Vmin8. Connect the output of the modulator to the input of demodulator circuit andobserve the outputMIST, Hyderabad – ECE DepartmentPage 11

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTExpected waveforms:-MIST, Hyderabad – ECE DepartmentPage 12

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTEXPERIMENT -24.2 DSB-SC modulation and demodulation4.2.1 AIM: To study Balanced modulator for DSB-SC modulation, demodulation.4.2.2Theory:In Balanced modulator, two non-linear devices are connected in the balanced mode, soas to suppress the carrier wave.The Balanced Modulator consists of summing devices (operational amplifiers) and twomatched nonlinear elements. If x(t) is band limited to fx and if fc 2fx, then the band pass filteroutput will be the desired product signal.Figure shows IC that has been specifically designed for use as balanced modulators.Figure is the 1496 balanced modulator which is manufactured by Motorola, National, andSignetics. This device uses a differential amplifier configuration. Its carrier suppression israted at a minimum of -50dB with a typical value -65dB at 500 KHz.PHYSITECH'S trainer contains a balanced modulator using a 1496 integrated circuit.You will verify that it does suppress the carrier and also adjust it for optimum carriersuppression.4.2.3 MATLAB programProgram:f1 input('enter the baseband signal frequency')f2 input('enter the carrier signal frequency')T input('enter the duration over which the signal is to be plotted')fs input('enter the sampling frequency')t 0:T/fs:T;M cos(2*pi*f1*t);N cos(2*pi*f2*t);O M.*N;P O.*N;C input('enter the value of the capacitor of the filter')R 1/(2*pi*f1*C);H (1/(R*C))*exp(-t/(R*C));h conv(H,conv(P,H));t1 t;for i length(t) 1:length(h)t1(i) 0;endsubplot(2,2,1)plot(t,M)title('Baseband Signal')MIST, Hyderabad – ECE DepartmentPage 13

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTsubplot(2,2,2)plot(t,N)title('Carrier Signal')subplot(2,2,3)plot(t,O)title('Modulated d Signal')Result:enter the baseband signal frequencyf1 10enter the carrier signal frequencyf2 100enter the duration over which the signal is to be plottedT 0.4000enter the sampling frequencyfs 1000enter the value of the capacitor of the filterC 1.0000e-008Baseband SignalCarrier Signal110.50.500-0.5-0.5-100.10.20.30.4-1Modulated Carrier120.5100-0.5-1-100.10.20.3MIST, Hyderabad – ECE Department0.4-200.10.20.30.46x 10 Demodulated Signal00.10.20.30.4Page 14

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MIST4.2.4 Hardware:- Apparatus1. PHYSITECH's Balanced Modulator trainer.2. Function Generator (2)3. CRO4. BNC Probes-Circuit diagram X1(t)Non linearity AX(t)C- Cos W Ct- X (t) 2 Y(t)XC(t)BPFCentre fCBW 2fxNon linearityBLOCK DIAGRAM OF BALANCED MODULATORMIST, Hyderabad – ECE DepartmentPage 15

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTProcedure:1. Switch on the trainer.2. Connect 200 Hz sine wave, and 100 KHz square wave from the function Generators. AdjustR1, (1k linear pot). Connect your oscilloscope to the output.3. Vary R1 (1K) both clockwise and counter clockwise. Observe the output.4. Disconnect the SINE input to R1(1K). The output should now be close to zero.5. Increase the oscilloscope's vertical input sensitivity to measure the output voltage. E out carrieronly.6. Set the vertical input control to 1V /cm. Connect the SINE input to R1(1K) and adjust R1 formaximum output without producing clipping. Measure the peak side band output voltage.Epk sidebands .7. Calculate the carrier suppression in dB.Epk sidebanddB -20 LogEout carrier only-Expected waveforms:-MIST, Hyderabad – ECE DepartmentPage 16

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTEXPERIMENT - 34.3 SSB-SC modulation and demodulation (Phase shift method)4.3.1 Aim: To generate SSB using phase method and demodulation of SSB signal usingSynchronous detector.4.3.2 TheoryThe phase shift method makes use of two balanced modulators and two phase shift networksas shown in fig. One of the modulators receives the carrier signal shifted by 900 and themodulating signal with 00 (sine)phase shift, whereas the other receives modulating signalshifted by 900 (co-sine) and the carrier (RF) signal with 00 phase shift voltage.Both modulators produce an output consisting only of sidebands. It will be shown that bothupper sidebands lead the input carrier voltage by 900. One of the lower sidebands leads thereference voltage by 900, and the other lags it by 900. The two lower sidebands are thus out ofphase, and when combined in the adder, they cancel each other. The upper sidebands are inphase at the adder and therefore they add together and gives SSB upper side band signal.When they combined in the subtractor, the upper side bands are cancel because in phase andlower side bands add together and gives SSB lower side band signal4.3.3 MATLAB ProgramProgram:f1 input('enter the base band signal frequency')f2 input('enter the carrier signal frequency')t 0:0.001:0.4;fs input('enter sampling frequency')M cos(2*pi*f1*t);N cos(2*pi*f2*t);DSB1 M.*N;M1 cos(2*pi*f1*t-(pi/2));N1 cos(2*pi*f2*t-(pi/2));DSB2 M1.*N1;USB DSB1-DSB2;LSB DSB1 Base band signal and its Hilbert itle('Carrier Signal and its Hilbert Transform')subplot(5,1,3)plot(t,USB)title('Upper side band signal')MIST, Hyderabad – ECE DepartmentPage 17

Analog Communication Lab Manual , Prepared by Nakka. Ravi Kumar Asst. Prof. & Roopalakshmi Asst. Prof MISTsubplot(5,1,4)plot(t,LSB)title('Lower Side band Signal')USBMULT USB.*N;[den num] butter(2,(2*pi*f1)/fs);Filter1 filter(den,num,USBMULT);Filter2 filter(den,num,Filter1);Filter3 filter(den,num,Filter2);Filter4 r4)title('Demodulated Signal from USB')Results:enter the base band signal frequencyf1 25enter the carrier signal frequencyf2 50enter sampling frequencyfs 1000Base band signal and its Hilbert 250.3Carrier Signal and its Hilbert Transform0.350.400.050.10.150.20.25Upper side band signal0.30.350.400.050.10.150.20.25Lower

The MATLAB program code for each experiment is given in the following section. The students have to write the programs in PC and execute them using MATLAB software and make sure that they get the expected waveforms as shown in this manual. The students are also advised to change certain parameters in the MATLAB program and see

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