Communication Lab Manual                                    SSIT, Tumkur       COMMUNICATION LAB MANUAL                   ...
Communication Lab Manual                                         SSIT, TumkurSRI SIDDHARTHA INSTITUTE OF TECHNOLOGY       ...
Communication Lab Manual                                           SSIT, Tumkur       TESTING OF EQUIPMENTS BEFORE STARTIN...
Communication Lab Manual                                          SSIT, TumkurCIRCUIT DIAGRAM: -II-Order Active Low Pass F...
Communication Lab Manual                                                SSIT, TumkurExperiment No:                        ...
Communication Lab Manual                                       SSIT, TumkurTabulation:High Pass Filter                    ...
Communication Lab Manual                                       SSIT, TumkurTabulation:Low Pass Filter                     ...
Communication Lab Manual                                       SSIT, TumkurCIRCUIT DIAGRAM: -II-Order Active Band Pass Fil...
Communication Lab Manual                                                SSIT, TumkurExperiment No:                        ...
Communication Lab Manual                                         SSIT, TumkurDesign:Specifications:Pass band gain AV = 1.5...
Communication Lab Manual                                          SSIT, TumkurTabulation:Band Elimination Filter          ...
Communication Lab Manual                                                   SSIT, TumkurCIRCUIT DIAGRAM: -            T-Typ...
Communication Lab Manual                                              SSIT, TumkurExperiment No:                          ...
Communication Lab Manual                                                   SSIT, Tumkur           Lattice-Type Attenuator ...
Communication Lab Manual                                          SSIT, TumkurDesign:-    3. Lattice-Type attenuators:-   ...
Communication Lab Manual                                           SSIT, TumkurCIRCUIT DIAGRAM: -              Collector A...
Communication Lab Manual                                        SSIT, TumkurExperiment No:                                ...
Communication Lab Manual                                                SSIT, TumkurTabulation:-ModulationTuned frequency ...
L1  L2
15
Communication Lab Manual                                        SSIT, TumkurWAVE FORMS: -     (a) Carrier wave, (b) Sinuso...
Communication Lab Manual                                    SSIT, TumkurCIRCUIT DIAGRAM: -                        Balanced...
Communication Lab Manual                                          SSIT, Tumkur Experiment No:                             ...
Communication Lab Manual                                           SSIT, TumkurCIRCUIT DIAGRAM: -                         ...
Communication Lab Manual                                         SSIT, Tumkur Experiment No:                              ...
Communication Lab Manual                                                               SSIT, TumkurCircuit Diagram: -Frequ...
Communication Lab Manual                                       SSIT, Tumkur Experiment No:                                ...
Communication Lab Manual                                        SSIT, TumkurDesign-1: -      1. FM modulator circuit.     ...
Communication Lab Manual                                           SSIT, TumkurDesign:-Specification:                     ...
Communication Lab Manual                                    SSIT, TumkurCircuit Diagram: -Radio Receiver: -               ...
Communication Lab Manual                                                 SSIT, TumkurExperiment No:                       ...
Communication Lab Manual                                        SSIT, TumkurCircuit Diagram: -Pre-emphasis                ...
Communication Lab Manual                                           SSIT, Tumkur Experiment No:                            ...
Communication Lab Manual                                               SSIT, TumkurCircuit Diagram: - AM Modulator using M...
Communication Lab Manual                                         SSIT, Tumkur Experiment No:                              ...
Communication Lab Manual                                                   SSIT, TumkurCircuit Diagram: -Pulse amplitude m...
Communication Lab Manual                                          SSIT, TumkurExperiment No:                              ...
Communication Lab Manual                              SSIT, TumkurCircuit Diagram: -Pulse Width modulation and demodulatio...
Communication Lab Manual                                        SSIT, TumkurExperiment No:                                ...
Communication Lab Manual                                                           SSIT, TumkurDesign: -Specifications: - ...
Communication Lab Manual        SSIT, TumkurWaveforms:-Conclusion :-Staff-in-charge:-                           36
Communication Lab Manual                                                  SSIT, TumkurCircuit Diagram: -Pulse Position mod...
Communication Lab Manual                                           SSIT, TumkurExperiment No:                             ...
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Communicationlabmanual

  1. 1. Communication Lab Manual SSIT, Tumkur COMMUNICATION LAB MANUAL FOR V SEMESTER B.E (E & C) (For private circulation only) VISHVESHWARAIAH TECHNOLOGICAL UNIVERSITY NAME: ___________________________ DEPARTMENT OF ELECTRONICS & COMMUNICATION
  2. 2. Communication Lab Manual SSIT, TumkurSRI SIDDHARTHA INSTITUTE OF TECHNOLOGY MARLUR, TUMKUR-572105 CONTENTS 1. II-Order Low Pass and High Pass Active Filters 2. II –Order Band Pass and Band Elimination Filters 3. Attenuators 4. Collector Amplitude Modulation & Demodulation 5. Balanced Modulator 6. Class-C Tuned Amplifier 7. Frequency Modulation and Demodulation 8. Radio Receiver Characteristics 9. Pre & De – Emphasis Networks 10. AM IC Circuit-Modulation and Demodulation 11. Pulse Amplitude Modulation 12. Pulse Width Modulation 13. Pulse Position Modulation 14. Transistor Mixer
  3. 3. Communication Lab Manual SSIT, Tumkur TESTING OF EQUIPMENTS BEFORE STARTING THE CONDUCTION 1. OP AMP Apply sine wave of amplitude 1 volt (1 kHz) as shown in ckt diagram, if IC is good the output be a square wave with peaks at + VSAT and – Vsat. 2. 555 Timer : If IC is good for the applied 5 V D.C supply as in ckt diagram the voltage at pin no. 5 will be 2/3 Vcc (3.3 Volts) 3. Transistor Identify emitter, base and collector of the transistor, with DMM in diode position, if transistor junctions are good it should indicate a low resistance upon forward biasing emitter base junction or collector – base junction and should indicate either OL or 1.(depending on DMM) upon reverse biasing EB or CB junctions. 4. Source impedance of ASG: 1. Connect the DRB with the maximum resistance to ASG as in figure. 2. Adjust the amplitude of sine wave of 5V pp at 1 KHz. 3. Start reducing the resistance of DRB this reduces the output voltage also. Source resistance Rs is that value of DRB resistance when the amplitude of the output signal is half of the initial value. (2.5 V pp)
  4. 4. Communication Lab Manual SSIT, TumkurCIRCUIT DIAGRAM: -II-Order Active Low Pass FilterII-Order Active High Pass FilterDesign:- (LPF & HPF)Assume Pass band gain AV = 2, Cutoff frequency fC = 5KHz Rf 1. Amplifier: AV = 1 + = 2, then Rf = R, choose Rf = R = 10KŸ R 1 2. Filter Circuit : Cut off frequency fC = = 5KHz 2SR1C1 Choose C1 = 0.01Pf then R1 = 3.183 KŸ a 3.3 KŸ Rf = 10KŸ, R1 = 3.3KŸ, C1 = 0.01Pf, Op-amp = PA741 1
  5. 5. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ II – Order Low Pass and High Pass Active FiltersAIM: - Design a second order Butterworth active low pass / high pass filter for agiven cut-off frequency fC = ______Hz. Conduct an experiment to draw frequencyresponse and verify the roll off.PROCEDURE: - 1. Connections are made as shown in the circuit diagram. 2. Apply sine wave i/p signal of peak amplitude 5 volts. 3. Check the gain of non-inverting amplifier by keeping the frequency of the input signal in the pass band of the filter. Note down the output voltage VO max. 4. Keeping the input signal amplitude constant, vary the frequency until the output voltage reduces to 0.707 Vo max, the corresponding frequency is the cut-off frequency (fC) of the filter.To find the Roll-off factor :- 1. For LPF :- Keeping the input signal amplitude constant, adjust the input frequency at 10fC. Note down the output signal amplitude. The difference in the gain of the filter at fC and 10fC gives the Roll-of factor. 2. For HPF :- Keeping the input signal amplitude constant, adjust the input frequency at 0.1fC, note down the output signal amplitude. The difference in the gain of the filter at fC and 0.1fC gives the Roll-of factor.Conclusion: 2
  6. 6. Communication Lab Manual SSIT, TumkurTabulation:High Pass Filter Vi p-p = Volts (Constant) I/P frequency in O/P Voltage Gain magnitude Gain magnitude in DB Hz VO P-P (volts) (Vo/Vi) 20log(Vo/Vi)Roll off = - (G1 - G2) db/decade =Frequency Response for High Pass Filter 3
  7. 7. Communication Lab Manual SSIT, TumkurTabulation:Low Pass Filter Vi p-p = Volts (Constant) I/P frequency in O/P Voltage Gain magnitude Gain magnitude in DB Hz VO P-P (volts) (Vo/Vi) 20log(Vo/Vi)Roll off = - (G1 - G2) db/decade =Frequency Response for Low Pass FilterStaff-in-charge: 4
  8. 8. Communication Lab Manual SSIT, TumkurCIRCUIT DIAGRAM: -II-Order Active Band Pass FilterII-Order Active Band Elimination FilterDesign:- 1. BPF : - R = 10KŸ, Rf = 5.86 KŸ, R1 = 1.989 KŸ, R2 = 3.3 KŸ, C1 = 0.01Pf, C2 = 0.01Pf, Op-amp = PA741 2. BSF : - R = 10KŸ, Rf = 5.86 KŸ, Ra = 3.3 KŸ, Rb = 1.989 KŸ, C1 = 0.01Pf, C2 = 0.01Pf, Op-amp = PA741 5
  9. 9. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ II – Order Band Pass and Band Elimination Active FiltersAIM: - Design a second order band pass and band stop active filter for a givenfrequencies fC1 = ______Hz and fC2 = ______Hz. Conduct an experiment to drawfrequency response and verify the Roll off (Band Width = 3 to 5 KHz).PROCEDURE: - 1. Connections are made as shown in the circuit diagram. 2. Apply sine wave i/p signal of peak amplitude 5 volts. 3. Check the gain of non-inverting amplifier by keeping the frequency of the input signal in the pass band of the filter. Note down the output voltage VO max. 4. Keeping the input signal amplitude constant, vary the frequency on either side of pass band until the output voltage reduces to 0.707 Vo max, the corresponding frequencies are the lower cut-off frequency (fL) and the upper cut-off frequency (fH) of the filter.To find the Roll-off factor :- 1. For LPF :- Keeping the input signal amplitude constant, adjust the input frequency at 10fC, note down the output signal amplitude. The difference in the gain of the filter at fC and 10fC gives the Roll-of factor. 2. For HPF :- Keeping the input signal amplitude constant, adjust the input frequency at 0.1fC, note down the output signal amplitude. The difference in the gain of the filter at fC and 0.1fC gives the Roll-of factor. 6
  10. 10. Communication Lab Manual SSIT, TumkurDesign:Specifications:Pass band gain AV = 1.586, cut -off frequency fH = 5 KHz, fL=8 KHz, BW= 3 KHz1. Amplifier:Voltage gain AV = 1 + Rf / R = 1.586, choose R = 10K:,Then Rf = 5.86 k: (use 5.6 k:+ 220 : std value)2. Filter:Cut - off frequency fH= 1/2S R2C2= 5 KHzChoose C2= 0.01Pf, then R2 = 3.183 k: (Select R2 = 3.3 k:)Cut - off frequency fL = 1/2S R1 C1 = 8 k HzChoose C1= 0.01Pf, then R1= 1.989 k : (Select R1 = (1.5 k: + 470:))Tabulation:Band Pass Filter Vi p-p = Volts (Constant) Frequency Gain in DB O/P Voltage VO PP (volts) Gain (Vo/Vi) Hz 20 log (Vo/Vi) Vomax =fL = G10.1fL = 0.707 Vomax = G210fH=f H= 0.707 Vomax = G2’Roll off = - (G1 - G2) db/decade =Frequency Response for Band Pass Filter 7
  11. 11. Communication Lab Manual SSIT, TumkurTabulation:Band Elimination Filter Vi p-p = Volts (Constant) Frequency Gain in DB O/P Voltage VO PP (volts) Gain (Vo/Vi) Hz 20 log (Vo/Vi) Vomax =fL = G10.1fL = 0.707 Vomax = G210fH=f H= 0.707 Vomax = G2’Roll off = - (G1 - G2) db/decade =Frequency Response for Band Elimination FilterConclusion:Staff-in-charge: 8
  12. 12. Communication Lab Manual SSIT, TumkurCIRCUIT DIAGRAM: - T-Type Attenuator S-Type AttenuatorDesign:-Specification: Vi = 5v, Vo = 2.5v, f = 1KHzT- Type R O (N 1) R O 2N R1 R2 (N 1) (N 2 - 1) RO =RS =600: (Assuming RS of ASG as 600:) N = Attenuation factor = Vi / Vo = 2, Therefore R1 = 200:, R2= 800:, R1 = 200:, R2 = 800:, RL = 600:S- Type R O (N 2 1) R O (N 1) R1 R2 2N (N - 1) RO=RS=600: (Assuming Rs. of ASG as 600:) N = attenuation factor Vi / Vo = 2,Therefore R1 = 450:, R2 = 1.8 K:. R1 = 450:, R2 = 1.8 K:, RL = 600: Type Vi volts VO volts N = Vi/VO T-Type S-Type 9
  13. 13. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Attenuators – T, S, Lattice and O-Pad TypesAIM: - Design the attenuation circuits using T, S, O-Pad and Lattice typenetworks to attenuate a given signal of amplitude _______volts and frequency______Hz to be reduced to 50% of the amplitude. Test the circuit and record theresults.PROCEDURE: - 1. Find the source resistance RS of ASG. 2. Connections are made as shown in the circuit diagram. 3. Adjust the amplitude of the input signal at 5VP-P at 1KHz. 4. Measure the amplitude of the output signal. 5. Find the attenuation factor N.Design:- 1. T-Type attenuators:- (N - 1) R1 RO 200 (N 1) For N=2 and RS = RO = 600Ÿ, then N R2 2R O 800 (N 1) 2 2. S-Type attenuators:- (N 2 - 1) R1 RO 450 2N For N=2 and RS = RO = 600 , then (N 1) R2 RO 1.8K (N 1) 10
  14. 14. Communication Lab Manual SSIT, Tumkur Lattice-Type Attenuator O-Pad Type AttenuatorDesign:-Specification: Vi = 5v, Vo = 2.5v, f = 1KHzLattice- Type R O (N 1) R O 2N R1 R2 (N 1) (N 2 - 1) RO =RS =600: (Assuming RS of ASG as 600:) N = Attenuation factor = Vi / Vo = 2, Therefore R1 = 200:, R2= 800:, R1 = 200:, R2 = 800:, RL = 600:O-Pad Type R O (N 2 1) R O (N 1) R1 R2 2N (N - 1) RO=RS=600: (Assuming Rs. of ASG as 600:) N = attenuation factor Vi / Vo = 2,Therefore R1 = 450:, R2 = 1.8 K:. R1 = 450:, R2 = 1.8 K:, RL = 600: Type Vi volts VO volts N = Vi/VO Lattice-Type O-Pad Type 11
  15. 15. Communication Lab Manual SSIT, TumkurDesign:- 3. Lattice-Type attenuators:- (N - 1) R1 RO 200 (N 1) For N=2 and RS = RO = 600 , then N R2 2R O 800 (N 1) 2 4. O-Pad Type attenuators:- (N 2 - 1) R1 RO 450 2N For N=2 and RS = RO = 600 , then (N 1) R2 RO 1.8K (N 1)Conclusion:-Staff-in-charge:- 12
  16. 16. Communication Lab Manual SSIT, TumkurCIRCUIT DIAGRAM: - Collector AM and Demodulation using Envelop DetectorDesign:-Specifications: -Tuned frequency = fIFT, Assume fIFT = 455 KHz, t = 2.19 PsecRC t, i.e., RC = 100 t = 0.219 msecChoose C = 0.01 Pf, then R = 21.97 KŸ, Select R = 22KŸ (Std. value) 1 1Envelope detector: - ! R1 C1 ! fm fcLet R1C1 = 100 / fc ~ 0.219 msecChoose C1 = 1 Pf, then R1 = 219:, Select R1 = 220 : (std. value) R1 = 220 :, C1 = 1 Pf, R = 22K:, C = 0.01PfCheck point: - x Ensure that AFT is not loading the ASG. x Check the transistor (See self checking) x Adjust the carrier frequency exactly equal to fIFT. x Observe the clamped signal at the base of the transistor. 13
  17. 17. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Collector AM Demodulation using Envelop DetectorAIM:- Conduct an experiment to generate an AM signal using collectormodulation for an fC = _______KHz and fm = _______Hz. Plot the variations ofmodulating signal amplitude v/s modulation index.PROCEDURE: - 1. Connections are made as shown in circuit diagram. 2. By switching off the modulating signal, find the tuned frequency of IFT by varying the carrier signal frequency. 3. Keeping the carrier frequency the tuned frequency of IFT switch on the modulating signal and observe the AM signal at the output of IFT. 4. Find the modulation index ‘m’, the amplitude of the carrier signal Vc and the amplitude of the message signal Vm from the AM output by measuring Vmax and Vmin. Measure Vmax Vmin (i) from the AM o/p (ii) from the Trapezoidal w/f 5. By varying amplitude of the modulating signal note down ‘m’, ‘Vm’, ‘Vc’ from Vmax and Vmin. Make sure that Vc is remaining constant. 6. Plot graph of Vm v/s % m. 7. Connect the envelope detector ckt to the IFT o/p and observe the demodulated signal.Note: To obtain the trapezoidal wave from, feed the modulating signal toChannel ‘A’ and the modulated signal to channel ‘B’ of CRO and time / Div knobin X via A position. 14
  18. 18. Communication Lab Manual SSIT, TumkurTabulation:-ModulationTuned frequency of IFT, fIFT = ____________KHz Vmax - Vmin Vmax - Vmin Vmax VminSl.No Vmax (V) Vmin (V) m= Vm = Vc = Vmax Vmin 2 2Demodulation Sl.No Vo (V) fo (Hz) (Vmax Vmin) (Vmax Vmin) (Vmax Vmin) m , Vm , Vc (Vmax Vmin) 2 2 m L1 L2
  19. 19. L1 L2
  20. 20. 15
  21. 21. Communication Lab Manual SSIT, TumkurWAVE FORMS: - (a) Carrier wave, (b) Sinusoidal wave, (c) Amplitude modulated signal.Conclusion:-Staff-in-charge:- 16
  22. 22. Communication Lab Manual SSIT, TumkurCIRCUIT DIAGRAM: - Balanced Modulator (Using Diodes)D1, D2, D3, D4 – OA79Waveforms- 17
  23. 23. Communication Lab Manual SSIT, Tumkur Experiment No: DATE: __/__/____ Balanced Modulator (Using Diodes) Aim:- Rig up a balanced modulator (Ring modulator) circuit. Test its operation and record the waveforms.Procedure: - 1. Connections are made as shown in the circuit diagram. 2. Apply the modulating signal (Sine wave) with frequency fm and the carrier signal (square wave) with frequency fC (fC = 10 f m). 3. Observe the phase reversal of 1800 at each Zero crossing of modulating signal in the output DSBSC signal. Tabulation:- Sl.No. VC Volts fC Hz Vm Volts fm Hz Conclusion:- Staff-in-charge:- 18
  24. 24. Communication Lab Manual SSIT, TumkurCIRCUIT DIAGRAM: - Class-C Tuned Amplifier 2 VO PDC VDC u IC PAC f Hz VO volts VDC volts IC mA RL ohms PAC mW 8R L mW PDCDesign:-Specification:Frequency f = 150 KHz, t = 6.66 usec R1C1 t, i.e, R1C1 = 100 t Choose C1 = 0.01Pf, the R1 = 66.6 K:.Select R1 = 68 K: (std value)Tank ckt: f 150KHz S If C = 0.001Pf, then L = 1.125 mH a1mH. Then Factual = 159 KHz. R1 = 68K:, C1 = 0.01Pf, C= 0.001Pf, L = 1mHCheck points: - x Check the transistor (See self checking) x Adjust i/p frequency exactly equal to tuned frequency. x Observe the clamped signal at the base of the transistor. 19
  25. 25. Communication Lab Manual SSIT, Tumkur Experiment No: DATE: __/__/____ Class-C Tuned Amplifier Aim:- Design and test a Class-C Tuned amplifier to work at fO = ______KHz (Center frequency). Find its maximum efficiency at optimum load.Procedure: - 1. Connections are made as shown in circuit diagram. 2. Adjust the input frequency of the signal to get maximum output at the load. 3. For the applied DC voltage adjust the amplitude of input sine wave signal so that the output signal peak to peak amplitude is twice of the DC voltage (without any distortion). 4. Vary the load resistance RL around 10 KW. 5. Note Vo, VDC, IC and RL to find PAC and PDC hence the efficiency. (Note: While measuring Vo, short the Ammeter connection) Ideal graph:- Conclusion :- Staff-in-charge:- 20
  26. 26. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Frequency Modulation Circuit: -Frequency Demodulation Circuit: - BT 2 Sl.No fc Hz fm Hz Vm volts fcmax Hz fcmin Hz G1 Hz G2 Hz G Hz fm 1 f cmax - f c , 2 f c - f cmin , Max of 1 or 2 21
  27. 27. Communication Lab Manual SSIT, Tumkur Experiment No: DATE: __/__/____ Frequency Modulation Demodulation Aim:- Design and conduct a suitable experiment to generate an FM wave using IC8038. Find the modulation index E and the bandwidth of operation BT. Display the various waveforms.Procedure: - 1. Connections are made as shown in the circuit diagram. 2. By switching off the modulating signal m(t), note down the carrier sine wave of frequency of fC at pin 2 of IC 8038. 3. Apply the modulating signal m(t) with suitable amplitude to get undistorted FM signal. 4. Note down maximum and minimum frequency of the carrier in FM signal (i.e., fC max and fCmin) 5. Find the frequency deviation, modulation index operation band width. 6. Test the demodulator circuit by giving FM output from IC8038 as an input for the demodulator circuit. 22
  28. 28. Communication Lab Manual SSIT, TumkurDesign-1: - 1. FM modulator circuit. Let carrier frequency fC = 3 KHz, fC = 0.3/R Ct. Choose R = 10KŸ = Ra = Rb, then Ct = 0.01Pf. Take RL = 10KŸ, CC = 0.01Pf. 2. Demodulator using PLL. Let fO = fC = 3 KHz, fO = 1.2/4R1C1. Choose C1 = 0.001Pf, then R1 = 100KŸ. Filter design: Let fm = 1 KHz = 1/2SRC Choose C = 0.1Pf, then R = 1.59 KŸ a 1.5 KŸDesign - 2: - 1. FM modulator circuit. Let carrier frequency fC = 5 KHz, fC = 0.3/R Ct. Choose R = 10KŸ = Ra = Rb, then Ct = 0.001Pf. Take RL = 10KŸ, CC = 0.01Pf. 2. Demodulator using PLL. Let fO = fC = 3 KHz, fO = 1.2/4R1C1. Choose C1 = 0.001Pf, then R1 = 100KŸ. Filter design: Let fm = 1 KHz = 1/2SRC Choose C = 0.1Pf, then R = 1.59 KŸ a 1.5 KŸWave Form: - 23
  29. 29. Communication Lab Manual SSIT, TumkurDesign:-Specification: 0.3 Carrier frequency fC = 3 kHz, f c RC t Choose R= 10 KŸ, Ra = Rb, then Ct = 0.01Pf (use DCB) Ra = Rb = 10 KŸ, RL = 10 KŸ, Ct = 0.01Pf (use DCB). R = 82 KŸ, CC = 0.01Pf.Note: - Usually the carrier frequency of the FM signal is in the range of 100s of KHz, but is chosen in terms of 1s of KHz to enable proper measurement of frequency deviating G.Check Points: - Ensure that a square wave and a triangular wave at pin 9 and 3 of IC 8038 respective.Conclusion :-Staff-in-charge:- 24
  30. 30. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Radio Receiver: - R = 10K:, C = 0.1Pf, RL = 100:Selectivity: -fm = _____Hz, %m = ______ Sl.No fC Hz Vo voltsFidility: -fm = _____Hz, %m = ______ Sl.No fC Hz Vo voltsSensitivity: -fm = _____Hz, %m = ______ fC Hz Vi volts Vo volts 25
  31. 31. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Radio Receiver CharacteristicsAim:- Plot the sensitivity/selectivity/fidelity graphs of a given AM Broadcast receiver inMW band by conducting suitable experiment.Procedure: - 1. Connections are made as shown in the circuit diagram. 2. Ensure the Radio Receiver is in MW band. 3. Adjust the modulation index of AM signal at 30 % fm = 400 Hz. 4. Let the receiver be tuned to 800 KHz. (can be anywhere between 540 KHz 1450 KHz). 5. Keeping the carrier frequency of the AM signal at 800 KHz, observe the demodulated signal and note down its amplitude.Selectivity: - 1. Repeat the step 5 by changing the carrier frequency at 805, 810, 815 and 795, 790, 785 KHz. 2. Plot a graph of carrier frequency of AM signal Vs the amplitude of the output signal (Vo Vs fc).Sensitivity: - 1. Repeat the steps 1 to 5. 2. Vary the amplitude of the AM signal to get a standard value of output voltage (Volts). All the other parameters are kept constant (i.e., fc, fm, m). Note the change in the amplitude of the output signal. 3. Repeat step 9 for different values of fc. 4. Plot a graph of amplitude of input signal v/s carrier frequency of AM signal (Vi v/s fc).Fidelity: - 1. Repeat the steps 1 to 5. 2. Vary the frequency of the modulating signal keeping all other parameters constant (i.e., fc, VAM, m). Note the change in the amplitude of the output signal. 3. Plot a graph of amplitude of output signal Vs frequency of the modulating signal (Vo Vs fm).Conclusion:-Staff-in-charge:- 26
  32. 32. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Pre-emphasis De-emphasisTABULATION: - Pre-Emphasis N/W Vo Normalized gain Normalized Gain f Hz Vo volts Gain Vi Gain/Go In dbDe-Emphasis N/W Vo Normalized gain Normalized Gain f Hz Vo volts Gain Vi Gain/Go In db 27
  33. 33. Communication Lab Manual SSIT, Tumkur Experiment No: DATE: __/__/____ Pre-emphasis and De-emphasis Networks Aim:- Design and conduct an experiment to test a pre-emphasis and de-emphasis circuit for 75Ps between 2.1KHz to 15KHz and record the results..Procedure: - 1. Connections are made as shown in the circuit diagram. 2. Apply a sine wave of 5Vpp amplitude, vary the frequency and note down the gain of the circuit. 3. Plot a graph of normalized gain Vs frequency. Design: - 1. Pre-emphasis circuit. Given f1 = 2.1 KHz, f2 = 15KHz. f1 = 1/2SrC, f2 = 1/2SRC Choose C = 0.1Pf then r = 820Ÿ and R = 100Ÿ. Also r/R = Rf/R1, then R1 = 2.2KŸ and Rf = 15KŸ. 2. De-emphasis circuit. fC = 1/2SRdCd. Choose Cd = 0.1Pf and fC = f1 = 2.1KHz Then Rd = 820Ÿ. Conclusion :- Staff-in-charge:- 28
  34. 34. Communication Lab Manual SSIT, TumkurCircuit Diagram: - AM Modulator using MC1496AM Demodulator using MC1496 Tabulation:- Vmax - Vmin Vmax - Vmin Vmax Vmin Sl.No Vmax (V) Vmin (V) m= Vm = Vc = Vmax Vmin 2 2 29
  35. 35. Communication Lab Manual SSIT, Tumkur Experiment No: DATE: __/__/____ AM – IC Circuit (Modulation Demodulation) Aim:- Using IC1496, rig up an AM modulation and Demodulation circuit. Test its operation and record the waveforms.Procedure: - a) AM Modulation 1. Connections are made as shown in the circuit diagram. 2. Give the modulating signal of 2VPP (1KHz). 3. Give the carrier signal of 1VPP (600KHz). 4. Note down the AM modulated signal at pin 6 and also at the emitter of the buffer (emitter follower). 5. Change the amplitude levels of the modulating signal, keeping fC and fm as constant and find the depth of modulation. b) AM Demodulation 1. Give the AM wave to pin1 of MC1496. 2. Also give the AM wave from the buffer o/p. 3. Note the demodulated signal at pin 12 of MC1496. Design: - Select Vdc = +12V, IC = 3mA. RL = + Vdc/ IC = 4KŸa3.9KŸ. Vbe = 700mV, I = 160mA, Voltage at pin 5 = 1.7V. Vbias = (-8+1.7) = -6.3V RS = Vbias/I = 6.3/160mA = 7KŸa6.8KŸ Conclusion :- Staff-in-charge:- 30
  36. 36. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Pulse amplitude modulation and demodulationDesign: -Specifications: -IC = 1ma, hFE = 100, VCEsat = 0.3 V, VBEsat = 0.7v (assume), fm = 100hz. 1. Biasing: - Vm(t) = IC *RC + VCEsat ----- 1 Let Vm(t) = 2.5 v w.f peak + 3v DC shift = 5.5 V peak signal Then Rc = 5.2 kŸ, select Rc = 4.7 k Ÿ(std. Value). Vc (t) = IB*RB + VBEsat --------2 Let Vc(t) = 2 Vpp ( 1 V peak ) , Since IB = Ic / hFE = 10uA Then RB = 30 k Ÿ Select RB = 22 k Ÿ (Std. Value). 2. Filter: - Cut off frequency of the filter fo fm Choose fo = 500 Hz = 1 / 2 S RC Choose C = 0.1 P f, then R = 3.3 k Ÿ Rc = 4.7 K Ÿ RB = 22k Ÿ, R = 3.3k Ÿ, C = 0.1Pf Check Points: - 1. Ensure that square wave signal at the base of the transistor should have amplitude VJ. 2. Ensure that m (t) is having sufficient dc shift. Tabulation: - VC(pp) volts fC (Hz) Vm(pp) volts fm (Hz) Reconstructed output VO volts fO (Hz) 31
  37. 37. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Pulse Amplitude Modulation DemodulationAim:- Conduct an experiment to generate PAM signal and also design a circuit todemodulate the obtained PAM signal and verify sampling theorem. Plot therelevant waveforms.Procedure: - 1. Connections are made as shown in the circuit diagram. 2. Apply the square wave carrier signal of 2V peak to peak amplitude with frequency fc = 5 kHz. 3. Apply sine wave modulating signal with frequency fm = 100 Hz with 5 Vpp amplitude and 3 V DC shift (use function generator). 4. Observe the PAM output. 5. Observe the demodulated signal at the output of the low pass filter. 6. Repeat the steps 2 to 5 for fc = 2 fm fc 2 fm.Waveforms:Conclusion :-Staff-in-charge:- 32
  38. 38. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Pulse Width modulation and demodulation Pulse Width Demodulation 33
  39. 39. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Pulse Width Modulation DemodulationAim:- Conduct an experiment to generate PAM signal and also design a circuit todemodulate the obtained PAM signal and verify sampling theorem. Plot therelevant waveforms.Procedure: - 1. Connections are made as shown in the circuit diagram. 2. Keeping the modulating signal with minimum amplitude, observe the output of astable multivibrator with 50 % duty cycle at frequency fc. 3. Apply the modulating signal with frequency fm and the amplitude less than the critical amplitude observe the PWM signal. 4. Verify the variation of width of the pulses with respect to clamped modulating signal (at point A).To find the critical amplitude: - As the amplitude of the modulating signal is increase the width of thepulses during the negative half of the modulating signal keeps on reducing andthat at the positive half of the modulating signal is increased the width of thepulses during the negative half of the modulating signal keeps on reducing andthat at the positive half of the modulating signal keeps on increasing. 34
  40. 40. Communication Lab Manual SSIT, TumkurDesign: -Specifications: - Frequency fc = 1 KHz, duty cycle: 50 % T = 1 ms, Ton = Tb= 0.5 msI) Astable multivibrator: - Where RcH = charging resistance, RDCH = Discharging Resistance, Rf = Diode forward resistance Ct = timing capacitor TON = 0.69 (RCH + Rf ) Ct Toff = 0.69 (RDCH + Rf) Ct Ton = Toff = 0.5 ms Choose Ct = 0.1 Pf, then (RCH + Rf) = (RDCH + Rf) = 7.246 k: Assuming Rf of diode = 100:, Then RCH = RDCH = 7.146 k: (use 6.8 k: + 330: std value)II) Clamping ckt Negative peak of the modulating signal clamped to zero Rc 1 /fm, fm = 100Hz RC = 100 /fm, choose C= 10 f, then R = 100K. RCH = RDCH = (6.8K + 330 ), R = 100K , Ct = 0.1 f, C = 10 f.Check points: -With modulating signal zero, the voltage at pin 5 of 555 timer should be 2/3 VCC.Ensure that modulating signal is clamped. Tabulation: - Unmodulated carrier PWM Output Demodulator Dynamic Modulating Ton Toff Max.width Min.width fc Hz range frequency VO(V) fO(Hz) ms ms ms ms volts fm Hz 35
  41. 41. Communication Lab Manual SSIT, TumkurWaveforms:-Conclusion :-Staff-in-charge:- 36
  42. 42. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Pulse Position modulation and demodulation Design: m(t) = 1KHz, T = 1ms T = RC, Let C = 0.01uf Then R = 1Ÿ Pulse Position DemodulatorDesign: -Specifications: - 1. Monostable Multivibrator: - PW = 1.1 Rch Ct Choose Ct = 0.01 Pf, then Rch = 18.18 k : (std. Value) 2. Differentiator : - Rs * Cs 1 / fc Choose Rs * Cs = 0.01 ms, Choose Cs = 0.001Pf, then Rs = 10k : Rch = 18 k:. Ct = 0.01Pf, Rs = 10 k:, Cs = 0.001PfCHECK POINTS: -x With modulating signal zero, the voltage at pin 5 of 555 timer should be 2 /3 Vcc.x Ensure that wave form at pin 2 of 555 timer should have a trailing edge going below 1 /3 Vcc. 37
  43. 43. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Pulse Position Modulation DemodulationAim:- Conduct an experiment to generate PAM signal and also design a circuit todemodulate the obtained PAM signal and verify sampling theorem. Plot therelevant waveforms.Procedure: - 1. Connections are made as shown in the circuit diagram. 2. Check the working of 555 timer as a monostable multivibrator by giving an unmodulated PWM signal. Verify the pulse width of output signal for the designed value. 3. By applying the PWM signal note the change in the position of the pulses i.e. PPM signal. 4. Critical amplitude of the modulating signal is that value of m(t) at which the pulse in PPM just disappears.Waveforms:-Conclusion:-Staff-in-charge:- 38
  44. 44. Communication Lab Manual SSIT, TumkurCircuit Diagram: -Transistor MixerDesign: -Specifications: - VCC = 6V, VCE = 5V, assume IC = 1ma, hFE = 100, VBEsat = 0.6v. VCC = VCE + IE * RE Since IE ~ IC, then RE = 1 K: Vb = IB * RB + VBEsat + IE * RE ------ (1) Where Vb = VCC * R2 /R1 + R2, RB = R1 + R2, RB = R1 * R2 /R1 + R2 From eq (1) it can be found that R1 ~ 2.5 R2, Choose R2 = 18 K:, then R1 45 K: R1 = 47 K:, R2 = 18 K:, RE = 1K:, CC = 0.1:f, CE = 10PfCheck points: -During the mixer operation under on circumstance the frequency of local oscillator orfrequency of the carrier should be kept at tuned frequency of IFT. (i.e., fLO = fIFT = fS)Tabulation: -fIFT = __________, Vmax = ___________, Vmin = _________, %m = __________Operation fS Hz fLO Hz fO Hz fLO + fS HzUp ConversionDown Conversion 39
  45. 45. Communication Lab Manual SSIT, TumkurExperiment No: DATE: __/__/____ Transistor MixerAim:- Conduct an experiment to generate PAM signal and also design a circuit todemodulate the obtained PAM signal and verify sampling theorem. Plot therelevant waveforms.Procedure: -1. Connections are made as shown in the circuit diagram.2. Keeping the amplitude of the local oscillator in minimum position, find the tuned frequency of IFT (fIFT) by varying the carrier frequency (fs) of the input AM signal.Down conversion: -3. Adjust the carrier frequency of the AM signal more than the tuned frequency of IFT, now adjusting the local oscillator frequency (fLO = fs + fIFT) (Note: local oscillator amplitude z 0). Observe the output AM signal with carrier frequency at fIFT.4. Repeat the step 3 for different carrier frequencies.Up conversion: -5. Adjust the carrier frequency of the AM signal less than the frequency of IFT, now adjusting the local oscillator frequency (f LO = fS + f IFT) (Note : local oscillator amplitude z 0). Observe the output AM signal with carrier frequency at f IFT.6. Repeat the step 5 for different carrier frequencies.Formulas: Zo = Vo rms/Io, gc = Vo rms/ (Vi rms.Zo)Conclusion:-Staff-in-charge:- 40

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