SEM: V EXAM MARKS: 50 BRANCH: EC IA MARKS: 25 SUBJECT: ANALOG COMMUNICATION & LIC LAB SUB CODE: 06ECL58

Transcription

1 LIST OF EXPERIMENTS SEM: V EXAM MARKS: 50 BRANCH: EC IA MARKS: 25 SUBJECT: ANALOG COMMUNICATION & LIC LAB SUB CODE: 06ECL58 1) Active low pass & high pass filters second order 2) Active band pass & band reject filters second order 3) Schmitt trigger design and test a Schmitt trigger circuit for the given values of UTP and LTP 4) Frequency synthesis using PLL 5) Design and test R-2R DAC using OP-AMP. 6) Design and test the following circuits using IC 555 (a) Astable multivibrator for given frequency and duty cycle (b) Monostable multivibrator for given pulse width W. 7) Class-C single tuned amplifier 8) Amplitude modulation using Transistor/FET (Generation and Detection) 9) Pulse Amplitude modulation and Detection 10) PWM and PPM 11) Frequency modulation using 8038/ ) Precision Rectifiers- both Full Wave and Half Wave

2 CYCLE WISE EXPERIMENTS SEM: V EXAM MARKS: 50 BRANCH: EC IA MARKS: 25 SUBJECT: ANALOG COMMUNICATION & LIC LAB SUB CODE: 06ECL58 CYCLE - 1 1) Active low pass & high pass filters second order 2) Active band pass & band reject filters second order 3) Schmitt trigger design and test a Schmitt trigger circuit for the given values of UTP and LTP CYCLE - 2 4) Precision Rectifiers- both Full Wave and Half Wave 5) Design and test R-2R DAC using OP-AMP. 6) Design and test the following circuits using IC 555 CYCLE - 3 (a) Astable multivibrator for given frequency and duty cycle (b) Monostable multivibrator for given pulse width W. 7) Class-C single tuned amplifier 8) Amplitude modulation using Transistor/FET (Generation and Detection) 9) Pulse Amplitude modulation and Detection CYCLE ) PWM and PPM 11) Frequency modulation using 8038/ ) Frequency synthesis using PLL

3 EXPERIMENT N0 1(A) SECOND ORDER ACTIVE LOW PASS FILTER Aim: To obtain the frequency response of an active low pass filter for the desired cut off frequency. Components required: Resistors- 33KΩ, 10KΩ, 5.86 KΩ Capacitors 2200pF, opamp μa 741 Design For a 2 nd order Filter, F H = 1 / 2π RC Hz Let F H = 2 KHz and R = 33 KΩ = 1 / 2 π C C = 2200 pf The pass band gain of the filter, A F = (1+R f / R 1) For a second order filter, A F = 1.586, Let R 1 = 10KΩ R F = 5.86 k Ω

4 4 7 ANALOG COMMUNICATION LAB MANUAL, V SEM EC L o w p a s s c i r c u i t D i a g r a m R 1 R f 1 0 K 1 0 k R k R 3 3 k u A V + V - V o V 1 0 C C P f P f 0 0 Procedure: 1. Before wiring the circuit, check all the components. 2. Design the filter for a gain of and make the connections as shown in the circuit diagram. 3. Set the signal generator amplitude to 10V peak to peak and observe the input voltage and output voltage on the CRO 4. By varying the frequency of input from Hz range to KHz range, note the frequency and the corresponding output voltage across pin 6 of the op amp with respect to the gnd. 5. The output voltage (V O) remains constant at lower frequency range. 6. Tabulate the readings in the tabular column. 7. Plot the graph with f on X-axis and gain in db on Y axis. Result:

5 EXPERIMENT N0 1(B) SECOND ORDER ACTIVE HIGH PASS FILTER Aim: To obtain the frequency response of an active high pass filter for the desired cut off frequency. Components required: Resistors- 33KΩ, 10KΩ, 5.86 KΩ Capacitors 2200pF, opamp μa 741 Design: For a 2 nd order Filter, F L = 1 / 2π RC Hz Let F L = 2 KHz and R = 33 KΩ = 1 / 2 π C C = 2200 pf The pass band gain of the filter, A F = (1+R f / R 1 ) For a second order filter, A F = 1.586, Let R 1 = 10KΩ R F = 5.86 k Ω

6 4 7 ANALOG COMMUNICATION LAB MANUAL, V SEM EC H i g h p a s s c i r c u i t D i a g r a m R 1 R f 1 0 K 1 0 k 0 C C u A V + V - V o V P f P f R R 3 3 k 3 3 k Procedure: 1. Before wiring the circuit, check all the components. 2. Design the filter for a gain of and make the connections as shown in the circuit diagram. 3. Set the signal generator amplitude to 10V peak to peak and observe the input voltage In addition, output voltage on the CRO. 4. By varying the frequency of input from HZ range to KHA range, note the frequency And the corresponding output voltage across pin 6 of the op amp with respect to the gnd. 5-.The output voltage (V O ) remains constant at lower frequency range. 6. Tabulate the readings in the tabular column. 7. Plot the graph with f on X-axis and gain in db on Y axis. Result:

7 EXPERIMENT N0 2(A) SECOND ORDER ACTIVE BAND PASS FILTER Aim: To obtain the frequency response of an active band pass filter for the desired cut off frequency and to verify the roll off. Components required: Design: Resistors- 33KΩ, 10KΩ, 5.86 KΩ Capacitors 2200pF, opamp μa 741 For a 2 nd order Filter, F= 1 / 2π RC Hz (i) For High pass section Let F L = 2 KHz and R = 33 KΩ = 1 / 2 π C C = 2200 pf (ii) For low pass section Let F H = 10 KHz And R = 33 kω = 1 / 2 π C C = 470 pf The pass band gain of the filter, A F = (1+R f / R 1 ) For a second order filter, A F = 1.586, Let R 1 = 10KΩ R F = 5.86 k Ω The Center frequency F C = F H F L Hence F C = 4.5 KHz

8 ANALOG COMMUNICATION LAB MANUAL, V SEM EC Circuit Diagram:- B A N D P A S S F I L T E R R 1 R f R 1 R f 0 V V 1 C R k C 2 3 R - + V + u A V k 6 R V o 0 C 1 0 k ' R 2 3 C ' V + u A V k V o Procedure: 1. Before wiring the circuit, check all the components. 2. Design the two filters for the desired cut off frequencies and make the connections as shown in the circuit diagram. 3. Set the signal generator amplitude to 10V peak to peak and observe the input voltage And output voltage on the CRO. 4. By varying the frequency of input from Hz range to KHz range, note the frequency And the corresponding output voltage across pin 6 of the op amp with respect to the gnd. 5-.The output voltage (V O ) remains constant at lower frequency range. 6. Tabulate the readings in the tabular column. 7. Plot the graph with f on X-axis and gain in db on Y axis. Result:

9 EXPERIMENT N0 2(B) SECOND ORDER ACTIVE BAND REJECT FILTER Aim: To obtain the frequency response of an active band reject filter for the desired cut off frequency and to verify the roll off. Components required: Design: Resistors- 33KΩ, 10KΩ, 5.86 KΩ Capacitors 2200pF, opamp μa 741 For a 2 nd order Filter, F= 1 / 2π RC Hz (ii) For High pass section Let F L = 10 KHz and C = 0.01 µ F, F L = 1 / 2π RC Hz = 1 / 2 π R R = 1.59 k Ω (ii) For low pass section Let F H = 2 KHz And R = 33 k Ω = 1 / 2 π C C = 2200 pf The pass band gain of the filter, A F = (1+R f / R 1 ) For a second order filter, A F = 1.586, Let R 1 = 10K Ω R F = 5.86 k Ω

10 ANALOG COMMUNICATION LAB MANUAL, V SEM EC Circuit Diagram:- B A N D R E J E C T F I L T E R R 1 R f 1 0 k 5. 8 K H I G H P A S S u A C C S E C T I O N u F u F R R k 0 R ' R ' 3 2 V + V - R 0 R f = 5. 8 K L O W P A S S S E C T I O N - + V + u A V - R 2 = 1 0 k R 4 = 1 0 k R 5 = 3. 3 K R 3 = 1 0 k S U M M E R V + u A V - C ' C ' 0

11 Procedure: 1. Before wiring the circuit, check all the components. 2. Design the two filters for the desired cut off frequencies and make the connections as shown in the circuit diagram. 3. To simplify the design, set R 2 =R 3 =R and C 2 =C 3 =C then choose a value of C <=1 µf Calculate the value of R using the equation R= 1 / (2 π f H C ) R =1 / (2 π f L C ) 4. Because of the equal resistor R 2 =R 3 and C 2 =C 3 values the pass band voltage gain A F = (1+R f / R 1 ) of the second order low pass and high pass filter has to be equal To i.e. R f =0.586 R 1.This gain is necessary to guarantee Butterworth filter response. Hence choose the value of R1 <100K and calculate the value for RF 5. Set the signal generator amplitude to 10V peak to peak and observe the input voltage And output voltage on the CRO. 6. By varying the frequency of input from HZ range to KHA range, note the frequency And the corresponding output voltage across pin 6 of the op amp with respect to the Ground. 7-.The output voltage (V O ) remains constant at lower frequency range. 8. Tabulate the readings in the tabular column. 9.Plot the graph with f on X-axis and gain in db on Y axis. Result:

12 EXPERIMENT NO. 3 DESIGN AND TEST A SCHMITT TRIGGER CIRCUIT FOR THE GIVEN VALUES OF UTP AND LTP AIM: Design a square wave generator for a given UTP and LTP. COMPONENTS REQUIRED: Op-Amp - µ A741 1 Resistors 1kΩ - 1, 2.2kΩ - 1 THEORY: Schmitt Trigger is also known as Regenerative Comparator. This is a square wave generator which generate a square based on the positive feedback applied. As shown in the fig. below, the feedback voltage is V a. The input voltage is applied to the inverting terminal and the feedback voltage is applied to the non-inverting terminal. In this circuit the op-amp acts as a comparator. It compares the potentials at two input terminals. Here the output shifts between + V sat and V sat. When the input voltage is greater than V a, the output shifts to V sat and when the input voltage is less than V a, the output shifts to + V sat. Such a comparator circuit exhibits a curve known as Hysterisis curve which is a plot of V in vs V 0. The input voltage at which the output changes from + V sat to V sat is called Upper Threshold Point (UTP) and the input voltage at which the output shifts from V sat to + V sat is called Lower Threshold Point (LTP). The feedback voltage V a depends on the output voltage as well as the reference voltage. A Zero Cross Detector is also a comparator where op-amp compares the input voltage with the ground level. The output is a square wave and inverted form of the input.

13 ANALOG COMMUNICATION LAB MANUAL, V SEM EC CIRCUIT DIAGRAM: Schmitt Trigger + V c c U U A R 1 V o V i n - V c c 2. 2 k R 2 1 k + V r e f Zero Cross Detector + V c c U 2 V i n V o U A V c c DESIGN: Given UTP = + 4V and LTP = - 2V Let I 1 be the current through R 1 and I 2 be the current through R 2. W.K.T the current into the input terminal of an op-amp is zero. I 1 + I 2 = 0

14 I 1 = ( V 0 V a ) / R 1 I 2 = ( V ref V a ) / R 2 ( V 0 V a ) / R 1 + ( V ref V a ) / R 2 = 0 Va = ( V 0 R 2 + V ref R 1 ) / ( R 1 + R 2 ) When V 0 = + V sat, V a = UTP When V 0 = - V sat, V a = LTP [ ( V sat R 2 ) / ( R 1 + R 2 ) ] + [ ( V ref R 1 ) / ( R 1 + R 2 ) ] = UTP (1) [ ( - V sat R 2 ) / ( R 1 + R 2 ) ] + [ ( V ref R 1 / (R 1 + R 2 ) ] = LTP (2) (1) (2) ( 2 V sat R 2 ) / ( R 1 + R 2 ) = UTP LTP = 6V Simplifying this equation we get, 7 R 2 = 3 R 1 Assume R 2 = 1kΩ R 1 = 2.2kΩ (1) + (2) ( 2 V ref R 1 ) / ( R 1 + R 2 ) = UTP + LTP = 2V Simplifying the above equation, we get V ref = 1.4V PROCEDURE: 1. Rig up the connections as shown in the circuit diagram. 2. Give a sinusoidal input of 10V peak to peak and 500 Hz from a signal generator. 3. Check the output at pin no. 6 (square wave). 4. Coincide the point where the output shifts from + Vsat to Vsat with any point on the input wave. 5. Measure the input voltage at this point. This voltage is UTP. 6. Coincide the point where the output shifts from Vsat to + Vsat with any point on the input wave. 7. Measure the input voltage at this point. This voltage is LTP. 8. Another method of measuring UTP and LTP is using the Hysterisis Curve.

15 V in 5 ANALOG COMMUNICATION LAB MANUAL, V SEM EC 9. To plot the hysterisis curve give channel 1 of CRO to the output and channel 2 of CRO to the input. 10. Press the XY knob. Adjust the grounds of both the knobs. 11. Measure UTP and LTP as shown in the fig. and check whether it matches with the designed values. WAVEFORMS: 4 0 t Schmitt Trigger V t - 10 Zero Cross Detector V t

16 HYSTERISIS CURVE: V 0 + V sat LTP UTP V in - V sat NOTE: The same circuit can be designed for different values of UTP and LTP. For UTP = 4V and LTP = 2V, R 1 = 10kΩ, R 2 = 1kΩ and V ref = 3.3V. Check whether the circuit works properly for these values. RESULT:

17 EXPERIMENT N0 4 CLASS C - TUNED AMPLIFIER AIM: To design and test a class c tuned amplifier to work at f0 = 734 khz and to find its max efficiency at optimum load COMPONENTS REQUIRED THEORY: SLNO COMPONENTS RANGE QUANTITY 1. Dc Regulated Power Supply +5V 1 2. Ammeter 0-10MA 1 3 Inductor 100MH 1 4. Capacitors 470Pf mf mf 1. 5 Resistors 15k Transistor BF CR0 Probe Springs - 1 Springs - 10 Class C Tuned Amplifier Amplify Large signal at radio frequency with better frequency response. Efficiency is more than 78% and it increases with decrease in conduction angle. It is used in radio transmitters and receivers with class c operation the collector current flows for less than half a cycle. A parallel resonant circuit can filter the pulses of collector current and produce a pure sine wave of output voltage. The max efficiency of a tuned class c amplifier is 100% the Ac voltage drives the base and an amplified and inverted signal is then capacitive coupled to the load resistance. Because of the parallel resonant circuit, the output voltage is max at resonant frequency f0 = 1/2xLC On either side of the voltage gain drops off shown class C is always intended to amplify a narrow ban of frequency.

18 DESIGN: F O = 1/2π LC Let L = 100 µ F and C = 470 pf F O = 1 / F O = 734 KHz T = 1/F O T = 1/ T = 1.36 µ S Use Standard Value R B C B 10 T O Where T O = 1/F O R B C B = 10 1/ F O C B = 10 / F O R B Let R B = 15 k Ω C B = 10 / C B = 908 pf C B = 1000 Pf CONDUCTION ANGLE θ = T e / T Where T e = Time period across emitter T = time period across collector DUTY CYCLE D = ω / T Or D = θ / 360 0

19 TABULAR COLUMN: ( V in = 5 volts) Sl.No R ( L Ω ) V OUT (V) I dc (ma) P ac = V O2 /8R L P dc = VCC I dc η = P ac / P dc % η PROCEDURE 1. Make the connections as shown in circuit diagram set input signal frequency to the tuned circuit resonant frequency 2. Vary input voltage to get an undistorted approx sine wave by keeping load resistance to a fixed value by varying load resistance note down the output voltage and calculate current Iac 3. Tabulate the reading in tabular column\ 4. Plot the graph of rl along x axis and n across y axis From the graph, determine optimum load to calculate conduction angle the output is taken across emitter RESULT A class C tuned amplifier Is designed to work at a reasonable frequency fo 734 khz The max optimum load is 400 and conduction angle 0 = 77.

20 EXPERIMENT N0 5 EXPT R-2R DAC USING OP-AMP AIM: network. Demonstrate Digital to Analog conversion for digital (BCD) inputs using R-2R COMPONENTS REQUIRED: Op-amp - µ A741 Resistors 10kΩ kΩ - 6 Dual power supply, Multimeter, bread board, connecting wires. THEORY: Nowadays digital systems are used in many applications because of their increasingly efficient, reliable and economical operation. Since digital systems such as microcomputers use a binary system of ones and zeros, the data to be put into the microcomputer have to be converted from analog form to digital form. The circuit that performs this conversion and reverse conversion are called A/D and D/A converters respectively. D/A converter in its simplest form uses an op-amp and resistors either in the binary weighted form or R-2R form. The fig. below shows D/A converter with resistors connected in R-2R form. It is so called as the resistors used here are R and 2R. The binary inputs are simulated by switches b 0 to b 3 and the output is proportional to the binary inputs. Binary inputs are either in high (+5V) or low (0V) state.

21 ANALOG COMMUNICATION LAB MANUAL, V SEM EC The analysis can be carried out with the help of Thevenin s theorem. The output voltage corresponding to all possible combinations of binary inputs can be calculated as below. V 0 = - R F [ (b 3 /2R) + (b 2 /4R) + (b 1 /8R) + (b 0 /16R) ] Where each inputs b 3, b 2, b 1 and b 0 may be high (+5V) or low (0V). The great advantage of D/A converter of R-2R type is that it requires only two sets of precision resistance values. In weighted resistor type more resistors are required and the circuit is complex. As the number of binary inputs is increased beyond 4 even D/A converter circuits get complex and their accuracy degenerates. Therefore in critical applications IC D/A converter is used. Some of the parameters must be known with reference to converters. They re resolution, linearity error, settling time etc. Resolution = 0.5V / 2 8 = 5 / 256 = WAVEFORMS: R - 2 R L A D D E R N E T W O R K F = 2 k v c c U 1 0 R R R R 2 R 2 R 2 R 2 R 2 R v c c U A V o L S B b 0 b 1 b 2 b 3 M S B 0 V r e f 0

22 DESIGN: The equation for output voltage is given by V 0 = - R F [ (b 3 /2R) + (b 2 /4R) + (b 1 /8R) + (b 0 /16R) ] V 0 = - R F. V ref [ (b 3 /2R) + (b 2 /4R) + (b 1 /8R) + (b 0 /16R) ] Case (i) If b 0 b 1 b 2 b 3 = for 0.5 volts change in output for LSB change = - 20 x 10 3.V ref [ (1 / (16 x )) ) V ref = 4V Case (ii) If V ref = 5V and b 0 b 1 b 2 b 3 = , then V 0 = [ (0 + (1/ ( )) ) ] V 0 = V TABULAR COLUMN: Inputs Output voltage b 3 b 2 b 1 b 0 Theoretical Practical

23 PROCEDURE: 1. Test the op-amp and other components before rigging up the circuit. 2. Rig up the circuit as shown in the fig. 3. Apply different combination of binary inputs using switches. 4. Observe the output at pin no. 6 of op-amp using multimeter or CRO. 5. Tabulate the readings as shown. 6. Calculate the resolution of the converter. RESULT:

24 ASTABLE MULTIVIBRATOR AIM: To design and verify the operation of astable multivibrator using 555 Timer for given frequency and duty cycle. APPARATUS REQUIRED: Timer Resistors 10kΩ kΩ k- 1 Capacitors 0.01µ F-1 0.1µ F-1

25 Signal Generator, DC power supply, CRO and connecting wires THEORY: A 555 timer is a monolithic timing circuit that can produce accurate and highly stable time delays or oscillations, some of the applications of 555 are square wave generator, astable and monostable multivibrator. Astable multivibrator is a free running oscillator has two quasi stable state in one state o/p voltage remains low for a time interval of Toff and then switches over to other state in which the o/p remains high for an interval of Ton the time interval Ton and Toff are determined by the external resistors a capacitor and it does not require an external trigger, when the power is switched on the timing capacitor begins to charge towards 2/3 Vcc through R A & R B, when the capacitor voltage has reached this value, the upper comparator of the timer triggers the flip flop in it and the capacitor begins to discharge through R B when the capacitor voltage reaches 1/3 Vcc the lower comparator is triggered and another cycle begins, the charging and discharging cycle repeats between 2/3 Vcc and 1/3Vcc for the charging and discharging periods t 1 and t 2 respectively. Since the capacitor charges through R A and R B and discharges through R B only the charge and discharge are not equal as a consequence the output is not a symmetrical square wave and the multivibrator is called an asymmetric astable multivibrator CIRCUIT DIAGRAM: ASSYMETRIC MULTIVIBRATOR R A 8 4 V c c + 5 V R B 7 6 D I S C H A R G E T H R E S H O L D VCC RESET O U T P U T 3 2 T R IG G E R 1 GND 5 C R O CONTROL C u f 0

26 SYMMETRIC MULTIVIBRATOIR Vcc+5V Ra 8 VC C 4 RE SE T D1 Rb D2 7 DISCHARGE 555D OUTPUT 3 O/P C1 6 2 THRESHOLD TRIGGER GN D CO NT RO L 1 5 C2 0 DESIGN: ASSYMETRIC: Given f = 1khz Duty cycle = 60% T = 0.693(Ra + 2Rb) C F = 1.45/ [(Ra + 2Rb) C] Duty cycle = (Ra + Rb)/Ra + 2Rb) 1K = 1.45/ [(Ra + 2Rb) 0.1*10-6 ] Ra + 2Rb = 14.5K Ra + Rb = 8.7K

27 Assume Ra = 4.7K Rb = 9.57K 10K SYMETRIC Given f = 1khz Duty cycle = 50% Charging time = Discharging time T = TON =TOFF T = 0.693(Ra + Rb) C F = 1.45/ [(Ra + Rb) C] Duty cycle = (Ra + Rb)/Ra + Rb) 1K = 1.45/ [(Ra + Rb) 0.1*10-6 ] Ra + 2Rb = 14.5K Since the duty cycle is 50%, Ra = Rb 2Ra = 14.5K Ra = 7.25K 6.8K Rb = 7.25K 6.8K PROCEDURE: 1. Connections are made as shown in the circuit diagram 2. Switch on the DC power supply unit 3. Observe the wave form on CRO at pin 3 and measure the o/p pulse amplitude 4. Observe the wave form on CRO at pin 6 and measure Vcmax and Vc min 5. Verify that Vcmax=2/3Vcc and Vc min=1/3 Vcc

28 6. Calculate the duty cycle D, o/p frequency and verify with specified value TABULAR COLUMN Ra Rb C F(theo) = 1.45/(Ra + Rb) Ton Toff T F DY WAVEFORMS: Vc at pin 6 2/3VCC Upper threshold voltage Lower threshold 1/3VCC 0V t Vout 5V at pin 3 0V Ton Toff t Result:

29 MONOSTABLE MULTIVIBRATOR AIM: To design and verify the operation of monostable multivibrator using 555 Timer for given Pulse width. APPARATUS REQUIRED: Timer Resistors 10kΩ - 1 Capacitors 0.01µ F-1 0.1µ F-1 Signal Generator, DC power supply, CRO and connecting wires THEORY: Monostable multivibrator has a stable state and a quasi stable state, the output of it is normally low and it corresponds to reset of the flip flop in the timer, on the application of

30 ANALOG COMMUNICATION LAB MANUAL, V SEM EC external negative trigger pulse at pin 2 the circuit is triggered and the flip flop in the timer is set which in turn releases the short across C and pushes the output high, At the same time the voltage across C rises exponentially with the time constant R A C and remains in this state for a period R A C even if it is triggered again during this interval, When the voltage across the capacitor reaches 2/3 Vcc, the threshold comparator resets the flip flop in the timer which discharges C and the output is driven low the circuit will remain in this state until the application of the next trigger pulse CIRCUIT DIAGRAM V c c + 5 V B Y R t R A I n p u t C t 2 T R I G G E R VCC 6 3 O U T P U T C GND RESET T H R E S H O L D D I S C H A R G E CONTROL C R O u f 0

31 DESIGN: Given Tp = 1ms F = 1KHz T = 1.1R C Let C = 0.1uF R = (1*10-3 ) / (1.1*0.1*10-6 ) R = 9.09 K 10K PROCEDURE: 1. Rig up the circuit as shown in the figure after checking all the components. 2. Apply suitable inputs to the astable multivibrator (DC & Trigger inputs) 3. Observe the waveform across the timing capacitor in one channel and the output in the other channel.. 4. Verify the designed values and the repeat the above procedure for different set of values. TABULAR COLUMN R C Tp = 1.1RC Tp(prac)

32 WAVEFORMS: Vc c T Input trigger pulses Trigger pulses at pin 2 t Capacitor voltage Vc at pin 5 Output pulse at pin 3 t Upper threshold voltage 2/3*Vcct T p T t RESULT:

33 EXPERIMENT N0 7 COLLECTOR MODULATION Aim: - To generate AM signal, information signal given the collector. Also, demodulate it. Measure the modulation index using two different methods. Components Required:- IFT, AFT, SL 100/BF 194 transistor, resistors, capacitors, diode 0A79, connecting board, connecting wires and CRO. Circuit Diagram:-

34 VCC +6v AFT (GREEN) MESSAGE SIGNAL OPEN FM = 2kHz VAMPL = 5v(p-p) IFT (RED) o/p AM wave 0.01microF BF k microF -6v COLLECTOR AMPLITUDE MODULATION Theory: - The modulator is a linear power amplifier that takes the low-level modulating signal and amplifies it to a high power level. The modulating output signal is coupled through a modulating transformer to the Class C amplifier. The secondary winding of the modulation transformer is connected in series with collector supply voltage Vcc of the Class C amplifier. This means that modulating signal is applied in series with the collector power supply supply voltage of the Class C amplifier applying collector modulation.

35 In the absence of the modulating input signal, there will be zero modulation voltage across the secondary of the transformer. Therefore, the collector supply voltage will be applied directly to the Class C amplifier generating current pulses of equal amplitude and output of the tuned circuit will be a steady sine wave. When the modulating signal occurs, the a.c. voltage across the secondary of the modulating transformer will be added to and subtracted from the collector supply voltage. This varying supply voltage is then applied to the Class C amplifier resulting in variation in the amplitude of the carrier sine wave in accordance with the modulating signal. The tuned circuit then converts the current pulses into an amplitude-modulated wave. Assuming value of C=0.01μF Substituting value of C and f m =1 khz, we get R=9.5kΩ 10kΩ m= (Vmax-Vmin)/ (Vmax+Vmin) V m = (Vmax-Vmin)/2 Design:- Let f m = khz m= RC>>t c or RC (1/mω m ) Or RC/3= (1/mω m ) ω m= 2πf m Waveform:-

36 Procedure:- 1. Design the collector modulator circuit assuming f m =1 khz and m=0.5 take C=0.01μF. 2. Before wiring, check all components using multimeter. 3. Make connections as shown in figure. 4. Set the carrier frequency to 2v and 455 khz. 5. Set the modulating signal to 5v and 1 khz. 6. Keep carrier amplitude constant and vary the modulating voltage in steps and measure V max and V min, and calculate modulation index. 7. Tabulate the reading taken. 8. Feed AM output to Y-plates and modulation signal yo X-plates of CRO. Obtain trapezoidal pattern. 9. Plot the graph of modulating signal versus modulation index. Observations:- V max in volts V min in volts μ(mod index) V m in volts

37 Graph:- m Vm Result: - EXPERIMENT N0 8 ENVELOPE DETECTOR Aim: - conduct an experiment to demonstrate envelope detector for an input AM signal. Plot variation of output signal amplitude versus depth of modulation. Components required -0A79 diodes, resistors, capacitors, function generator, connecting board and CRO.

38 0A79 0.6v AM SIGNAL 2 VAMPL = 2v FC = 455kHz MOD = 0.5 FM = 2kHz 0.1microF 1 6k output ENVELOPE DETECTOR Theory: - An envelope detector is a simple and highly effective device that is well suited for the demodulation of a narrow band AM wave, for which the percentage modulation is less than 100%. In an envelope detector, the output of the detector follows the envelope of the modulated signal, hence the name to it. Figure above shows the circuit of an envelope detector. It consists of a diode and a resistor-capacitor filter. This circuit is also known as diode detector. In the positive, half cycle of the AM signal diode conducts and current flows through R whereas in the negative half cycle, diode is reverse biased and no current flows through R. As a result, only positive half of the AM wave appears across RC. During the positive half cycle, the diode is forward biased and the capacitor C charges up rapidly to the peak value of the input signal. When the input signal falls below this value, the diode becomes reverse biased and the capacitor C slowly discharges through the load resistor R L. The discharging process continues until the next positive half cycle when the input signal becomes greater than the voltage across capacitor, the diode conducts again and the process is repeated. Circuit Diagram:- Waveforms:-

39 Design:- Let f m =1 khz m= f c =455 khz C=0.01µf Let R c >>f c Or RC=3/ (mω m ) Substituting value of C and ω m in above equation we get, Therefore, R=10 kω Procedure:- 1. Before wiring the circuit, check all the components using the multimeter. 2. Make the connections as shown in the figure. 3. From the function generator apply the AM wave to the input. 4. Vary the modulation index knob, note down the Vmax and Vmin simultaneously, and note down the output voltage the output V O in steps. 5. Modulation index is given by m= (Vmax-Vmin)/ (Vmax+Vmin) 6. Plot the graph V o versus modulation index m. Tabular column:- Modulation index m Output in volts V o

40 Graph:-

41 Vo m

42 RESULT:- EXPERIMENT N0 9 FREQUENCY MODULATION USING IC 8038 AIM:To design and conduct an experiment to generate FM wave IC8038 with f= 33 khz. COMPONENTS REQUIRED: SL. NO COMPONENTS RANGE QUANTITY IC 8038 Signal generator Resistors (0-100)MHz 10 k ohms 4.7k ohms, 22k ohms, 82k ohms CRO probes Voltage supply Capacitors Mother board 12 V 0.1 micro F 1.00 micro F

43 DESIGN: Let R=Ra=Rb Let f=33 khz f= 3*(2*Ra-Rb)/10*Rac*Ra Substituting for R&C in above equation, we get f=0.3/rc

44 Let R=10k ohms Therefore C =0.001*10-6 F Calculation Frequency deviation =Fmax-Fmin Modulation index= Frequency deviation / f m GRAPH:

45 THEORY: Frequency modulation: FM is that form of angle modulation in which the instantaneous frequency is varied linearly with the message signal. The IC 8038 waveform generator is a monolithic integrated circuit capable of producing high accuracy sine square, triangular, saw tooth and pulse waveforms with a minimum number of external components. Block diagram of ICL 8038 Basis principle of IC 8038 The operation of IC 8038 is based on charging and discharging of a grounded capacitor C, whose charging and discharging rates are controlled by programmable current generators I a and I b. When switch is at position A, the capacitor charges at a rate determined by current source I a. Once the capacitor voltage reaches Vut, the upper comparator (CMP 1) triggers and reset the flip-flop out put. This causes a switch position to change from position A to B. Now, capacitor charge discharging at the rate determined by the current sink I b. Once the capacitor reaches lower threshold voltage, the lower comparator (CMP 2) triggers and set the flip-flop output. This causes the switch position to change from position B to A. And this cycle repeats. As a result, we get square wave at the output of Flip flop and triangular wave across capacitor. The triangular wave is then passed through the on chip wave shaper to generate sign wave.

46 To allow automatic frequency controls, currents I a and I b are made programmable through an external control voltage Bi. For equal magnitudes of Ia and I b, output waveforms are symmetrical conversely, when two currents are unequal, output waveforms are asymmetrical. By making, one of the currents much larger than other we can get saw tooth waveform across capacitor and rectangular waveform at the output of flip-flop. Working The frequency of the waveform generator is direct function of the dc voltage at terminal 8. By altering this voltage, frequency modulation is performed. For small deviations, the modulating signal can be applied to pins, merely providing dc-dc coupling with a capacitor. An external resistor between pins 7and 8 is not necessary but it can be used to increase input impedance from about 8k. The sine wave has relatively high output impedance. The circuit may use a simple op_amp follower to provide a buffering gain and amplitude adjustments. The IC 8038 is fabricated with advanced monolithic technology, using Schottky-barrier diodes and thin film resistors, and the output is stable over a wide range of temperatures and supply variations. PROCEDURE: 1. Rig up the circuit as shown in the figure. 2. Apply +12,-12V from the supply. 3. Observe the sinusoidal waveform at pin 2.It should be same as design carrier frequency.

47 4. Switch on signal generator and apply the signal amplitude of 0.5V and frequency of 1 khz. 5. Observe the output between pin 2 and ground. 6. Sketch the waveforms. Show the graph of message carrier and modulation signal. RESULT: The frequency modulation is seen and the transmission bandwidth was found to be khz. EXPERIMENT NO 11 PULSE AMPLITUDE MODULATION AIM: To conduct an experiment to generate PAM signal and design a circuit to demodulate the PAM signal COMPONENTS REQUIRED: SLNO COMPONENTS RANGE QUANTITY 1 Transistor SL Resistor 22 K Ω 3 4.7K Ω 1 10 K Ω Ω 1 3 Capacitor Function Generator 0.1 µ f 1 4 Diode 0A Signal Generator CRO 30MHZ 1 THEORY: In PAM the amplitude of the pulses are varied in accordance with the modulating signal. (Denoting the modulating signal as m (t). PAM is achieved simply by multiplying the carrier with the m (t) signal. The balanced modulators are frequency used as multipliers for this purpose. The Output is a series of pulses, the amplitude of which vary in proportion to the modulating signal. The form of pulse Amplitude modulation shown in the circuit diagram is referred to as natural PAM because the tops of the pulses follow the shape of the modulating signal. As shown in fig, the samples are taken at regular interval of time. If enough samples are

48 taken, a reasonable approximation of the signal being sampled can be constructed at the receiving end. This is known as PAM. P U L S E A M P L I T U D E M O D U V c c + 5 V Q 1 C 1 0 K B E S L K C ( t ) 4. 7 K V o m ( t ) D E M O D U L A T I O N D 1 O A 7 9 R C P A M I / P D E M O D u F

49 DESIGN Fc>> 1/RC i.e., R>1/FcC Let Fc =15 khz and C=0.1μF Therefore R~680Ω PROCEDURE: 1. Make the Connections as shown in circuit diagram. 2. Set the carrier amplitude to 2 Vpp and in the frequency of 5 khz to 15 khz. 3. Set the i/p Signal amplitude to around 1V (p-p) and frequency to 2 khz. 4. Connect the CRO at the emitter of the transistor and observe the Pam waveform. 5. Now connect the O/p(i.e. PAM) signal to the demodulation circuit and observe the signal if it matched plot the waveform RESULT: The circuit to generate PAM signal and to demodulate the PAM signal were designed and the waveform were observed.

50 EXPERIMENT NO 12 PULSE WIDTH MODULATION AIM : To Conduct an Experiment to generate a PWM Signal for the given analog signal of frequency less than 1 khz and to design a demodulation circuit. COMPONENTS REQUIRED THEORY: SLNO COMPONENTS RANGE QUANTITY 1 Op- Amp ( µ A 741) ± 12 V 3 2 Resistors 10 K Ω 3 15K Ω 1 3 Capacitor Function 0.01 µ f 2 Generator 4 DC Regulated Power supply ± 12 V 1 5 Signal Generator CRO Probes CRO 30MHZ 1 8 Springs Pulse width Modulation (PWM) is also known as Pulse duration Modulation (PDM). Three variations of PWM are possible. In One variation, the leading edge of the pulse is held constant and change in the pulse width with signal is measured with respect to the leading edge. In other Variable, the tail edge is held in constant and w.r.t to it, the pulse width is measured in the third variation, the centre of the pulse is held constant and pulse width changes on either side of the centre of the pulse. The PWM has the disadvantage when compared to PDM that its pulses are of varying width and

51 therefore of varying power content, this means the transmitter must be powerful enough to handle the max width pulses. P W M M O D U L A T I O N m ( t ) 1 k H z 1 0 k 1 0 K R 1 c ( t ) 2 > 1 k H 1z 0 k V + u A V V + u A V P W O / P 0 0 D E M O D U L A T I O N R V + P W 1 M 0 k u A P W M I / P C 2 O / P u 3F 1 n + V - R 2 = 1 5 k C u F m ( t 0 0

52 DESIGN RC >>T Time Period Tp=0.1ms R 1 C 1 =Tp Let R 1 =10K C 1 =0.01µF Fc=1/2пR2C2 Fc=1KhZ Let R 2 =15KΩ C 2 =0.01µF PROCEDURE: 1. Make the connections as shown in the circuit diagram, 2. Set the carrier amplitude to 2vpp and frequency 1 KHz (Say 1 5khz) 3. Set the signal amplitude to 2 Vpp and frequency < 1khz (Say 560 khz) 4. Observe the o/p signal at pin 6of 2 nd op-amp and observe the variation in pulse width by varying the modulating signal amplitude. 5. Draw PWM Waveform 6. Now connect the output to the demodulate circuit and observe the signal it matches with m(t) RESULT: The circuit to generate a PWM signal is designed and the output waveforms are observed. In addition, a circuit to demodulate the PWM signal is designed and the output is observed.

53 ANALOG COMMUNICATION LAB MANUAL, V SEM EC EXPERIMENT NO 13 PULSE POSITION MODULATION 4 7 AIM : To conduct an experiment to generate PPM signal of pulse width(between 100 ms and 200ms) for a given modulating signal. COMPONENTS REQUIRED THEORY : SLNO COMPONENTS RANGE QUANTITY 1 Op amplifier Ma Timer Resistors 10 K Ω 1 18 K Ω 1 5 Capacitor 0.01mf 2 6 Dc Regulated Power Supply + 5v 1 7 Function Generator CRO 30mhz 1 In this type of modulation, the amplifier and width of the pulses is kept constant while the position of each pulse with reference to the position of a reference pulse is changed according to the instantaneous sampled value of the modulating signal. Pulse position modulation is observed from pulse width modulation. Any pulse has a leading edge and trailing edge in this system the leading edge is held in fixed position while the trailing edge varies towards or away from the leading edge in accordance to the instantaneous value of sampled signal m ( t ) V c c + 5 V 1 k H z 1 0 k 1 0 K B Y R t R A R 1 c ( t ) > 2 K H 1 z 0 k u A V + V V + u A V - 6 P W O / P I n p u t C t C R O 2 3 T R I G G E R O U T P U T GND VCC CONTROL RESET T H R E S H O L D D I S C H A R G E C u f

54 DESIGN Pulse Width = 200μs Tp=1.1 RC Let C=0.01μF Therefore R=18KΩ PROCEDURE 1. Make the connections as shown in the circuit diagram. 2. Set the carrier amplitude to around 4v (p-p) and frequency = 1khz. 3. se the signal amplitude to around 2v (p-p) and frequency around (< 1khz) 4. Observe the output signal at pin no : 3 of the 555 timer and also observe the variation in pulse position by varying the modulating signal amplitude 5. Draw the PPM waveform RESULT The circuit to generate a PPM signal of pulse width 200 ms is designed and the output waveform of PPM was observed.

55 EXPT PRECISION RECTIFIER AIM: Design and test the working of Full Wave Precision Rectifier using op-amp. COMPONENTS REQUIRED: OP-Amp - µ A741-1 Resistors - 10kΩ kΩ kΩ - 1 Diodes - BY127-2 THEORY: Precision Rectifier name itself suggests that it rectifies even lower input voltages i.e. voltages less than 0.7v (diode drop). A rectifier is a device, which converts AC voltage to DC voltage. Precision rectifier converts AC to pulsating DC. Normal rectifiers using transformers cannot rectify voltages below 0.7v, so we go for precision rectifiers. In this circuit the diodes are placed in such a way that one diode is forward biased in the positive half cycle and the other in the negative half cycle. Consider the circuit diagram shown below. Here in the positive half cycle D 1 is forward biased and D 2 is reverse biased. The simplified circuit will act as two inverted amplifiers connected in series. Hence the total gain will be the product of individual gains. During the negative half cycle, D 1 is reverse biased and D 2 is forward biased. Hence the simplified circuit is an inverting amplifier connected in series with a non-inverting amplifiers. Hence the output

56 will be inverted and a DC output (unidirectional) is obtained.the precision rectifier we are using is a full wave rectifier. CIRCUIT DIAGRAM: R 1 = 2 2 k R = 1 0 k R = 1 0 k V i n 2 R = 1 0 k 3 G N D D 1 + V c c U A V c c - V c c - V c c D 2 6 V o u U A DESIGN: R 2 = 3. 3 K Given : Vo = +0.5V in the +ve cycle = +0.1V in the -ve cycle During the +ve half cycle the simplified circuit will be as shown below. v V = (-R 1 / R) V in V 0 = (-R / R)V

57 = (-R / R) (-R 1 / R) V in V 0 = (R 1 /R) V in As V 0 = 0.5V, V in = 0.25V R 1 / R = 0.5 / 0.25 = 2 Assume R = 10kΩ, then R 1 = 20kΩ NOTE: A DRB can be used in the place of R 1 and that resistance can be adjusted to 20KΩ or 22KΩ resistance can be used. During the negative half cycle, the simplified circuit will be shown below. I 1 R 1 R V R I 2 V i n A R = 1 0 k B I G N D V c c 6 U A V c c - V c c V c c 6 V o u U A R 2 point A I 1 = I 2 + I 3 From virtual ground concept V A = 0 ( V B = 0) V Applying KCL at I 1 = V in / R, I 2 = -V / ( R 1 +R ), I 3 = -V / R 2 V in / 10k = - V ( (1 / 30k) + (1 / R 2 ) ) As V in = / 10k = -V ( (1 / 30k) + (1 / R 2 ) ) (1) As the second Op-Amp works as a non inverting amplifier V 0 = (1 + (R / R 1 ) + R) V = (1 + (10k / 30k) ) V (2) From (1) V = / 10k = - V ( (R k) / (30k x R 2 ) )

58 V = 0.75 R 2 / ( R k ) Substituting this in the equation (2) we get V 0 = (1 + 1 / 3) (0.75 R 2 / (R k) ) 0.1 R 2 + 3k = R R 2 = 3k R 2 = 3.3kΩ PROCEDURE: 1. Rig up the circuit as shown in the circuit diagram. 2. Give an input of 0.5V peak to peak (sine wave). 3. Check and verify the designed values. 4. Design the same circuit for a different set of values. WAVEFORMS: V in t 0.5 V t RESULT:

59 Viva questions for analog communication lab 1. Define the word communication. 2. What are the basic components of electronic communication. 3. What is Transmitter. 4. What is receiver 5. What is communication channel? 6. State two types of communication? 7. What is baseband signal? 8. What is baseband transmission? 9. What is the need for modulation? 10.Define the carrier signal? 11.What is the classification of modulation? 12.What is frequency deviation? 13.Define noise? 14.Define the basic sources of noise? 15.What is shot noise? 16.Define signal to noise ratio? 17.What is noise factor? 18.State the equation for noise factor for cascade connection? 19.Define amplitude modulation? 20.Define modulation index? 21.State the bandwidth required for amplitude modulation? 22. What is frequency domain display? 23. What is time domain display? 24. What is maximum power of sideband of AM? 25. What is the maximum total power of AM wave? 26. Define a high level modulation? 27. Define a low level modulation? 28.Why amplitude modulation is used for broadcasting? 29.What is the position of the operating point of class-c? 30.What is the advantage of SSB over DSB-SC? 31.What is the function of Transistor mixer? 32.What is the principle of Envelope detector?

60 33.Where SSB transmission is used? 34.State sampling theorem? 35.What is Nyquist criteria? 36.What is Roll-off factor? 37.Define the order of the filter? 38.What are the classification of filters? 39.Differentiate between butter-worth and cheybeshev filter? 40.Define selectivity? 41.What is quadrature null effect? 42.Define FM? 43.What is percentage modulation? 44.Define pre-emphasis and De-emphasis? 45.What are the advantages of using pre and de-emphasis? 46.List of some advantages of FM over AM? 47.Define wideband FM? 48.What is carson s rule? 49.State advantages of PWM? 50.State various Pulse modulation methods?