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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
Communication Lab Manual SSIT, Tumkur
SRI 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
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)
Communication Lab Manual SSIT, Tumkur
CIRCUIT DIAGRAM: -II-Order Active Low Pass Filter
II-Order Active High Pass Filter
Design:- (LPF & HPF) Assume Pass band gain AV = 2, Cutoff frequency fC = 5KHz
1. Amplifier: AV = 1 + RRf = 2, then Rf = R, choose Rf = R = 10K�
2. Filter Circuit : Cut off frequency fC = 112
1CR�
= 5KHz
Choose C1 = 0.01�f then R1 = 3.183 K� � 3.3 K�
Rf = 10K�, R1 = 3.3K�, C1 = 0.01�f, Op-amp = �A741
1
Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
II – Order Low Pass and High Pass Active Filters
AIM: - Design a second order Butterworth active low pass / high pass filter for a given cut-off frequency fC = ______Hz. Conduct an experiment to draw frequency response 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
Communication Lab Manual SSIT, Tumkur
Tabulation:
High Pass Filter Vi p-p = Volts (Constant) I/P frequency in
Hz O/P Voltage VO P-P (volts)
Gain magnitude (Vo/Vi)
Gain magnitude in DB 20log(Vo/Vi)
Roll off = - (G1 - G2) db/decade = Frequency Response for High Pass Filter
3
Communication Lab Manual SSIT, Tumkur
Tabulation: Low Pass Filter Vi p-p = Volts (Constant) I/P frequency in
Hz O/P Voltage VO P-P (volts)
Gain magnitude (Vo/Vi)
Gain magnitude in DB 20log(Vo/Vi)
Roll off = - (G1 - G2) db/decade = Frequency Response for Low Pass Filter
Staff-in-charge:
4
Communication Lab Manual SSIT, Tumkur
CIRCUIT DIAGRAM: -II-Order Active Band Pass Filter
II-Order Active Band Elimination Filter
Design:-
1. BPF : - R = 10K�, Rf = 5.86 K�, R1 = 1.989 K�, R2 = 3.3 K�, C1 = 0.01�f, C2 = 0.01�f, Op-amp = �A741
2. BSF : - R = 10K�, Rf = 5.86 K�, Ra = 3.3 K�, Rb = 1.989 K�, C1 = 0.01�f, C2 = 0.01�f, Op-amp = �A741
5
Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
II – Order Band Pass and Band Elimination Active Filters
AIM: - Design a second order band pass and band stop active filter for a given frequencies fC1 = ______Hz and fC2 = ______Hz. Conduct an experiment to draw frequency 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
Communication Lab Manual SSIT, Tumkur
Design: Specifications: Pass band gain AV = 1.586, cut -off frequency fH = 5 KHz, fL=8 KHz, BW= 3 KHz 1. 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= 1/2� R2C2= 5 KHz Choose C2= 0.01�f, then R2 = 3.183 k� (Select R2 = 3.3 k�) Cut - off frequency fL = 1/2� R1 C1 = 8 k Hz Choose C1= 0.01�f, then R1= 1.989 k � (Select R1 = (1.5 k� + 470�)) Tabulation: Band Pass Filter Vi p-p = Volts (Constant)
Frequency Hz O/P Voltage VO PP (volts) Gain (Vo/Vi) Gain in DB
20 log (Vo/Vi)
Vomax =
fL = G1
0.1fL = 0.707 Vomax = G2 10fH=
fH= 0.707 Vomax = G2’ Roll off = - (G1 - G2) db/decade = Frequency Response for Band Pass Filter
7
Communication Lab Manual SSIT, Tumkur
Tabulation: Band Elimination Filter Vi p-p = Volts (Constant)
Frequency Hz O/P Voltage VO PP (volts) Gain (Vo/Vi) Gain in DB
20 log (Vo/Vi)
Vomax =
fL = G1
0.1fL = 0.707 Vomax = G2 10fH=
fH= 0.707 Vomax = G2’ Roll off = - (G1 - G2) db/decade = Frequency Response for Band Elimination Filter
Conclusion:
Staff-in-charge:
8
Communication Lab Manual SSIT, Tumkur
CIRCUIT DIAGRAM: -T-Type Attenuator �-Type Attenuator
Design:-
Specification: Vi = 5v, Vo = 2.5v, f = 1KHz T- Type
1)-(N2NRR
1)(N1)(NRR 2
O2
O1 �
��
�
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�
�- Type
1)-(N1)(NRR
2N1)(NRR O
2
2O
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
�-Type
9
Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Attenuators – T, �, Lattice and O-Pad Types
AIM: - Design the attenuation circuits using T, �, O-Pad and Lattice type networks to attenuate a given signal of amplitude _______volts and frequency ______Hz to be reduced to 50% of the amplitude. Test the circuit and record the results.
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:-
For N=2 and RS = RO = 600�, then 800�
1)(NN2R R
200�1)(N1)-(NR R
2O2
O1
��
�
��
�
2. �-Type attenuators:-
For N=2 and RS = RO = 600�, then 1.8K�
1)(N1)(NR R
450�2N
1)-(NR R
O2
2
O1
���
�
��
10
Communication Lab Manual SSIT, Tumkur
Lattice-Type Attenuator O-Pad Type Attenuator
Design:-
Specification: Vi = 5v, Vo = 2.5v, f = 1KHz Lattice- Type
1)-(N2NRR
1)(N1)(NRR 2
O2
O1 �
��
�
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
1)-(N1)(NRR
2N1)(NRR O
2
2O
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
Communication Lab Manual SSIT, Tumkur
Design:-
3. Lattice-Type attenuators:-
For N=2 and RS = RO = 600�, then 800�
1)(NN2R R
200�1)(N1)-(NR R
2O2
O1
��
�
��
�
4. O-Pad Type attenuators:-
For N=2 and RS = RO = 600�, then 1.8K�
1)(N1)(NR R
450�2N
1)-(NR R
O2
2
O1
���
�
��
Conclusion:-
Staff-in-charge:-
12
Communication Lab Manual SSIT, Tumkur
CIRCUIT DIAGRAM: -Collector AM and Demodulation using Envelop Detector
Design:-Specifications: -
Tuned frequency = fIFT, Assume fIFT = 455 KHz, t = 2.19 �sec
RC >> t, i.e., RC = 100 t = 0.219 msec
Choose C = 0.01 �f, then R = 21.97 K�, Select R = 22K� (Std. value)
Envelope detector: - fc1 C R
fm1
11
Let R1C1 = 100 / fc ~ 0.219 msec
Choose C1 = 1 �f, then R1 = 219�, Select R1 = 220 � (std. value)
R1 = 220 �, C1 = 1 �f, R = 22K�, C = 0.01�f
Check point: - Ensure that AFT is not loading the ASG. Check the transistor (See self checking) Adjust the carrier frequency exactly equal to fIFT. Observe the clamped signal at the base of the transistor.
13
Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Collector AM & Demodulation using Envelop Detector
AIM:- Conduct an experiment to generate an AM signal using collector modulation for an fC = _______KHz and fm = _______Hz. Plot the variations of modulating 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 to Channel ‘‘A’ and the modulated signal to channel ‘‘B’ of CRO and time / Div knob
in X via A position.
14
Communication Lab Manual SSIT, Tumkur
Tabulation:-ModulationTuned frequency of IFT, fIFT = ____________KHz
Sl.No Vmax (V) Vmin (V) m = minmax
minmax
VVV-V
�Vm =
2V-V minmax Vc =
2VV minmax �
Demodulation Sl.No Vo (V) fo (Hz)
2Vmin)(Vmax Vc,
2Vmin)(Vmax Vm,
Vmin)(VmaxVmin)(Vmaxm �
��
���
�
� �� �21
21
LLLLm
��
�
15
Communication Lab Manual SSIT, Tumkur
WAVE FORMS: -
(a) Carrier wave, (b) Sinusoidal wave, (c) Amplitude modulated signal.
Conclusion:- Staff-in-charge:-
16
Communication Lab Manual SSIT, Tumkur
CIRCUIT DIAGRAM: -Balanced Modulator (Using Diodes)
D1, D2, D3, D4 – OA79
Waveforms-
17
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
Communication Lab Manual SSIT, Tumkur
CIRCUIT DIAGRAM: -Class-C Tuned Amplifier
f Hz VO volts VDC volts IC mA RL ohms mW8RVP
L
2O
AC � mW
IVP CDCDC � DC
AC
PP� �
Design:-
Specification: Frequency f = 150 KHz, t = 6.66 usec
R1C1 >> t, i.e, R1C1 = 100 t Choose C1 = 0.01�f, the R1 = 66.6 K�.Select R1 = 68 K� (std value)
Tank ckt: ��
�f 150KHz
If C = 0.001�f, then L = 1.125 mH �1mH. Then Factual = 159 KHz.
R1 = 68K�, C1 = 0.01�f, C= 0.001�f, L = 1mH
Check points: - Check the transistor (See self checking) Adjust i/p frequency exactly equal to tuned frequency. Observe the clamped signal at the base of the transistor.
19
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
Communication Lab Manual SSIT, Tumkur
Circuit Diagram: -Frequency Modulation Circuit: -
Frequency Demodulation Circuit: -
Sl.No fc Hz fm Hz Vm volts fcmax Hz fcmin Hz �1 Hz �2 Hz � Hz mf� � � T 2� B �
21cminc2ccmax1 �or � ofMax � ,f - f � ,f - f � ���
21
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 � 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
Communication Lab Manual SSIT, Tumkur
Design-1: - 1. FM modulator circuit.
Let carrier frequency fC = 3 KHz, fC = 0.3/R Ct. Choose R = 10K� = Ra = Rb, then Ct = 0.01�f. Take RL = 10K�, CC = 0.01�f.
2. Demodulator using PLL. Let fO = fC = 3 KHz, fO = 1.2/4R1C1. Choose C1 = 0.001�f, then R1 = 100K�. Filter design: Let fm = 1 KHz = 1/2�RC Choose C = 0.1�f, then R = 1.59 K� � 1.5 K�
Design - 2: - 1. FM modulator circuit.
Let carrier frequency fC = 5 KHz, fC = 0.3/R Ct. Choose R = 10K� = Ra = Rb, then Ct = 0.001�f. Take RL = 10K�, CC = 0.01�f.
2. Demodulator using PLL. Let fO = fC = 3 KHz, fO = 1.2/4R1C1. Choose C1 = 0.001�f, then R1 = 100K�. Filter design: Let fm = 1 KHz = 1/2�RC Choose C = 0.1�f, then R = 1.59 K� � 1.5 K�
Wave Form: -
23
Communication Lab Manual SSIT, Tumkur
Design:- Specification:
Carrier frequency fC = 3 kHz, t
c RC0.3 f �
Choose R= 10 K�, Ra = Rb, then Ct = 0.01�f (use DCB)Ra = Rb = 10 K�, RL = 10 K�, Ct = 0.01�f (use DCB). R = 82 K�, CC = 0.01�f.
Note: - Usually the carrier frequency of the FM signal is in the range of 100s ofKHz, but is chosen in terms of 1s of KHz to enable proper measurement offrequency deviating �.
Check Points: -
Ensure that a square wave and a triangular wave at pin 9 and 3 of IC 8038respective.
Conclusion :- Staff-in-charge:-
24
Communication Lab Manual SSIT, Tumkur
Circuit Diagram: -Radio Receiver: -
R = 10K�, C = 0.1�f, RL = 100�
Selectivity: - fm = _____Hz, %m = ______ Sl.No fC Hz Vo volts
Fidility: - fm = _____Hz, %m = ______ Sl.No fC Hz Vo volts
Sensitivity: - fm = _____Hz, %m = ______ fC Hz Vi volts Vo volts
25
Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Radio Receiver Characteristics Aim:- Plot the sensitivity/selectivity/fidelity graphs of a given AM Broadcast receiver in MW 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
Communication Lab Manual SSIT, Tumkur
Circuit Diagram: -Pre-emphasis De-emphasis
TABULATION: - Pre-Emphasis N/W
f Hz Vo volts GainViVo Normalized gain
Gain/GoNormalized Gain
In db
De-Emphasis N/W
f Hz Vo volts GainViVo Normalized gain
Gain/GoNormalized Gain
In db
27
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 75�s 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 = 1/2�rC, f2 = 1/2�RC Choose C = 0.1�f then r = 820� and R = 100�. Also r/R = Rf/R1, then R1 = 2.2K� and Rf = 15K�.
2. De-emphasis circuit. fC = 1/2�RdCd. Choose Cd = 0.1�f and fC = f1 = 2.1KHz Then Rd = 820�.
Conclusion :- Staff-in-charge:-
28
Communication Lab Manual SSIT, Tumkur
Circuit Diagram: - AM Modulator using MC1496
AM Demodulator using MC1496
Sl.No Vmax (V) Vmin (V) m = minmax
minmax
VVV-V
� Vm =
2V-V minmax Vc =
2VV minmax �
Tabulation:-
29
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 = 4K��3.9K�. Vbe = 700mV, I = 160mA, Voltage at pin 5 = 1.7V. Vbias = (-8+1.7) = -6.3V RS = Vbias/I = 6.3/160mA = 7K��6.8K�
Conclusion :- Staff-in-charge:-
30
Communication Lab Manual SSIT, Tumkur
Circuit Diagram: - Pulse amplitude modulation and demodulation
Design: -Specifications: - IC = 1ma, hFE = 100, VCEsat = 0.3 V, VBEsat = 0.7v (assume), fm = 100hz.
1. BBiasing: - 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 k�, select Rc = 4.7 k �(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 � Select RB = 22 k � (Std. Value).
2. FFilter: - Cut off frequency of the filter fo >> fm Choose fo = 500 Hz = 1 / 2 � RC Choose C = 0.1 � f, then R = 3.3 k � Rc = 4.7 K � RB = 22k �, R = 3.3k �, C = 0.1�f
Check Points: - 1. Ensure that square wave signal at the base of the transistor should have
amplitude > V�. 2. Ensure that m (t) is having sufficient dc shift.
Tabulation: - Reconstructed output VC(pp) volts fC (Hz) Vm(pp) volts fm (Hz) VO volts fO (Hz)
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Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Pulse Amplitude Modulation & Demodulation Aim:- Conduct an experiment to generate PAM signal and also design a circuit to demodulate the obtained PAM signal and verify sampling theorem. Plot the relevant 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
Communication Lab Manual SSIT, Tumkur
Circuit Diagram: - Pulse Width modulation and demodulation
Pulse Width Demodulation
33
Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Pulse Width Modulation & Demodulation Aim:- Conduct an experiment to generate PAM signal and also design a circuit to demodulate the obtained PAM signal and verify sampling theorem. Plot the relevant 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 the pulses during the negative half of the modulating signal keeps on reducing and that at the positive half of the modulating signal is increased the width of the pulses during the negative half of the modulating signal keeps on reducing and that at the positive half of the modulating signal keeps on increasing.
34
Communication Lab Manual SSIT, Tumkur
Design: -
Specifications: - Frequency fc = 1 KHz, duty cycle: 50 % T = 1 ms, Ton = Tb= 0.5 ms
I) 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 �f, 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
Ton ms
Toff ms fc Hz Max.width
ms Min.width
ms Dynamic
range volts
Modulating frequency
fm Hz VO(V) fO(Hz)
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Communication Lab Manual SSIT, Tumkur
Waveforms:-
Conclusion :- Staff-in-charge:-
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Communication Lab Manual SSIT, Tumkur
Circuit Diagram: - Pulse Position modulation and demodulation
Pulse Position Demodulator
Design: m(t) = 1KHz, T = 1ms T = RC, Let C = 0.01uf
Then R = 1�
Design: -Specifications: -
1. Monostable Multivibrator: - PW = 1.1 Rch Ct
Choose Ct = 0.01 �f, then Rch = 18.18 k � (std. Value) 2. Differentiator : -
Rs * Cs <<1 / fc
Choose Rs * Cs = 0.01 ms, Choose Cs = 0.001�f, then Rs = 10k �
Rch = 18 k�. Ct = 0.01�f, Rs = 10 k�, Cs = 0.001�f
CHECK POINTS: - With modulating signal zero, the voltage at pin 5 of 555 timer should be 2 /3 Vcc. Ensure that wave form at pin 2 of 555 timer should have a trailing edge going below 1
/3 Vcc.
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Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Pulse Position Modulation & Demodulation Aim:- Conduct an experiment to generate PAM signal and also design a circuit to demodulate the obtained PAM signal and verify sampling theorem. Plot the relevant 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:-
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Communication Lab Manual SSIT, Tumkur
Circuit Diagram: - Transistor Mixer
Design: -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 = 10�f Check points: - During the mixer operation under on circumstance the frequency of local oscillator or frequency 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 Hz
Up Conversion
Down Conversion
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Communication Lab Manual SSIT, Tumkur
Experiment No: DATE: __/__/____
Transistor Mixer Aim:- Conduct an experiment to generate PAM signal and also design a circuit to demodulate the obtained PAM signal and verify sampling theorem. Plot the relevant 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 � 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 lless than the frequency of IFT, now adjusting the local oscillator frequency (f LO = fS + f IFT) (Note : local oscillator amplitude � 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:-
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