Communication System(TC)

7/29/2019 Communication System(TC)

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PRACTICAL WORK BOOK

For The Course

EE-394 Communication System

For

Third Year

(Telecommunication Engineering)Name of Student: _________________________________________________

Class: ________________________________Batch :____________________

Discipline: __________________________________________________

Class Roll No.: ________________Examination Seat No._________________

Compiled by: Engr. Jagdesh K Shivani (Lecturer)

Supervised by: Dr. Abdul Qadir (Professor)

TELECOMMUNICATION LAB

DEPARTMENT OF ELECTRICAL ENGINEERINGNED University of Engineering & Technology, Karachi-75270, Pakistan

s y e d m e h m o o d s h a h _ t e l e c o m @ y m a i l . c o m / i e t / g u


2/22

INDEX

CS (TC)

S.NO DATE OBJECTIVES SIGNATURE

1 Fourier synthesis of a square wave.

2To observe the normal operation of Pulse amplitude

modulator and demodulator.

3To study / investigate the behavior and characteristics of

LOW PASS FILTER using variable filter module.

4To study / investigate the behavior and characteristics ofHIGH PASS FILTER using variable filter module.


BAND PASS FILTER using variable filter module.


BAND STOP FILTER using variable filter module.

7To Construct, Study / Investigate basic AM Modulator and

Demodulator circuits.

8To Construct, Study / Investigate basic AM Transmitter and

Receiver circuits.

9 To observe the normal operation of a 2- Channel PAM time-division multiplex system (PAM TDM) system.

10To Observe the effect of Linear and Non linear quantization

in PCM (Pulse code modulation) System.



3/22

LAB # 01

OBJECTIVE:-

Fourier Synthesis of a square wave.

EQUIPMENTS REQUIRED: -

Modules T10H.

+/- 12Vdc Supply

Oscilloscope.Frequency counter.

Multimeter.

INTRODUCTORY INFORMATION:-

A square wave spectrum is made of the sum of all the harmonics being odd

of the fundamental with decreasing amplitude according to the said law. Inother words the square wave shown in fig 2.1 can be obtained by summing

up the infinite sine waves as per the following relation:

S(t) = sin(2Ft)/1 + sin(23Ft)/3 + sin(25Ft)/5 + ..

PROCEDURE AND OBSERVATIONS:-

1- Odd harmonics (1, 3, 5, 7, 9): two way switches -/0/+ on + and twoway switches sin/cos on sin.

2- Even harmonics (2, 4, 6, 8): two way switches -/0/+ on 0.3- Connect the oscilloscope with the amplifier output of the fundamental

(1st) and adjust the amplitude at 10Vp-p.

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4- Connect the oscilloscope with the output of the third harmonicamplifier (3

RD) and adjust the amplitude at 10/3 303Vp-p.

5- Connect the oscilloscope with the output of the 5TH harmonicamplifier (5

TH) and adjust the amplitude at 10/5 = 2Vp-p.

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6- Connect the oscilloscope with the output of the seventh harmonicamplifier (7

TH) and adjust the amplitude at 10/7 1.4Vp-p.

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7- Connect the oscilloscope with the output of the 9th harmonic amplifier(9

TH) and adjust the amplitude at 10/9 1.1Vp-p

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8- Connect the oscilloscope with OUT and check that there is the signalcorresponding to the components sum.

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9-Remove some harmonics (put the relating two way switch on 0) and

check

10-In case there is not a perfect phase relation among the different harmonics

adjust the phase from the rear of the module.



5/22

EXPERIMENT NO 2

OBJECT:-

To observe the normal operation of Pulse amplitude modulator and demodulator.

EQUIPMENTS REQUIRED:-

1- PAM modulator module 736061

1- PAM demodulator module 736071.1- Function generator module 72695

1- Power supply module 72686.

1- Frequency counter module 726991- Digital storage oscilloscope.

1- Multimeter.

Bridging plugsCable pairs.

THEORY:-

It is a modulation technique in which analog signal is sampled and sampled values are

used to modify certain parameters of a periodic pulse train to convert information into

form for transferring pulses from a source to a destination.There are two categories of pulse modulation

Digital pulse modulation

Analog pulse modulation

PAM is analog pulse modulation in which amplitude of a constant width and constantposition pulse train is varied according to the amplitude of the analog signal this process

is termed as sampling of the analog signal.PAM signal is time discrete and value continuous.

PAM signal is neither digital nor analog and it is not suitable for transmission.

We are dealing with bipolar PAM as a both positive and negative value arises.To avoid aliasing sampling theorem must be followed

PAM is used as an intermediate stage of the Pulse code modulation PCM.

PROCEDURE:-

1- Set up the experiment as specified in the diagram.2- Set the pulse generator (G) to t/Tp = max and fp = 15 kHz feed into the input

filter CH1 a sinusoidal signal with fm = 500Hz.

3- Observe the output of the filter by using oscilloscope with Vp-p unchanged andchange fm.

4- Measure the amplitude of the output of the low pass CH-1 and calculate the gainof the low pass filter from Am and Ao.

5- Connect CH2 of the oscilloscope at the output of the demodulator repeat theexperiment at different t/Tp with pulse frequency fp unchanged observe the effect

on the output signal at CH-1.



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6- Set the pulse duty factor t/Tp to max and lower the sampling frequency and takereadings at different fp values, observe the effect on the output signal of the

demodulator at CH-1 using oscilloscope.

OBSERVATIONS:-

a-Filter ResponseINPUT SIGNAL

Type of Signal--------------------------

OUTPUT SIGNAL

Type of Signal--------------------------

Vp-p Frequency Vp-p Frequency

b- Influence of Pulse duty factor on PAM signal.

t/Tp fpINPUT

SIGNAL

OUTPUT

SIGNAL

Variable Fixed Vp-p fi Vp-pfo



7/22

c- Influence of sampling frequency on PAM signal.

t/Tp fp INPUT

SIGNAL

OUTPUT

SIGNAL

Max Variable Vp-p fi Vp-pfo

RESULT:-

- What did you analyze about the influence of pulse duty factor and sampling frequencyon PAM signal describe in quantitative terms.



8/22

LAB # 03

OBJECT: -

To study / investigate the behavior and characteristics of LOW PASSFILTER using variable filter module.


Variable filter unit.

Function generator.

Dual display oscilloscope.

BNC to alligator cables.

THEORY: -

Filter

A filter network is a device that passes electrical signals at certain

frequencies or frequency ranges while preventing the passage of others.

There are two basic categories of filters.

a- Passive filters use passive components.b- Active filters use op-amp.c- Filters are used to intentionally remove unwanted noise or other

frequency components that interfere.

Low pass filter.

A filter circuit that pass the frequencies less than the Cutoff frequencies and

attenuates the signals having frequencies more than the cutoff frequency.

It means it has one pass band and one stop band.

PROCEDURE: -

1- Turn ON the variable filter unit and set it to LOW PASS FILTER.2- Set the cutoff frequency of the low pass filter to 10 KHz.3- Set the function generator to generate sinusoidal wave.

4-Set the Amplitude at 2Vp-p.

5-Connect the oscilloscope probe to the output of the filter unit and make the

observation column between input signal frequency and the output voltage at

different frequencies.

6-Take a calibration of 1 kHz between each reading.



9/22

OBSERVATIONS: -

OBSERVATION TABLE

Input SignalVi

Input SignalFi

Output SignalVo

Vo / Vi GaindB.

CALCULATIONS: -

Formula

Gain = Vo / Vi.

Gain dB = 20 log G.

Calculating the gain of each reading and then the final reading of the gain is

the average of all the gains calculated individually.

GRAPH: -

Plot the graph between the input signal frequency fi and the output signal

voltage Vo.



10/22

LAB # 04

OBJECT: -

To study / investigate the behavior and characteristics of HIGH PASS

FILTER using variable filter module.



Function generator.



THEORY: -

Filter




d- Passive filters use passive components.e- Active filters use op-amp.f- Filters are used to intentionally remove unwanted noise or other


High pass filter.

A filter circuit that pass the frequencies more than the Cutoff frequency and

attenuates the signals having frequencies less than the cutoff frequency.

It means it has one pass band and one stop band.

PROCEDURE: -

2- Turn ON the variable filter unit and set it to HIGH PASS FILTER.2- Set the cutoff frequency of the high pass filter to 10 kHz.

3- Set the function generator to generate sinusoidal wave.





6-Take a calibration of 1 kHz between each reading.



11/22

OBSERVATIONS: -

OBSERVATION TABLE

Input SignalVi

Input SignalFi

Output SignalVo

Vo / Vi GaindB.

CALCULATIONS: -

Formula

Gain = Vo / Vi.Gain dB = 20 log G.



GRAPH: -


voltage Vo.



12/22

LAB # 05

OBJECT: -

To study / investigate the behavior and characteristics of BAND PASSFILTER using variable filter module.



Function generator.



THEORY: -

Filter




g- Passive filters use passive components.h- Active filters use op-amp.i- Filters are used to intentionally remove unwanted noise or other


Band Pass filter.

A filter circuit that pass a band of frequencies between lower and upper

Cutoff frequencies and attenuates the signals having frequencies less than

the lower cutoff frequency and more than the upper cutoff frequency.

It means it has one pass band and two stop bands.

PROCEDURE: -

3- Turn ON the variable filter unit and set it to BAND PASS FILTER.2- Set the cutoff frequency of the low pass filter to 10 KHz by the frequency

selector and high pass filter to 5 KHz.






6-Take a calibration of 1 KHz between each reading.

7-It means the pass band is from 5 KHz to 10 KHz.



13/22

OBSERVATIONS: -

OBSERVATION TABLE

Input Signal

Vi

Input Signal

Fi

Output Signal

Vo

Vo / Vi Gain

dB.

CALCULATIONS: -

FormulaGain = Vo / Vi.

Gain dB = 20 log G.

BW = fu fl = 10 KHz 5KHZ = 5KHZ.



GRAPH: -


voltage Vo.



14/22

LAB # 06

OBJECT: -

To study / investigate the behavior and characteristics of BAND STOP

FILTER using variable filter module.



Function generator.



THEORY: -

Filter




j- Passive filters use passive components.k- Active filters use op-amp.l- Filters are used to intentionally remove unwanted noise or other


Band Stop filter.

A filter circuit that stops a band of frequencies between lower and upper

Cutoff frequencies and attenuates the signals having frequencies less than

the lower cutoff frequency and more than the upper cutoff frequency.

It means it has one stop band and two pass bands.

PROCEDURE: -

4- Turn ON the variable filter unit and set it to BAND STOP FILTER.2- Set the cutoff frequency of the low pass filter to 5 KHz by the frequency

selector and high pass filter to 10 KHz.






6-Take a calibration of 1 KHz between each reading.

7-It means the stop band is from 5 KHz to 10 KHz.



15/22

OBSERVATIONS: -

OBSERVATION TABLE

Input SignalVi

Input SignalFi

Output SignalVo

Vo / Vi GaindB.

CALCULATIONS: -

Formula

Gain = Vo / Vi.Gain dB = 20 log G.

BW = fu fl = 10 KHz 5KHZ = 5KHZ.



GRAPH: -


voltage Vo.



16/22

EXPERIMENT NO 9

OBJECT:-

To observe the normal operation of a 2- Channel PAM time-divisionmultiplex system (PAM TDM) system.


1- PAM modulator module 7360611- PAM demodulator module 736071.

2- Function generator module 72695.

1- Power supply module 72686.1- Frequency counter module 72699.

1- Digital storage oscilloscope.

1- Multimeter.Bridging plugs

Cable pairs.

THEORY:-

Multiplexing

Multiplexing is the process of simultaneously transmitting more than one individualsignals over a single communication link Multiplexing has the effect of increasing

The number of communication channels so that more information can be transmitted.

There are two basic types of multiplexing1- FDM (Frequency division multiplexing)2- TDM (Time division multiplexing)

In TDM each signal can occupy the entire bandwidth of the channel however each

channel is transmitted for a brief period of time.

PROCEDURE:-

1- Set up the experiment as specified in the figure.2- Feed in a triangular shaped signal with fm1 = 200Hz and Am1 = 5V in channel

1(CH1).

3- Feed in a sinusoidal signal with fm2 = 300Hz and Am2 = 6V into channel 2(CH2).4- Set the sampling frequency to maximum fp = 15 KHz.5- Set the Pulse duty factor to maximum.6- Display the input signals simultaneously on the oscilloscope and sketch these into

diagram 1.

7- Display the PAM-TDM signal and sketch in the diagram 1.8- Display the respective input and output signal of the demodulator low pass filter

of CH1 and CH2 in diagram 2.9- Display the CLOCK signal and the demux trigger signal on the oscilloscope and

set delta t so that the trigger signal is delayed by 90 degree w.r.t the CLOCK

signal.



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10-Display the respective input and output signal of the demodulator low pass filterof CH1 and CH2.

11-Adjust delta t with 180 degree phase difference you will observe that thedemodulated signals from CH1 and CH2 are interchanged completely.

12-Display the respective input and output signal of the demodulator low pass filterof CH1 and CH2.

13-Now vary the pulse-duty factor from min to max and see the effect at the outputsignals of the CH1 and CH2 low pass filters. Alternate from PAM1 to PAM2 bychanging the bridging plug at the PAM modulator.

14-Connect the input of the low pass filter CH2 in the PAM demodulator with theoutput of the S & H stage by reconnecting the bridging plug at the low pass input

OBSERVATIONS:-

Diagram 1: CH1 , CH2 , PAM1 and PAM2 signals.

Diagram 2: Input and output signals of CH1 and CH2 low pass filters 0 degree delay.Diagram 3: Input and output signals of CH1 and CH2 low pass filters 90 degree delay.

Diagram 4: Input and output signals of CH1 and CH2 low pass filters 180 degree delay.

Table 1: Influence of Sample and Hold (S&H) circuit in the demodulator.

CH1 Input

signal

CH2 Input

signal

Pulse duty

factor t/Tp

Sampling

frequency

fp

Output

signal CH1

Without

S&H

Output

signal CH2

With S&H

Vp-p

f1

Vp-p

f2

Variable Fixed (max) Vp-p f1 Vp-p f2

10%

20%

25%

30%

35%

40%

45%

50%



18/22

LAB # 10

OBJECTIVES:-

To observe the effect of Linear and Non linear quantization in PCM (Pulse codemodulation) System.


1 PAM modulator 736061

1 PAM demodulator 7360711 PCM modulator 736101

1 PCM demodulator 736111

1 Function generator 0-200kHz 726951 Frequency counter 726991 Power supply 15V

1 Digital storage oscilloscope

Bridging plugsCable pairs

INTRODUCTORY INFORMATION:-

Quantization means the narrowing down of all possible signal values to a finite number.

The quantization process takes an infinite number of all possible continuous signals.

The quantization interval can be either equidistant discrete or logarithmic steps. In thecase of equidistant quantization intervals this is referred to as linear quantization. In the

case of logarithmic steps this is called non linear quantization. The quantization becomesmore precise with an increasing number of steps and there is a decrease in the

quantization noise.

PROCEDURE AND OBSERVATIONS:-

1- Use the experiment setup according to figure Ex 5.2-1.2- By pressing the MODE button several times switch to the

operating mode: PCM linear quantization (recognizable when the

appropriate LED lights up).3- Enable all of the bits. For this press the push button SELECT until

all (red) LEDs on the PCM modulator indicate ACTIVE.

4- The toggle switch on the PCM demodulator must be set to CH2.



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Linear quantization.

5- Connect the DC voltage source of the PCM modulator as the inputU1.

6- The quantified voltage is U2 and can be tapped at the DAconverter of the PCM demodulator.7- Set to -9.5V on the 10 stage potentiometer.8- Alternately measure U1 and U2 using the multimeter and note

down the voltages together with the binary coded bit sequence of

the PCM bit modulator in Table 7.1

9- The bit sequence is displayed by LEDs whereby the LSB is at thetop.

10-Now increase the input voltage U1 in steps of approx. 1V andrepeat the recording of the measurement value until the uppermodulation limit of the PCM modulator is reached.

11-Display the curve of U2 versus U1 as a quantization characteristicin Diagram 7.1.

Table 7.1 linear Quantization Characteristic

U1

V

U2

V

U1

V

U2

V

-9.5 1

-9 2

-8 3

-7 4

-6 5

-5 6

-4 7

-3 8

-2 9

-1 9.5

0



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Non linear quantization.

12-By pressing the MODE push button on the PCM modulator severaltimes switches to the operating mode: PCM non linear

quantization. The PCM demodulator remains in linear operation.

(a)Compressor characteristic

13-Record the compressor characteristic. Proceed in the same manneras for the recording of the linear quantization characteristic in

Table 7.2.

14-Plot the curve of U2 versus U1 as a compressor characteristic inDiagram 7.2.

Table 7.2 Non-linear quantization Compressor characteristic

U1V

U2V

U1V

U2V

-9.5 1

-9 2

-8 3

-7 4

-6 5

-5 6

-4 7

-3 8

-2 9

-1 9.5

0

(b) Expander characteristic

15-For this set the PCM modulator to linear quantization PCMdemodulator to non linear quantization.

16-Plot the curve of U2 versus U1 as an expander characteristic indiagram 7.3.



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Table 7.3 Non-linear quantization Expander characteristic

U1

V

U2

V

U1

V

U2

V-9.5 1

-9 2

-8 3

-7 4

-6 5

-5 6

-4 7

-3 8

-2 9

-1 9.5

0

(c) Non Linear transmission

16- In order to record the Non linear transmission characteristic switchthe PCM modulator and demodulator to non linear mode.

17- Record the transmission characteristic in Table 7.4

18- Plot the curve of U2 versus U1 in Diagram 7.4



22/22

Table 7.3 Non-linear Transmission Characteristic

U1

V

U2

V

U1

V

U2

V-9.5 1

-9 2

-8 3

-7 4

-6 5

-5 6

-4 7

-3 8

-2 9

-1 9.5

0


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Communication System(TC)