Communications Lab Manual Amplitude modulation and DSB-SC

8/9/2019 Communications Lab Manual Amplitude modulation and DSB-SC

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BIRZEIT

UNIVERSITY

ELECTRICAL

ENGINEERING

DEPARTMENT

ANALOG AND DIGITAL

COMMUNICATION LAB

(ENEE 411)

Last Update: January -2013


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Table of Contents

Experiment 1 AM Modulation and Detection .............................................................. 4

Experiment 2 DSB-SC and SSB ................................................................................. 11

Experiment 3 FM Modulation and Demodulation .................................................... 19

Experiment 4 FDM ..................................................................................................... 26

Experiment 5 ADC ...................................................................................................... 34

Experiment 6 DAC ...................................................................................................... 42

Experiment 7 PCM ...................................................................................................... 52

Experiment 8 TDM ..................................................................................................... 57

Experiment 9 ASK (Amplitude Shi ft Keying) ............................................................ 63

Experiment 10 FSK (F requency Shift Keying) .......................................................... 70

Experiment 11 BPSK(Binar y Phase Shi ft Keying) .................................................... 75

Experiment 12 QPSK(Quadri - Phase Shi ft Keying) .................................................. 80

Experiment 13 Delta Modulation and Demodulation ............................................... 83


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EXPERIMENT.1

AM Modulation and Demodulation

Objectives:

To understand the theory of amplitude modulation and demodulation.

To design and implement the two types of AM modulator: transistor and balanced

modulator.

To design and implement the two types of AM demodulator: the diode detection and the

product detection.

To understand the measurements and adjustments of AM modulator and demodulator.

PrelaB Work:

Use MATLAB command and M files to draw the demodulated signal after the envelope detector

given that:

)cos()]cos(1[)( t t At S cmc AM

1. Write the mathematical expression for the demodulated signal.

2. Use MATLAB command and M files to draw the demodulated signal for the following three

cases:

a. Ac=16v, modulation index=0.22, modulating signal frequency=800Hz

b. Ac=16v, modulation index=1, modulating signal frequency=800Hz

c. Ac=16v, modulation index=1.85, modulating signal frequency=800Hz

3. Discuss your result in each part .you must write the commands which are used in the Pre-lab.

Equipment Required:

2 AC Function Generators

DC Power Supply

ETEK ACS-3000-02 Module

Connection wires


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Theory:

Modulation: the process by which some characteristic (like: amplitude, frequency or phase) of

a carrier signal is varied in accordance with the modulating signal (message signal).The signal

modulation is used in order to transmit messages over long distances and also to transmit signals

from various sources simultaneously over a common channel.

Amplitude Modulation (AM): The process in which the amplitude of the carrier varies linearlywith message signal.

The general formula for the modulated AM signal:

From the above formula we find that in order to generate an AM signal we just need to add a DC

signal with the message signal then multiply the added signal with the carrier signal.

The analog multiplier is the basic modulator that is used to generate AM signal as shown in

fig1.1:

Fig(1.1): Analog Multiplier.

unit.with voltsignalcarriertheof Amplitude:

signal.carriertheof Frequency:

signal.messagetheof Frequency:

unit.with voltsignalmessagetheof Amplitude:

.toequalishindex whicModulation:

)11...().........2cos()2cos(1)(

c

m

m

c

m

m

c

mc AM

A

fc

f

A

A

A

fct t f A

A At S


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The Modulation Index µ:

There is an important parameter in the AM modulation which is called the modulation index (µ)

which is equal to Am/Ac .

The Frequency Spectrum for the AM modulated signal:

Equation (1-1) can be written as :

()

[ (( )) (( ))] () ( )

The first term of equation (1-2) represents the double side band signals .While the second term

represents the carrier signal. Since the audio signal is hidden in the double side bands and the

carrier signal does have no data, the AM modulation is lower efficiency than double side band

suppressed carrier (DSB-SC) modulation but its demodulation circuit is much simpler.

If the double side bands get stronger then the transmission efficiency is getting better. From

equation (1-2) we find that the double side bands are proportional to µ so larger µ is getting

better efficiency.

The transmission power efficiency η:

( )

The modulation index is smaller or equal to .So if µ


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Detection Using Envelope detector:

Fig(1-2) shows the envelope detector operation. After the diode rectifies the AM signal

(removing the negative part) then the RC low pass filter obtains the AM envelope which is the

message signal. The envelope detector is able to recover the message signal if the following

conditions are achieved:

1- fcRC>>Tm .Where Tc=1/fc, Tm=1/fm, RC is the time constant of the RC low pass

filter .

Fig(1.2): Envelope detector.

If there is an over modulation we can use the product detector in order to recover the signal.


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Detection Using Product detector:

Fig(1.3): Product detector.

The output of the product as shown in fig (1-3):

()

()

[ ()] () ( )

The first term of eq(1-4) is a DC signal while the second is the message signal , the third term is

the second harmonic of the AM signal which is rejected by the low pass filer.

The two types of the detectors have its own advantages and disadvantages. For the envelope

detector which is asynchronous detector, its circuit is simple but its performance is not better asthe product detector .However, the product detector’s circuit is more complicated and requires

synchronous for both carrier signal and AM signal (same phase and same frequency), otherwise

the quality of the output will be affected.

Procedure:

Transistor AM modulator:

1- Refer to ACS3-1 on ETEK kit ACS-3000-02 module.

2- At the audio input port (Audio I/P) ,use the function generator to input a sine wave

600mV amplitude and 1KHz frequency. At the carrier signal port (Carrier I/P) ,input

a sine wave 1.7 amplitude and 500 KHz frequency.

3- By using the oscilloscope, observe the AM modulated signal at the modulator output

port (AM O/P).Adjust VR1 so that the AM signal is maximum without distortion

(VR1 is used to change the operation point of the transistor and it also controls the

magnitude of the carrier) .

4- Observe the signals at TP1,TP2 and TP3.


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5- Try to change the frequency and the amplitude of the message signal. record your

results.

Balanced AM modulator:

1- Refer to ACS3-2 on ETEK kit ACS-3000-02 module.

2- Let J1 short,J2 open so that R10=6.8KΩ (R10 determines the magnitude of the bias

current for the modulator).

3- At the audio input port (Audio I/P) ,use the function generator to input a sine wave

500mV amplitude and 1KHz frequency. At the carrier signal port (Carrier I/P) ,input

a sine wave 2V amplitude and 500 KHz frequency.

4- By using the oscilloscope, observe the AM modulated signal at the modulator output

port (AM O/P).Adjust VR2 so that the AM signal is maximum without distortion

(VR2 controls the gain of the modulator) . Adjust VR1 so that the value of µ is less

than 1 (VR1 controls the value of µ). Record your results.

5- Change the value of VR1 until µ=1 (100% modulation). Let µ


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5- Connect the carrier signal input of the product detector (Carrier I/P) with the same

carrier signal in AM modulator (for synchronization).

6- Adjust the value of VR1 (controls the amplitude of the carrier),VR2(controls the

amplitude of the message signal) and VR3(controls the gain of the detector) so that

the signal at the output of the detector is maximum without distortion.

7- Try to change the frequency of the message signal and the frequency of the carrier.

Observe the signal at the detector output.

Questions:

1. Calculate the power efficiency for different modulation index µ=0.25, µ =0.5, µ =0.75,

µ =1

2. An AM detector gets a wave with the following mathematical expression:

V(t) = 5(1 + 0.5sin(2 l000t)sin(2 455000t)

Explain what is this wave and the meaning of the parameters:

5,0.5, 1000, 455000

What is the modulation coefficient of the above wave and what is the relation between

the modulated wave amplitude and the' carrier wave amplitude?

What is the bandwidth of this AM modulated wave?


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EXPERIMENT.2:

DSB-SC and SSB

Objectives:

To understand the theory of DSB-SC and SSB modulation and demodulation.

To design and implement the DSB-SC and SSB modulators and demodulators.

To understand the waveforms and frequency spectrums of DSB-SC and SSB signals.

To understand the measurements and adjustments of DSB-SC and SSB modulators and

demodulators.

PreLab work:

Using Matlab software and Simulink, to show graphically the time domain of SSB-SC

modulated Signal. Taking the modulating signal t t m )1500(2cos)( and the carrier signal

t t c )100000(2cos4)( .

Equipment Required:

2 AC Function Generators

DC Power Supply

ETEK ACS-3000-03 Module

Connection wires.

Theory:

DSB-SC and SSB modulation:

Recall that the AM modulated signal is given by:

()

[ (( )) (( ))] () ( )


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Fig(2-1): Frequency spectrum of AM.

Since the message signal is hidden in the double side bands and the carrier does not contain any

signal, therefore, the power is consumed in the carrier during the transmission of AM signal.

This will explain that the AM modulation has a low transmission efficiency (it could be only

33% in the best case). So the idea from Double Side Band Suppressed Carrier modulation (DSB-

SC) is to suppress the carrier or in other words, to make the carrier amplitude equals to zero. This

technique will improve the power efficiency.

We can use DSB-SC to obtain SSB modulation.

It is not necessary to transmit both side-bands.

Either one can be suppressed at the transmitter without any loss of information.

The information

represented by the modulating signal is contained in both the upper and the lower sidebands.

In SSB modulation we eliminate the carrier and one sideband, a power savings of over 83

percent is realized. Additionally, the bandwidth required for SSB is theoretically one-half that

required when both sidebands are transmitted.

Fig(2-2): Frequency spectrum of DSB-SC.


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Fig(2-3):Frequency spectrum of SSB ( Lower sideband).

Fig(2-4):Frequency spectrum of SSB ( Upper sideband).

Fig(2-5):block diagram of DSB-SC modulation.

We can also use the DSB-SC modulation to obtain SSB modulation. We utilize two DSB-SC

modulators and let the phase difference between the two audio signals and the two carriers to become 90 degree, i.e: (DSB-SC)Q- quadrature component and (DSB-SC)I-in phase component

where:

(DSB-SC)I = cos2π(fc-fm)t+ cos2π(fc+fm)t ……………………………………. (2-2)

(DSB-SC)Q = cos2π(fc-fm)t - cos2π(fc+fm)t ……………………………………. (2-3)


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Equations (2-2) and (2-3) show that both (DSB-SC)I and (DSB-SC)Q connect to an adder to

obtain USSB or LSSB at the output port.

LSSB= (DSB-SC)I+ (DSB-SC)Q= cos2π(fc-fm)t ………………………………. (2- 4)

USSB= (DSB-SC)I- (DSB-SC)Q= cos2π(fc + fm)t ……………………………….(2- 5)

During transmission, the power consumption of SSB modulation is less than DSB-SC

modulation so the sequence of power consumption for these different types of modulation is asfollows: AM


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Fig(2-7):Circuit diagram of SSB modulator.

Fig(2-8):Circuit diagram of phase shifter.


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Fig(2-9):Circuit diagram of linear adder.

DSB-SC and SSB demodulation:

As we know:

() ()()…………………..….(2- 6)

Multiply equation (2-6) by 2cos(2πfct):

() () () ()

()[( ) ] ( )

By using Fourier Transform on equation (2-7) we get:

() ( ) [( ) ( )] ( )

When () passes through a low pass filter which its bandwidth equals or larger than the bandwidth of the message signal but smaller than 2fc then the only term left in equation (2-8) is

0.5M(f). The block diagram for the DSB-SC demodulator is shown in the figure below:

Fig(2-10):Block diagram of DSB-SC demodulator (Coherent).


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From equations (2-4) and (2-5) we conclude that we can use the demodulator above figure (2-

10)as a SSB demodulator.

Implementation of DSB-SC and SSB demodulator:

DSB-SC and SSB demodulator which is called a coherent product detector will be implemented

in this circuit using MC1496 as shown in the diagram.

Fig(2-11):Circuit diagram of the coherent product detector.

Procedure:

Part 1: DSB-SC and SSB modulators:

1-

Refer to module ACS5-1 on ETEK ACS-3000-03 Kit.2- At the audio input port (Audio I/P) put a sine wave with 400mV amplitude and 1KHz

frequency. Then at the carrier input port (Carrier I/P) put a sine wave with also 400

mV amplitude and 200KHz frequency.

3- By using oscilloscope, observe the signals at the audio output ports TP1 and TP2 at

the same time. Adjust the variable resistor “QPS” so that the phase shift between TP1

and TP2 is 90º.

4- By using oscilloscope, observe the signals at the carrier output ports TP3 and TP4 at

the same time. Adjust the variable resistor “Phase Adjust” so that the phase shift

between TP3 and TP4 is 90º.

5- By using oscilloscope, observe TP5 (DSB-SC(Q)) then adjust VR1(gain adjustment)so that the output amplitude is maximum without distortion. Also, adjust VR3

(modulation index µ) so that µ=1.Record your result.

6- By using oscilloscope, observe TP6 (DSB-SC(I)) then adjust VR2(gain adjustment)

so that the output amplitude is maximum without distortion. Also, adjust VR4

(modulation index µ) so that µ=1.Record your result.


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7- Try to change the amplitude of the message signal then its frequency and observe the

effects.

8- Try to change the amplitude of the carrier signal then its frequency. Record your

results.

9- Keep all connections as they are.

Part 2: DSB-SC demodulator:

1- To implement the product detector of DSB-SC refer to ACS6-1 on ETEK ACS-

3000-03 module. Let J1 be short circuit and J2 open circuit.

2- Connect the modulated DSB-SC(I) signal in module ACS5-1 to the input terminal

(DSB-SC/SSB I/P) of the product detector in module ACS6-1.At the same time,

input the same carrier signal in ACS5-1 to the carrier signal input port (Carrier I/P)

in ACS6-1.

3- By using Oscilloscope, observe the output signal of the product detector (Audio O/P)

in ACS6-1.

4-

Adjust VR1 and VR2 so that the amplitude at (Audio O/P) is maximum withoutdistortion then record the waves of the product detector at TP1 and TP2 .

5- Let J1 is open and J2 is short and repeat the steps above.

6- Keep only the connections at the modulator side.

Part 3: SSB demodulator:

1- Connect the modulated SSB signal (SSB O/P) in module ACS5-1 to the input

terminal (DSB-SC/SSB I/P) of the product detector in module ACS6-1.At the same

time, input the same carrier signal in ACS5-1 to the carrier signal input port (Carrier

I/P) in ACS6-1.

2- By using Oscilloscope, observe the output signal of the product detector (Audio O/P)

in ACS6-1.

3- Adjust VR1 and VR2 so that the amplitude at (Audio O/P) is maximum without

distortion then record the waves of the product detector at TP1 , TP2 and (Audio

O/P) .

4- Let J1 is open and J2 is short and repeat the steps above.


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EXPERIMENT.3

FM Modulation and Demodulation

Objectives:

Creating a modulated FM wave using MC4046 and LM566 Modulators.

Investigating the influence of changing the frequency of the signal at the modulator

voltage output.

Calculation of the frequency deviation and the bandwidth.

Modulation and detection of the FM signal using MC4046 and LM565 detectors.

Calculation of the modulation coefficient.

Equipment Required:

ETEK ACS-3000-04(MC4046 and LM566 Modules)

Power supply

Oscilloscope

Audio signal generator

Banana wires

PreLab work:

Consider the frequency modulated signal:

)]2sin(4)17(2cos[)( t t t S

a. Find the message signal m(t).

b. Plot s(t) versus t for -1 ≤ t ≤ 1.

c. Differentiate s(t) with respect to t and plot ds(t)/dt for -1 ≤ t ≤ 1. Notice how this

operation transforms an FM waveform into an AM waveform.

d. Apply ds(t)/dt to an ideal envelope detector, subtract the dc term and show that the

detector’s output is linear ly proportional to m(t).


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Theory:

Frequency Modulation: the process by which frequency of the carrier must be varied with

respect to the message signal.

FM modulation (Direct Method):

In practice, FM modulation is implemented by controlling the instantaneous frequency of a

voltage-controlled oscillator (VCO). The amplitude of the input signal voltage controls the

oscillation frequency of the VCO output signal.

The instantaneous frequency given by:

)()( t Kfm fct fi ……………………………………………………………….... (3.1)

Where Kf: is the proportionality constant with unit (HZ/volt)

A typical characteristics of VCO looks like these:

Fig(3-1): A typical characteristics of VCO.

The General Formula of FM Modulated Wave

t

c FM d m Kf fct At S )(22cos)( ………………………………………….... (3.2)

When message signal )2cos()( fmt At m m

What is the formula of FM modulated wave?

The modulation coefficient fm KfA

fm f m ……………………………………… (3.3)

Where f : is the peak frequency deviation.

Fm: message signal frequency


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Band width of FM Modulated signal:

The band width of fm modulated signal given by Carson’s rule as the following:

)(2 fm f BW FM ................................................................................................... (3.4)

)1(2 fm BW FM …………………………………………………………..….... (3.5)

Advantages of FM Modulation :

1. Constant power

2. Better noise immunity [good quality]

3. Power efficiency: the total transmitted power is constant and is independent of the

message signal.

FM DeModulation :

FM signals can be demodulated using different techniques. Our focus in this experiment will be

on the Slope Method, which uses a cascaded differentiator with an envelope detector circuit as

illustrated in Fig (3.2). The differentiator basically produces an AM-like signal that is then

demodulated by the envelope detector block.

Fig (3.2): FM modulator and demodulator.

))(22(cos)(

0

d mk t f At s

t

f cc …………………………………………….. (3.6)

Where:

)(t m = modulating signal

c f = carrier frequency

c A = carrier amplitude


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f k = sensitivity factor

If we let the modulating signal be a pure sinusoid t f At m mm 2cos)( , then equation (1.1)

becomes

t f t f At f f

Ak t f At s mccm

m

m f

cc 2sin2(cos2sin2(cos)(

…………… (3.7)

Where f Ak m f = frequency deviation

=m f

f = Modulation index (Deviation ration)

There are two types of FM signals depending on the value of ; NBFM ( 1 ) and WBFM

(all ).

Differentiating s(t) in (3.7)with respect to t we get:

))(22(sin)(22

)(

0

d mk t f At mk f dt

t ds t

f cc f c ………………….…. (3.8)

Note that equation (3.8) similar to AM modulated signal.

The output after the envelope detector given as the following:

)(22 t mk f Ac f c ………………………………………………………………... (3.9)

You must add capacitor to do dc blocking.

What is the output after the capacitor?

Procedure:

Part One: Modulation and Demodulation using MC4046 and PLLMC4046Modules fig

(3.3) and fig (3.4):

1. Connect the oscilloscope to (FM O/P) output in CD4046 module and observe the output

signal .adjust the variable resistor VR1 so that the output signal 20 KHz square wave.

2. Connect the signal generator to Audio signal input (Audio I/P) and set the amplitude of

the generator 10vp-p and 1 KHz frequency of the sine wave.

3. Connect the oscilloscope to the output of the modulator (FM O/P) and observe the output

signal and take at least three measurements of frequency variations.

4. Repeat step 2 and step 3 for triangular input signal and square input signal and draw the

Modulated signal in each case.


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5. Adjust the free running frequency (fo) of the VCO output port TP1 to 20KHz in

PLLCD4046 Module.

6. Connect the output port (FM/OP) of the VCO MC4046 to the input port (FM I/P) of the

PLLMC4046.

7. At the Audio input port (Audio I/P) of the VCO connect the function generator choose

sine wave with frequency 1 KHz and choose a suitable value of amplitude to recover the

output.

Fig.(3.3): FM Modulation and demodulation using MC4046 module.

Fig (3.4): FM Modulation and demodulation using PLL MC4046 module.

Part Two: Modulation using LM566 Modules:


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1. Set J1 and J3 short circuit and J2 open circuit the selected capacitor C4=10nf in the FM

modulator LM566 Module

2. Connect the oscilloscope to (FM O/P) port adjust the variable resistor VR1 so that the

frequency of the (FM O/P) output equal to 20 KHz

3. Connect the signal generator to Audio signal input port (Audio I/P) and select sinusoidal

signal with amplitude 10vp-p and frequency 1 KHz.

4. Connect the oscilloscope to the output of the FM modulator (FM O/P) port then measure

at least three variations in frequency and draw the FM modulated signal.

5. Repeat step 3 and step 4 for triangular and square signal and calculate the maximum

frequency deviation, the modulation coefficient, the desired bandwidth for the square

modulating signal.

Fig (3.5): FM modulator and demodulator using LM566 module.

Part Three: Modulation and Demodulation using PLL LM565 Module:

1. Set J3 short circuit and J1 and J2 open circuit to choose C5=10nf in LM565 module.

2. Connect the oscilloscope to (VCO O/P) port adjust the variable resistor VR1 so that the

free running frequency fo equal to 20 KHz.

3. Connect the output port of (FM O/P) of the VCO LM566 module to the input port (FM

I/P) of the PLL LM565.

4. At the Audio input port (Audio I/P) Connect the function generator and select sinusoidal

signal with maximum amplitude and 1 KHz frequency.

5. Connect the oscilloscope to the output of the FM detector (Audio O/P) and draw the

output.

Part Four: Voltage and Frequency conversion using LM565 module:


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1. Set J2 short circuit and J3 and J1 open circuit C2=100nf

2. Adjust the variable VR1 so that the free running frequency fo of the (VCO O/P) equal 2

KHz.

3. Set J1 open circuit this means that SW1 is open

4. At the demodulated FM input port (FM I/P) connect the signal generator and choose

square wave with 5vp-p and 2 KHz frequency. Then change the input frequency as

shown in the table (2-1) and measure the amplitude of (Audio O/P) at each frequency.

5. Draw the frequency vs the voltage output (Characteristic of the VCO).

Frequency 0.5KHz 1KHz 1.5KHz 2KHz 2.5KHz 3KHz 3.5KHz 4KHz 0.5KHz

Amplitude

Table (3-1)

Fig (3.6): Voltage and frequency conversion using LM565 module.

6. Set J3 short circuit and J1 and J2 open circuit C5=10nf

7. Adjust the variable VR1 so that the free running frequency fo of the (VCO O/P) equal 20

KHz.

8. Set J1 open circuit this means that SW1 is open

9. At the demodulated FM input port (FM I/P) connect the signal generator and choose

square wave with 5vp-p and 20 KHz frequency. Then change the input frequency as

shown in the table (2-2) and measure the amplitude of (Audio O/P) at each frequency.


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Bessel function table

Hint to solve the question:

a. Jn (β) are Bessel functions of the first kind of order n and argument β. β appears in

Brackets because the Bessel functions are dependent on β.

b. Carrier wave in fc frequency and Vc . J0 (β) power.

c. Waves in f c ± n· f m frequencies and Vc . Jn (β)) power for n>0.


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EXPERIMENT.4

FDM Multiplexer and Demultiplexer

Objectives:

To understand the operation theory of frequency Division Multiplexing FDM and

Demultiplexing.

To design and implement the FDM multiplexer and Demultiplexer.

Equipment Required:

ACS11-1 and ACS12-1 of ETEK ACS-3000-06 module.

DC Power Supply.

Connection wires.

Theory:

If the transmission channel consists only of one modulated signal, then the usage of the channel

is very low and the efficiency is also not good. Therefore, in order to comfort with the economic

benefit, the channel must be able to transmit multiple signals, such as in the telephone system.

As you know the frequency range of the sound is 300Hz to 3 KHz so in order to transmit this

kind of signal via a single channel, we must divide the signal into several slots to prevent the

interference then we can obtain the signal at the receiver. There are two types of signal division

Time Division Multiplexing (TDM) and Frequency Division Multiplexing (FDM).

FDM Multiplexing:

Figure (4.1) is the system block diagram of FDM. Like TDM, FDM is used to transmit multiple

signals over the same communication channel simultaneously. However, unlike TDM, FDM

does not use pulse modulation. Figure (4.1) assumes that all the input audio signals are low pass

pattern and after each input signal, there will be a low pass filter to remove all the unwanted

signals except the audio signals. Then the audio signals will be sent into the modulator so that the

frequency range of the signals will shift to different region. The conversion of the frequency is

controlled by the carrier signal. Therefore, we utilize the simplest technique which is the AM

modulation to implement the modulator. Then the modulated signal will pass through a band

pass filter which can limit the signal bandwidth to prevent the interference between each signal.

Finally, the signals will be added by a linear adder. As compare to TDM, we utilize AM

modulation to implement FDM system and sampling to implement TDM system.


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Fig.(4.1):Block diagram of FDM Multiplexer.

In this experiment, we build each balanced modulator by utilizing MC1496 and use different

carriers for each modulator. As you know, the output from each balanced modulator is a DSB-

SC signal. Then, the DSB-SC signals will be added by a linear adder in order to produce the

FDM signal.

Fig.(4.2):Circuit diagram of DSB-SC modulation by utilizing MC1496.


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Fig.(4.3):Circuit diagram of the linear adder.

FDM Demultiplexing:

There are two ways to implement FDM demultiplexer. The first way is shown in figure (4.4). Let

the FDM signals pass through a band pass filter, this filter will remove the signal which its

frequency is larger and lower than f0 and only left a single DSB-SC modulated signal. After that,

this signal will pass through the LPF which recover the modulated signal and obtain the original

audio signal. While Figure (4.5) shows the second way to implement the FDM demultiplexer

which is called synchronous product detection. After the signal passes through the synchronous

product detector, we will add a LPF to remove all the unwanted signals and recover the original

audio signal.

Fig.(4.4):Block diagram of FDM demultiplexer (first method).


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Fig.(4.5):Block diagram of synchronous product detector.

Fig.(4.6):Circuit diagram of synchronous product detector.

Fig.(4.7):Circuit diagram of the LPF.


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Procedure:

FDM Multiplexing:

1- Refer to the audio signal generator in ACS11-1 of ETEK ACS-3000-06 module.

2- Using the oscilloscope to observe the audio signal from the signal generator 1 output

(TP1) .Adjust the variable resistors “Audio Frequency Adjust1” and “Audio Gain

Adjust1” to obtain an output audio signal with 500 Hz frequency and 620mV amplitude.



Adjust2” to obtain an output audio signal with 800 Hz frequency and 620mV amplitude.



Adjust3” to obtain an output audio signal with 1.2 kHz frequency and 620mV amplitude.

5- Refer to the carrier signal generator in ACS11-1 of ETEK ACS-3000-06 module.

6- Using the oscilloscope to observe the carrier signal from the carrier signal generator 1

output (TP2) .Adjust the variable resistor “Carrier Gain Adjust1” so that the output

amplitude of the carrier is 620mV.







9- Using the oscilloscope to observe output signal of the balanced modulator 1(TP5) .Adjust

the variable resistor “Modulator Adjust 1” so that the output is DSB -SC modulated

signal.

10- Using the oscilloscope to observe output signal of the balanced modulator 2(TP6). Adjust

the variable resistor “Modulator Adjust 2” so that the output is DSB-SC modulated

signal.

11- Using the oscilloscope to observe output signal of the balanced modulator 3(TP9). Adjust

the variable resistor “Modulator Adjust 3” so that the output is DSB -SC modulated

signal.


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12- Using the oscilloscope to observe output signal waveform of FDM output port (FDM

O/P).

FDM Demultiplexing:

1- To implement a product detector (shown in fig.(4.5)) and the low pass filter (shown in

fig.(4.6)), refer to figure ACS12-1 on ETEK ACS-3000-06 module.

2- Connect (FDM O/P) in ACS11-1 to (FDM I/P) in ACS12-1.

3- Connect the carrier signal (TP2) in ACS11-1 to (Carrier I/P1) in ACS12-1, (TP4) to

(Carrier I/P2) and (TP8) to (Carrier I/P3).

4- Using oscilloscope to observe the output signal waveforms of (Audio O/P1), (Audio

O/P2) and (Audio O/P3), then adjust the variable resistors “Carrier Adjust 1”, “Gain

Adjust 1”, “Carrier Adjust 2”, “Gain Adjust 2”, “Carrier Adjust 3” and “Gain Adjust 3”

so that the output waveforms are maximum without distortion. Record your results.


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logic will store all the bit s and reset to" 0 ", follow by the most significant bit, MSB D7 is set to

" 1 ". Thus, the output voltage of DAC is:

Fig(5-1)

Fig(5-2)

This voltage is half of the reference voltage Vref, If the input voltage Vin is higher than V( D),

then D0 to D7 remains at " 1 ", otherwise alters to " 0 ". Next, make second bit D6 as " 1 ", after


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passing through a DAC then obtain an output voltage V(D), at this moment comparing the new

V(D) and Vin, if Yin is higher than V(D), then D6 remains at " 1 " otherwise alters to " 0 ".

Similarly for the others until the comparison of D0 to D7 have been completed, then we can

obtain the complete D7 to D0 digital output.

ADC0804 Analog to Digital Converter

ADC0804 is a 20-pin DIP package with an 8-bit resolution single channel IC. The analog input

voltage range is from 0 V to 5 V with single 5 V power supply, 15 mW power consumption and

100 us conversion time . As a result of this IC contains of 8-bit resolution, so it has 2^8=256

quantization steps, if the reference voltage is 5 V , each step will be 5/256 = 0.01953 V .

00000000 (OOH) represents 0.00 V and 1111111 (FFH) represents 4.9805 V. The unadjusted

error of ADC0804 is ±1 LSB, which is 0.01953 V, which includes full-scale error, offset error

and non-linearity error. Figure 5-3 shows the pins diagram of ADC0804. In figure 5-3, the D0 to

D 7 of ADC0804 is the 8-bit output pins , when CS and RD are low, the digital data will be sentto the output pins. If any pins of CS and RD are high, then D0 to D7 are in floating condition.

WR is the write control signal, when CS and WR are Low, ADC0804 will do the clear action,

when WR backs to high, ADC will start the conversion. CLK IN (Pin 4) is the clock input , the

frequency range starts from 100 kHz to 800 kHz. During the conversion period, INTR is at high

level and then after the conversion completed, INTR will alter to low. Pin6 Vin (+) and pin7 Vin

(-) are differential analog signal inputs, ordinarily used single input terminal and Vin ( - ) is

connected to ground. ADC0804 has two ground terminals, one is analog ground (A GND) and

another one is digital ground (D GND). Pin 9 (Vref /2) is 1/2 of the reference voltage, if pin 9 is

floating , then the 1/2 reference voltage equals to power supply voltage Vee. ADC0804 has a

built-in Schmitt trigger as shown in figure 5-4. If we add a resistor and capacitor at CLK R (pin

19) and CLK IN (pin 4), then we can generate the ADC operating time.

Fig(5-3)


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Therefore, we need not input an external clock signal to CLK IN terminal . We can determine the

clock signal by the external R and C via pin 4 and pin 19.

Figure 5-5 is the circuit diagram of ADC0804 analog to digital converter, the analog signal input

range is controlled by VR2 and input through the Vin ( +) terminal and at the same time, the Vin

( -) is short circuit. Vref / 2 is provided by R1 , R2 and VR1. C1 and R3 is used to control the

clock of the circuit, CS and RD are short circuit, so that the IC is enable, then let WR and INTR

connect to SW1 in order to simulate the control signal.

Fig(5-4)

Procedure:

ADC0804 analog to digital converter

1. Refer to the circuit diagram in figure 5-4 on ETEK ACS-3000-07 module. Set J1 be open

circuit.

2. Use the digital voltage meter to measure the reference voltage input port (TP1). Adjust

VR1 so that the voltage of TP1 is 2.5 V. At this moment, ADC0804 analog voltage input

range is 0 V to 5 V.

3. By using oscilloscope, observe on the TP2.

4. Adjust VR2 so that the input voltage of the analog signal input port (TP3) is 0 V, and

record the measured results in table 5-1.


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5. Set J1 be short circuit to maintain the output digital signal. Observe on the changes of

LED, LED "on" represents " I", LED "off' represents "0".

ADC0809 analog to digital converter

1. Refer to the circuit diagram in figure 5- 5 on ETEK ACS-3000-07 module.

2. At the CLK input port (CLK I/P), input 120 kHz frequency and a TTL signal with 5 V

offset.

3. Let SW3, SW2 and SW1 switch to GND (push down the slide switch), at this moment,

the multiplexer selects to channel 0 and the analog signal is inputted from the IN0 input.

4. Use the digital voltage meter to measure the TP1 of channel 0. Adjust VR1 so that the

input voltage of TP1 is similar to the values in table 5-2. Observe on the changes of LED,

LED "on" represents “1’’. LED "off' represents "0", then record the measured result s in

table 5-2.5. Use the digital voltage meter to measure the TP2 of channel 1 until TP7 of channel 6, and

then record the measured results in table 5-3.

Fig(5-5)


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Table(5-1)

Table(5-2)


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Table(5-3)


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EXPERIMENT.6

Digital to Analog Conversion (DAC)

Objectives:

To understand the operation theory of digital to Analog converter. To implement the digital to analogue converter by using ADC0804 and ADC0809.

Equipment Required:

ETEK-DCS-3000-07 module

Signal Generator

Oscilloscope DC-Power supply

Theory:Digital to analog converter (DAC) is a device, which converts the digital signal to analog signal. We

normally store a digital signal in a media or transmission line. Then a DAC changes the digital signal

to an analog signal in order to control data display or further analog signal processing. For example,

from a digital communication system, when a receiver receives the digital modulation signal , then

after via a demodulator and decoder, we can obtain the digital signal, and follow by using DAC to

convert this digital signal to the analog signal. Next we will discuss the basic operation theory of

DAC.

Basically, DAC is a digital code that represents digital value converted to analog voltage or current.

Figure 6-1(a) is a genera 14-bit DAC binary codes , the digit al input terminal [D3 D2 D1 D0] are

manipulated by the register in a digital system . The 4-bit code represent s 2^4= 16 groups of 2 . binary

state value, as shown in figure 6-1(b). For every binary code input, DAC will output a voltage (Vout),

which is double or other order of the binary value. According to this, analog output voltage Vout and the

digital input binary values are the equivalent. If the DAC output is current, l out, the theory is similarly.

Figure 6-2 is the basic block diagram of DAC. The reference voltage (Vref) is used to providethe reference voltage during conversion, Then due to the magnitude of the input binary code , the

digital control switch will output different binary codes to the resistors network. Normally, the

DAC analog output is represented by current, if we want to obtain the voltage output, we need to

connect an operational amplifier, which can convert the current to voltage level.


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Fig(6-1a)

Fig(6-1b)

Fig(6-2)

Resolution and Step Size:

The resolution of DAC illustrates that when the digital input terminal changes a unit, it will

produce a small change at the analog output terminal, which is normally the LSB levels. Refer to


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figure 6-1(b), when the digital input value changes a unit Vout will change at least 1 V, so the

resolution is 1V.

Resolution is also called step size because Vout will change, when the digital input step varies

from one to another. Figure 6-3 shows a 4-bit binary counter as DAC digital input signal, the

counter has a clock input, so it can output 16 types of statuses continuously in cycle . The output

waveform of DAC is every step with 1V change. When the counter generates 1111, the DAC

output is the maximum value, which is 15 V. We call this situation as full-scale output. When the

counter generates 0000, the DAC output is 0 v. Resolution or step size is to indicate the

difference between two steps. For example, if the step size is 1 V then the difference between the

steps is 1V.

Figure 6-3 shows 16 types digital inputs corresponding to the 16 levels of output steps

waveform. From 0 V to 15 V (full-scale) , there are only 15 steps size. Generally, N bits of DAC

will produce 2N different levels and 2N-1 steps size.

Fig(6-3)

DAC 0800 Digital to Analog Converter:

DAC 0800 is a cheap and commonly used 8-bit DAC, the internal circuit consists of reference

voltage power supply, R-2R ladder resistors network and transistor switch. The voltage power

supply range is between ± 4.5 V to ± 18 V, under the ± 5 V condition, the power loss is

approximately 33mWand the settling time is approximately 85 ns. Figure 6-4 is the pins diagram


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of DAC0800. Figure 6-5 is the circuit diagram of DAC0800 single polarity voltage output, which

D7 ~ Do are the 8-bit digital input s. The positive reference voltage is + 5V and passes through

R1 to connect to Vref(+) (pin14). The negative reference voltage is GND and passes through R2

to connect to Vref (-) (pin 15). The reference current Iref that passes through R1 can be

expressed as Iref in the following equation (6-1):

At the current output terminal (pin4), the output current as in equation(6-2) below I out is:

Fig(6-4)


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Fig(6-5)

Procedure:

Part1: R-2 R network DAC:

1. Refer to the circuit diagram in figure 6-6(b) or figure ACS14-1 on ETEK ACS-3000-07

module.2. Let SW I, SW2, SW3 and SW4 switch to 1 ("0" represents as GND, " 1" represents as

"+5 V").

3. By using voltage meter to measure TP1 , TP2 , TP3, TP4, TP5 of R-2Rnetwork and

output port of D/A converter (Vout) . According to the switching of SW 1, SW2, SW3

and SW4 in table 6-l, record the measured results in table 6-1.

Fig(6-6)

Part 2: DAC0800 unipolar voltage output

1. Refer to the circuit diagram in figure 6-7 or figure ACS 14-2 on ETEK ACS-3000-07

module.


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5. Let J1 and J2 be short circuit, J3 be open circuit. Using digital voltage meter to measure

the output voltage Vout , then record the measured results in table 6-3 .

6. Let J1 and J3 be open circuit, J2 be short circuit. Connect the digital current meter to J1,

then measure the output current Iout . Finally record the measured results in table 6-3.

7. Let J2 and 13 be open circuit, J1 be short circuit. Connect the digital current meter on J2

to measure the output current Iout. Finally record the measured results in table 6-3 .

8. Calculate I out + I~out and record the measured results in table 6-3.

Table(6-1)


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Table(6-2)


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Table(6-3)


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EXPERIMENT.7

Pulse Code Modulation (PCM)

Objectives:

T o study the operation of a PCM encoder.

To study the operation of a PCM decoder.

To consider reasons for using digital signal transmission of analog signals.

Equipment Required:

ETEK-DCS-6000-03 module Signal Generator

Oscilloscope DC-Power supply

Prelab works:

Consider the sinusoidal test signal )2cos()( t t x this signal is applied to a sampler operating at

10 sample per second followed by a 8 level quantizer with a range of (-1, +1).the quantized

samples are then applied to a natural binary encoder. (i.e, one that assigns 000 to the first level

and 111 to the eight levels).

a. Plot x(t) for 10 t

b. Find the values of the sampled signal over 10 t

c. Find the quantized values of x(t) for 10 t

d. Find the sequence of binary digits observed at the encoder output for 10 t

Theory:

Pulse-code modulation (PCM) is a digital representation of an analog signal where the

magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of

symbols in a digital (usually binary) code. PCM has been used in digital telephone systems and

is also the standard form for digital audio in computers.

http://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Digitalhttp://en.wikipedia.org/wiki/Signalling_%28telecommunication%29http://en.wikipedia.org/wiki/Sampling_%28signal_processing%29http://en.wikipedia.org/wiki/Quantization_%28signal_processing%29http://en.wikipedia.org/wiki/Binary_numberhttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Digital_audiohttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Computerhttp://en.wikipedia.org/wiki/Digital_audiohttp://en.wikipedia.org/wiki/Telephonehttp://en.wikipedia.org/wiki/Binary_numberhttp://en.wikipedia.org/wiki/Quantization_%28signal_processing%29http://en.wikipedia.org/wiki/Sampling_%28signal_processing%29http://en.wikipedia.org/wiki/Signalling_%28telecommunication%29http://en.wikipedia.org/wiki/Digitalhttp://en.wikipedia.org/wiki/Modulation


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Sampler should operate at a rate of w fs 2

Absolute error less than2

where is the step of the quantizer, and n is the number of

bits per sample.

If 2Ais the peak to peak variation of the message signal and Q is the number of

quantization levels, then

Q

A2 where

nQ 2

The above fig represent a uniform quantizer with A=4v,Q=8.

18

8


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Procedure:

Consider the circuit diagram in figure 7-1 in ETEK DCS-6000-03 module.

Fig (7.1)

1. Set J1 short circuit and from the signal input terminal (I/P), connect the signal generator and

Set the amplitude of the sinusoidal signal 5 vp-p and 500Hz frequency.

2. Connect the oscilloscope to observe on the output terminal of low-pass filter (Tl), input

terminal of audio signal (T2), feedback point of output signal (T3) and output signal Terminal of

PCM (OP). After that connect the output terminal (T4) with2048 kHz square wave to the CH1 of

the oscilloscope and output terminal (T6) of modulated signal to CH2 of the oscilloscope, then

Draw the output of each terminal and determine the amplitude and the frequency of each output.

Consider the circuit diagram in figure 7-2 in ETEK DCS-6000-03 module.

Fig (7.2)

3. Set J1 of DCS6-1 short circuit and connects the output terminal (PCMO/P) of modulated PCM

signal of DCS5-1 to the input terminal (PCM I/P) of demodulation PCM signal of DCS6- 1. By


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using oscilloscope, observe on the output terminal of buffer (TI), 2048 kHz square wave

generator (T2), 8 kHz square wave generator (T3), demodulated PCM signal output Terminal

(T4) and signal output terminal (Audio O/P), then record the measured results and draw each

output and determine the frequency and the amplitude for each output.

4. Repeat step (1-3) when the frequency of the function generator change to 1 KHz.

5. Set J2 short circuit and J1 open and from the signal input terminal (I/P), connect the signal

generator and Set the amplitude of the sinusoidal signal 5 vp-p and 500Hz frequency.

6. Connect the oscilloscope to observe on the output terminal of low-pass filter (Tl), input

terminal of audio signal (T2), feedback point of output signal (T3) and output signal Terminal of

PCM (OP). After that connect the output terminal (T4) with 2048 kHz square wave to the CH1

of the oscilloscope and output terminal (T6) of modulated signal to CH2 of the oscilloscope, then

Draw the output of each terminal and determine the amplitude and the frequency of each output.

7. Set J2 of DCS6-1 short circuit and J1 open and connects the output terminal (PCM O/P) of

modulated PCM signal of DCS5-1 to the input terminal (PCM I/P) of demodulation PCM signal

of DCS6- 1.

8. connect the oscilloscope, observe on the output terminal of buffer (TI), 2048 kHz square

wave generator(T2), 8 kHz square wave generator (T3), demodulated PCM signal output

Terminal (T4) and signal output terminal (Audio O/P), then record the Measured results and

draw each output and determine the frequency and the amplitude for each output.

9. Repeat step (5-8) when the frequency of the function generator change to 1 KHz.


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EXPERIMENT.8

TDM Multiplexer and Demultiplexer

Objectives:

To understand the operation theory of Time Division Multiplexing TDM and

Demultiplexing.

To design and implement the TDM multiplexer and Demultiplexer.

Equipment Required:

ACS9-1 and ACS10-1 of ETEK ACS-3000-05 module.

DC Power Supply.

Connection wires.

Theory:

Time Division Multiplexing TDM:

TDM means multiple signals can be transmitted over the same transmission channel. Time

division indicates the signal is divided into several slots in time domain, and then these slots will

transmitted to the receiver by following a fixed time slots. Therefore, these slots are also called

as sampling values. If the fixed time slot is large enough for other sampling value of other signal

to fill in, then this method can achieve the function of multiplexing. The basic structure of TDM

system is shown in figures 8.1 and 8.2 below:

Fig(8.1): TDM with two signals m1(t) and m2(t).


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Fig(8.2): Circuit structure of TDM system.

The implementation of the TDM Multiplexer:

As a result of TDM uses the same channel to transmit several group of signals .Therefore, in this

experiment we utilize sinusoidal, square and triangle waves as the several groups of signals to

achieve the TDM modulation.

Since the TDM uses the time slots to transmit signal so we need to produce a time generator

circuit (shown in fig 8.3) which can generate a fixed timing as the switching circuit.

Fig(8.3): Circuit diagram of time generator.


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Fig(8.4): Time sequence of time generator.

The fig (8.5) shows the circuit diagram of TDM multiplexer. When t1 is high the triangular wave

will occur at the output port while when t2 is high then the square wave will be at the output port

and when t3 is high the output will be the sinusoidal wave.

Fig(8.5): Circuit diagram of TDM multiplexer.

TDM Demultiplexing:

After we divided the time of transmission channel into several time slots, there will be a smallgap between each time slots which is known as guard time and it is used to prevent the

interference between the symbol and jitter of the multiplexer. Therefore, we can utilize the pulse

at a certain period to process different number of channels. On the other hand, according to the

synchronous signal at the transmitter, the receiver can also separate the signals of different

channels accurately. The example of a simple TDM system is shown below in fig (8.6).


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Fig(8.6): Transmission diagram of TDM system.

The implementation of the TDM Demultiplexer:

Fig (8.3) is also used as a synchronous signal generator for Demultiplexing. The most importantthing is the synchronization between both time generators in the transmitter and receiver so the

system will be able to recover the original signal. Fig (8.7) is the circuit diagram of TDM

demultiplexer. When TDM signal inputs by matching with the synchronous signal generator,

then we can obtain the input sequences which are the triangle, square and sinusoidal waveforms.

Fig(8.7): Circuit diagram of TDM demultiplexer.

Procedure:

TDM Multiplexing:

Refer to figure ACS9-1 of ETEK ACS-3000-05 module.


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1- By using oscilloscope, observe the output signal of triangular wave output port (TP1),

adjust the variable resistor VR3 so that the amplitude of TP1 is maximum without

distortion. Record your result.

2- Observe the output signal of square wave output port (TP2), adjust the variable resistor

VR1 so that the amplitude of TP2 is maximum without distortion. Record your result.

3- Observe the output signal of sine wave output port (TP3), adjust the variable resistor VR3

so that the amplitude of TP3 is maximum without distortion. Record your result.

4- Turn the variable resistor “Clock Adj.” left to the end, at this moment the counter of theclock is slow. By using CH1 of the oscilloscope, observe the output signal of the

triangular wave at port (TP4) .Use CH2 to observe TDM output port (TDM O/P). Record

your result.

5- By using CH1 of the oscilloscope, observe the output signal of the square wave at port

(TP5) .Use CH2 to observe TDM output port (TDM O/P). Record your result.

6- By using CH1 of the oscilloscope, observe the output signal of the sine wave at port

(TP6) .Use CH2 to observe TDM output port (TDM O/P). Record your result.

TDM Demultiplexing:

Refer to figure ACS10-1 of ETEK ACS-3000-05 module.

1- Connect the output port (TDM O/P) of TDM multiplexer in ACS9-1 to the input port

(TDM I/P) of TDM demultiplexer in ACS10-1.

2- Observe the output signal of (TP1) of TDM demultiplexer. Record your result.

3- Connect the triangular wave output port (TP4) of TDM multiplexer to (TP2) of TDM

demultiplexer.

4- Connect the square wave output port (TP5) of the TDM multiplexer to the square wave

input port (TP3) of the TDM demultiplexer.

5- Connect the sine wave output port (TP6) of the TDM multiplexer to the sine wave input

port (TP4) of the TDM demultiplexer.

6- Using the oscilloscope to observe the signals at (TP2) and (O/P1) of the TDM

demultiplexer.

7- Again use CH1 and CH2 of the oscilloscope to observe (TP2) and the square wave output

port (O/P2) of the TDM demultiplexer.

8- Also observe both (TP2) and the sine wave output port (O/P3) of the TDM demultiplexer.

9- Use the oscilloscope to observe (TP3) and the output signal of triangular wave output


10- Observe again (TP3) and the output signal of square wave output port (O/P2) of the TDMdemultiplexer.

11- Observe again (TP3) and the output signal of sine wave output port (O/P3) of the TDM

demultiplexer.

12- Use the oscilloscope to observe (TP4) and the output signal of triangular wave output


13- Observe again (TP4) and the output signal of square wave output port (O/P2) of the TDM

demultiplexer.


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14- Observe again (TP4) and the output signal of sine wave output port (O/P3) of the TDM

demultiplexer.


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EXPERIMENT.9

Amplitude Shift Keying (ASK)

Objectives:

Creation of ASK an modulated signal

Detection of the modulated signal using envelope detector

Detection of the modulated signal using bandpass filter followed by an envelope

detector

Equipment Required:

TPS3-3431

Power supply

Banana wires

Theory:

The general block diagram that represent the generation of ASK signal given bellow

The bit stream consists of a sequence of binary digits as demonstrated below for the sequence

(10110100):

The data after converting it to uni-polar non-return to zero [u-NRZ] is as the following:


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The data after multiplication with a carrier [vcos(2pifct)] is an ASK signal as the following:

The detection of an ASK signal is done using envelope detection as the follows:

Refer to envelope detection of AM signal

Try to find the output after each stage of envelope detector.

Note it is not enough to do detection using envelope detector you must use two Schmitt

trigger to convert the analogue output to digital output.

The output after the two Schmitt trigger must be as the following (in the case of perfect data

recovery):


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Demodulation process using non-coherent demodulator:

Disadvantage of ASK modulated signal

1. Amplitude not constant this causes the detection process to be very difficult.

2. Usable only for Low data rate .

Remarks:

The spectrum of ASK signal resembles that of Normal AM modulation.

Procedure:

Connect the trainer to the power supply.

Connect the power supply to the Mains and turn it ON.

Connect the data transmitter output to the ASK modulator input

Set the BIN/QUAD switch to the BIN position.


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Connect the CH1 scope probe to the modulator input.

You should see the transmitted data on channel CH1.

Set the switches to the binary number 0101010 1 and watch the transmitted Data signals.

Connect the CH2 scope probe to test point TP 1.You should see the Fl carrier wave.

Measure or calculate the frequency of the carrier wave.

This frequency should be approximately 12 KHz. Move the output of the CH2 scope probe to the modulator output.

In your notebook, draw the shape of the signals - the modulator (at the

Modulator input) and the signal at the modulator output.

Connect the modulator output to the envelope detector input.

Move the CH2 scope probe from the modulator output to the detector's Output. Decrease the time base a little in order to see more FI cycles during Transmission.

Because of the low sampling rate, you can notice only some of the F1Cycles.

In your notebook draw the shape of the signals-the modulated signal (at the detector

input) and the output of the detector.

Connect the output of the detector to the upper Schmitt trigger amplifier


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Move channel 2 of the scope probe from the detector output to the amplifier output.

In your notebook draw the shape of the signals-the modulated signal (at the detector

input) and the signal at the amplifier output..

Connect the output of the ASK modulator to the input of the bandpass filter(BPF)

Connect channel 2 of the scope probe to the filter input.

Draw the filter input

Connect channel 2 of the scope probe to the output of the filter

Draw the output of the filter

Connect the filter output to the envelope detector input

Connect the detector output to the upper Schmitt amplifier input

Connect the Schmitt trigger1 output to the Schmitt trigger2 input

Connect the Schmitt trigger2 output to the data receiver input


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Make sure that the binary number indicated on the data transmitter switches appears on

the lights of the data receiver.

Repeat all the steps for different data sequence:00110011,00001111,00111100

Check whether the frequency of the modulating signal (in the data transmitted) has an

effect on the filtration and detection signals.

Questions:

An ASK modulated signal is transmitted to an AM detector. The modulating signal is a

symmetrical square wave at a frequency of 1000HZ .The carrier wave is at an intensity of 20 vp-

p and a frequency of 15 KHZ.

Draw the signal described in the mathematical expression .

What will the shape of the wave at the next filter output be?

What will the shape of the wave at the next filter output be?


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EXPERIMENT.10

Frequency Shift Keying (FSK)

Objectives:

Creation of FSK modulated signal

Detection of the FSK signal using non-coherent detector

Equipment Required:

TPS3-3431

Power supply

Banana wires

Theory:

In binary FSK symbols (1) and (0) are distinguished from each other by transmitting one of the

Two sinusoidal signals that differ in frequency.

Generation of FSK signal

1. Direct method of generation using VCO [voltage controlled oscillator].

2. In-direct method of generation

Two type of FSK modulated signal

1. Coherent FSK

2. Non-coherent FSK

What is the major difference between the two types of FSK signal?

The formula of FSK modulated signal

t f At s 11 2(cos)( ………………..for binary (0)

t f At s 22 2(cos)( ………….….for binary (1)


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The general shape of the FSK modulated signal

The detection of FSK modulated signal done using:

BPF[band-pass filter]

Envelope detector

Two Schmitt trigger

What is the operation of each detection parts?

Direct Methods of FSK generation:

1. Two oscillator method

2. Voltage control oscillator


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Demodulation using non-coherent demodulator:

Procedure:


Connect the power supply to the Mains and turn it ON. Connect the data transmitter output to the FSK modulator input




Set the switches to the binary number 01010101 and watch the transmitted Data signals.

Connect the CH2 scope probe to test point TP 2. You should see the F2 carrier wave.

Measure or calculate the frequency of the carrier wave.

This frequency should be approximately 25 KHz.

Move the output of the CH2 scope probe to the modulator output.


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In your notebook, draw the shape of the signals - the modulator (at the Modulator input)

and the signal at the modulator output.

Connect the modulator output to the Bandpass filter input(BPF).

Connect channel 2 of the scope probe to the filter input.

Draw the filter input

Connect channel 2 of the scope probe to the output of the filter

Draw the output of the filter

Connect the filter output to the envelope detector input

Connect the detector output to the upper Schmitt amplifier input

Connect the Schmitt trigger1 output to the Schmitt trigger2 input

Connect the Schmitt trigger2 output to the data receiver input

Make sure that the binary number indicated on the data transmitter switches appears on

the lights of the data receiver.

Repeat all the steps for different data sequence:00110011,00001111,00111100

Check whether the frequency of the modulating signal (in the data transmitted) has an

effect on the filtration and detection signals.


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EXPERIMENT.11

Binary Phase Shift Keying (BPSK)

Objectives:

Creation of a BPSK modulated signal

Detection of the signal using a BPSK detector

Equipment Required:

TPS3-3431

Power supply

Banana wires

Theory:

General block diagram for BPSK generation:

Prove that the output of the following diagram is given by:

02(cos)(1 t f At s c ………………....for binary (0)

t f At s c2(cos)(2 ………………..for binary (1)

The following fig represents the BPSK modulated signal.


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Note that bits 1 and 0 have the same amplitude and the same frequency but they differ in

phase.

BPSK Detection:

The detection of BPSK is achieved by:

1. XOR-gate

2. LPF [low pass filter]

Exercise: draw the block diagram and explain its operation

Detection of BPSK using coherent demodulator:

Exercise: Analyze the operation of each block in the above block diagram.

Remarks:

The spectrum of the binary BSK resembles that of double sideband suppressed carrier

modulation.

The following table represents Null to Null band width for each digital modulation technique:

Digital modulation technique Null to Null band width

ASK 2rb

BPSK 2rb

FSK 3rb

QPSK 2rs= rb


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Where:

rb: represent the data rate

r s: symbol rate (One symbol consists of two binary digits)

Procedure:


Connect the power supply to the Mains and turn it ON.

Connect the data transmitter output to the modulator input




Set the switches to the binary number 01010101 and watch the transmitted Data signals.

Connect the CH1 scope probe to test point TP1.You should see the F1 carrier wave.

Connect the CH2 scope probe to test point TP4.

You should see the carrier wave F1 in the phase shift 180

Move the output of the CH2 scope probe to the modulator output and return probe of

CH1 to the modulator input.

In your notebook, draw the shape of the signals - the modulator (at the Modulator input)

and the signal at the modulator output.

Connect the BPSK modulator output to the BPSK detector input.

Connect the BPSK detector output to the data receiver input.


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the sum of the two components. The topmost waveform alone matches the description given for

BPSK as shown below.

The general block diagram of the modulator:

Generation of QPSK signal using two

Where:

Basis function1= )2cos(2

t f Ts

c


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Basis function2= )2sin(2

t f Ts

c

Detection of QPSK using the above generator:

Space representation of QPSK:

General block diagram of the QPSK receiver:


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Connect the CH2 scope probe to the Dinl modulator input. You should see the

transmitted data on channel CH2 according to the clock pulses.

Draw on a graph the clock pulses, the Dout0 and the Doutl channels Signals.

Move the CH2 probe output to the modulator output. It is very difficult to see the phase

changes because the data rate is much lower than the signal frequency.

Connect the QPSK modulator output to the QPSK detector input.

Connect the detector outputs to the corresponding data receiver inputs.

Check that the binary number indicated by the switches on the data Transmitter appears

in the lights on the data receiver.

Connect the CH1 scope probe to test point TP9 (the receiver clock).

Connect the CH2 scope probe to the Din0 receiver input. You should see the received

data on channel CH2 according to the clock pulses.

Connect the CH2 scope probe to the Din1 receiver input. You should see the received

data on channel CH2 according to the clock pulses.

Draw on a graph the clock pulses, the Dout0 and the Doutl channels Signals.

Repeat the above steps for the binary numbers: 00110011 and 11100100.


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EXPERIMENT.13

Delta Modulation and Detection

Objectives:

To understand the delta modulation.

To understand the signal waveforms of delta modulation.

Design and implementation of delta modulator.

To understand the operation of the delta demodulation.

Equipment Required:

ETEK-DCS-6000-04 module

Signal Generator

Oscilloscope

DC-Power supply

Theory:

The Operation Theory of Delta Modulation:

Delta modulation is a kind of source coding which can convert the analog signal to digital signal.

After that we can deal with the digital signal easily such as encoding, filtering the unwanted

signal and so on. Furthermore, the transmission quality of digital signal is better than analog

signal , this is because digital signal can recover the original signal easily by the comparator.

The block diagram of delta modulator is shown in figure 4-1. From figure 4-1, the subtraction

between the low frequency signal x(t) and the signal xs(t) will produce a difference signal d(t) ,

where Xs(t) is a reference signal, which is the former sampling value. Therefore the expression

of the difference signal d(t) is given as:

d(t)= x(t)-xs(t)

However the difference signal d(t) will be converted by a limiter, then we can obtain a signal

given as:

∆(t)={+ ∆ if ∆(t)>0}


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∆(t)={-∆ if ∆(t)8fs /2= 4fs = 8 W , which is 8

times more than the original bandwidth. Although PCM modulation increases the quality of

transmission, it also increases the transmission bandwidth. However delta modulation can reduce

the transmission bandwidth and achieve the quality of transmission as PCM modulation.

Figure 13-2 is the basic circuit diagram of delta modulation. The audio signal will pass through a

low -pass filter to remove the unwanted signals, which can prevent the interference from noise.

The comparator is to compare the audio signal and the output signal of integrator, then the

difference will be sampled by the D-type flip -flop and the output signal is a TTL digital signal.

After that the output signal will feedback to integrator for integration and the output signal of

integrator will again compare to the input signal to obtain the value of +∆ or -∆ .


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We modified the circuit diagram of delta modulation in figure 13-2 to figure 13-3. From figure

13-3 we add a multiplexer to control the gain of the integrator. This is because the gain of the

integrator will affect the slope of the output signal of integrator; therefore, this method can

prevent the occurrence from slope overload. U1is the comparator, which can compare the audio

signal and the output signal of integrator, then the output square wave sign al will be sampled by

a D-type flip -flop and finally the output signal is the delta modulation signal. U2 is the

conversion of unipolar to bipolar circuit. Since there is no output signal from integrator by

inputting the unipolar square wave signal, therefore, we need to convert the unipolar signal to

bipolar signal. Analog switch is a structure of multiplexer. Tile purpose of the analog switch is

the selection of the amplified gain of integrator. When AB=OO, the signal will pass through R14

, R13 , R12 , R11 and send into integrator; when AB=11 , the signal will pass through R14 to

integrator. U3 is an inverse integrator. The expression without R16 is given as:

Vo=-Vc= ∫

By adding a shunt resistor R16 between integrator U3 and capacitor C1, we can improve the low

frequency response of the integrator. Assume that R16 and C1 are equivalent impedance, then

we get :Av=vo/vin=(R16/R15)/(1+S/WH)

Where :WH=1/R16*C1

Fig(13-2)


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Fig(13-3)

Procedure:

1. To implement a delta modulator circuit as shown in figure (1) or refer to figure DeS7-1

on ETEK DCS-6000-04 module.

Fig (1)

2. Set J2 and J3 be short circuit the connection between Xo and X is on. At the signal

input port (I/Pl), input a 5 Vp-p and 500 Hz sine wave frequency. Next at the CLK

input port (I/P2), input a 5 Vp-p and 32 kHz TTL signal. Then observe the input

signal (TP1), the output port of comparator (TP2), the output port of the conversion from

unipolar to bipolar (TP3), the output port of tunable gain (TP4), the output port of

integrator (TP5) and the output port of delta modulation signal (O/P) by using

oscilloscope. Finally record the measured results.


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3. To implement a delta demodulator circuit as shown in figure (2) or refer to figure DCS8-l

on ETEK DCS-6000-04 module.

Fig (2)

4. Connect the modulated delta signal (O/P) in figure DCS7-l to the input terminal (I/P l) of

the delta demodulator in figure DCS8-1. At the CLK input port (I/P2) of the delta

demodulator, input a 5 Vp-p and 32 kHz TTL signal. Then by using oscilloscope,

observe on the output signal waveforms of sampling signal output port (TPl), unipolar-to-

bipolar (TP2), tunable gain (D), low-pass filter (TP4) , integrator (TP5) and signal output

port (O/P). Finally, record the measured results.

5. Change the input signal to 5 Vp-p and 2KHz frequency and same input CLK , repeat

steps 2-4 and record the measured results.

6. Change the input CLK TLL signal to 5 Vp-p and 128KHz frequency and input

signal 5 Vp-p and 500Hz frequency repeat steps 2-4 and record the measured results.

7. Change the input CLK TTL signal to 5 Vp-p and 128KHz frequency and inputsignal 5 Vp-p and 2KHz frequency repeat steps 2-4 and record the measured results.

8. Set J2 and J4 be short circuit, the connection between XJ and X is on for both

modulator and demodulator circuit.

9. At the signal input port (I/P l), input a 5 Vp-p and 500Hz sine wave frequency. Next at

the CLK input port (I/P2), input a 5Vp-p and 64 kHz TTL signa1. Then by using

oscilloscope, observe on the output signal waveforms of TP1, TP2, TP3, TP4, TP5 and

O/P signal. Finally record the measured results.

10. Connect the modulated delta signal (O/P) in figure DCS7-l to the input terminal (UP1) of

the delta demodulator in figure DCS8-1. At the CLK input port (UP2) of the delta

demodulator, input a 5 Vp-p and 64 kHz TTL signal. Then by using oscilloscope,


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observe on the output signal waveforms of TP1, TP2, TP3, TP4, TP5 and O/P signal.

Finally record the measured results.

11. Change the input signal to 5 Vp-p and 1.5KHz frequency, repeat step 9-10 with same

CLK and record the measured results.

12. Change the input CLK TLL signal to 5 Vp-p and 128KHz frequency and input

signal 5 Vp-p and 500Hz frequency repeat steps 9-10 and record the measured results.

13. Change the input CLK TTL signal to 5 Vp-p and 128KHz frequency and input

signal 5 Vp-p and 1.5KHz frequency repeat steps 9-10 and record the measured results.

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