medc lab-2014-15(1)

IV B.Tech. ECE-I Semester Microwave and Digital Communications

Laboratory Manual

Bhoj Reddy Engineering College for Women, Saidabad, Hyderabad-59 of 52

BHOJ REDDY ENGINEERING

COLLEGE FOR WOMEN

Microwave and Digital Communications

Laboratory Manual

ECE IV YEAR -I SEM

DEPARTMENT OF ELECTRONICS &COMMUNICATION ENGINEERING

(Affiliated to Jawaharlal Nehru technological university & Recognized by AICTE) 17-1-209/B, Vinaynagar, Saidabad, Hyderabad-500059 Ph:No: 040-24537282,040-24531725,Fax: 040-2537281

www.brecw.ac.in Email:[email protected]


Laboratory Manual


INDEX

Sl.No. NAME OF THE EXPERIMENT Page No.

PART - A 1

FREQUENCY AND WAVE LENGTH MEASUREMENT

4

2 REFLEX KLYSTRON MODE CHARACTERISTICS

8

3 SCATTERING MATRIX OF A MAGIC TEE

11

4 CHARACTERISTICS OF GUNN OSCILLATOR

14

5 DIRECTIONAL COUPLER CHARACTERISTICS

17

6 MEASUREMENTS OF A SCATTERING PARAMETERS OF CIRCULATOR

20

7 MEASUREMENT OF IMPEDENCE OF A GIVEN LOAD

23

PART – B 1

PULSE CODE MODULATION AND DEMODULATION

27

2 TIME DIVISION MULTIPLEXING & DEMULTIPLEXING

30

3 FREQUENCY SHIFT KEYING

34

4 PHASE SHIFT KEYING MODULATION AND DEMODULATION

38

5 DIFFERENTIAL PHASE SHIFT KEYING MODULATION AND DEMODULATION

42

6 DELTA MODULATION AND DEMODULATION

46

7 DIFFERENTIAL PULSE CODE MODULATION & DEMODULATION

50


Laboratory Manual


PART – A

Microwave Engineering


Laboratory Manual


Experiment No 1

FREQUENCY AND WAVE LENGTH MEASUREMENT

AIM: To measure the frequency and wavelength of the microwave signal generated by Reflex Klystron in a wave-guide by two methods.

1. Frequency meter or Cavity meter method 2. Slotted line method

APPARATUS: Klystron power supply Klystron mount with Reflex klystron Isolator Frequency meter Variable attenuator Slotted line Tunable probe Short circuit & Matched Termination VSWR meter Cables Cooling fan Wave guide Stands Block Diagram:

Klystron power Supply

Klystron mount with tube

Isolator

Variable Attenuator

Frequency Meter

Slotted line

Matched Terminator

Crystal Detector

VSWR meter

Short circuit Terminator


Laboratory Manual


THEORY: The relationship among the free space wave length λ, guide wave length λg and the cutoff wave length λc is given by

1/ λ2 =1/ λg2+1/ λc

2 The cutoff wavelength λc is given by λ c=2/√ [m/a)2+(n/b)2] For the dominant TE10 mode m=1 n=0 λc=2a where ‘a’ is the broader side dimension of wave guide X band frequency range is 8.2 GHz to 12.4 GHz For ‘X’ band rectangular wave guide(WR90), the dimensions of rectangular waveguide are 0.9” × 0.4” A =0.9 × 2.54 = 2.286 cm λc = 2a =2 × 2.286 = 4.572 cm The guide wavelength λg varies with respect to free space wavelength λ and which is governed by frequency of oscillations. Though the guide wavelength λg doesn’t depend upon the type of termination we use short circuit for getting a clear standing wave pattern as shown in fig The resonant frequency of the Cavity can be varied between 8.2 to 12.4 GHz. In an absorption type cavity meter if the resonant frequency fr doesn’t equal to the signal frequency fs no power will be absorbed by the cavity meter and the signal will be passed on to the next section without any attenuation. If the resonant frequency fr equals to the signal frequency fs most of the signal will be absorbed by the cavity itself and power available to SWR meter will be quite low so a Dip (min deflection) can be observed in SWR meter. When a Dip is observed the resonant frequency fr and the signal frequency fs will be equal. To find the signal frequency generated using the cavity meter, change the resonant frequency slowly and observe the deflection in VSWR meter. If a Dip is observed it means that fr and fs are equal. Find the resonant frequency that is nothing but the signal frequency. PROCEDURE:

1. Arrange the microwave bench as per the diagram shown. Put the matched termination as a load.

2. Switch ON the klystron fan or blower.


Laboratory Manual


3. Put the select display knob in ‘off’ position, Beam voltage knob in ‘minimum’ position and rep voltage knob in ‘maximum’ position and now switch on the Klystron power supply.

4. Put the select display knob in ‘v’ (voltage) position and adjust the beam voltage to 300V.

5. Put the select display knob in ‘rep’ (repeller voltage) position and adjust the repeller voltage to get VSWR as ‘1’.

6. Tune the frequency meter to get a ‘dip’ on the VSWR meter and note down the operating signal frequency directly from the frequency or wave or cavity meter

7. Detune the frequency meter. Now remove the matched load and put the short circuit as a load.

8. Move the probe along the slotted section and observe the standing wave pattern. It is moved to the minimum deflection point and its position is noted down.

9. Move the probe to the next position and record the probe position again. 10. The guided wavelength is calculated as twice the distance between the

minima. 11. By using the expression 1/ λ2 = 1/ λg

2 + 1/λc2 calculate λ and then calculate

the frequency as f = c/ λ 12. Compare this frequency with the frequency obtained through the

frequency meter. They both should be same. MODEL GRAPH:


Laboratory Manual


OBSERVATIONS:

(i) Cavity meter method:- Beam Voltage = Repeller voltage = Current = Frequency = Wave length =

(ii) Slotted line method:- Positions of minima: First (d1) = Second (d2) = Third (d3) = λg/2 = [(d2-d1)+(d3-d2)]/2 λc = 2a = 4.572 cm 1/ λ2 = 1/ λg2 + 1/ λc2 F=c/ λ

RESULT: Frequency and wavelength of the microwave signal generated by

Reflex Klystron in a wave-guide measured

SAMPLE VIVA QUESTIONS: 1. Indicate the frequency Vs wave length for X-band 2. Explain the principle of isolator & circulator? 3. Explain the principle of frequency meter? 4. What type of frequency meter used in microwave test bench? 5. What is the function of the frequency meter in the microwave bench? 6. What are the techniques for measuring the frequency? 7. What technique is used for the measurement of frequency accurately?


Laboratory Manual


Experiment No 2

REFLEX KLYSTRON MODE CHARACTERISTICS

AIM: To study and plot & the mode characteristis of Reflex Klystron tube.

APPARATUS: Klystron power supply Klystron mount with Reflex klystron Isolator Frequency meter Variable attenuator Crystal detctor VSWR meter Cables Cooling fan Wave guide Stands BLOCK DIAGRAM: THEORY:

The reflex klystron makes use of velocity modulation to transform a continuous electron beam into microwave power. Electron emitted from cathode are accelerated & passed through the +ve resonator towards –ve electron reflector, which retards and finally reflects the electron & the electron turn back towards the resonator. Suppose an RF field exists between the grids of resonators, the electron traveling forward will be accelerated or retarded as the voltage at the resonator



Isolator

Variable Attenuator

Frequency Meter

Crystal Detector

VSWR meter


Laboratory Manual


changes in amplitude. The accelerated electron leaves the resonator at an increased velocity and the retarded electron leave at the reduced velocity; The electron leaving the resonator will need different time to return due to change in velocity. As a result returning electron group together in bunches. As the electron bunches pass through grids, if the bunches pass the grid at such time that the electrons are lsowed down by the voltage energy will be delivered to resonator and klystron will oscillate. Hence it is obvious that the e bench should reach the resonator cavity at a time when the RF field retard the bunch and give up energy to reinforce the oscillations i.e. it should have proper transit time. Optimum transit time for the bunch to arrive at the cavity is (n + ¾ ) cycles ofter the beam initially left the cavity transit time = (n + 3/4 ) T, where n = 0,1,2,3,4,………… T = Time period of RF voltage Ref klystron can be operated with diff transit times, which across the gap are referred to as modes.

Mone number N = (n+3/4 ) The frequency is primarily determined by the dimensions of resonant cavity.

Hence by changing the volume of resonator, mechanical tuning range of klystron is possible. Also a small frequency change can be obtained by adjusting the reflector voltage. This is called Electronic tuning range. PROCEDURE:


2. Switch ON the klystron fan or blower. 3. Put the select display knob in ‘off’ position, Beam voltage knob in

‘minimum’ position and rep voltage knob in ‘maximum’ position and now switch on the Klystron power supply.

4. Put the select display knob in ‘v’ (voltage) position and adjust the beam voltage to 300V and adjust the repeller voltage to get the maximum deflection to the meter reading. Also keep the attenuation to a desired level.

5. Change the repeller voltage in steps of 5 to 10V and note down the output power and also measure the frequency of the signal using cavity meter.

6. Plot the characteristics as shown in the fig below.


Laboratory Manual


OBSERVATIONS: Mode Number

Repeller voltage (-ve) (volts)

Frequency (GHz)

Power (dB)

1 ¾ 2 ¾

3 ¾

RESULT: The characteristics of the reflex klystron is observed. Questions: 1) What is klystron tube? 2) What is velocity modulation? 3) What is bunching? 4) Importance of multicavity klystron? 5) What is electronic tuning? 6) What is difference between the two cavity Klystron amplifier and the reflex Klystron? 7) What is the frequency range of the reflex Klystron? 8) What is the output power and efficiency of the reflex Klystron? 9) List out various applications of reflex Klystron. 10) a) Define transit time b) What is the value of reflex Klystron transit time? 12)What are the governing factors of transit time?


Laboratory Manual


Experiment No 3

SCATTERING MATRIX OF A MAGIC TEE AIM: To study the characteristics of Magic Tee and to obtain its scattering matrix.

APPARATUS: Klystron power supply Klystron mount with Reflex klystron Isolator Frequency meter Variable attenuator Magic Tee Matched loads Crystal detctor VSWR meter Cables Cooling fan Wave guide Stands BLOCK DIAGRAM:



Isolator

Variable Attenuator

Frequency Meter

Magic Tee

Crystal Detector

VSWR meter


Laboratory Manual


THEORY: Magic Tee is a four port device with the following properties

• When power is given to port 1 it will be divided equally & in phase between E & H arms and no power is coupled to port 2 i.e. ports 1 and 2 are isolated.

• When power is given to port 2 it will be equally divided between E * H arms but out of phase, no power is coupled to port 1.

• When power is given to H arm it will be divided equally & in phase between ports 1 & 2 and no power is coupled to E arem i.e. E & H arms are isolated.

• When power is given to E arm it will be equally divided between ports 1 & 2 but out of phase

• When two powers which are equal in magnitude and in phase are given to ports 1 and 2 they get added in H arm.

• When two powers which are equal in magnitude and out of phase are given to ports 1 and 2 they get added in E arm.

PROCEDURE:


2. Switch ON the klystron fan or blower. 3. Put the select display knob in ‘off’ position, Beam voltage knob in

‘minimum’ position and rep voltage knob in ‘maximum’ position and now switch on the Klystron power supply.

4. Put the select display knob in ‘v’ (voltage) position and adjust the beam voltage to 300V and vary the repeller voltage frequency and amplitude of the modulating signal for obtaining maximum deflection in VSWR meter and also tune the probe for maximum deflection.

5. Adjust the attenuation by using the variable attenuator and make the deflection to read 0dB in VSWR meter. The signal of 0dB reference level will be given as input to the magic tee.

6. Now insert the Tee as shown in fig. the signal of 0dB reference is given as input to port 1. Measure the power at port 2 by connecting the matched termination at E and H arms, similarly measure the powers at E and H arms by connecting matched loads at other ports.

7. Now the signal of 0dB reference should be given to port 2 and measure the power at other ports. Repeat the procedure by giving the signals to arms E &H.


Laboratory Manual


OBSERVATIONS: Input Port (0dB reference)

Matched Ports Output ports Ideal readings

Practical Readings

1

E E H

H 2 2

2 H E

-∞ -3dB -3dB

2

E E H

H 1 1

1 H E

-∞ -3dB -3dB

E

1 1 2

2 H H

H 2 1

-∞ -3dB -3dB

H

E 1 E

1 2 2

2 E 1

-3dB -∞ -3dB

RESULT:

The characteristics of the magic tee have observed and the scattering parameters of the magic tee are calculated.

Viva Questions: 1) What is magic tee? Why it is called so? 2) How many ports does it have? 3) Difference between magic tee to directional coupler? 4) What is magic behind this? 5) What are the applications of a magic tee? 6) What is meant by scattering matrix? What is the scattering matrix of a magic tee? 7) What does an isolator mean? 8) What are the applications of an isolator? 9) Which principle is used in isolator?


Laboratory Manual


Experiment No 4

CHARACTERISTICS OF GUNN OSCILLATOR

AIM: To study and plot the V-I characteristics of Gunn Oscillator.

APPARATUS: Gunn power supply

Gunn oscillator Frequency meter PIN modulator Isolator Variable Attenuator Wave guide detector Cables Wave guide Stands Cooling fan VSWR meter

Block Diagram: THEORY:

The Gunn Oscillator is based on negative differential conductivity effect in

bulk semi conductors, which has two conduction band minima separated by an energy

Gunn power Supply

Gunn Oscillator

PIN modulator

Isolator

Variable Attenuator

Frequency Meter

Crystal Detector

VSWR meter


Laboratory Manual


gap. In the first band the electrons have high mobility and low effective mass and in the other it will have low mobility and high effective mass because of this the device exhibits negative resistance.

In a Gunn oscillator the Gunn diode is placed in a resonant cavity. In this case the oscillation frequency is determined by cavity dimensions than by the diode itself. Although Gunn oscillator can be amplitude modulated with the bias voltage. Separated use of PIN modulator through PIN diode has been made for square wave modulation. PROCEDURE:

Set the equipment as shown in the figure initially set the variable attenuator for maximum attenuation. Keep the control knob of Gunn power supply as shown below: Meter Switch - OFF Gunn bias knob - Fully anticlockwise PIN bias knob - Fully anticlockwise PIN MOD frequency - Any position Set the micrometer of Gunn Oscillator for required frequency of operation. ‘ON’ the Gunn power supply and cooling fan.

1. The voltage in increased in steps of 0.25V and the corresponding current is read from the meter on the Gunn Power supply by switching alternatively to current & voltage.

2. Plot the voltage and current reading on the graph as shown in figure. 3. Measure the threshold voltage, which corresponds to maximum current.


Laboratory Manual


OBSERVATIONS: Voltage (V) Current (mA) RESULT:

The Gunn Diode characteristics have observed and the threshold voltage has found.

Questions: 1. What is Gunn diode? 2. Draw the equivalent Circuit for Gunn diode ? 3. What are the different modes in Gunn diode oscillator? 4. How many junctions are there in Gunn diode? 5. Explain the transferred electron effect in Gunn diode? 6. What are applications of Gunn diode? 7. What are the applications of Gunn diode? 8. What is the drawback of Gunn diode? 9. What is the frequency range and efficiency of the Gunn diode? 10 What is the basis behind the Gunn Effect? 11 What is meant by population inversion? 12 In which frequency mode the Gunn oscillator will oscillate? 13. What is the noise factor of the Gunn diode when compared to the IMPATT diode?


Laboratory Manual


Experiment No 5

DIRECTIONAL COUPLER CHARACTERISTICS AIM: To study the function of multi-hole directional coupler by measuring the

following parameters.

1. The Coupling factor, Insertion Loss and Directivity of the Directional coupler

APPARATUS: Klystron power supply Klystron mount with Reflex klystron Isolator Frequency meter Variable attenuator Directional Coupler Matched loads Crystal detctor VSWR meter Cables Cooling fan Wave guide Stands Block Diagram:

Klystron Power Supply

Klystron Mount with tube

Isolator Variable Attenuator

Frequency Meter

Directional Coupler

Crystal Detector

VSWR meter

Matched load

Matched Load


Laboratory Manual


THEORY: A directional coupler is a device with which it is possible to measure the incident and

reflected wave separately. It consist of two transmission lines the main arm and

auxiliary arm, electromagnetically coupled to each other Refer to the Fig.1. The

power entering, in the main-arm gets divided between port 2 and 3, and almost no

power comes out in port (4) Power entering at port 2 is divided between port 1 and 4.

The coupling factor is defined as Coupling (db) = 10 log10 [P1/P3] where port 2 is terminated, Isolation (dB) = 10

log10 [P2/P3] where P1 is matched.

With built-in termination and power entering at Port 1, the directivity of the coupler is

a measure of separation between incident wave and the reflected wave. Directivity is

measured indirectly as follows:

Hence Directivity D (db) = I-C = 10 log10 [P2/P1] Main line VSWR is SWR measured, looking into the main-line input terminal when

the matched loads are placed at all other ports.

Auxiliary live VSWR is SWR measured in the auxiliary line looking into the output

terminal when the matched loads are placed on other terminals.

Main line insertion loss is the attenuation introduced in the transmission line by

insertion of coupler, it is defined as:

Insertion Loss (dB) = 10 log10 [P1/P2] PROCEDURE:

1. Set up the equipments as shown in the Figure.

2. Energize the microwave source for particular operation of frequency .

3. Remove the multi hole directional coupler and connect the detector mount to

the slotted section.

4. Set maximum amplitude in CRO with the help of variable attenuator, Let it be X.

5. Insert the directional coupler between the slotted line and detector mount.

Keeping port 1 to slotted line, detector mount to the auxiliary port 3 and

matched termination to port 2 without changing the position of variable

attenuator.

6. Note down the amplitude using CRO, Let it be Y.

7. Calculate the Coupling factor X-Y in dB.


Laboratory Manual


8. Now carefully disconnect the detector mount from the auxiliary port 3 and

matched termination from port 2 , without disturbing the setup.

9. Connect the matched termination to the auxiliary port 3 and detector mount to

port 2 and measure the amplitude on CRO, Let it be Z.

10. Compute Insertion Loss= X – Z in dB.

11. Repeat the steps from 1 to 4.

12. Connect the directional coupler in the reverse direction i.e., port 2 to slotted

section, matched termination to port 1 and detector mount to port 3, without

disturbing the position of the variable attenuator.

13. Measure and note down the amplitude using CRO, Let it be Y0.

14. Compute the Directivity as Y-Y0 in dB.

OBSERVATIONS:

Input Port

Matched Ports Output ports Output

Power dB 1 3 2 1 2 3 2 1 3

RESULT: The characteristics of directional coupler are studied SAMPLE VIVA QUESTIONS: 1) What is directional coupler? 2) How many ports does it have? 3) What is the difference between directional coupler and magic tee? 4).What is the purpose the directional couplers? 5).What is meant by coupling factor and what is its formula? 6).What is meant by directivity of D.C. and how can it express? 7).What is meant by isolation and how it can express? 8). How many types of directional coupler are there and which is the most commonly used one? 9). Summaries the properties of an ideal directional coupler.


Laboratory Manual


Experiment No 6

MEASUREMENTS OF A SCATTERING PARAMETERS OF CIRCULATOR

AIM: To study the Isolator and circulators and measure the Insertion Loss and

Isolation of Circulator.

APPARATUS:

Klystron power supply Klystron mount with Reflex klystron Isolator Frequency meter Variable attenuator Directional Coupler Matched loads Crystal detctor VSWR meter Cables Cooling fan Wave guide Stands Block Diagram:



Isolator Variable Attenuator

Frequency Meter

Ciculator

Crystal Detector

VSWR meter

Matched load


Laboratory Manual


CIRCULATOR: Circulator is defined as device with ports arranged such that energy entering a port is

coupled to an adjacent port but not coupled to the other ports. This is depicted in

figure circulator can have any number of ports.

PROCEDURE:

1. Remove the isolator or circulator from slotted line and connect the detector

mount to the slotted section. The output of the detector mount should be

connected with CRO.

2. Energize the microwave source for maximum output for a particular frequency

of operation. Tune the detector mount for maximum output in the CRO.

3. Set any reference level of output in CRO with the help of variable attenuator, Let it be V1.

4. Carefully remove the detector mount from slotted line without disturbing the

position of the set up. Insert the isolator/circulator between slotted line and

detector mount. Keep input port to slotted line and detector its output port. A

matched termination should be placed at third port in case of Circulator.

5. Record the output in CRO, Let it be V2.

6. Compute Insertion loss given as V1-V2 in db. OBSERVATIONS: Input Port Matched Ports Output ports Ideal Practical


Laboratory Manual


readings Readings

1

3 2

2 3

0 dB -∞ dB

2

1 3

3 1

0 dB -∞ dB

3

1 2

2 1

-∞ dB 0 dB

RESULT: The characteristics of circulator are studied SAMPLE VIVA QUESTIONS: 1. Indicate the frequency Vs wave length for X-band? 2. Explain the principle of isolator & circulator? 3. Explain the principle of frequency meter? 4. What type of frequency meter used in microwave test bench? 1. What is the function of the frequency meter in the microwave bench? 2. What are the techniques for measuring the frequency? 3. What technique is used for the measurement of frequency accurately? 4. What does circulator mean? 5. What type of transition takes place in circulator? 6. By what angle the wave is titled as it moves from one port to another in clockwise direction.

7. How circular acts as duplexer. 8. How VSWR measurement can be made by a circulator?


Laboratory Manual


Experiment No 7

MEASUREMENT OF IMPEDENCE OF A GIVEN LOAD

AIM: To measure an unknown impedance using the smith chart. APPARATUS:

Klystron power supply Klystron mount with Reflex klystron Isolator Frequency meter Variable attenuator Matched loads Crystal detctor VSWR meter Cables Cooling fan Wave guide Stands Slotted Section with movable Probe Short circuit Load whose impedence is tobe measured Block Diagram:



Isolator

Variable Attenuator

Frequency Meter

Slotted Line

Crystal Detector

VSWR meter

load


Laboratory Manual


THEORY: The measurement is performed in the following way. The unknown device is connected to the slotted line and the position of one minima is

determined. The unknown device is replaced by movable short to the slotted line.

Two successive minima portions are noted. The twice of the difference between

minima position will be guide wave length. One of the minima is used as reference for

impedance measurement. Find the difference of reference minima and minima

position obtained from unknown load. Let it be ‘d’. Take a smith chart, taking ‘1’ as

centre, draw a circle of radius equal to S. Mark a point on circumference of smith

chart towards load side at a distance equal to d/λg. Join the center with this point. Find the point where it cut the drawn circle. The co-ordinates of this point will show the normalized impedance of load. PROCEDURE:

1. Calculate a set of Vmin values for short or movable short as load.

2. Calculate a set of Vmin values for S-S Tuner + Matched termination as a load. Note: Move more steps on S-S Tuner

3. From the above 2 steps calculate d = d1~d2

4. With the same setup as in step 2 but with few numbers of turns (2 or 3).

5. Calculate low VSWR.

Note: High VSWR can also be calculated but it results in a complex procedure. 6. Draw a VSWR circle on a smith chart.

7. Draw a line from center of circle to impedance value (d/λg) from which

calculate admittance and Reactance (Z = R+jx)

Model Graph:

Observations:


Laboratory Manual


Beam Voltage = Current = Repeller Votage = Power = When Load is Connected: First min = Second min = Third min = When Short circuit is Connected: First min = Second min = Third min = Average Value of VSWR= Reflection Co-effiecent = dmin= RESULT;. The method of measuring unknown load impedance is studied by measuring VSWR and the position of the voltage minimum. SAMPLE VIVA QUESTIONS: 1. Indicate the frequency Vs wave length for X-band? 2. Explain the principle of isolator & circulator? 3. Explain the principle of frequency meter? 4. What type of frequency meter used in microwave test bench? 1. Mention the methods used for the measurement of impedance? 2. For measuring low impedance which method is used? 3. In which method both impedance and reflection coefficient can be measured?


Laboratory Manual


PART – B

Digital Communication


Laboratory Manual


EXPERIMENT – 1

PULSE CODE MODULATION AND DEMODULATION AIM

i. To study the PCM bit pattern (8 bits) corresponding to the applied a.c. or d.c. voltage signals

ii. To study the demodulated output corresponding to the applied 8-bit pattern. APPARATUS REQUIRED

i. Pulse Code Modulation and Demodulation trainer kit. ii. Dual Trace and dual channel CRO – 20/30MHz iii. Patch Chords and CRO BNC Probes

BLOCK DIAGRAM

THEORY PCM means Pulse Code Modulation. The message signal is sampled (Sampling) and the amplitude of each sample is rounded off to the nearest one of a finite set of allowable values (Quantization), so that both time and amplitude will be in discrete form. This allows the message to be transmitted by the means of coded electrical signals (Encoder), thereby distinguishing PCM from all other methods of modulation. The essential operations in the transmitter of a PCM system are sampling, quantizing and encoding. The encoding and quantizing operations are usually performed in the same circuit called analog – to – digital converter (ADC). The essential operations in the receiver are regeneration of quantized samples. Sampling The incoming message wave is sampled with narrow rectangular pulses so as to closely approximate the nearest one of a finite set of allowable values, so that time will be in discrete form. To avoid loss of message signal, in ideal case infinite number of samples must be generated. Quantizing The conversion of an analog sampled amplitudes of signal to a discrete amplitude signal is called quantizing process. In this the difference between two adjacent discrete values is called a quantum. The amplitude difference between quantized level and sampled amplitude is called quantization error.


Laboratory Manual


Encoding In this process, each of the discrete value from the above two processes is represented by discrete events called ‘codes’. The binary code (i.e. 0 & 1) representation is more advantageous since it withstands a relatively high level of noise & is easy to regenerate using regenerative repeater at regular distances of channel. PROCEDURE

i. Connect the clock generator output to clock input. ii. Connect the variable d.c. output of the signal generator to input of A/D

converter. iii. Minimum amplitude d.c. signal is applied. Note down the PCM output bit

pattern and measure its corresponding demodulated output voltage using multimeter.

iv. The d.c. voltage is incremented in steps of 0.5V and step 3 is repeated until reaching the maximum d.c. out voltage.

v. From the above DC Voltage values an analog signal and its corresponding demodulated signal is constructed.

vi. Apply an analog a.c. signal of frequency 1KHz to input of A/D converter. vii. The modulated PCM output and the demodulated PCM output are observed. viii. Observe that the demodulated a.c. signal output is in phase with the message

signal applied OBSERVATIONS Analog a.c. Signal Amplitude= Frequency= Demodulated a.c signal Amplitude= Frequency= GRAPHS The modulated and its demodulated outputs with input d.c. signal & a.c. signal are plotted by taking time on X-axis and voltage on Y-axis.

Modulating a.c. signal

De modulating a.c. signal


Laboratory Manual


RESULT For a.c. and d.c. input voltages, Pulse Code Modulation and Demodulation techniques are studied. VIVA QUESTIONS: 1. What is the expression for transmission bandwidth in a PCM system? 2. What is the expression for quantization noise /error in PCM system? 3. What are the applications of PCM? 4. What are the advantages of the PCM? 5. What are the disadvantages of PCM?

PCM Modulated and Demodulated Waves

-15

-10

-5

0

5

10

15

0 5 10 15 20

Time

Voltage

Modulated Output Demodulated Output


Laboratory Manual


EXPERIMENT – 2 TIME DIVISION MULTIPLEXING & DEMULTIPLEXING

AIM : To study the Time Division multiplexing and De multiplexing using the following

1. Using four sine waves with different frequency and amplitudes 2. Using a sine wave, Triangular wave and square wave with different

frequency and amplitudes

APPARATUS REQUIRED

i. Time Division Multiplexing and Demultiplexing trainer. ii. Dual Trace and dual channel CRO – 20/30MHz iii. Patch Chords and CRO BNC Probes

THEORY Time Division Multiplexing (TDM) is a technique used for transmitting several analog message signals over a single common communication channel by dividing the time frame into slots, one slot for each message signal. The important feature of pulse amplitude modulation is conversation of time. For a given message signal, transmission of the associated PAM wave engages the communication channel for only a fraction of the sampling interval on a periodic basis. Hence, some of the time interval between adjacent pulses of the PAM wave is cleared for use by other independent message signals on a time –shared basis. By doing so, we obtain a time division multiplex system, with operation of the pulse modulator. The narrow samples produced at the pulse demodulator output are distributed to the appropriate low pass reconstruction filter by means of a decommutator, which operates in synchronism with the commutator in the transmitter. The synchronization is essential for a satisfactory operation of the system. TDM is immune to amplitude non linearities in the channel as a source of cross talk, because the different message signals are not simultaneously


Laboratory Manual


impressed on the channel. The maximum channel bandwidth required to avoid cross talk in a channel containing N inputs is N.fm. Comparison of TDM & FDM shows that the band width required for both the techniques is the same i.e., N.fm, but FDM can be used only when the message signal is in analog form, whereas TDM can be used for both analog and digital signals. But the disadvantage of TDM is that it requires synchronization between the commutator and decommutator. TDM and FDM are dual of each other. Also, in TDM a guard band is provided because the commutator switch cannot move from one slot to another immediately. PROCEDURE

i. The amplitude of each message signal is set to different amplitudes. ii. The natural sampled PAM outputs are observed at TP5, TP6, TP7 & TP8. iii. The outputs are observed by varying the duty cycle pot (P5) with 10% to 50%

duty cycle. iv. The TDM output is observed at TP9 and all the multiplexer channels are during

the full period of the clock 1/ (32 KHz). v. The TDM output is observed by varying the amplitude of the modulating signal

using pots P1, P2, P3 and P4. vi. TDM multiplexer output (TP9) is connected to TDM de multiplexer input

(TP12). vii. The demodulated outputs are observed at TP13, TP14, TP15 & TP 16

respectively. viii. The low pass filter outputs for each channel are observed at TP17, TP18, TP19

& TP20. These signals are observed to be true replica of the inputs with lower amplitudes.

ix. Steps I to viii are repeated with different frequency and amplitudes of a sine wave, triangular wave and square waves.

GRAPHS The output wave forms of modulating signals, Multiplexed signal, de multiplexed signal and demodulated signal are drawn correspondingly.


Laboratory Manual


RESULT


Laboratory Manual


The Time Division Multiplexing and Demultiplexing are studied. VIVA QUESTIONS: 1. What is meant by multiplexing technique and what are the different types of Multiplexers? 2. Briefly explain about TDM&FDM? 3. What is the transmission band width of a PAM/TDM signal? 4. Define crosstalk effect in PAM/TDM system? 5. What are the advantages of TDM system? 6. What are major differences between TDM&FDM? 7. Give the value of Ts in TDM system? 8. What are the applications of TDM system and give some example? 9. What is meant by signal overlapping? 10. Which type of modulation technique will be used in TDM?


Laboratory Manual


EXPERIMENT – 3

FREQUENCY SHIFT KEYING AIM i. To generate FSK Modulation and Demodulate FSK signals. ii. Study of different line codes for the given data input signal 0011001100.

APPARATUS REQUIRED

i. Frequency Shift Keying trainer kit. ii. Dual Trace and dual channel CRO – 20/30MHz iii. Patch Chords and CRO BNC Probes

BLOCK DIAGRAM

THEORY Binary FSK is a form of constant amplitude non linear angle modulation and the modulating signal is a binary pulse stream that varies between two discrete voltage levels but not continuously changing analog signal. In FSK the carrier amplitude (Vc) remains constant with modulation and the carrier radian frequency (Wc) shifts by an amount equal to (∆w/2). The frequency shift (∆w/2) is proportional to the amplitude and polarity of the input binary signal. For example a binary 1 could be +1 Volt and a binary 0 could be -1 Volt producing frequency shifts of +∆w/2 and -∆w/2 respectively. The rate of change the binary input signal Vm(t). Thus the output carrier frequency deviates (shifts) between Wc + ∆w/2 and Wc - ∆w/2 at the rate equal to fm. Non Return to Zero Level (NRZ-L): This is a level type code and is one that is widely used in serial data transmission. Logic 1 is represented by High amplitude level and Logic 0 is represented by another level lower than logic 1 but not zero amplitude.


Laboratory Manual


Non Return to Zero Mark (NRZ-M): This encoding is commonly referred to as just NRZ in other contexts. Here logic 1 is represented by a change in amplitude level and logic 0 is represented by no change n level Return to zero (RZ): This is an impulse type code where a ‘1’ is represented by a high level that returns to zero after a half bit interval. Its advantage is power conservation as transmission takes place only for a ‘1’. Biphase (Mark): It is inverse to the Manchester coding Biphase (Manchester): In telecommunication, Manchester code (also known as Phase Encoding) is a form of data communications line code in which each bit of data is signified by at least one voltage level transmission. Manchester encoding is therefore considered to be self clocking, which means that accurate synchronization of a data stream is possible. Each bit is transmitted over a predefined time period. It provides simple way to encode arbitrary binary sequences without ever having long periods without level transitions, thus preventing the loss of clock synchronization or bit errors from low frequency drift on poorly equalized analog links. In this Manchester code ( as per IEEE 802.3)used in Ethernet communications as: logic 1 is represented by High and low amplitudes each for a half bit duration and logic 0 is represented by Low and High amplitudes each for a half bit duration. PROCEDURE

i. Switch on the power supply. ii. Select the data selection switch (DATA SELECTION) to the desired code (say

11001100). iii. Set the switch (DATA ON-OFF) in ON position. Observe the 8 bit pattern at TP

12. iv. Observe the data clock at TP 1 and also observe the NRZ (L) at TP 2, RZ at TP

3, NRZ (µ) at TP 4, BIPHASE (MARK) at TP 5 and BIPHASE (MANCHESTER) at TP 6.

v. Connect the patch chord as shown in fig 1. Observe the corresponding FSK output at TP 8 (when data is logic ‘1’ the frequency is high and data is logic ‘0’ the frequency is low).

vi. Repeat step 5 for other inputs (like NRZ (M), RZ, BIPHASE), observe corresponding FSK outputs.

vii. Now change the data selection and repeat above 3 to 6 steps and observe the corresponding outputs.

viii. For demodulation connect the circuit as shown in fig: 2. ix. The incoming FSK input is observed at TP 9. x. The output of square wave converted is available at TP 10. The serial data

output is available at TP 11. xi. Repeat above steps for other serial data input and observe corresponding serial

data output. These output are true replica of original input.


Laboratory Manual


GRAPHS The output wave forms of data input, clock signal, modulated and the demodulated signals are drawn.

Data Clock

Data

NRZ (L)

RZ

Bi Phase Mark

Manchester

NRZ (L)

NRZ (L)

FSK Output


Laboratory Manual


RESULT Frequency shift keying Modulation and Demodulation are studied. VIVA QUESTIONS: 1.Explain the concept of FSK?

2.Compare ASK, FSK & PSK?

3.Draw the waveforms of FSK?

4.What is M-ray signaling? What is its advantages over 2-ary signaling?

5.What are the different data coding formats & draw the waveforms and what is advantages

of Manchaster coding over other formats?

6.Explain the demodulation scheme of FSK?

7.What is the formula for Band Width required in FSK?

8.What is the minimum B.W for an FSK signal transmitting at 2000bps(half duplex),if

carriers are separated by 3KHz?

9.Is the FSK spectrum, a combination of two ASK spectra centered around two frequencies?

10.Is the FSK band width is more than ASK band width for a given band rate?

11.Is it more susceptible to noise than ASK?

12.What are the limiting factors of FSK?

13.Is the band rate & bit rate are same for FSK?


Laboratory Manual


EXPERIMENT – 4

PHASE SHIFT KEYING MODULATION AND DEMODULATION AIM

i. To study the operation of Phase shift keying modulation and demodulation techniques.

APPARATUS REQUIRED

i. Phase Shift Keying trainer. ii. Dual Trace and dual channel CRO – 20/30MHz iii. Patch Chords and CRO BNC Probes

THEORY To transmit the digital data from one place to another we have to choose transmission medium. The simplest possible method to connect the transmitter to receiver with a piece of wire. This works satisfactorily for short distances in some cases. But for long communication with the aircraft ship vehicle this is not feasible. Here we have to obtain for the radio transmitter. It is not possible to send the digital data directly over the antenna because the antenna of practical size works on very high frequencies, much higher than over data transmission rate and processing and have continued to develop into a major industry providing the interconnection of computer peripherals and transmission of data between distant sites, phase shift keying is relatively new system in which the carrier may be phase shifted by 90° for a mark and -90° for a space. PSK has a no. of similarities to PSK in many aspects as in PSK frequency of the carrier is shifted according o modulation square wave. CIRCUIT DESCRIPTION In this IC 8038 is a basic wave form generator which generates sine, square and triangular wave forms. The sine wave generated by this 8038 IC is used as carrier signal to the system. This square wave is used as a circuit input to a decade counter (IC 7490) which generates the modulating data outputs. The digital signal applied to the modulating input for PSK generation is bipolar having equal positive and negative voltage levels. When the modulating input is negative for output of modulator is sine wave in phase with carrier input where as for the positive voltage levels the output modulator is a sine wave which is shifted out of differential data stream. This happens because the carrier output is now multiplied by negative constant level. Thus the output changes in phase when a change in polarity of modulating signal results. Modulation: IC CD 4051 is an analog multiplexer to which carrier is applied with and without 180° phase shift to the two multiplex inputs of IC. Modulating data input is applied to control input, depending upon the level of control, signal, carrier signal applied with or without phase shift to the carrier signal created by an operational amplifier using IC 741. Demodulation: During the demodulation of PSK signal is converted into a +5V sequence wave signal using a transistor and is applied to one input of an EX-OR gate. To the second input of the gate carrier signal is applied after conversion into a +5V signal, so the EX-OR gate output is equivalent to the modulating data signal.


Laboratory Manual


BLOCK DIAGRAM

PROCEDURE

i. Switch on the power supply. ii. Observe the carrier output at TP1, data outputs at D1, D2, D3, D4. iii. Connect the carrier output to the carrier input (TP2) and D1 to data input of the

PSK modulator (TP3). iv. Observe the PSK modulated output wrt data input. v. For demodulation connect the PSK modulated output to the input of the

demodulation (TP4). vi. Connect the carrier output to the demodulator (TP5). vii. Now observe the demodulated output wave wrt data input on the CRO. viii. Observe that the demodulated output is true replica of data input. ix. By connecting the different data inputs observe the modulated and demodulated

waves.

GRAPHS


Laboratory Manual


Draw the output wave forms of data input, carrier, modulated and the demodulated signals.

CARRIER SIGNAL

D1 INPUT

PSK DE-MODULATED OUTPUT

PSK MODULATED OUTPUT

D1

D2

D3

D4


Laboratory Manual


RESULT Phase shift keying Modulation and Demodulation techniques are studied. SAMPLE VIVA VOCE QUESTIONS

1. What is the What are the types of digital modulation schemes?

2. difference between analog modulation and digital modulation?

3. How PSK is non linear modulation scheme?

4. What are the advantages and disadvantages of PSK over other digital modulation

schemes?

5. What are the applications of PSK?

6. What is the difference between PSK & DPSK?

7. Explain the concept of PSK?

8. Compare ASK, FSK, PSK?

9. Draw the waveforms of PSK?

10. What is M-ary signaling? What are its advantages over 2-ary signaling?

11. Explain the demodulation scheme of PSK?.

12. What is the advantage of PSK over ASK, FSK?

13. Will the smaller variations in the signal can be detected reliably by PSK?

14. Can we transmit data twice as for using 4-PSK as we can using 2-PSK?

15. What is the minimum B.W required in PSK?

16. Is the B.W in PSK is same as in ASK?

17. Is the maximum bit rate in PSK is greater than ASK?

18. Is the maximum baud ate in PSK & ASK are same?


Laboratory Manual


EXPERIMENT – 5

DIFFERENTIAL PHASE SHIFT KEYING MODULATION AND DEMODULATION

AIM:

i. To study the operation of Differential Phase shift keying modulation and demodulation techniques.

APPARATUS REQUIRED:

i. Differential Phase Shift Keying trainer. ii. Dual Trace and dual channel CRO – 20 MHz iii. Patch Chords and CRO Probes

THEORY: Modulation also allows different data streams to be transmitted over the same channel (trans medium). This process is called as multiplexing and result in considerable saving in band width no. of channels to be used. Also it increases the channel efficiency. Some of the basic modulation techniques are ASK, FSK, PSK, DPSK and QPSK. CIRCUIT DESCRIPTION: In this IC 8038 is a basic wave form generator which generates sine, square and triangular wave forms. The sine wave generated by this 8038 IC is used as carrier signal to the system. This square wave is used as a circuit input to a decade counter (IC 7490) which generates the modulating data outputs. The digital signal applied to the modulating input for DPSK generation is bipolar i.e., having equal positive and negative voltage levels. When the modulating input is negative for output of modulator is sine wave in phase with carrier input where as for the positive voltage levels the output modulator is a sine wave which is shifted out of phase by 180° from the carrier input. Thus the output changes in phase when a change in polarity of modulating signal results. Figure shows the functional blocks of the modulator & demodulator. Modulation: The differential signal to the modulating signal is generated using ex-or gate and 1 bit delay circuit. IC CD 4051 is an analog multiplexer to which carrier is applied with and without 180° phase shift (created by using an op-amp connected in inverting amplifiers mode) to the two inputs of IC TL084. Differential signal generated by ex-or gate (IC 7486) is given to the multiplexer’s control signal input. Depending upon the level of the control signal, carrier signal applied with or without phase shift is steered to the input. 1-bit delay generation of drift signal to the i/p created by using a D flip flop (IC 7474).


Laboratory Manual


Demodulation: During the demodulation, the DPSK signal is converted into a +5V square wave signal using a transistor and is applied to one input of an EX-OR gate. To the second input of the gate carrier signal is applied after conversion into a +5V signal, so the EX-OR gate output is equivalent to the differential data and the second input after first delay the same signal is given so the output of this ex-or gate is modulating signal. BLOCK DIAGRAM:

PROCEDURE:

i. Switch on the power supply. ii. Observe the carrier output at TP 1, data outputs at D1, D2, D3, D4. iii. Connect the carrier output to the carrier input (TP 2) and D1 to data input of the

DPSK modulator (TP 3). iv. Observe the differential data output at TP 9. v. Observe the DPSK modulation output wrt to differential output. vi. Connect the modulation output (TP 11) to modulation input (TP 12) of the

demodulator, the carrier output (TP 2) to carrier input (TP 13) of the demodulator and the clock output to the clock input (TP 14) of the demodulator.

vii. Observe the demodulated output at TP 15.


Laboratory Manual


GRAPHS: Draw the output wave forms of data input, carrier, modulated and the demodulated signals.

Clock Signal

D1

D2

D3

D4

D1

Differential data

Carrier signal

D1

Demodulated message signal D1

DPSK


Laboratory Manual


RESULT: Differential Phase shift keying Modulation and Demodulation techniques are studied. 1.How does DPSK differ from PSK?

2.Explain theoretical modulation & demodulation of DPSK using arbitrary bit sequence and

assuming initial bit 0 and 1?

3.What is the advantage of DPSK over PSK?

4.Why do we need 1 bit delay in DPSK modulator & demodulator?

5.What does a synchronous detector (multiplier) do in DPSK demodulator?

6.what is the relation between carrier frequency & the bit interval „T‟?

7.What is the disadvantages of DPSK.?

8.Is the error rate of DPSK is greater than PSK?

9.What is the expression for DPSK error?

10.What are the applications of DPSK?


Laboratory Manual


EXPERIMENT – 6

DELTA MODULATION AND DEMODULATION AIM

i. To study the Delta Modulation and Demodulation process by comparing the present signal with the previous signal of given modulating signal.

APPARATUS REQUIRED

i. Delta Modulation and Demodulation trainer. ii. Dual Trace and dual channel CRO – 20/30MHz iii. Patch Chords and CRO BNC Probes

THEORY In Delta Modulation, an incoming message signal is over sampled to purposely increase the correlation between the adjacent samples of the signal. This is done to permit the use of a simple quantizing strategy for constructing the encoded signal. Delta Modulation is one bit version of DPCM. In its basic form DM provides a stair case approximation to the over sampled version of the message signal. The difference between the input and the approximation is quantized into only two levels, ±δ, corresponding to positive and negative differences respectively. Thus if the approximation level falls below the signal at any sampling epoch, it is increased by δ. If, on the other hand, the approximation lies above the signal, it is diminished by δ provided that the signal does not change too rapidly from sample to sample. We find that the stair case approximation remains with in ±δ of the input signal. The principle virtue of DM is its simplicity. It may be generated by applying the sampled version of the incoming base band signal to a modulator that involves a summer, quantizer and accumulator. DPCM and DM are basically similar; except for two important differences namely, the use of a one bit (2 level) quantizer in the delta modulator and the replacement of the prediction filter by a single delay element. Delta Modulation systems are subjected to two types of quantizing error.

1. Slope overload distortion 2. Granular noise

If the step size is of too small for the stair case approximation slope overload occurs and the error is known as slope overload distortion. If the step size is too long granular noise occurs. The use of delta modulation is only in certain special cases (1) If it is necessary to reduce the bit rate below 40kbps and limited voice quality is tolerable. (2) If extreme circuit simplicity is of over riding importance and the accompanying use of high bit rate is acceptable. Slope Overloading: A serious problem in delta modulation scheme arises due to the rate of noise overloading. When x (t) is changing x (t) & x’ (t) follow x (t) in a step wise fashion as long as successive samples of x (t) do not differ by an amount greater than the step size 8. When the difference is greater than ∆, x (t) and x (t) can no longer follow x (t). This type of over load not determined by amplitude of the message signal x (t) but rather by its slope. Hence, the name slope overload. To drive a condition for preventing slope overload in DM systems let us assume that x (t) = A Cos (2∏fxt). Than the maximum signal is [dx(t)/dt]max = A2∏fx.The maximum sample to


Laboratory Manual


sample change in the value of x (t) then is A2∏fx T’s < ∆ or the peak signal amplitude at which slope overload occurs is given by A = ∆/2∏ * f’ s/fx. A better way to avid slope overload is to detect the overload condition and make step size larger when overloading is detected. Hunting occurs in DM systems when the signal changes very slowly and slope overloading occurs when the slope of the signal is very high. BLOCK DIAGRAM:

PROCEDURE

i. Switch on the power supply. ii. Connect the transmitter clock (TP2) to transmitter clock input (TP6). iii. In order to ensure the correct operation of the system, we first take the input to

0V from DC variable at TP 3. So the positive input is connected to the delta modulators & voltage comparator to 0V.

iv. Observe the integrator output at TP9 and output of level change at TP8. v. The relative amplitudes of level changers positive and negative output levels can

be varied by adjusting the level adjust present in the bi stable and level changer circuit.

vi. Disconnect the positive input from 0V and connect it to the 2KHz sine wave from TP1.

vii. Observe the integrator output is by varying the amplitude of modulating signal. viii. Observe the modulator output at TP7 together with the analog input at TP4. ix. Connect the modulation output to integrator input and observe the output at

TP11. x. Connect the TP 11 to LPF input (TP12) and observe the output. xi. Connect TP13 to amplifier input (TP14) and observe the demodulation output at

TP15.


Laboratory Manual


Graphs: Draw the output wave forms of data input, carrier, modulated and the demodulated

signals.

Message Signal

Demodulated message signal

Sampling Signal

DM Output Signal

Slop Overload distortion

Normal

Hunting/ Granular distortion


Laboratory Manual


RESULT Delta Modulation and Demodulation techniques are studied. VIVA QUESTIONS:

1. What are the advantages of Delta modulator?

2. What are the disadvantages of delta modulator?

3. How to overcome slope overload distortion?

4. How to overcome Granular or ideal noise?

5. What are the differences between PCM & DM?

6. Define about slope over load distortion?

7. What is the other name of Granular noise?

8. What is meant by staircase approximation?

9. What are the disadvantages of Delta modulator?

10. Write the equation for error at present sample?


Laboratory Manual


EXPERIMENT – 7

DIFFERENTIAL PULSE CODE MODULATION & DEMODULATION AIM

i. To study the Differential Pulse Code Modulation and Demodulation by sending variable 10Hz to 500Hz frequency sine wave.

APPARATUS REQUIRED

i. Differential Pulse Code Modulation and Demodulation trainer. ii. Dual Trace and dual channel CRO – 20/30MHz iii. Patch Chords and CRO BNC Probes

THEORY These systems are particularly more efficient when the sampled message signal has high sample to sample correlation. For example in the transmitter of picture (video) information, appreciable portions of the signal describe background level; if these tonal values do not change appreciably. Then we are essentially transmitting repeated sample values. One way to improve the situation is to send only the digitally encoded differences between successive samples. Thus a picture that has been quantized to 256 levels (eight bits) may be transmitted with comparable fidelity using 4-bit differential encoding. This reduces the transmission band width by a factor of 2. PCM systems using differential quantizing schemes are known as Differential Pulse Code Modulation (DPCM) systems. A DPCM system that is particularly simple to implement results when the difference signal is quantized into two levels. The output of the quantizer is represented by a single binary digit, which indicates the sign of the sample to sample difference. This PCM system is known as Delta Modulation (DM). Delta Modulation systems have an advantage over M-ary PCM and M-ary DPCM systems. In that the hardware required for modulation at the transmitter and demodulation at the receiver are much simpler. BLOCK DIAGRAM:


Laboratory Manual


PROCEDURE

i. Switch on the power supply and observe the sine wave (TP 1) and clock (TP 5) on the CRO. This is the sampling rate for the system.

ii. Observe the 2 MHz clock on the circuit; this is the system clock for ADC. iii. Observe the control signals ALE, SOC, EOC for ADC are observed. iv. Observe the modulation and demodulation outputs on CRO.

v. The demodulated output may not be same as the input signal because in DPCM

differential present sample pulse provision sample is shunt to receiver. vi. At higher frequencies the difference will be greater than 4 bits so receiver will

not be able to reconstruct the input signal. The maximum frequency + amplitude at which this kit will be able to demodulate the transmitted signal is 500 Hz, 1 Vpp amplitude. If the frequency is greater than 500 Hz the difference will be more than 4 bits and some information is lost so demodulated signal will not represent the transmitted signal.

RESULT Differential Pulse Code Modulation and Demodulation techniques are studied.


Laboratory Manual


Clock Signal

Message Signal

DPCM Output

Demodulated Signal

medc lab-2014-15(1)

Documents