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INDEX

S.No Date NAME OF THE EXPERIMENT Marks Sign

1 Amplitude modulation & demodulation

2 Frequency modulation & demodulation

3 Pulse Amplitude modulation & demodulation

4 Radio Receiver measurements-Sensitivity, Selectivity & Fidelity

5 Measurement of half power beam width (HPBW) and gain of a half

wave dipole antenna.

6 Measurement of radiation pattern of a loop antenna in principal

planes.

7 Time division multiplexing

8 Pulse code modulation

9 Delta modulation

10 Frequency shift keying

11 QPSK modulation & demodulation

12 Differential phase shift keying

13 Time division multiplexing using MAT LAB

14 Pulse code modulation using MAT LAB

15 Delta modulation using MAT LAB

16 Frequency shift keying using MAT LAB

17 QPSK modulation & demodulation using MAT LAB

18 Differential phase shift keying using MAT LAB

ANALOG & DIGITAL COMMNICATIONS LAB III YEAR I SEM

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1. AMPLITUDE MODULATION & DEMODULATION

Aim:

1. To generate amplitude modulated wave and determine the percentage modulation.

2. To Demodulate the modulated wave using envelope detector

Apparatus:

1. Amplitude Modulation & Demodulation trainer Kit

2. Dual trace oscilloscope

3. Patch cords.

Theory:

Amplitude Modulation is a process in which the amplitude of the carrier wave c(t) is

varied linearly with the instantaneous amplitude of the message signal m(t).The standard Form

of amplitude modulated (AM) wave is defined by

s(t)= Ac(1+ Ka m(t) cos 2πfct)

Where Ka is a constant called the amplitude sensitivity of the modulator.

The demodulation circuit is used to recover the message signal from the incoming AM

wave at the receiver. An envelope detector is a simple and yet highly effective device that is

well suited for the demodulation of AM wave, for which the percentage modulation is less than

100%.Ideally, an envelope detector produces an output signal that follows the envelop of the

input signal wave form exactly; hence, the name. Some version of this circuit is used in almost

all commercial AM radio receivers.

The Modulation Index is defined as, m=

Where Emax and Emin are the maximum and minimum amplitudes of the modulated wave.

.


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Circuit Diagrams:

Modulation


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Demodulation:


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Procedure:

1. As the circuitry is already wired you just have to trace the circuit according to the circuit

diagram given

2. Connect trainer to the mains and switch ON the power supply

3. Measure the output voltages of regulated power supply circuit that is ,+12v and -12v.

4. Observe output of RF and AF signal generator using CRO .Note that RF voltage is

approximately 300mv pp of 1 MHZ frequency and AF voltage is 10 v pp of 2 KHZ frequency.

Modulator

1. Now connect RF and AF signals to the respective inputs of modulator.

2. Initially set both the signals at Zero level.

3. Connect one of the input of oscilloscope to modulator output and other input to AF

signal

4. Adjust RF signal amplitude with the help of potentiometer so that output of the

modulator is nil pp by keeping AF signal at zero level

5. Now vary the amplitude of AF signal and observe the amplitude modulated wave at

output. Note the percentage of modulation for different values of AF signal.

Percentage of modulation can be calculated by below formula

% modulation =

Demodulator:

1. Now connect the modulator output to the demodulator input

2. Observe demodulated signal at output of modulator at approximately 50 % modulation

using oscilloscope

3. Compare it with the original AF signal.( Note only wave shape ,amplitude will be

attenuated ,phase may change)

4. Find the detected signal is same as the AF signal applied.Thus no information is lost in

the process of modulation.


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If you want to observe AM wave at different frequencies then connect AF signal from external

signal generator to the modulator and observe amplitude modulated wave at different

frequencies.

Waveforms:

Result:

Viva -Voice

1. Define AM and draw its spectrum?

2. Give the significance of modulation index?

3. What are the different degrees of modulation?

4. What are the limitations of square law modulator?

5. Compare linear and nonlinear modulators?


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2. FREQUENCY MODULATION AND DEMODULATION

Aim:

1. To generate frequency modulated signal and determine the modulation index and

bandwidth for various values of amplitude and frequency of modulating signal.

2. To demodulate a Frequency Modulated signal using FM detector.

Apparatus:

1. Frequency Modulation & Demodulation ACLT002 trainer kit

2. Dual trace oscilloscope

3. Patch cords

Theory: The process, in which the frequency of the carrier is varied in accordance with the

instantaneous amplitude of the modulating signal is called “Frequency Modulation”.

The FM signal is expressed as

S (t) =Ac sin (2πfct+β Sin (2πfmt)

Where Ac is amplitude of the carrier signal, fc is the carrier frequency,β is the modulation index

of the FM wave.


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Circuit Diagrams:

Modulation


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Demodulation:


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Procedure:

1. As the circuitry is already wired you just have to trace the circuit according to the circuit

diagram given

2. Connect trainer to the mains and switch ON the power supply

3. Measure the output voltages of regulated power supply circuit that is ,+15v and -15v,

+5v and -5v

4. Observe output of AF signal generator using CRO .Note that AF voltage is approximately

20v pp of 500KHZ & 5KHZ frequency.(Switch is provided to change the frequency )

Modulation:

1. Connect the patch cord SO1 AF output to Modulating signal input SO2.

2. Connect ground to ground SG1 to SG2.

3. Vary the modulation POT

4. Observe the FM output on SO4 or TP4

Demodulation:

1. Connect the patch cords from SO4 to SO5

2. Connect the patch cords from GND to GND

3. Observe the Demodulation output at SO6 or TP6

Tabular columns:

Modulating signal Modulated signal Demodulated signal

Amplitude

Time period

frequency


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Waveforms:

Result:

Viva –Voice:

1. Define FM & PM.

2. What are the advantages of Angle modulation over amplitude modulation?

3. What is the relationship between PM and FM?

4. With a neat block diagram explain how PM is generated using FM.

5. What is broadcasting range of FM


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3. PULSE AMPLITUDE MODULATION & DEMODULATION

Aim: To generate the Pulse Amplitude modulated and demodulated signals.

pparatus:

1. Pulse amplitude Modulation & Demodulation trainer kit

2. Dual trace Oscilloscope

3. Patch cords

Theory:

In Flat top sampling, the amplitude of the samples remain constant at an instant of time unlike

in natural sampling where the amplitude of the samples vary in accordance with the amplitude

of the input signal that is to be sampled.

The generation of flat top samples involves two stages as shown in the figure given below.

Single polarity Flat-top samples

For generating the flat top samples, the signal to be sampled is first fed to a Sample and hold

amplifier which generates the staircase waveform as represented in the above graph at the point

D. The sampling clock selected determines the hold period of the S/H waveform.

The resulting waveform is then passed on to a electronic switch (sampler), which latches the

samples of the S/H waveform for the period determined by the duty cycle of the input sampling

clock. The resulting samples are flat-topped corresponding to the flat portions of the input S/H

wave.

Analog S/H o/p

Signal Flat-top

Samples

Sampling clock

Sample & Hold Switch


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Circuit Diagram:

Modulation

Demodulation:

E1 E B1 B2

B2 B F1 Phase

Adjust

VR8

B F1

B2 Phase

Adjust

PAM

Modulator Demodulator

( S & H)

Amplifier

LPF

Fc =3.4KHz

Switch to Natural

A1 A2 C

E1

PAM

C

VR3

Pulse width

Natural PAM generator

1

KHz

2

KHz

Signa

l

Sourc

e

PAM

Modulator

&

Transmitt

er

4 KHz

8 KHz

16 KHz

32 KHz

Switch

Samplin

g

Frequen

cy

0.5+1+

2


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Procedure:

Modulation

1. Connect signal source 1 KHz (A1) to (A) as shown in the interconnection diagram with

the help of the patch cords given.

2. Select sampling frequency to 8 KHz

3. Select natural sampling by pushing the switch to the extreme left as shown in the figure

4. Adjust pulse width potentiometer to extreme anti clockwise

5. Connect the oscilloscope with the input analog signal A1 and with the PAM modulator

output E1.

Observations:

1. The PAM modulator output will be a product of input analog signal and regularly

spaced pulse train.

2. Note the pulse width of PAM and by varying the pulse width potentiometer, record

the pulse width of PAM

3. Determine the minimum and maximum duty cycle of pulse

4. Determine the minimum and maximum duty cycle of pulse at 4 KHz, 16 KHz and 32

KHz.

5. Repeat the above experiment by connecting 2 KHz (A2) to (A)

Demodulation

1. Connect the signal source 1 KHz (A1) to (A), PAM output (E1) to receiver input (E) and

PAM demodulator output (B2) to LPF input (B).

2. Select sampling frequency to 8 KHz

3. Select flat sampling

4. Connect the oscilloscope with the signal B1 and sampling pulse regenerator output G.

Observations:

1. Observe the relative position of PAM pulses and sampling pulses.

2. Record the PAM demodulator output at B2.

3. Vary the phase adjust potentiometer gradually till the sampling pulses are in middle of

PAM pulses

4. Record the PAM demodulator output at B2, which will be a step signal.

5. Observe the reconstructed output at F1.

6. Vary the pulse width of PAM pulses and observe the reconstructed output at F1

7. Repeat the above procedure at other sampling frequencies

8. Explain the distortion if the sampling frequency is 4 KHz.

N O TE: For phase adjust at 16 & 32 KHz vary the potentiometer VR11


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Modulated Wave forms:

Demodulation Waveforms


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Result:

Viva –Voice:

1. Explain the modulation circuit operation?

2. Explain the demodulation circuit operation?

3. Is PAM & Demodulation is sensitive to Noise?

4. What is cross talk in the context of time division multiplexing?

5. Which is better, natural sampling or flat topped sampling and why?


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4. Radio receiver measurements –sensitivity selectivity and Ffidelity

AIM: To transmit a modulating signal after frequency modulation using VCT-12 and receive

the signal back after demodulating using VCT-13

APPARATUS REQUIRED:

1. VCT-12 trainer kit

2. VCT-13 trainer kit

3. CRO

4. Patch cards

HARDWARE DESCRIPTION OF FM TRANSMITTER TRAINER VCT-12:

The FM transmitter trainer kit VCT-12 has the following section:

1. On-board sine wave generator

2. MIC pre amplifier with a socket for external dynamic MIC

3. Audio amplifier for amplification of low level external input signal

4. Frequency modulation

5. Telescopic whip antenna

SINE WAVE GENERATOR:

A sine wave generator acts as an on board modulating signal source and generates an

audio frequency sine wave .The amplitude of this sine wave generator varies from 0-5 V.

However the output voltage from this source is controlled using a Trim pot to get an output

signal in the range of 0-3V.The frequency of the signal varies from 300Hz to 15KHz.Since the

amplitude of the source is large enough to modulate the carrier it need not be amplified ,instead

it can be directly connected to the input of the amplitude modulator .

MIC PRE AMPLIFIER:

The MIC pre amplifier is capable of accurately amplifying even a very low level signal,

picked up by the MIC to the required level to modulate the carrier. This section has a EP socket

at its input stage where, in an external dynamic MIC can be plugged in the gain of the

stage can be controlled by the user by adjusting the potentiometer Pot4.The maximum gain of

this stage can be achieved in this is 200.The maximum level of the input signal to this amplifier,

so as to produce an amplified output without saturation is 60mV.

AUDIO AMPLIFIER:

The audio amplifier stage has a BJT common emitter configuration. This audio amplifier

can be used to amplify any lower level external modulating signal whose voltage level is below

100mV.The gain of this stage can also be controlled by the user by varying the pot meter POT-

5.The maximum gain of this audio amplifier is 10.


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FREQUENCY MODULATION:

The frequency modulator circuit is constructed around a BF495, high frequency small

signal BJT. The collector circuit of the transistor consists of a tank circuit formed by a inductor

and capacitor. This tank circuit together with the transistor acts as an oscillator and produces the

carrier frequency .The transistor circuit appears to the oscillator as a variable capacitance. This

capacitance adds to the capacitance of the oscillator-tuned circuit.

The size of this capacitance depends on the change in the collector current which occurs

for a given change in base voltage and this is determined by the Trans conductance of the

transistor .The transistor trans conductance depends on the bias voltage applied to the transistor

base. The larger the bias voltage, the larger the value of gm and the larger the value of gm and

the larger capacitance which is added to the capacitance of the oscillator tuned circuit

consequently the transistor circuit behaves as a voltage variable capacitance .The bias voltage

applied to the transistor base determines the overall capacitance seen by the oscillator and hence

the frequency of the carrier. This resulting in FM signal

TELSCOPIC WHIP ANTENNA:

A telescopic whip antenna is used to radiate the AM signal generated by the amplitude

modulator.

HARDWARE DESCRIPTION OF FM RECEVIER TRAINER

The FM receiver trainer VCT-13 has the following sections

1. FM super heterodyne receiver

2. Buffer and filter

3. Audio power amplifier

FM SUPER HETERODYNE RECEIVER:

The FM receiver is built with the dedicated FM receiver IC-CXA1619IC consists of the

following sections namely RF amplifier ,Mixer and oscillator , IF amplifier and quadrature

detector .The circuit details and the description of IC-CXA1619IC are given in appendix

BUFFER AND FILTER:

A buffer is used to prevent any loading to the previous stage .The filter section consists

of a BPF with a Pass band to 20KHZ –15MHZ.A notch filter is also included to eliminate the

50Hz power supply noise


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AUDIO POWER AMPLIFIER:

The Audio power amplifier is constructed using ICTBA810 to increase the power

level of the demodulated message signal to the required level. The gain of this amplifier can be

adjusted by the user by varying the pot meter POT-1.the maximum gain of this audio amplifier

is 25. The amplified signal can be given to a loud signal which can be extremely plugged into

the VCT-13 trainer

FM Transmitter:

Message signal Antenna

FM Receiver:

PROCEDURE:

1. The circuit wiring is done as shown in diagram

2. A modulating signal input given to the Frequency modulator can also be given

From a external function generator or an AFO.

3. If an external signal source with every low voltage level is used then this signal

Audio Oscillator

Output Amplifier FM Modulator

Carrier generator

RF Amplifier

AF Amplifier Discriminator Local

Oscillator

Mixer IF amplifier


SIETK Page | 20

Can be amplified using the audio amplifier before connecting to the input of the

FM modulator

4. Now increase the amplitude of the modulated signal to the required level.

5. The amplitude and the time duration of the modulating signal are observed

Using CRO.

6. The amplitude and time duration of the modulated signal are observed using a CRO and

tabulated

7. The final demodulated signal is viewed using a CRO Also the amplitude and

time duration of the demodulated wave are noted down.

TABULATION:

Wave form Amplitude(V) Time Period(ms) Frequency(Hz)

Modulating Signal

Demodulated Signal

RESULT:

Viva –Voice:

1. Define Sensitivity, Selectivity & Fidelity?

2. What is modulation & Demodulation?

3. What is the range of voice & audio?

4. What is broadcasting range of FM?

5. What is broadcasting range of AM?


SIETK Page | 21

5. Measurement of half power beam width (HPBW) and gain of a half wave

dipole antenna

AIM: To Study & measure half power width and gain of a half wave

dipole antenna

Apparatus:

1. Gunn oscillator 737 0

2. 1 Isolator 737 06

3. 1 Pin Modulator 737 05

4. 1 Large Horn Antenna 737 21

5. 2 RF cable, L = 1 m 501 02

6. 2 Supports for waveguide components 737 15

7. 2 Stand base MF 301 21

8. 1 Set of microwave absorbers 737 390

9. 1 Set of 10 thumb screws M4 737 399

10. 1 Remote control for rotating antenna platform 737 401

11. 1 Dipole antenna kit 737 410

Theory:

The half wave dipole is perhaps the simplest and most fundamental antenna design possible.

Hertz used a dipole antenna during his initial radio experimentation. This is why a dipole is

often referred to as the “hertz dipole” antenna. The dipole is so practical that it is utilized (in

some form) in at least half of all antenna systems used today. Here are some key principles of

the dipole antenna:

1.) A dipole antenna is a wire or conducting element whose length is half the transmitting

wavelength. To calculate the length of a half wave dipole in free space, one may use the

following equation: length (ft) = 492 / frequency (MHz).

The half-wave dipole antenna is just a special case of the dipole antenna, but its important

enough that it will have its own section. Note that the "half-wave" term means that the length of

this dipole antenna is equal to a half-wavelength at the frequency of operation. To make it

crystal clear, if the antenna is to radiate at 600 MHz, what size should the half-wavelength

dipole .One wavelength at 600 MHz is = c / f = 0.5 meters. Hence, the half-wavelength

dipole antenna's length is 0.25 meters.

http://www.antenna-theory.com/antennas/dipole.php


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Radiation pattern of half wave dipole

Block Diagram


SIETK Page | 23

Procedure:

1. Arrange the setup as given in the block diagram

2. Mount Half wave dipole antenna on the transmitter mask

3. Bring the detector assembly near to main and adjust the height of both transmitting and

receiving antenna

4. Keep Detector assembly away from the main unit approximately 1.5 meter and align both of

them .Ensure that there is no reflector sort things in the vicinity of the experiment such as a

steel structure ,pipes, cables etc.

5. Keep the RF level and FS adjust to minimum and unidirectional coupler switch to

FWD(Forward adjustment knob).

6. Keep detector level control in the center approximately

7. Increase RF level gradually and see that there is deflection in the detector meter

8. Adjust RF level and detector level, so that the deflection in detector meter is approximately

30-35mA.

9. Align arrow mark on the disk with zero of the goniometer scale

10. Start taking the reading at the interval of 10 degree, and note the deflection on the detector

assembly.

11. Using conversion chart convert mA readings into db.

12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dBs

Tabular column :

S.No Angle in degrees Detector readings in mA Gain In db

Result:

Viva-Voice:

1. Define half wave dipole.

2. Draw the radiation pattern of half wave dipole antenna.

3. Give the application of half wave dipole antenna.

4. Write the frequency range of RF signal


SIETK Page | 24

6. Measurement of radiation pattern of a loop antenna in principal planes

AIM: To Study the radiation pattern of loop antenna in principal planes

Apparatus:

1. Gunn oscillator 737 0

2. 1 Isolator 737 06

3. 1 Pin Modulator 737 05

4. 1 Large Horn Antenna 737 21

5. 2 RF cable, L = 1 m 501 02

6. 2 Supports for waveguide components 737 15

7. 2 Stand base MF 301 21

8. 1 Set of microwave absorbers 737 390

9. 1 Set of 10 thumb screws M4 737 399

10. 1 Remote control for rotating antenna platform 737 401

11. 1 Loop antenna kit 737 410

Theory:

A loop antenna is a radio antenna consisting of a loop (or loops) of wire, tubing, or other

electrical conductor with its ends connected to a balanced transmission line. Within this

physical description there are two very distinct antenna designs: the small loop (or magnetic

loop) with a size much smaller than a wavelength, and the resonant loop antenna with a

circumference approximately equal to the wavelength.

Small loops have a poor efficiency and are mainly used as receiving antennas at low

frequencies. Except for car radios, almost every AM broadcast receiver sold has such an

antenna built inside it or directly attached to it. These antennas are also used for radio direction

finding. In amateur radio, loop antennas are often used for low profile operating where larger

antennas would be inconvenient, unsightly, or banned. Loop antennas are relatively easy to

build.

A small loop antenna, also known as a magnetic loop, generally has a circumference of less than

one tenth of a wavelength, in which case there will be a relatively constant current distribution

along the conductor

https://en.wikipedia.org/wiki/Antenna_%28radio%29

https://en.wikipedia.org/wiki/Electrical_conductor

https://en.wikipedia.org/wiki/Balanced_line

https://en.wikipedia.org/wiki/Transmission_line

https://en.wikipedia.org/wiki/Electrically_short

https://en.wikipedia.org/wiki/Resonant

https://en.wikipedia.org/wiki/Antenna_efficiency

https://en.wikipedia.org/wiki/AM_broadcast

https://en.wikipedia.org/wiki/Radio_direction_finding

https://en.wikipedia.org/wiki/Radio_direction_finding


SIETK Page | 25

Block Diagram

Procedure:

1. Arrange the setup as given in the block diagram

2. Mount Loop antenna on the transmitter mask

3. Bring the detector assembly near to main and adjust the height of both transmitting and

receiving antenna

4. Keep Detector assembly away from the main unit approximately 1.5 meter and align both of

them .Ensure that there is no reflector sort things in the vicinity of the experiment such as a

steel structure ,pipes, cables etc.

5. Keep the RF level and FS adjust to minimum and unidirectional coupler switch to FWD

(Forward adjustment knob).

6. Keep detector level control in the center approximately

7. Increase RF level gradually and see that there is deflection in the detector meter

8. Adjust RF level and detector level, so that the deflection in detector meter is approximately

30-35mA.

9. Align arrow mark on the disk with zero of the goniometer scale

10. Start taking the reading at the interval of 10 degree, and note the deflection on the detector

assembly.

11. Using conversion chart convert mA readings into db.

12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dBs


SIETK Page | 26

Tabular column:

S.No Angle in degrees Detector readings in mA Gain In dB

Result:

VIVA-VOICE:

1. Draw the radiation pattern Loop antenna.

2. Give the application of Loop antenna.

3. Write the frequency range of RF signal

4. What is the need of isolator


SIETK Page | 27

DIGITAL COMMUNICATION

SYSTEMS


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1. TIME DIVISION MULTIPLEXING AND DEMULTIPLEXING

Aim: To transmit a multiplexed output of different frequency message signals through single

Channel using TDM system and recover back the original message signals through a

Demultiplexer at receiver end.

Apparatus:

1. TDM trainer kit

2. CRO

3. Patch cords

4. Probes

Theory:

One of the richest benefits unearthed from Sampling is the concept of Time Division

Multiplexing. In Time Division Multiplexing, use is made of the fact that narrow pulses with

wide spaces between them can be used by signals from other sources. More ever, although the

spaces are relatively fixed in width, pulses may be made as narrow as desired, thus permitting

the generation of high-level hierarchies. Four input signals, all band limited to FS by the input

filters, are sequentially sampled at the transmitter by a rotary switch or commutator. The switch

makes FS revolutions per second and extracts one sample form each input during each

revolution.

The output at the switch is a PAM waveform-containing sample of the input signals

periodically interlaced in time. The samples from adjacent input message channels are separated

by Ts/M, where M is the number of input channels. A set of M pulses consisting of one sample

form each of the M-input channels is called a frame.

Suppose, in a 24 channel, have a sampling rate of 8000 samples per second, 8 bits(256

sampling levels) per sample, and a pulse width of approximately 0.625 S. This means that the

sampling interval is 1/8000 = 0.000125s = 125s, and the period required for each pulse group

is 8 * 0.625 = 5 s. If there was no multiplexing and only one channel was sent, the

transmission would consist of 8000 frames per second, each made up of furious activity during

the first 5 s and nothing at all during the remaining 120s.

This would clearly be wasteful and would represent an unnecessarily complicated

method of encoding a single channel, and so this system exploits the large spaces between the

pulse groups. In fact, each 125 s frame is used to provide 24 adjacent channel time slots, with

the twenty-fifth slot assigned for synchronization.

Each frame consists of 193 bits-24 * 8 for each channel, plus 1 for sync, and since there

are 8000 frames per second; the bit rate is 1.544 Mbits/sec.


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Circuit diagram:

Experimental Procedure:

Multiplexing:

1. Connect the four channel inputs 250 Hz, 500Hz, 1KHz, 2 KHz to the input of transmitter CHO,

CH1, CH2 and CH3 respectively.

2. Observe the Time Division Multiplexed PAM waveform at the output of the Multiplexer (TXD).

3. Observe the four different signals placed in their respective time slots.

4. Vary each of the amplitude of each channel and see the effect on the TDM waveform.

Observation:

1. From the above set up, we can observe that the four different signals are interleaved in their

respective time slots without overlapping each other.

2. Their positions and identification can be highlighted by reducing the other three signal

amplitudes to zero and then gradually increasing them to observe them occupying their positions

Demultiplexing:

1. Connect the four channel inputs 250 Hz, 500Hz, 1KHz, 2 KHz to the input of transmitter

CHO, CH1, CH2 and CH3 respectively

2. Connect TXCLOCK (Transmitter Clock) to RXCLOCK (Receiver Clock).

3. Connect TXCH0 (Transmitter Sync) to RXCH0 (Receiver Sync).

4. Connect the TXD (Transmitter Data) to RXD (Receiver Data).


SIETK Page | 30

5. Observe the multiplexed data at TDX, Transmitter Clock at TXCLOCK and Transmitter

Sync at TXCHO.

6. Observe the Demultiplexed signals at the receiver across the output of fourth order low pass

filter at CHO, CH1,CH2 and CH3 respectively.

Observations:

1. From the above set up, we can observe that the signals are recovered at the receiver

faithfully and are very distinct from each other.

2. By removing the other two lines apart from the TXD, we find that

the reconstructed signals suffer from severe distortion.

Waveforms: (Transmitting Signals)

ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL 2015-16

31 | P a g e III YEAR I SEM

Demultiplexed output:

Result

Viva Voice:

1. Define TDM?

2. Distinguish between the two basic multiplexing techniques?

3. In what situation multiplexing is used?



2. PULSE CODE MODULATION

Aim: To convert an analog signal into a pulse digital signal using PCM system

Apparatus:

1. PCM transmitter trainer.

2. PCM receiver trainer.

3. CRO and connecting wires.

Theory:

Pulse-code Modulation (PCM), like PAM, is a digital communication technique that

sends samples of the analog signal taken at a sufficiently high rate (higher than the Nyquist rate).

In addition, PCM differs than PAM in that it quantizes the samples by constraining them to only

take a limited number of values, and then converts each value into a binary string of bits that are

transmitted on the communication line. Typically, in digital telephony where PCM is widely

used, the sampling rate is 8 kHz (higher than twice the voice band), and the quantization uses

256 levels (i.e., each sample is mapped into an 8-bit PCM code).

In practice, PCM is typically combined with Time Division Multiplexing (TDM), which

is the process of combining many PCM signals representing different messages and transmitting

them over the same channel on a time-sharing basis. Each PCM signal is assigned a timeperiod

called a slot on the transmission line, and slots are arranged in groups called frames.The main

advantages of PCM transmission are: lower cost, ease of multiplexing and switching, and better

noise immunity. Its main disadvantage is the stringent timing and synchronization requirements.

Nowadays, PCM-TDM systems form the backbone for all digital telephony networks worldwide

(refer to your textbooks for more details).

Block diagram:



Procedure:

1. Connect 500 Hz to CH0 and 1 KHz to CH1

2. Set the speed selection switch to FAST mode

Observation:

1. Connect the scope to CH0 and CH1 for observing the channel input.

2. Connect the scope to observe the sampling clock at TP7 and TP8.

3. Observe the sampling amplifier output at TP12 with respective sampling clock.

The multiplexer output shows the proper alignment of samples in their respective time slots.

Also verify that the amplitude of the samples at any instant of the is equal to the amplitude of the

sampled signals at that instant of time.

Waveforms:

Result:

Viva –Voice:

1. List advantages and disadvantages of digital modulation communication systems.

2. List various steps in pulse code modulation.

3. Discuss the problems associated with quantization

4. What do you mean by band rate?

5. Draw the waveforms of TDM-PCM systems.



3. DELTA MODULATION AND DEMODULATION

Aim: To transmit an analog message signal in its digital form and again reconstruct back the

original analog message signal at receiver by using Delta modulator.

Apparatus:

1. Delta modulator trainer kit

2. CRO

3. Probes & patch cards

Theory:

DM uses a single bit PCM code to achieve digital transmission of analog signal. With

conventional PCM each code is binary representation of both sign and magnitude of a particular

sample. With DM, rather than transmitting a coded representation of a sample a single bit is

transmitted, which indicates whether the sample is smaller or larger than the previous sample.

The algorithm for a delta modulation system is a simple one. If the current sample is smaller than

the previous sample then logic 0 is transmitted or logic 1 is transmitted if the current sample is

larger than the previous sample. The input analog is sampled and converted to a PAM signal

followed by comparing it with the output of the DAC. The output of the DAC is equal to the

regenerated magnitude of the previous sample which was stored in the up/down counter as a

binary number. The up/down counter is incremented or decremented whether the previous

sample is larger or smaller than the current sample. The up/down counter is clocked at a rate

equal to the sample rate. So, the up/down counter is updated after each comparison.

Block diagram:

Modulator



Block diagram for demodulator:

Procedure:

Modulator:

1. Connect PLA1 to PLAA.

2. Connect channel 1 to CRO to TPA1/TPAA ; adjust VR1 to minimum to get zero level

signal.

3. Connect channel 1 to TP1 and channel 2 to TPB1 and adjust VR2 to obtain square wave

half the frequency of the clock rate selected (Output at TP1).

4. Connect Channel 1 to TP2 and set voltage/div of channel 1 to mV range and Observe a

triangle waveform, which is output of integrator. It can be observed that as the clock rate

is increased, amplitude of triangle waveform decreases. This is called minimum step size

(Clock rate can be changed by depressing SW1 switch).

5. Connect channel 1 to TPA1/TPAA; adjust VR1 in order to obtain a 1 KHz sinewave of

500 mV pp approximately.

6. Signal approximating 1 KHz is available at the integrator output (TP2); this signals

obtained by integrating the digital output resulting from Delta Modulation.



7. Connect channel 1 to TP2 and channel 2 to TPB1; it can be observed that the digital high

makes the integrator output to go upwards and digital low makes the integrator output to

go downwards.

8. With an oscilloscope displaying three traces,, it is possible to simultaneously observe the

input signal of the modulation, the digital output of the modulator and the signal obtained

by the integration from the modulator digital output.

9. Notice that, when the output (Feedback signal) is lower than the analog input the digital

output is high, whenever it is low when the analog input is lower than the integrated

output.

10. Increase the amplitude of 1 KHz sinewave by rotating VR1 to1 Vpp and observe that the

integrator output follows the input signal.

11. Increase the amplitude of 1 KHz sinewave further high, and observe that the integrator

output cannot follow the input signal. State the reason.

12. Repeat the above mentioned procedures with different signal sources and selecting

different clock rates and observe the response of the linear Delta Modulator

Demodulator:

1. Prearrange the connections of Linear Delta Modulator.

2. Connect PLB1 (Digital o/p of Delta Modulator) to PLBB (i/p of Linear Delta

Modulator).

3. Connect PLC1 (Linear Delta Demodulator output) to either PLCA (i/p of fourth order

LPF) or PLCB (i/p of second order LPF).

Observations:

Observe the reconstructed output of the forth order LPF at TPD1 and also observet he

out of the second order filter at TPD2.

Waveforms:

Result:



Viva -Voice

1. What is a Modulator?

2. Define Bit Rate?

3. Explain Delta Modulation Technique?

4. Explain delta sigma Modulation?

5. What are the Applications of Delta modulations?



4. FREQUENCY SHIFT KEYING

Aim: To generate the frequency shift keying signal for a given binary data and also

demodulate the original data input.

Apparatus:

1. Band Pass modulator and Demodulator trainer kit.

2. C.R.O

3. Patch Cards and probes

Theory:

Communication systems often involve modulation of a carrier, which results, of course, in a

band pass waveform. Radio & Television signals are good examples involving analog messages.

A good example where the message is digital is the modem, a device used to connect a remote

computer terminal to the main computer. The modulation-De modulation apparatus modulates a

carrier with the terminal’s data stream for transmission to the computer (often over telephone

lines) and recovers the data stream sent by the computer via a similar modulation.

Band pass Modulation is the process by which an information signal is converted to a sinusoidal

waveform; for digital modulation, such a sinusoid of duration T is referred to as a digital symbol.

The sinusoid has just three features that can be used to distinguish it from other sinusoids:

amplitude, frequency, and phase. Thus band pass modulation can be defined as the process

whereby the amplitude, frequency, or phase of a RF carrier, or a combination of them, is varied

in accordance with the information to be transmitted. The general form of the carrier wave, C (t),

is as follows:

C(t) = A(t) cos θ(t)

Where A(t) is the time-varying amplitude and θ(t) is the time-varying angle. It is convenient to

write

In this type of modulation, the modulated output shifts between two frequencies for all ‘one’ to

‘zero’ transitions. Let the two carrier frequencies be represented by 1 and 2 and then we have:

M (t)=A (t) cos1t, if the data is ‘one’

=A (t) cos2t, if the data is ‘zero’

where0 is the radian frequency of the carrier and Φ(t) is the phase. The terms f and will each

be used to denote the frequency.



Block diagram:

Experimental Procedure:

FSK Modulator:

Connect SIN1 to the INPUT-1 of the Modulator

Connect SIN2 to the INPUT-2 of the Modulator

Connect data to the control input of the Modulator

Connect the scope to the Control Input and the other channel to the Modulated output

FSK Demodulator:

Establish the same connections for FSK modulation in DCLT 005

Set DCLT-005 in conjunction with DCLT 005

Connect the FSK Modulated output to the FSK I/P of the FSK Demodulator (DCLT 006)

Connect the scope to the CONTROL INPUT and the DATA OUTPUT



Observations:

1. Observe the FSK Modulated output and the modulating data in the two channels of the

oscilloscope.

2. Observe the incoming modulated carrier and recovered data with respect to the modulating data.

Waveforms:

.

Result:

Viva Voice:

1. Compare FSK and FM?

2. Compare ASK and FSK?

3. What are the different techniques to demodulate FSK?

4. Define FSK?



5. QPSK MODULATION AND DEMODULATION

Aim: To generate a QPSK for a given binary digital signal and Observe. Demodulate the same

QPSK to get back the Original digital signal, using carrier receiving circuit and Demodulator.

Components Required: 1.Patch chords ,

2.Signal generator,

3.CRO,

4.Probes

Theory:

QPSK is another form of angle-modulated, constant-amplitude digital modulation. It is an

M-ary encoding technique where M=4. With QPSK four output phases are possible for a single

carrier frequency. Two bits are clocked into the bit splitter. After both bits have been serially

inputted, they are simultaneously parallel outputted. One bit is directed to the I channel and the

other to the Q channel. The I bit modulates a carrier that is in phase with the reference oscillator

and the Q bit modulates a carrier that is 900 out of phase with the reference carrier.

QPSK modulator is two BPSK modulators combined in parallel. The input QPSK signal

is given to the I and Q product detectors and the carrier recovery circuit. The carrier recovery

circuit produces the original transmit carrier oscillator signal. The recovered carrier must be

frequency and phase coherent with the transmit reference carrier. The QPSK signal is

demodulated in the I and Q product detectors, which generate the original I and Q data bits. The

output of the product detectors are fed to the bit combining circuit, where they are converted

from parallel I and Q data channels to a single binary output data stream.

Procedure:

1. Connect the binary input data to I-channel.

2. Connect the binary input data to Q-channel.

3. Connect the sine wave input to balanced modulator (I channel) as a carrier signal and

to sine wave input to balanced modulator (Q channel) as a carrier signal.

4. Switch on the power supply.

5. Display binary input data on CRO. Adjust pot1 and pot3 to get bipolar data.

6. Adjust gain control pot to set equal amplitude in I and Q channel.

7. Obtain QPSK signal.

8. Connect the QPSK to input of QPSK demodulator.

9. Obtain the demodulated QPSK signal



Block Diagram:

Model waveforms:



Tabular Column:

S.No Name of the signal Amplitude in V Time period in Sec Frequency in Hz

1 Modulating Signal

2 Carrier Signal

3 Modulated Signal

4 Demodulated

Signal

Result:

Viva -Voice

1. What is the difference between PSK&QPSK?

2. What is the band width requirement of a QPSK?

3. Explain the operation of QPSK detection?

4. What are the advantages of QPSK?

5. What is meant by differential encoding



6. DIFFERENTIAL PHASE SHIFT KEYING

Aim: To generate differentially phase shift keying signal and also demodulate the original

Binary data.

Apparatus:

1. DPSK modulation and demodulation trainer kit

2. CRO

3. Patch cards

Theory:

DPSK may be viewed as the non-coherent version of PSK. It eliminates the need for a

coherent reference signal at the receiver by combining two basic operations at the transmitter:

1. Differential encoding of the input binary wave and

2. Phase-Shift Keying hence, the name, differential phase shift keying (DPSK).

In effect to send symbol 0, we phase advance the current signal wave-form by 1800, and

to send symbol 1, we leave the phase of the current signal waveform unchanged. The receiver is

equipped with a storage capability, so that it can measure the relative phase difference between

the waveforms received during two successive bit intervals. Provided that the unknown phase θ

contained in the received wave varies slowly, the phase difference between wave forms received

in two successive bit intervals will be independent of θ.



Block diagram:

RESET

DPSK

ENCODER

SERIAL DATA

S - CLOCK

DPSK CONTROL

PLL CLOCK FROM DCLT-006 TP12

CLOCK

DIVIDER

DPSK

DECODER DPSK MODULATED DATA FROM DCLT-006

S-DATA WITH ONE BIT DELAY

T6

T5

S6

S5

T7 S7

S10 T10 S15 T15

T13 S13

D

P

SK

M

O

D

D

P

SK

D

E

M

O

D

Data Simulator

s-clock s-data

CARRIER GENERATION LOGIC

SIN1 SIN2* SIN

2 UNIPOLAR TO BI POLAR

BI POLAR TO UNIPOLAR

DATA OUTPUT

MODULATION

CARRIER MODULATION CODING LOGIC

NRZ-

L

NRZ-

M NRZ-S

URZ

BIO-L

BIO-

M BIO-S

AMI

CLOCK

INPUT DATA

GND

INPUT 1

INPUT 2

CONTROL

INPUT

INPUT OUTPUT

INPUT

UNITED ELECTROTECHNOLOGIES DCL - 005



Procedure: (Modulator)

Establish the connection for DPSK modulation and connect the DCLT 006 in conjunction

with the DCLT- 005 & DCLT-011

Feed the PSK Modulated Output to the PSK I/P of the PSK Demodulator of DCLT 006

Connect the scope to the PSK I/P and the DATA O/P for PSK Demodulated o/p

Observe the PSK Demodulated output w.r.t the control input of the Modulator DCLT-005

Feed the Demodulated DPSK signal to DCLT-011 (S15) and the recovered clock to the

DPSK Decoder at S10.

Connect the Scope to the S-Data of DCLT-005 and Decoded S-Data of DCLT-011

Refer page for connection Diagram.

Observations:

The DPSK modulated output and the Demodulating data using the two channels of the

oscilloscope.

The DPSK Demodulated Data with DPSK Coded Data.

The S-Data with DPSK Decoded Data. (with 1 bit delay)

Wave forms:

Result:

Viva -Voice

1. Explain DPSK Modulation technique?

2. Difference between DPSK & PSK?

3. The Non coherent Version of PSK is known as……

4. Define Modulation?

5. Define Modulation Index?



DIGITAL COMMUNICATIONS

USING MATLAB



1. TIME DIVISION MULTIPLEXING Aim: To perform the generation of Time division multiplexing using MATLAB

Apparatus: 1. Hardware Tools: Computer system

2. Software Tool: MATLAB 7.0

Program:

% % % % % % % % % % % % % % % % % % % % % Code for Time Division Multiplexing

clc;

close all;

clear all;

% Signal generation

x=0:.5:4*pi; % siganal taken upto 4pi

sig1=8*sin(x); % generate 1st sinusoidal signal

l=length(sig1);

sig2=8*triang(l); % Generate 2nd traingular Sigal

% Display of Both Signal

subplot(2,2,1);

plot(sig1);

title('Sinusoidal Signal');

ylabel('Amplitude--->');

xlabel('Time--->');

subplot(2,2,2);

plot(sig2);

title('Triangular Signal');


xlabel('Time--->');

% Display of Both Sampled Signal

subplot(2,2,3);

stem(sig1);

title('Sampled Sinusoidal Signal');


xlabel('Time--->');

subplot(2,2,4);

stem(sig2);

title('Sampled Triangular Signal');


xlabel('Time--->');

l1=length(sig1);

l2=length(sig2);

for i=1:l1



sig(1,i)=sig1(i); % Making Both row vector to a matrix

sig(2,i)=sig2(i);

end

% TDM of both quantize signal

tdmsig=reshape(sig,1,2*l1);

% Display of TDM Signal

figure

stem(tdmsig);

title('TDM Signal');


xlabel('Time--->');

% Demultiplexing of TDM Signal

demux=reshape(tdmsig,2,l1);

for i=1:l1

sig3(i)=demux(1,i); % Converting The matrix into row vectors

sig4(i)=demux(2,i);

end

% display of demultiplexed signal

figure

subplot(2,1,1)

plot(sig3);

title('Recovered Sinusoidal Signal');


xlabel('Time--->');

subplot(2,1,2)

plot(sig4);

title('Recovered Triangular Signal');


xlabel('Time--->');



OUTPUTS:

0 10 20 30-10

-5

0

5

10Sinusoidal Signal

Am

plit

ude--

->

Time--->

0 10 20 300

2

4

6

8Triangular Signal

Am

plit

ude--

->

Time--->

0 10 20 30-10

-5

0

5

10Sampled Sinusoidal Signal

Am

plit

ude--

->

Time--->

0 10 20 300

2

4

6

8Sampled Triangular Signal

Am

plit

ude--

->

Time--->

0 10 20 30 40 50 60-8

-6

-4

-2

0

2

4

6

8TDM Signal

Am

plit

ude--

->

Time--->



0 5 10 15 20 25 30-10

-5

0

5

10Recovered Sinusoidal Signal

Am

plit

ude--

->

Time--->

0 5 10 15 20 25 300

2

4

6

8Recovered Triangular Signal

Am

plit

ude--

->

Time--->

Results:



2. Pulse code modulation

Aim: To perform the generation of Pulse code modulation using MATLAB



Program :

% % % % % % % % % % % % % % % % % % % % % % Code for Pulse Code

Modulation

clc;

close all;

clear all;

n=input('Enter n value for n-bit PCM system : ');

n1=input('Enter number of samples in a period : ');

L=2^n;

% % Signal Generation

% x=0:1/100:4*pi;

% y=8*sin(x); % Amplitude Of signal is 8v

% subplot(2,2,1);

% plot(x,y);grid on;

% Sampling Operation

x=0:2*pi/n1:4*pi; % n1 nuber of samples have tobe selected

s=8*sin(x);

subplot(3,1,1);

plot(s);

title('Analog Signal');


xlabel('Time--->');



subplot(3,1,2);

stem(s);grid on;

title('Sampled Sinal');


xlabel('Time--->');

% Quantization Process

vmax=8;

vmin=-vmax;

del=(vmax-vmin)/L;

part=vmin:del:vmax; % level are between vmin and vmax with difference of del

code=vmin-(del/2):del:vmax+(del/2); % Contaion Quantized valuses

[ind,q]=quantiz(s,part,code); % Quantization process

% ind contain index number and q contain quantized values

l1=length(ind);

l2=length(q);

for i=1:l1

if(ind(i)~=0) % To make index as binary decimal so started from 0 to N

ind(i)=ind(i)-1;

end

i=i+1;

end

for i=1:l2

if(q(i)==vmin-(del/2)) % To make quantize value inbetween the levels

q(i)=vmin+(del/2);

end

end

subplot(3,1,3);

stem(q);grid on; % Display the Quantize values

title('Quantized Signal');


xlabel('Time--->');



% Encoding Process

figure

code=de2bi(ind,'left-msb'); % Cnvert the decimal to binary

k=1;

for i=1:l1

for j=1:n

coded(k)=code(i,j); % convert code matrix to a coded row vector

j=j+1;

k=k+1;

end

i=i+1;

end

subplot(2,1,1); grid on;

stairs(coded); % Display the encoded signal

axis([0 100 -2 3]); title('Encoded Signal');


xlabel('Time--->');

% Demodulation Of PCM signal

qunt=reshape(coded,n,length(coded)/n);

index=bi2de(qunt','left-msb'); % Getback the index in decimal form

q=del*index+vmin+(del/2); % getback Quantized values

subplot(2,1,2); grid on;

plot(q); % Plot Demodulated signal

title('Demodulated Signal');


xlabel('Time--->');

INPUT:

Enter n value for n-bit PCM system : 5

Enter number of samples in a period : 10



OUTPUT:

0 5 10 15 20 25-10

0

10Analog Signal

Am

plit

ude--

->

Time--->

0 5 10 15 20 25-10

0

10Sampled Sinal

Am

plit

ude--

->

Time--->

0 5 10 15 20 25-10

0

10Quantized Signal

Am

plit

ude--

->

Time--->

0 10 20 30 40 50 60 70 80 90 100-2

-1

0

1

2

3Encoded Signal

Am

plit

ude--

->

Time--->

0 5 10 15 20 25-10

-5

0

5

10Demodulated Signal

Am

plit

ude--

->

Time--->

Results:



3. Delta Modulation

Aim: To perform the generation of Delta modulation using MATLAB



Program:

% DELTA MODULATiON

clc;

clear all;

close all;

a=2;

t=0:2*pi/50:2*pi;

x=a*sin(t);

l=length(x);

plot(x,'r');

delta=0.2;

hold on

xn=0;

for i=1:l;

if x(i)>xn(i)

d(i)=1;

xn(i+1)=xn(i)+delta;

else

d(i)=0; xn(i+1)=xn(i)-delta;

end

end

stairs(xn)

hold on

for i=1:d

if d(i)>xn(i)

d(i)=0;

xn(i+1)=xn(i)-delta;

else

d(i)=1; xn(i+1)=xn(i)+delta

end

end

plot(xn,'c')

legend('Analog signal','Delta modulation','Demodulation')

title('DELTA MODULATION / DEMODULATION ')



OUTPUT:

0 10 20 30 40 50 60-2

-1.5

-1

-0.5

0

0.5

1

1.5

2DELTA MODULATION / DEMODULATION

Analog signal

Delta modulation

Demodulation

RESULT:



4.Frequency shift keying

Aim: To perform the generation of Frequency shift keying using MATLAB



Program:

clc;

close all;

clear all;

x=input('enter the binary input');

l=length(x);

for i=1:1:l

m(((i-1)*100)+1:i*100)=x(i);

end

figure;

subplot(4,1,1);

plot(m);

xlabel('time');

ylabel('amplitude');

title('modulating signal');

f=100;

t=0:(1/f):(l-(1/f));

f1=10;

f2=5;

c1=sin(2*pi*f1*t);

y1=m.*c1;

subplot(4,1,2);

plot(t,y1);

xlabel('time');


for j=1:l

if x(j)==1

x(j)=0;

else x(j)=1;

end

m1((j-1)*100+1:j*100)=x(j);

end

c2=sin(2*pi*f2*t);

y2=m1.*c2;

subplot(4,1,3);

plot(t,y2);

xlabel('time');




y=y1+y2;

subplot(4,1,4);

plot(t,y);

xlabel('time');


title('FSK modulated wave');

r=randn(size(y));

F=y+r;

figure;

subplot(3,1,1);

plot(F);

xlabel('time');


title('noise added FSK signal');

l1=length(F);

t1=0:0.01:.99;

r1=sin(2*pi*f1*t1);

r1=fliplr(r1);

l2=length(r1);

l3=l1+l2-1;

u=fft(F,l3);

v=fft(r1,l3);

k1=u.*v;

k11=ifft(k1,l3);

r2=sin(2*pi*f2*t1);

r2=fliplr(r2);

w=fft(r2,l3);

k2=u.*w;

k22=ifft(k2,l3);

k=k11-k22;

subplot(3,1,2);

plot(k);

xlabel('time');


title('correlated signal');

for z=1:l

t(z)=k(z*100);

if t(z)>0

s(z)=1;

else

s(z)=0;

end

end

subplot(3,1,3);

stem(s);

xlabel('time');




title('Demodulated output signal');

INPUT:

Enter the binary input [1 0 0 1 0 1 1]

OUTPUT:

0 100 200 300 400 500 600 7000

0.51

time

am

plit

ude modulating signal

0 1 2 3 4 5 6 7-1

01

time

am

plit

ude

0 1 2 3 4 5 6 7-1

01

time

am

plit

ude

0 1 2 3 4 5 6 7-1

01

time

am

plit

ude FSK modulated wave

0 100 200 300 400 500 600 700-5

0

5

time

am

plit

ude

noise added FSK signal

0 100 200 300 400 500 600 700 800-100

0

100

time

am

plit

ude

correlated signal

1 2 3 4 5 6 70

0.5

1

time

am

plit

ude

Demodulated output signal

RESULT:



5.QPSK modulation & demodulation

Aim: To perform the generation of QPSK modulation & demodulation using MATLAB



Program:

clc;

clear all;

close all;

data=[0 1 0 1 1 1 0 0 1 1]; % information

%Number_of_bit=1024;

%data=randint(Number_of_bit,1);

figure(1)

stem(data, 'linewidth',3), grid on;

title(' Information before Transmiting ');

axis([ 0 11 0 1.5]);

data_NZR=2*data-1; % Data Represented at NZR form for QPSK modulation

s_p_data=reshape(data_NZR,2,length(data)/2); % S/P convertion of data

br=10.^6; %Let us transmission bit rate 1000000

f=br; % minimum carrier frequency

T=1/br; % bit duration

t=T/99:T/99:T; % Time vector for one bit information

% XXXXXXXXXXXXXXXXXXXXXXX QPSK modulatio

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

y=[];

y_in=[];

y_qd=[];

for(i=1:length(data)/2)

y1=s_p_data(1,i)*cos(2*pi*f*t); % inphase component

y2=s_p_data(2,i)*sin(2*pi*f*t) ;% Quadrature component

y_in=[y_in y1]; % inphase signal vector

y_qd=[y_qd y2]; %quadrature signal vector



y=[y y1+y2]; % modulated signal vector

end

Tx_sig=y; % transmitting signal after modulation

tt=T/99:T/99:(T*length(data))/2;

figure(2)

subplot(3,1,1);

plot(tt,y_in,'linewidth',3), grid on;

title(' wave form for inphase component in QPSK modulation ');

xlabel('time(sec)');

ylabel(' amplitude(volt0');

subplot(3,1,2);

plot(tt,y_qd,'linewidth',3), grid on;

title(' wave form for Quadrature component in QPSK modulation ');



subplot(3,1,3);

plot(tt,Tx_sig,'r','linewidth',3), grid on;

title('QPSK modulated signal (sum of inphase and Quadrature phase signal)');



% XXXXXXXXXXXXXXXXXXXXXXXXXXXX QPSK demodulation

XXXXXXXXXXXXXXXXXXXXXXXXXX

Rx_data=[];

Rx_sig=Tx_sig; % Received signal

for(i=1:1:length(data)/2)

%%XXXXXX inphase coherent dector XXXXXXX

Z_in=Rx_sig((i-1)*length(t)+1:i*length(t)).*cos(2*pi*f*t);

% above line indicat multiplication of received & inphase carred signal

Z_in_intg=(trapz(t,Z_in))*(2/T);% integration using trapizodial rull

if(Z_in_intg>0) % Decession Maker

Rx_in_data=1;

else

Rx_in_data=0;

end

%%XXXXXX Quadrature coherent dector XXXXXX



Z_qd=Rx_sig((i-1)*length(t)+1:i*length(t)).*sin(2*pi*f*t);

%above line indicat multiplication ofreceived & Quadphase carred signal

Z_qd_intg=(trapz(t,Z_qd))*(2/T);%integration using trapizodial rull

if (Z_qd_intg>0)% Decession Maker

Rx_qd_data=1;

else

Rx_qd_data=0;

end

Rx_data=[Rx_data Rx_in_data Rx_qd_data]; % Received Data vector

end

figure(3)

stem(Rx_data,'linewidth',3)

title('Information after Receiveing ');

axis([ 0 11 0 1.5]), grid on;

% XXXXXXXXXXX end of program XXXXXXXXXX

OUTPUT:

0 1 2 3 4 5 6 7 8 9 10 110

0.5

1

1.5 Information before Transmiting



0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 10-6

-1

0

1 wave form for inphase component in QPSK modulation

time(sec) a

mplit

ude(v

olt0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 10-6

-1

0

1 wave form for Quadrature component in QPSK modulation

time(sec)

am

plit

ude(v

olt0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 10-6

-2

0

2QPSK modulated signal (sum of inphase and Quadrature phase signal)

time(sec)

am

plit

ude(v

olt0

0 1 2 3 4 5 6 7 8 9 10 110

0.5

1

1.5Information after Receiveing

RESULT:



6. Differential phase shift keying

Aim: To perform the generation of Differential phase shift keying using MATLAB



Program :

clear all;close all;clc;

fc=2; % carrier frequency

samp=100;

t=linspace(0,2*pi,samp);

ph1=cos(fc*t);

ph2=-cos(fc*t);

b=mod(randperm(12),2); % The random binary stream

x=0;

nb(1)=not(xor(b(1),0));

for i=2:length(b)+1

nb(i)=not(xor(b(i-1),x));

x=nb(i);

end;

dpsk=[];bin1=[];bin2=[];

for j=1:length(nb)

if nb(j)==0

dpsk=[dpsk,ph1];

bin1=[bin1,zeros(1,samp)];

elseif nb(j)==1

dpsk=[dpsk,ph2];

bin1=[bin1,ones(1,samp)];

end;

end;

for k=1:length(b)

if b(k)==0

bin2=[bin2,zeros(1,samp)];

elseif b(k)==1

bin2=[bin2,ones(1,samp)];

end;

end;

subplot(311),plot(bin2,'r');

axis([0 samp*length(b) -0.2 1.2]);

xlabel('Time index'); ylabel('Amplitude');

title('The random binary Input','FontSize',12);

bn=num2str(b);



bx=['The Random binary string is',bn];

gtext(bx,'FontSize',12);

subplot(312),plot(bin1,'LineWidth',1.5);

axis([0 samp*length(nb) -0.2 1.2]);hold on;


title('The random binary (differential)Input','FontSize',12);

bn=num2str(nb);

bx=['The Differential binary string is',bn];

gtext(bx,'FontSize',12);

subplot(313),plot(dpsk,'LineWidth',1.5);

axis([0 samp*length(nb) -1.2 1.2]);


title('The simulated DPSK Output','FontSize',12);

OUTPUTS:

0 200 400 600 800 1000 1200

0

0.5

1

Time index

Am

plitu

de

The random binary Input

The Random binary string is0 1 0 0 1 1 0 0 1 1 0 1

0 200 400 600 800 1000 1200

0

0.5

1

Time index

Am

plitu

de

The random binary (differential)Input

The Differential binary string is1 1 1 0 1 1 1 0 1 1 1 0 0

0 200 400 600 800 1000 1200

-1

0

1

Time index

Am

plitu

de

The simulated DPSK Output

Result :

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