Cs Lab Manual

SURYA COLLEGE OF ENGINEERING & TECHNOLOGY

SURYA NAGAR, VIKIRAVANDI– 605 652, VILLUPURAM DISTRICT,

VIKRAVANDI

EC2307 - COMMUNICATION SYSTEMS LABORATORY MANUAL

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CONTENTS

S.NO. NAME OF THE EXPERIMENT PAGE NO.

1Amplitude Modulation and Demodulation

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2Frequency Modulation and Demodulation

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3

Pulse Modulation13

(i). Pulse Amplitude Modulation(PAM)(ii). Pulse Width Modulation(PWM) 16(iii).Pulse Position Modulation(PPM) 18

4Pulse Code Modulation and Demodulation

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5 Delta Modulation and Demodulation 24

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Digital Modulation27(i) Amplitude Shift Keying(ASK)

(ii) Frequency Shift Keying(FSK) 31(iii)Phase Shift Keying(PSK) 35(iv)Quadrature Phase Shift Keying(QPSK)

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7Designing, assembling and testing of Pre-emphasis and De-emphasis

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8 Line Coding and Decoding 44

9Sampling and Time Division Multiplexing

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10 Frequency Division Multiplexing 54

11MATLAB program for digital modulation

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12 Error control coding using MATLAB 59

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1. AMPLITUDE MODULATION AND DEMODULATION

OBJECTIVE To perform the amplitude modulation and demodulation and to calculate the modulation index

HARDWARE REQUIRED AM trainer kit, CRO,patch chords,CRO probes.

THEORY- AMPLITUDE MODULATION

Modulation is defined as the process by which some characteristics of a carrier signal is varied in accordance with a modulating signal. The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal.

Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal. The envelope of the modulating wave has the same shape as the base band signal provided the following two requirements are satisfied

The carrier frequency fc must be much greater then the highest frequency components fm of the message signal m (t) i.e. fc >> fm

The modulation index must be less than unity. if the modulation index is greater than unity, the carrier wave becomes over modulated.

BLOCK DIAGRAM

AMPLITUDE MODULATER

Amplitude amplitude modulated signal Carrier signal modulator

Message signal

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MODEL GRAPH

AMPLITUDE MODULATED SIGNALFORMULA USED

Modulation index (m) =

Vm=Amplitude of message signal

Vc=Amplitude of carrier signal

Percentage of Modulation index (m) = X 100 =

THEORY- AMPLITUDE DEMODULATION

The process of detection provides a means of recovering the modulating Signal from modulating signal. Demodulation is the reverse process of modulation. The detector circuit is employed to separate the carrier wave and eliminate the side bands. Since the envelope of an AM

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wave has the same shape as the message, independent of the carrier frequency and phase, demodulation can be accomplished by extracting envelope.

An increased time constant RC results in a marginal output follows the modulation envelope. A further increase in time constant the discharge curve become horizontal if the rate ofmodulation envelope during negative half cycle of the modulation voltage is faster than the rate of voltage RC combination ,the output fails to follow the modulation resulting distorted output iscalled as diagonal clipping : this will occur even high modulation index.

The depth of modulation at the detector output greater than unity and circuit impedance isless than circuit load (Rl > Zm) results in clipping of negative peaks of modulating signal. It iscalled “negative clipping”.

BLOCK DIAGRAM

AMPLITUDE DEMODULATION

AM signal LPF amplifier demodulated o/p

MODEL GRAPH

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AMPLITUDE DEMODULATED SIGNAL

CIRCUIT DIAGRAM

DESIGN PROCEDURE

Given VC = 50mV, fc = 500 KHz, fm = 1KHz.

Set modulating voltage Vm = 10 V.

Emax = 1.6 V, Emin = 0.7 V

Modulation index (m) = Emax- Emin

Emax+Emin *100 =39.13%

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PROCEDURE

1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to amplitude modulator4. The high frequency carrier signal is also applied to the amplitude modulator5. The amplitude modulated signal is obtained as an output from the amplitude modulator.6. Using the Emax and Emin the modulation index is calculated.7. The readings are noted and the values are tabulated.

TABULATION

Waveform Amplitude (volts) Time division (sec.)

Message signal

Carrier signal

Modulated Signal

Demodulated Signal

RESULT

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Thus the amplitude modulation and demodulation were performed and the modulation index for various modulating voltage were calculated.

2. FREQUENCY MODULATION AND DEMODULATION

OBJECTIVE To perform the Frequency modulation and demodulation using IC 565 and to calculate the modulation index for various modulating voltages.

HARDWARE REQUIREDIC NE565, Resistors, Capacitor, CRO, Bread board and connecting wires, RPS

THEORYFrequency modulation is a process of changing the frequency of a carrier wave in accordance with the slowly varying base band signal. The main advantage of this modulation is that it can provide better discrimination against noise.

CIRCUIT DIAGRAM

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FREQUENCY MODULATION

PIN DIAGRAM AND DESCRIPTION OF XR2206

Pin no.

Symbol Description

1 AMSI Amplitude Modulating Signal Input.

2 STO Sine or Triangle Wave Output.

3 MO Multiplier Output.

4 VCC Positive Power Supply.

5 TC1 Timing Capacitor Input.

6 TC2 Timing Capacitor Input.

7 TR1 Timing Resistor 1 Output.

8 TR2 Timing Resistor 2 Output.

9 FSKI Frequency Shift Keying Input.

10 BIAS Internal Voltage Reference.

11 SYNCO Sync Output.

12 GND Ground pin.

13 WAVEA1 Wave Form Adjust Input 1.

14 WAVEA2 Wave Form Adjust Input 2.

15 SYMA1 Wave Symmetry Adjust 1.

16 SYMA2 Wave Symmetry Adjust 2.

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CIRCUIT DIAGRAM

FREQUENCY DEMODULATION

PIN DIAGRAM OF NE565

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MODEL GRAPH

FREQUENCY MODULATION

MODEL GRAPH

FREQUENCY DEMODULATION

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TABULATION:


Message signal

Carrier signal

Frequency Modulated output

Frequency Demodulated

output

PROCEDURE

1. The circuit connection is made as shown in the circuit diagram.2. The modulating signal FM is given from an FG (1KHZ)3. For various values of modulating voltage Vm the values of Fmax and Fmin are noted4. The values of the modulation index are calculated.

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RESULTThus the frequency modulation and demodulation was performed and the modulation index was found.

3. PULSE MODULATION – PAM / PWM / PPM

(a)PULSE AMPLITUDE MODULATION

OBJECTIVE To perform the pulse amplitude modulation and demodulation using PAM trainer kit

HARDWARE REQUIRED PAM trainer kit, CRO ,patch chords.

THEORYPulse amplitude modulation is a scheme, which alters the amplitude of regularly spaced rectangular pulses in accordance with the instantaneous values of a continuous message signal. Then amplitude of the modulated pulses represents the amplitude of the intelligence. A train of very short pulses of constant amplitude and fast repetition rate is chosen the amplitude of these pulse is made to vary in accordance with that of a slower modulating signal the result is that of multiplying the train by the modulating signal the envelope of the pulse height corresponds to the modulating wave .the Pam wave contain upper and lower side band frequencies besides the modulating and pulse signals. The demodulated PAM waves, the signal is passed through a low pass filter having a cut – off frequencies equal to the highest frequency in the modulating signal. At the output of the filter is available the modulating signal along with the DC component PAM has the same signal to noise ratio as AM and so it is not employed in practical circuits

BLOCK DIAGRAM MODULATOR

continuous PAM modulatingsignal signal

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multiplier

Pulse train generator

DEMODULATOR

PAM signal demodulated o/p

MODEL GRAPHMODULATION

DEMODULATION

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Low pass filter

PROCEDURE1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to multiplier4. The high frequency carrier signal is also applied to the multiplier5. The pulse amplitude modulated signal is obtained as an output from the multiplier6. The readings are noted and the values are tabulated.

TABULATION


Baseband signal (sine wave)

Carrier signal (square waveform)

TON

TOFF

PAM Output signalTON

TOFF

Demodulated signal

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RESULTThus the pulse amplitude modulation was performed and its corresponding demodulation was also performed.

(b) PULSE WIDTH MODULATION

OBJECTIVE To perform the pulse width modulation and demodulation using PWM trainer kit.

HARDWARE REQUIRED PWM trainer kit,CRO, patch chords.

THEORY

Pulse width modulation (PWM) is a powerful technique for controlling analog circuits with a processor's digital outputs. PWM is employed in a wide variety of applications, ranging from measurement and communications to power control and conversion. It can be used for TDM signal where more than one input signal can be Transmitted one time standard basis is PWM or Pulse length Modulation.

BLOCK DIAGRAM

PULSE WIDTH MODULATOR

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Pulse width modulator

continuous PWM modulating signal signal


MODEL GRAPH

PROCEDURE

1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to pulse width modulator

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4. The high frequency carrier signal is also applied to the pulse width modulator5. The modulated signal is obtained as an output from the pulse width modulator.6. The readings are noted and the values are tabulated.

TABULATION

Waveform Amplitude (Volts) Time Period (sec)Input

PWMTON

TOFF

RESULTThus the pulse width modulation was performed and its corresponding demodulation was

also performed.

(c)PULSE POSITION MODULATION

OBJECTIVE To perform the pulse width modulation and demodulation using PPM trainer kit.

HARDWARE REQUIRED PPM trainer kit,CRO, patch chords.

THEORY Pulse position modulation is similar to pulse width modulation, but the frequency is not constant. Like pulse width modulator circuit, pulse position modulator can be easily constructed.

BLOCK DIAGRAM

PULSE POSITION MODULATOR

continuous PPM modulatingsignal signal

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Pulse position modulator


MODEL GRAPH

PROCEDURE1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to pulse position modulator4. The high frequency carrier signal is also applied to the pulse position modulator5. The modulated signal is obtained as an output from the pulse position modulator.6. The readings are noted and the values are tabulated.

TABULATION

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Waveform Amplitude (Volts) Time Period (sec)Input

PWMTON

TOFF

RESULTThus the pulse position modulation was performed and its corresponding demodulation

was also performed. 4. PULSE CODE MODULATION AND DEMODULATION

OBJECTIVE To perform pulse code modulation and demodulation and to plot the waveforms for binary data at different frequencies.

HARDWARE REQUIRED PCM trainer kit,CRO,patch chords

THEORY In Pulse code modulation (PCM) only certain discrete values are allowed for the modulating signals. The modulating signal is sampled, as in other forms of pulse modulation. But any sample falling within a specified range of values is assigned a discrete value. Each value is assigned a pattern of pulses and the signal transmitted by means of this code. The electronic circuit that produces the coded pulse train from the modulating waveform is termed a coder or encoder. A suitable decoder must be used at the receiver in order to extract the original information from the transmitted pulse train. This PCM system consists of

BLOCK DIAGRAM

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PCM Modulator AND Demodulator

MODEL GRAPH

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CIRCUIT DIAGRAM

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PIN DIAGRAM OF IC 44233

PROCEDURE

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1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The input signal gets processed from ADC,shift register in the transmitter side and

through DAC and shift bregister in receiver side 4. The modulated signal is obtained as an output.5. The readings are noted and the values are tabulated.

TABULATION

Waveform Amplitude (Volts) Time Period (sec)

PCM Modulation

PCM Demodulation

RESULTThus the Pulse Code modulation and demodulation were performed and graphs were plotted.

5. DELTA MODULATION & DEMODULATION

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OBJECTIVE To study the operation of delta modulation and demodulation with the help of kit.

HARDWARE DM kit, CRO and connecting probes

THEORY

Delta modulation is the DPCM technique of converting an analog message signal to a digital sequence. The difference signal between two successive samples is encoded into a single bit code. The block and kit diagrams show the circuitry details of the modulation technique. A present sample of the analog signal m(t) is compared with a previous sample and the difference output is level shifted, i.e. a positive level(corresponding to bit 1) is given if difference is positive and negative level(corresponding to bit 0)if it is negative. The comparison of samples is accomplished by converting the digital to analog form and then comparing with the present sample. This is done using an Up counter and DAC as shown in block diagram. The delta modulated signal is given to up counter and then a DAC and the analog input is given to OPAMP and a LPF to obtain the demodulated output.

BLOCK DIAGRAM

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PROCEDURE

1. Switch on the kit. Connect the clock signal and the modulating input signal to the modulator

block. Observe the modulated signal in the CRO.

2. Connect the DM output to the demodulator circuit. Observe the demodulator output on the

CRO.

3. Also observe the DAC output on the CRO. 4. Change the amplitude of the modulating signal and observe the DAC output. Notice the slope

overload distortion. Keep the tuning knob so that the distortion is gone. Note this value of the amplitude. This is the minimum required value of the amplitude to overcome slope overload distortion.

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5. Calculate the sampling frequency required for no slope overload distortion. Compare the

calculated and measured values of the sampling frequency.

TABULATION


RESULTThus the Delta modulation and demodulation were performed and graphs were plotted.

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6. DIGITAL MODULATION & DEMODULATION – ASK, PSK, FSK

(a)ASK MODULATION AND DEMODULATION

OBJECTIVE To perform ASK modulation and demodulation and to plot the waveforms for thegiven binary data

HARDWARE REQUIRED

ASK Trainer Kit, patch chords, CRO and probes.

THEORY-AMPLITUDE SHIFT KEYING

ASK is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant.

On-off keying (OOK) the simplest form of amplitude-shift keying (ASK) modulation that represents digital data as the presence or absence of a carrier wave. In its simplest form, the presence of a carrier for a specific duration represents a binary one, while its absence for the same duration represents a binary zero. In a ASK system, the pair of signal S1(t) used to represent binary symbols 1 & 0 are defined by

S1 (t) = √2Eb/τb Cos 2πfct0 where 0 ≤ t< Tb andEb = Transmitted signed energy for bitThe carrier frequency fc =n/Tb for some fixed integer n.

BLOCK DIAGRAM ASK TRANSMITTER

The input binary symbols are represented in polar form with symbols 1 & 0 represented by constant amplitude levels √Eb & -√Eb. This binary wave is multiplied by a sinusoidal carrier in a product modulator. The result is a ASK signal.

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ASK RECEIVER

The received ASK signal is applied to a correlator which is also supplied with a locally generated reference signal Ø1 (t). The correlated o/p is compared with a threshold of zero volts. If x1> 0, the receiver decides in favour of symbol 1. If x1< 0, it decides in favour of symbol 0

CIRCUIT DIAGRAM

DESIGN PROCEDUREGeneration

Let Ie = Ic = 2.5mA, hfe=100, Vre=2.5V

Then, Re = Vre/Ic = 1KΩAssuming a peak to peak value of 7V,300Hz for m(t), we get,

Vrb =( Vmp-p/2) – Vbe sat –Vre(max)

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=3.5-0.7-2.5=0.3V

Ib = Ic/hfe = 25µA

Ib(sat) = 1.2Ib = 30µA

Rb = Vrb/Ib(sat)

=10kΩDetection

Given fm = 300Hz

fm = 1/2πRC

let C = 0.1µF then R = 5.6KΩ

PROCEDURE

1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to product modulator4. The high frequency carrier signal is also applied to the product modulator5. The modulated signal is obtained as an output from the product modulator.6. The readings are noted and the values are tabulated.

MODEL GRAPH

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TABULATION


RESULT Thus the ASK modulation and demodulation were performed and required graphs were plotted.

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(b) FSK MODULATION AND DEMODULATION

OBJECTIVE To perform FSK modulation and demodulation and to plot the waveforms for thegiven binary data.

HARDWARE REQUIRED FSK Trainer Kit ,CRO,probes,patch chordsTHEORYFrequency Shift Keying (FSK) is a modulation Data transmitting technique in which carrier frequency is shifted between two distinct fixed frequencies to represent logic 1 and logic 0. The low carrier frequency represents a digital 0 (space) and higher carrier frequency is a I (mark). FSK system has a wide range of applications in low speed digital data transmission systems. FSK Modulating & Demodulating circuitry can be developed in number of ways, familiar VCO and PLL circuits are used in this trainer.BLOCK DIAGRAM

FSK MODULATOR

i/p FSK o/p

FSK DEMODULATOR

FSKi/p o/p

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Square wave

generator FSK modulator

Debounce logic

Phase comparatorError amplifier

VCO

CIRCUIT DIAGRAM

DESIGN PROCEDUREGeneration

Let Ie = Ic = 2.5mA, hfe=100, Vre=2.5V

Then, Re = Vre/Ic = 1KΩAssuming a peak to peak value of 7V,300Hz for m(t), we get,

Vrb =( Vmp-p/2) – Vbe(sat) –Vre(max) =3.5-0.7-2.5=0.3V

Ib = Ic/hfe

= 25µA

Ib(sat) = 1.2Ib = 30µA

Rb = Vrb/Ib(sat)

=10kΩ

Detection

Given

For low pass filter

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f1= 1/2πR1C1

given f1 = 3kHz, assuming C1=0.1µF we get, R1=560Ω

given fm = 300Hz

fm = 1/2πRC

let C2= 0.1µF then R2 = 5.6KΩ

MODEL GRAPH

PROCEDURE

1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to square wavegenerator.4. The high frequency carrier signal is also applied to the product modulator5. The modulated signal is obtained as an output from the product modulator.6. The readings are noted and the values are tabulated.

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TABULATION

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Waveform Amplitude Time period

RESULTThus the FSK modulation and demodulation were performed and required graphs were plotted.

(c)PSK MODULATION AND DEMODULATION

OBJECTIVE To perform the operation of PSK (binary) modulation and demodulation and to plot the PSK waveforms for binary data at different frequencies.

HARDWARE REQUIRED PSK Trainer Kit ,CRO,patch chords

THEORYPhase shift keying is a modulation/data transmitting technique in which phase of the carrier signal is shifted between two distinct levels. In a simple PSK(ie binary PSK) unshifted carrier Vcosω 0t is transmitted to indicate a 1 condition, and the carrier shifted by 1800 ie – Vcosω0t is transmitted to indicate as 0 condition. PSK waveforms are shown.

PSK ModulatorFigure shows the PSK modulator. IC CD 4052 is a 4 channel analog multiplexer and is used as an active component in this circuit. One of the control signals of 4052 is grounded so that 4052 will act as a two channel multiplexer and other control is being connected to the binary signal ie data to be transmitted. Unshifted carrier signal is connected directly to CH1 and carrier shifted by 1800 is connected to CH2.phase shift network is a unity gain inverting amplifier using OP-amp (TL084). When input data signal is 1 ie control signal is at high voltage, output of the 4052 is connected to CH1 and unshifted (or 0 phase)carrier is passed on to output. Similarly When data signal is 0 ie control signal is at zero voltage output of 4052 is connected to CH2 and carrier shifted by 1800 is passed on to output.

PSK DemodulatorDemodulation of PSK is achieved by subtracting the received carrier from a derived synchronous reference carrier of constant phase. Figure shows the simple coherent(synchronous) PSK demodulator. Received PSK signal is converted to square wave using an op-amp(TL084) basedzero crossing detector and connected to EX-OR circuit. The derived reference carrier is connected to other input of the EX-OR Gate through an op-amp based zero crossing detector. For the simplicity same carrier is used at receiver as reference carrier (In practical communication system reference carrier is generated at receiver).We can observe the exact operation of demodulator with the help of waveforms at various nodes in the circuit.

BLOCK DIAGRAM

PSK MODULATOR

Clock data PSK o/p

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Balanced

modulator

Carrier signal

PSK DEMODULATOR

PSK i/p o/p

CIRCUIT DIAGRAM

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Balanced demodulator

LPF & comparator

Carrier signal

PSK DEMODULATOR

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MODEL GRAPH

PROCEDURE

1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to balanced modulator4. The high frequency carrier signal is also applied to the balanced modulator5. The modulated signal is obtained as an output from the balanced modulator.6. The readings are noted and the values are tabulated.

TABULATION

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Waveform Time period Amplitude

RESULTThus the PSK modulation and demodulation were performed and graphs were plotted.

(d)QPSK MODULATION AND DEMODULATION

OBJECTIVE To perform the operation of QPSK (binary) modulation and demodulation and to plot the QPSK waveforms for binary data at different frequencies.

HARDWARE REQUIRED QPSK Trainer Kit ,CRO, patch chords

THEORY

QPSK is another modulation technique used in digital communication.sometimes known as quaternary or quadriphase PSK or 4-PSK,QPSK uses four points on the constellation diagram,equispaced around a circle. With four phases QPSK can encode two bits per symbol with gray coding to minimize the BER-twice the rate of BPSK.Although QPSK can be viewed as a quaternary modulation it is easier to see it as two independently modulated quadrature carriers. With this interpretation the even(or odd) bits are used to modulate the in-phase component of the carrier,while the odd(or even) bits are used to modulate the quadrature-phase component of the carrier.BPSK is used on both carriers and they can be independently demodulated.

BLOCK DIAGRAM

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MODEL GRAPH

PROCEDURE

1. The connection is made as per the block diagram.

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2. Switch on the trainer kit.3. The modulating signal is given as a input to balanced modulator4. The high frequency carrier signal is also applied to the balanced modulator5. The modulated signal is obtained as an output from the balanced modulator.6. The readings are noted and the values are tabulated.

TABULATION

RESULTThus the QPSK modulation and demodulation were performed and graphs were plotted.

7. PRE –EMPHASIS AND DE-EMPHASIS CIRCUITS

OBJECTIVE To determine how the characteristics of Pre-emphasis and De-emphasis differ from each other.

HARDWARE REQUIREDTransistor, AFO, IC NE566, Resistors, Capacitor, CRO, RPS.

THEORY

PRE-EMPHASISThe circuits are the transmitting side of the frequency modulator. It is used to increase the gain of the higher frequency component as the input signal frequency increased, the impendence of the collector voltage increase. If the signal frequency is lesser then the impendence decrease which increase the collector current and hence decrease the voltage.DE-EMPHASISThe circuit is placed at the

receiving side. It acts as allow pass filter. The boosting gain for higher frequency signal in the

transmitting side is done by the pre-emphasis circuit is filtered to the same value by the low pass filter. The cut off frequency is given by the formulafc = 1/(2p RC) (4-1)Where R = 2 p fc L

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CIRCUIT DIAGRAM

PRE-EMPHASIS

DE-EMPHASIS

MODEL GRAPH

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Pre-Emphasis & De-Emphasis Model Graph

DESIGN FORMULA

fc = (assume:R = 10 KΩ, C = 0.01μf)

R = 2 pfcL; L=

TEST PROCEDURE1. The circuit connection are made as shown in the circuit diagram for the pre-emphasis and de-emphasis circuits2. A power supply of 10V is given to the circuit3. For a constant value of input voltage the values of the frequency is varied and the output is noted on the CRO4. A graph is plotted between gain and frequency5. The cut frequencies are practical values of the values of cut off frequency are found, compared and verified.

TABULATION

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RESULTSThe characteristics of pre-emphasis and de-emphasis circuits were studied and a graph wasdrawn between gain (in db) and frequency.

8.LINE CODING

OBJECTIVETo code and Decode the given data using Line coding & Decoding trainer kit.

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HARDWARELine coding & Decoding Kit, CRO, Patch chords.

THEORYLine coding is one of the method of Digital to Digital Conversion. It performs coding & Decoding which uses the combinational circuits.The sent data needs to be somehow coded into an electromagnetic signal to be sent over the wire, and later decoded back. There are many ways of encoding signals, with each scheme having some pros and cons.Primarily, there are three major categories of line coding: Unipolar, Polar, and Bipolar.UNIPOLARThe most primitive encoding technique is Unipolar. The signal is basically this: high voltage on a ‘1’ bit, and low (zero) voltage on a ‘0’ bit. There is no synchronization information, and the signal has a DC component.POLARThere are three categories of Polar line coding: NRZ, RZ, and Biphase.NRZNRZ is Nonreturn to Zero. This basically means that after each bit is transmitted, the signal doesn’t return to zero voltage. There are two major categories of NRZ, the NRZ-L, and NRZ-I. The NRZ-L is similar to Unipolar, in that the voltage directly depends on the bit it represents. A positive voltage generally represents a ‘1’, and a negative voltage represents a ‘0’ (or vice versa). Unlike the unipolar scheme, NRZ-L alleviates the problem of the DC component. The NRZ-I does a voltage transition (positive to negative, or negative to positive) on a ‘1’ bit, and no change on a ‘0’ bit. It is the change in the voltage that matters, not the actual voltage itself. NRZ-I is better than NRZ-L because the destination can use the voltage change to synchronize its clock with the sender—assuming messages don’t have long sequences of ‘0’ bits (which don’t have a transition). RZ A pretty simple scheme. Positive voltage indicates a ‘1’, negative voltage indicates a ‘0’. The voltage goes down to zero in the middle of every tick.BIPHASEThere are two primary Biphase coding schemes: Manchester (Ethernet LANs), and Differential Manchester (Token Ring LANs).Manchester, like RZ has a transition in the middle of a bit interval. There is a transition for every bit. A low to high transition indicates a ‘1’ bit, and a high to low transition indicates a ‘0’ bit. Differential Manchester is somewhat similar to NRZ-I. In the beginning of a bit interval, there is a voltage change on a ‘0’ bit, and no voltage switch on a ‘1’ bit. There is always a voltage change in the middle of a bit interval.BIPOLARBipolar scheme is similar to RZ (also has 3 voltage levels). It uses zero voltage to represent a ‘0’ bit, and a ‘1’ bit is represented by either a positive or negative voltage (alternating).

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PROCEDURE1. Switch ON the Line Coding & Decoding Trainer Kit.2. Give an input to Unipolar, Polar, Bipolar & Manchester Respectively.3. Get the Output for each NRZ & RZ.4. Give the coding input to the Decoded circuit & get the corresponding Decoded output.5. Tabulate and plot the values.

TABULATION

RESULTThus the given data was coded & Decoded by using Line coding & decoding Process.

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9. SAMPLING & TIME DIVISION MULTIPLEXING

(a)SAMPLINGOBJECTIVE To perform Sampling and reconstruction for the given Baseband Signal.

HARDWARE REQUIRED

Sampling trainer kit, CRO, patch chords, probes.

THEORY

SAMPLING THEOREM Sampling theorem states that a band limited signal having no frequency components

above fm hertz can be determined uniquely by values sampled at uniform intervals of Ts≤1/2fm

BLOCK DIAGRAM

SAMPLING

message signal sampling o/p

carrier signal

RECONSTRUCTION

i/p signal LPF amplifier demodulated o/p

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sampler

MODEL GRAPH

Message signal

Pulse signal

sampled and hold o/p

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PROCEDURE

1. The connection is made as per the block diagram.2. Switch on the trainer kit.3. The modulating signal is given as a input to sampler4. The high frequency carrier signal is also applied to the sampler5. The modulated signal is obtained as an output from the sampler.6. The readings are noted and the values are tabulated.

TABULATION

RESULTThus the given Message Signal was Sampled and the corresponding graph was plotted.

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(b) TIME DIVISION MULTIPLEXING

OBJECTIVE To perform Time division multiplexing and de-multiplexing using PAM signals.

HARDWARE REQUIREDTDM Trainer Kit, CRO ,Patch Chords, Probes.

THEORYAn important feature of pulse-amplitude modulation is a conservation of time. That is, 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 the other independent message signals on a time-shared basis. By so doing, we obtain a time-division multiplex system (TDM), which enables the joint utilization of a common channel by a plurality of independent message signals without mutual interference.Each input message signal is first restricted in bandwidth by a low-pass pre-alias filter to remove the frequencies that are nonessential to an adequate signal representation. The pre-alias filter outputs are then applied to a commutator, which is usually, implemented using electronic switching circuitry. The function of the commutator is two-fold: (1) to take a narrow sample of each of the N input messages at a rate fs that is slightly higher than 2W, where W is the cutoff frequency of the pre-alias filter, and (2) to sequentially interleave these N samples inside a sampling interval Ts 1/fs. Indeed, this latter function is the essence of the time-division multiplexing operation. Following the commutation process, the multiplexed signal is applied to a pulse-amplitude modulator, the purpose of which is to transform the multiplexed signal into a form suitable for transmission over the communication channel.At the receiving end of the system, the received signal is applied to a pulse- amplitude demodulator, which performs the reverse operation of the pulse amplitude modulator. The short pulses produced at the pulse demodulator output are distributed to the appropriate low-pass reconstruction filters by means of a de-commutator, which operates in synchronism with the commutator in the transmitter. . This synchronization is essential for satisfactory operation of the TDM system, and provisions have to be made for it.

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BLOCK DIAGRAM

Transmitted end Receiving end

CH1

CH2

CH3

CIRCUIT DIAGRAM

DESIGN PROCEDURE

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Transmission

medium

RECONSTRUCTION

GIVEN fm = 300Hz

fm = 1/2πRC

let C = 4700pF then R = 112kΩ

PROCEDURE

1. Take the signals from the function generator and give it to the channels (CH0 ... CH3) present in the transmitter using patch chords. Note down the amplitude and time period of each signal.2. Measure the amplitude and time period at the transmitter output point.3. Using a patch chord, connect transmitter output to receiver input.4. For synchronization purpose, connect the transmitter clock and receiver clock and also transmitter CH0 and receiver CH0.5. See the output before the filter and after the filter for all the channels connected.

MODEL GRAPH

TRANSMITTER SECTION

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RECEIVER SECTION

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TABULATION

RESULTTime division multiplexing and de-multiplexing using PAM signals were performed and

respective waveforms were plotted.

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10.FREQUENCY DIVISION MULTIPLEXING

OBJECTIVETo perform the frequency division multiplexing for the two given input signals.

APPARATUS REQUIREDResistors,capacitors,IC741,FG,CRO,bread board and connecting wires

THEORYAn important signal processing us multiplexing whereby a number of independent signals can be contained into a composite signal suitable for transmission over a common channel.In this method of multiplexing each message of maximum frequency function is translated to different frequency spectrum by the use of the carrier.These messages are combined in the adder circuit.At the receiving end a broad band receiver receives this signal and passes it onto base band receiver which receives signals corresponding to the respective baseband frequency.

CIRCUIT DIAGRAM

PROCEDURE1. The circuit connections are made as per the circuit diagram2. A power supply of 15 V is given to the circuit.3. Two input signals of different frequencies are given to the circuit.4. Now note down the amplitude and time period of the input signals.5. The fdm o/p is observed from the pin no. 6.6. Now note down the amplitude and time period for the fdm o/p.7. Plot the graph.

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MODEL GRAPH

TABULATION

RESULTTime division multiplexing and de-multiplexing using PAM signals were performed and

respective waveforms were plotted.

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11.MATLAB PROGRAM FOR DIGITAL COMMUNICATION

OBJECTIVE

To write a MATLAB program for generating waveforms of digital communication techniques such as ASK,PSK and FSK APPARATUS REQUIRED

PC with MATLAB software

PROCEDURE

1. Open the MATLAB software2. Select the assembly file in file menu3. Type the program4. Save the program as assembly5. Goto debug and run the program6. Give the required input and view the corresponding output7. Stop the process

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PROGRAM

clc;clear all;close all;t=0:0.000001.01;disp(‘digital message signal’);vm=input(‘amplitude:’);fm=input(‘frequency’);wm=2*pi*fm;disp(carrier signal’);vm=input(‘amplitude:’);fm=input(‘frequency’);wm=2*pi*fc;vm=vm*(square(wm*t));subplot(5,1,1);plot(t,vm);title(‘digital message signal’);xlabel(‘time’);ylabel(‘amplitude’);vc=vc*sin(wc*t));subplot(5,1,2);plot(t,vc);title(‘carrier signal’);xlabel(‘time’);ylabel(‘amplitude’);q=vm.*vc+vc;subplot(5,1,3);plot(t,q);title(‘ask signal’);xlabel(‘time’);ylabel(‘amplitude’);r=vm.*vc;subplot(5,1,4);plot(t,r);

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title(‘psk signal’);xlabel(‘time’);ylabel(‘amplitude’);x=sin(2*pi*(fc+1500*vm).*t);subplot (5,1,5);plot(t,x);title(‘fsk signal’);xlabel(‘time’);ylabel(‘amplitude’);

MODEL GRAPH

RESULTThus the MATLAB program for digital modulation techniques is written and the

output is hence verified.

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12.MATLAB PROGRAM FOR ERROR CONTROL CODING

OBECTIVE

To write a MATLAB program for error control coding techniques (HUFFMAN CODING). APPARATUS REQUIRED

PC with MATLAB software

PROCEDURE

1. Open the MATLAB software2. Select the assembly file in file menu3. Type the program4. Save the program as assembly5. Goto debug and run the program6. Give the required input and view the corresponding output7. Stop the process

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PROGRAM

HUFFMAN CODING (SOURCE CODING TECHNIQUE)

clc;

clear all;

close all;

s=[0.25 0.25 0.3 0.1 0.05 0.05];

e=dsort(s);

for i=1:6

for j=1:6

c1(i,j)=0;

d(i,j)=0;

end;

end;

for i=1:6

for j=1:6

if j= =1

c1(:,j)=e;

end;

end;

end;

k=6;

for i=2:6;

for j=2:6;

if(k>1)

e(k-1)=e(k-1)+e(k);

e(k)=0;

e=dsort(e);

c1(:,j)=e;

k=k-1;

end;

end;

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x=1;

y=5;

while x<=6&&y>=1

if c1(x,y)~=0

d(x,y)=0;

d(x+1,y)=1;

x=x+1;

y=y-1;

end;

end;

p=0;

q=1;

p1=num2str(p);

p2=strcat(p1,p1);

q1=num2str(q);

pq=strcat(p1,q1);

qp=strcat(q1,p1);

qqp=strcat(q1,q1,p1);

qqqp=strcat(q1,q1,q1,p1);

qqqq=strcat(q1,q1,q1,q1);

disp(sprintf(`code(0.3)=%s’,p2));

disp(sprintf(`code(0.25)=%s’,pq));

disp(sprintf(`code(0.25)=%s’,qp));

disp(sprintf(`code(0.1)=%s’,qqp));

disp(sprintf(`code(0.05)=%s’,qqqp));

disp(sprintf(`code(0.05)=%s’,qqqq));

length=length(p2)*0.3+length(pq)*0.25+length(qP)*0.25+length(qqp)*0.1+length(qqqp)*0.005+length(qqqq)*0.05;

entropy=-(0.3*(log(0.3)?log(2))+2*(0.25*(log(0.25)?log(2)))+0.1*(log(0.1)?log(2))+2*(0.05*(log(0.05)?log(2))));

efficiency+[entropy/length];

redundancy=[1-efficiency];

disp(sprint(`\nlength:%d’,length));

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disp(sprint(`\nentropy:%d’,entropy));

disp(sprint(`\nefficiency:%d’,efficiency));

disp(sprint(`\nredundancy:%d’,redundancy));

end

OUTPUT:

code(0.3)=00

code(0.25)=01

code(0.25)=10

code(0.1)=110

code(0.05)=1110

code(0.05)=1111

length:2.300000e+000

entropy:2.285475e+000

efficiency:9.936849e-001

redundancy:6.315088e-003

RESULTThus the MATLAB program for error control coding (HUFFMAN CODING) is

written and the output is hence verified.

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Cs Lab Manual

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