Einstein EC57-Communication Systems Lab

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EINSTEINCOLLEGE OF ENGINEERINGSir.C.V.Raman Nagar, Tirunelveli-12

Department of Electronics and Communication Engineering

Subject Code: EC57Communication Systems Lab

Name Reg No Branch Year & Semester

: : : : Einstein College of Engineering Page 1 of 86

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INDEX

EX.NO.

DATE

NAME OF THE EXPERIMENTS

PAGE NO.

MARKS REMARKS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Amplitude modulation and Demodulation Frequency modulation and Demodulation Sampling techniques Pulse Modulation-PAM Pulse Modulation-PWM Pulse Code Modulation Time Division Multiplexing Line Coding Techniques Amplitude Shift Keying Phase Shift Keying Frequency Shift Keying Quadrature Phase Shift Keying Delta Modulation Differential PCM Phase Locked Loop Pre-Emphasis/ De-Emphasis Error Control coding using MATLAB Characteristics of AM Receiver-Study

Einstein College of Engineering Page 2 of 86

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Experiment No : 1 AMPLITUDE MODULATION & DEMODULATION AIM:

Date :

To construct a Amplitude modulator circuit & demodulate the Amplitude modulated wave.

COMPONENTS REQUIRED: S.NO 1) 2) 3) 4) 5) 6) COMPONENTS Transistor Diode Capacitors Resistors CRO Bread Board,power supply 7) THEORY : The modulation is simply a method of combining two different signals and is used in the transmitter section of a communication system. The two signals that are used are the information signal and the carrier signal. Amplitude Modulation is the simplest form of signal processing in which the carrier amplitude is simply changed according to the amplitude of the information signal hence the name Amplitude modulation. When the information signals amplitude is increased the carrier signals amplitude is increased and when the information signals amplitude is decreased the carrier signals amplitude is Connecting Wires RANGE BC 107 IN4001 0.01F, 0.1F,10F 22K, 10K,1.2K,1.1K


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AMPLITUDE MODULATION CIRCUIT DIAGRAM:

DEMODULATION CIRCUIT DIAGRAM:


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Decreased. The purpose of any detector or demodulator is to recover the original modulating signal with the minimum of distortion and interference. The simplest way of dealing with an AM signal is to use a simple half- wave rectifier circuit. If the signal were simply passed through a diode to a resistive load, the output would be a series of half-cycle pulses at carrier frequency. So the diode is followed by a filter, typically a capacitor and resistor in parallel. The capacitor is charged by the diode almost to the peak value of the carrier cycles and the output therefore follows the envelope of the amplitude modulation. PROCEDURE: 1. 2. 3. 4. 5. 6. 7. 8. Circuit connections are given as shown in the circuit diagram. The power supply is connected to the collector of the transistor. Using AFO the carrier signal is given to the base of the transistor. The modulating (message or base band) signal is given to the emitter of the transistor. From the collector of the transistor, the modulated wave is noted down using CRO. By varying the amplitude of the modulating signal the values of Emax and Emin are noted down to find the modulation index. The amplitude modulated wave is now given as the input to the detector circuit. The demodulated (message) wave amplitude and frequency is noted down from the CRO.


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MODEL GRAPH:

OBSERVATION:

Amplitude

Time

Frequency

m

Message Signal

Carrier signal

AM signal

Demodulated Signal


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VIVA QUESTIONS: 1.What is meant by Modulation? 2.Define Modulation index(m). 3.Applications of AM 4.Types of Demodulation of AM. 5.What is the band width for AM?

RESULT: Amplitude Modulator and Demodulators are constructed and its waveforms are analyzed by using the above circuits.


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FREQUENCY MODULATION CIRCUIT DIAGRAM:

FM DEMODULATOR:


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Experiment No : 2 FREQUENCY MODULATION & DEMODULATION

Date :

AIM: To construct & Design Frequency modulator using IC XR2206 & demodulate the Frequency modulated wave by using IC565. COMPONENTS REQUIRED: S.NO 8) COMPONENTS Integrated Circuits RANGE IC X R2206, IC NE565 9) 10) 11) 12) 13) 14) Resistors Capacitors Function Generator DSO Bread Board Connecting Wires 0 1 Mhz

THEORY : Frequency modulation is also called as angle modulation. Frequency modulation is defined as changing the frequency of the carrier with respect to the message signal amplitude. Here the amplitude of the carrier remains fixed & timing parameter frequency is varied. When the modulating signal has zero amplitude, then the carrier has frequency of Fc as amplitude of the modulating signal increases. The frequency of the carrier increases, similarly, as the amplitude of the modulating signal decreases, the frequency of the carrier decreases.


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PIN DIAGRAM (XR-2206):

MODEL GRAPH


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The modulation index is defined as the ratio of the maximum frequency deviation to the modulating frequency. The maximum frequency deviation is the shift from center frequency Fc when the amplitude of the modulating signal is maximum.

By Carlsons rule BW = 2 (F+ Fm(max)) Where F Fm(Max) = Maximum frequency deviation = Maximum modulating frequency

MODULATION PROCEDURE:

Connections are given as per the circuit diagram. Measure the carrier signal frequency at the pin2 of IC XR2206. Apply modulating AF signal at pin7 of IC XR2206. Observe the frequency-modulated signal on DSO. Calculate the modulation index. Calculate the BW.

DEMODULATION PROCEDURE: Connections are made as per the circuit diagram. Modulated signal is given as the input to 565. In demodulated output the original message signal is recovered.


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OBSERVATION:

Amplitude Message Signal

Time

Frequency

Carrier signal

FM signal

Demodulated Signal

VIVA QUESTIONS: 1.What is meant by FM? 2.Define Frequency Deviation. 3.Applications of FM 4.Types of Angle Modulation. 5.What is the band width for FM?

RESULT: Frequency Modulator and Demodulators are constructed and its waveforms are analyzed by using CRO.


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SAMPLING CIRCUIT DIAGRAM

PIN DIAGRAM:


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Experiment No : 3 SAMPLING TECHNIQUES

Date :

AIM: To obtain the sampled version of given analog signal using operational amplifier and draw the spectrum. APPARATUS REQUIRED: Apparatus IC741 FET Capacitor RPS CRO FG Bread board THEORY: The Sample and Hold circuit uses two buffers to keep a voltage level stored in a capacitor. Ssample will charge the capacitor to the present signal level, while the input buffer ensures the signal won't be changed by the charging process. From there, the output buffer will make sure that the voltage level across the storage cap won't decrease over time. Sclear will short out the storage cap, discharging it and setting the output to 0V.In actual practice, the switches used are various forms of transistor switch, which provides cleaner switching and also allows another circuit to control the sample and clearing operations. Excellent Sample and Hold circuits like the LF398 are available on a single chip for cheap and easy use. Sample and Hold circuits are used internally in Analog to Digital conversion. We might also use them to hold a given signal value from any particular sensor on a robot, for analysis and later use. BFW10 0.01F Range Quantity 2 2 1 1 1 1 1


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PROCEDURE: The sample and hold circuit is assembled with the desired components. The input signal is given to the circuit from the function generator. The amplitude of the input signal should not exceed 10 volts. The frequency of the input signal is set to 600 Hz. The frequency of the sample signal is set to 5600 Hz. The next sample available is zero order holding device, integrate the signal between consequence sampling inputs.

VIVA QUESTIONS: 1.What is the need for sampling? 2.Define sampling. 3.Define Nyquist rate. 4.What is the usage of capacitor in the circuit diagram? 5.What is zero order hold?

RESULT: Thus the sample and hold circuit output is obtained using OP- amp.


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PAM CIRCUIT DIAGRAM: MODULATION CIRCUIT:

DEMODULATION CIRCUIT:


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Experiment No: 4 PULSE MODULATION PAM AIM:

Date :

To generate pulse amplitude modulated signals and demodulates it to get the original signal. APPARATUS REQUIRED: Apparatus Transistor Resistor Range 2N2222 10Kohm 22Kohm Capacitor CRO FG Bread board THEORY: In pulse amplitude modulation, the amplitudes of regularly spaced rectangular pulses vary with the instantaneous sample values of a continuous message signal in a one to one fashion. The pulse in PAM can be of rectangular or the type that we have arrival in natural sampling. The carrier under goes amplitude modulation in PAM. The width of the pulse remains fixed. Natural sample method is used here to generate the PAM signal. The diodes are used as a switching element. If the closing time t of the diode approaches zero, the output gives only the instantaneous value. Since the width of the pulse approaches zero. The instantaneous sampling gives train of impulses. The area of each sampled section is equal to the instantaneous value of the signal input. This signal is modulated with the message signal. Thus we get the PAM output. 0.1F Quantity 1 2 3 3 1 2 1


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MODEL GRAPH:


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PROCEDURE: 1. 2. 3. 4. 5. Make connections as shown in the diagram. Set the input signal and carrier signal. Obtain PAM signal Measure the amplitude and frequency Demodulate the PAM signal.

TABULATION:


Time

Frequency

Carrier signal

PAM signal

Demodulated Signal

VIVA QUESTIONS: 1.Define PAM. 2.What is frame in PAM? 3.What is aperture effect? 4. What is the need for speech coding at low bit rates? 5. What do you mean by companding? Define compander.

RESULT: Thus the PAM signal is obtained and the original signal is demodulated from PAM signal.


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PWM CIRCUIT DIAGRAM: MODULATION CIRCUIT:



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Experiment No : 5 PULSE MODULATION PWM

Date :

AIM: To generate pulse width modulated signals and demodulates it to get the original signal. APPARATUS REQUIRED:

Apparatus IC Resistor

Range 555 47Kohm 10Kohm

Quantity 1 1 1 1 1 1 1 1

Capacitor RPS CRO FG Bread board

0.01F 0-30v

THEORY: The PWM is also known as pulse duration modulation. It modulates the time parameter of the pulses. The width of PWM pulses varies. The amplitude is constant; width of the pulse is proportional to the amplitude of the modulating signal. Bandwidth on transmission channel depends on rise time of the pulse. The demodulation circuit used is a simple filter circuit that demodulator the PWM signal and gives the original message input.


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MODEL GRAPH:


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PROCEDURE: 1. 2. 3. 4. 5. Make connections as shown in the diagram. Set the input signal and carrier signal. Obtain PWM signal Measure the amplitude and frequency Obtain the demodulated output.

TABULATION:


Time

Frequency

Carrier signal

PWM signal

Demodulated Signal

VIVA QUESTIONS: 1.Define PWM. 2. What is the disadvantage of uniform quantization over the non-uniform Quantization? 3.Define deviation ratio 4.What is carrier recovery? 5.Define bandwidth efficiency. RESULT: Thus the PWM signal is obtained and the original signal is demodulated from PWM signal. Einstein College of Engineering Page 23 of 86

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CIRCUIT DIAGRAM: MODULATION CIRCUIT:



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Experiment No : 6 PULSE CODE MODULATION AIM:

Date :

To generate pulse code modulated signals and demodulates it to get the original signal. APPARATUS REQUIRED:

Apparatus PCM kit CRO Patch card THEORY:

Range VCT07

Quantity 1 1

Pulse Code modulation come under digital communication technique. In PCM the message signal is represented by a sequence of coded pulse which accomplished by representing the signal in discrete form in both time and amplitude. PCM consist of a receiver and transmitter part. Transmitter section consists of sampler, quantizer, encoder and parallel to serial converter. Receiver part consists of serial to parallel set converter. Digital to analog converter and LPF are constituted as receiver part. Sampling, Quantizing and Encoding operations are performed in the same circuit which is called as analog to digital converter.

PROCEDURE: 1. 2. 3. 4. 5. Make connections as shown in the diagram. Set the start of conversion switch from low to high and high to low. Set the input signal and obtain the PCM signal. Obtain the demodulated output. Measure the data and plot the graph.


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TABULATION: Message Signal: Amplitude in Time in Frequency in

PCM Signal: Amplitude in ON Time in OFF Time in Frequency in

Demodulated Signal: Amplitude in Time in Frequency in


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VIVA QUESTION: 1.Write the equation for probability of error 2.Define quadbit 3.Explain M-ary 4.State the concept of PCM 5.PCM is analog or digital modulation ,Explain.

RESULT: Thus the PCM signal is obtained and the original signal is demodulated from PCM signal.


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BLOCK DIAGRAM:


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Experiment No :7 TIME DIVISION MULTIPLEXING

Date :

AIM: To obtain time division multiplexed signal from different channel and make it to transmit in a single channel.

APPARATUS REQUIRED:

Apparatus

Range

Quantity

TDM kit CRO Patch card

VCT02

1 1

THEORY: Time Division multiplexing is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices. In such a case, multiple transmission can occupy a single link by subdividing them and interleaving the portions. TDM can be implemented in two ways. Synchronous TDM and Asynchronous TDM. In synchronous, the multiplexer allocates exactly the same time slot to each device at all times whether or not a device has anything to transmit. PROCEDURE: 1. 2. 3. 4. 5. Make connections as shown in the diagram. Adjust the potentiometer to set the input signal. View the modulated output. Obtain the demodulated output. Measure the data and plot the graph.


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TABULATION: Message Signal: Amplitude in Time in Frequency in

Carrier Signal: Amplitude in Time in Frequency in

Modulated Signal: Amplitude in Time in Frequency in

Demodulated Signal: Amplitude in Time in Frequency in


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VIVA QUESTIONS:

1.What are the 4 primary causes for ISI? 2.What is Multiplexing? 3.State the concept for TDM. 4.Explain the ideal channel noise. 5.What is coding efficiency.

RESULT:

Thus the TDM signal is obtained and the original signal is demodulated from TDM signal.


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BLOCK DIAGRAM


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Experiment No :8 LINE CODING TECHNIQUES

Date :

AIM: To obtain the standard digital codes from the source coded signals using various techniques.

APPARATUS REQUIRED: Apparatus Range Quantity 1 1

Trainer kit VCT37 CRO Patch card

THEORY: In digital systems, the electrical waveforms are coded representations of the original information. If the original information is an analog signal, this must be converted to a series of discrete values that can be transmitted digitally. The process of converting the original information into a data sequence is referred to as source coding. The line coding is the process of converting source coded signals into standard digital codes for the purpose of transmission over the channel. There are many possible ways of assigning the waveforms into the digital data. Simplest form of coding is ONOFF, where a 1 is transmitted by a pulse and a 0 is transmitted by no pulse. Generally the line coding is used in transmitter section while decoding in receiver section. The line decoding is the process of converting standard digital codes into source coded waveforms.


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Various line coding formats are 1. 2. 3. 4. 5. 6. Unipolar RZ Polar RZ Polar NRZ Bipolar NRZ Bipolar RZ Manchester coding

PROCEDURE: 1. Connect the PRBS (test point P5) to various line coding formats. Obtain the coded output as per the requirement. 2. Connect coded signal test point to corresponding decoding test point as inputs. 3. Set the SW1 as per the requirement. 4. Set the potentiometer P1 in minimum position. 5. Switch ON the power supply. Press the switch SW2 once. 6. Display the encoded signal on one channel of CRO and decoded signal on second channel of CRO.


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MODEL GRAPH:


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TABULATION:

No Coding techniques 1 2 3 4 5 6 Unipolar RZ Polar RZ Polar NRZ Bipolar NRZ Bipolar RZ Manchester coding

ON time

OFF time

VIVA QUESTIONS: 1.What are the different types of coding techniques for digital data? 2.State the concept of Manchester coding. 3.Differentiate polar and bipolar. 4.What is codec? 5.Explain Line coding.

RESULT:

Thus the various line encoding and decoding techniques were studied and the corresponding waveforms were drawn by using VCT-37 trainer kit.


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CIRCUIT DIAGRAM:

MODULATION CIRCUIT:


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Experiment No :9 AMPLITUDE SHIFT KEYING

Date :

AIM: To generate ASK modulated and demodulated signal.

APPARATUS REQUIRED:

Apparatus

Range

Quantity 1 1

Trainer kit VCT17 CRO Patch card THEORY:

ASK or ON-OFF key is the simplest digital modulation technique. In this method there is only one unit energy carrier it is switched ON/OFF depending upon the input binary sequence to transmit symbol 0 & 1. No pulse is transmitted output contains some complete no of cycle of carrier frequency. The disadvantage of ASK is the modulated carrier signal is not continuously transmitted. The peak power requirement is also high. The bit error probability rate is also not required in this technique. PROCEDURE: 1. 2. 3. 4. 5. Make connections as shown in the diagram. Set the input signal and carrier signal. Obtain ASK signal Measure the amplitude and frequency Obtain the demodulated output.


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MODEL GRAPH:

.


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TABULATION: INPUT DATA: Amplitude in ON Time in OFF Time in

CARRIER SIGNAL: Amplitude in Time in Frequency in

MODULATED SIGNAL: Amplitude in Time in Frequency in

DEMODULATED SIGNAL: Amplitude in ON Time in OFF Time in


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PROGRAM FOR ASK:


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VIVA QUESTIONS: 1.Define OOK. 2.Define information capacity 3.What is the Baud rate for ASK? 4.What is Digital Transmission? 5. Why do we go for Gram-Schmidt Orthogonalization procedure?

RESULT:

Thus the modulated and demodulated signal was obtained for amplitude shift keying techniques


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BLOCK DIAGRAM


Communication Systems Lab Experiment No : 10 PHASE SHIFT KEYING Date :

AIM: To obtain the modulated and demodulated output waveform by using Phase Shift Keying technique. APPARATUS REQUIRED: Apparatus PSK Kit CRO Patch cards THEORY: PSK is a digital modulation scheme which is analogues to phase modulation. In binary phase shift keying two output phases are possible for a single carrier frequency one out of phase represent logic 1 and logic 0. As the input digital binary signal change state the phase of output carrier shift two angles that are 180o out of phase. In a PSK modulator the carrier input signal is multiplied by the digital data. The input carrier is multiplied by either a positives or negatives consequently the output signal is either +1sinwct or 1sinwct. The first represent a signal that is phase with the reference oscillator the latter a signal that is 180o out of phase with the reference oscillator. Each time a change in input logic condition will change the output phase consequently for PSK the output rate of change equal to the input rate range and widest output bandwidth occurs when the input binary data are alternating 1/0 sequence. The fundamental frequency of an alternate 1/0 bit sequence is equal to one half of the bit rate. PROCEDURE: 1. 2. 3. 4. 5. Make connections as shown in the diagram. Set the input signal and carrier signal. Obtain PSK signal Measure the output data and draw the graph. Obtain the demodulated output. Page 44 of 86 Einstein College of Engineering Range VCT21 Quantity 1 1

Communication Systems Lab MODEL GRAPH:

.

:

Page 45 of 86 Einstein College of Engineering

Communication Systems Lab TABULATION: INPUT DATA: Amplitude in ON Time in OFF Time in



DEMODULATED SIGNAL: Amplitude in ON Time in OFF Time in


Communication Systems Lab PROGRAM FOR PSK:


Communication Systems Lab

VIVA QUESTIONS: 1.Explain Coherent detection 2.Difference between PSK and FSK 3.Advantages of PSK 4. What is maximum likelihood detector? 5.What is correlator?

RESULT: Thus the modulated and demodulated signal was obtained for phase shift keying techniques.


Communication Systems Lab FSK CIRCUIT DIAGRAM:


Communication Systems Lab Experiment No :11 FREQUENCY SHIFT KEYING Date :

AIM: To obtain the modulated and demodulated output waveforms by using hardware kit and in Matlab program for Frequency Shift Keying technique. APPARATUS REQUIRED:

Apparatus IC Transistor Resistor

Range 555 BC547 47Kohm 10Kohm

Quantity 1 1 1 1 2 2 1 1 1

Potentiometer 50Kohm Capacitor FG RPS CRO 0.01F

THEORY: In digital data communication, binary code is transmitted by shifting a carrier frequency between two preset frequencies. This type of transmission is called frequency shift keying technique. A 555 timer in astable mode can be used to generate FSK signal. The standard digital data input frequency is 150Hz. When input is HIGH, transistor Q is off and 555 timer works in the normal astable mode of operation. fo=1.45/(Ra+2Rb)c



THEORETICAL CALCULATION:


Communication Systems Lab PROGRAM:




MODULATED SIGNAL: Symbol Amplitude Time period No.of cycle Frequency

Symbol 1

Symbol 0


Communication Systems Lab PROCEDURE:

1. 2. 3. 4. 5.

Make connections as shown in the circuit diagram. Set the input signal and carrier signal. Obtain FSK signal Tabulate the output data and draw the graph. Justify the obtained output with theoretical calculation.

VIVA QUESTIONS: 1.What are the Different types of Digital modulation? 2.Define PSK,QPSK. 3.Advantage of PSK over ASK&FSK? 4.What is base band signal receiver? 5.Define h-factor in FSK

RESULT:

Thus the Frequency Shift Keying modulated output waveform is obtained and it is justified with theoretical calculation.


Communication Systems Lab BLOCK DIAGRAM: QPSK MODULATOR:

QPSK DEMODULATOR


Communication Systems Lab Experiment No :12 QUADRATURE PHASE SHIFT KEYING Date :

AIM: To obtain the modulated and demodulated output waveforms by using hardware kit and by Matlab program for Quadrature phase Shift Keying technique. APPARATUS REQUIRED:

Apparatus QPSK Kit CRO Patch cards

Range VCT29

Quantity 1 1

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 (a dibit) 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.




Communication Systems Lab PROGRAM:


Communication Systems Lab TABULATION:

INPUT DATA: Amplitude in ON Time in OFF Time in


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 carroer 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. RESULT: Thus the Quadurate Phase shift Keying modulated and demodulated output waveform is obtained.


Communication Systems Lab BLOCK DIAGRAM: DM MODULATOR:

DM DEMODULATOR:


Communication Systems Lab Experiment No :13 DELTA MODULATION AIM: The objective of this equipment is to examine and study the technique of delta modulation and demodulation. APPARATUS REQUIRED: Date :

Apparatus QPSK Kit CRO Patch cards THEORY:

Range VCT32

Quantity 1 1

Delta modulation transmits only 1 bit per sample. The modulator comprises of comparator, quantizer and integrator. With conventional PCM, each code is a binary representation of both the sign and magnitude of a particular sample, therefore multiple-bit code is required to represent a one sample. With DM, rather than transmit a coded representation of the sample, only a single bit is transmitted, which simply indicates whether that the sample is larger or smaller than the previous sample. If the current sample is smaller than previous sample, a logic level 0 is transmitted. If the current sample is larger than the previous sample, a logic 1 is transmitted. PROCEDURE: 1. Switch on the power supply. Ensure that the following initial condition exits on VCT-32 a. Keep the signal ON/OFF switch in OFF position. b. Keep all potentiometer controls in min. 2. Set the sine wave by adjusting OFFSET and AMP 3. Vary the sine wave from 150Hz. Note that the amplitude of sine wave decreases at 2KHz of frequency 4. Set clock frequency as 8KHz. Turn ON the left side ON/OFF switch and right side ON/OFF, now adjust the offset control signal. Note down the quantizer output, integrated output and biphase NRZ encoder. 5. Obtain the modulated output. Connect modulator output to demodulator input. 6. Obtain the demodulated output. Page 61 of 86 Einstein College of Engineering




INTEGRATOR SIGNAL: Amplitude in Time in Frequency in


DEMODULATED SIGNAL: Amplitude in Time in Frequency in



VIVA QUESTIONS: 1.Define delta modulation. 2.What is slope over load? 3.Define Granular noise. 4.Define Adaptive DM. 5.How the noises are reduced in DM?

RESULT: Thus the delta modulated and demodulated waveforms were obtained.



BLOCK DIAGRAM: DPCM MODULATOR:

DPCM DEMODULATOR:


Communication Systems Lab Experiment No : 14 Date : DIFFERENTIAL PULSE CODE MODULATION

AIM: The objective of this equipment is to examine and study the technique of differential PCM and demodulation.

APPARATUS REQUIRED: Apparatus DM Kit CRO Patch cards Range VCT34 Quantity 1 1

THEORY: In a PCM Encoded waveform, there are often successive samples taken in which there is little difference between the amplitudes of the two samples. This necessitates transmitting several identical PCM codes, which is redundant. DPCM is designed specifically to take advantage of the sample to samples redundancies in such waveforms. With DPCM, the difference in the amplitude of two successive samples s transmitted rather than the actual sample. Because the range of sample differences is typically less than the range of individual samples. Fewer bits are required for DPCM than conventional PCM. PROCEDURE: 1. Switch on the power supply. Keep DC voltage in minimum position 2. Connect DC voltage and vary to 1.5v. Now display the output of zeros and ones in the CRO. 3. Obtain the modulated output. Now connect modulated output to demodulator input 4. Now vary the DC control POT, the ADC coded data ranges which also reflects at the output of the LATCH.



TRAINER KIT DIAGRAM:






DEMODULATED SIGNAL: Amplitude in Time in Frequency in


Communication Systems Lab VIVA QUESTIONS: 1.Say the difference between PCM and DPCM. 2.Define Vocoder. 3.Bit rate of DPCM. 4.Define baseband transmission 5. Define Dibit.

RESULT: Thus the differential PCM modulated and demodulated waveforms were obtained.


Communication Systems Lab CIRCUIT DIAGRAM:

+6V R T =6.8 K C=0.001f

C=1f

10 2Vin Input

8 7

Demodulated output Reference Output

NE565 3 9 1

6 4 5

VCO output (fo)

C T =0.001f

-6V

Fig.1


Communication Systems Lab Experiment No :15 PHASE LOCKED LOOP Date :

AIM: To study the characteristics of Phase Locked Loop .

APPARATUS REQUIRED:

S.NO 1) 2) 3) 4) 5) 6)

COMPONENTS Transistor IC Capacitors Resistors CRO Bread Board,power supply

RANGE BC 107 NE565, IC7490

7)

Connecting Wires


Communication Systems Lab DESIGN:

THEORY:

If an input signal Vs of frequency fs is applied to the PLL, the phase detector compares the phase and frequency of the incoming signal to that of the output Vo of the VCO. It the two signals differ in frequency and /or phase, an error voltage Ve is generated. The phase detector is basically a multiplier and produces the sum (fs+fo) and difference (fs-fo) components at its output. The high frequency component (fs+fo) is removed by the low pass filter and the difference frequency component is amplified and then applied as control voltage Vc to VCO. The signal Vc shifts the VCO frequency in a direction to reduce the frequency difference between fs and fo. The VCO continues to change frequency till its output frequency is exactly the same as the input signal frequency. The circuit is then said to be locked.


Communication Systems Lab PIN DIAGRAM:

-Vcc Input Input VCO Output Phase Comparator VCO Input Reference Output Demodulated Output

1 2 3 4 5 6 7

14 13

NC NC NC NC +Vcc External Capacitor for VCO External Resistor for VCO

NE 565 1211 10 9 8

OBSERVATION: f1=755Hz, f2=1640Hz, f3=1250Hz, f4=360Hz


Communication Systems Lab PROCEDURE:

1. 2. 3. 4.

Make the circuit connection as shown in Fig 1. Measure the practical free running frequency of VCO for zero input. Set the input square wave of 1Vp-p at 1KHz. Increase the input frequency till PLL is locked. This frequency f1 gives the lower end of the capture range. Go on increasing the input frequency to f2 (upper end of the lock range), till PLL tracks the input signal. 5. Now gradually decrease the input frequency till f3 when the PLL is again locked. This is the upper end of the capture range. Keep on decreasing the input frequency till f4 when the loop is unlocked. This is the lower end of the lock range. 6. Compare theoretical and practical values of lock range and capture range. VIVA QUESTIONS: 1.What is VCO? 2.Define Lock range,Capture range. 3.What are the applications of PLL? 4.Define PLL. 5.What is frequency synthesizer?

RESULT:

Thus the PLL characteristics are studied Theoretical Lock range fL= Practical Lock range fL= Theoretical Capture range fC= Practical Capture range fC=


Communication Systems Lab CIRCUIT DIAGRAM: PRE-EMPHASIS:

DE-EMPHASIS:


Communication Systems Lab Experiment No :16 PRE-EMPHASIS / DE-EMPHASIS Date :

AIM: Design and conduct an experiment to test a pre-emphasis and de-emphasis circuit for 75Ps between 2.1KHz to 15KHz and record the results. APPARATUS REQUIRED: S.NO 1) 2) 3) 4) 5) COMPONENTS IC Capacitors Resistors CRO Bread Board,power supply 6) Connecting Wires RANGE IC741

PROCEDURE: 1. Connections are made as shown in the circuit diagram. 2. Apply a sine wave of 5Vpp amplitude, vary the frequency and note down the gain of the circuit. 3. Plot a graph of normalized gain Vs frequency.



DESIGN 1. Pre-emphasis circuit. Given f1 = 2.1 KHz, f2 = 15KHz. f1 = 1/2SrC, f2 = 1/2SRC Choose C = 0.1Pf then r = 820 and R = 100. Also r/R = Rf/R1, then R1 = 2.2K and Rf = 15K. 2. De-emphasis circuit. fC = 1/2SRdCd. Choose Cd = 0.1Pf and fC = f1 = 2.1KHz Then Rd = 820.

MODEL GRAPH:


Communication Systems Lab TABULATION: PRE-EMPHASIS: Vi= Frequency(Hz) VO Gain= VO/ Vi Gain in dB

DE-EMPHASIS: Vi= Frequency(Hz) VO Gain= VO/ Vi Gain in dB



VIVA QUESTIONS: 1.What is advantage of FM over Am? 2.Define Pre-emphasis and De-emphasis. 3.Define capture effect. 4.What are the types of FM? 5.Define transmission efficiency.

RESULT: Thus the Pre-Emphasis and De-Emphasis circuit was designed and analysed using IC741.


Communication Systems Lab Experiment No :17 ERROR CONTROL CODING USING MATLAB Date :

AIM: To write a program in MATLAB for error control coding techniques.

ALGORITHM: 1.Get the input binary sequcence. 2.Calculate the reundancy bits for the corrosponding code. 3.Transmit the signal that contains message bits+redundancy bits added at the end. 4.Calculate the redundancy bits once again for the received bits. 5.If the redundancy bits=0 then no error in the transmission otherwise some error in the transmission.



PROGRAM:



RESULT: Thus the error control coding techniques are executed using MATLAB programs.


Communication Systems Lab Experiment No :18 CHARACTERISTICS OF AM RECEIVER Date :

AIM: To study the characteristics of AM receiver.

APPARATUS REQUIRED: 1. VCT 06KIT. 2. CRO 3. Patch card. THEORY: Heterodyne means to mix two frequencies together in a non-linear device or to translate one frequency to another frequency using non-linear mixing. The first section is the RF section which consists of a predictor is a broad tuned BPF with an adjustable centre frequency that is tuned to the desired carrier frequency. Selectivity is a receiver parameter that is used to measure the ability of the receiver to accept a given band of frequencies and reject all others. For example, with the commercial AM broadcast band, each stations transmitter is allocated a 10KHz bandwidth. Therefore, for a receiver to select only those frequencies assigned to a single channel, the receiver must limit its bandwidth to 10KHz. If the pass band is greater than 10KHz, more than one channel may be received and demodulated simultaneously. If the pass band of a receiver is less than 10KHz, a portion of the modulating signal information for that channel is rejected or blocked from entering the demodulator and, consequently lost.

PROCEDURE: 1. Switch ON the trainer kit. 2. Initial setup is made as follows. a. Set audio oscillator frequency as 1KHz and amplitude as 1Vp-p b. Adjust the carrier frequency of AM transmitter to one position. c. Adjust the gain of the audio amplifier in some position.


Communication Systems Lab BLOCK DIAGRAM:


Communication Systems Lab TABULATION:

No 1 2

dB -3 -60

Bandwidth

1. Now tune the gang capacitance in the preselector block, such that the output is of maximum amplitude. 2. Connect CRO across test point and find out -3db bandwidth of IF amplifier. Also find out -60db bandwidth of IF amplifier 3. Calculate Shape factor for various input signal. VIVA QUESTIONS: 1.Define Selectivity. 2.What is sensitivity? 3.Define Q factor in AM receiver. 4.What are the three noises present in the AM reciver? 5.Define shape factor.

RESULT : Thus the characteristics of the AM receiver is studied.
