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DIGITAL COMMUNICATION LAB (04 1x74)

LABORATORY MANUAL

Bhagalpur College of Engineering, Bhagalpur

FACULTY NAME: ANSHU KUMARI ASSISTANT PROFESSOR Department of Electronics and Communication Engineering

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List of Experiments 1. Verification of Sampling Theorem. 2. Study of generation of Unipolar NRZ, Polar NRZ, Unipolar RZ and Polar RZ line code. 3. Study of generation and detection of Pulse Code Modulation (PCM). 4. Study of generation and detection of Delta Modulation. 5. Study of generation and detection of Amplitude Shift Keying (ASK). 6. Study of generation and detection of Phase Shift Keying (PSK). 7. Study of generation and detection of Frequency Shift Keying (FSK). 8. Analysis of the process of Time Division Multiplexing and demultiplexing.

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EXPERIMENT No.-1 TITLE: Verification of sampling theorem. AIM OF THE EXPERIMENT: 1. To obtain the sampled output for given modulating signal input. 2. Verify the sampling theorem for different modulating frequencies fs< 2fm, fs= 2fm and fs >2fm. 3. Reconstruct the original signal from the sampled signal. EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1. 2. 3. 4. 5. 6.

Name of the Equipment/ Component Sampling Theorem Trainer Kit Digital storage oscilloscope Power supply Probes Patch cord Connecting wires

Specifications/ Range 100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

THEORY: Sampling is the process of conversion of analog signal to discrete signal. Sampling Theorem shows that a continuous-time band-limited signal may be represented perfectly by its samples at uniform intervals of T seconds, if T is small enough. In other words, the continuous-time signal may be reconstructed perfectly from its samples; sampling at a high enough rate is information-lossless. Sampling theorem states that 1. The band limited signal of finite energy, which has no frequency component higher than w hertz, is completely described by specifies the value of signal at instant of time separated by 1/2w second. 2. The band limited signal of finite energy, which has no frequency component higher than w hertz, must be completely recovered from knowledge of its samples taken at rate of 2w per second. Fs >= 2 fm If the sampling frequency is less than Nyquist rate, then a distortion is called aliasing. 

g  (t ) 

 g (nT ) (t  nT ) s

s

n 

g  (t )  the ideal sampled signal fs 

1 : sampling rate Ts

Ts : sampling period 3

PROCEDURE: 1. 2. 3. 4. 5. 6.

Connections are given as per the block diagram. Take the sine wave as input of 1KHZ from signal generator block. Observe the carrier waveform and note down the amplitude and time period of the signal. Observe the sampled signal and note down the amplitude and time period of the signal. Observe the sampled and hold signal and note down the amplitude and time period of the signal. Then the sampled signal is given as an input to low pass filter and then reconstructed waveform is obtained in output of low pass filter. 7. Plot the graph for the Sampled signal and Sample and Hold Signal. BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

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GRAPH:

OBSERVATION: Modulating signal Signal Type Sine Wave

Time Period

Signal Type

Carrier signal

Frequency Amplitude

Signal Type Square Wave

Time Period

Demodulated Output Time Period Frequency

Frequency Amplitude

Amplitude

Sine Wave RESULTS: The sampling theorem is verified successfully. CONCLUSION: The modulating signal can be reconstructed from sampled signal successfully when Fs >= 2 fm. PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply. 5

EXPERIMENT No.-2 TITLE: Study of various encoding schemes. AIM OF THE EXPERIMENT: To generation Unipolar NRZ, Polar NRZ, Unipolar RZ and Polar RZ line code. EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1. 2. 3. 4. 5. 6.

Name of the Equipment/ Component Data encoding Trainer Kit Digital storage oscilloscope Power supply Probes Patch cord Connecting wires

Specifications/ Range 100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

THEORY: „1‟ and „0‟ can be represented in various formats in different levels and waveforms. The selection of coding technique depends on system band width, system ability to pass dc level information, error checking facility. Non return to Zero (level): The NRZ(L) waveform simply goes low for one bit time to represent a data „0‟ and high to represent data „1‟.For lengthy data the clock is lost in asynchronous mode. The maximum rate at which NRZ can change is half the data clock, when alternate 0‟s and 1‟s are there. DC Level: A length data will have only a dc level as its waveform, a dc voltage cannot be used in circuits which involve transformers like telephone, AC coupled amplifiers, capacitors, filter etc. Manchester Bi-phase : „0‟ is encoded low during first half of bit time & high for other half of bit & vice versa for „1‟.There is no synchronization problem in the receiver. It is independent of DC levels, since there is a transition occurring in each bit. Its max frequency is equal to data clock rate. There is at least one transition per bit. Since there is midway transition, it makes clock regeneration difficult so we use special bi phase clock recovery circuit. Return to Bias: It is a 3 level code, consists of positive, negative and zero. Easy clock synchronization is possible.‟1‟ for positive,‟0‟ for negative in first half and zero bias for second half. Maximum frequency is equal to data clock frequency. A DC level of waveforms depends on strings of 1‟s and 0‟s.Hence we cannot use AC coupled communication link. Timing information is easily obtained. The system is referred to as „self-clocking system‟, as magnitude of waveform is original data signal. It requires complex transmitters. PROCEDURE: 1.

Connect the data generator output to code generator kit. This gives the random binary sequence to the kit. 6

2. Connect the clock signal to the trainer kit. 3. Connect the output to the DSO channel along with the clock signal. 4. Observe the waveforms with respect to clock on a dual channel CRO, and compare with the model graph. 5. Plot the waveforms for different codes. BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

GRAPH:

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OBSERVATION: Signal Input Output

Amplitude

Time period

RESULTS: Thus the different coding techniques were studied and observed for a given binary data, and their corresponding waveforms plotted. CONCLUSION:From the above experiment, we conclude that by using these techniques we can encode our data easily which helps to secure our data PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply.

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EXPERIMENT No.-3 TITLE: Pulse code modulation and demodulation AIM OF THE EXPERIMENT: To Study the generation and detection of Pulse Code Modulation (PCM). EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1. 2. 3. 4. 5. 6.

Name of the Equipment/ Component PCM modulation and demodulation trainer kit Digital storage oscilloscope Power supply Probes Patch cord Connecting wires

Specifications/ Range

100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

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. PROCEDURE: 1. Make the connections as per the diagram as shown in the Fig.1.and switch on the power supply of the trainer kit. 2. Clock generator generates a 20 KHz clock .This can be given as input to the timing and control circuit and observe the sampling frequency fs= 2 KHz approximately at the output of timing and control circuit. 3. Apply the signal generator output of 6V(p-p) approximately to the A to D converter input and note down the binary word from LED‟s i.e. LED “ON” represents „1‟ & “OFF” represents „0‟. 4.

Feed the PCM waveform to the demodulator circuit and observe the waveform at the output of D/A which is quantized level.

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BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

GRAPH:

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OBSERVATION: SIGNAL Message signal Clock signal PCM modulated output Demodulated signal

AMPLITUDE(v)

TIME PERIOD

FREQUENCY

RESULTS: Pulse Code Modulation and Demodulation are verified in the hardware kit and its waveforms are studied. CONCLUSION: From the above experiment, the amplitude of demodulated signal is obtained as……… PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply.

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EXPERIMENT No.-4 TITLE: Generation and detection of Delta Modulation. AIM OF THE EXPERIMENT: To Study the generation and detection of Delta Modulation. EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1.

Name of the Equipment/ Component DM modulation and demodulation trainer kit 2. Digital storage oscilloscope 3. Power supply 4. Probes 5. Patch cord 6. Connecting wires THEORY:

Specifications/ Range

100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

Delta Modulation is a form of pulse modulation where a sample value is represented as a single bit. This is almost similar to differential PCM, as the transmitted bit is only one per sample just to indicate whether the present sample is larger or smaller than the previous one. The encoding, decoding and quantizing process become extremely simple but this system cannot handle rapidly varying samples. This increases the quantizing noise. PROCEDURE: 1. 2. 3. 4. 5.

The connections are given as per the block diagram. Connect power supply in proper polarity to kits DCL-07 and switch it on. Keep the Switch S2 in Delta position. Keep the Switch S4 High. Observe the various tests points in delta demodulator section and observe the reconstructed signal through 2nd order and 4th order filter.

BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

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GRAPH:

OBSERVATION: SIGNAL Message signal Digital sampler output Integrator-3 output Filter output

AMPLITUDE(v)

TIME PERIOD

FREQUENCY

RESULTS: Delta Modulation and Demodulation are verified in the hardware kit and its waveforms are studied. CONCLUSION: From the above experiment, the amplitude of demodulated signal is obtained as……… PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply.

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EXPERIMENT No.-5 TITLE: ASK modulation and demodulation AIM OF THE EXPERIMENT: To study the generation and detection of Amplitude Shift Keying (ASK). EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1. 2. 3. 4. 5. 6.

Name of the Equipment/ Component ASK modulation and demodulation trainer kit Digital storage oscilloscope Power supply Probes Patch cord Connecting wires

Specifications/ Range

100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

THEORY: The binary ASK system was one of the earliest form of digital modulation used in wireless telegraphy. In a binary ASK system binary symbol 1 is represented by transmitting a sinusoidal carrier wave of fixed amplitude Ac and fixed frequency fc for the bit duration Tb whereas binary symbol 0 is represented by switching of the carrier for Tb seconds. This signal can be generated simply by turning the carrier of a sinusoidal oscillator ON and OFF for the prescribed periods indicated by the modulating pulse train. For this reason the scheme is also known as on-off shift testing. PROCEDURE: 1. The connections are given as per the block diagram. 2. Connect the power supply in proper polarity to the kit and & switch it on. 3. Set the amplitude and frequency of the carrier wave as desired. 4. Set the message data bit. 5. Observe the waveforms at the a. Message data b. Carrier signal c.

ASK modulator output

d. ASK demodulator output 6. Plot it on graph paper.

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BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

GRAPH:

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OBSERVATION: SIGNAL Message signal Carrier Signal ASK modulated signal Demodulated output

AMPLITUDE(v)

TIME PERIOD

FREQUENCY

RESULTS: BASK Modulation and Demodulation are verified in the hardware kit and its waveforms are studied. CONCLUSION: From the above experiment, the amplitude of demodulated signal is obtained as……… PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply.

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EXPERIMENT No.-6 TITLE: Phase Shift Keying (PSK) modulation and demodulation. AIM OF THE EXPERIMENT: To study the generation and detection of Phase Shift Keying (PSK). EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1.

Name of the Equipment/ Component

Specifications/ Range

PSK modulation and demodulation trainer

Quantity 1

kit 2.

Digital storage oscilloscope

100MHz,1GSa/S

1

3.

Power supply

1

4.

Probes

As per req.

5.

Patch cord

As per req.

6.

Connecting wires

As per req.

THEORY: Phase 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 (i.e. binary PSK) un-shifted carrier Vcosωt is transmitted to indicate a 1 condition, and the carrier shifted by 180o i.e. – Vcosωt is transmitted to indicate as 0 condition. PROCEDURE: 7. The connections are given as per the block diagram. 8. Connect the power supply in proper polarity to the kit and & switch it on. 9. Set the amplitude of the sine wave as desired. 10. Observe the waveforms at the e. Clock f.

SIN 1 & SIN 2

g.

MODULATOR OUTPUT

h. PSK OUT 11. Plot it on graph paper.

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BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

GRAPH:

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OBSERVATION: SIGNAL Clock Signal Input1 Input2 Modulator Output Demodulated output

AMPLITUDE(v)

TIME PERIOD

FREQUENCY

RESULTS: BPSK Modulation and Demodulation are verified in the hardware kit and its waveforms are studied. CONCLUSION: From the above experiment, the amplitude of demodulated signal is obtained as………

PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply.

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EXPERIMENT No.-7 TITLE: Frequency Shift Keying (FSK) modulation and demodulation. AIM OF THE EXPERIMENT: To study the generation and detection of Frequency Shift Keying (FSK). EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1. 2. 3. 4. 5. 6.

Name of the Equipment/ Component FSK modulation and demodulation trainer kit Digital storage oscilloscope Power supply Probes Patch cord Connecting wires

Specifications/ Range

100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

THEORY: FSK signaling schemes find a wide range of applications in low-speed digital data transmission system. FSK schemes are not as efficient as PSK in terms of power and bandwidth utilization. In binary FSK signaling the waveforms are used to convey binary digits 0 and 1 respectively. The binary FSK waveform is a continuous, phase constant envelope FM waveform. The FSK signal bandwidth in this case is of order of 2MHz, which is same as the order of the bandwidth of PSK signal. PROCEDURE: 1. The connections are given as per the block diagram. 2. Connect the power supply in proper polarity to the kit and & switch it on. 3. Set the amplitude of the sine wave as desired. 4. Observe the waveforms at the i.

Clock

j.

SIN 1 & SIN 2

k.

MODULATOR OUTPUT

l.

PSK OUT

5. Plot it on graph paper

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BLOCK DIAGRAM/ CIRCUIT DIAGRAM:

GRAPH:

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OBSERVATION: SIGNAL Clock Signal Input1 Input2 Modulator Output Demodulated output

AMPLITUDE(v)

TIME PERIOD

FREQUENCY

RESULTS: BFSK Modulation and Demodulation are verified in the hardware kit and its waveforms are studied. CONCLUSION: From the above experiment, the amplitude of demodulated signal is obtained as……… PRECAUTIONS: 1. 2. 3. 4.

Do not use open ended wires to connect 230V, 50Hz power supply. Check the connection before giving the power supply. Observations should be done carefully. Disconnect the circuit after switched off the power supply.

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EXPERIMENT No.-8 TITLE: TDM Multiplexing and demultiplexing. AIM OF THE EXPERIMENT: To analyse the process of Time Division Multiplexing and demultiplexing. EQUIPMENTS/ APPARATUS REQUIRED : Sl.No. 1. 2. 3. 4. 5. 6.

Name of the Equipment/ Component TDM multiplexing and demultiplexing trainer kit Digital storage oscilloscope Power supply Probes Patch cord Connecting wires

Specifications/ Range

100MHz,1GSa/S

Quantity 1 1 1 As per req. As per req. As per req.

THEORY: Time Division is a technique of transmitting more than one information on the same channel. The samples consist of short pulses followed by another pulse after a long time intervals. This no-activity time intervals can be used to include samples from the other channels as well. This means that several informations can be transmitted over a single channel by sending samples from different information sources at different moments in time. This technique is known as Time Division Multiplexing or TDM. TDM is widely used in digital communication systems to increase the efficiency of the transmitting medium. TDM can be achieved by electronically switching the samples such that they interleave sequentially at correct instant in time without mutual interference. PROCEDURE: 1. Connections are made as per the block diagram. 2. The message signal1 is connected to the channel 0 and note down the amplitude and time period of the signal. 3. The message signal 2 is connected to the channel 1 and note down the amplitude and time period of the signal. 4. Observe the TDM wa...