dc manual complete

7/31/2019 DC Manual Complete

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RVR Institute of Engineering and Technology

Experiment: 1

AMPLITUDE SHIFT KEYING

Objective:

To generate and demodulate an amplitude shift keyed (ASK) signal for different frequencies

of data signal.

Equipment Required:

ASK Trainer kit-1

Dual Trace Oscilloscope-1

Patch cords

Block Diagram:

Fig:1.1 ASK Modulator & Demodulator Block Diagram

Theory:

Amplitude shift keying - ASK - in the context of digital communications is a modulation process,

which imparts to a sinusoid two or more discrete amplitude levels. These are related to the number of levels

adopted by the digital message.

For a binary message sequence there are two levels they are zero and one. In BASK, for binary digit

1: an amplitude level will be transmitted and for binary zero, no signal will be transmitted.

One of the disadvantages of ASK, compared with FSK and PSK, for example, is that it has not got a

constant envelope. This makes its processing (eg, power amplification) more difficult, since linearity

becomes an important factor. However, it does make for ease of demodulation with an envelope detector.

Department of ECE 1 ME& DC Lab


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Model wave forms:

Data Signal

Carrier Signal

ASK modulated signal

Demodulated Signal

Procedure:

1. switch on the trainer and measure the regulated power supply +5v and -5 v wrt ground.

2. Observe and notedown the frequency and amplitude of the carrier generator with hhte help of

Oscilloscole.

3.Observe and measure the data signal with the help of Oscilloscope./this will be a squqre wave of 5 v p-

swith varying frequency between 20Hz and 200Hz

Modulation:

4. Set any data sequence with a fixed frequency(say 100Hz)

5. Connect the data signal and carrier signals to the ASK modulator and observe the output .

6. Draw the ASK output.

Demodulation:

7. Connect ASK signal to the ASK demodulator.

8. Observe the demodulated signal and compare that with the original Data signal appliesd to the modulator

using CRO.

9. Repeat steps 4 to 8 for different data sequences.

Result:



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Experiment: 2

FREQUENCY SHIFT KEYING

Aim:

Study the operation of FSK modulation & Demodulation and to plot the Frequency Shift Keying

waveforms for binary data.

Equipment Required:

1. Frequency Shift Keying Trainer kit

2. Dual trace C.R.O (20MHz)

3. Patch chords

Block Diagram:

Fig 2.1: Block Diagram of FSK modulation and Demodulation System

Theory:

As its name suggests, a frequency shift keyed transmitter has its frequency shifted by the message.

Although there could be more than two frequencies involved in an FSK signal, in this experiment the

message will be a binary bit stream, and so only two frequencies will be involved. The word keyed

suggests that the message is of the on-off (mark-space) variety, such as one (historically) generated by

a morse key, or more likely in the present context, a binary sequence. Conceptually, and in fact, the

transmitter could consist of two oscillators (on frequencies f0 and f1), with only one being connected to

the output at any one time. Unless there are special relationships between the two oscillator frequencies

and the bit clock there will be abrupt phase discontinuities of the output waveform during transitions of

the message.

Bandwidth:

Practice is for the tones f0 and f1 to bear special inter-relationships, and to be integer multiples of the bit

rate. This leads to the possibility of continuous phase, which offers advantages, especially with respect

to bandwidth control. FSK signals can be generated at baseband, and transmitted over telephone lines

(for example). In this case, both f0 and f1 would be audio frequencies. Alternatively, this signal could be

translated to a higher frequency. Yet again, it may be generated directly at carrier frequencies.



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Other forms of FSK:

Minimum frequency-shift keying or minimum-shift keying (MSK) is a particularly spectrally efficient

form of coherent FSK. In MSK the difference between the higher and lower frequency is identical to

half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a

carrier period. This is the smallest FSK modulation index that can be chosen such that the waveforms for

0 and 1 are orthogonal. A variant of MSK called GMSK is used in the GSM mobile phone standard.

FSK is commonly used in Caller ID and remote metering applications

Audio frequency-shift keying(AFSK) is a modulation technique by which digital data is represented by

changes in the frequency (pitch) of an audio tone, yielding an encoded signal suitable for transmission

via radio or telephone. Normally, the transmitted audio alternates between two tones: one, the "mark",

represents a binary one; the other, the "space", represents a binary zero. AFSK differs from regular

frequency-shift keying in performing the modulation at baseband frequencies. In radio applications, the

AFSK-modulated signal normally is being used to modulate an RF carrier (using a conventional

technique, such as AM or FM) for transmission. AFSK is not always used for high-speed data

communications, since it is far less efficient in both power and bandwidth than most other modulation

modes. In addition to its simplicity, however, AFSK has the advantage that encoded signals will pass

through AC-coupled links, including most equipment originally designed to carry music or speech.

Procedure:

1. Study the theory of operation.

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

3. Verify the operation of the logic source using CRO. Output should be zero volts in logic 0 position and

12V in logic 1 position.

4. Observe the output of the data signal using oscilloscope. It should be a square wave of 20Hz to 180Hz

@ 10Vpp. ( For frequency variation potentiometer is provided).

FSK Modulation:

5. Connect output of the logic source to data input of the FSK modulator.

6. Set logic source switch in 0 position.

7. Connect FSK modulator output to oscilloscope.

8. Set the output frequency of the FSK modulator as per your desire( say 2KHz) with the help of control

F0 knob in FSK Modulator which represents logic 0

9. Set logic source switch in 1 position.

10. Set the output frequency of the FSK modulator as per your desire ( say 4 KHz) with the help of

control F1 knob in FSK modulator which represents logic 1.



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11. Now remove connection between Logic source and FSK modulator, connect output of the data signal

generator to the data input of the FSK modulator.

12. Keep CRO in dual mode connect CH1 input of the oscilloscope to the input of the FSK modulator

and CH2 input to the output of the FSK modulator.

13. Observe the FSK signal for different data signal frequencies and plot them. By this we can observe

that the carrier frequency shifting between two predetermined frequencies as per the data signal i.e2

KHz when data signal is 0 and 4KHz when data input is 1 in this case.

14. Compare these plotted wave forms with the theoretically drawn in figure 2.2.

FSK Demodulation:

15. Now connect the FSK modulator output to the FSK input of the demodulator.

16. Connect CH1 input of the Oscilloscope to the data signal at modulator and CH2 input to the output of

the FSK demodulator (keep CRO in dual mode) By varying control knob at FSK demodulator,

Obtain Demodulated (Data) signal

17. Observe and plot the output of the FSK demodulator for different frequencies of data signal. Compare

the original data signal and demodulated signal, by this we can observe that there is no loss in process

of FSK modulation and demodulation.Expected Wave forms:

Fig 2.2: Model wave forms of FSK Modulation and Demodulation



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Result:

Question bank:

1. Explain the concept of FSK?

2. Compare ASK, FSK & PSK?

3. Draw the waveforms of FSK?

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

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

coding over other formats?

6. Explain the demodulation scheme of FSK?

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

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

separated by 3KHz?

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

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

11.What are the limiting factors of FSK?

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



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RVR Institute of Engineering and TechnologyExperiment: 3

PHASE SHIFT KEYING

Aim:

Study the operation of PSK modulation & Demodulation and to plot the Phase Shift Keying

waveforms for binary data.

Equipment Required:

1. Phase Shift Keying Trainer kit


3. Patch chords

Block Diagram:

Fig 3.1: Block Diagram of PSK modulation and Demodulation System

Theory:

Phase Shifting Keying (PSK) is a modulating / 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 VmcosWot is transmitted to indicate Logic 1 condition , and the

carrier shifted by 180o i.e -Vm cos Wo t is transmitted to indicate Logic 0 condition. Wave

forms are shown in Figure3.2. PSK Modulating & Demodulating circuitry can be developed in

number of ways one of the simple circuit is used in this trainer.

Procedure:

1. Study the theory of operation.

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

3. Observe the output of the carrier generator using CRO, it should be an 8 KHz Sine with 5

Vpp amplitude.

4. Observe the various data signals (1 KHz, 2 KHz and 4 KHz) using CRO.



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Modulation:

5. Connect carrier signal to carrier input of the PSK Modulator.

6. Connect any one of data signals say 4 KHz from data source to data input of the

modulator.

7. Keep CRO in dual mode.

8. Connect CH1 input of the CRO to data signal and CH2 to the output of the PSK

modulator

9. Observe the PSK o/p Signal with respect to data signal and plot the wave forms

Compare the plotted

waveforms with given wave forms.

Demodulation:

10. Connect the PSK output to the PSK input of the demodulator.

11. Connect carrier to the carrier input of the PSK demodulator

12. Keep CRO in dual mode.

13. Connect CH1 to the data signal (at Modulator) and CH2 to the output of the

demodulator.

14. Compare the demodulated signal with original data signal, By this we can notice that

there is no loss in

modulation and demodulation process.15. Repeat the steps 7 to 15 with different data signals i.e 2 KHz and 1 KHz.

Expected Wave forms:



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Fig 3.2: Model wave forms of PSK Modulation and Demodulation

Result:

Question bank:

1. Explain the concept of PSK?

2. Compare ASK, FSK, PSK?

3. Draw the waveforms of PSK?

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

5. Explain the demodulation scheme of PSK?.

6. What is the advantage of PSK over ASK, FSK?7. Will the smaller variations in the signal can be detected reliably by PSK?

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

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

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

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

12. Is the maximum baud rate in PSK & ASK are same?



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Experiment: 4

TIME DIVISION MULTIPLEXING AND DEMULTIPLEXING

Objective:

Study the operation of Time Division Multiplexing and de-multiplexing of four(4) baseband signals.

Equipment Required:

1. Time Division Multiplexing and De-multiplexing Trainer kit


3. Patch chords

Block Diagram:

Fig 4.1: Block Diagram of TDM and De-multiplexing System

Theory:

Time-division multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two

or more signals or bit streams are transferred apparently simultaneously as sub-channels in one



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communication channel, but are physically taking turns on the channel. The time domain is divided into

several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-

channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of

one timeslot per sub-channel. After the last sub-channel the cycle starts all over again with a new frame,

starting with the second sample, byte or data block from sub-channel 1, etc.

Applications examples :

The plesiochronous digital hierarchy (PDH) system, also known as the PCM system, for digital

transmission of several telephone calls over the same four-wire copper cable (T-carrier or E-carrier)

or fiber cable in the circuit switched digital telephone network

The SDH and synchronous optical networking (SONET) network transmission standards, that have

surpassed PDH.

The RIFF (WAV) audio standard interleaves left and right stereo signals on a per-sample basis

The left-right channel splitting in use for stereoscopic liquid crystal shutter glasses

TDM can be further extended into the time division multiple access (TDMA) scheme, where several

stations connected to the same physical medium, for example sharing the same frequency channel, can

communicate. Application examples include:

The GSM telephone system

Procedure:

1. Connect power supply in proper polarity to the kit & Switch on.

2. Observe all message signals (250Hz, 500Hz, 1 KHz and 2 KHz sine wave), adjust

different

amplitude levels to each signal using CRO.

3. Connect ALL signals to the multiplexer input channels CH1, CH2, CH3, and CH4

by means of the

patch- chords provided.

4. Observe output of TDM Multiplexer and compare them with model graph shown

in fig 4.2( only two

message signals are given).

5. Connect the multiplexed output of the transmitter section to the input of the

de-multiplexer section.

6. Observe the individual de-multiplexed signals at output of de-multiplexer(AtCH1, CH2, CH3, and

CH4 respectively)

7. Apply De-Multiplexed signals to amplifier and observe the de-modulated output

by selecting proper

gain.

8. Take observations as mentioned below.

a. Sampling Clock

b. Multiplexed Output at multiplexer.

c. De-multiplexer Output at de-multiplexer.

d. Reconstructed signal using amplifier.

Expected Wave forms:



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Fig 4.2: Model wave forms of TDM and De-multiplexing a) Message 1 b) Message 2 c) TDM wave

Result:

Question bank:

1. Draw the TDM signal with 2 signals being multiplexed over the channel?2. Define guard time & frame time?3. Explain block schematic of TDM?4. How TDM differ from FDM?5. What type of filter is used at receiver end in TDM system?

6. what are the applications of TDM?7. If 2 signal band limited to 3 kHz, 5KHz & are to be time division multiplexed.What is the maximum

permissible interval between 2 successive samples.?8. Is the bandwidth requirement for TDM & EDM will be same?9. Is the circuitry needed in FDM.?10.Is TDM system is relatively immune to interference with in channels (interchannel cross talk) as

compared to FDM?Experiment 5:

DELTA MODULATION AND DEMODULATION

Objective:To observe the modulation and demodulation of a RF signal using Delta modulation technique.

Equipment required:DM modulator trainer kit

DM demodulator trainer kit

Dual trace oscilloscope

Patch chords.

Block Diagram:Modulator:



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Demodulator

Fig: 5.1 : Delta modulation and demodulation block diagram

Theory:

It is the differential pulse code modulation scheme in which different signal is encoded into a single

bit, in digital transmission system the analog signal is sampled & digitally coded, this code represent the

sampled amplitude of the analog signal. The digital signal is sent to the receiver through any channel in

serial form. At the receiver the digital signal is decoded & filtered to get reconstructed analog signal

sufficient no. of samples are required to allow the analog signal to be reconstructed accurately. DM is an

encoding process where logic levels of the transmitted pulses indicate whether the decoded o/p should rise

or fall at each pulse.

Delta demodulation: The delta demodulation consists of D- f/f followed by an integrator & a second &fourth order low pass Butterworth filter. The delta demodulator then receives the data stream from D f/f of

delta modulator. It catches this data at every rising edge of receiver clock. This data stream then fed to



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integrator its o/p tries to contains sharp edge which is smoothened by the low pass filter whose o/p freq is

just above the audio band.

The practical use of delta modulation is limited due to

1. Noise: It is any unwanted random waveform with in signal

2. Distortion: It means that the receiver o/p is not true copy of analog i/p signal at the transmitter. In the

delta modulation when analog signal is greater than integrator o/p the integrator ramps up to meet the

analog signal.

3. Delta modulation is unable to pass DC information.

Procedure:

DM modulator:

1. Connect the trainer to the mains and switch on the power supply.

2. Observe the output of AF generator using CRO, It should be a sine wave of 100 Hz frequency with

3 v P-P Amplitude.

3. Verify the output of DC source with CRO, It should vary 0 to +4V.4. Observe the output of the clock generator using CRO; it should be 4 kHz frequency of square wave

with 5V P-P amplitude.

5. Connect AF Signal from AF generator to the inverting input of the comparator and set output

amplitude at 3V P-P.

6. Observe and plot the signals at D/A converter output, DM signal using CRO and compare them with

signals shown in fig:5.2.

DM Demodulator:

7. Connect DM signal to the DM Input of the demodulator.

8. Connect clock(4kHz) from modulator to the clock input of the demodulator. Connect Input of theUP/DOWN counter to the clock from transmitter with the help of connecting wires.

9. Observe digital output(LED Indication) of the UP/ DOWN Counter at transmitter and receiver , they

are same .

10. Observe and plot the output of the D/A Converter and compare it with wave given in fig :5.3.

11. Connect D/A Output to the LPF input, LPF output to the amplifier input and observe DM

demodulated signal and compare it with original message (AF) signal.

Model Wave forms:



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Fig: 5.2 DM modulation for AF signal

Fig: 5.3 DM demodulation for AF signal

Result:

Experiment: 6

PULSE CODE MODULATION AND DEMODULATION

Objective:



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Equipment Required:

Block Diagram:

Fig:1.1 ASK Modulator & Demodulator Block Diagram

Theory:

Model wave forms:

Procedure:

Modulation:

Demodulation:

Result:


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