Dc Lab Manual

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DIFFERENTIAL PULSE CODE MODULATION

AIM:

To study the operation of differential pulse code modulator and Demodulator.

APPARATUS:

1. DPCM modulator trainer kit.

2. 2. DPCM demodulator kit.

3. 3. Storage oscilloscope.

4. Digital multimeter.

5. Coaxial cables.

6. C.R.O. probes & connecting wires.

THEORY:

In this DPCM redundancy is reduced from over all bit value will decrease and

number of bits required to transmit one sample will also be reduced. This type of digital

pulse modulation scheme is called differential pulse code modulation.The differential

pulse code modulation works on the principle of predetection . The value of the present

sample value is predicted from the samples. The predetection may not be exact but it is

very close to the actual sample value , shows the transmitting of differential pulse code

modulation system works on the principle of predetection. The present sample value is

predicted but it is very close to the actual sample value.

PROCEDURE:

1. Verify the circuit as per the circuit diagram.

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2. Observe the output of the A.F. generator .it should be a Sine wave of 400 HZ

frequency with 5Vp-p

3. Verify the output of the D.C. source

.

4. Observe the output of the clock generator using C.R.O. it Should be 64 KHZ

and 8 KHZ. Frequency of square Wave with 5Vp-p.FOR MODULATION:

5. Keep the C.R.O. in dual mode .connect one channel to8 KHZ signal and

another channel to open outputs.

6. Observe the DPCM output with respect to the 8KHZ Signal.FOR

DEMODULATION

7. Connect the DPCM signal to the demodulator input.

8. Connect the clock signal from transmitter to the receiver Using co-axial cable.

9. Observe the D/A converter output using storage Oscilloscope and compare

with the original signal and Observe that there is no information loss in process of

Conversion and transmission.

10 . similarly verify for different values of modulating Signal voltage

.PRECAUTIONS:

1. Check the connections before switch on the power supply.

2. Avoid loose connections.

3. Observe the output on C.R.O and take the readings without parallax error.

RESULT:



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VIVA-VOICE:

1.What is the aim of the experiment ?

2. Wat is DPCM ?

3.What is PCM ?

4. What is the difference between DPCM & PCM ?

5.Why we need coding ?

DELTA MODULATION

AIM:

To study the delta modulation process by comparing the present signal with the

previous signal of the given modulating signal.

APPARATUS:

1. Delta modulation trainer kit

2..Dual trace CRO

3.Digital multi meter

4.CRO probes and set of patch cards

THEORY:

Delta modulation is a differential PCM technique in witch the difference signal

between two successive samples is encoded into a single bit code . The process of

encoding is as follows .The comparator compares the in put signal m(t) and r(t) .If m(t)

>r(t) logic 1 is generated at the out put of the comparator. Otherwise a logic 0 is

generated. the value of logic 1 or logic 0 is termed as Δ(t) is held for the bit duration by

the sample and hold current to generate So(t) , the delta modulated out put .This out put



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So(t) is fed to the 8bit binary up/down counter to control its count direction . A logic’1’

at the mode control in put increases the count value by one And a logic ‘0’ decrements the

count value by one . All the eight out puts of the counter are given to DAC to reconstruct

the original signal .In essence the counter and decoder forms the delta modulation in the

feed back loop of the comparator .Thus if the input signal is higher then the

reconstructed signal the counter increments at each step so as to enable the DAC out put

to reach to the input signal values.Similarly the in put signal m(t) is lower then the

reconstructed signal r(t) , the counter decrements at each step and the DAC output gets

reduced to reach a value m(t) .

PROCEDURE:

1.Verify the circuit as per circuit diagram .

2. connect clock signal to the delta modulator .

3. Connect modulating signal to the input of delta modulator and observe the

same on channel one .

4.Observe the delta modulation out put on channel 2.

5.Connect this delta modulator out put to the demodulator.

6.Also connect the clock signal to de modulator .

7.Observe the de modulator out put with and without RC filter on CRO.

PRECAUTIONS:

RESULT:



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VIVA VOICE:

1.What is the aim of the experiment?

2.What is delta modulation ?

3. What is demodulation ?

4. Why we need modulation ?

5. What is the use of modulation ?

TIME DIVISION MULTIPLEXING

AIM:

To study the Time division multiplexing and demultiplexing for two different

frequency signals

APPARATUS :

1. 2 channel TDM multiplexer kit – 1

2. Audio frequency signal generator – 1

3. Clock generator – 1

4. 2 channel TDM demultiplexer – 1

5. Passive low pass filter – 2

6. Audio amplifier

7. Dual trace C.R.O – 2

8. C.R.O probes

9. Connecting wires

THEORY:



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MultiplexerTime division multiplexer is the technique for simultaneous transmission of

more than one intelligence signals on one channel and the signal carrier by utilizing the

time scale without loss of identity of an individual signal.In TDM multiplexer

CD4052IC is used to generate TDM wave. It is a 4 channel analog multiplexer and is

used as an active components in this circuit. One of the four channels (pin9) of 052 is

grounded. So that 4052 acts as a two channel multiplexer and the other channel being

terminated with control (pin10) signal of TDM multiplexer. The message signals that are

to be transmitted has to be connected to CH-1 and CH-2 i/p’s of the CD4052.When

control signal i/p 1 i;e logic high (+5v)o/p of the 4052 is connect to CH-1 and whatever

signal at CH-1 is there will be passed onto o/p. Similarly when control signal is 0(0v) o/p

of the multiplexer connected to CH-2 and the signal at this i/p will be passed on to o/p.

When drive the control signal with a clock signal of desired freq .the o/p of the

multiplexer will be connected to CH-1 and CH-2 automatically in sequence depend on

clock signal condition. i;e ON/OFF time. So multiplexer samples each the I/p signals in

sequence and transmits over a single channel.DEMULTIPLEXER:IC CD4052 is a 4

channel analog demultiplexer one of the four channels (pin9) grounded and other one

(pin10) is being terminated of control signal of a two channel TDM demultiplexer. So

that CD4052 will act as a two channel TDM demultiplexer. When control signal is 1 I;e

logic high (+5v) I/p of the 4052 is connect to CH-1 o/p and the signal which is at I/p

will be passed on to o/p. When drive the control signal with a clock signal of desired freq.

The i/p of the demultiplexer will be connect to CH -1 o/p and CH-2 o/p automatically is

sequence depend on clock signal condition i;e. ON/OFF time. Demultiplexer at the

receiver should be operate in synchronize with the multiplexer which is at transmitter in

order to recover the original signals without any loss.

PROCEDURE:

MULTIPLEXER

1. Trace the circuit as per circuit diagram.



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2. Observe the o/p of AF generator, it should be a sine wave of 100Hz with 3Vp-

p amplitude.

3. Observe the o/p of AF generator2; it should be a sine of 200Hz with 3Vp-p

amplitude.

4. Verify the operation of logic source with multimeter, o/p should be +5v in logic

1 and 0v in logic 0.

5. Verify the clock generator o/p, it should be a square of 500Hz to 15KHz freq

with 5Vp-p amp.

6. Connect the CH-1& CH-2 inputs of the TDM multiplexer to the o/p of AF

generator 1& 2 respectively.

7. Connect control i/p of the TDM multiplexer to the o/p of the logic source.

8. Keep control signal at logic 1 and observe the o/p of the TDM multiplexer and

notice that the o/p of the TDM multiplexer is a signal which has been connected

to CH-1 i/p. In this condition the signal at CH-2 i/p has no effect on mux o/p.

9. Repeat the above step-8 for logic source at 0 positions.

10. Disconnect logic source and connect clock o/p to the control I/p.

11. Observe TDM waveform using C.R.O at different values of clock freq I/p

signal voltage level.

DEMULTIPLEXER

1. Verify the circuit as per circuit diagram.



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2. Verify the operation of logic source with multimeter/ scope,o/p should be ±5v

in logic-1 and ov in logic-0 position.

3. Observe the clock generator; it should be a square wave of 500Hz to 15 KHz

freq with 5Vp-p.

4. Connect TDM signal to I/p of TDM de-multiplexer with the help of coaxial

cable.

5. Connect control I/p to logic source o/p.

6. Put logic source to 1 position and observed that entire TDM is transferred to

CH-1 o/p and has no signal at CH-2 o/p.

7. Repeat the above step-6 for logic -0.

8. Now disconnect logic source and connect clock from the transmitter.

9. Connect CH-1,CH-2 o/p to low pass filter and observe the o/p of the filter

and compare with original A.F signals. Both are same in freq and shape.

PRECAUTIONS:

1. Check the connections before switch on the power supply.

2. Avoid loose connections.

3. Observe the output on C.R.O and take the readings without parallax error.

RESULT:



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VIVA VOICE:

1. What is meant by multiplexing?

2. What is the difference between F.D.M and T.D.M?

3. What is the Aim of your expt?

4. What are the advantages by using T.D.M?In which type of communication we

are using T.D.M(either A.C or D.C)?

FREQUENCY SHIFT KEYING

AIM:

To study the operation of FSK modulation and de modulation and to plot the

graph.

APPARATUS:

1. Frequency shift keying system

2. Dual trace oscilloscope

3. Connecting wires

4. Dual multi meter

5 .Digital frequency counter

THEORY:

In FSK system two sinusoidal carrier waves of the same amplitude Ac but

different frequencies fc1 and fc2 are used represent binary symbols ‘1’ and ‘0’ respectively

.The Binary FSK wave S(t) may be represented asS (t) = Ac cos (2Πfc1T) for ‘1’ = Ac cos

(2Πfc2T) for ‘0’The binary FSK wave form is illustrated in figure for the arbitory



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sequence .It can be easily verified that binary FSK wave form is essentially a super

position of two binary ASK wave forms, one with a frequency fc1.

PROCEDURE:

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

2. Measure the o/p voltage of the RPS i.e., +12V with the help of digital

multimeter

3. Verify the operation of the logic source using ‘0’ Position and 12V in logic ‘1’

position

4. Observe the o/p of the data signal using oscilloscope it should be a Square wave

of 20Hz to 180Hz at 10Vp-pFOR MODULATION:

5. Connect the out put of the logic source to data p/p of the FSK modulator.

6. Set the logic source switch in ‘0’ position.

7. Connect the FSK modulator out put to CRO as well as frequency counter

CRO.

8. Set the o/p frequency of the FSK modulator per your desire with the help of

control to which represents logic ‘0’.

9. Set the logic ‘0’ switch in ‘1’ position.

10. As per your desire with the help of control F, which represents logic ‘1’.



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11. Now connect the data p/p of the FSK modulator to the o/p of the data signal

generator.

12. Keep CRO in dual trace mode, connect with c1+1, i/p 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 is shifting bin two pre determined

frequencies at the data signal i.e., 1 KHz when data signal is zero and 2.4 KHz

when data output is ‘1’ in its case and the other with frequency fc2. Hence the

Power density spectrum of FSK is the sums of two ASK spectra at frequencies fc1

and other frequency fc2. Hence the power density spectrums of FSK signal.It may

be noted that the bandwidth of FSK is higher than that of ASK (or) PSK, the

spectrum of FSK signal. FSK signaling scheme find a wide range of applications

for low-speed digital data transmission.

14. Compare these plotted waveforms with theoretically.For Demodulation:

15. Again connect the i/p of the FSK modulator to the help of to control.

16. Now put data source switch in ‘1’ position and set the FSK o/p frequency to

2225 Hz with the help of F1 control without disturb the F0.

17. Disconnect the FSK i/p of the modulator from logic source and connect data

signal generator.

18. Now put data source switch in’1’ position and set the FSK o/p frequency to

2225 Hz with the help of F1 control without disturbing the F0.

19. Disconnect the FSK i/p of the modulator from logic source and connect the

data generator.



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20. Observe the o/p of the modulator using CRO &compare them with the given

wave forms.

21. Now connect the FSK modulator o/p to the FSK i/p of the demodulator.

22. Connect CH-1 i/p of the CRO to the data signal at modulator and CH-2 i/p

of the o/p of the FSK modulator.

23. Observe the o/p and plot the o/p of the FSK demodulator compare the

original data signal and demodulated signal by this we observe that there is no

demodulated signal in FSK modulation.

PRECATIONS:

1. Connections are made without loose connections.

2. Readings are taken without parallax error.

3. Plot the graph care fully.

RESULT :



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Dc Lab Manual