VSB ENGINEERING COLLEGE COMMUNICATION SYSTEMS LABORATORY

KARUDAYAMPALAYAM, KARURCOMMUNICATION SYSTEMS LABORATORYPREPARED BYMr.K.KarthickMs.K.R.DeepaCOMMUNICATION SYSTEMS LABORATORY

1. AMPLITUDE MODULATION AND DEMODULATIONAIM:

To design a circuit for amplitude modulation and demodulation.

APPARATUS REQUIRED:

S.NO.APPARATUS NAME RANGEQUANTITY

1Digital trainer kit

-1

2 Power chord--

3CRO30MHZ1

4Connecting wires-REQUIRED

THEORY:

Amplitude modulation is the process of converging message signal with the carrier signal is always greater than the massage signal. Amplitude demodulation is the process of recovering the message signal from the modulated signal.PROCEDURE:1. Connect the power supply to the trainer.

2. switch on the trainer and check the power supply.

connect the oscilloscope to the output of AF genertor and verify the sine wave by changing the frequency and amplitude controls frequency 10HZ TO 10KHZ and amplitude 10V approximately.

3. Some for RF generator and verify the frequency 10KHZ to 150KHZ and amplitude 10V.

4. Switch off the trainer patch the circuit as show in the diagram.

5. Connect the CRO at AF generator output and switch ON the trainer kit(200HZ) modulating sine wave signal by frequency control.

6. Set 100KHZ carrier frequency by using frequency plot in RF generator unit.

7. Connect the oscilloscope at the output of AM and observe the waveform.

8. From the waveform measure Emax and Emin . calculate the % of modulating using the formula

%Modulation=(Emax-Emin)/(Emax+Emin) *100

9. Increase the amplitude of modulation signal and calculate the % of modulation for various ranges.

DIAGRAMMODELGRAPH:

TABULATION:

Type of signalAmplitude (in V)Time (in ms)

Message Signal

Carrier Signal

Modulated

signal

Demodulated Signal

RESULT:

Thus amplitude modulation and demodulation was designed and verified successfully.

2. FREQUENCY MODULATION AND DEMODULATIONAIM:

To study and observe the characteristics of frequency modulation and demodulation using digital modulation trainer kit.

APPARATUS REQUIRED:

SNOAPPARATUS

NAME RANGE QUANTITY

1FM modulation kit

- 1

2Power chord - -

3 CRO - -

THEORY:

FREQUENCY MODULATION:

When frequency of the carrier wave varies as per amplitude modulation signal, then it is called as frequency modulation. Amplitude of the modulated carrier wave remains constant.

It represented by

E(t)=Ec.sin[wct+k1Em/wm .sinwmt]

PROCEDURE:

1. Turn on te trainer kit and check power supply and sine wave generator output.

2. Switch off the trainer , patch the circuit as shown in wiring diagram.

3. Connect CRO to the ouput wave generator and set 200Hz frequency and amplitude

at maximum pattern.

4. Observe the FM output wave , it is slightly blurred sine wave as shown in the figure

this graphically derivation of FM output.

DIAGRAM:

FM MODULATION:Type of signalAmplitude (in V)Time (in ms)

Message Signal

modulated Signal

RESULT:

Thus the frequency modulation and frequency demodulation was designed and the outputs are verified successfully.

3. PULSE MODULATION PAM/PWM/PPMPULSE AMPLITUDE MODULATION

AIM:

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

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 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.

PROCEDURE:

1. Make connections as shown in the diagram.

2. Set the input signal and carrier signal.

3. Obtain PAM signal

4. Measure the amplitude and frequency

5. Demodulate the PAM signal.

DIAGRAM:

TABULATION:

RESULT:

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

PULSE WIDTH MODULATION AND DEMODULATIONAIM: To study and observe the characteristics of pulse width modulation and demodulation by using the pulse width modulation trainer kit.

APPARATUS REQURIED: S.NO APPARATUS

NAME RANGEQUANTITY

1Pulse width modulation

Trainer kit - 1

2Patch chord - -

3 CRO 30MKHZ 1

THEORY:

In this small sample is made up of modulating signal and then a pulse is transmitted. In this wave some characteristics of pulse is varied in accordance with sample of modulating signal. The sample in actual measure of modulating signal of a specification there are several types of pulse modulation system in advance.PROCEDURE:

1.Patch up the circuit as shown.

2.Connect the 1KHZ sine signal from sine wave generator to input of PWM and channel at output.

3.verify signal polarity by varying the carrier signal.

4. Draw the graph of the output taken and verify.

DIAGRAM:

MODEL GRAPH:

RESULT:Thus the pulse width modulation and demodulation is performed using trainer kit and output is verified.

PULSE POSITION MODULATIONAim:

To design and test a PPM generator circuit.

Apparatus Required:

IC 555

-1No

Resistor (39K(, 3.9k()

-Each 1No

Capacitor (0.01F)

-1No

AFO with dc shift (0-1MHz)

-1No

DSO(Digital Storage Oscilloscope-1No

Connecting wires and breadboard

Design for astable: T = 0.565ms

TON = TOFF = 0.2825 ms

TLOW =0.69RBC

0.2825ms =0.69 x RB x 0.01FRB = 0.2825 ms 0.69 x 0.01 F

RB = 39 K

THIGH = 0.69 ( RA+RB)C

0.2825 ms = 0.69 x 0.01F( RA+RB)(RA+RB) = 0.2825 ms 0.0069 x 10F

RA = 3.9 K

Theory:

Pulse Position Modulation (PPM):

Pulse position modulation is defined as an analog modulation technique in which the signal is sampled at regular intervals such that the shift in position of each sample is proportional to the instantaneous value of the signal at the sampling instant.

Pulse-Position Modulator:

The Pulse-position modulation can be constructed by applying a modulating signal to pin 5 of a 555 timer connected for astable operation as shown in fig. The output pulse position varies with the modulating signal, since the threshold voltage and hence the time delay is varied.

TABULATION:

Type of signalAmplitude (in V)Time (in ms)

Message Signal

Carrier Signal

Pulse width modulated

signal

Demodulated Signal

RESULT:

Thus the pulse width modulation and demodulation is performed using trainer kit and output is verified.

4. PULSE CODE MODULATIONAIM:

To study and observe the characteristics of PCM by using TDM pulse code modulation trainer kit.

APPARATUS REQUIRED:

S.NO. APPARATUS NAME RANGE QUANTITY

1.TDM pulse code modulation

Trainer kit _ 1

2.Patch chord _ _

3.CRO 30MHZ 1

THEORY:

PCM is the major form of digital pulse modulation. In PCM the two modulation signal is sampled just as in other forms of pulse modulation. The sample amplitude is then converted into a binary code and transmitted as the stream of pulses.

In other forms of PCM , the same amplitude is converted into PAM duration or position however in PCM since. The amplitude must transmitted as a specific number the sample amplitude must be converted into nearest quantum.

PROCEDURE:

1. Patch the circuit as per diagram.

2. Connect the DC voltage to the input of both channel.

3. Select the circuit frequency to 240 KHz.

4. Connect CRO channel 1 to synchronous and channel to the output of PCM.

5. Vary that the input voltage of channel 1 and verify that the output channel of voltage and verify the output appear on next.

DIAGRAM:

MODEL GRAPH:

TABULATION:

SignalAmplitude (in V)_Time (in ms)

Input

Sampled Signal

PCM Signal

Demodulated Signal

RESULT:

Thus the characteristics of PCM is studied and verified.

5. DELTA MODULATION AND ADAPTIVE DELTA MODULATIONAIM: To study and observe the waveform of the delta modulation and demodulation.

APPARATUS REQUIRED:

S.NO.APPARATUS

NAMERANGEQUANTITY

1DM trainerkit - 1

2Patch chord - -

3CRO 30MHZ 1

THEORY:

Delta modulation transmits one bit per sample. That is present sample value is compared with the previous sample value and the indication whether the amplitude is increased or decreased is sent. The step size is fixed. The transmitter and receiver implementation is very much simple for deltamodlation.

In deltamodlation dis advantage are slope overload distortion and granular noise.PROCEDURE:

1. Connect the main supply and make connection as per circuit diagram.

2. Ensure that the clock frequency selection switched A and B are in A=0, B=0.

3. Ensure that the integration block 142 switched are in following position.

4. Turn on the trainer kit and connect 250Hz sine wave signal from the function generator to the input of comparator.

5. The output of the comparator is given to a bistable circuit and clock input is applied to the clock generator 6. Then plot the waveform.

DIAGRAM:

MODEL GRAPH:

TABULATION:Type of signalAmplitude (in V)Time (in ms)

Message Signal

Integrator output

Delta modulated

signal

Delta demodulated

Signal

RESULT:

Thus the delta modulation and adaptive delta modulation was verified successfully.6. DIGITAL MODULATION AND DEMODULATION ASK, PSK, QPSK, FSK (HARDWARE AND MATLAB)

AIM:

To study and observe the waveform of amplitude shift keying, Phase Shift Keying, Quadrature Phase Shift Keying, Frequency Shift Keying.APPARATUS REQUIRED:

S.NO.

APPARATUS

NAME RANGE QUANTITY

1.Data conditioning and carrier modulation

Frame kit _ 1

2.CRO 30MHZ 1

3.Power chord _ _

THEORY:

Amplitude shift keying or ON-OFF keying is the simplest digital modulation technique. In the method, there is only one unit energy carrier and if switched ON or OFF depending upon the input binary sequence. The ASK waveform can be represented as

s(t) = root of (2P3 * cos(2*Pi*Fo*t)

PROCEDURE:

1. Clock input and data input is given to data conditioning frame trainer.

2. Connect NRZ output to modulation input carrier modulation technique.

3. Carrier generators produces two carrier frequencies.

4. Give one of the modulator input carrier frequency to carrier modulation circuit which produces modulated output.

5. Different modulation signals can be generated for different digital input.

DIAGRAM:

CIRCUIT DIAGRAM:

TABULATION:

SignalAmplitude (in V)_Time (in ms)

Carrier

Ask Output

RESULT:

Thus the amplitude shift keying, Phase Shift Keying, Quadrature Phase Shift Keying, Frequency Shift Keying was designed and output is verified successfully.

7. DESIGNINIG, ASSEMBLING AND TESTING OF PREEMPHASIS/ DEEMPHASIS CIRCUITSAIM:

To study the characteristics of pre-emphasis and de-emphasis.APPARATUS REQUIRED:

S.NO .APPARATUS

NAMERANGEQUNNTITY

1AFO1

2Resister15K ,22KEACH 1

3IC 7411

4CRO30 MHZ1

5RPS(0-30V)1

6Capacitor0.1MF1

THEORY: PRE-EMPHASIS:

This circuit is in 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 impedenceof the collector voltage increase. If the signal frequency is lower then impedence decrease which increase the collector current and hence decrease the voltage.

DE-EMPHASIS:

The circuit is placed at the receiving side. It acts as a low pass fillter. The boosting gain for higher frequency signal in the circuit transmitting side is done by the pre-emphasis circuit is filtered to the same value by the low pass fillter. The cut off frequency is given by the formula

Fo =1/2PRC where R=2PFcL

L=1/2piPF Assume R=10k, c=0.01MF

PROCEDURE:1. The circuit connections are made as shown in the circuit diagram for pre-emphasis and de-emphasis.

2. As power supply of 10v is given to the circuit.

3. For a constant value of input voltage the values of the frequency is varied and output is noted in the CRO.

4. A graph is plotted between gain and frequency.

5. The cut off frequency and predicted values of cut off frequency are found compared and verifide.

DIAGRAM (PRE-EMPHASIS):

DIAGRAM (DE-EMPHASIS):

TABULATION:

DE-EMPHASISFrequency (in Hz)VO (in V)VO/VINNormalised Gain

2olog(VO/VIN)

TABULATION: PRE-EMPHASISFrequency (in Hz)VO (in V)VO/VINNormalised Gain

2olog(VO/VIN)

RESULT: Thus the characteristics of pre-emphasis and de-emphasis was studied successfully.

8. PLL AND FREQUENCY SYNTHESIZER

AIM:

To test the characteristics of frequency Synthesis using PLL.

APPARATUS REQUIRED:

S .NO. APPRATUS NAME

RANGE QUANTITY

1. PLL Trainer Kit _ 1

2. CRO 30MHZ _

3. Power chord _ _

THEORY:

PLL is basically a closed loop feedback system. Action of the PLL is to lock the output frequency and phase to the frequency and phase of the input signal lock range. The input signal frequency over which the loop can maintain the lock is called PULL IN TIME.

This depends on the lock initial pulse and frequency difference between two signals as well as on the loop gain and filter characteristics.

PROCEDURE:

1. Switch on the kit and check the power supply .

2. Connections are made as per the circuit diagram.

3. Connect the CRO with the output of the IC 4046.

4. Observe the waveform and plot the graph.

DIAGRAM:

MODELGRAPH:

TABULATION:

SignalAmplitude (in V)_Time (in ms)

Input

Output

RESULT:

Hence the characteristics of frequency synthesis is successfully studied using phase locked loop.

9. LINE CODING

AIM :

To study different line coding techniques.

Apparatus Required:

1. Communication trainer kit: DCL-005

2. Multi Output Power Supply.

3. Patch cords.

4. DSO (Digital Storage Oscilloscope)

THEORY:

We need to represent PCM binary digits by electrical pulses in order to transmit them through a base band channel.

The most commonly used PCM popular data formats are being realized here.

1. Non Return To Zero signals:

These are easiest data formats that can be generated. They are called Non-return to zero because the signals do not return to zero with the clock. The frequency components associated with these signals are half of the clock frequency. The following data formats come under this category.

a. Non-return to zero LEVELNRZ L

b. Non-return to zero MARK NRZ M

C. Non-return to zero SPACENRZ S

a. Non-return to zero LEVEL coding (NRZ L)

This is the most extensively used waveform in digital logics. The data format is very simple where all 1s are represented by high and all 0s are represented by lows. The data format is directly got at the output of all digital data generation logics and hence very easy to generate. Here all the transistors take place at the rising edge of the clock.

b. Non-return to zero MARK coding (NRZ M)

This waveform is extensively used in magnetic tape recording. In this data format, all ones are marked by change in levels and all zeros by no transitions., and the transitions take place at the rising edge of the clock.

74LS08

NRZ L NRZ-M

clock CP Q

AND gate 1 D Q

Delay flipflop

1 0 1 1 0 0 0 1 1 0 1

+v

-v NRZ -L

+v NRZ -M

-v

c. Non-return to zero SPACE coding (NRZ-S ):This type of waveform is marked by change in levels for zeros and no transition of for ones and the transition take place at the rising edge of the clock. This format is also used in magnetic tape recording

NRZ- L NRZ- L*

74 LS 08 74 LS 74

NRZ-L*

Cp Q NRZ-S

Clock 1

And gate

D Q

Delay flip flop

1 0 1 1 0 0 0 1 1 0 1

+v

-v NRZ - L

+v NRZ -S

-v

.2) Return To Zero Signals:

These signals are called Return to zero signals, since they return to zero with the clock. In this category, only one data format, i.e., the unipolar return to zero (URZ) signal is discussed in DCL-005 and DCL-006.

a. Unipolar Return to zero coding (URZ) :

With the URZ, a one is represented by a half bit wide pulse and a zero is represented by the absence of a pulse.

NRZ-L URZ

Clock

1 0 1 1 0 0 0 1 1 0 1

+v NRZ -L

-v

+v

URZ

0v

3) Biphase Signals (Phase Encoded Signals) :

a) BiPhase LEVEL (Manchester Coding)

b) Biphase MARK and

c) Biphase Space Signals

These schemes are used in magnetic recording, optical communications and in satellite telemetry links. This phase encoded signals are special in the sense that they are composed of both the in phase and out-of-phase components of the clock.

a. Manchester Coding (Biphase L):

With the Biphase L, a one is represented by a half bit wide pulse positioned during the first half of the bit interval and a zero, is represented by a half bit wide pulse positioned during the second half of the bit interval.

X-OR Inverter

NRZ -L

Biphase- L

Clock

1 0 1 1 0 0 0 1 1 0 1

+v

-v NRZ - L

+v

-v Bi-phase - L b. Biphase Mark Coding (Biphase M):

With the Biphase M, a transition occurs at the beginning of every bit interval. A one is represented by a second transition, one half bit later whereas a zero has no second transition.

74 LS 08 2

NRZ - L Cp Q BiPhase- M

Clock

1 Clk/2

Clock* D Q

Delay flip-flop

74 LS 393

Clock* 2Q0 Clk/2

Binary ripple counter

+v 1 0 1 1 0 0 0 1 1 0 1

NRZ -L

-v

+v

Bi-phase - M

-v

c. Bi-Phase Space coding (Biphase S):

With a Biphase S also a transition occurs at the beginning of every bit interval. A zero is marked by a second transition, one half bit later, where as a one has no second transition. 74 LS 08

NRZ - L

Cp Q Bi phase- S Clock

Clk/2

And gate1

D Q

Delay flip flop +v 1 0 1 1 0 0 0 1 1 0 1

NRZ - L

-v

+v

Bi-phase - S

-v

4 Multi level signals:

Multilevel signals use three or more levels of voltages to represent the binary digits, ones and zeros instead of the normal highs and lows.

Return to zero Alternate Mark Inversion (RZ-AMI) is the most commonly used multilevel signal and under the category of multilevel signal .Return to zero Alternate Mark Inversion Coding (RZ-AMI):

This coding scheme is most often used in telemetry systems. This scheme comes under both the category of return to zero scheme and multilevel scheme. The ones are represented by pulse width of half the bit duration existing in the alternate direction whereas zeros are represented by absence of the pulse. 74 LS 08 74 LS 74

NRZ - L OUT-1

Clock Cp Q

OUT-2

And gate

D Q

Delay flip flop

OUT-1

OUT-3

OUT-4

OUT-2

CD 4051(Analog MUX)

A1 A

A0 E

S2

-5V A2

OUT-3 OUT-4

PROCEDURE:

1.Give the connections as per the experimental set up.

2.Observe the clock signal & the data and measure them.

3.Observe the standard data & the coded data formats and verify with the known formats.

Result:

Thus different coding techniques are studied.

10. ERROR CONTROL CODING USING MATLABAIM:

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

ALGORITHM:

1.Get the input binary sequence.

2.Calculate the redundancy bits for the corresponding 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.

11. SAMPLING AND TIME DIVISION MULTIPLEXINGAIM:

To obtain the sampled version of given analog signal using operational amplifier and draw the spectrum.

APPARATUS REQUIRED:

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.

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.

CIRCUIT DIAGRAM:

RESULT:

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

12. FREQUENCY DIVISION MULTIPLEXINGAIM:

To model a FDM system using the Communication Trainer KitEquipment Emona Telecoms-Trainer 101 (plus power-pack)

Dual-channel 20MHZ oscilloscope

Two Emona Telecoms-Trainer 101 oscilloscope leads

Assorted Emona Telecoms-Trainer 101 patch leads

One set of headphones(stereo)

Procedure 1. Set up a single channel PCM communication System

2. Activate the PCM Encoder and Decoder Modules.

3. Transmit two signals to model a TDM system

Setting up the PCM encoding decoding scheme 1. Locate the VCO module and turn its Gain control fully anti-clockwise.

2. Turn the VCO modules Frequency Adjust control fully anti-clockwise.

3. Set the VCO modules Range control to the LO position.

4. Connect the set-up shown

5.Adjust the VCO modules Frequency Adjust control to obtain a 3kHz sine wave.

6. Locate the Tunable Low-pass filter module and set its Gain to about the middle of its travel.

7. Adjust the Tunable Low-pass Filter modules Cut-off Frequency control for the highest cut-off frequency.

8. Set the PCM Encoder modules Mode switch to the PCM position.

9. Connect the set-up shown

This set-up can be represented by the block diagram shown. The VCO module is used to produce a 3kHz sinewave message signal for the PCM Encoder module. The PCM Encoder module converts the message signal to a sampled version of the original signal. The tunable Low-pass Filter module is a reconstruction filter (also known as an anti-alias filter).to recover the message on the decoders output.

10. Set the scopes Mode control to the DUAL position to view the signal on the reconstruction filters output (that is, the Tunable Low-pass Filter modules output) as well as the message.

Result The Time Division Multiplexing System was studied from the Communication Trainer Kit.

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