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INDEX
S.No Date NAME OF THE EXPERIMENT Marks Sign
1 Amplitude modulation & demodulation
2 Frequency modulation & demodulation
3 Pulse Amplitude modulation & demodulation
4 Radio Receiver measurements-Sensitivity, Selectivity & Fidelity
5 Measurement of half power beam width (HPBW) and gain of a half
wave dipole antenna.
6 Measurement of radiation pattern of a loop antenna in principal
planes.
7 Time division multiplexing
8 Pulse code modulation
9 Delta modulation
10 Frequency shift keying
11 QPSK modulation & demodulation
12 Differential phase shift keying
13 Time division multiplexing using MAT LAB
14 Pulse code modulation using MAT LAB
15 Delta modulation using MAT LAB
16 Frequency shift keying using MAT LAB
17 QPSK modulation & demodulation using MAT LAB
18 Differential phase shift keying using MAT LAB
ANALOG & DIGITAL COMMNICATIONS LAB III YEAR I SEM
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1. AMPLITUDE MODULATION & DEMODULATION
Aim:
1. To generate amplitude modulated wave and determine the percentage modulation.
2. To Demodulate the modulated wave using envelope detector
Apparatus:
1. Amplitude Modulation & Demodulation trainer Kit
2. Dual trace oscilloscope
3. Patch cords.
Theory:
Amplitude Modulation is a process in which the amplitude of the carrier wave c(t) is
varied linearly with the instantaneous amplitude of the message signal m(t).The standard Form
of amplitude modulated (AM) wave is defined by
s(t)= Ac(1+ Ka m(t) cos 2πfct)
Where Ka is a constant called the amplitude sensitivity of the modulator.
The demodulation circuit is used to recover the message signal from the incoming AM
wave at the receiver. An envelope detector is a simple and yet highly effective device that is
well suited for the demodulation of AM wave, for which the percentage modulation is less than
100%.Ideally, an envelope detector produces an output signal that follows the envelop of the
input signal wave form exactly; hence, the name. Some version of this circuit is used in almost
all commercial AM radio receivers.
The Modulation Index is defined as, m=
Where Emax and Emin are the maximum and minimum amplitudes of the modulated wave.
.
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Procedure:
1. As the circuitry is already wired you just have to trace the circuit according to the circuit
diagram given
2. Connect trainer to the mains and switch ON the power supply
3. Measure the output voltages of regulated power supply circuit that is ,+12v and -12v.
4. Observe output of RF and AF signal generator using CRO .Note that RF voltage is
approximately 300mv pp of 1 MHZ frequency and AF voltage is 10 v pp of 2 KHZ frequency.
Modulator
1. Now connect RF and AF signals to the respective inputs of modulator.
2. Initially set both the signals at Zero level.
3. Connect one of the input of oscilloscope to modulator output and other input to AF
signal
4. Adjust RF signal amplitude with the help of potentiometer so that output of the
modulator is nil pp by keeping AF signal at zero level
5. Now vary the amplitude of AF signal and observe the amplitude modulated wave at
output. Note the percentage of modulation for different values of AF signal.
Percentage of modulation can be calculated by below formula
% modulation =
Demodulator:
1. Now connect the modulator output to the demodulator input
2. Observe demodulated signal at output of modulator at approximately 50 % modulation
using oscilloscope
3. Compare it with the original AF signal.( Note only wave shape ,amplitude will be
attenuated ,phase may change)
4. Find the detected signal is same as the AF signal applied.Thus no information is lost in
the process of modulation.
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If you want to observe AM wave at different frequencies then connect AF signal from external
signal generator to the modulator and observe amplitude modulated wave at different
frequencies.
Waveforms:
Result:
Viva -Voice
1. Define AM and draw its spectrum?
2. Give the significance of modulation index?
3. What are the different degrees of modulation?
4. What are the limitations of square law modulator?
5. Compare linear and nonlinear modulators?
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2. FREQUENCY MODULATION AND DEMODULATION
Aim:
1. To generate frequency modulated signal and determine the modulation index and
bandwidth for various values of amplitude and frequency of modulating signal.
2. To demodulate a Frequency Modulated signal using FM detector.
Apparatus:
1. Frequency Modulation & Demodulation ACLT002 trainer kit
2. Dual trace oscilloscope
3. Patch cords
Theory: The process, in which the frequency of the carrier is varied in accordance with the
instantaneous amplitude of the modulating signal is called “Frequency Modulation”.
The FM signal is expressed as
S (t) =Ac sin (2πfct+β Sin (2πfmt)
Where Ac is amplitude of the carrier signal, fc is the carrier frequency,β is the modulation index
of the FM wave.
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Procedure:
1. As the circuitry is already wired you just have to trace the circuit according to the circuit
diagram given
2. Connect trainer to the mains and switch ON the power supply
3. Measure the output voltages of regulated power supply circuit that is ,+15v and -15v,
+5v and -5v
4. Observe output of AF signal generator using CRO .Note that AF voltage is approximately
20v pp of 500KHZ & 5KHZ frequency.(Switch is provided to change the frequency )
Modulation:
1. Connect the patch cord SO1 AF output to Modulating signal input SO2.
2. Connect ground to ground SG1 to SG2.
3. Vary the modulation POT
4. Observe the FM output on SO4 or TP4
Demodulation:
1. Connect the patch cords from SO4 to SO5
2. Connect the patch cords from GND to GND
3. Observe the Demodulation output at SO6 or TP6
Tabular columns:
Modulating signal Modulated signal Demodulated signal
Amplitude
Time period
frequency
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Waveforms:
Result:
Viva –Voice:
1. Define FM & PM.
2. What are the advantages of Angle modulation over amplitude modulation?
3. What is the relationship between PM and FM?
4. With a neat block diagram explain how PM is generated using FM.
5. What is broadcasting range of FM
ANALOG & DIGITAL COMMNICATIONS LAB III YEAR I SEM
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3. PULSE AMPLITUDE MODULATION & DEMODULATION
Aim: To generate the Pulse Amplitude modulated and demodulated signals.
pparatus:
1. Pulse amplitude Modulation & Demodulation trainer kit
2. Dual trace Oscilloscope
3. Patch cords
Theory:
In Flat top sampling, the amplitude of the samples remain constant at an instant of time unlike
in natural sampling where the amplitude of the samples vary in accordance with the amplitude
of the input signal that is to be sampled.
The generation of flat top samples involves two stages as shown in the figure given below.
Single polarity Flat-top samples
For generating the flat top samples, the signal to be sampled is first fed to a Sample and hold
amplifier which generates the staircase waveform as represented in the above graph at the point
D. The sampling clock selected determines the hold period of the S/H waveform.
The resulting waveform is then passed on to a electronic switch (sampler), which latches the
samples of the S/H waveform for the period determined by the duty cycle of the input sampling
clock. The resulting samples are flat-topped corresponding to the flat portions of the input S/H
wave.
Analog S/H o/p
Signal Flat-top
Samples
Sampling clock
Sample & Hold Switch
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Circuit Diagram:
Modulation
Demodulation:
E1 E B1 B2
B2 B F1 Phase
Adjust
VR8
B F1
B2 Phase
Adjust
PAM
Modulator Demodulator
( S & H)
Amplifier
LPF
Fc =3.4KHz
Switch to Natural
A1 A2 C
E1
PAM
C
VR3
Pulse width
Natural PAM generator
1
KHz
2
KHz
Signa
l
Sourc
e
PAM
Modulator
&
Transmitt
er
4 KHz
8 KHz
16 KHz
32 KHz
Switch
Samplin
g
Frequen
cy
0.5+1+
2
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Procedure:
Modulation
1. Connect signal source 1 KHz (A1) to (A) as shown in the interconnection diagram with
the help of the patch cords given.
2. Select sampling frequency to 8 KHz
3. Select natural sampling by pushing the switch to the extreme left as shown in the figure
4. Adjust pulse width potentiometer to extreme anti clockwise
5. Connect the oscilloscope with the input analog signal A1 and with the PAM modulator
output E1.
Observations:
1. The PAM modulator output will be a product of input analog signal and regularly
spaced pulse train.
2. Note the pulse width of PAM and by varying the pulse width potentiometer, record
the pulse width of PAM
3. Determine the minimum and maximum duty cycle of pulse
4. Determine the minimum and maximum duty cycle of pulse at 4 KHz, 16 KHz and 32
KHz.
5. Repeat the above experiment by connecting 2 KHz (A2) to (A)
Demodulation
1. Connect the signal source 1 KHz (A1) to (A), PAM output (E1) to receiver input (E) and
PAM demodulator output (B2) to LPF input (B).
2. Select sampling frequency to 8 KHz
3. Select flat sampling
4. Connect the oscilloscope with the signal B1 and sampling pulse regenerator output G.
Observations:
1. Observe the relative position of PAM pulses and sampling pulses.
2. Record the PAM demodulator output at B2.
3. Vary the phase adjust potentiometer gradually till the sampling pulses are in middle of
PAM pulses
4. Record the PAM demodulator output at B2, which will be a step signal.
5. Observe the reconstructed output at F1.
6. Vary the pulse width of PAM pulses and observe the reconstructed output at F1
7. Repeat the above procedure at other sampling frequencies
8. Explain the distortion if the sampling frequency is 4 KHz.
N O TE: For phase adjust at 16 & 32 KHz vary the potentiometer VR11
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Modulated Wave forms:
Demodulation Waveforms
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Result:
Viva –Voice:
1. Explain the modulation circuit operation?
2. Explain the demodulation circuit operation?
3. Is PAM & Demodulation is sensitive to Noise?
4. What is cross talk in the context of time division multiplexing?
5. Which is better, natural sampling or flat topped sampling and why?
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4. Radio receiver measurements –sensitivity selectivity and Ffidelity
AIM: To transmit a modulating signal after frequency modulation using VCT-12 and receive
the signal back after demodulating using VCT-13
APPARATUS REQUIRED:
1. VCT-12 trainer kit
2. VCT-13 trainer kit
3. CRO
4. Patch cards
HARDWARE DESCRIPTION OF FM TRANSMITTER TRAINER VCT-12:
The FM transmitter trainer kit VCT-12 has the following section:
1. On-board sine wave generator
2. MIC pre amplifier with a socket for external dynamic MIC
3. Audio amplifier for amplification of low level external input signal
4. Frequency modulation
5. Telescopic whip antenna
SINE WAVE GENERATOR:
A sine wave generator acts as an on board modulating signal source and generates an
audio frequency sine wave .The amplitude of this sine wave generator varies from 0-5 V.
However the output voltage from this source is controlled using a Trim pot to get an output
signal in the range of 0-3V.The frequency of the signal varies from 300Hz to 15KHz.Since the
amplitude of the source is large enough to modulate the carrier it need not be amplified ,instead
it can be directly connected to the input of the amplitude modulator .
MIC PRE AMPLIFIER:
The MIC pre amplifier is capable of accurately amplifying even a very low level signal,
picked up by the MIC to the required level to modulate the carrier. This section has a EP socket
at its input stage where, in an external dynamic MIC can be plugged in the gain of the
stage can be controlled by the user by adjusting the potentiometer Pot4.The maximum gain of
this stage can be achieved in this is 200.The maximum level of the input signal to this amplifier,
so as to produce an amplified output without saturation is 60mV.
AUDIO AMPLIFIER:
The audio amplifier stage has a BJT common emitter configuration. This audio amplifier
can be used to amplify any lower level external modulating signal whose voltage level is below
100mV.The gain of this stage can also be controlled by the user by varying the pot meter POT-
5.The maximum gain of this audio amplifier is 10.
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FREQUENCY MODULATION:
The frequency modulator circuit is constructed around a BF495, high frequency small
signal BJT. The collector circuit of the transistor consists of a tank circuit formed by a inductor
and capacitor. This tank circuit together with the transistor acts as an oscillator and produces the
carrier frequency .The transistor circuit appears to the oscillator as a variable capacitance. This
capacitance adds to the capacitance of the oscillator-tuned circuit.
The size of this capacitance depends on the change in the collector current which occurs
for a given change in base voltage and this is determined by the Trans conductance of the
transistor .The transistor trans conductance depends on the bias voltage applied to the transistor
base. The larger the bias voltage, the larger the value of gm and the larger the value of gm and
the larger capacitance which is added to the capacitance of the oscillator tuned circuit
consequently the transistor circuit behaves as a voltage variable capacitance .The bias voltage
applied to the transistor base determines the overall capacitance seen by the oscillator and hence
the frequency of the carrier. This resulting in FM signal
TELSCOPIC WHIP ANTENNA:
A telescopic whip antenna is used to radiate the AM signal generated by the amplitude
modulator.
HARDWARE DESCRIPTION OF FM RECEVIER TRAINER
The FM receiver trainer VCT-13 has the following sections
1. FM super heterodyne receiver
2. Buffer and filter
3. Audio power amplifier
FM SUPER HETERODYNE RECEIVER:
The FM receiver is built with the dedicated FM receiver IC-CXA1619IC consists of the
following sections namely RF amplifier ,Mixer and oscillator , IF amplifier and quadrature
detector .The circuit details and the description of IC-CXA1619IC are given in appendix
BUFFER AND FILTER:
A buffer is used to prevent any loading to the previous stage .The filter section consists
of a BPF with a Pass band to 20KHZ –15MHZ.A notch filter is also included to eliminate the
50Hz power supply noise
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AUDIO POWER AMPLIFIER:
The Audio power amplifier is constructed using ICTBA810 to increase the power
level of the demodulated message signal to the required level. The gain of this amplifier can be
adjusted by the user by varying the pot meter POT-1.the maximum gain of this audio amplifier
is 25. The amplified signal can be given to a loud signal which can be extremely plugged into
the VCT-13 trainer
FM Transmitter:
Message signal Antenna
FM Receiver:
PROCEDURE:
1. The circuit wiring is done as shown in diagram
2. A modulating signal input given to the Frequency modulator can also be given
From a external function generator or an AFO.
3. If an external signal source with every low voltage level is used then this signal
Audio Oscillator
Output Amplifier FM Modulator
Carrier generator
RF Amplifier
AF Amplifier Discriminator Local
Oscillator
Mixer IF amplifier
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Can be amplified using the audio amplifier before connecting to the input of the
FM modulator
4. Now increase the amplitude of the modulated signal to the required level.
5. The amplitude and the time duration of the modulating signal are observed
Using CRO.
6. The amplitude and time duration of the modulated signal are observed using a CRO and
tabulated
7. The final demodulated signal is viewed using a CRO Also the amplitude and
time duration of the demodulated wave are noted down.
TABULATION:
Wave form Amplitude(V) Time Period(ms) Frequency(Hz)
Modulating Signal
Demodulated Signal
RESULT:
Viva –Voice:
1. Define Sensitivity, Selectivity & Fidelity?
2. What is modulation & Demodulation?
3. What is the range of voice & audio?
4. What is broadcasting range of FM?
5. What is broadcasting range of AM?
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5. Measurement of half power beam width (HPBW) and gain of a half wave
dipole antenna
AIM: To Study & measure half power width and gain of a half wave
dipole antenna
Apparatus:
1. Gunn oscillator 737 0
2. 1 Isolator 737 06
3. 1 Pin Modulator 737 05
4. 1 Large Horn Antenna 737 21
5. 2 RF cable, L = 1 m 501 02
6. 2 Supports for waveguide components 737 15
7. 2 Stand base MF 301 21
8. 1 Set of microwave absorbers 737 390
9. 1 Set of 10 thumb screws M4 737 399
10. 1 Remote control for rotating antenna platform 737 401
11. 1 Dipole antenna kit 737 410
Theory:
The half wave dipole is perhaps the simplest and most fundamental antenna design possible.
Hertz used a dipole antenna during his initial radio experimentation. This is why a dipole is
often referred to as the “hertz dipole” antenna. The dipole is so practical that it is utilized (in
some form) in at least half of all antenna systems used today. Here are some key principles of
the dipole antenna:
1.) A dipole antenna is a wire or conducting element whose length is half the transmitting
wavelength. To calculate the length of a half wave dipole in free space, one may use the
following equation: length (ft) = 492 / frequency (MHz).
The half-wave dipole antenna is just a special case of the dipole antenna, but its important
enough that it will have its own section. Note that the "half-wave" term means that the length of
this dipole antenna is equal to a half-wavelength at the frequency of operation. To make it
crystal clear, if the antenna is to radiate at 600 MHz, what size should the half-wavelength
dipole .One wavelength at 600 MHz is = c / f = 0.5 meters. Hence, the half-wavelength
dipole antenna's length is 0.25 meters.
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Radiation pattern of half wave dipole
Block Diagram
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Procedure:
1. Arrange the setup as given in the block diagram
2. Mount Half wave dipole antenna on the transmitter mask
3. Bring the detector assembly near to main and adjust the height of both transmitting and
receiving antenna
4. Keep Detector assembly away from the main unit approximately 1.5 meter and align both of
them .Ensure that there is no reflector sort things in the vicinity of the experiment such as a
steel structure ,pipes, cables etc.
5. Keep the RF level and FS adjust to minimum and unidirectional coupler switch to
FWD(Forward adjustment knob).
6. Keep detector level control in the center approximately
7. Increase RF level gradually and see that there is deflection in the detector meter
8. Adjust RF level and detector level, so that the deflection in detector meter is approximately
30-35mA.
9. Align arrow mark on the disk with zero of the goniometer scale
10. Start taking the reading at the interval of 10 degree, and note the deflection on the detector
assembly.
11. Using conversion chart convert mA readings into db.
12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dBs
Tabular column :
S.No Angle in degrees Detector readings in mA Gain In db
Result:
Viva-Voice:
1. Define half wave dipole.
2. Draw the radiation pattern of half wave dipole antenna.
3. Give the application of half wave dipole antenna.
4. Write the frequency range of RF signal
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6. Measurement of radiation pattern of a loop antenna in principal planes
AIM: To Study the radiation pattern of loop antenna in principal planes
Apparatus:
1. Gunn oscillator 737 0
2. 1 Isolator 737 06
3. 1 Pin Modulator 737 05
4. 1 Large Horn Antenna 737 21
5. 2 RF cable, L = 1 m 501 02
6. 2 Supports for waveguide components 737 15
7. 2 Stand base MF 301 21
8. 1 Set of microwave absorbers 737 390
9. 1 Set of 10 thumb screws M4 737 399
10. 1 Remote control for rotating antenna platform 737 401
11. 1 Loop antenna kit 737 410
Theory:
A loop antenna is a radio antenna consisting of a loop (or loops) of wire, tubing, or other
electrical conductor with its ends connected to a balanced transmission line. Within this
physical description there are two very distinct antenna designs: the small loop (or magnetic
loop) with a size much smaller than a wavelength, and the resonant loop antenna with a
circumference approximately equal to the wavelength.
Small loops have a poor efficiency and are mainly used as receiving antennas at low
frequencies. Except for car radios, almost every AM broadcast receiver sold has such an
antenna built inside it or directly attached to it. These antennas are also used for radio direction
finding. In amateur radio, loop antennas are often used for low profile operating where larger
antennas would be inconvenient, unsightly, or banned. Loop antennas are relatively easy to
build.
A small loop antenna, also known as a magnetic loop, generally has a circumference of less than
one tenth of a wavelength, in which case there will be a relatively constant current distribution
along the conductor
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Block Diagram
Procedure:
1. Arrange the setup as given in the block diagram
2. Mount Loop antenna on the transmitter mask
3. Bring the detector assembly near to main and adjust the height of both transmitting and
receiving antenna
4. Keep Detector assembly away from the main unit approximately 1.5 meter and align both of
them .Ensure that there is no reflector sort things in the vicinity of the experiment such as a
steel structure ,pipes, cables etc.
5. Keep the RF level and FS adjust to minimum and unidirectional coupler switch to FWD
(Forward adjustment knob).
6. Keep detector level control in the center approximately
7. Increase RF level gradually and see that there is deflection in the detector meter
8. Adjust RF level and detector level, so that the deflection in detector meter is approximately
30-35mA.
9. Align arrow mark on the disk with zero of the goniometer scale
10. Start taking the reading at the interval of 10 degree, and note the deflection on the detector
assembly.
11. Using conversion chart convert mA readings into db.
12. Plot the polar graph in degrees of rotation of antenna against level in the detector in dBs
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Tabular column:
S.No Angle in degrees Detector readings in mA Gain In dB
Result:
VIVA-VOICE:
1. Draw the radiation pattern Loop antenna.
2. Give the application of Loop antenna.
3. Write the frequency range of RF signal
4. What is the need of isolator
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1. TIME DIVISION MULTIPLEXING AND DEMULTIPLEXING
Aim: To transmit a multiplexed output of different frequency message signals through single
Channel using TDM system and recover back the original message signals through a
Demultiplexer at receiver end.
Apparatus:
1. TDM trainer kit
2. CRO
3. Patch cords
4. Probes
Theory:
One of the richest benefits unearthed from Sampling is the concept of Time Division
Multiplexing. In Time Division Multiplexing, use is made of the fact that narrow pulses with
wide spaces between them can be used by signals from other sources. More ever, although the
spaces are relatively fixed in width, pulses may be made as narrow as desired, thus permitting
the generation of high-level hierarchies. Four input signals, all band limited to FS by the input
filters, are sequentially sampled at the transmitter by a rotary switch or commutator. The switch
makes FS revolutions per second and extracts one sample form each input during each
revolution.
The output at the switch is a PAM waveform-containing sample of the input signals
periodically interlaced in time. The samples from adjacent input message channels are separated
by Ts/M, where M is the number of input channels. A set of M pulses consisting of one sample
form each of the M-input channels is called a frame.
Suppose, in a 24 channel, have a sampling rate of 8000 samples per second, 8 bits(256
sampling levels) per sample, and a pulse width of approximately 0.625 S. This means that the
sampling interval is 1/8000 = 0.000125s = 125s, and the period required for each pulse group
is 8 * 0.625 = 5 s. If there was no multiplexing and only one channel was sent, the
transmission would consist of 8000 frames per second, each made up of furious activity during
the first 5 s and nothing at all during the remaining 120s.
This would clearly be wasteful and would represent an unnecessarily complicated
method of encoding a single channel, and so this system exploits the large spaces between the
pulse groups. In fact, each 125 s frame is used to provide 24 adjacent channel time slots, with
the twenty-fifth slot assigned for synchronization.
Each frame consists of 193 bits-24 * 8 for each channel, plus 1 for sync, and since there
are 8000 frames per second; the bit rate is 1.544 Mbits/sec.
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Circuit diagram:
Experimental Procedure:
Multiplexing:
1. Connect the four channel inputs 250 Hz, 500Hz, 1KHz, 2 KHz to the input of transmitter CHO,
CH1, CH2 and CH3 respectively.
2. Observe the Time Division Multiplexed PAM waveform at the output of the Multiplexer (TXD).
3. Observe the four different signals placed in their respective time slots.
4. Vary each of the amplitude of each channel and see the effect on the TDM waveform.
Observation:
1. From the above set up, we can observe that the four different signals are interleaved in their
respective time slots without overlapping each other.
2. Their positions and identification can be highlighted by reducing the other three signal
amplitudes to zero and then gradually increasing them to observe them occupying their positions
Demultiplexing:
1. Connect the four channel inputs 250 Hz, 500Hz, 1KHz, 2 KHz to the input of transmitter
CHO, CH1, CH2 and CH3 respectively
2. Connect TXCLOCK (Transmitter Clock) to RXCLOCK (Receiver Clock).
3. Connect TXCH0 (Transmitter Sync) to RXCH0 (Receiver Sync).
4. Connect the TXD (Transmitter Data) to RXD (Receiver Data).
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5. Observe the multiplexed data at TDX, Transmitter Clock at TXCLOCK and Transmitter
Sync at TXCHO.
6. Observe the Demultiplexed signals at the receiver across the output of fourth order low pass
filter at CHO, CH1,CH2 and CH3 respectively.
Observations:
1. From the above set up, we can observe that the signals are recovered at the receiver
faithfully and are very distinct from each other.
2. By removing the other two lines apart from the TXD, we find that
the reconstructed signals suffer from severe distortion.
Waveforms: (Transmitting Signals)
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Demultiplexed output:
Result
Viva Voice:
1. Define TDM?
2. Distinguish between the two basic multiplexing techniques?
3. In what situation multiplexing is used?
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2. PULSE CODE MODULATION
Aim: To convert an analog signal into a pulse digital signal using PCM system
Apparatus:
1. PCM transmitter trainer.
2. PCM receiver trainer.
3. CRO and connecting wires.
Theory:
Pulse-code Modulation (PCM), like PAM, is a digital communication technique that
sends samples of the analog signal taken at a sufficiently high rate (higher than the Nyquist rate).
In addition, PCM differs than PAM in that it quantizes the samples by constraining them to only
take a limited number of values, and then converts each value into a binary string of bits that are
transmitted on the communication line. Typically, in digital telephony where PCM is widely
used, the sampling rate is 8 kHz (higher than twice the voice band), and the quantization uses
256 levels (i.e., each sample is mapped into an 8-bit PCM code).
In practice, PCM is typically combined with Time Division Multiplexing (TDM), which
is the process of combining many PCM signals representing different messages and transmitting
them over the same channel on a time-sharing basis. Each PCM signal is assigned a timeperiod
called a slot on the transmission line, and slots are arranged in groups called frames.The main
advantages of PCM transmission are: lower cost, ease of multiplexing and switching, and better
noise immunity. Its main disadvantage is the stringent timing and synchronization requirements.
Nowadays, PCM-TDM systems form the backbone for all digital telephony networks worldwide
(refer to your textbooks for more details).
Block diagram:
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Procedure:
1. Connect 500 Hz to CH0 and 1 KHz to CH1
2. Set the speed selection switch to FAST mode
Observation:
1. Connect the scope to CH0 and CH1 for observing the channel input.
2. Connect the scope to observe the sampling clock at TP7 and TP8.
3. Observe the sampling amplifier output at TP12 with respective sampling clock.
The multiplexer output shows the proper alignment of samples in their respective time slots.
Also verify that the amplitude of the samples at any instant of the is equal to the amplitude of the
sampled signals at that instant of time.
Waveforms:
Result:
Viva –Voice:
1. List advantages and disadvantages of digital modulation communication systems.
2. List various steps in pulse code modulation.
3. Discuss the problems associated with quantization
4. What do you mean by band rate?
5. Draw the waveforms of TDM-PCM systems.
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3. DELTA MODULATION AND DEMODULATION
Aim: To transmit an analog message signal in its digital form and again reconstruct back the
original analog message signal at receiver by using Delta modulator.
Apparatus:
1. Delta modulator trainer kit
2. CRO
3. Probes & patch cards
Theory:
DM uses a single bit PCM code to achieve digital transmission of analog signal. With
conventional PCM each code is binary representation of both sign and magnitude of a particular
sample. With DM, rather than transmitting a coded representation of a sample a single bit is
transmitted, which indicates whether the sample is smaller or larger than the previous sample.
The algorithm for a delta modulation system is a simple one. If the current sample is smaller than
the previous sample then logic 0 is transmitted or logic 1 is transmitted if the current sample is
larger than the previous sample. The input analog is sampled and converted to a PAM signal
followed by comparing it with the output of the DAC. The output of the DAC is equal to the
regenerated magnitude of the previous sample which was stored in the up/down counter as a
binary number. The up/down counter is incremented or decremented whether the previous
sample is larger or smaller than the current sample. The up/down counter is clocked at a rate
equal to the sample rate. So, the up/down counter is updated after each comparison.
Block diagram:
Modulator
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Block diagram for demodulator:
Procedure:
Modulator:
1. Connect PLA1 to PLAA.
2. Connect channel 1 to CRO to TPA1/TPAA ; adjust VR1 to minimum to get zero level
signal.
3. Connect channel 1 to TP1 and channel 2 to TPB1 and adjust VR2 to obtain square wave
half the frequency of the clock rate selected (Output at TP1).
4. Connect Channel 1 to TP2 and set voltage/div of channel 1 to mV range and Observe a
triangle waveform, which is output of integrator. It can be observed that as the clock rate
is increased, amplitude of triangle waveform decreases. This is called minimum step size
(Clock rate can be changed by depressing SW1 switch).
5. Connect channel 1 to TPA1/TPAA; adjust VR1 in order to obtain a 1 KHz sinewave of
500 mV pp approximately.
6. Signal approximating 1 KHz is available at the integrator output (TP2); this signals
obtained by integrating the digital output resulting from Delta Modulation.
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7. Connect channel 1 to TP2 and channel 2 to TPB1; it can be observed that the digital high
makes the integrator output to go upwards and digital low makes the integrator output to
go downwards.
8. With an oscilloscope displaying three traces,, it is possible to simultaneously observe the
input signal of the modulation, the digital output of the modulator and the signal obtained
by the integration from the modulator digital output.
9. Notice that, when the output (Feedback signal) is lower than the analog input the digital
output is high, whenever it is low when the analog input is lower than the integrated
output.
10. Increase the amplitude of 1 KHz sinewave by rotating VR1 to1 Vpp and observe that the
integrator output follows the input signal.
11. Increase the amplitude of 1 KHz sinewave further high, and observe that the integrator
output cannot follow the input signal. State the reason.
12. Repeat the above mentioned procedures with different signal sources and selecting
different clock rates and observe the response of the linear Delta Modulator
Demodulator:
1. Prearrange the connections of Linear Delta Modulator.
2. Connect PLB1 (Digital o/p of Delta Modulator) to PLBB (i/p of Linear Delta
Modulator).
3. Connect PLC1 (Linear Delta Demodulator output) to either PLCA (i/p of fourth order
LPF) or PLCB (i/p of second order LPF).
Observations:
Observe the reconstructed output of the forth order LPF at TPD1 and also observet he
out of the second order filter at TPD2.
Waveforms:
Result:
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Viva -Voice
1. What is a Modulator?
2. Define Bit Rate?
3. Explain Delta Modulation Technique?
4. Explain delta sigma Modulation?
5. What are the Applications of Delta modulations?
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4. FREQUENCY SHIFT KEYING
Aim: To generate the frequency shift keying signal for a given binary data and also
demodulate the original data input.
Apparatus:
1. Band Pass modulator and Demodulator trainer kit.
2. C.R.O
3. Patch Cards and probes
Theory:
Communication systems often involve modulation of a carrier, which results, of course, in a
band pass waveform. Radio & Television signals are good examples involving analog messages.
A good example where the message is digital is the modem, a device used to connect a remote
computer terminal to the main computer. The modulation-De modulation apparatus modulates a
carrier with the terminal’s data stream for transmission to the computer (often over telephone
lines) and recovers the data stream sent by the computer via a similar modulation.
Band pass Modulation is the process by which an information signal is converted to a sinusoidal
waveform; for digital modulation, such a sinusoid of duration T is referred to as a digital symbol.
The sinusoid has just three features that can be used to distinguish it from other sinusoids:
amplitude, frequency, and phase. Thus band pass modulation can be defined as the process
whereby the amplitude, frequency, or phase of a RF carrier, or a combination of them, is varied
in accordance with the information to be transmitted. The general form of the carrier wave, C (t),
is as follows:
C(t) = A(t) cos θ(t)
Where A(t) is the time-varying amplitude and θ(t) is the time-varying angle. It is convenient to
write
In this type of modulation, the modulated output shifts between two frequencies for all ‘one’ to
‘zero’ transitions. Let the two carrier frequencies be represented by 1 and 2 and then we have:
M (t)=A (t) cos1t, if the data is ‘one’
=A (t) cos2t, if the data is ‘zero’
where0 is the radian frequency of the carrier and Φ(t) is the phase. The terms f and will each
be used to denote the frequency.
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Block diagram:
Experimental Procedure:
FSK Modulator:
Connect SIN1 to the INPUT-1 of the Modulator
Connect SIN2 to the INPUT-2 of the Modulator
Connect data to the control input of the Modulator
Connect the scope to the Control Input and the other channel to the Modulated output
FSK Demodulator:
Establish the same connections for FSK modulation in DCLT 005
Set DCLT-005 in conjunction with DCLT 005
Connect the FSK Modulated output to the FSK I/P of the FSK Demodulator (DCLT 006)
Connect the scope to the CONTROL INPUT and the DATA OUTPUT
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Observations:
1. Observe the FSK Modulated output and the modulating data in the two channels of the
oscilloscope.
2. Observe the incoming modulated carrier and recovered data with respect to the modulating data.
Waveforms:
.
Result:
Viva Voice:
1. Compare FSK and FM?
2. Compare ASK and FSK?
3. What are the different techniques to demodulate FSK?
4. Define FSK?
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5. QPSK MODULATION AND DEMODULATION
Aim: To generate a QPSK for a given binary digital signal and Observe. Demodulate the same
QPSK to get back the Original digital signal, using carrier receiving circuit and Demodulator.
Components Required: 1.Patch chords ,
2.Signal generator,
3.CRO,
4.Probes
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 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.
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 carrier 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
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Block Diagram:
Model waveforms:
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Tabular Column:
S.No Name of the signal Amplitude in V Time period in Sec Frequency in Hz
1 Modulating Signal
2 Carrier Signal
3 Modulated Signal
4 Demodulated
Signal
Result:
Viva -Voice
1. What is the difference between PSK&QPSK?
2. What is the band width requirement of a QPSK?
3. Explain the operation of QPSK detection?
4. What are the advantages of QPSK?
5. What is meant by differential encoding
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6. DIFFERENTIAL PHASE SHIFT KEYING
Aim: To generate differentially phase shift keying signal and also demodulate the original
Binary data.
Apparatus:
1. DPSK modulation and demodulation trainer kit
2. CRO
3. Patch cards
Theory:
DPSK may be viewed as the non-coherent version of PSK. It eliminates the need for a
coherent reference signal at the receiver by combining two basic operations at the transmitter:
1. Differential encoding of the input binary wave and
2. Phase-Shift Keying hence, the name, differential phase shift keying (DPSK).
In effect to send symbol 0, we phase advance the current signal wave-form by 1800, and
to send symbol 1, we leave the phase of the current signal waveform unchanged. The receiver is
equipped with a storage capability, so that it can measure the relative phase difference between
the waveforms received during two successive bit intervals. Provided that the unknown phase θ
contained in the received wave varies slowly, the phase difference between wave forms received
in two successive bit intervals will be independent of θ.
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Block diagram:
RESET
DPSK
ENCODER
SERIAL DATA
S - CLOCK
DPSK CONTROL
PLL CLOCK FROM DCLT-006 TP12
CLOCK
DIVIDER
DPSK
DECODER DPSK MODULATED DATA FROM DCLT-006
S-DATA WITH ONE BIT DELAY
T6
T5
S6
S5
T7 S7
S10 T10 S15 T15
T13 S13
D
P
SK
M
O
D
D
P
SK
D
E
M
O
D
Data Simulator
s-clock s-data
CARRIER GENERATION LOGIC
SIN1 SIN2* SIN
2 UNIPOLAR TO BI POLAR
BI POLAR TO UNIPOLAR
DATA OUTPUT
MODULATION
CARRIER MODULATION CODING LOGIC
NRZ-
L
NRZ-
M NRZ-S
URZ
BIO-L
BIO-
M BIO-S
AMI
CLOCK
INPUT DATA
GND
INPUT 1
INPUT 2
CONTROL
INPUT
INPUT OUTPUT
INPUT
UNITED ELECTROTECHNOLOGIES DCL - 005
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Procedure: (Modulator)
Establish the connection for DPSK modulation and connect the DCLT 006 in conjunction
with the DCLT- 005 & DCLT-011
Feed the PSK Modulated Output to the PSK I/P of the PSK Demodulator of DCLT 006
Connect the scope to the PSK I/P and the DATA O/P for PSK Demodulated o/p
Observe the PSK Demodulated output w.r.t the control input of the Modulator DCLT-005
Feed the Demodulated DPSK signal to DCLT-011 (S15) and the recovered clock to the
DPSK Decoder at S10.
Connect the Scope to the S-Data of DCLT-005 and Decoded S-Data of DCLT-011
Refer page for connection Diagram.
Observations:
The DPSK modulated output and the Demodulating data using the two channels of the
oscilloscope.
The DPSK Demodulated Data with DPSK Coded Data.
The S-Data with DPSK Decoded Data. (with 1 bit delay)
Wave forms:
Result:
Viva -Voice
1. Explain DPSK Modulation technique?
2. Difference between DPSK & PSK?
3. The Non coherent Version of PSK is known as……
4. Define Modulation?
5. Define Modulation Index?
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DIGITAL COMMUNICATIONS
USING MATLAB
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1. TIME DIVISION MULTIPLEXING Aim: To perform the generation of Time division multiplexing using MATLAB
Apparatus: 1. Hardware Tools: Computer system
2. Software Tool: MATLAB 7.0
Program:
% % % % % % % % % % % % % % % % % % % % % Code for Time Division Multiplexing
clc;
close all;
clear all;
% Signal generation
x=0:.5:4*pi; % siganal taken upto 4pi
sig1=8*sin(x); % generate 1st sinusoidal signal
l=length(sig1);
sig2=8*triang(l); % Generate 2nd traingular Sigal
% Display of Both Signal
subplot(2,2,1);
plot(sig1);
title('Sinusoidal Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
subplot(2,2,2);
plot(sig2);
title('Triangular Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
% Display of Both Sampled Signal
subplot(2,2,3);
stem(sig1);
title('Sampled Sinusoidal Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
subplot(2,2,4);
stem(sig2);
title('Sampled Triangular Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
l1=length(sig1);
l2=length(sig2);
for i=1:l1
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sig(1,i)=sig1(i); % Making Both row vector to a matrix
sig(2,i)=sig2(i);
end
% TDM of both quantize signal
tdmsig=reshape(sig,1,2*l1);
% Display of TDM Signal
figure
stem(tdmsig);
title('TDM Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
% Demultiplexing of TDM Signal
demux=reshape(tdmsig,2,l1);
for i=1:l1
sig3(i)=demux(1,i); % Converting The matrix into row vectors
sig4(i)=demux(2,i);
end
% display of demultiplexed signal
figure
subplot(2,1,1)
plot(sig3);
title('Recovered Sinusoidal Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
subplot(2,1,2)
plot(sig4);
title('Recovered Triangular Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
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OUTPUTS:
0 10 20 30-10
-5
0
5
10Sinusoidal Signal
Am
plit
ude--
->
Time--->
0 10 20 300
2
4
6
8Triangular Signal
Am
plit
ude--
->
Time--->
0 10 20 30-10
-5
0
5
10Sampled Sinusoidal Signal
Am
plit
ude--
->
Time--->
0 10 20 300
2
4
6
8Sampled Triangular Signal
Am
plit
ude--
->
Time--->
0 10 20 30 40 50 60-8
-6
-4
-2
0
2
4
6
8TDM Signal
Am
plit
ude--
->
Time--->
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0 5 10 15 20 25 30-10
-5
0
5
10Recovered Sinusoidal Signal
Am
plit
ude--
->
Time--->
0 5 10 15 20 25 300
2
4
6
8Recovered Triangular Signal
Am
plit
ude--
->
Time--->
Results:
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2. Pulse code modulation
Aim: To perform the generation of Pulse code modulation using MATLAB
Apparatus: 1. Hardware Tools: Computer system
2. Software Tool: MATLAB 7.0
Program :
% % % % % % % % % % % % % % % % % % % % % % Code for Pulse Code
Modulation
clc;
close all;
clear all;
n=input('Enter n value for n-bit PCM system : ');
n1=input('Enter number of samples in a period : ');
L=2^n;
% % Signal Generation
% x=0:1/100:4*pi;
% y=8*sin(x); % Amplitude Of signal is 8v
% subplot(2,2,1);
% plot(x,y);grid on;
% Sampling Operation
x=0:2*pi/n1:4*pi; % n1 nuber of samples have tobe selected
s=8*sin(x);
subplot(3,1,1);
plot(s);
title('Analog Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
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subplot(3,1,2);
stem(s);grid on;
title('Sampled Sinal');
ylabel('Amplitude--->');
xlabel('Time--->');
% Quantization Process
vmax=8;
vmin=-vmax;
del=(vmax-vmin)/L;
part=vmin:del:vmax; % level are between vmin and vmax with difference of del
code=vmin-(del/2):del:vmax+(del/2); % Contaion Quantized valuses
[ind,q]=quantiz(s,part,code); % Quantization process
% ind contain index number and q contain quantized values
l1=length(ind);
l2=length(q);
for i=1:l1
if(ind(i)~=0) % To make index as binary decimal so started from 0 to N
ind(i)=ind(i)-1;
end
i=i+1;
end
for i=1:l2
if(q(i)==vmin-(del/2)) % To make quantize value inbetween the levels
q(i)=vmin+(del/2);
end
end
subplot(3,1,3);
stem(q);grid on; % Display the Quantize values
title('Quantized Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
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% Encoding Process
figure
code=de2bi(ind,'left-msb'); % Cnvert the decimal to binary
k=1;
for i=1:l1
for j=1:n
coded(k)=code(i,j); % convert code matrix to a coded row vector
j=j+1;
k=k+1;
end
i=i+1;
end
subplot(2,1,1); grid on;
stairs(coded); % Display the encoded signal
axis([0 100 -2 3]); title('Encoded Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
% Demodulation Of PCM signal
qunt=reshape(coded,n,length(coded)/n);
index=bi2de(qunt','left-msb'); % Getback the index in decimal form
q=del*index+vmin+(del/2); % getback Quantized values
subplot(2,1,2); grid on;
plot(q); % Plot Demodulated signal
title('Demodulated Signal');
ylabel('Amplitude--->');
xlabel('Time--->');
INPUT:
Enter n value for n-bit PCM system : 5
Enter number of samples in a period : 10
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OUTPUT:
0 5 10 15 20 25-10
0
10Analog Signal
Am
plit
ude--
->
Time--->
0 5 10 15 20 25-10
0
10Sampled Sinal
Am
plit
ude--
->
Time--->
0 5 10 15 20 25-10
0
10Quantized Signal
Am
plit
ude--
->
Time--->
0 10 20 30 40 50 60 70 80 90 100-2
-1
0
1
2
3Encoded Signal
Am
plit
ude--
->
Time--->
0 5 10 15 20 25-10
-5
0
5
10Demodulated Signal
Am
plit
ude--
->
Time--->
Results:
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3. Delta Modulation
Aim: To perform the generation of Delta modulation using MATLAB
Apparatus: 1. Hardware Tools: Computer system
2. Software Tool: MATLAB 7.0
Program:
% DELTA MODULATiON
clc;
clear all;
close all;
a=2;
t=0:2*pi/50:2*pi;
x=a*sin(t);
l=length(x);
plot(x,'r');
delta=0.2;
hold on
xn=0;
for i=1:l;
if x(i)>xn(i)
d(i)=1;
xn(i+1)=xn(i)+delta;
else
d(i)=0; xn(i+1)=xn(i)-delta;
end
end
stairs(xn)
hold on
for i=1:d
if d(i)>xn(i)
d(i)=0;
xn(i+1)=xn(i)-delta;
else
d(i)=1; xn(i+1)=xn(i)+delta
end
end
plot(xn,'c')
legend('Analog signal','Delta modulation','Demodulation')
title('DELTA MODULATION / DEMODULATION ')
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OUTPUT:
0 10 20 30 40 50 60-2
-1.5
-1
-0.5
0
0.5
1
1.5
2DELTA MODULATION / DEMODULATION
Analog signal
Delta modulation
Demodulation
RESULT:
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4.Frequency shift keying
Aim: To perform the generation of Frequency shift keying using MATLAB
Apparatus: 1. Hardware Tools: Computer system
2. Software Tool: MATLAB 7.0
Program:
clc;
close all;
clear all;
x=input('enter the binary input');
l=length(x);
for i=1:1:l
m(((i-1)*100)+1:i*100)=x(i);
end
figure;
subplot(4,1,1);
plot(m);
xlabel('time');
ylabel('amplitude');
title('modulating signal');
f=100;
t=0:(1/f):(l-(1/f));
f1=10;
f2=5;
c1=sin(2*pi*f1*t);
y1=m.*c1;
subplot(4,1,2);
plot(t,y1);
xlabel('time');
ylabel('amplitude');
for j=1:l
if x(j)==1
x(j)=0;
else x(j)=1;
end
m1((j-1)*100+1:j*100)=x(j);
end
c2=sin(2*pi*f2*t);
y2=m1.*c2;
subplot(4,1,3);
plot(t,y2);
xlabel('time');
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ylabel('amplitude');
y=y1+y2;
subplot(4,1,4);
plot(t,y);
xlabel('time');
ylabel('amplitude');
title('FSK modulated wave');
r=randn(size(y));
F=y+r;
figure;
subplot(3,1,1);
plot(F);
xlabel('time');
ylabel('amplitude');
title('noise added FSK signal');
l1=length(F);
t1=0:0.01:.99;
r1=sin(2*pi*f1*t1);
r1=fliplr(r1);
l2=length(r1);
l3=l1+l2-1;
u=fft(F,l3);
v=fft(r1,l3);
k1=u.*v;
k11=ifft(k1,l3);
r2=sin(2*pi*f2*t1);
r2=fliplr(r2);
w=fft(r2,l3);
k2=u.*w;
k22=ifft(k2,l3);
k=k11-k22;
subplot(3,1,2);
plot(k);
xlabel('time');
ylabel('amplitude');
title('correlated signal');
for z=1:l
t(z)=k(z*100);
if t(z)>0
s(z)=1;
else
s(z)=0;
end
end
subplot(3,1,3);
stem(s);
xlabel('time');
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ylabel('amplitude');
title('Demodulated output signal');
INPUT:
Enter the binary input [1 0 0 1 0 1 1]
OUTPUT:
0 100 200 300 400 500 600 7000
0.51
time
am
plit
ude modulating signal
0 1 2 3 4 5 6 7-1
01
time
am
plit
ude
0 1 2 3 4 5 6 7-1
01
time
am
plit
ude
0 1 2 3 4 5 6 7-1
01
time
am
plit
ude FSK modulated wave
0 100 200 300 400 500 600 700-5
0
5
time
am
plit
ude
noise added FSK signal
0 100 200 300 400 500 600 700 800-100
0
100
time
am
plit
ude
correlated signal
1 2 3 4 5 6 70
0.5
1
time
am
plit
ude
Demodulated output signal
RESULT:
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5.QPSK modulation & demodulation
Aim: To perform the generation of QPSK modulation & demodulation using MATLAB
Apparatus: 1. Hardware Tools: Computer system
2. Software Tool: MATLAB 7.0
Program:
clc;
clear all;
close all;
data=[0 1 0 1 1 1 0 0 1 1]; % information
%Number_of_bit=1024;
%data=randint(Number_of_bit,1);
figure(1)
stem(data, 'linewidth',3), grid on;
title(' Information before Transmiting ');
axis([ 0 11 0 1.5]);
data_NZR=2*data-1; % Data Represented at NZR form for QPSK modulation
s_p_data=reshape(data_NZR,2,length(data)/2); % S/P convertion of data
br=10.^6; %Let us transmission bit rate 1000000
f=br; % minimum carrier frequency
T=1/br; % bit duration
t=T/99:T/99:T; % Time vector for one bit information
% XXXXXXXXXXXXXXXXXXXXXXX QPSK modulatio
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
y=[];
y_in=[];
y_qd=[];
for(i=1:length(data)/2)
y1=s_p_data(1,i)*cos(2*pi*f*t); % inphase component
y2=s_p_data(2,i)*sin(2*pi*f*t) ;% Quadrature component
y_in=[y_in y1]; % inphase signal vector
y_qd=[y_qd y2]; %quadrature signal vector
ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL 2015-16
62 | P a g e III YEAR I SEM
y=[y y1+y2]; % modulated signal vector
end
Tx_sig=y; % transmitting signal after modulation
tt=T/99:T/99:(T*length(data))/2;
figure(2)
subplot(3,1,1);
plot(tt,y_in,'linewidth',3), grid on;
title(' wave form for inphase component in QPSK modulation ');
xlabel('time(sec)');
ylabel(' amplitude(volt0');
subplot(3,1,2);
plot(tt,y_qd,'linewidth',3), grid on;
title(' wave form for Quadrature component in QPSK modulation ');
xlabel('time(sec)');
ylabel(' amplitude(volt0');
subplot(3,1,3);
plot(tt,Tx_sig,'r','linewidth',3), grid on;
title('QPSK modulated signal (sum of inphase and Quadrature phase signal)');
xlabel('time(sec)');
ylabel(' amplitude(volt0');
% XXXXXXXXXXXXXXXXXXXXXXXXXXXX QPSK demodulation
XXXXXXXXXXXXXXXXXXXXXXXXXX
Rx_data=[];
Rx_sig=Tx_sig; % Received signal
for(i=1:1:length(data)/2)
%%XXXXXX inphase coherent dector XXXXXXX
Z_in=Rx_sig((i-1)*length(t)+1:i*length(t)).*cos(2*pi*f*t);
% above line indicat multiplication of received & inphase carred signal
Z_in_intg=(trapz(t,Z_in))*(2/T);% integration using trapizodial rull
if(Z_in_intg>0) % Decession Maker
Rx_in_data=1;
else
Rx_in_data=0;
end
%%XXXXXX Quadrature coherent dector XXXXXX
ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL 2015-16
63 | P a g e III YEAR I SEM
Z_qd=Rx_sig((i-1)*length(t)+1:i*length(t)).*sin(2*pi*f*t);
%above line indicat multiplication ofreceived & Quadphase carred signal
Z_qd_intg=(trapz(t,Z_qd))*(2/T);%integration using trapizodial rull
if (Z_qd_intg>0)% Decession Maker
Rx_qd_data=1;
else
Rx_qd_data=0;
end
Rx_data=[Rx_data Rx_in_data Rx_qd_data]; % Received Data vector
end
figure(3)
stem(Rx_data,'linewidth',3)
title('Information after Receiveing ');
axis([ 0 11 0 1.5]), grid on;
% XXXXXXXXXXX end of program XXXXXXXXXX
OUTPUT:
0 1 2 3 4 5 6 7 8 9 10 110
0.5
1
1.5 Information before Transmiting
ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL 2015-16
64 | P a g e III YEAR I SEM
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 10-6
-1
0
1 wave form for inphase component in QPSK modulation
time(sec) a
mplit
ude(v
olt0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 10-6
-1
0
1 wave form for Quadrature component in QPSK modulation
time(sec)
am
plit
ude(v
olt0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
x 10-6
-2
0
2QPSK modulated signal (sum of inphase and Quadrature phase signal)
time(sec)
am
plit
ude(v
olt0
0 1 2 3 4 5 6 7 8 9 10 110
0.5
1
1.5Information after Receiveing
RESULT:
ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL 2015-16
65 | P a g e III YEAR I SEM
6. Differential phase shift keying
Aim: To perform the generation of Differential phase shift keying using MATLAB
Apparatus: 1. Hardware Tools: Computer system
2. Software Tool: MATLAB 7.0
Program :
clear all;close all;clc;
fc=2; % carrier frequency
samp=100;
t=linspace(0,2*pi,samp);
ph1=cos(fc*t);
ph2=-cos(fc*t);
b=mod(randperm(12),2); % The random binary stream
x=0;
nb(1)=not(xor(b(1),0));
for i=2:length(b)+1
nb(i)=not(xor(b(i-1),x));
x=nb(i);
end;
dpsk=[];bin1=[];bin2=[];
for j=1:length(nb)
if nb(j)==0
dpsk=[dpsk,ph1];
bin1=[bin1,zeros(1,samp)];
elseif nb(j)==1
dpsk=[dpsk,ph2];
bin1=[bin1,ones(1,samp)];
end;
end;
for k=1:length(b)
if b(k)==0
bin2=[bin2,zeros(1,samp)];
elseif b(k)==1
bin2=[bin2,ones(1,samp)];
end;
end;
subplot(311),plot(bin2,'r');
axis([0 samp*length(b) -0.2 1.2]);
xlabel('Time index'); ylabel('Amplitude');
title('The random binary Input','FontSize',12);
bn=num2str(b);
ANALOG & DIGITAL COMMUNICATIONS LAB MANUAL 2015-16
66 | P a g e III YEAR I SEM
bx=['The Random binary string is',bn];
gtext(bx,'FontSize',12);
subplot(312),plot(bin1,'LineWidth',1.5);
axis([0 samp*length(nb) -0.2 1.2]);hold on;
xlabel('Time index'); ylabel('Amplitude');
title('The random binary (differential)Input','FontSize',12);
bn=num2str(nb);
bx=['The Differential binary string is',bn];
gtext(bx,'FontSize',12);
subplot(313),plot(dpsk,'LineWidth',1.5);
axis([0 samp*length(nb) -1.2 1.2]);
xlabel('Time index'); ylabel('Amplitude');
title('The simulated DPSK Output','FontSize',12);
OUTPUTS:
0 200 400 600 800 1000 1200
0
0.5
1
Time index
Am
plitu
de
The random binary Input
The Random binary string is0 1 0 0 1 1 0 0 1 1 0 1
0 200 400 600 800 1000 1200
0
0.5
1
Time index
Am
plitu
de
The random binary (differential)Input
The Differential binary string is1 1 1 0 1 1 1 0 1 1 1 0 0
0 200 400 600 800 1000 1200
-1
0
1
Time index
Am
plitu
de
The simulated DPSK Output
Result :