NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.01
AM Modulation and Demodulation
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 1 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - Observe the Modulation and Demodulation of AM Signal.
Apparatus: - CRO, Patch chords, Trainer kit
Theory: AM modulated waveform is in the form.
Fig1.1 Amplitude modulated waveform
This wave is transmitted from transmitter and received by antenna at receiver. To
obtain original signal from the received signal we give this AM- signal as an input
to diode detector. Diode detector follow the envelop of the received signal.
Page 2 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
The original resides in the envelop hence we get the original signal at the out put
of the detector. This can be verified with the help of CRO. The process of
recovering original from modulated signal is called demodulation.
Fig1.2 AM Demodulator
Procedure: 1. Generate AM signal in AM Transmitter Trainer.
2. Connect the output of AM Transmitter to the input of AM Receiver.
3. Observe the Demodulated wave on tp 40,39,38 in AM receiver Trainer.
4. Observe the frequency of the demodulated signal be same as that of the
original signal.
Page 3 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Calculation: - The modulation index of AM wave is determined by
m = Vmax – Vmin / Vmax + Vmin
where
Vmax = maximum amplitude of AM wave
Vmin = minimum amplitude of AM wave
Results: The waveform of AM modulation and Demodulation are trace on CRO.
Precautions:1.
Connect the patch cord properly.
2.
Power cable plugged properly.
3.
Adjust the CRO for tracing the different Waveform.
4.
Check the connection before starting the kit.
Lab Quiz:1. In RF communications, modulation impresses information on which
of the following types of waves?
(A) Carrier wave
(B) Complex wave
(C) Modulated wave
(D) Modulating wave
2. A carrier is amplitude modulated to a depth of40%. The increase in
power is.
(A) 40%
(B) 20%
(C) 16%
Page 4 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(D)
8%
3. The most suitable method for detecting a modulated signal
(2.5+5 cosωmt) cosωct is
A.
Envelope detector
B.
Synchronous detector
C.
Ratio detector
D.
Both A and B
4. An AM wave is given by eAM = 10(1 + 0.4cos103t + 0.3cos104t)cos106t
A.
0.4
B.
0.5
C.
0.3
D.
0.9
5. Following is not the purpose of modulation
A. Multiplexing
B. Effective radiation
C. Narrow banding
D. Increase in signal power
6. Draw the frequency spectrum of Full Am wave.
7. Write the expression of AM wave.
8. What does Fourier Transform do?
9. Write the different type of AM.
10. Write down different type Generation and Detection technique for
AM.
Page 5 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Book: Lab experiment related theory available in following
books:
1. B.P. Lathi : Communication Systems, BS Publication
2. Taub and Schilling : Principles of communication Systems, TMH
3. Singh and Sapre : Communication Systems, TMH
4. S Haykin : Communication Systems, John Wiley and Sons Inc
Page 6 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.2
Generation of DSB-SC AM
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Page 7 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Signature
Name of faculty in-charge:
Name of Technical Assistant:
OBJECT: 1. To study the DSB-SC AM Generation through Balanced Modulator.
2. To observe the DSB-SC AM signals on Oscilloscope and measure its depth of
modulation.
APPARATUS REQUIRED: DBS-SC AM Generation kit, Oscilloscope, Patch chords and BNC Chord
Theory: -
Page 8 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Consider the diagrams below
Fig2.1 (c) is a result of the multiplication (t) cosct 1/2[F(+c)+F(c)]
The function f(t) cosct is Amplitude Modulated .The above signal shows phase reversal
at the zero crossing of envelop. It also observed that impulses at c are missing which
means
a. The carrier term c is suppressed in the spectrum.
b. The base band is present twice in modulated spectrum.The term  (c+m) is
upper side band and the term  (cm) is lower side band .Hence it is known as
Double Side Band- Suppressed Carries Amplitude Modulation system.
BALANCED MODULATORS: -
Page 9 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
In a balanced modulator two non-linear devices are connected in the balanced mode so as
to suppress the carrier wave. Below is the diagram of balanced modulator using two
devices as non-linear elements.
e1 = cosct +f (t)
e2 = cosctf (t)
For non- linear circuits current is given by
I = ae + be2
Hence
I1 = ae1 + be12
= a [cosct+ f (t)] + b[cosct +f(t)]2…………………(1)
and
I2 =ae2 + be22
= a[cosct f(t)] + b[cosct f(t)]2…………………(2)
Voltage at the input of band pass filter is given by
V0 = V1V2 = i1R  i2R
V0 = 2R[af (t) +2bf(t) cosct]
The output of band pass filter centered around c is given by
Output = 2bf(t) cosct
= Kbf (t) cosct…………………………………………………
Equation (3) given DSB-SC signal.
Fig.2.2 Circuit Diagram of BALANCED MODULATOR
Page 10 of 78
(3)
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
PROCEDURE:-
Fig2.3 DSB SC AM TRANSMITTER

Ensure that the following initial conditions exist on the board

AUDIO INPUT SELECT switch in INT position;

MODE switch in DSB position.

Output amplifier gain preset in fully clockwise position.

SPEAKERS switch in OFF position.

Turn the Audio Oscillator blocks Amplitude Preset to its fully clockwise position,
and examine the block output on an oscilloscope. This is audio frequency, which
will be our modulating signal. Its frequency and amplitude can change by oscillator
frequency preset and oscillator amplitude respectively.

Turn the BALANCE preset, in the BALANCED MODULATOR & BANDPASS
FILTER CIRCUIT 1 block, to its fully clockwise position. It is this block that we will
used to perform Double-Side Band Amplitude Modulation.

Monitor, in turn, the two inputs to the BALANCED MODULATOR & BANDPASS
FILTER CIRCUIT 1 block, at t.p. 1 and t.p. 9. Note that:

The signal at t.p. 1 is the audio-frequency sine waveform the AUDIO
OSCILLATOR block. This is the modulating input to our double-sideband
modulator.

Test point 9 carries a sine wave of frequency 1 MHZ and amplitude 12mV pk/pk
approx. This is the carrier input to our double-sideband modulator.

The out put from the BALANCED Modulator & BALANCED FILTER circuit block (at
tp3) is a double side band Am waveform, which has been formed by amplitude
Page 11 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
modulating the 1 MHz carries sine wave with the Audio-frequency sine wave from
Audio oscillator.

To determine the depth of modulation, measure the maximum amplitude (Vmax)
and the minimum amplitude (Vmin) of the AM waveform at t.p. 3, and use the
following

Formula:

Percentage Modulation = V max – V min


Where VMAX and VMIN are the maximum and minimum amplitudes shown in
o

V max + V min
Fig 2. 4
Now vary the amplitude and frequency of the frequency sine wave, by adjusting the
AMPLITUDE and FREQUENCY present in the AUDIO OSCILLATOR block.
Results: The waveform of DSB-SC AM modulation and Demodulation are trace on CRO and
DSO.
Precautions:Page 12 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
1. Connect the circuit properly.
2. Connect the patch cord properly.
3. Power cable plugged properly.
4. Adjust the CRO for tracing the different Waveform.
5. Check the connection before starting the kit.
6. Apply the required voltages wherever needed.
7. Do not apply stress on the components.
Lab Quiz:-
Q.1 An DSB signal with a maximum level of 200 V p-p into a 50- load results in a PEP
a.
b.
c.
d.
20W
50W
100W
800W
Q. 2 The Bandwidth of DSB-SC is.
a.
b.
c.
d.
ωm
2ωm
Greater than ωm
none of the above
Q. 3 DSB-SC is an example of
a.
b.
c.
d.
AM
FM
PM
PWM
Q. 4 In a balanced-ring modulator, the carrier suppression is accomplished by.
a.
b.
c.
d.
A dual-gate FET having symmetry
The nonlinearity of the diodes that are used
Symmetrical differential amplifier stages
none of the above
Page 13 of 78
rating of.
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Q. 5 Which cannot be used successfully to convert DSBSC to SSB?
a.
b.
c.
d.
Crystal filter
Ceramic filter
Mechanical filter
Tank circuit
Q.6 Another term for ripple amplitude for a ceramic filter is.
a.
b.
c.
d.
The shape factor
The insertion loss
QUALITY FACTOR
None
Q.7 Describe the oscilloscope waveform of a DSB transmitter's balanced modulator if it exhibits
carrier leak through.
a.
b.
c.
d.
Trapezoidal wave
Sine wave
AM wave
FM waves
Q.8 An DSB receiver re-creates the original intelligence signal by.
a.
b.
c.
d.
Amplifying the dc term produced by mixing action
Filtering out the harmonics
parabola
none
Q.9 The advantages provided by carrier elimination in SSB do not apply to transmission of.
a. code
b. music
c. noise
Page 14 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
d. all
Q.10 The types of SSB-Sc generations from DSB-SC are.
a.
b.
c.
d.
frequency discrimination
phase discrimination
both
none
Book: Lab experiment related theory available in following
books:
1. B.P. Lathi : Communication Systems, BS Publication
2. Taub and Schilling : Principles of communication Systems, TMH
3. Singh and Sapre : Communication Systems, TMH
4. S Haykin : Communication Systems, John Wiley and Sons Inc
Page 15 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.3
Frequency Modulation and Demodulation
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty in charge:
Name of Technical Assistant:
Page 16 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Objective: 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 Balance Slope FM
detector.
Apparatus:

FM Trainer Kit
Connecting wires, CRO, DSO LED, Bread board.
Theory: In the communication information like audio signal or speech writing signal is to be
transmitted from one point to another. But if it is transmitted directly through the
antenna then transmitting antenna must be ¼ to ½ wavelengths long. To reduce
the antenna size, there low frequency information (audio) signal is mixed with
higher frequency. Such process is called as frequency modulation (FM). This
higher frequency is called as carrier signal. At the receiver side, this signal is
converted back to audio frequency called as demodulation process.
Frequency Modulation: In these modulating signal em is used to vary the carrier signal frequency. Let the
change in the carrier frequency be kem where k is a constant know as frequency
deviation constant, then the instantaneous carrier frequency is
fi = fc + kem
Where fc is the unmodulated carrier frequency.
Let modulating signal is sine wave given by
em = emmax sinmt
Then instantaneous carrier frequency becomes
Page 17 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
fi = fc + kemmax sinmt
The peak frequency deviation of the signal is defined to be
f = kemmax
Therefore
fi = fc + f sinmt
Fig. 3.1 Frequency Modulated Waveform
Fig 3.1shows the FM waveform if modulating signal increase in positive direction
towards positive peak, then carrier frequency at o/p (FM) increases it become max
at positive peak. If modulating signal decreases from positive peak towards
negative half cycle it decreases the carrier frequency at o/p. when modulating
signal returns to zero, the carrier frequency returns to it’s center frequency. When
modulating signal is at it’s negative peak, the carrier frequency become zero at o/p.
therefore the modulating signal produces a frequency- modulated waveform as
Page 18 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
shows in fig 1. The carrier changes equally above and below it’s center frequency.
The amount of frequency change is called as the frequency deviation. The rate of
frequency deviation is determined by the frequency of the modulating signal but not
be the amount of deviation e.g. if carrier changes continuously from 90 MHZ to
90.2 MHZ then frequency deviation is +0.2 MHZ or 200 kHz. If the 500hz audio
tone is used to modulate the above carrier then it will changes equally above &
below it’s center frequency 500 times per second. As the amplitude of modulating
signal deviation will change for fixed value of modulating frequency hence the
amount of carrier deviation is directly proportional to the amplitude of the
modulating signal.
FM o/p wave consists of constant amplitude but changes in
frequency.
Modulation Index: It is defined as the ratio of maximum frequency deviation of FM from carrier
frequency (fc) fd to the modulating frequency (fm) and is given by
fd
M = ________
fm
In FM it’s value can reach to a high value as compared to AM.
Deviation ratio: - It is the ratio of max frequency deviation to max modulating
frequency.
fdmax
Deviation Ratio = ____________
fm max
If fm max is 18KHZ & fdmax = 90KHZ
90KHZ
Then deviation ratio = _________________ = 5
18KHZ
Band width: -
Page 19 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
BW = 2fm * highest order side band
[for derived modulation index from chart]
fd
Where modulation index m =
________
fm
10KHZ
e.g. If m =___________________ = 2
5KHZ
From table for modulation index 2, highest order side band is 5th
Therefore, the bandwidth is
BW = 2fm * highest order side band
= 2 * 5KHZ * 5
BW = 50KHZ
Page 20 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Procedure: 1. Study the circuit diagram provided on the front panel of the kit.
2. Connect sine wave input of 100Hz, 10Vp-p from signal generator to the
point marked “AF i/p”.
Page 21 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
3. Connect CRO at pin 7 of IC * R 2206. Observe the i/p waveform change by
potentiometer R1.
4. Now connect your oscilloscope at FM o/p pin 2, observed the waveform for
zero amplitude of modulating signal. This o/p is called as carrier.
5. Now change R, the carrier o/p frequency will change producing a waveform
shown below, called frequency-modulated waveform.
6. Change position of R1 amplitude of modulating signal will change which will
change the amount of frequency deviation note it’s minimum and max
frequency deviation.
7. Keep pot R1 at mid position change freq of modulating signal, note &
observed the change in frequency deviation it should remains constant.
Observation Table: Frequency of modulating signal FM
 Amplitude of modulating signal AM
 Frequency of carrier signal Fc
 Amplitude of carrier signal Ac
Calculation:Thus by changing the amplitude of the modulating signal. The amount of deviation
will change. But it remains constant for any change in modulating signal frequency.
Any slight change in division for change in modulating frequency were due to
generator output amplitude changes
Results: - Result display on Laboratory Session.
Conclusion:Precautions:-
Page 22 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
1. Connect the circuit properly.
2. Apply the required voltages wherever needed.
3. Do not apply stress on the components.
Suggestions:Lab Quiz :-
1. Frequency modulation is defined as ____
2. The advantages of indirect method of FM generation are __
3. Modulation index and frequency deviation of FM is ____
4. The advantages of FM are ______
5. Narrow band FM is _____
6. Compare narrow band FM and wide band FM?
7. Differentiate FM and AM _____
8. FM wave can be converted into PM wave _____
9, State the principle of reactance tube modulator _____
10. The bandwidth of FM system is ___
Book: Lab experiment related theory available in following books:
Book Name
Author
1.
2.
3.
4.
5.
Web resources:
1.
2.
3.
4.
5.
Page 23 of 78
Page No.
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.4
Frequency Demodulation using Foster Seeley Detector
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty in charge:
Name of Technical Assistant:
Page 24 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Objective: 1. To observe Frequency Demodulation using Foster Seeley Detector
Apparatus:

FM Trainer Kit
Connecting wires, CRO, DSO LED, Bread board.
Theory: It is a widely used discriminator. The circuit dig in fig 1.1 is a double tuned circuit
in which both primarily and secondary are tuned to same frequency intermediate
frequency. The center of the secondary is connected to top of the primary
through capacitor c3
The capacitor c3 performs following functions: 1. It blocks the dc from primary to secondary
2. It couples the signal frequency from primary to center topping of the
secondary. The primary voltage Vfm (signal voltage) thus appears across l,
except a small drop across c3
Page 25 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Fig 4.1 FM Demodulator
The center tapping of the secondary has an equal and opposite voltage across
each half winding. There fore V1and V2 are equal in magnitude but opposite in
phase
Va1=Vbm+V1
Va2= V3-V2
Procedure: (1)
Ensure that the following condition exist on the board.
1. Audio input select switch in INT position.
2. Mode switch in DSB position.
3. Out put amplifiers gain preset in fully clockwise position.
4. Speakers switch in off position.
Page 26 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(2) Turn the AUDIO OSCILLATOR blocks out put (t. p. 14) On an oscilloscope. This
is the audio frequency sine wave, which will be as our modulation signal. Note
that the sine wave’s frequency can be adjusted from about 300Hz to
approximately 3.4 KHz, by adjusting the Audio Oscillator’s Frequency preset.
Return the amplitude present to its MAX position.
Fig. 4.2 BLOCK DIAGRAM OF FOSTER SEELEY DETECTOR
3) Turn the BALANCE preset, in the BALANCED MODULATIOR 7 BANDPASS FILTER
CIRCUIT 1 block, to its fully clockwise position. It is this block that we used to
perform double-side band amplitude
modulation. Select the foster- seeley
detector by putting the switch in the FOSTER- SEELEY position.
4) Initially, we will use the VARACTOR MODULATIOR to generate our FM
signal, since this is the more linear of the two modulators, as far as its
frequency / voltage characteristic is concerned. To select the VARACTOR
MODULATOR put the REACTANCE / VARACTOR switch in the VARACTOR
position.
5) The Audio Oscillator’s out put signal (which appears at t.p. 1) is now being
used by the VARACTOR MODULATIOR, to frequency – modulate a 445 KHz –
carrier sine wave. As we saw earlier, this FM waveform appears at the FM
OUTPUT socket from the MIXER / AMPLIFIER block
Page 27 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
6) Now monitor the audio input signal to the VARACTOR MODULATOR
block ( at t.p. 14) together with the FOSTER-SEELEY
OUTPUT (at t. p. 52) triggering the oscilloscope on t.p. 14.
The signal at t.p. 52 should contain two components:
A sine wave has the same frequency as the audio signal at t.p. 14’
7) The LOW- PASS FILTER/ AMPLIFIER strongly attenuates this high –
frequency ripple component and also blocks any small D.C. offset
voltage that might exist at the detector’s out put. Consequently the signal
at the output of the LOW – PASS FILTER/ AMPLIFIER block (at t. p.
73) should very closely resemble the original audio modulating signal
8) Monitor the audio input to the VARACTOR MODULATIOR ( at t.p.
73) and adjust the GAIN preset (in the LOW PASS FILTER/
AMPLIFIER block’s) until the amplitudes of the monitored audio
waveforms are the same.
9) Adjust the AUDIO OSCILLATOR block’s AMPLITUDE
andFREQUENCY presets, and compares the original audio signal with the
final demodulated signal.
Observation Table: Frequency of modulating signal FM
 Frequency of carrier signal Fc
Calculation:-
Page 28 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Thus by changing the amplitude of the modulating signal. The amount of deviation
will change. But it remains constant for any change in modulating signal frequency.
Any slight change in division for change in modulating frequency were due to
generator output amplitude changes
Results: - Result display on Laboratory Session.
Conclusion:-
Precautions:-
1. Connect the circuit properly.
2. Apply the required voltages wherever needed.
3. Do not apply stress on the components.
Suggestions:-
Lab Quiz :-
1. Consider two message signals, m1(t) = A cos(2 π fm t) and m2(t) = A cos(4
π fm t), with the same amplitude but m2 having double the frequency.
Would the two modulated FM signals (by m1 and m2) have different
frequency deviations? What about their bandwidth? Explain.
2. What are zero crossing detectors?
3. What is the secondary name of foster seeley discriminator.?
4. Draw the frequency response of foster seeley discriminator?
5. What is the draw back of foster seeley discriminator?
6. What is the meant by the term “significant side bands “ in frequency
modulated wave.
7. Write the comparison of balanced slope detector and foster seeley
discriminator.
8. What is the effect of changing the value of the sensitivity factor f k?
9. List and compare all the other methods you know about for demodulating an
FM signal?\
Page 29 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
10. Plot x(t) and y(t). Also, plot the magnitude spectrum for y(t).
Book: Lab experiment related theory available in following books:
Book Name
Author
1.
2.
3.
4.
5.
Web resources:
1.
2.
3.
4.
5.
Page 30 of 78
Page No.
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.05
To Study and Observe The Pulse Position Modulation And Demodulation.
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 31 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - To Study and Observe The Pulse Position Modulation And
Demodulation.
Apparatus: - 1. ST2110 with power supply cord
2. CRO with connecting probe
3. Connecting cords
Theory: The Amplitude and width of the pulses is kept constant in this system while the
position of each pulse, in relation to the position of a recurrent reference pulse is
varied by each instantaneous sampled value of the modulating wave. Pulseposition modulation has the advantage of requiring constant transmitter power
output. And the disadvantage of depending on transmitter and receiver is
synchronization.
Fig.6.1
Page 32 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
pulse position modulation system the message is recovered by a low pass filter.
The type of filter used is very important, as the signal above the cut-off frequency
would affect the recovered signal if they were not attenuated sufficiently
Filter Basic:
The simplest type of filter is a resistance- capacitance (RC) filter. The high pass
filter and low pass RC filters are as shown in Fig. The analysis of these filters
becomes easier if we think of them as AC potential dividers. The reactance of the
capacitor is frequency dependent with a high value at low frequencies and a low
value at high frequencies. In case of high pass filter, the series capacitance has
high reactance at low frequencies and hence results in reduction in output
voltage. An increase in frequency causes an increase in output voltage with Vout
approaching input voltage Vin. The effect of capacitors is just opposite case of low
pass filter. Here, the capacitance is in short and hence Vout reduces as frequency
increases there by decreasing its reactance. The ratio of Vout / Vin is known as
transfer function for the circuit. For RC low pass filter, the transfer function can be
derived by using potential divider resistance.
Page 33 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
So, This is the half-power point of the filter i.e. at frequency =RC, the output
power decreases to half of the input power. This is also known as the cutoff
frequency (Fc).The filter not only causes amplitude but a change in phase is also
experienced. A typical response of a low pass filter is as shown Figure
Page 34 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Procedure:
-
Page 35 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Results: - Verified the PPM Modulation and Demodulation
Precautions:1.
2.
Check the connections before giving the supply.
Observations should be done carefully.
Lab Quiz:Q.1 Which of the following delays should be used in a jumpreturn experiment on a 500 MHzinstrument to have maximum
intensity at 9 ppm? Assume that the water resonance is at4.8
ppm.
A.
B.
C.
D.
467μs
11.9μs
119μs
none
Q. 2 A mixer is used to
A.
B.
C.
D.
subtract the frequencies of two input signals
add the frequencies of two input signals
multiply the frequencies of two input signals
produce IF frequency
Q.3 Which of the following frequencies cannot be an
intermediate frequency (IF)?
A. 20 MHz
B. 10 MHz
C. 30 MHz
D. 200 MHz
Q. 4 What is the purpose of using LO?
Page 36 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
A. To combine with carrier frequency at transmitter
B. To make a frequency higher than the spectrometer
base frequency
C. To use a fixed-frequency receiver for all nuclei
D. To use a fixed-frequency preamplifier for all nuclei
Q. 5 Pick the odd main out
A. PWM
B. PPM
C. PDM
D. QAM
Q.6 The PDM needs
A. More power than PPM
B. More samples than PPM
C. High pass filter
D. none
Q.7 The PPM signal can be detected by.
A. BPF
B. BSF
C. HPF
D. LPF
Q.8 which of the following is digital in nature
A.
B.
C.
D.
PAM
PPM
PCM
PWM
Page 37 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Q.9 QUANTIZATION NOISE OCCURE IN
(A) PAM
(B) PPM
(C) PCM
(D) PWM
Q.10 The bandwidth of PPM signa is
A. Lower than PAM
B. Lower than PCM
C. Higher than PWM
D. None
Book: Lab experiment related theory available in following books:
1. Communication systems, Singh & Sapre, Communication System, TMH, P.P-47
2. Taub & shilling, Communication System, TMH
3. Hsu; Analog and digital communication (Schaum); TMH
4. B.P. Lathi, Modern Digital and analog communication system,
Web resources: http://en.wikibooks.org/wiki/Communication_Systems/TimeDivision_Multiplexing
Page 38 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.06
Study& Observe The of Differential pulse code modulation and demodulation
Technique.
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 39 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - Study& Observe The of Differential pulse code modulation and
demodulation Technique.
Apparatus: - ST2113, DPCM Trainer Board
2. CRO
3. Multimeter
4. Patch Cords, etc
Theory: Differential pulse code modulation In Practical system bandwidth requirement for
transformation of information is very important aspect, since if bandwidth requirement
is less, more number of channels can be multiplexed on a single line and full utility of
transmitting media is extracted out. In a system in which a base band signal m (t) is
transmitted by sampling, there is available a scheme of transmission which is an
alternative to transmitting the sample values (quantized or not) at each sampling time.
We can instead, at each sampling time, say the kth sampling time, transmit the
difference between the sample value m(k) at sampling time k and the sample value m(k 1) at time k - 1. If such changes are transmitted, then simply by adding up
(accumulating) these changes we shall generate at the receiver a waveform identical in
form to m (t). There can be a difference in dc components between transmitted and
received signals but, almost invariably; such dc components are of no interest. Such a
differential scheme has special merit when these differences are to be transmitted by
pulse code modulation. For we may well anticipate that the differences m(k) - m(k - 1)
will be smaller than the sample values themselves. Hence fewer levels will be required
Page 40 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
to quantize the difference than are required to quantize m (k) and correspondingly,
fewer bits will be needed to encode the levels. For example, suppose that m (k) extends
over a range VH - VL, and using PCM, m (k) is encoded using 28 = 256 levels. Then the
step size is S = (VH - VL)/28, that is VH- VL = 256S. If, however, the difference signal m (k)
- m (k - 1) extends only over the range ± 2S then the quantized levels needed are at ±
O.5S and at ± l.5S. There are now only four levels and two bits per sample difference are
adequate. In an analog system, where we are able, at least in principle, to transmit the
differences exactly, the differential system described above would operate in
accordance with our description. In a digital (quantized) system we encounter the
complication that the differences are not generally transmitted exactly because of the
quantization. Further, we have the problem that the difference may be larger than the
maximum that can be accommodated because of the restricted number of encoding bits
we have provided. Hence it might well be that at some time there might be a large
discrepancy between the original signal m(t) and the signal m(t) generated at the
receiver by accumulation. Suppose that over a number of samplings, while m (t) is
increasing, the transmitted differences were too small so that m (k) had fallen
substantially short of keeping up with m (t). Suppose, further, that in the interval
sampling times k and k + 1, m (t) should decrease slightly. Clearly if we transmitted the
negative change of m (t) we would be giving the wrong signal. In a digital differential
system we circumvent the difficulty we have just described by making available at the
transmitter a duplicate of the receiver accumulator so that at the transmitter we have
available the same signal m (t). Then we arrange that the transmitted signal should not
convey the most recent change in m (t) but conveys instead the difference between m
(t) and m’ (t).
Page 41 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Procedure :- 1. Connect the sine wave output of the audio signal generator to
one of the inputs of the difference amplifier as shown in the figure 10.
2. Connect the output of the difference amplifier to the input of the ADC.
3. Connect the output of parallel to serial converter to the input of serial to
parallel converter of the receiver accumulator.
4. Connect the output of the DAC to the other input of the difference amplifier as
shown in the above figure.
Page 42 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
5. Now switch ‘On’ the power supply. Observe the sine wave output of the sine
wave generator on the CRO. Adjust the frequency of sine wave at 1 KHz.
6. Observe the signal at the output of DAC. You will see the stair case
approximation of the input signal at the output of DAC. Also observe the
output of low pass filter and see that it is nearly same as the input signal.
7. Now observe various controls and clock signal shown in the control and clock
section and try to relate these signals with the timing diagram of figure 9.
8. Note that the sampling starts with the R/W signal pulse that has a frequency of
8 KHz. For a small duration when pulse is high, ADC reads the input port and
for the rest of the low period it provides this data at the output of the ADC.
9. Now observe the clock and reset signal of the parallel to serial converter.
Observe that for the time period when reset is low, exactly five clock pulses
shift the content of the shit register.
10. Observe the LE2 and OE 2of previous data latch and relate them with timing
diagram of fig.
11. You may find it difficult to appreciate the entire control signals
simultaneously with a normal two channels CRO but nevertheless an intuitive
sense of relative time based occurrences of all these signals can make the task
easier. You can see all these signals simultaneously on the screen with the help
of logic analyzer too.
12. Also it is to be taken into consideration that the data flow through the entire
system is fast enough random as well so it is not feasible to observe the data
Page 43 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
exactly at any point. But still you can have an overview of the data statistics
at any test point of the data bus.
Results: - Verified the DPCM Modulation and Demodulation
Precautions:3.
4.
Check the connections before giving the supply.
Observations should be done carefully.
Lab Quiz:A. Q.1 For a 10-bit PCM system, the signal to quantization
noise ratio is 62dB. If the number of bits is increased by 2,
then how would the signal to quantization noise ratio
change?
(A) Increase by 6 dB
(B) Decrease by 6 dB
(C) Increase by 12 dB
(D) Decrease by 12 dB
Q. 2 The sequence of the binary digits representing the outcomes
of parity checks in Hamming codes is known as
A. Look-up entry
B. Hamming distance
Page 44 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
C. Radix
D. d. Syndrome
Q. 3 The sequence of the binary digits representing the outcomes
of parity checks in Hamming codes is known as
A. Look-up entry
B. Hamming distance
C. Radix
D. Syndrome
Q. 4 The error represented by the difference between the
original and quantized signals set a fundamental limitation to the
performance of PCM systems known as __________________.
A. Dynamic range
B. Detection-error
C. Quantization noise
D. Correction-error
Q. 5 Which of the following is the error-detection and correction
method?
A. Parity
B. Hamming code
C. Checksum checking
D. Cyclic redundancy checking
Q.6 In a DPCM , the quantization noise depends on
(A) Sampling rate
(B) levels
Page 45 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(C) power
(D) All
Q.7 The main advantages of DPCM over PCM are.
(A) Less BW
(B) Less power
(C) Better s/n ratio
(D) Simple circulatory
Q.8 Figure
(A)
(B)
(C)
(D)
of merit is always unity in.
SSB-SC
AM
FM
ALL
Q.9 The main advantage of DPCM.
A. Less BW
B. Less power
C. Better s/n ratio
D. Simple circuratury
Q.10 which is not a type of pulse modulation?
A.
B.
C.
D.
DPCM
PCM
PWM
none
Book: Lab experiment related theory available in following books:
1. Communication systems, Singh & Sapre, Communication System, TMH, P.P-47
Page 46 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
2. Taub & shilling, Communication System, TMH
3. Hsu; Analog and digital communication (Schaum); TMH
4. B.P. Lathi, Modern Digital and analog communication system,
Web resources: http://en.wikibooks.org/wiki/Communication_Systems/TimeDivision_Multiplexing
Page 47 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.07
Study & Observe The Pulse Width Modulation using different Sampling
Frequency.
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 48 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - Study & Observe the Pulse Width Modulation using different
Sampling Frequency.
Apparatus: - 1. ST2110 with power supply cord
2. CRO with connecting probe
3. Connecting cords.
Theory: Pulse modulation may be used to transmit information, such as continuous
speech or data. It is a system in which continuous waveforms are sampled at
regular intervals.
Information regarding the signal is transmitted only at the sampling times,
together with any synchronizing pulses that may be required. At the receiving
end, the original mwaveforms may be reconstituted from the information
regarding the samples, if these
are taken frequently enough. Despite the fact that information about the signal is
not supplied continuously, as in AM and FM, the resulting receiver output can
have negligible distortion. Pulse modulation may be subdivided broadly into two
categories, analog and digital. In the former case, the indication of sample
amplitude is the nearest variable, while in
the latter case, a code, which indicates the sample amplitude to the nearest
Page 49 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
predetermined level, is sent. Pulse amplitude and pulse time modulation, to be
treated next, are both analog.
Theory of sampling:
The signals we use in the real world, such as our voice, are called "analog" signals.
To process these signals for digital communication, we need to convert analog
signals to "digital" form. While an analog signal is continuous in both time and
amplitude, a digital signal is discrete in both time and amplitude. To convert
continuous time signal to discrete time signal, a process is used called as
sampling. The value of the signal is measured at certain intervals in time. Each
measurement is referred to as a sample.
Principle of sampling:
Consider an analogue signal x(t) that can be viewed as a continuous function of
time, as shown in figure1. We can represent this signal as a discrete time signal by
using values of x(t) at intervals of nTs to form x(nTs) as shown in figure 1. We are
"grabbing" points from the function x(t) at regular intervals of time, Ts, called the
sampling period.
PROCEDURE:-
1. Connect the circuit as shown in Figure 7.1 and also described below for clarity.
a) 1 KHz sine wave output of function generator block to modulation input
of PWM block.
b) 64 KHz square wave output to pulse input of PWM block.
2. Switch ‘On’ the power supply & oscilloscope.
3. Observe the output of PWM block.
Page 50 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
4. Vary the amplitude of sine wave and see its effect on pulse output.
5. Vary the sine wave frequency by switching the frequency selector switch to 2
KHz.
6. Also, change the frequency of the pulse by connecting the pulse input to
different pulse frequencies viz. 8 KHz, 16 KHz, 32 KHz and see the variations
in the PWM output.
7. Switch ‘On’ fault No. 1, 2, & 5 one by one & observes their effect on PWM
output and tries to locate them.
Results: - Verified the TDM Modulation and Demodulation
Precautions:5.
6.
Check the connections before giving the supply.
Observations should be done carefully.
Lab Quiz:Q.1 Which is not a type of pulse modulation?
A.
B.
C.
D.
Pulse-amplitude modulation (PAM)
ppm
pcm
all
Q. 2 Pick the odd mainout
(A)
PWM
(B)
PPM
(C)
PDM
(D)
QAM
Page 51 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Q.3The PDM needs
(E)
More power than PPM
(F)More samples than PPM
(G)
High pass filter
(H)
none
Q.4 The PPM signal can be detected by.
A. BPF
B. BSF
C. HPF
D. LPF
Q.5which of the following is digital in nature
(E)
PAM
(F)PPM
(G)
PCM
(H)
PWM
Q.6 QUANTIZATION NOISE OCCURE IN
(E)
PAM
(F)PPM
(G)
PCM
(H)
PWM
Q.7 The bandwidth of PPM signa is
(E)
Lower than PAM
(F)Lower than PCM
(G)
Higher than PWM
(H)
None
Book: Lab experiment related theory available in following books:
Page 52 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
1. Communication systems, Singh & Sapre, Communication System, TMH, P.P-47
2. Taub & shilling, Communication System, TMH
3. Hsu; Analog and digital communication (Schaum); TMH
4. B.P. Lathi, Modern Digital and analog communication system,
Web resources: http://en.wikibooks.org/wiki/Communication_Systems/TimeDivision_Multiplexing
Page 53 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.08
To study and Observe the Delta Modulation & Demodulation.
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 54 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - To study and Observe the Delta Modulation & Demodulation
Apparatus: 1. ST2105 with power supply cord
2. CRO with connecting probe
3. Connecting cords
Theory: Delta modulation is a system of digital modulation developed after
pulse code modulation. In this system, at each sampling time, say
the Kth sampling time, the difference between the sample value at
sampling time K and the sample value at the previous sampling
time (K-1) is encoded into just a single bit. i.e. at each sampling
time we ask simple question.
Has the signal amplitude increased or decreased since the last
sample was taken? If signal amplitude has increased, then
modulator's output is at logic level 1. If the signal amplitude has
decreased, the modulator output is at logic level 0. Thus, the output
from the modulator is a series of zeros and ones to indicate rise and
Page 55 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
fall of the waveform since the previous value. One way in which
delta modulator and demodulator is assembled is as show in figure
1 and figure 2.
Delta Modulator
Figure 8.1
Delta Modulator
Figure 8.2
ST2105
The Delta Modulator Works as follows:
The analog signal which is to be encoded into digital data is applied
to the +ve input of the voltage comparator which compares it with
the signal applied to its -ve input from the integrator output (more
about this signal in forth coming paragraph).
The comparator's output is logic '0' or '1' depending on whether the
input signal at +ve terminal is lower or greater then the -ve
terminals input signal.
The comparator's output is then latched into a D-flip-flop which is
clocked by the transmitter clock. Thus, the output of D-flip-Flop is
a latched 'l' or '0' synchronous with the transmitter clock edge.
Page 56 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
This binary data stream is transmitted to receiver and is also fed to
the unipolar to
Suppose at some time-instance t = 0, the integrator output voltage
is lower than the analog input. This causes the voltage comparator
voltage to go high i.e. logic '1'. This data is latched in the D- FlipFlop at the rising edge of transmitter clock., The latched '1' output
of D- flip is translated to - 4V by the unipolar to bipolar converter
block. The integrator then ramps up to catch analog signal. ST2105
Scientech Technologies Pvt. Ltd. 8 At the next clock cycle t = 1, the
integrator output becomes more than the analog input, so a '0' is
latched into D-Flip-Flop. The integrator now ramps downward as
+4V voltage signal from unipolar to bipolar converter appears at its
input. Thus, the ramp signal again tries to catch the fallen analog
signal.
As we can observe, after several clock cycles the integrator output is
approximation of the analog input which tries to catch up the
analog input at each sample time. The data stream from D-flip-flop
is the delta modulators output.
The delta demodulator consists of a D-Flip-Flop a unipolar to
bipolar converter followed by an integrator and a low pass filter. The
delta demodulator receives the data from D-Flip-Flop of delta
modulator. It latches this data at every rising edge of receiver clock,
Page 57 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
which is delayed by half clock period with respect to transmitter
clock. This has been done so that the data from transmitter may
settle down before being latched into the receiver Flip-Flop.
The unipolar to bipolar converter changes the output from D-FlipFlop to either - 4V or + 4V for logic '1' and '0' respectively.
As it has been seen in case of modulator when the output from
unipolar to bipolar converter is applied to integrator, its output tries
to follow the analog signal in ramp fashion and hence is a good
approximation of the signal itself. The integrator's output contains
sharp edges, which are 'smoothened out' by the low - pass filter,
whose cutoff frequency is just above the audio band.
Delta modulation offers many advantages as listed below
Simple system / circuitry
Distortion means that the receiver's output is not the true copy of
the analog input signal at the transmitter.
Distortion in delta modulation occurs due to following causes:
As it has been seen, when the analog signal is greater then the
integrator output, the integrator ramps up to meet the analog
signal. The ramping rate of integrator is constant. Therefore, if the
rate of change of analog input is faster than the ramping
Page 58 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
rate, the modulator is unable to catch up with the information
signal. This causes a ST2105 Scientech Technologies Pvt. Ltd. 9
large disparity between the information signal and its quantized
approximation. This error / phenomenon is known as slope overloading
and
causes
the
loss
of
rapidly
changing
the
information. Information Loss due to Rapid input Changes At first it
may look as though the problem of slope overloading can be solved
increasing the ramping rate of the integrator. But as it can be seen
from the figure the effect of the large step-size is to add large sharp
edges at the integrator output and hence it adds to noise problem
faced at receiver. This effect itself leads to distorted receiver output.
Increasing sampling rate cannot be the solution to the slope overloading problem as it determines how fast the samples are
taken and not the ramping rate of the
The VCO is an oscillator whose output frequency is directly related
to the voltage at its input. With no input the VCO supplies a signal
at its natural (free running) frequency. When a signal is applied to
the input, the VCO will generate an output whose frequency follows
the amplitude of the input in accordance with the applied voltage
.
Page 59 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Figure 10.1 Voltage Controlled Oscillator
Although we use sinusoidal signals in our analysis, most
commercially available VCO IC’s generate square signals. The PLL is
an important part of communications systems. Figure 1.2 shows
the building blocks of a simple PLL.
Figure 10.2 PLL Block Diagram
The Phase Detector is simply a multiplier whose output is related to
the product of both its inputs. We shall use simple equations to
clarify the operation of the PLL. Let the i/p x(t) be a sinusoid:
x(t)= Ax cos(wx t+qx)
and o/p of the PLL r(t):
r(t)= Ar cos(wr t+qr)
Before applying x(t) to the PLL i/p, the signals x(t) and r(t) will be
different, i.e.
Page 60 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
wx ¹ wr and qx ¹ qr. When x(t) is applied to the PLL, the internal
circuitry will drive r(t) to lock on to the frequency and phase of x(t).
Under lock condition we get:
r(t)= Ar cos(w xt+qr ' )
This means that a PLL is a frequency locked loop. As for the phases,
we shall
find that
Figure 10.3 LM566 VCO Block Diagram
This is a general purpose VCO. It can be used to generate square
and triangular
Waves, the frequency of which is a linear function of a controlling
voltage. The
Page 61 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Frequency is also controlled by an external resistor (pin6) and
capacitor (pin7), whose values control the free running frequency.
Figure 1.3 shows the block diagram of this IC.
The output frequency can be found from the formula:
Where Ro and Co are the resistor and capacitor connected to pins 6 and 7
respectively.
Procedure :1. Connect the mains supply
2. Make connection on the board as shown in the figure 7
3. Ensure that the clock frequency selector block switches A & B are in A = 0 and
B = 0 position.
4. Ensure that integrator 1 block's switches are in following position:
a) Gain control switch in left-hand position (towards switch A & B).
b) Switches A & B in A=0 and B=0 positions.
5. Ensure that the switches in integrator 2 blocks are in following position:
a) Gain control switch in left-hand position (towards switch A & B)
Page 62 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
b) Switches A & B are in A = 0 and B = 0 positions.
6. Turn 'ON' of the trainer.
7. In order to ensure for correct operation of the system, we first take the input to
0V. So connect the '+' input of the delta modulator's voltage comparator to 0V
and monitor on an oscilloscope the output of integrator 1 (TP17) and the output
of the transmitter's level changer (TP15)
If the transmitter's level changer output has equal positive and negative output
Results: - Verified the TDM Modulation and Demodulation
Precautions:7.
8.
Check the connections before giving the supply.
Observations should be done carefully.
APPLICATION:Phase-locked loops are widely used for synchronization purposes; in
space communications for coherent demodulation and threshold extension, bit
synchronization, and symbol synchronization. Phase-locked loops can also be
used to demodulate frequency-modulated signals. In radio transmitters, a PLL is
used to synthesize new frequencies which are a multiple of a reference
frequency, with the same stability as the reference frequency.
Other applications include:
 Demodulation of both FM and AM signals
 Recovery of small signals that otherwise would be lost in noise .
Page 63 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
 Recovery of clock timing information from a data stream such as from
a disk drive
 Clock multipliers in microprocessors that allow internal processor elements
to run faster than external connections, while maintaining precise timing
relationships
 DTMF decoders, modems, and other tone decoders, for remote
control and telecommunications
 DSP of video signals; Phase-locked loops are also used to synchronize phase
and frequency to the input analog video signal so it can be sampled and
digitally processed
Lab Quiz:Q.1 Consider the following statements about analog communication and
multiplexing :
1. Noise problem for analog communication has the greatest effect on
TDsystem.
2. Noise problem for analog communication has the least effect on SDM
system.
Which of the statements given above is/are correct ?
(A) 1 only
(B) 2 only
(C) Both 1 and 2
(D) Neither 1 nor 2
Q. 2 What are the three steps in generating DM in the correct sequence ?
(A) Sampling, quantizing and encoding
(B) Encoding, sampling and quantizing
(C) Sampling, encoding and quantizing
(D) Quantizing, sampling and encoding
Q. 3 What is the main objective of trellis coding ?
(A) To narrow the bandwidth
(B) To simplify modulation
(C) To increase the data rate
(D) To reduce the error rate
Q. Quantization noise occurs in
(A) Pulse amplitude modulation
Page 64 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(B) Pulse width modulation
(C) Pulse code modulation
(D) Pulse position modulation
Q. 5 Which of the following is not an analog-to-analog conversion?.
(E) DM
(F) PM
(G) FM
(H) QAM
Q.6 The phase sensitivity of the delta modulator is expressed in ______.
(I) dB
(J) watts
(K) kwatts
(L) All
Q.7 Which one of the following statements is correct ?
Quantising noise is produced in
A) all pulse modulation systems
(B) PCM
(C) all modulation systems
(D) DM
Q.8 Figure of merit is always unity in.
(I) SSB-SC
(J) DM
(K) FM
(L) ALL
Q.9 Quantization noise occurs in.
(I) PAM
(J) PPM
(K) DM
Page 65 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(L) PCM
Q.10 Delta modulation has-----------bandwidth than PCM
(I) More
(J) less
(K) equal
(L) none
Book: Lab experiment related theory available in following books:
1. Communication systems, Singh & Sapre, Communication System, TMH, P.P-47
2. Taub & shilling, Communication System, TMH
3. Hsu; Analog and digital communication (Schaum); TMH
4. B.P. Lathi, Modern Digital and analog communication system,
Web resources: http://en.wikibooks.org/wiki/Communication_Systems/TimeDivision_Multiplexing
Page 66 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.09
To study the sampling of continuous signal.
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 67 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - To study the sampling of continuous signal.
.
Apparatus: - St2202 kit, CRO, Patch chords
Theory: Need of sampling: - whenever we want to digitize a continuous signal the first operation
evolve is sampling. In which we restrict time domain of our continuous signal to finite
values.
In sampling we multiply continuous signal with a train of pulses after multiplication we
get the sampled version of the continuous signal.
Let m (t) be a signal which is band limited such that its highest frequency spectral
component is m. let the values of m (t) be determined at regular intervals separated by
times. Ts  (1/2fm) i.e., the signal is periodically sampled every Ts seconds. Then these
samples m (nTs), where n is an integer, uniquely determined the signal, and the signal
may be reconstructed from these samples with no distortion. The time Ts is called
sampling time.
Page 68 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Fig.9.1 Sampling of g(t)
Procedure:
-
1. Connect 1KHZ signal from function generator to CRO.
2. Measure frequency at TP11.
3. Observe the signal at TP7, which is pulse signal.
4. Observe the sampled output at TP20.
Results: - Verified the sampling and Desampling of a signal
Precautions:Check the connections before giving the supply.
10. Observations should be done carefully.
9.
Page 69 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
APPLICATION:Phase-locked loops are widely used for synchronization purposes; in
space communications for coherent demodulation and threshold extension, bit
synchronization, and symbol synchronization. Phase-locked loops can also be
used to demodulate frequency-modulated signals. In radio transmitters, a PLL is
used to synthesize new frequencies which are a multiple of a reference
frequency, with the same stability as the reference frequency.
Other applications include:
 Demodulation of both FM and AM signals
 Recovery of small signals that otherwise would be lost in noise .
 Recovery of clock timing information from a data stream such as from
a disk drive
 Clock multipliers in microprocessors that allow internal processor elements
to run faster than external connections, while maintaining precise timing
relationships
 DTMF decoders, modems, and other tone decoders, for remote
control and telecommunications
 DSP of video signals; Phase-locked loops are also used to synchronize phase
and frequency to the input analog video signal so it can be sampled and
digitally processed
Lab Quiz:Q.1 Why sampling is required?.
It is required for modulation
(B) It is necessary to suppress the effect of noise in
communication channel
(C) Sampling is necessary before an analogue signal can be
converted into digital form.
(A)
(D) all
Q. 2 sampling theorem states that __________________
.
Page 70 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(A)
(B)
(C)
(D)
Fs> fm
Fs<fm
both
none of the above
Q. 3 sampling is the process by which we can change ______signal in -----------signals
(E)
(F)
(G)
(H)
Fs> fm
Fs<fm
both
none of the above
Q. 4 In sampling aliasing condition is achieved when
(A)
(B)
(C)
(D)
Fs> fm
Fs<fm
both
none of the above
Q. 5 Which of the following is not an analog-to-digital conversion?.
(I)
(J)
(K)
(L)
AM
PM
PPM
QAM
Q.6 The sensitivity of the flat top sampler must be
(M) higher
(N) lower
(O) higher than fm
(P) none
Q.7 Nyquest interval is.
(E) T=1/2fm
(F) T=1/fm
(G) T=2fm
Page 71 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
(H) none
Q.8 Which sampling has highest speed.
(M) natural
(N) flattop
(O) both
(P) none
Q.9 A sampling circuit requires
(M) switch
(N) hold circuit
(O) tank circuit
(P) ALL
Q.10 In TDM sampling, the FM detector has the bandwidth
(M) More
(N) less
(O) equal
(P) none
Book: Lab experiment related theory available in following
books:
Book: Lab experiment related theory available in following books:
1. Communication systems, Singh & Sapre, Communication System, TMH, P.P-47
2. Taub & shilling, Communication System, TMH
3. Hsu; Analog and digital communication (Schaum); TMH
4. B.P. Lathi, Modern Digital and analog communication system,
Web resources: http://en.wikibooks.org/wiki/Communication_Systems/TimePage 72 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Division_Multiplexing
1.
Page 73 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
EXPERIMENT NO.10
TDM Modulation and Demodulation
Date of conduction:-
Date of submission:-
Submitted by other members:1.
2.
3.
4.
5.
6.
7.
8.
Group no:-
Signature
Name of faculty incharge:
Page 74 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Name of Technical Assistant:
Objective: - To study the TDM Modulation and Demodulation
Apparatus: - CRO, Patch chords, Trainer kit
Theory: When there is only signal channel is available for transmission but we have more
than one signal available at transmitter. Then we need to multiplex the signal in
time domain. Multiplexing is done as fallows.
We take sample of first signal and transmitted it then we take the sample of
second signal and transmit the second signal these signals are separated in time
therefore there is no overlapping takes places. By using same approach we can
send number of signal over a signal communication channel.
At the transmitting end on the left a number of band-limited signal are connected
to the correct point of a rotary switch. We assumed that the signals are similarly
band limited. For e.g. They may all be voice signals, limited to 3.3 KHz. As the
rotary arm at receiving end is in sync with the switch at the sending end. The two
switches make connect simultaneously at similarly numbered contacts. With each
revolution of the switch, one sample is taken to each input signal and presenting
to the correspondingly numbered contact of the receiving end switch. The train of
samples at, say, terminal 1 in the receiver, pass through low pass filter1, and at
Page 75 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
the filter output the original signals m1 (t) appear reconstructed. Of course, if Fm
is the highest frequency spectrum component present in any of the input signals
the switches must at least 2 Fm revolutions per second.
In this switching process, the switch at left side that samples the signals is called
communicator and switch at the right side is called de commutator.
Procedure: 1. Connect 250 Hz signal to CH0, 500Hz signals to CH1, 1Khz signal to CH2 and
2Khz signal to CH3.
2. Connect Tx output to Rx Input.
3. Connect Tx Clock to Rx Clock.
4. Connect Tx CH0 to Rx CH0.
5. Measure the signal frequency at TP11, TP13, TP15 and TP17.
6. Observe the TDM modulation out at TP20.
Page 76 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
7. Observe the Demodulation signal frequency at TP42, TP44, TP46, and TP48
and verify that they are same as at TP11, TP13, TP15, and TP17
respectively.
Results: - Verified the TDM Modulation and Demodulation
Precautions:11. Check the connections before giving the supply.
12. Observations should be done carefully.
Lab Quiz:Q-1. Which multiplexing technique transmits analog signals?
1) FDM,
2) TDM,
3) WDM, 4) 1 and 2
Q-2. Which multiplexing technique transmits digital signals?
1) FDM,
2) TDM,
3) WDM,
4) 1 and 2
Q-3. Which multiplexing technique shifts each signal to a different carrier
frequency?
1) FDM ,
2) TDM,
3) both 1 and 2,
4) none
Q-4. In synchronous TDM, for n signal sources of the same data rate, each frame
contains ___slots.
1) n
2) n+1,
3) n-1,
4) 0 to n
Q-5. In TDM, the transmission rate of the multiplexed path is usually _______
the sum of the transmission rates of the signal sources.
1) less than , 2) greater than , 3) equal to , 4) not related to
Q-6. ______ is an analog multiplexing technique to combine optical signals.
1) FDM,
2) TDM ,
3) WDM ,
4) none
Page 77 of 78
NAME OF LABORATORY: Analog and Digital Communication
LAB SUBJECT CODE: CS-405
NAME OF DEPARTMENT: Electronics and communication
Q-7. In ________, we combine signals from different sources to fit into a larger
bandwidth.
1) spread spectrum , 2) line coding, 3) block coding ,4) none
Q-8. The _______ technique uses M different carrier frequencies that are
modulated by the source signal. At one moment, the sign modulates one
carrier frequency; at the next moment, the signal modulates another
carrier frequency.
1) FDM, 2) DSSS ,3) FHSS ,4) TDM
Book: Lab experiment related theory available in following books:
1. Communication systems, Singh & Sapre, Communication System, TMH, P.P-47
2. Taub & shilling, Communication System, TMH
3. Hsu; Analog and digital communication (Schaum); TMH
4. B.P. Lathi, Modern Digital and analog communication system,
Web resources: http://en.wikibooks.org/wiki/Communication_Systems/TimeDivision_Multiplexing
Page 78 of 78