COMMUNICATION LAB PPT CONTAINS BOTH HARDWARE AND SOFTWARE

25/11/2024 Department of ECE 1
communication lab
&
18ECL67
Pavithra A C
Assistant Professor

Course objectives:
• This course will enable students to:
• Design and test the communication circuits for different analog
modulation schemes.
• Design and demonstrate the digital modulation techniques
• Demonstrate and measure the wave propagation in microstrip antennas
• Characteristics of microstrip devices and measurement of its parameters.
• Understand the probability of error computations of coherent digital
modulation schemes.

Laboratory Experiments
1. Amplitude Modulation and Demodulation: i) Standard AM, ii)DSBSC (LM741 and LF398 ICs can be used)
2. Frequency modulation and demodulation ( IC 8038/2206 can be used)
3. Pulse sampling, flat top sampling and reconstruction
4. Time Division Multiplexing and Demultiplexing of two bandlimited signals.
5. FSK and PSK generation and detection
6. Measurement of frequency, guide wavelength, power, VSWR and attenuation in microwave test bench.
7. Obtain the Radiation Pattern and Measurement of directivity and gain of microstrip dipole and Yagi
antennas.
8. Determination of
• a. Coupling and isolation characteristics of microstrip directional coupler.
• b. Resonance characteristics of microstrip ring resonator and computation
• of dielectric constant of the substrate.
• c. Power division and isolation of microstrip power divider

PART-B: Simulation Experiments using
SCILAB/MATLAB/Simulink or LabVIEW
1.Simulate NRZ, RZ, half-sinusoid and raised cosine pulses and generate eye diagram for binary polar signaling.
2. Pulse code modulation and demodulation system.
3. Computations of the Probability of bit error for coherent binary ASK,
FSK and PSK for an AWGN Channel and Compare them with their
Performance curves.
4. Digital Modulation Schemes i) DPSK Transmitter and receiver, ii) QPSK
Transmitter and Receiver.

Course Outcomes
• Determine the characteristics and response of microwave waveguide.
• Determine the characteristics of microstrip antennas and devices and
compute the parameters associated with it.
• Design and test the digital and analog modulation circuits and display
the waveforms.
• Simulate the digital modulation systems and compare the error
performance of basic digital modulation schemes.

CD4051 IC DETAILS

ASK

Detector

OUTPUT WAVEFORM

FSK

Detector

OUTPUT WAVEFORM

PSK

Detector

OUTPUT Waveform

Aim: To demonstrate the Time Division Multiplexing and Demultiplexing for two band limited signals using IC CD4051.
Objective: To understand the working principle and importance of Time Division Multiplexing and Demultiplexing
scheme in communication system.
Apparatus Required:

4.Time Division Multiplexing and Demultiplexing of two bandlimited signals.

OUTPUT WAVEFORM

Tabulation

Determination of
a. Coupling and isolation characteristics of microstrip directional
coupler.
b. Resonance characteristics of microstrip ring resonator and
computation of dielectric constant of the substrate.
c. Power division and isolation of microstrip power divider

a. Coupling and isolation characteristics of microstrip directional
coupler.
Aim: To determine the coupling and isolating characteristic of Microstrip Directional
Coupler.
Objective: To understand the coupling and isolation characteristics of directional
coupler.

• Apparatus Required:
Sl.No Apparatus Range Quantity
1 Microwave signal source with modulation 2.1 to 3 GHz 1
2 Attenuator pad 3dB 1
3 Coaxial Detector 2 to 3 GHz 1
4 VSWR Meter 1
5 Matched Loads 50Ω 2
6
Directional Coupler
(Microstrip parallel coupled coupler )
2 to 3 GHz 1
7 Connecting Cables

Directional Coupler

Measured Data and Calculation of Coupling
Frequency
(GHZ)
VSWR METER READING COUPLING
C(dB)=P’1i-P’3s
P1i P3s P’1i P’3s
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

Department of ECE
Measured Data and Calculation of Isolation
Frequency
(GHZ)
VSWR METER READING ISOLATION(dB)
=P’1i-P’4s
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

b. Resonance characteristics of microstrip ring resonator and
computation of dielectric constant of the substrate.
Aim: To determine the resonance characteristics of a Microstrip Ring Resonator and to
calculate the relative dielectric constant r of the substrate.
Objective: To understand resonance characteristics of ring resonator.

Apparatus Required:
4 VSWR Meter 1
5 Microstrip Ring Resonator 2 to 3 GHz 1
6 Connecting Cables

Layout of Microstrip ring resonator with input and output lines.

εr=
R Mean radius of the ring
n Mode number
λg  Guide wave length in microstrip
eff =Effective dielectric constant of microstrip
V0 Free space velocity
fr Resonant frequency of the ring
r Relative dielectric constant of the substrate
h Height of the substrate
w Width of the substrate

Ring resonator

Measured Data to identify resonant frequency
Frequency (GHZ) Vswr Meter Reading

Calculation
h=
w=
R=
fr=
n=1
v0=
eff =
r =
Outcome: After the completion of experiment the students are able to
understand the resonance characteristics of ring resonator.

c. Power division and isolation of microstrip power divider
Aim: To determine the power division and isolation characteristic of Microstrip Power
Divider.
Objective: To understand the power division and isolation characteristic of Microstrip Power
Divider.

Apparatus Required:
4 VSWR Meter 1
5 Matched Loads 50Ω 1
6 Microstrip Power divider 2 to 3 GHz 1
7 Connecting Cables

Power Divider

Measured Data and Calculation of Power Division
Frequency
(GHZ)
VSWR METER READING Power Division
Port1 and 2
P’1i-P’2s
Power Division
Port1 and 3
P’1i-P’3s
P1i P2s P3s P’1i P’2s P’3s
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

Measured Data and Calculation of Isolation
Freq(GHZ) VSWR METER READING ISOLATION
P’2i-P’3s
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8

DIRECTIVITY OF ANTENNA

• Directivity: It is a fundamental antenna parameter. It is a measure of how 'directional' an antenna's radiation
pattern is. An antenna that radiates equally in all directions would have directivity 1 (or 0 dB).
• The directivity can be calculated by approximate formula
• D= =
• The radiation pattern of a practical antenna generally includes minor lobes. If we neglect the effect of minor
lobes and amount of power loss in minor lobes then the approximate formula to obtain directivity in practice is :
• D=
• The directivity is dimension less quantity and in decibels directivity is given as
D (dBi)=10log10(D)

Antenna test setup for measurement of radiation pattern

Measured Data for E-plane Pattern (Yagi antenna)

Measured Data for H-plane Pattern (Yagi antenna)

• Observation and calculation:
• From the plot of radiation pattern
• Half power beam width for E-plane pattern==_________
• Half power beam width for H-plane pattern==_________
• Directivity of Yagi antenna: D= =_________
• Directivity of Yagi antenna in dB: (D) in dB=10log10 (D) =_______

Measured Data for E-plane Pattern (Printed Dipole antenna)

Measured Data for H-plane Pattern (Printed Dipole antenna)

• Observation and calculation:
• From the plot of radiation pattern
• Half power beam width for E-plane pattern==_________
• Half power beam width for H-plane pattern==_________
• Directivity of printed dipole antenna: D= =_________
• Directivity of printed dipole antenna in dB: (D) in dB=10log10 (D) =_______

• Result: radiation pattern and to calculate directivity of Yagi antenna and printed dipole
antenna is obtained
• Outcome: After the completion of experiment the students are able to understand and
plot the radiation pattern and to calculate directivity of Yagi antenna and printed dipole
antenna

Amplitude Modulation and Demodulation: i) Standard AM, ii)DSBSC
(LM741 and LF398 ICs can be used
Aim:To design a collector modulator for frequency of 455 KHz, To calculate power with and without modulation.
Objectives:
This experiment enables students to get practical experience in design, assembly, testing and evaluation of
amplitude modulation using transistor/FET

Design:
• f = 455 kHz
•  T=2.2sec
• For clamping;
• RbCb >> T
•  Let RbCb =100T
• With Rb = 10k, we get Cb = 0.022F
• Formulae:
1. Power without modulation = Pc =Vc
2
/ 8RL
2. Modulation Index .m = (Emax – Emax) / (Emax + Emin)
3. Total power of AM Signal, Pt = Pc( 1+m2
/2)

CIRCUIT DIAGRAM:

Model Plots:

Tabular Column:
Sl.No. Vm(p-p) volts Vc (p-p)volts Emax Emin
Modulation index
`m`

Demodulator

• Demodulated output:

• Result: AM modulation and demodulation waveforms are observed. The total power of the Modulated signal
is calculated.
• Outcomes:
Following are the program outcomes of AM signal using transistors/FET
 Students understand the concept high level modulation and low level modulation (AM).
 They also understand the principles and limitations of Envelope detectors.

1. What is modulation?
• Ans: Modulation is the process of varying characteristics of a periodic waveform, called the carrier signal, with a
modulating signal that typically contains information to be transmitted.
• 2. What is amplitude modulation?
Ans: Amplitude Modulation is the process of varying amplitude of carrier signal, with respect
to amplitude of modulating signal
• 3. What are the different types of analog modulation?
Ans: There are three basic types of analog modulations.
i. AM or Amplitude Modulation
ii. FM or Frequency Modulation
iii. PM or Phase modulation
VIVA QUESTIONS

• 4. What is the need for modulation?
Ans: need for modulation
i) to reduce the antenna height
ii) to multiplex the more number of signals
iii) to reduce the noise & distortions
iv) to narrow banding the signal
v) to reduce equipment complexity
• 5. What are the objectives met by modulation?
Ans: Length of antenna is shortened, signal loss is reduced, ease of radiation, adjustment of bandwidth,
shifting signal frequency of the assigned value.

• 6. What is Transmission Bandwidth?
• Ans: Transmission bandwidth of an AM wave,For positive frequencies, the highest frequency component of the AM
wave equals fc + W, and the lowest frequency component equals fc – W. The difference between these two
frequencies defines the transmission bandwidth BT for an AM wave.
• 7. Limitations of Amplitude Modulation (DSBFC)?
• Ans: Waste of power in the information-less “with-carrier” part.
• Wasteful of power and bandwidth
• 8. What is envelope detector?
• Ans: A circuit containing a diode in series with an RC network, used to perform demodulation. An envelope
detector, which demodulates an AM signal, cannot demodulate an SSB signal

FREQUENCY MODULATION USING 8038/2206
Aim: To generate Frequency Modulated Signal using IC 8038.
Objectives:
• After completion of this experiment the students are able to to perform the Frequency modulation using IC
8038/2206 and Build simple envelope detector for FM demodulation and to calculate the modulation index
for various modulating voltages.

PIN Details and specifications of IC 8038
Parameter
Specific
ation
Supply Voltage
(V- to V+) 36V
Input Voltage V- to V+
Input Current 25mA
Output Sink
Current 25mA
Temperature
Range
0°C to
70°C

Functional Block diagram of IC 8038

Circuit Diagram
• Design:
• Assume the frequency = 30 KHz
• F = 1 / (5/3 RAC [1 + RB /(2RA –RB)])
• Let RA = RB = R
•  F = 3 /[5 (2RC)] = 0.3 /RC
• Let R = 10 K
•  C = 0.3 /RF
• = 1000 Pf

Model Plot

• Formulae:
• Modulation Index = m = f / fm
• BW = 2(f + fm)
• From Wave form
• f= (fH – fL)/2
• Modulation index m = f / fm

Result:
Frequency modulation circuit is verified.
Outcomes:
Following are outcomes of Frequency modulation using IC 8038/2206 and demodulation.
• This experiment enables students to
 Students understand the concept high level modulation and low level modulation (FM).
 Anayse the changes in the wave under FM when the amplitude or frequency of the modulating signal is
increased
 Anayse the happens when a stronger signal and a weaker signal both overlap at the same frequency in FM

Viva Questions:
1. What is frequency deviation?
Ans: Frequency deviation – the maximum frequency change between a modulated and un modulated carrier signal.
2. What is discriminator?
Ans: Discriminator is a device that demodulates an FM signal.
3. FM modulation index?
Ans: FM modulation index – the ratio of frequency deviation to the message signal frequency.
4. What is Angle Modulation?
Ans: The angle of the carrier is varied in accordance with the base band signal.
Commonly used angle modulation i) Phase modulation ii) Frequency modulation

PULSE SAMPLING, FLAT TOP SAMPLING AND
RECONSTRUCTION
Aim: Demonstrate Pulse sampling, flat top sampling and reconstruction.
Objectives:
• After completion of this experiment the students are able to design and set up the Pulse sampling circuit, flat top
sampling circuit and reconstruction circuit for the original signal.

Circuit Diagram
Design: Demodulator
fm= 1/2πRC = 200 Hz
Let C=0.1 f
R= 1/ 2πfmC = 7.96 K 10 K

Model Plot

Result: PAM signal is generated and demodulated.
Outcomes:
Following are outcomes of Pulse sampling, flat top sampling and reconstruction.
This experiment enables students to
 Gain hands-on experience in building Pulse sampling, flat top sampling ang reconstruction.
 Differentiate between Impulse sampling, Natural sampling, Flat Top sampling.
 Analyze output waveforms of pulse and flattop sampling and reconstructed signal waveforms.

Viva Questions:
1. What is sampling? What is Sampling Theorem?
Ans: Sampling is defined as the process in which analog signals are converted into digital signals. It means that a continuous time
signal is converted into a discrete time signal.
Sampling Theorem is defined as : ’The continuous time signal that can be represented in its samples and recovered back if the
sampling frequency (fs) is greater than the maximum frequency of the signal (fm) that is fs >2fm’.
2. Define PAM and write down its drawbacks?
Ans: Pulse Amplitude Modulation is the process by which the amplitude of the regularly spaced pulses varies according to the
amplitude of the modulating signal.
The drawbacks are:
a. Since the amplitude of the pulses varies therefore the peak power of the modulating s/g is much greater.
b. The bandwidth required for transmitting is greater since the amplitude varies.

3. What do you mean by Nyquist rate?
Ans: In case of Nyquist rate, the sampling frequency is equal to the maximum frequency of the signal and therefore the
successive cycles of the spectrum does not overlap.
4. What is under sampling?
Ans: Under sampling is also known as aliasing effect in which the sampling frequency is less than the maximum
frequency of the signal and therefore the successive cycles of the spectrum overlap.
5. How can be aliasing be avoided?
Ans: Aliasing can be avoided if:
i. Sampling frequency must be greater than the frequency of the modulating signal.
ii. The frequency should be band limited to maximum frequency of the signal(fm) Htz.
iii. If pre-alias filter is used.

COMMUNICATION LAB PPT CONTAINS BOTH HARDWARE AND SOFTWARE

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