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Experiment No. 1
Aim: To simulate AM Modulation.
Software Used : VisSim Comm 6.0
Theory:-Amplitude modulation is a process in which the amplitude of a carrier signal is varied in
accordance with modulating signal. Amplitude modulation (AM) is a method of impressing data
onto an alternating-current carrier waveform. The highest frequency of the modulating data is
normally less than 10 percent of the carrier frequency. The instantaneous amplitude(overall
signal power) varies depending on the instantaneous amplitude of the modulating data.
= initial phase of Carrier , A= Amplitude of Wave
Block Diagram:
Fig:- 1 Amplitude Modulation
Waveform:-
Result:- The Amplitude Modulation has been studied & Designed.
Experiment no. 2
Aim: To simulate FM Modulation.
Software Used: VisSim. Comm 6.0
Theory: Frequency Modulation is type of continuous wave modulation. FM may be defined
as the process in which a frequency of a signal called carrier is varied in accordance to
instantaneous value of another signal called modulating signal. The signal resulting from the
process of frequency modulation is called frequency modulated signal.
Modulation index:
As with other modulation indices,this quantity indicates by how much the modulated variable
varies around its unmodulated level. It relate to the variations in the frequency of the carrier
signal.
Frequency modulation is a technique of modulating the frequency of the carrier signal in
accordance with the frequency of the modulating or the information signal. As the information
signal has a very low frequency, therefore it cannot be transmitted over long distances. To
increase the efficiency of the modulating signal it is fed upon a carrier signal which has a very
high frequency. Now, this frequency of carrier signal is changed in accordance with the
information signal.
ωi = instantaneous frequencyωc = carrier frequencyΔω = carrier deviationωm = modulation frequency
Block Diagram:
Plot
Time (sec)0 2.5 5 7.5 10
-1
1
-1
1
sig
ph
FM ModFc= 2 Hz
Fig :- 2(a) FM Modulation
Waveforms:
Result : The Frequency Modulation has been simulated and verified.
Experiment No. 3
Aim : To study and simulate the Amplitude shift keying(ASK) modulation and demodulation.
Software Used: VisSim. Comm 6.
Theory: Basically digital modulation techniques may be classified into coherent and non -coherent
techniques ,depending upon whether the receiver is equipped with phase recovery circuit or not.
They are:
1. Coherent digital modulation techniques.
2. non- coherent digital modulation techniques.
Coherent Digital Modulation Techniques:
These are those techniques which employ coherent detection .In coherent detection ,the local
carrier generated at receiver is phase locked with carrier at transmitter.
Non – Coherent Digital Modulation Techniques:
These are those techniques in which the detection process does not need the receiver carrier to be
phase locked with transmitter.
Amplitude Shift Keying:
It is a coherent digital modulation technique. In this method there is only one energy carrier and
it is switched on or off depending upon the input binary sequence. It is also known as on –off
keying.
Block diagram
ASK MODULATION
ASK DEMODULATION
Waveforms:
Result: The Amplitude shift keying (ASK) has been simulated and studied.
Experiment No. 4
AIM : To study and stimulate the Frequency shift keying (FSK) Modulation and demodulation
Software Used: VisSim Comm. 6.0.
Theory:Frequency – Shift Keying (FSK) is a frequency modulation scheme in which digital information
is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary
FSK (BFSK). BFSK literally implies using a pair of discrete frequencies to transmit binary (0s
and 1s) information . With this scheme , the “1” is called the mark frequency and the “0” is
called the space frequency.
BlockDiagram:
Fig:- 5 (Frequency Shift Keying modulation and Demodulation)
Waveform:
Result: The Frequency Shift Keying (FSK) Modulation and Demodulation has been studied & Simulated.
Experiment No. 5
Aim:- To study and simulate Phase Shift Keying(PSK).
Simulator Used:- Vis Sim Version 6.0
Theory:- In Phase Shift Keying (PSK) modulation technique, the modulated output switches
between in-phase and out-of phase component of the carrier for every “one” to “zero” transitions
of modulating signal. The carrier frequency chosen for PSK modulation are 1MHZ (0 Degree)
and 1 MHZ (180 Degree).The phase detector works ion the principle of squaring loops. First step
in PSK detection is the square wave conversion using a Schmitt trigger. This enables the PSK
detector to be built around digital IC’s. BPSK (also sometimes called PRK, Phase Reversal
Keying, or 2PSK) is the simplest form of phase shift keying (PSK). It uses two phases which are
separated by 180° and so can also be termed 2-PSK. A binary phse shift keying signal can be
given as:
s(t) = A m(t) cos 2πfct
Block Diagram:
Fig. 5(a) Phase Shift Keying Modulation and Demodulation
Waveforms:-
Fig. 5(b) Carrier Signal
Fig. 5(c) Modulating Signal
Fig. 5(d) Modulated Signal
Fig. 5(e) Demodulated Signal
Result:- The Phase Shift Keying(PSK) modulation and demodulation has been studied and simulated .
Experiment-6
Aim: To study and simulate Pulse Amplitude Modulation.
Software used: VisSim Comm. Version 6.0
Theory:-Pulse-amplitude modulation, acronym PAM, is a form of signal modulation where the message
information is encoded in the amplitude of a series of signal pulses.. In this the signal is sampled
at regular intervals and each sample is made proportional to the magnitude of the signal at the
instant of sampling.These sampled pulses may then be sent either directly by a channel to the
receiving end or may be made to modulated using a carrier wave before transmission.
Block Diagram:-
Fig:- 8 (Pulse Amplitude Modulation)
Waveforms:-
Result: The Pulse amplitude Modulation has been studied and simulated.
Experiment-7
Aim : To study and simulate Pulse Position Modulation.
Software used: VisSim Comm. Version 6.0
Theory:-
Pulse-position modulation (PPM) is a form of signal modulation in which M message bits are
encoded by transmitting a single pulse in one of 2M possible time-shifts. This is repeated every T
seconds, such that the transmitted bit rate is M/T bits per second. It is primarily useful for optical
communications systems.
Block Diagram:-
Fig:- 8 Pulse Position Modulation
Waveforms:-
Result: The Pulse Position Modulation has been studied and simulated.
Experiment No. 8
Aim: To simulate DPSK Modulation.
Software Used: VisSim. Comm 6.0
Theory: Differential phase shift keying (DPSK), a common form of phase modulation conveys data by
changing the phase of carrier wave. In Phase shift keying, High state contains only one cycle but
DPSK contains one and half cycle. High state is represented by a M in modulated signal and low
state is represented by a wave which appears like W in modulated signal DPSK encodes two
distinct signals of same frequency with 180 degree phase difference between the two. This
experiment requires two 180 degree out of phase carrier and modulating signals. Sine wave from
oscillator is selected as carrier signal. DSG converts DC input voltage into pulse trains. These
pulse trains are taken as modulating signals. In actual practice modulating signal is digital form
of voice or data. Sine wave is selected as carrier and 180 degree phase shift is obtained using
Opamp as shown in figure below.
Block Diagram:
Fig 9-1 DPSK modulation
Waveforms:
Result:- The DPSK modulation has been studied and stimulated.
Experiment No. 9
Aim: To simulate DPSK Demodulation.
Software Used: VisSim. Comm 6.0
Theory:
Differential phase shift keying (DPSK), a common form of phase modulation conveys data by
changing the phase of carrier wave. In Phase shift keying, High state contains only one cycle but
DPSK contains one and half cycle. High state is represented by a M in modulated signal and low
state is represented by a wave which appears like W in modulated signal DPSK encodes two
distinct signals of same frequency with 180 degree phase difference between the two. This
experiment requires two 180 degree out of phase carrier and modulating signals. Sine wave from
oscillator is selected as carrier signal. DSG converts DC input voltage into pulse trains. These
pulse trains are taken as modulating signals. In actual practice modulating signal is digital form
of voice or data. Sine wave is selected as carrier and 180 degree phase shift is obtained using
Opamp as shown in figure below.
Block Diagram:
Fig 9-1 DPSK Demodulation
Waveforms:
Result: - The DPSK Demodulation has been studied and stimulated.