INDEX

SNo. NAME OF THE EXPERIMENT DATE REMARKS

1. To simulate Amplitude Modulation (AM). 16-08-2011

2. To simulate Frequency Modulation (FM). 23-08-2011

3. To study and simulate Amplitude Shift Keying(ASK). 30-08-2011

4. To study and simulate Frequency Shift Keying(FSK). 06-09-2011

5. To study and simulate Phase Shift Keying(PSK). 20-09-2011

6. To Study and simulate PAM Modulation. 04-10-2011

7. To Study and simulate PPM Modulation and demodulation.

18-10-2011

8. To simulate DPSK Modulation. 01-11-2011

9. To simulate demodulation of DPSK. 08-11-2011

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 ModulationWaveform:-

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.