Analog Data to Analog Signal, Data Communication Fundamentals Electronics and Communication Engineering (ECE) Notes | EduRev

Electronics and Communication Engineering (ECE) : Analog Data to Analog Signal, Data Communication Fundamentals Electronics and Communication Engineering (ECE) Notes | EduRev

 Page 1


 
 
 
 
 
 
 
Module 
2 
 
 
 
    Data 
Communication 
Fundamentals 
 
Version 2 CSE   IIT, Kharagpur 
Page 2


 
 
 
 
 
 
 
Module 
2 
 
 
 
    Data 
Communication 
Fundamentals 
 
Version 2 CSE   IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
Lesson 
5 
 
 
Analog Data to  
Analog Signal 
 
 
Version 2 CSE   IIT, Kharagpur 
Page 3


 
 
 
 
 
 
 
Module 
2 
 
 
 
    Data 
Communication 
Fundamentals 
 
Version 2 CSE   IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
Lesson 
5 
 
 
Analog Data to  
Analog Signal 
 
 
Version 2 CSE   IIT, Kharagpur 
Specific Instructional Objective 
 
On completion, the student will be able to: 
• Explain the need for Modulation 
• Distinguish different modulation techniques 
• Identify the key features of Amplitude modulation 
• Explain the advantages of SSB and DSBSC transmission 
• Explain how the baseband signal can be recovered 
 
2.5.1 Introduction 
 
Although transmission of digital signal is preferred, it is not always feasible to transmit in 
digital form because it requires channel of high bandwidth having low pass 
characteristics. On the other hand, an analog transmission requires lower bandwidth 
having band pass characteristics. The process involved in analog transmission is known 
as modulation, which requires manipulation of one or more of the parameters of the 
carrier that characterizes the analog signal. Figure 2.5.1 depicts the modulation process to 
get analog signal. 
 
 
 
 
 
 
 
 
 
 
Figure 2.5.1 Translation of analog data to analog signal 
 
 
Some of the important advantages of modulation are summarized below: 
 
Frequency translation: Modulation translates the signal from one region of frequency 
domain to another region. This helps to transmit the modulated signal with minimum 
attenuation through a particular medium. 
 
Practical size of antenna: Modulation translates baseband signal to higher frequency, 
which can be transmitted through a bandpass channel using an antenna of smaller size. 
This has made communication practical. 
Narrowbanding: As modulation translates a signal from lower frequency domain to 
higher frequency domain, the ratio between highest to lowest frequency of the modulated 
signal becomes close to 1.  
 
Version 2 CSE   IIT, Kharagpur 
Page 4


 
 
 
 
 
 
 
Module 
2 
 
 
 
    Data 
Communication 
Fundamentals 
 
Version 2 CSE   IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
Lesson 
5 
 
 
Analog Data to  
Analog Signal 
 
 
Version 2 CSE   IIT, Kharagpur 
Specific Instructional Objective 
 
On completion, the student will be able to: 
• Explain the need for Modulation 
• Distinguish different modulation techniques 
• Identify the key features of Amplitude modulation 
• Explain the advantages of SSB and DSBSC transmission 
• Explain how the baseband signal can be recovered 
 
2.5.1 Introduction 
 
Although transmission of digital signal is preferred, it is not always feasible to transmit in 
digital form because it requires channel of high bandwidth having low pass 
characteristics. On the other hand, an analog transmission requires lower bandwidth 
having band pass characteristics. The process involved in analog transmission is known 
as modulation, which requires manipulation of one or more of the parameters of the 
carrier that characterizes the analog signal. Figure 2.5.1 depicts the modulation process to 
get analog signal. 
 
 
 
 
 
 
 
 
 
 
Figure 2.5.1 Translation of analog data to analog signal 
 
 
Some of the important advantages of modulation are summarized below: 
 
Frequency translation: Modulation translates the signal from one region of frequency 
domain to another region. This helps to transmit the modulated signal with minimum 
attenuation through a particular medium. 
 
Practical size of antenna: Modulation translates baseband signal to higher frequency, 
which can be transmitted through a bandpass channel using an antenna of smaller size. 
This has made communication practical. 
Narrowbanding: As modulation translates a signal from lower frequency domain to 
higher frequency domain, the ratio between highest to lowest frequency of the modulated 
signal becomes close to 1.  
 
Version 2 CSE   IIT, Kharagpur 
Multiplexing: Different base band signals originating from different sources can be 
translated to different frequency ranges. This allows transmission of different signals 
through the same medium using frequency division multiplexing (FDM) to be discussed 
in the following lesson.  
The modulation technique can be broadly divided into two basic categories; Amplitude 
modulation and Angle modulation. The Angle modulation can be further divided into two 
more categories; Frequency and Phase modulations as shown in Fig. 2.5.2. Various 
modulation techniques are discussed in the following sections. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.5.2 Categories of modulation techniques 
 
2.5.2 Amplitude Modulation (AM) 
  
This is the simplest form of modulation where the amplitude of the carrier wave is 
modulated by the analog signal known as the modulating signal. A signal to be 
modulated, a carrier and the modulated signal are shown in Fig. 2.5.3. Let the modulating 
waveform is given by e
m
(t) = E
m
 cos (2 pf
m
t) and the carrier signal is given by e
c
(t) = E
c 
cos (2 pf
c
t + F
c
). Then the equation of the modulated signal is given by 
     s(t) = (E
c 
+ E
m 
cos 2 pf
m
t) cos 2 pf
c
t   
 
Modulation Index: The modulation index, represented by m, is given by  
m = (E
max 
-  E
min 
)/ (E
max 
+  E
min 
) = E
m 
/ E
c,  
where E
max 
= E
c 
+  E
m 
,   
E
min 
= E
c 
-  E
m
, and s(t) = E
c 
(1 + m cos 2 pf
m
t) cos 2 pf
c
t, 
 
The envelope of the modulated signal is represented by 1+m e
m
(t) for m
 
< 1. The 
envelope of the modulated signal for different modulation index is shown in Fig. 2.5.4.  
Loss of information occurs when m
 
> 1. 
Version 2 CSE   IIT, Kharagpur 
Page 5


 
 
 
 
 
 
 
Module 
2 
 
 
 
    Data 
Communication 
Fundamentals 
 
Version 2 CSE   IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
 
 
 
 
 
 
Lesson 
5 
 
 
Analog Data to  
Analog Signal 
 
 
Version 2 CSE   IIT, Kharagpur 
Specific Instructional Objective 
 
On completion, the student will be able to: 
• Explain the need for Modulation 
• Distinguish different modulation techniques 
• Identify the key features of Amplitude modulation 
• Explain the advantages of SSB and DSBSC transmission 
• Explain how the baseband signal can be recovered 
 
2.5.1 Introduction 
 
Although transmission of digital signal is preferred, it is not always feasible to transmit in 
digital form because it requires channel of high bandwidth having low pass 
characteristics. On the other hand, an analog transmission requires lower bandwidth 
having band pass characteristics. The process involved in analog transmission is known 
as modulation, which requires manipulation of one or more of the parameters of the 
carrier that characterizes the analog signal. Figure 2.5.1 depicts the modulation process to 
get analog signal. 
 
 
 
 
 
 
 
 
 
 
Figure 2.5.1 Translation of analog data to analog signal 
 
 
Some of the important advantages of modulation are summarized below: 
 
Frequency translation: Modulation translates the signal from one region of frequency 
domain to another region. This helps to transmit the modulated signal with minimum 
attenuation through a particular medium. 
 
Practical size of antenna: Modulation translates baseband signal to higher frequency, 
which can be transmitted through a bandpass channel using an antenna of smaller size. 
This has made communication practical. 
Narrowbanding: As modulation translates a signal from lower frequency domain to 
higher frequency domain, the ratio between highest to lowest frequency of the modulated 
signal becomes close to 1.  
 
Version 2 CSE   IIT, Kharagpur 
Multiplexing: Different base band signals originating from different sources can be 
translated to different frequency ranges. This allows transmission of different signals 
through the same medium using frequency division multiplexing (FDM) to be discussed 
in the following lesson.  
The modulation technique can be broadly divided into two basic categories; Amplitude 
modulation and Angle modulation. The Angle modulation can be further divided into two 
more categories; Frequency and Phase modulations as shown in Fig. 2.5.2. Various 
modulation techniques are discussed in the following sections. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.5.2 Categories of modulation techniques 
 
2.5.2 Amplitude Modulation (AM) 
  
This is the simplest form of modulation where the amplitude of the carrier wave is 
modulated by the analog signal known as the modulating signal. A signal to be 
modulated, a carrier and the modulated signal are shown in Fig. 2.5.3. Let the modulating 
waveform is given by e
m
(t) = E
m
 cos (2 pf
m
t) and the carrier signal is given by e
c
(t) = E
c 
cos (2 pf
c
t + F
c
). Then the equation of the modulated signal is given by 
     s(t) = (E
c 
+ E
m 
cos 2 pf
m
t) cos 2 pf
c
t   
 
Modulation Index: The modulation index, represented by m, is given by  
m = (E
max 
-  E
min 
)/ (E
max 
+  E
min 
) = E
m 
/ E
c,  
where E
max 
= E
c 
+  E
m 
,   
E
min 
= E
c 
-  E
m
, and s(t) = E
c 
(1 + m cos 2 pf
m
t) cos 2 pf
c
t, 
 
The envelope of the modulated signal is represented by 1+m e
m
(t) for m
 
< 1. The 
envelope of the modulated signal for different modulation index is shown in Fig. 2.5.4.  
Loss of information occurs when m
 
> 1. 
Version 2 CSE   IIT, Kharagpur 
 
 
Figure 2.5.3 Amplitude Modulation 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 2.5.4 (a) Envelope of the signal 1+m e
m
(t) for m
 
< 1 
 
 
 
 
 
Version 2 CSE   IIT, Kharagpur 
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