Power Efficiency of AM Signal Bandwidth of AM signal Types of Amplitude Modulation (AM)

1. EC8491-Communication Theory
Dr.Arun Chokkalingam
Professor
 Power Efficiency of AM
Signal
 Bandwidth of AM signal
 Types of Amplitude
Modulation (AM)
Amplitude Modulation-AM

2. Important Recourses of Communication System
1. Transmitting power
2. Bandwidth

3. Power Efficiency of AM
 %𝜼 =
𝑷𝒐𝒘𝒆𝒓 𝒊𝒏 𝒔𝒊𝒅𝒆𝒃𝒂𝒏𝒅𝒔
𝑻𝒐𝒕𝒂𝒍 𝑷𝒐𝒘𝒆𝒓
× 𝟏𝟎𝟎 =
𝑷𝑳𝑺𝑩+𝑷𝑼𝑺𝑩
𝑷𝑻
× 𝟏𝟎𝟎
 %𝜼 =
𝒎𝟐𝑽𝒄
𝟐
𝟖𝑹 + 𝒎𝟐𝑽𝒄
𝟐
𝟖𝑹
𝑽𝒄
𝟐
𝟐𝑹 𝟏+
𝒎𝟐
𝟐
× 𝟏𝟎𝟎
 %𝜼 =
𝒎𝟐
𝟐+𝒎𝟐 × 𝟏𝟎𝟎 Assuming m=1(100% modulation), %𝜼 =
𝟏
𝟑
× 𝟏𝟎𝟎 = 𝟑𝟑. 𝟑%.
 This means that only 33.3% of total power is useful and remaining power is wasted by the
transmission of carrier.
 The amount of useful message power present in AM wave is expressed by the term
called transmission efficiency
 It is the ratio of total sideband power to the total transmitted power

4. Bandwidth of AM signal
▪ The difference between upper and lower side frequencies will be 2fm and this is
the bandwidth of AM signal.
▪ BW =(fc+fm)-(fc-fm)
=fc+fm-fc+fm)
=2fm

5. Types of Amplitude Modulation (AM)
1. AM-Double Side Band Full Carrier (DSB-FC)
2. AM-Double Side Band Suppressed Carrier (DSB-SC)
3. AM-Single Side Band Suppressed Carrier (SSB-SC)
4. Vestigial Sideband Modulation (VSB)
Frequency domain representation of AM wave, 𝑽𝑨𝑴 (𝒕) = 𝑽𝒄𝒄𝒐𝒔𝝎𝒄𝒕 +
𝒎𝑽𝒄
𝟐
𝒄𝒐𝒔 𝝎𝒄 − 𝝎𝒎 +
𝒎𝑽𝒄
𝟐
𝒄𝒐𝒔 𝝎𝒄 + 𝝎𝒎 𝒕
Carrier LSB USB

6. Cont. .
Objective of different types of AM
1. To saveTransmitter power
2. To save bandwidth
b. Objective of AM-DSB-SC
1. To save power only
c&d. Objective of AM-SSB-SC
1.To save both power and Bandwidth

7. S.No DSB-FC DSB-SC SSB-SC VSB
1 It is a double side band
along with carrier AM.
It is a double side band
without carrier AM.
It is only one side band
AM, without carrier.
One Sideband and part of
LSB
2 B and width = 2fm Band width = 2 fm Band width = fm fm < Band width <2fm
3 Less number of channels
in a given frequency
range.
Less number of channels in a
given frequency range.
More number of
channels in a given
frequency range.
Moderate no .of channels
in a given frequency range
4 More power consumption. Moderate power
consumption
Least power
consumption
Moderate power
consumption
5 Power saved = 0% 67.7% 83.3% 75%
6 Transmission Efficiency
=33.33%
100% 100% 33.3 < Efficiency <100%
7 Easy reconstruction
at Receiver end.
Moderately difficult
reconstruction.
Difficult reconstruction. Difficult reconstruction.
8 No need of
synchronization.
Tracking might be required. synchronization or
tracking is essential.
synchronization or
tracking is essential
9 Radio Communication Telegraphy and telephone
communication
Telegraphy and
telephone
communication
TV Communication