Detailed Explanation of AM Modulation (Amplitude Modulation), its working principle, and basic Need of Modulation.
Communication is a process of conveying information at a distance. If the distance is involved is beyond direct communication, electronic communication comes into the picture. One of the principal techniques used in electronic communication is the modulation.
Modulation is the process of having the information signal to be transmitted alters a higher-frequency signal for the purpose of transmitting the information somewhere at the higher distance.
In electronic communication we usually study three types of modulation techniques:
- AM Modulation (Amplitude Modulation)
- FM Modulation (Frequency Modulation)
- PM Modulation (Phase Modulation)
The oldest and simplest method is AM Modulation Also known as Amplitude Modulation. And in this article, we will learn about Amplitude Modulation Step by Step.
What is AM Modulation (Amplitude Modulation)?
AM Modulation (Amplitude Modulation) is the technique in which the Amplitude of Carrier wave varies with the variation in the frequency and amplitude of Information Signal.
Few points to Remember:
- A carrier wave is High-Frequency, Sinusoidal Signal which has a greater frequency compared to the Information Signal.
- An Information signal may be audio, video signal which is sinusoidal in nature and it is also referred to as Baseband signal or Modulating Signal.
The concept of AM Modulation (Amplitude Modulation):
In order to transfer information signal at the higher distance, we use Modulation technique and one of the best modulation technique is AM Modulation (Amplitude Modulation) Technique. “In AM Modulation, the carrier wave amplitude changes in accordance with the amplitude and frequency variations of the information signal”.
Give figure below shows the information signal modulating a high-frequency carrier wave. In the modulation process, the carrier’s frequency remains constant only its amplitude varies with the variation of the information signal.
An increase in the amplitude of information signal can cause the increase in the carrier amplitude. Both positive and negative peaks of carrier wave vary with the variation of amplitude of information signal. An imaginary line connecting the positive peaks and negative peaks of the carrier waveform gives the exact shape of the information signal. This imaginary line on the carrier waveform is known as the envelope.
This envelope contains the real information of information signal as it has the exact shape as an information signal. And in order to maintain the real information in the envelope.
The amplitude of the modulating signal should be less than the amplitude of the carrier. When the amplitude of the modulating signal is greater than the amplitude of the carrier, distortion will occur, causing incorrect information to be transmitted.
υm < υc
- Here Vm is modulating Signal voltage also known as Information Signal voltage:
- Vc is Carrier voltage.
- where υm is the instantaneous value of information sine signal
- Vm = peak amplitude of information sine signal
- fm = frequency of modulating sine signal
υc= Vc sin(2πfct)
- where υc is the instantaneous value of carrier sine signal
- Vc = peak amplitude of carrier sine signal
- fc = frequency of carrier sine signal
Using this value of carrier wave voltage and information wave voltage we can calculate the overall modulated wave.
An envelope is consisting of the information signal in his top and bottom, in order to find out the envelope voltage either for the top or the bottom we can use the equation.
υ1= Vc+ υm= Vc+Vm(sin2πfmt)
Thus, we can write the instantaneous value of the complete modulated wave υ2 by substituting υ1 for the peak value of carrier voltage Vc as follows:
Now substituting the previously derived expression for v1 and expanding, we get the following:
= Vc (sin2πfct)+ (Vmsin2πfmt)*(sin 2πfct)
where υ2 is the instantaneous value of the AM wave, Vcsin2πfct is the carrier waveform, and (Vm (sin2πfmt))(sin 2πfct) is the carrier waveform multiplied by the information signal waveform.
It is the second part of the expression that is characteristic of AM Modulation.
A circuit must be able to produce a mathematical multiplication of the carrier and modulating signals in order for AM to occur. The AM wave is the product of the carrier and modulating signals.
The circuit used for producing AM is called a modulator. Amplitude modulators perform the product of the carrier and modulating signals.
Generation of an AM wave can be accomplished simply by using a nonlinear device (e.g., diode) in a square-law modulator.
Need for modulation:
Modulation is needed in a communication system to achieve the following basic needs
- Multiplexing (Process of transmitting two or more signals simultaneously over a channel)
- Reduction of antennas Size. (We will cover this in our upcoming articles)
- Narrow banding (Using modulation technique the bandwidth is reduced we can transmit our information with the less wasting of bandwidth).
Advantages of AM Modulation (Amplitude modulation):-
- Generation and detection of AM signals are very easy
- It is very cheap to build, due to this reason it is most commonly used in AM radio broadcasting.
Disadvantages of AM Modulation (Amplitude modulation):-
- Amplitude modulation is wasteful of power: The upper and lower sidebands of an envelope are same hence they utilize the amount of power in the Amplitude Modulation.
- Amplitude modulation is wasteful of bandwidth: The upper and lower sidebands of an AM wave are identical hence they have the same information. This means for the transmission of information only one sideband is necessary. In light of this observation, amplitude modulation is wasteful of channel bandwidth as it requires a transmission bandwidth equal to twice the message bandwidth.
In order to overcome these two limitations of AM Modulation (Amplitude Modulation), we make some sort of modifications in AM Modulation.
These modifications in AM Modulation are known as:
- Double Side Band Suppressed Carrier (DSB-SC):
- Single Side Band Suppressed Carrier (SSB-SC):
- Single Side Band (SSB)
- Vestigial Sideband (VSB)
All of these Amplitude Modulation techniques are covered, Click here
Application of AM Modulation (Amplitude modulation):-
- AM Radio Broadcasting
Also, Read our Article:
- Introduction to Electronic Communication.
- Types of Electronic Communication (Simplex, Duplex, and Half Duplex).
- Practical Applications of Simplex and Duplex Communication.
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