Exploring the Concepts of AM Modulation

In summary, AM (amplitude modulation) wave is produced by multiplying the carrier wave and modulation wave, but the equation includes a constant because the amplitude of the carrier is changing with time due to the modulating signal. In single sideband AM, cancelling one sideband does not affect the information in the wave, and the transformation from double sideband to single sideband causes the amplitude to change according to the instantaneous value of the modulating signal.
  • #1
atomic_light11
3
0
AM amplitude modulation---

Hi everyone, I am learning AM recently, but I have some question that keep troubling me..

1. We know that AM wave is produced by the multiplication of carrier wave and modulation wave. But why does the equation of AM wave is not a direct multiplication of Vm×Vc but consist of a constant? Can anyone explain the general concept of the AM wave equation?

Why it is
Vam = [Ec + Emcos(ωmt)]cos(ωct)

but not
Vam = [Eccos(ωct)] [Emcos(ωmt)]

2. In single sideband AM, why does the cancelling of one sideband doesn't affect the information in the wave? And what is the effect to the wave pattern after the AM wave has been transform from double sideband (DSBFC) to single sideband (SSBFC)?

Thanks!
 
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  • #2
Hi! :smile:

The amplitude of the carrier is EC. This is the base amplitude of the carrier. when it is modulated with a modulating signal eM, It's amplitude is changing according to the instantaneous value of eM.

Have a look at the waveforms:

Capture4.PNG


Vam = [Ec + Emcos(ωmt)]cos(ωct)

In this equation,
[Ec + Emcos(ωmt)] refers to the instantaneous amplitude of the am wave, which is, you know, changing with time...
cos(ωct) is the frequency component of the wave.

Compare with v = Vm sin (ωt + [itex]\phi[/itex])

If it was Vam = [Eccos(ωct)] [Emcos(ωmt)]

That means [Eccos(ωct)] is the amplitude. In this case, the amplitude goes negative in one half cycle. It is meaningless. So the main amplitude (with zero modulating signal) is EM. But the instantaneous value of the modulating signal ADDS to this main amplitude EM. So that's why you have that equation! Have a closer and more detailed look at that waveform, it will be clear to you!
 

1. What is AM amplitude modulation?

AM amplitude modulation is a method of transmitting data or information through radio waves by varying the amplitude (strength) of the wave. This allows for the transmission of audio signals, such as music or speech, to be received and decoded by a radio receiver.

2. How does AM amplitude modulation work?

AM amplitude modulation works by superimposing the audio signal onto a carrier wave. The amplitude of the carrier wave is varied in proportion to the amplitude of the audio signal, creating a modulated wave that can be transmitted over long distances. The receiver then extracts the audio signal by detecting and amplifying the changes in amplitude.

3. What are the advantages of using AM amplitude modulation?

The main advantage of AM amplitude modulation is that it is a simple and cost-effective method of transmitting audio signals. It also has a wide coverage area and can penetrate buildings and other obstacles, making it suitable for broadcasting. Additionally, AM signals can be received by a wide range of receivers, making it accessible to a larger audience.

4. What are the limitations of AM amplitude modulation?

One of the main limitations of AM amplitude modulation is that it is susceptible to interference from other radio signals. This can result in poor sound quality or complete loss of the signal. AM also has a limited bandwidth, meaning it can only transmit a narrow range of frequencies, which can affect the sound quality. Additionally, AM signals are more prone to atmospheric disturbances, such as static and noise.

5. How is AM amplitude modulation used in everyday life?

AM amplitude modulation is commonly used in radio broadcasting for AM radio stations. It is also used in some forms of two-way communication, such as citizens band (CB) radio and aircraft communication. AM modulation is also used in some types of data transmission, such as shortwave radio and amateur radio.

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