B Amplitude Modulation: Unique Frequency & Bandwidth

AI Thread Summary
Amplitude Modulation (AM) involves a carrier wave with a single frequency, but varying amplitudes lead to a range of frequencies, creating bandwidth. This phenomenon is linked to the variations in the modulating signal frequencies, as amplitude changes introduce additional frequency components. The Fourier transform illustrates this, showing that a sine wave with constant amplitude has a single frequency, while one with varying amplitude results in a spectrum of frequencies. Tools like Mathematica or Matlab can visualize these effects by transforming different modulated sine waves. Understanding these principles clarifies why AM signals have bandwidth despite the carrier's unique frequency.
Tulio Cesar
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1) I am studying modulation of carrier waves, but I still can't understand something: knowing that in AM the carrier wave has only one frequency and just only its amplitudes vary according to variations in modulating signal amplitudes, why AM carrier waves have bandwidth if the frequency is supposed to be unique? Does it have any point with variations in the modulating signal frequencies? If it does, what about simple signals with only just one frequency? Thank you all for the answers.
 
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The only way it can have one frequency is to have a constant amplitude. Once you start varying the amplitude, it necessarily consists of a range of frequencies. Are you familiar with the Fourier transform? If you take the Fourier transform of a sine wave of constant amplitude, it is a delta function, meaning it has only a single frequency. But if you take the Fourier transform of a sine wave of varying amplitude, it will consist of a range of frequencies. If you have a program that can take the Fourier transform of different functions (Mathematica, Matlab, ...) try putting in sine waves with different modulations and you will see the result.
 
Tulio Cesar said:
1) I am studying modulation of carrier waves, but I still can't understand something: knowing that in AM the carrier wave has only one frequency and just only its amplitudes vary according to variations in modulating signal amplitudes, why AM carrier waves have bandwidth if the frequency is supposed to be unique? Does it have any point with variations in the modulating signal frequencies? If it does, what about simple signals with only just one frequency? Thank you all for the answers.
this article may answer your questions

http://www.pa2old.nl/files/am_fundamentals.pdf Dave
 
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