Why do you get sideband frequencies for amplitude modulation (AM)?

Thread starter CraigH
Start date May 15, 2012
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Amplitude Frequencies Modulation

In summary, the AM carrier frequency is constant but the modulation signal can change. When modulating the carrier frequency with a pure sine wave, the resulting AM waveform can be viewed as a product of two sine waves or as a sum of three sine waves: the carrier and two side bands. This is due to the non-linear nature of AM mixing, which can be simplified using trigonometry. The side bands exist during transmission and are necessary for the signal to be properly transmitted and received. They can be observed using spectrum analysis and are a result of the modulation process, where the average energy over a period of time can make it seem like there are distinct frequencies with related phases.

Feb 6, 2014

sophiecentaur

Science Advisor

Gold Member

Is there some 'agreed subset' of Maths that is allowed and anything harder has to be explained in those limited terms?
Using Maths-based terms like sine wave and frequency is, apparently, OK but we must exclude aspects of Calculus or exponentials? Sounds pretty arbitrary to me and it's bound to limit the depth of understanding. Fair enough, as long as people realize that limit and don't try to make valid predictions beyond it.

<h2>1. Why do you get sideband frequencies for amplitude modulation (AM)?</h2><p>Sideband frequencies are a result of the process of amplitude modulation, where the amplitude of a carrier wave is varied in proportion to the amplitude of the modulating signal. This variation creates new frequencies, known as sidebands, that are located above and below the carrier frequency.</p><h2>2. How are sideband frequencies calculated in AM?</h2><p>The sideband frequencies in AM are calculated using the formula fc ± fm, where fc is the carrier frequency and fm is the modulating frequency. The plus sign represents the upper sideband (USB) and the minus sign represents the lower sideband (LSB).</p><h2>3. What is the purpose of sideband frequencies in AM?</h2><p>The sideband frequencies in AM contain the information that is being transmitted. They allow for the modulation of the carrier wave, which carries the signal, without altering the original frequency. This makes it possible to transmit multiple signals at different frequencies simultaneously.</p><h2>4. Can sideband frequencies be eliminated in AM?</h2><p>No, it is not possible to completely eliminate sideband frequencies in AM. However, techniques such as single sideband (SSB) modulation can be used to suppress one of the sidebands, resulting in a more efficient use of the transmission bandwidth.</p><h2>5. Are sideband frequencies present in other types of modulation?</h2><p>Yes, sideband frequencies can also be found in other types of modulation, such as frequency modulation (FM) and phase modulation (PM). However, the sideband frequencies in these types of modulation are not as prominent as in AM, as the carrier wave is not directly affected by the modulating signal.</p>

1. Why do you get sideband frequencies for amplitude modulation (AM)?

Sideband frequencies are a result of the process of amplitude modulation, where the amplitude of a carrier wave is varied in proportion to the amplitude of the modulating signal. This variation creates new frequencies, known as sidebands, that are located above and below the carrier frequency.

2. How are sideband frequencies calculated in AM?

The sideband frequencies in AM are calculated using the formula fc ± fm, where fc is the carrier frequency and fm is the modulating frequency. The plus sign represents the upper sideband (USB) and the minus sign represents the lower sideband (LSB).

3. What is the purpose of sideband frequencies in AM?

The sideband frequencies in AM contain the information that is being transmitted. They allow for the modulation of the carrier wave, which carries the signal, without altering the original frequency. This makes it possible to transmit multiple signals at different frequencies simultaneously.

4. Can sideband frequencies be eliminated in AM?

No, it is not possible to completely eliminate sideband frequencies in AM. However, techniques such as single sideband (SSB) modulation can be used to suppress one of the sidebands, resulting in a more efficient use of the transmission bandwidth.

5. Are sideband frequencies present in other types of modulation?

Yes, sideband frequencies can also be found in other types of modulation, such as frequency modulation (FM) and phase modulation (PM). However, the sideband frequencies in these types of modulation are not as prominent as in AM, as the carrier wave is not directly affected by the modulating signal.