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Name: Scot
Status: student
Age: 40s
Location: N/A
Country: N/A
Date: 1999 

Why does amplitude modulation of a carrier signal produce both an upper and a lower sideband?

When you amplitude modulate a carrier, you are mixing a radio-frequency wave with an audio-frequency wave (the audio signal). The mixing of two frequencies produces both the sum and difference of the frequencies, for the simple reason that:

cos(w1 t) cos(w2 t) = 0.5 ( cos[(w1+w2)t] + cos[(w1-w2)t] )

w1 is the carrier frequency, w2 is the audio frequency. You see the two sidebands (w1+w2 and w1-w2) right there. Typically most of the power goes into the original carrier (w1) because the mixing isn't very efficient. So you get three signals.


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