Frequencies of Amplitude Modulated Wave
From equation (4), we have :
Cm(t) = Ac(1+(Am/Ac)sin(ωmt))sin(ωct ) = Acsin(ωct) + Acμsin(ωmt)sin(ωct)
The above equation can be re-written as :
Cm(t) = Acsin(ωct) + (Acμ/2) × [cos(ωc-ωm) – cos(ωc+ωm)] ( ∵ sinA.sinB = (1/2) × [cos(A-B)-cos(A+B)]
Cm(t) = Acsin(ωct) + (Acμ/2) × cos(ωc-ωm)- (Acμ/2) × cos(ωc+ωm) ……………….. 6
From the above equation, we can see that amplitude modulated wave is the sum of three sine or cosine waves.
Thus, there are three frequencies in amplitude modulated waves- f1 ,f2 and f3 corresponding to ωc, ωc + ωm and ωc – ωm respectively.
ω1 = ωc ⇒ it is corresponding f1 = fc
ω2 = ωc + ωm ⇒ it is corresponding f2 = fc+fm
ω3 = ωc – ωm ⇒ it is corresponding f3 = fc-fm
where
- fc is Carrier wave frequency
- fc + fm is Upper side band frequency
- fc – fm is Lower side band frequency
- fm is Modulating signal frequency
In general fc >> fm
Amplitude Modulation – Definition, Types, Expression
Amplitude Modulation or AM, is a modulation technology mainly used for radio carrier wave-based message transmission which modifies the carrier wave’s amplitude (signal intensity) in accordance with the message signal, such as an audio signal, i.e., a modulating signal.
In this article, we will learn what amplitude modulation is, its definition, historical overview, equations to explain the process , its applications in telecommunication, and some related methodologies. We will also solve some numerical problems based on amplitude modulation and attempt to answer FAQs regarding this topic