In general, we can imagine amplitude modulating a carrier with a modulation input
where all the modulation's frequency components, 
, are all within some Information bandwidth (or Modulation bandwidth), 
, which extends from about zero Hertz up to a maximum frequency, 
.
This produces an AM wave
which, after a bit of maths manipulation, can be shown to be the same as
The modulated wave is said to consist of three parts:-
- The carrier,
, which is unaffected by the modulation.
- The Upper Sideband Components,
, which are an ‘up converted’ copy of the original modulation spectrum.
- The Lower Sideband Components,
, which are a ‘mirror image’ of the upper sideband spectrum.
This process is illustrated in figure 9.4 shown above.
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