One
method of performing single sideband modulation is to employ a
quadrature modulator. A quadrature modulator mixes the message with two
carriers. Both carriers operate at the same frequency, but are shifted
in phase by 90 degrees relative to one another (hence the “quadrature”
term). This simply means that the two carriers can be expressed as
cos(2πfct) and sin(2πfct).

The
message, too, is modified to consist of two separate signals: the
original and a 90 degree phase-shifted version of the original. The
original is mixed with the cosine component of the carrier and the
phase-shifted version is mixed with the sine component of the carrier.
These two modifications result in the implementation of the single
sideband function.

Trigonometrically, this can be expressed as:

Just by changing the sign of the left hand side term i.e. to negative from positive we can easily get the upper sideband only.

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