What does DSB-SC stand for in communication system engineering?

In communication system engineering, DSB-SC stands for Double Sideband Suppressed Carrier.

Concept:

In a balanced modulator, 2 AM modulators are connected in a way that the resultant signal does not contain the carrier spectrum, i.e. to generate a Double Side-band suppressed carrier (DSB-SC).

Analysis:

The circuit diagram of a balanced modulator is as shown:

\( {s_{AM'}}\left( t \right) = {A_c}\left[ {1 + {k_a}m\left( t \right)} \right]\cos 2\pi {f_c}t\)

\(\\ {s_{AM''}}\left( t \right) = {A_c}\left[ {1 - {k_a}m\left( t \right)} \right]\cos 2\pi {f_c}t\)

The resultant DSB signal is the difference of the two, i.e.

\({s_{DSB}}\left( t \right) = {s_{AM'}}\left( t \right) - {s_{AM''}}\left( t \right) \)

Hence,

\({s_{DSB}}\left( t \right) = \;2{A_c}{k_a}m\left( t \right)\cos 2\pi {f_c}t\)

\( {s_{DSB}}\left( t \right) = \;{A_c}'m\left( t \right)\cos 2\pi {f_c}t\)

The frequency spectrum of the DSB-SC signal:

The standard DSB-SC equation is given as:

\({S_{DSB}}\left( t \right) = \;{A_c}m\left( t \right)\cos 2\pi {f_c}t\)

Assuming a single tone message signal as:

\(m\left( t \right) = \;{A_m}\cos 2\pi {f_m}t\)

The DSB-SC signal can be written as:

\({S_{DSB}}\left( t \right) = \frac{{{A_c}{A_m}}}{2}\cos 2\pi ({f_c} + {f_m})t + \;\frac{{{A_c}{A_m}}}{2}\cos 2\pi ({f_c} - {f_m})t\)

∴ The output of balanced modulator contains the modulation frequency, LSB and USB.