Subject : Principle of Communication Engineering

Topic : Amplitude Modulation and Demodulation

Difficulty : Low

Single side band (SSB) is an amplitude modulation technique in which only one sideband (upper or lower) is transmitted and Double side band (DSB) is a modulation technique in which both the upper and lower sidebands are transmitted simultaneously.

Advantages of SSB over full carrier DSB wave

• The bandwidth requirement of the SSB is half than required by DSB.

• Since SSB system utilizes half the bandwidth than DSB, the thermal noise power is reduced to half that of DSB system.

• The full carrier DSB wave has poor efficiency since the major transmitted power is concentrated in the carrier which contains no information. Thus the total power transmitted in SSB is less than the total power in DSB. Percentage of power saving in SSB is 83.33%.

• In the spectrum of AM wave, both the sidebands carry same amount of information which makes it meaningless to transmit same information in both the sidebands thus leading to power wastage. This is overcome in the SSB technique by suppressing undesired sideband.

Disadvantages of SSB over full carrier DSB wave

• The generation of SSB is quite complex as the suppression of one of the sidebands is difficult.

• The generation of SSB requires sharp cut off characteristics of the sideband suppression filter.

• SSB receivers require more precise tuning than DSB

• SSB receivers require carrier recovery and synchronization circuit which adds to their cost, complexity and size.