Subject : Principle of Communication Engineering

Topic : Introduction to Electronic Communication

Difficulty : Low

Vestigle sideband (VSB)

• The stringent frequency response requirement on the side band filter in SSB-SC system can be relaxed by allowing a part of the unwanted sideband called as Vestige to appear in the output of the modulator.
• Due to this the design of this sideband filter is simplified to a great extent. But the bandwidth of the system is increased slightly.
• To generate a VSB signal first the DSB-SC signal and then pass it through a sideband filter. This filter will pass the wanted sideband as it is along with a part of unwanted signal.
• The VSB signal obtained at the output of filter is applied to a chain of linear amplifiers and raised in power by the power amplifiers

• The amplified signal is then applied to the transmitting antenna for transmission of signal.

  

Advantages of VSB:

• The main advantage of VSB Modulation is the reduction in bandwidth is the reduction in bandwidth. It is almost as efficient as SSB.

• Due to allowance of transmitting a part of lower sideband, the constraint on the filters have been relaxed.

• It possesses good phase characteristics and makes the transmission of low frequency components possible Practical filters can be used for partial suppression of LSB.

Applications

• VSB modulation has become standard for the transmission of Television signals. Because the video signals need a large transmission bandwidth using DSB-FC or DSF-SC techniques.
• This is a special type of AM system which is used mainly for the TV transmission all over the world. In the TV transmission it is necessary to transmit the video information and audio information simultaneously.
• In the VSB transmission the upper sideband of video signal and picture carrier are transmitted without any suppression. Whereas a vestige i.e. a part of lower sideband is transmitted and the remaining part is suppressed.