Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 5M

Year: May 2014

• Vestigial Sideband (VSB) is an amplitude modulation technique in which carrier with one sideband is transmitted and the other sideband is partially suppressed. This system is called vestigial sideband system. It is also called as Asymmetric sideband system.
• In VSB the desired sideband is allowed to pass completely and only a trace (vestige) of the undesired sideband is allowed to pass. The carrier is transmitted at full power.
• The transmitted vestige of the undesired sideband compensates for the loss of the required sideband.
• The advantage of SSB is the reduction in the bandwidth requirement as compared to DSB modulation. But major drawback of SSB is the difficulty in suppressing the unwanted sideband. This difficulty is overcome by VSB modulation technique, which is a compromise between SSB and DSB modulation.
• VSB is employed in applications such as television broadcasting. The vestigial sideband system for TV video transmission is shown below in Fig1.

• The transmission bandwidth of 9 MHz is required for video transmissions in DSB system for TV transmission.

• The distribution of the channel bandwidth is explained below.

1. 0-1.25 MHz: This is vestigial sideband as the LSB is attenuated up to 1.25 MHz.

2. 1.25-5.25 MHz: This is full upper sideband which is transmitted.

   i. The total picture bandwidth is = 5 + 1.25 = 6.25 MHz is transmitted instead of 9MHz resulting in a saving of 3MHz.

3. 6.25-7 MHz: Sound carrier is positioned at 6.75 MHz in the channel bandwidth.