What is Vestigial Sideband Modulation?

Vestigial Sideband Modulation (VSB) refers to the process where the “vestige” part of a signal is modulated alongside one sideband. A vestigial sideband is a form of amplitude modulation (AM) that encodes data in a signal by altering the amplitude of the carrier frequency.

It’s important to note that in AM, it’s not the carrier itself that fluctuates in amplitude. Instead, it’s the modulating data that appears as signal components (sidebands) oscillating at frequencies that may be slightly lower or higher compared to that of the carrier.

The components that appear at frequencies below that of the carrier are collectively referred to as Lower Sideband (LSB), while those that appear at frequencies above that of the carrier are referred to as the Upper Side Band (USB)

Information is transmitted in the sidebands as opposed to the carrier frequency, with both carrying the same information. The two channels mirror each other, meaning one can be discarded, and the information would still get transmitted.

VSB works a lot like Single-Sided Band (SSB) transmission except that, in this case, the second band isn't fully removed. Instead, it works as a filter to remove specific frequencies leaving only the desired range.

The most prominent application of VSB is in the transmission of television signals. Zenith developed the very first eight-level VSB (8-VSB), which has since been incorporated into the Advanced Television Systems Committee (ATSC) standards. Using VSB to transmit television signals is the most efficient and convenient technique, especially in scenarios where you need to keep bandwidth usage at a minimum.

Not only does it make the transmission of low-frequency components possible, but the filter design also doesn't require high accuracy. VSB is the standard for TV broadcasting worldwide since it supports the transmission of both audio and video signals at the same time.