Editing Single-sideband modulation (section)

==Vestigial sideband (VSB)==
[[File:VSB bandform.svg|thumb|VSB modulation]]
Limitation of single-sideband modulation being used for voice signals and not available for video/TV signals leads to the usage of '''vestigial sideband'''. A '''vestigial sideband''' (in [[radio]] communication) is a [[sideband]] that has been only partly cut off or suppressed.  Television broadcasts (in analog video formats) use this method if the [[video]] is [[transmission (telecommunications)|transmitted]] in [[amplitude modulation|AM]], due to the large [[bandwidth (signal processing)|bandwidth]] used. It may also be used in digital transmission, such as the [[ATSC standard]]ized [[8VSB]].

The broadcast or transport channel for TV in countries that use [[NTSC]] or [[ATSC]] has a bandwidth of 6&nbsp;MHz. To conserve bandwidth, SSB would be desirable, but the video signal has significant low-frequency content (average brightness) and has rectangular synchronising pulses. The engineering compromise is vestigial-sideband transmission. In vestigial sideband, the full upper sideband of bandwidth W2 = 4.0&nbsp;MHz is transmitted, but only W1 = 0.75&nbsp;MHz of the lower sideband is transmitted, along with a carrier. The carrier frequency is 1.25&nbsp;MHz above the lower edge of the 6&nbsp;MHz wide channel. This effectively makes the system AM at low modulation frequencies and SSB at high modulation frequencies. The absence of the lower sideband components at high frequencies must be compensated for, and this is done in the [[IF amplifier]].