Which of the following describes the use of vestigial sideband in analog fast-scan TV transmissions?
Why Analog NTSC video extends to about 4.2 MHz, so double-sideband AM would need roughly 8.5 MHz of spectrum. Filtering out one sideband completely is impractical because the low video frequencies sit right next to the carrier and a sharp filter there would distort them and lose phase information. The compromise is vestigial sideband: the upper sideband is transmitted in full while only a vestige of the lower sideband (about 0.75 MHz) is kept, which trims the channel to 6 MHz yet preserves the low frequency video content that carries the large-area brightness of the picture.
Watch out The audio is a separate FM carrier 4.5 MHz above the video carrier, and chroma rides on the 3.58 MHz color subcarrier in the main sideband, so neither lives in the vestige.
Vestigial = keep a sliver of the second sideband so the LOW video frequencies survive; 6 MHz channel instead of 8+.