Vestigial sideband

A radio communication sideband that has been only partly cut off or suppressed.

The 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 transmitted in AM, due to the large bandwidth used. It may also be used in digital transmissions, such as the ATSC standardized 8VSB.

The broadcast or transport channel for TV in countries that use NTSC or ATSC has a bandwidth of 6 MHz. To conserve bandwidth, SSB would be desirable, but the video signal has significant low-frequency content (average brightness) and has rectangular synchronizing pulses. The engineering compromise is the vestigial-sideband transmission. In the vestigial sideband, the full upper sideband of bandwidth W2 = 4.0 MHz is transmitted, but only W1 = 0.75 MHz of the lower sideband is transmitted, along with a carrier. The carrier frequency is 1.25 MHz above the lower edge of the 6MHz 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.

  • VSB
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Last modified on May 23, 2021, 2:38 pm is a service provided by Codecide, a company located in Chicago, IL USA.