Hanover bars

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Hanover bars, in the simplest PAL television video format, are an undesirable artefact in the reception of a television image.

Two signals, B-Y (U) and R-Y (V) are used in the PAL system to carry the color information for a picture, with the phase of the V signal reversed (i.e. shifted through 180 degrees) on alternate lines (hence the name phase alternate line). This is done to cancel minor phase errors in the reception process. However if gross errors occur, complementary errors from the V signal carry into the U signal, and thus stripes -- Hanover bars occur.

Later PAL systems introduced alterations to ensure that Hanover bars do not occur, introducing a "swinging burst" to the color synchronization. Other PAL systems may handle this problem differently.