Hanover bars

[1][2] The name refers to the city of Hannover, in which the PAL system developer Telefunken Fernseh und Rundfunk GmbH was located.

The U (corresponding to B-Y) and V (corresponding to R-Y) signals 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 PAL, or phase alternate line).

This is done to cancel minor phase errors in the reception process.

[3] Later PAL systems introduced alterations to ensure that Hanover bars do not occur, introducing a swinging burst to the color synchronization.

[4] This causes phase errors to cancel out, at the cost of vertical color resolution, and in early designs, also a loss of color saturation proportional to the phase error.

Simulated strong Hanover bars shown on a Philips PM5544 test pattern . Note: Hanover bars can only be seen by viewing full-size image
Simulated cancellation of Hanover bars through a chroma delay line