phase alternating line

phase alternating line

   <television> (PAL) The {video} signal format used in the UK
   [where else?].

   PAL uses {Amplitude Modulation} for the video information, and
   {Frequency Modulation} for the {audio} information.  The phase
   of the {colour subcarrier} is reversed on alternate lines
   which (together with the use of a delay line) allows the
   receiver to cancel any phase errors introduced in the path
   between the studio and the end-user's receiver.  Such phase
   errors are quite common and would cause the displayed colours
   to shift in {hue}.

   The US equivalent, {NTSC}, does not have this feature and thus
   requires a user control to correct for transmission phase
   errors, hence the mis-expansion "Never Twice the Same Colour".

   (2001-06-08)