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)