Phase Alternating Line (PAL)
PAL is the type of video system used in many countries outside of the US. In order for you to watch a video, your video source must send an electronic signal to your television. This signal is based upon the Alternating Current (AC) frequency in the country where you are viewing the video tape. Here in America, the AC current frequency is 60Hz. However, in many other countries, the AC frequency is 50Hz. Therefore, we have different television standard around the world.
Why different video system?
In most of Europe, Asia and Africa the power frequency is 50Hz, so they developed 2 television slandered which better suit the needs of these countries. One of the 50Hz standards is PAL and the other is SECAM (Sequential Color Avec Memorie).
|AC Frequency||Video Signal|
|60Hz||NTSC (National Television Standards Committee)|
|50Hz||PAL (Phase Alternating Line)
SECAM (Sequential Color Avec Memorie)
PAL and National Television Systems Committee an committee convened from time to time by the National Association of Broadcasters and the Electronic Industries Association to study and recommend television standards and specifications. NTSC system are very similar, a quadrature amplitude modulated sub carriers carrying the chrominance information is added to the luminance video signal to form composite video signal.
The frequency of this subcarrier is:
PAL » 4.43361875 MHz
NTSC » 3.579545 MHz
The color carrier = 283.75 color clock cycle per line plus.
The line frequency = 15625 Hz
Offset to avoid interferences = 25Hz
The color carrier frequency = (color carrier * line frequency) + Offset to avoid interferences
= (283.75 * 15625) Hz. + 25 Hz.
= 4.43361875 MHz