What is PAL

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PAL SYSTEMS

Not all the worlds video equipment work in the same way.

In order to work TV receivers require a source of field timing reference signals. These are signals that tell the TV receiver to be ready to receive the next picture in the stream of images. Early set designers decided to use the Mains power supply frequency as this source for two good reasons. The first was that with the older types of power supply, you would get rolling hum bars on the TV picture if the mains supply and power source were not at exactly the same frequency. The second was that the TV studios would have had enormous problems with flicker on their cameras when making programs.

There are two Mains power frequencies widely used around the World, 50Hz and 60Hz. This immediately divided the worlds TV systems into two distinct camps, the 25 frames per second camp (50Hz) and the 30 frames per second camp (60Hz).

Beyond the initial divide between 50 and 60Hz based systems, further sub-divisions have appeared within both camps since the inception of Color broadcasting. The majority of 60Hz based countries use a technique known as NTSC originally developed in the United States by a committee called the National Television Standards Committee. NTSC (often scurrilously referred to as Never Twice the Same Color) works perfectly in a video or closed circuit environment but can exhibit problems of varying hue when used in a broadcast environment.

This hue change problem is caused by shifts in the color sub-carrier phase of the signal. A modified version of NTSC soon appeared which differed mainly in that the sub-carrier phase was reversed on each second line; this is known as PAL, standing for Phase Alternate Lines (it has a wide range of facetious acronyms including Pictures At Last, Pay for Added Luxury (re: cost of delay line), and People Are Lavender). PAL has been adopted by a few 60Hz countries, most notably Brazil.

Amongst the countries based on 50Hz systems, PAL has been the most widely adopted. PAL is not the only color system in widespread use with 50Hz; the French designed a system of their own - primarily for political reasons to protect their domestic manufacturing companies - which is known as SECAM, standing for Sequential Color Avec Memory. The most common facetious acronym is System Essentially Contrary to American Method, SECAM was widely adopted in Eastern Block countries to encourage incompatibility with Western transmissions - again a political motive.

In general, since the field and scan rates are identical, you can expect to get a monochrome picture from a PAL video recording replayed on SECAM equipment, and vice versa. Transmission frequencies and encoding differences make equipment incompatible from a broadcast viewpoint. Transcoders between PAL and SECAM, while often difficult to find, are reasonably cheap.

In Europe, a few Direct Satellite Broadcasting services use a system called D-MAC. It's use is not wide-spread at present and it is transcoded to PAL or SECAM to permit video recording of it's signals. It includes features for 16:9 (widescreen) aspect ratio transmissions and an eventual migration path to Europe's proposed HDTV standard. There are other MAC-based standards in use around the world including B-MAC in Australia and B-MAC60 on some private networks in the USA. There is also a second European variant called D2-MAC which supports additional audio channels making transmitted signals incompatible, but not baseband signals.

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