Television System

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

PAL
This hue change problem is caused by shifts in the colour 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.

SECAM
Amongst the countries based on 50Hz systems, PAL has been the most widely adopted. PAL is not the only colour 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 Couleur Avec Memoire. 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.

SECAM ON PAL
Some Satellite TV transmissions (usually Russian) that are available over India, are in SECAM Since the field (25 frames /sec) and scan rates are identical, a SECAM signal will replay in B&W on a PAL TV and vice versa. However, transmission frequencies and encoding differences make equipment incompatible from a broadcast viewpoint. For the same reason, system converters 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.