Different countries use different types of broadcast TV system, most of which are to varying extents incompatible with each other.
Unfortunately, video recordings retain many of the characteristics of the original signal of which they are a recording. In general, recordings are more likely to be compatible than recieving equipment, but only with their own "family".
There are two Mains power frequencies widely used arround 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).
Later the 60Hz camp made a small adjustment and changed the field rate to 59.94Hz when they added colour to the signals. The issue of field frequency remained sufficently deep rooted in both TV standards that the vested interest remained long after the original technical justification had gone.
The biggest compatibility problems between TV standards remain related to the field rate; these are also the hardest problems to solve.
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 Lavendar). 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 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.
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 Satelite 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 varient called D2-MAC which supports additional audio channels making transmitted signals incompatible, but not baseband signals.
Further, there are differences between the encoding of the sound between countries using the same frequency bands. Within 50Hz PAL UHF transmissions, audio signals can be at 5.5Mhz offset (system G), or at 6MHz offset (system I). Similar differences exist between the Middle Eastern versions of SECAM (MESECAM) and the Eastern Bloc (OIRT) version.
In the cases of both stereo sound and additional textural information carried in the top few lines of the picture, there are three competing systems of varying technical merit. The oldest still operational of the stereo sound systems is the American MTS system based on NTSC transmissions, only slightly more recent is the twin channel FM-FM system used in Germany, Austrua, Australia, the Netherlands and Switzerland. The most recent system, NICAM 728, was designed by the BBC in the late 1980s using digital audio technology.
The oldest of the subtitling systems is almost definately the BBC and IBA designed TeleText system which has been is use in the UK since the mid 1970s. It is also the most widespread and the most flexible of the systems in widespread use. The US Closed Captioning mechanism came about through political pressure from the Deaf organisations in the USA and has not been developed beyond the simple job of producing subtitles for the Deaf. The French developed a subtitling and information system called Antiope which has not found favour elsewhere, largely due to the existing widespread use of the BBC developed TeleText system. A few US stations have now adopted the BBC-style Teletext and a few manufacturers, most notably Zenith, fit the decoders to their sets.
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TV Systems: A Comparison
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