How does an NTSC video signal synch on 50hz power mains?

Answer 1

Many years ago, television standards were chosen to be in line with mains frequencies to avoid interference between mains and video signals. In some cases, mains was used as a timing signal but mains instability soon led to independent timing. Improvements in electronics in later years helped to avoid some of the common causes of interference between mains and video signals. Although the need to have the two running at the same frequency was removed, the standards had been set - North America settling on 60Hz and Europe on 50Hz.

With the introduction of color systems, North American signals were changed to 59.94Hz with NTSC color encoding. Although the frequency change is tiny, it marked the end of the link betwen mains and video frequencies. Europe did not change from 50Hz and introduced PAL as the color encoding standard.

Television equipment no longer needs mains to be linked to video frequencies and therefore any frequency of video signal can work in any mains region. For many years, broadcast equipment has been capable of running at 50 or 60Hz although domestic televsions rarely had multi standard signal handling. NTSC material generally could not be used on PAL televisions, nor could PAL be used on NTSC televisions

The recent advances in television technologies has resulted in many domestic players and televisions being able to handle both NTSC and PAL signals. However, commercial pressures mean that most television content is now encoded with regional identities. The result is that although equipment is perfectly capable of displaying material, regional coding prevents DVDs bought in one region being played in another region.