SÉCAM: Encyclopedia II - SÉCAM - SÉCAM varieties

SÉCAM - SÉCAM varieties

There are three varieties of SÉCAM:

1. French SÉCAM (SÉCAM-L), used in France and its former colonies
2. SÉCAM-B/G, used in the Middle East, former East Germany and Greece
3. SÉCAM D/K, used in the Commonwealth of Independent States and Eastern Europe (this is simply SÉCAM used with the D and K monochrome TV transmission standards).

Reference is sometimes made to MESÉCAM as an alternative form of broadcast SÉCAM used in the Middle East. This is incorrect, MESÉCAM is meaningful only in terms of video recording. When a color signal is recorded onto VHS video tape, the luminance signal is recorded in its original form (albeit with some reduction of bandwidth) but the chrominance signal of about 4.4MHz is too high in frequency to be recorded directly. Instead, it is first down converted to the lower frequency of 630kHz, and the complex nature of the PAL sub carrier means that the down conversion must be done via a superhet mixer to ensure that information is not lost.

The SÉCAM sub carrier, being a simple FM signal, does not need such complex processing. The VHS specification requires that it be simply divided by 4 on recording to give a sub carrier of approximately 1.1MHz, and multiplied by 4 again on playback. A true dual-standard PAL and SÉCAM video recorder therefore requires two color processing circuits, adding to complexity and expense. Since some countries in the Middle East use PAL and others use SÉCAM, the region has adopted a shortcut, and uses the PAL mixer-down convertor approach for both PAL and SÉCAM. This works well and simplifies VCR design.

The resultant signal on tape is not, of course, compatible with a true standard SÉCAM recording, and so is referred to as MESÉCAM. This is the only time the term MESÉCAM is meaningful. It is interesting to note that it is often possible to record SÉCAM video on an unmodified PAL VCR, thus creating MESÉCAM tapes, which can be played back in color through another PAL VCR into a SÉCAM TV. Basic PAL VCRs work better for this, ones that are more sophisticated detect the SÉCAM signal as "not-PAL" and refuse to record it in color.

Around 1983-1984 a new color identification standard has been introduced in order to make more space available inside the signal for adding teletext information (originally according to the Antiope standard). Identification bursts have been made per-line (like in PAL) rather than per-picture. Very old SÉCAM TV sets might not be able to display color for today's broadcasts.

Adapted from the Wikipedia article "SÉCAM varieties", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki