Additionally, for compatibility, it is required to use no more bandwidth than the monochrome signal alone; the color signal has to be somehow inserted into the monochrome signal, without disturbing it.
This insertion is possible because the spectrum of the monochrome TV signal is not continuous (for most typical video content), hence empty space exists which can be utilized.
SECAM differs from the other color systems by the way the R-Y and B-Y signals are carried.
First, SECAM uses frequency modulation to encode chrominance information on the sub carrier.
However, owing to their FM nature, the color signal remains present, although at reduced amplitude, even in monochrome portions of the image, thus being subject to stronger cross color even though color crawl of the PAL type doesn't exist.