I have assembled this project http://cb2.qrp.gr which was lot of fun, but I have a TV with a composite video input only. Now I know there are ICs out there that can convert from RGB/HSYNC/VSYNC to composite video (PAL/NTSC), like the AD725, but I would like to investigate how such a conversion can be done in discrete components, if this is not too difficult to do. Is that possible and what parameters should I investigate? Note that the project has already a black and white composite video output, but I also need the colors to present.
SCART can carry either RGB or composite video, depending on which pins the source chooses to drive.
But if you have RGB, then there is no easy way to convert it to composite video. Conversion requires turning the RGB into luminance (monochrome) and chrominance signals, then modulating the chrominance signal on top of the luminance (in a way that is specific to either PAL or NTSC).