This post:
http://www.vcfed.org/forum/archive/index.php/t-16744.html
Seems to indicate that the Rainbow is a 15khz sync signal, more akin to
The Rainbow outputs a normal RS170-like composite video signal with the
same timings (so 15-odd kHz horizontal, 60Hz vertical). There is a setup
option for 50Hz vertical I think, if so it's going to be close to European
analogue TV rates.
This composite signal is the monochrome output. If you have a colour
video board, it is used as the green signal (which is thus SoG) and there
are separate red and blue signals. Obviously all at the same rate.
-tony