boxes for VGA->NTSC... they're inexpensive
now. An RGB to
NTSC converter may more properly be called a "scan converter",
"modulator" is typically the name given to NTSC -> RF over coax.
To me, a 'scan converter' has to convert the scanning rates -- say
between European and USA TV, or between VGA video and TV.
A box which converts TV-rate RGB video to an NTSC composite signal is an
'NTSC colour enocder', and I susepct is technically (at least in part) a
modulator [1].
[1] It amplitude- and phase- modulates the 3.58 colour subcarrier for one
thing...
-tony