Help

I need to transmit serial (or Ethernet data) over a radio link
designed to support video (RS-170) signals. The radio uses the video
sync. for timing so I can't just splice into the signal. So I am
looking for a modulator or multiplexor that will put the serial signal
into one of the video channels.

This is a one-way link and speed should not be a problem.

Any ideas or references would be appreciated. Thank You