Hmm. nevermind. looks like I was wrong, RDS is actually on a seperate 57khz signal that is modulated onto the original signal. So, can't encode an MP3 with RDS data. A lot of schematics exist to create a small RDS transmitter that will take data from a PC to inject RDS real time into a transmission, but that's about it. I guess my MP3 player was just sending that data along and my car stereo was picking it up. Drag.