I work in Radio Transmission . The system is called RDS Radio Data System . The way it works is at one end Studio there is an RDS encoder and at the other end Transmitter , and every transmitter that radiates RDS there is an encoder . Basically , the customer radio service will send Data through the RDS encoder down usually an ISDN line copper cable usually to the Transmitter encoder it then radiates to the listeners receiver . They literally write the text in one end and that radiates out of the other . Stolen from Wiki but here ' s the technical bit Both carry data at 1 , 187 . 5 bits per second on a 57 kHz subcarrier , so there are exactly 48 cycles of subcarrier during every data bit . The RBDSRDS subcarrier was set to the third harmonic of the 19 kHz FM stereo pilot tone to minimize interference and intermodulation between the data signal , the stereo pilot and the 38 kHz DSBSC stereo difference signal . The stereo difference signal extends up to 38 kHz 15 kHz 53 kHz , leaving 4 kHz for the lower sideband of the RDS signal . Any thing else ?