On April 9, 1998, the National Radio Systems Committee approved a revised edition of the United States RBDS Standard. The revised standard improves on the previous edition, adopted January 8, 1993, in many ways. Two significant improvements are the incorporation of the FCC’s Emergency Alert System (EAS) coding structure into the RDS signal, and the added ability, through the use of the “open data application” feature, for innovators to add new features to the RDS signal without first getting the standard modified (click here for more information about ODAs).
The RDS signal is a low bit rate data stream transmitted on the 57 kHz subcarrier of an FM radio signal. Its data rate is 1,187.5 bits per second – though 10 out of every 26 bits transmitted are error correction codes used to combat signal distortions that occur in the transmission path. Consequently, there is only about 730 bits per second of usable data in an RDS signal.
Radio listeners know RDS mostly through its ability to permit RDS radios to display call letters and search for stations based on their programming format. Special traffic announcements can be transmitted to RDS radios, as well as emergency alerts.
The U.S. RBDS Standard is based largely on the European RDS Standard, the latest version of which was published by the European Committee for Electrotechnical Standardization (CENELEC) in 1998. Scott Wright of Delco Electronics, who is the Chairman of the NRSC's RBDS Subcommittee, has prepared a document which compares the U.S. and European versions of this standard.