RDS (Radio Data System) is a method of transmitting text information through FM broadcasting stations. Usually, a station identification of eight alphanumeric characters is broadcast, which allows FM stations to be identified. However, only a few home and travel radios are RDS-compatible.
RDS is widespread in car radios in Europe; the programmes can be identified and also stored thanks to the station designation („PROGRAMME SERVICE NAME“). Part of the RDS signal also includes alternative frequencies, so that the car radio automatically tunes to the frequency of the next transmitter when driving out of range of a transmitter.
In Switzerland, Radiotext is also used; the name of the artist and the title of a piece of music can be transmitted in four blocks of a maximum of eight characters.
The RDS signal is broadcast 57 kHz above the centre frequency of an FM signal in PSK modulation, similar to the stereo pilot tone at 19 kHz.