Media UK

RDS

RDS is a data system carried as a sub-carrier at 57kHz on an FM signal. It uses a data rate of 1.1875 kbps. The smallest 'unit' into which these bits are packaged is an RDS group, which comprises 104 bits in total. Of these, 40 are used for error detection/framing etc, leaving 64 to carry information. There are 32 different RDS groups, each with different combinations of RDS features. The RDS 'features' are:

PI - Programme Identification A 4-character sixteen bit code that identifies the station uniquely within an area. The PI code is the most fundamental element of RDS - it acts as the 'address code' to which all other RDS features are referenced. It is a machine-readable code, and is not intended to be known to an end-user, and appears as the first 16 bits in each RDS group

PS - Programme Service The eight character 'plain text' identifier for station which can be in upper or lower case text or a combination. Some receivers cannot display lower case text.

AF - Alternative Frequencies A list of the frequencies on which the same station is carried from other transmitters. Used in conjunction with PI, the receiver uses this list to track from transmitter to transmitter in a mobile receiver.

PTY - Programme type A code (from 32 possibilities) to identify the general type of ouput from the station. e.g. 'pop' . 'news', 'sport' , 'science', 'rock' etc. May be used for station selection, or when combined with EON (below) to programme a receiver to switch on or over to a station when a particular genre is broadcast.

RT – Radiotext A 64-character text - used for general information or details of programme/track playing/ads. Receivers in vehicles are not permitted to display this information under UK law.

TP - Traffic Programme A single bit which when set to logic '1' indicates that the station provides traffic information as part of regular programming, and that when it does it will also switch on the TA flag. TP is used by the receiver to identify which stations provide this service.

TA - Traffic Announcement A single bit which when set to logic '1' indicates that the station is actually broadcasting a Traffic Announcement now. The setting of the TA flag to '1' in the RDS datastream typically causes the cassette/CD player in a car receiver to pause and revert to radio listening. It will raise the volume if the receiver is at a low level. When combined with EON, TA allows receivers to switch across from one station to another for traffic news and then reverty to the original.

EON - Enhanced Other Networks EON information is all the above features, but for 'other networks'. This means that the receiver will select a station from another network signed as being allied to the first when the station to which it is tuned becomes no longer receivable.