Radio Data System

From Academic Kids

Radio Data System, or RDS, is a standard for sending small amounts of digital information using conventional FM radio broadcasts. The RDS system standardizes several types of information transmitted, including time and station identification. RDS is widely used in Europe, but less so in North America.

Radio Broadcast Data System is the official name used for the U.S. version of RDS, though the "RDS" name seems to be at least as common in usage. The two standards are nearly identical, with only slight differences, mainly in which numbers are assigned to each of 31 musical and other program formats the RBDS system can identify. RBDS was approved by the NRSC, RDS by the EBU.

Both use a 57kHz subcarrier to carry data at 1187.5 bits per second. The 57kHz was chosen for being the third harmonic (3×) of the pilot tone for FM stereo, so it would not cause interference or intermodulation with it, or with the stereo difference signal at 38kHz (2×). The data format utilises error correction. RDS defines many features (see below), including how private (in-house) or other undefined features (such as differential GPS) can be "packaged" in unused program groups.

Content and implementation

The following information fields are normally contained in the RDS data:

  • AF, Alternate frequencies. This allows a receiver to re-tune to a different frequency providing the same station when the first signal becomes too weak (e.g. when moving out of range).
  • CT, Clock Time. Can synchronise a clock in the receiver or the main clock in a car.
  • EON, Enhanced Other Networks. Allows the receiver to monitor other stations for traffic broadcasts.
  • PS, Program Service. This is simply an eight-character static display that represents the call letters or station identity name. Most RDS capable receivers display this information and, if the station is stored in the receiver's presets, will cache this information with the frequency and other details associated with that preset.
  • PTY, Program Type. A number of pre-defined music types (e.g. classical, pop, middle-of-the-road music) allowing a user to find a similar station. A special program type, PTY31, seem to be reserved for catastrophe announcement.
  • REG, Regional links. This is mainly used in countries where national broadcasters run "region-specific" programming such as regional opt-outs on some of their transmitters. This functionality allows the user to "lock-down" the set to their current region or let the radio tune into other region-specific programming as they move into the other region.
  • RT, Radio Text, Radiotekst. This function allows a radio station to transmit free-form textual information that can be either static e.g. station slogans or in sync with the programming such as the title and artist of the currently-playing song.
  • TA, TP, Travel announcements. The receiver can often be set to pay special attention to this flag and e.g stop the tape or retune to receive a Traffic bulletin. The TP flag is used to allow the user to find only those stations that regularly broadcast traffic bulletins whereas the TA flag is used to stop the tape or raise the volume during a traffic bulletin.
  • TMC, Traffic Message Channel. Demands a RDS-TMC decoder.

As far as implementation is concerned, most car sets will support at least AF, EON, REG, PS and TA / TP. More expensive car sets will offer TMC, RT and / or PTY, perhaps with "NEWS" override. Home sets, especially hi-fi sets, will mainly support functions like PS, RT and PTY. There have been few implementations of RDS in portable, tabletop and personal (Walkman) radios because most of these sets are made to a price-point and the cost to implement RDS in these sets would place the sets beyond that price point. If RDS is implemented in these sets, they would at least support PS, RT, PTY and/or CT.

See also

External links

de:Radio Data System nl:Radio Data System fi:RDS pt:Radio Data System

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