What Is RDS All About?
What Is RDS All About?
RDS, or the Radio Data System, is a system by which useful information can be transmitted to a tuner or receiver. Any radio that has the RDS "figure of eight" logo and wording will be able to receive and decode RDS information. Information available will often include:
• the station name
• an indication as to whether the station broadcasts travel bulletins
• an outline of the programme currently being broadcast
• the current time
RDS works on the FM waveband only since the RDS information is encoded within the FM signal. RDS is not available on medium wave, long wave or the AM waveband.
Programme Service (PS)
This is the name of the station currently tuned to (known as the Programme Service or PS). For example, if you were listening to Radio 2 on a suitably-equipped radio, the frequency in the display would be replaced by _BBC_R2_. If Classic FM were tuned in, the display would switch from the frequency to CLASSIC_. The Programme Service name is limited to eight characters. Some radios, though not all, will store the name (PS) in memory when the station is added as a preset on the radio.
Alternative Frequency (AF)
Within the data sent to an RDS radio will be information about which other frequencies the station can be heard on. An RDS radio will retune to a different frequency when the current signal becomes too weak, assuming an alternative frequency is available for the station. For this to happen, the AF function must be switched on. Sometimes the radio will keep trying to find a stronger signal for the station. This can become distracting as the radio retunes itself, but can be overcome by switching the AF function off. In theory, if travelling around the country, it should be possible to listen to all the national stations via a car radio without having to manually retune. Some home tuners do not have the Alternative Frequency feature.
Some tuners will allow you to search for stations which use RDS. Since most stations on FM use RDS anyway, this feature is of limited value.
Traffic Programme (TP) and Traffic Announcement (TA)
The radio display can show if the station broadcasts travel information. Since most stations do anyway, this feature by itself is of limited value. The Traffic Announcement (TA) feature allows interruption of a CD or Minidisc when there is a travel report from the radio station that is currently tuned-in. The radio will automatically switch from CD or tape to the radio for the duration of the travel announcement.
Commercial radio stations will broadcast three tones or 'bleeps' before and after the travel bulletin, but BBC radio stations do not need this. These DTMF tones are used when the transmitter (where the RDS inserter physically is) is located remotely from the studio, and for reasons of cost or practicality there is no control path from the studio to the transmitter to tell the transmitter when to switch on the TA flag. The only link from studio to transmitter is the station audio itself.
In these situations, "in-band signalling" is used. A unit at the transmitter site listens out for the DTMF tones in order to switch the TA flag on and off. The DTMF tones are recorded on the traffic jingles to make life easier for the presenter. For the TA feature to work under any circumstances, however, the function marked TA, TI, TP or 'Traffic' must be switched on.
It is possible to search out only those stations broadcasting the Traffic Programme on some radios.
Enhanced Other Networks (EON)
Most RDS tuners are now fitted with the EON facility, which offers the ability for local stations to 'break into' a national station's broadcast for the duration of a Traffic Announcement. When listening to a BBC national station, such as BBC Radio 3, EON will tell the radio about any traffic bulletins being broadcast by BBC stations in the local area. The radio would switch to the local BBC radio station for the travel bulletin, then back to the national station when the bulletin had finished. For example, when travelling through Oxford whilst BBC Radio 2 is tuned-in, the radio will switch to BBC Radio Oxford for any travel bulletins, with the TA function switched on.
This feature is not usually implemented on commercial radio stations, such as Classic FM. While a proportion of the RDS datastream is used to provide programme and contact information for Classic FM, a small amount is classed as an "Additional Services Licence". This spare capacity on the RDS is used by Itis Holdings to provide a RDS-TMC (Radio Data System-Traffic Message Channel) service, using Classic FM's RDS. Cars fitted with the necessary electronics are able to decode this information and it is used to provide navigational and traffic information.
The EON feature will work even if a cassette or CD is being played; the CD or tape will be interrupted by a local or national travel bulletin if 'EON' is lit in the radio's display.
Programme Type (PTY)
Radio stations can assign different programme types to their shows, depending on what is being broadcast at a particular time of day. These can be picked up by an RDS radio. The listener can use the radio to search for a particular type of programme. The radio will then scan the dial to look for the programme type selected. If one is found, the radio will tune in to the station. There are several Programme Types. These include NEWS, CURRENT AFFAIRS, INFO(information), SPORT, EDUCATION, DRAMA, CULTURE, SCIENCE, POP MUSIC, ROCK MUSIC, MOR(middle of the road), LIGHT MUSIC(light classical music), OTHER MUSIC, CLASSICS(more 'serious' classical music) and VARIED (speech and/or music). For example, Bristol's Star 107.2 sets its programme type (PTY) to VARIED all the time. However, Radio 4 might set its PTY to AFFAIRS when it's broadcasting a programme about current affairs, but switch the programme type to NEWS at 6:00pm for the news bulletin. The PTY can be set, with the radio remaining tuned in to the current station, until a particular programme becomes available. For example, if the PTY is set to NEWS, the radio will wait until a NEWS programme becomes available before tuning in to the station broadcasting news. When the news has finished, the previous station will be tuned back in. It is therefore possible to listen to Radio 1 whilst being able to catch the news on Radio 2 using the PTY NEWS selection. For this to work, PTY must be switched on.
Most RDS radios can receive short messages which might include information about the presenter, station or programme you are listening to. For example, BBC Radio 1's RadioTEXT always gives information about the presenter and programme e.g. JOHN PEEL - TONIGHT IN SESSION.. ETC.., whereas Classic FM gives information which includes a web address for the station, e.g. CLASSIC FM ON THE WEB - WWW.CLASSICFM.COM. The information will usually scroll across the display on a home tuner, but this could be distracting to a driver in a car, so the RadioTEXT message in a car hi-fi does not scroll.
Clock Time (CT)
Some stations broadcast the time and date within the encoded RDS signal. Usually, the time of day is just displayed. The time signal is automatically adjusted for British Summer Time. Most local radio stations do not bother with the RDS Clock Time feature.
More information about RDS, including a forum for discussion about the service and latest press releases, can be found at the RDS website.