What is RDS ?
A Brief Introduction to RDS (Radio Data System for VHF/FM broadcasting)
The use of more and more frequencies for radio programmes in the VHF/FM range made it increasingly difficult to tune a conventional radio to a desired programme. This kind of difficulty is solved with the Radio Data System, that has been on the market since 1987, and whose spectacular evolution is still continuing.
RDS has by now conquered all receiver price classes and is nowadays a must in the standard functionality of any radio receiver.
Nowadays, almost 25 years later after that technology was created, almost all FM radios use RDS. ICs have become available that have an FM receiver and an RDS decoder on the same chip and the price for such a chip, if bought in quantities, is now extremely low, say to give the magnitude, only one to three Euro. The trend of this price is still falling and the quantity of such chips sold on the world market is still much increasing, now over 200 million units per year already.
Many applications of RDS are nowadays already within mobile phones and portable network devices. The more traditional car radios have sometimes a separate RDS decoder IC, but RDS decoding is very often an integral part of dedicated multi-purpose DSP’s, necessary for the product even without RDS. In these products the RDS function price is then almost zero, as it is done in software only.
The development of RDS started some 25 years ago in the European Broadcasting Union, EBU. The developers aimed at making radio receivers very user-friendly, especially car radios when these are used where a transmitter network with a number of alternative frequencies (AF) are present. In addition listeners should be enabled to see the programme service name (PS) on an eight character alpha-numerical display and the transmitter frequency information, displayed on non-RDS radios, is then only used, in the background, by an RDS radio. All this has become possible by the using, for many years, microprocessor controlled PLL tuner technology, permitting a radio to be retuned within milliseconds. During this process the audio signal is muted which, because of the short time, is usually not detected by the ear. Thus, the radio is able to choose the transmitter frequency, among a number of alternatives that gives the best reception quality. It is also ensured that the switch-over is made to exactly the same programme service by performing a kind of identity check using the programme identity (PI) code.
Travel information with RDS is possible using the Travel Programme (TP) and Travel Announcement (TA) flags.
RDS is also used for the digitally coded Traffic Message Channel (TMC), which is widely introduced all over Europe within funded European Union projects. RDS-TMC is nowadays generally used by GPS navigational devices that use the TMC messages also for dynamic re-routing.
Once a radio is tuned to a programme service broadcast within a network, using the RDS feature Enhanced Other Networks (EON) additional data about other programmes from the same broadcaster will be received. This enables the listener, according to his choice, to have his radio operating in an automatic switch-mode for travel information or a preferred Programme Type (PTY, e.g. News) and this information comes from a service that, at a given time, does not necessarily contain such travel information nor broadcasts the desired programme type.
Many of the receivers, apart from the usual RDS basic features (PI, PS, TP/TA, AF), implement also some of the dynamic RDS features such as Programme Type-PTY, Radiotext-RT and Clock-Time, displaying the time/date. Since 2005 the new feature, called RadioText Plus exists and it is already implemented in some receiver models.
The recent developments of highly integrated silicon tuner solutions with embedded RDS functionality has opened up a new range of products to the market. These products, generally of the portable type such as mobile phones and hand-held devices, are now incorporating FM receivers and also short-range transmitters with RDS.
RDS is absolutely future proof and will not be replaced by DAB, at least until such time as when FM broadcasting ceases to exist and this, for sure, is not going to happen within the next 10 years, in spite of the breathtaking developments of the new era of digital broadcasting.
RDS was inspired by the development of the Autofahrer-Rundfunk-Informationssystem (ARI) in Germany by the Institut für Rundfunktechnik (IRT) and the radio manufacturer Blaupunkt. ARI used a 57 kHz subcarrier to indicate the presence of traffic information in an FM radio broadcast.
The EBU Technical Committee launched a project at its 1974 Paris meeting to develop a technology with similar purposes to ARI, but which was more flexible and which would enable automated retuning of a receiver where a broadcast network transmitted the same radio programme on a number of different frequencies. The modulation system was based on that used in a Swedish paging system and the baseband coding was a new design, mainly developed by the British Broadcasting Corporation (BBC) and the IRT. The EBU issued the first RDS specification in 1984.
Enhancements to the alternative frequencies functionality were added to the standard and it was subsequently published as a European Committee for Electrotechnical Standardization (CENELEC) standard in 1990.
In 1992 the US National Radio Systems Committee issued the North American version of the RDS standard, called the Radio Broadcast Data System. The CENELEC standard was updated in 1992 with the addition of Traffic Message Channel and in 1998 with Open Data Applications and, in 2000, RDS was published worldwide as IEC standard 62106.
 Content and implementation
The following information fields are normally contained in the RDS data:
Alternative 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). This is often utilized in car stereo systems.
Clock Time Can synchronize a clock in the receiver or the main clock in a car. Due to transmission vagaries, CT can only be accurate to within 100 ms of UTC.
Enhanced Other Networks Allows the receiver to monitor other networks or stations for traffic programmes, and automatically temporarily tune into that station.
Programme Identification This is the unique code that identifies the station. Every station receives a specific code with a country prefix. In the US, PI is determined by applying a formula to the station’s call sign.
Programme 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.
Programme Type This coding of up to 31 pre-defined programme types – e.g. (in Europe): PTY1 News, PTY6 Drama, PTY11 Rock music, – allows users to find similar programming by genre. PTY31 seems to be reserved for emergency announcements in the event of natural disasters or other major calamities.
Regional 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.
Radio Text This function allows a radio station to transmit a 64-character 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.
Traffic Announcement, Traffic Programme The receiver can often be set to pay special attention to this flag and e.g. stop the tape/pause the CD 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.
Traffic Message Channel Digitally encoded traffic information. Not all RDS equipment supports this. Often available for Automotive navigation systems. In many countries only encrypted data is broadcast, and so a subscription and appropriate decoder is required to use.
Radio pirates steal listeners
|Raids on the pirates are believed to be imminent|
Illegal radio operators in the UK are forcing their broadcasts into motorists’ cars.
The pirate broadcasters have discovered how to hijack the Radio Data System (RDS) standard. This is used across Europe and South Africa and is now being adopted in Australia, China and the US.
RDS buries digital code in FM signals so that car radios can automatically seek out any local stations that are broadcasting traffic news.
|The pirates attack all RDS radios in range|
Because the pirate continually transmits the phoney flag, the radio stays tuned in until the car goes out of range or the driver switches off the RDS feature.
The radio investigators say they are now close to raiding and seizing the equipment of an RDS pirate operation. This will allow them to find out precisely how the pirates operate their listener-stealing trick. They then hope to help broadcasters around the world develop countermeasures.