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What is RDS ?


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 DSPs, 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.

More details on RDS you can also find in Wikipedia