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 make it inceasingly 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 one can easily imagine that it will soon be part of the standard equipment of any radio receiver.

The development of RDS started some 20 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, permiting 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 quality reception. It is also sure 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. Information is broadcast for motorists, identified in parallel with the ARI system with the corresponding RDS features TP/TA. But ARI is being replaced on a European scale, so it will cease after the year 2005. A more recent development of RDS is the digitally coded Traffic Message Channel (TMC) which is now planned to be introduced all over Europe, within projects funded by the European Union. However, present RDS radios are not yet suitable for RDS-TMC.

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 even broadcasts the desired programme type.

Many of the Hi-Fi home tuners or receivers at this IFA implement, apart from the usual RDS features (PI, PS, TP,TA, AF), some of the newer features such as Programme Type-PTY, Radiotext-RT and Clock-Time, displaying the time/date.

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 20 years, in spite of the breathtaking developments of the new era of digital broadcasting.

Issue Date 09 July 1998
Copyright 1997, 1998 EBU and RDS Forum. All rights reserved.