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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.
Radio Data System (RDS) feature listing
The list(s) of alternative frequencies give information on the various transmitters broadcasting the same programme in the same or adjacent reception areas, and enable receivers equipped with a memory to store the list(s), to reduce the time for switching to another transmitter. This facility is particularly useful in the case of car and portable radios.
Time and date codes should use Coordinated Universal Time (UTC) and Modified Julian Day (MJD). If MJD = 0 the receiver should not be updated. The listener, however, will not use this information directly and the conversion to local time and date will be made in the receiver's circuitry. CT is used as time stamp by various RDS applications and thus it must be accurate.
These bits indicate which possible operating modes are appropriate for use with the broadcast audio and to indicate if PTY codes are switched dynamically.
RDS uses its own country codes. The first most significant bits of the PI code carry the RDS country code. Their four bit coding structure only permits the definition of 15 different codes, 1 to F (hex). Since there are much more countries to be identified, some countries have to share the same code which does not permit unique identification. Hence there is the need to use the Extended Country Code. The ECC consists of eight bits.
This feature can be used to update the information stored in a receiver about programme services other than the one received. Alternative frequencies, the PS name, Traffic Programme and TrafficAnnouncement identification as well as Programme Type and Programme Item Number information can be transmitted for each other service. The relation to the corresponding programme is established by means of the relevant Programme Identification. Linkage information, consisting of four data elements, provides the means by which several programme services may be treated by the receiver as a single service during times a common programme is carried. Linkage information also provides a mechanism to signal an extended set of related services.
The EWS feature is intended to provide for the coding of warning messages. These messages will be broadcast only in cases of emergency and will only be evaluated by special receivers.
This refers to data to be decoded only by the operator. Some examples noted are identification of transmission origin, remote switching of networks and paging of staff. The applications of coding may be decided by each operator itself.
This is a two-state signal to provide information on whether music or speech is being broadcast. The signal would permit receivers to be equipped with two separate volume controls, one for music and one for speech, so that the listener could adjust the balance between them to suit his individual listening habits.
The Open Data Applications feature allows data applications, not previously specified in EN 50067, to be conveyed in a number of allocated groups in an RDS transmission. The groups allocated are indicated by the use of type 3A group which is used to identify to a receiver the data application in use in accordance with the registration details.
This information consists of a code enabling the receiver to distinguish between countries, areas in which the same programme is transmitted, and the identification of the programme itself. The code is not intended for direct display and is assigned to each individual radio programme, to enable it to be distinguished from all other programmes. One important application of this information would be to enable the receiver to search automatically for an alternative frequency in case of bad reception of the programme to which the receiver is tuned; the criteria for the change-over to the new frequency would be the presence of a better signal having the same Programme Identification code.
The code should enable receivers and recorders designed to make use of this feature to respond to the particular programme item(s) that the user has preselected. Use is made of the scheduled programme time, to which is added the day of the month in order to avoid ambiguity.
This is the label of the programme service consisting of not more than eight alphanumeric characters which is displayed by RDS receivers in order to inform the listener what programme service is being broadcast by the station to which the receiver is tuned. An example for a name is "Radio 21". The Programme Service name is not intended to be used for automatic search tuning and must not be used for giving sequential information.
This is an identification number to be transmitted with each programme item and which is intended to specify the current Programme Type within 31 possibilities. This code could be used for search tuning. The code will, moreover, enable suitable receivers and recorders to be pre-set to respond only to programme items of the desired type. The last number, i.e. 31, is reserved for an alarm identification which is intended to switch on the audio signal when a receiver is operated in a waiting reception mode.
The PTYN feature is used to further describe current PTY. PTYN permits the display of a more specific PTY description that the broadcaster can freely decide (eg PTY=4: Sport and PTYN: Football). The PTYN is not intended to change the default eight characters of PTY which will be used during search or wait modes, but only to show in detail the programme type once tuned to a programme. If the broadcaster is satisfied with a default PTY name, it is not necessary to use additional data capacity for PTYN. The Programme Type Name is not intended to be used for automatic PTY selection and must not be used for giving sequential information.
The RP feature is intended to provide radio paging using the existing VHF/FM broadcasts as a transport mechanism, thereby avoiding the need for a dedicated network of transmitters. Subscribers to a paging service will require a special pocket paging receiver in which the subscriber address code is stored.
This refers to text transmissions coded in accordance with annex E, primarily addressed to consumer home receivers, which would be equipped with suitable display facilities.
This is an on/off switching signal to indicate when a traffic announcement is on air. The signal could be used in receivers to:
After the end of the traffic announcement the initial operating mode will be restored
The transparent data channels consist of 32 channels which may be used to send any type of data.
This feature is intended to be used for the coded transmission of traffic information. The coding is separately defined by a set of standards issued by CEN [ENV 12313-1 and prENV 12313-2].
This is a flag to indicate that the tuned programme carries traffic announcements. The TP flag must only be set on programmes which dynamically switch on the TA identification during traffic announcements. The signal shall be taken into account during automatic search tuning.
Mick Evans 1999-2001
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