|
Radio Data System (RDS) is a technology that allows FM broadcasters (88-108 MHz)
to deliver a stream of data with the audio content providing the receiver with a
variety of capabilites aiding the tuning of a certain station or program.
The development of RDS started in the 80's in the European Broadcasting Union
(EBU). This system is aimed to portable receivers, especially car radios.
Among the main applications, the following can be referred:
- presentation, in the display's receiver, of data identifying the station or the network being tuned, and the program type being received (news, sports, music, etc).
- automatic tuning to a specified station.
- updating of the time indicated by the receiver.
- automatic reception of information related to traffic announcement.
- radio-paging: delivery of specified messages.
Below are some definitions of the RDS technology:
-
PI - Program Identification:
code that enables the receiver to distinguish between areas in which the same
program is transmitted, and the identification of the program itself.
-
PS - Program Service Name:
set of alphanumeric characters (up to eight characters)
showed in the display, informing what station is being
tuned (e.g.: RADIO 1).
-
RT - Radio Text:
this refers to text transmissions coded, fixed length (up to 64 characters),
primarily addressed to consumer home receivers, which would be equipped with
suitable display facilities.
-
AF - Alternating Frequencies:
list of alternative frequencies carrying out the same programmation;
a equipped receiver would then search for the frequency having the best signal.
-
TA - Traffic Announcement Identification:
indicates that a traffic announcement is being currently transmitted.
-
CT - Clock Time and Date:
time and date codes transmitted in order to synchronize this
information with the values registered in the receiver.
-
PTY - Programa Type Search:
enables the receiver to search for stations according the program type
(news, sports, music, etc).
The digital data stream is transmitted at a rate of 1187,5 bits/s, modulated by
a sub-carrier of 57 kHz, using DSBSC (double side band, supressed carrier).
The figure below shows the spectrum of the FM signal to be transmitted,
including the RDS signal.
|
