Radio Data System

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• published: 30 Nov 2010
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Radio Data SystemIn general, Radio Data System, or RDS, is a communications standard for frequency modulation broadcasts in the FM or VHF2 band within the range of very high frequencies. That is, the frequencies commonly used for radio broadcasting. It is well known mostly due to its expanded standard radio broadcast.They started to develop the system back in the 1970s, and it became widely used by the early nineties. The idea was that apart from the main signal FM radio broadcasts could transmit some other information that they could display. This information can include short text messages to let the driver learn about traffic jams, the weather, the name of the station or the song being broadcast, or even the type of the program (news or sports, for example). Automatic tuning is also available through RDS. The system has about two dozen features but not all of them are actively used. The required broadcast information appears on the radio display. Radio broadcasting uses a frequency modulation technology. Two frequency bands are responsible for stereo sound transmission, each one for each channel. RDS features a 57 kHz subcarrier set to the third harmonic and responsible for data transmission. It is higher than the transmitted stereo signal and doesn't cause interference to the signal. The 57 kHz subcarrier uses amplitude modulation while the baseband signal is digital. The data is sent in packages. The size of one package is 104 bits, and it includes four 26 bit blocks. Each block contains a 16 bit word with the data, and a 10 bit check word. Each block is assigned with a certain function. The first one, a package identifier, defines the package number and the radio station code, the second one identifies the type of the transmitted information, for example, whether it is an advertisement or a weather forecast, the next two packages contain the data to be shown on the display. The data goes to the RDS receiver which is an ordinary FM radio receiver enhanced with a special display to show the information, and the RDS unit itself. The received signal is demodulated into left and right channel audio sent to the dynamic speakers. Besides the signal is transmitted to the RDS demodulator that recovers data and synchronization pulse signals that are later fed into the RDS decoder which is a microcontroller. The decoder decodes the received and detected audio, and then sends the decoded information onto the display with the driver. As a result, we not only enjoy a high-fidelity audio, but also get useful information. Today, other promising models (except RDS) including the Japanese Data radio Chanell or DARC, are put into operation, but RDS does not lose ground and remains very popular.