Wednesday, July 23, 2008


When you see call letters displayed on the radio of your car this is why. Radio Data System, or RDS, is a communications protocol standard that actually originated in Europe. It allows a broadcaster to sending a small amount of data on a normal FM radio signals. RDS has been standard in Europe and Latin America since the early 1986. Were a tad behind. Again.

In the US we wildly under utilize the power of this system. In fact so few stations use it at all, many radios just disregard the data. With IBOC over the horizon (for better or worse) it appears to have the same destiny as Quadraphonic broadcasts. There are a handful of audiophile, and add-on devices that are compatible but they are not in common use. I see it mostly in rental cars for some reason.

Technically we use the Radio Broadcast Data System (RBDS) in the U.S. These systems are almost identical aside from the disputacious acronym.

To reduce interference to the FM stereo pilot tone RBDS uses a 57kHz subcarrier. (It's the third harmonic) When you see the RDS system at work in the U.S. you normally just see station identification. It can also contain track and artist info and much more. It compiles the following data fields.

AF - Alternative Frequencies, allows the radio to tune the station in on other frequencies
CT - Clock Time, to synchronize a clock
EON - Enhanced Other Networks , allows the receiver to monitor other signals for traffic information
PI - Program Identification, This is your stations slogan, brand, etc.
PS - Program Service, an eight-character display for the call letters
PTY - Program Type, up to 31 pre-defined program types, for scanning.. nobody uses thsi in America. Damn shame.
REG - Regional, allows the user to tune to region-specific programming
RT- Radio Text, a 64-character free-form textual information could be calls, random profanity, song names, slogans, it's free text.
TA - Traffic Announcement, receiver can be set to pay special attention to an EAS alert for example. It can even override your CD player.
TMC - Traffic Message Channel, Requires an RDS-TMC enabled decoder, which is licensed software. This can feed your car radio live traffic information based on your location.

It's difficult to say that there is a single inventor for either service as it gloms together dozens of individual patents to function. But even the NRSC even cops to the European origin of RBDS:

"The U.S. RBDS Standard is based largely on the European RDS Standard, the latest version of which was published by the European Committee for Electrotechnical Standardization (CENELEC) in 1998. Scott Wright of Delco Electronics, who is the Chairman of the NRSC's RBDS Subcommittee, has prepared a document which compares the U.S. and European versions of this standard."