Ever looked at your radio and noticed there's text there, showing the artist and title of the song you're hearing on your favorite FM station? Ever wonder what that is? I'll tell you: RDS! Starting in the early 1990's, radios in the USA had the ability to display Radio Broadcast Data System text information, more commonly known as RBDS or just RDS.
RDS is a low bitrate (1.1kbps) text stream "hidden" on the 57 kHz subcarrier. Accordingly, it only works on FM stations, not AM. The bitrate is so low that you can't send much information; just enough to update 64 characters every few seconds. It's designed to allow display of all sorts of useful information: call letters, program format (news, sports, rock, country, jazz, etc), even alternative frequencies. That latter one is really cool, as radio equipped to use it will automatically tune to an alternative frequency specified when the one you're listening to gets too weak as you drive out of range. It's more common in Europe where government-run radio networks make heavy use of it. It never really caught on in the USA since it's too easy for alt.freq to re-tune a radio to a competitor station by mistake.
But the big thing RDS can do is Radio Text or RT. This is where stations can display any text they want, and it's very, very popular. The big use is for artist/title info...known in the biz as Program Associated Data or PAD...in real time, but I've seen sports stations use it to display ballgame scores during play-by-play. Or NPR stations in pledge drive to display the call-in number to donate. The marketing/promotional possibilities are quite vast.
The National Radio Systems Committee finalized the RBDS/RDS standard for North America in 1992. It took a few years before radios that could display RDS started hitting the market, but by 2000 or so, stations experimenting with it started getting results; people were definitely seeing info they were pushing out on RDS. The advent of widespread high-speed internet in the early- to mid-2000's made it even easier to update RDS on the fly, and it became a must-have for most music FM stations.
Now, in Rhode Island Public Radio's case, we have had RDS but we haven't had much use for it. Our infrastructure did not lend itself to quick and easy updating the RDS info, and for our 102.7FM transmitter, we have an HD Radio system that also does PAD for HD receivers, but not RDS for analog. (it's possible to add RDS to a Nautel V7.5 transmitter, but it's nowhere near as easy)
Recently for our 88.1FM signal in Providence I added some gear that made it possible to remotely implement updates to our Inovonics 730 RDS encoder. So I have it set up to display the name of the show currently broadcasting, which updates on the fly.
It can also be overriden for special announcements, and at the moment I've got a message up promoting our new free daily e-mail newsletter: The Daily Catch. Here's a video of the RDS message playing on my Kenwood car radio, and please take a second to sign up at www.ripr.org/dailycatch !