WEBVTT

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Every FM radio station in the country has a little

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data stream hidden inside it. It's been there

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for decades. Most listeners don't know it exists.

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And I mean, why would you? A lot of radio stations

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forget it's even running or how to set it up

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properly. It's called RDS and it's the reason

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your car knows what's playing and can show it

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on your dash. And in parts of Europe, it'll actually

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interrupt your music to tell you that there's

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a wreck on the highway. This is the Tyler Woodward

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Project. I'm Tyler. Everything in this episode

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is from my point of view, and any opinions are

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my own. Today I'm talking about RDS and RBDS,

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where it came from, how it ended up in the United

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States, and why a 1984 data protocol is still

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holding up the metadata backbone of FM radio

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in the US in 2026. RDS stands for Radio Data

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System. RBDS is the Americanized version. Same

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tech, slightly different implementation because

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we like to be different. The data rate is about

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1 .2 kilobits per second. A single second of

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Spotify audio carries roughly 13 ,000 times more

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data than an RDS stream can send in a full second.

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This isn't a fire hose of data, it's more like

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a drip from a leaky faucet. And it's outlasted

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a dozen or so systems that were supposed to replace

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it. The German predecessor to RDS was called

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ARI, and it did exactly one thing. In the late

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1960s, German broadcasters wanted car radios

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to alert drivers when there was a traffic alert

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erring. Not play it, not switch to it, not display

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it. Just light up a little indicator on the dash.

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Yes or no. That was it. The European Broadcasting

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Union figured there was probably more you could

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do with that idea. They started a working group

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back in 1974. Ten years of field trials and competing

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proposals and the final spec was released in

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1984. Commercial RDS car radio showed up at the

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Berlin radio show in 1987. Volvo shipped the

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first factory -installed RDS unit that same year.

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The U .S. didn't have a standard until 1993,

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when the National Radio Systems Committee published

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the NRSC -4. That's the RBDS spec. Several revisions

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followed, and in 2021, the standalone American

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standard was retired. and folded back into the

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international IEC standard as a named variant.

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Now, we can't talk about RDS and RBDS without

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getting a tad bit technical, so strap in, because

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here we go. FM radio signals have a certain structure

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to them that most people never think about or

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would ever care to think about, unless you're

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like me and you work in the industry or you're

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just a nerd. Either way, this stuff is fascinating.

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FM stereo broadcast carries a 19kHz pilot tone

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above the left plus right summed audio. Your

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radio uses that as a reference clock. From that,

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the receiver decodes a 38kHz subcarrier carrying

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the stereo difference signal, also called left

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minus right, which is the information that separates

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the left audio channel from the right audio channel,

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if that wasn't clear from the left minus right.

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RDS sits at 57 kHz, three times the pilot tone,

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and that's not a coincidence. Locking RDS to

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the third harmonic of the pilot means it shares

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the same reference clock as everything else in

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the signal. A receiver already decoding a stereo

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signal has everything it needs to decode RDS.

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In the 1980s, that meant adding RDS to a car

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radio was cheap. The groundwork was already there.

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The 1 .2 kilobit data rate isn't a random number

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either. It comes straight from the math of the

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signal itself. Everything is locked together.

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the pilot tone, the subcarrier, the bit clock,

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one big synchronized system. Whoever designed

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this was smart. Way smarter than me, I'll give

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you that. Now, one question I get about RDS is,

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well, why doesn't AM have this? Well, there's

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no room. FM modulation gives you enough bandwidth

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to stack subcarriers above the audio without

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interference. That's how stereo works. That's

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how RDS works. AM is a 10 kilohertz wide channel.

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Think of it like Wi -Fi channels. 20 megahertz,

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40 megahertz, 80 megahertz, but much, much smaller.

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The audio, the carrier, everything has to sit

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in that 10 kilohertz. There's nowhere to hide

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a subcarrier without landing on your own audio

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channel or worse, a neighboring station. The

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NRSC actually had a placeholder for AMRDS and

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the early versions, but even with trials there

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was never a deployment because of physics. You

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can't fit it in there if there isn't room for

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it. This is why HD radio matters more so for

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AM stations than FM, at least on the metadata

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side alone. The digital sidebands carry song

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title, artist information, album art, station

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names, and station logos. For stations that converted,

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it works and looks absolutely amazing. For the

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majority of AM stations that haven't, Well, your

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dashboard shows a frequency and not much else.

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1040 AM. In 2026, that's just not good enough

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anymore. The data stream is organized into groups

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of 104 bits with error correction built right

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in. The first 16 bits of every group, every time

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is the program identification code, the pie.

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In the US, it's calculated from the call sign.

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Feed a receiver the Pi, and it can decode the

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call sign. Group Type 0 carries the program service

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name, the eight -character station name on your

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infotainment system. Eight characters. Because

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that's what could fit on a mid -1980s car radio

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screen. The limit was designed around hardware

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that... hasn't existed for 40 some odd years

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and it hasn't changed. Group type 2 is radio

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text up to a whopping 64 characters song title

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and artist. An extension called radio text plus

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adds position tags so the receiver knows which

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characters are the song title and which is the

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artist. That's what builds the now playing display

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in the song history. that shows up on modern

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head units. There are also groups for clock sync

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alternate frequencies so a car radio can follow

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a station across various transmitters as you

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drive. Traffic announcements and the data only

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traffic service called TMC that fed European

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navigation devices for about 15 years before

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Google Maps made that irrelevant. Most American

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stations don't use a lot of the features that

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are available. Typical small to mid -market FM

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stations typically put their call letters in

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the 8 -character PS field, a static radio text

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that says something like, thanks for listening

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to 93 .3 The Rock or whatever station. A genre

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code that was probably configured by whoever

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set up the encoder years ago. or whatever defaults

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shipped from the factory. There's a station out

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by where I'm at that continues to say undefined,

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and it's been that way for 10 plus years, it's

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probably not gonna get fixed. The RBDS encoder

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can be a standalone box, usually at the transmitter

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site, but it can also be placed at the studio

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and sent by a lot of different methods out to

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the transmitter site. like Micro -MPX. Sometimes

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RBDS encoders can be built into the transmitter

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themselves and processors like the Omnia 9. There's

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Inovonix out of Santa Cruz. They make the most

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common RBDS encoders in the US radio market.

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And there's WorldCast that handles European installs,

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major markets over there. There's a Czech company

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called Pura that's become sort of a cult item

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and low power in college radio stations. I've

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seen engineers recommending that specifically

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because it's so cheap, you can sort of treat

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it as disposable. You can usually find those

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for about one hundred and ninety to five hundred

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bucks. We had a couple of these at the last cluster

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I worked at and they just worked and they were

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simple little boxes to set up. Not much to them.

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Now, that said, the standalone encoder It's slowly

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becoming a thing of the past. Nontel exciters

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now have RDS built directly into the web interface.

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You log into the transmitter and you configure

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it right there. No separate box. There's Orban

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that just announced at NAB 2026 that the new

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Optimod 5950 has Q's visual radio platform baked

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directly into the audio processor itself. The

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whole chain. Audio processing, RDS encoding,

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metadata management collapsed into one box. Great

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news for small stations who don't want to manage

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various pieces of gear, but less great news if

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you're in the business of selling standalone

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encoders. When the automation to encoder chain

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is maintained, it works fine and it looks great.

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When it's ignored you get stations with the wrong

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format code set for years and While speaking

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of that there's a documented case of an engineer

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taking over a station after an ownership change

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and finding The encoder was still broadcasting

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the previous formats branding the format had

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ended nine years earlier nine years of wrong

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data Now how nobody noticed? I find that hard

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to believe, but it seems to have happened, at

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least from a post over on radio discussions about

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it. The 8 character scrolling thing has its own

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argument. The European standard says PS is a

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static name. Period. Full stop. The American

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RBDS standard allows changes if they're not too

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distracting. What did American radio hear? You

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can change it! And it immediately started running

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full slogans through the field eight characters

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at a time like a marquee sign. European automakers

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hate this. There's a radio world piece specifically

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about a new Audi putting the scrolling PS text

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right next to the speedometer in the driver's

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sightline. Don't be that station. Don't do that.

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Now parts of RDS and RBDS are aging out. The

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TMC traffic service over in Europe is shutting

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down. The eight character display limit is embarrassing

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at this point, but we got to talk about the Pi

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code because it's still doing something that

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nothing else can do. It's literally holding up

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the next generation of metadata in the radio.

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Xperi. The company behind HD radio runs a system

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called DTS Auto Stage. It's in over 16 million

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vehicles across 13 brands including BMW, Ford,

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Audi and Mercedes. It reads the pie code off

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the RDS stream, uses that as a lookup key against

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a cloud database and pulls down a high -res version

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of the station's logo, album art, and full metadata

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that the subcarrier itself could never carry

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in that one point something kilobit stream. The

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broadcast sends a 16 -bit identifier. The internet

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sends everything else. The bridge is a number

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from a 1984 standard. Only thing about this,

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it does rely on cellular data to support it.

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Radio DNS does the same thing from a different

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approach. It takes the Pi code, builds a DNS

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style query, and it gets back a URL with enriched

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metadata. Same Pi being used. Emergency alerting

00:14:36.580 --> 00:14:40.240
is another reason why radio hasn't fully disappeared.

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EAS runs on FM because FM works when cell networks

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fail. There are commercial alerting systems built

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onto the RDS subcarrier specifically to push

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emergency techs during tornadoes and tsunami

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warnings. FEMA certified it. It's active in 17

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plus states. It's called Alert FM and it's a

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separate platform that you can have run alongside

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your station. Switzerland tried to prove FM was

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done in obsolete. They shut off the National

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Public FM Network at the end of 2024 and lost

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25 % of the German -speaking audience almost

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immediately. By late last year, parliament reversed

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it. RDS is a foundation of radio, at least FM

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radio, that nobody thinks about. It runs quietly,

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and it's been running quietly for 40 -something

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years. And the industry mostly ignores it until

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something breaks. The Pi code is a good example

00:15:55.299 --> 00:16:00.740
of how these things go. Designed to let a receiver

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verify it had the right station before switching

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frequencies. Now it's the identifier connecting

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a broadcast signal to a cloud database of logos

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and album art. in over 16 million cars. It became

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load -bearing without anyone planning for it

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to become load -bearing. 40 years, about 1 .2

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kilobits per second, still doing its thing. If

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this made you want to see what your local FM

00:16:35.820 --> 00:16:39.940
station is sending, grab an SDR app that decodes

00:16:39.940 --> 00:16:43.019
RDS and pointed at your favorite radio station.

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It's a rabbit hole. I'm not going to be responsible

00:16:46.080 --> 00:16:50.039
for wherever that leads you. RDSpy is a free

00:16:50.039 --> 00:16:53.200
tool you can grab on GitHub if you want to go

00:16:53.200 --> 00:16:56.000
down that hole. Thanks for listening to the Tyler

00:16:56.000 --> 00:16:59.039
Woodward Project. This is an independently produced

00:16:59.039 --> 00:17:02.200
and written podcast by myself. And if you would

00:17:02.200 --> 00:17:05.779
like to support the project, head over to tylerwoodward

00:17:05.779 --> 00:17:08.799
.me slash subscribe and become a member today.

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It goes a long way and it makes me feel all.

00:17:12.059 --> 00:17:14.759
warm and fuzzy inside. You can also follow me

00:17:14.759 --> 00:17:17.220
on blueskythreads and instagram at tylerwoodward

00:17:17.220 --> 00:17:20.440
.me. I'll catch you guys next week.