I discovered mysterious hidden signals on a public radio channel (2013) [video] | Hacker News Reader

I discovered mysterious hidden signals on a public radio channel (2013) [video]

media.ccc.de

273 pointsjoebig67 comments

This was a such a refreshing talk. She was monitoring the FM channel using a spectrum analyser (as one does, of course, haha) and got curious about this strange signal showing up next to the FM radio Channel.

The talk is about her attempts to learn about the Radio RDS (Radio Data System) standard, using a sound card to decode signals, finding a bit of bus-related information in that stream is weakly encrypted and proceeding to chasing it down. Very entertaining.

I'm so glad such people exist. I wish I could be one of these fearless and supremely knowledgeable people!

> I wish I could be one of these fearless and supremely knowledgeable people!

There's no trick to it (or there's a massive trick to it), you just refuse to let a mystery go until you know what's happening, mostly because figuring things out is fun.

In the process, you gain a large amount of knowledge.

It comes down to genuine, natural unforced interest (its there or not) and mastering the ability to systematically deal with and how to tackle the next unknown. After years this make you a true wizard.

> mostly because figuring things out is fun

I also think that figuring things out is one of life's most rewarding experiences.

But I've found out a lot of people don't think like that. I've often been asked "but why are you doing this" on the topic of my "eccentric" projects. People often can't understand why I find it fascinating because they would only find it tormenting.

What if the data is encrypted? Do you keep on trying in a brute-force way?

You do whatever you think is fun, what do you mean?

I found on her website [1] that she released a RDS decoder tool [2] relatively recently (compared to the 2013 of the video at least). Looks like it works with a USB RTL-SDR [3] receiver or a pre-recorded file in a number of formats.

[1]: https://www.windytan.com

[2]: https://github.com/windytan/redsea

[3]: https://www.rtl-sdr.com/about-rtl-sdr

I’ve used this to experiment with TMC messages and trying to unscramble TMCPro. Fun times!

Are there still apps and the underlying hardware in smartphones to receive and decode FM RDS? IIRC some phone chips had FM radio receivers, but there were limitations like needing a wired headphone plugged in so that the headphone cable could be used as an antenna. I know a USB SDR could do it, but it would be neat if this were still a latent capability in the phone.

Of course I did a search in the Play Store but it's crowded with streaming radio apps and SDR apps.

Yes. My Samsung has an FM radio. A lot do.

https://www.gsmarena.com/results.php3?chkFMradio=selected returns 7010 models, lol.

edit: oops you mean specifically RDS. Of that I'm not sure. I just opened the "Radio" app on my phone (for the first time ever!) and you did have to have the headphones plugged in to receive, but I couldn't see anywhere in the really basic looking app for RDS info to show up.

One thing I often wonder about with RDS: How do they stop the traffic alert (“TA”) feature being abused by stations to grab listeners?

I think nobody has to prevent abuse because listeners will either turn off traffic alerts or switch to a different channel.

Besides that, FM broadcasting isn't a lawless place and is regulated by the government. Abuse will most likely lead to some kind of penalty, but I can't be bothered to read through the laws to confirm it :P

The same way the prevent stations from broadcasting 90 seconds or more of pure silence: you loose your license if you do.

> broadcasting 90 seconds or more of pure silence

Have a link or info on this? Sounds interesting but can't find anything.

It is a rule in Germany, I know about it because we did some distributed cooperation stuff with community radio stations and some hacking events during the pandemic, and making sure that no matter what happens with the network between the speakers, the coordinating host, and server of the radio station, we never send out silence, was quite an important concern. I can't quote you the exact line of the law,though.

They don't.

Back in the day, it wasn't uncommon for pirate radio stations to drum up listeners by using TA to advertise short snippets.

The almighty FCC fine is the deterrent

Not sure about TA, but definitely saw radio station in Indianapolis using RDS to broadcast advertisements. In between the artist/song info, ads for an injury lawyer appeared. Thought it was super lame use of RDS.

"So I got to work"...

I love that hacker mindset :)

Wow, was that 2013? I saw this talk irl, can't believe it has been that long

I was picking up WCBS in NYC at 5.105 GHz, near the antenna at Empire State. Never could figure it out, their engineers didn’t know why either.

It was probably getting picked up by some component in a microwave transmitter and getting mixed into the signal.

Not sure whether it’s part of her talk, but this demonstration of the RDS stream she uploaded on Soundcloud is pretty cool:

https://soundcloud.com/windytan-1/rds-mixdown

This was great, I love these rabbit holes people go down, and it's great when they then share the results. Very fun watch.

This makes me wonder, how do you reliably and securely encode steganographic content for distribution within a noisy medium?

In this case I think it's mostly about using different sub-carriers (kind of a "channel in the channel"), so that the data information and the audio are separated in frequency and do not disturb each other. That's generally called Frequency Division Multiple Access (FDMA), IIRC.

Another more advanced technique is Code Division Multiple Access (CDMA), e.g. used by GPS and some mobile communication modulation schemes. It allows you to have multiple senders on a single radio carrier frequency, and the receiver "selects" which sender to listen to by knowing its "code".

There's also Time Division Multiple Access (TDMA), i.e. senders take turns sending content in allocated time slots.

I love the CCC website and the fact they host their own videos for a lot of reasons, but for some folks here is the YouTube video link:

https://www.youtube.com/watch?v=CnnbFWTNxZI

They seem happy to host media for other conferences as well! <3

For what folks would that be, then? Genuinely wondering why you'd want to click the big tech instead of self hosted link instead

Someone wanting to subscribe to the YT-channel? I don't visit 500+ blogs per day just to check if there's something new. I do miss Google Reader, I think about it almost every single day, I tried using other tools but I really think the RSS-era is over.

Maybe I’m doing it wrong but RSS works just fine most of the time for me. I use NewsBlur and does everything I need and more. What did reader have that no other RSS service doesn’t?

There was an alternate timeline where RSS went on to prosper. Instead it turned out like OpenID - a standard most aren't really using and it's all just SSO instead.

If you're on a smartphone, the Youtube app probably works better than whatever browser you're using. On the flip side, it probably has ads.

FWIW me and my family have the ReVanced apps and we never see any ads.

https://revanced.app/

We need a tl;dr on this one!

At a very quick skim, seems she detected and decoded the RDS signal in the 57kHz subcarrier of an FM broadcast.

https://www.mediarealm.com.au/articles/fm-rds-radio-data-sys...

That Media Realm site is mine. Thanks for linking! RDS is one of those technologies that’s been around for decades and still amazes people. You can buy hardware encoders for about AU$500 these days, and I love introducing stations to it and getting their name and song data to show up on car radios.

This is the blog post[1] from the presenter explaining part of it, with this request in the messages lol:

- Sad to request, but can you take thisoffline. It is kind of our service you hacked :)

[1]https://www.windytan.com/2013/05/a-determined-hacker-decrypt...

Thank you for that! I didn’t have the patience for the video, but I found her pen-and-paper decryption in that blog post absolutely lovely.

That “take this post down on the first appearance of any complaint from any party” tact sure changed in a hurry, huh

1.75x, I can't watch any video at any other speed at this point.

Ever tried with Louis Rossmanns or Network Chuck videos? I can't watch them at more than 0.75.

The actual title of the page is "My journey into FM-RDS" which definitely gives a better summary than what the current HN title says.

I had switched it to that, but then noticed that joebig had used the subtitle, which is also legit.

I would have never read your title. The whole reason I clicked was because of the mystery element.

To me it sounded like click bait. So I checked comments and concluded that it was indeed about the very visible RDS signal and not some hidden channel used by some secretive agency that would indeed be somewhat mysterious.

I don't think the fact that it worked in generating clicks is really an argument for bait titles. Given the positive comments about the content I think some editorializing could have been helpful to focus on the hacking journey aspect though, which seems to be the point rather the specifics of RDS itself.

Why do you need to be manipulated into reading something? When it turns out they are calling standard radio data "mysterious" don't you feel lied to?

Isn't that the definition of clickbait?

(2013)

Added above. Thanks!

I’m curious how folks who have the know-how to dissect a phenomenon “miss the forest for the trees” when they stumble upon a “mysterious” signal.

Alternate data streams in FM like RDS, IBOC audio and FM time are not some new-fangled tech. This would/should be the first place to go to if you saw a signal that’s not modulated to analog audio.

Of course, the whole mystery aspect is just a hook and helps move the story along.

Yeah more realistically it was like:

> I was looking at FM radio channels on SDR (rtlsdr came out in 2010) and noticed the RDS. So I looked into it.

Oona (the author) knew about the existence of such things; it wasn't a mystery. The only reason it was strange is that because her radio had been knocked about during a move, it was strangely down-shifting the data channel ... she was not monitoring the FM (from what I could make out), but the actual audio from the radio.

This was just ('just' for her, impressive for me) an exercise of going down the rabbit hole, and then curating that tour for us.

Rather, I don't think the data channel was actually down-shifted, but that it wasn't filtered out (probably due to a broken analog filtering circuit after the fall), so it was still outside of the audible spectrum but available to the sound card and hence visible in her software spectrum analyzer. It also sounded like she was seeing some aliasing effect, i.e. that the data signal was probably out of band for the sound card ADC, but "folded" down into the sampler frequency range due to Nyquist folding "magic" (which is maybe what you meant with "down-shifting", now that I think about it?).

She does speak of aliasing.

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