Not really a hack. Subcarriers are how they added color to TV, stereo to FM radio, and so on. WWV/WWVH also sends machine-readable time codes at 100Hz like this.
Indeed--it was more of a hack sixty years ago perhaps. Since then, similar tricks have been used for closed captions, Dolby surround (the original kind), Radio Data System (which puts song names on your car dashboard via FM radio), TV Second Audio Program (listen to shows dubbed in a second language, just press the SAP button on your ancient high-end TV!)....
>Subcarriers are how they added [...] stereo to FM radio...
Set your time machine for 1958, or follow this link [0] to see how RCA did both FM stereo (throughout the article they call it "multiplex") and 67 KHz "SCA" subcarriers. Admire the awesome 5KW FM transmitter cabinetry and transformer shielding.
One thing I find particularly interesting about articles from this time period is that Hz is not yet the name for 1/s, and so everything is in "cycles per second".
According to Wikipedia, the transition started in 1960, so we're two years away when this article was published.
Quite funny - I know someone who uses a similar setup to send GPS Coordinates for a Quadcopter and a Plane via the audio channel of the video link (he flies the Quadcopter/Plane with video goggles) to the ground station.
There, an Arduino controls some stepper motors to point directional antennas at the copter/plane.
Using spare audio capacity like this is actually very common - prior to digital recording, engineers would dedicate one tape channel to recording a sync signal, and in mission-critical applications would even 'stripe' the tape with the sync signal beforehand (many pro recorders can have recording and read heads active simultaneously).
Oona's work is always amazing. Loads of interesting hardware stuff in her blog. I wish I would be better at some mechanical engineering/electrical engineering stuff, my work is mostly web-related or big data stuff, never really get my hands dirty :(
I wonder how much audio compression the signal can go through before getting lost, and if joint-stereo affected it. Might have to check out the data myself :) Props to Oona.
Given that most audio compression techniques are perceptual, and the signal here falls into the "most important" 300hz to 3.4khz range that gets special attention in human hearing, I'd guess it is pretty resilient to run of the mill compressed audio codecs.
can this become/or is/ part of forensic science? if its possible to do the same on a mobile phone, and merely speaking into the phone, you give away your travel trajectory?
They're way ahead of you :-
They can take any audio recording (from any source) in the UK and get an exact time-stamp of its recording and detect whether it has been edited in any way : http://www.bbc.co.uk/news/science-environment-20629671
I love Oona Räisänen's blog. She's my hero. She combines a love of figuring stuff out with lots of fun hacks. And when I read her blog it makes me happy to see someone with that joy of uncovering mysteries.
It started the day after Christmas, though I did travel on second Christmas day. Totally worth it in my opinion. This was my first year and I can say that an extra day of that experience is always worth it.
Also WiFi totally rocked on day -1, but if you want that I guess you could also go wired any other day (symmetric gigabit and the best abuse policy in the world yay!).
But of course you can also travel on the day it starts and miss a few talks, it's up to you and your family how much of an issue it is to miss 2nd Christmas day. I was home in plenty of time for new year though, you still have that ;)
The talk was first given at 44CON in September in 2013 (but only available on the DVD, not posted on the youtube channel).
Funnily enough, this isn't the first time Oona's RDS adventures have been on HN[1]. Indeed, there's a comment from a while back on here[2] from the time I was trying to convince her to submit to 44CON. The thing that really surprises a lot of people is that Oona does this sort of thing in her spare time.
I just wanted to reply here with "You are my hero" .
But someone beat me to it. I must subscribe now.
This also fires up my drive to get more into Radio's and radio astronomy. It so fun to be able to grab all that stuff from the air that most people are unaware of.
I got my first handheld a while ago, and people were like "WOW amaze" when There was a really clear night in Budapest, Hungary with the ISS 70deg. overhead, and I was picking up Russian com while pointing to the illuminated station.
( -- yes unlicensed (but I don't TX) ). And now planning to get a license because more bands for the win, and licensed radio operators actually get much love from government and rescue services.
There's also lots of stuff that you can do with a cheap DVB-T tuner and simple (DIY) aerial.
And here I always consider myself paranoid when wondering whether odd patterns in anything mean anything. Guess I'm just too noob and inpersistent to find anything.
Amazing!!! I would have just dismissed it as static interference, and not even think twice.
Hmmm, makes me think twice about the beeping sounds I hear when my phone is right next to my radio. I know it's data being transmitted/received, but I wonder if it can be deciphered in this manner.
It's the phone checking in with the base station. As someone who records sound for a living, this is one of the banes of my professional life - I tell people on film sets to turn their phones off, and they think I mean 'don't use your phone' whereas in fact I mean 'shut it down completely.'
Can someone explain how she plotted the car's position? Did she manually reconstruct it based on the video and the information she derived from the helicopter's noise?
I'd had a copy of her dialup decoded poster on my wall for a while; forgot where I found it but it was immediately something I wanted to hang up... glad to see its being monetized via poster sales, its quite a lovely work of art.
Of course, I also find chip tape outs beautiful, much to my wife's dismay.
Several people in the restaurant were waiting for orders with their similar devices, which suggested to me this could be a pager system of some sort. Turning the receiver over, we see stickers with interesting information, including a UHF carrier frequency. For this kind of situations I often carry my RTL2832U-based television receiver dongle with me (the so-called rtl-sdr).
It's so cheap it's practically free (I mean come on, 3.2MHz BW for that price?). The included antenna is horrible but it suffices for small things like finding out something about the restaurant buzzers.
Oona is doing an extremely important service for Ham radio communities etc. She is bringing the knowledge of all of this to a wider audience on the internet.
Also, surprisingly, after being exposed to things like this over and over again, people in CS community still underestimate the capabilities of technology.
I didn't get how she can get so much sense out of what is basically line noise - until the comment that asked what tools she uses, and she says Perl. Ah, just a day in the life :)
82 comments
[ 3.7 ms ] story [ 128 ms ] threadSet your time machine for 1958, or follow this link [0] to see how RCA did both FM stereo (throughout the article they call it "multiplex") and 67 KHz "SCA" subcarriers. Admire the awesome 5KW FM transmitter cabinetry and transformer shielding.
[0] http://fmamradios.com/BTE-10B.html
According to Wikipedia, the transition started in 1960, so we're two years away when this article was published.
Project is at https://github.com/KipK/Ghettostation - video at https://www.youtube.com/watch?v=tiO4YCX7hJo - you can hear the modulation in https://www.youtube.com/watch?v=nm0okv8mTsg
They usually use simple FSK just like the "real life" helicopter in the article.
Here's an example of a common simple protocol:
http://www.flytron.com/pdf/audio_modem.pdf
Also WiFi totally rocked on day -1, but if you want that I guess you could also go wired any other day (symmetric gigabit and the best abuse policy in the world yay!).
But of course you can also travel on the day it starts and miss a few talks, it's up to you and your family how much of an issue it is to miss 2nd Christmas day. I was home in plenty of time for new year though, you still have that ;)
Funnily enough, this isn't the first time Oona's RDS adventures have been on HN[1]. Indeed, there's a comment from a while back on here[2] from the time I was trying to convince her to submit to 44CON. The thing that really surprises a lot of people is that Oona does this sort of thing in her spare time.
[1] - https://news.ycombinator.com/item?id=5656677
[2] - https://news.ycombinator.com/item?id=5657930
e.g., about those restaurant light-up/buzz pagers: http://www.windytan.com/2013/09/the-burger-pager.html
This also fires up my drive to get more into Radio's and radio astronomy. It so fun to be able to grab all that stuff from the air that most people are unaware of. I got my first handheld a while ago, and people were like "WOW amaze" when There was a really clear night in Budapest, Hungary with the ISS 70deg. overhead, and I was picking up Russian com while pointing to the illuminated station. ( -- yes unlicensed (but I don't TX) ). And now planning to get a license because more bands for the win, and licensed radio operators actually get much love from government and rescue services.
There's also lots of stuff that you can do with a cheap DVB-T tuner and simple (DIY) aerial.
Hmmm, makes me think twice about the beeping sounds I hear when my phone is right next to my radio. I know it's data being transmitted/received, but I wonder if it can be deciphered in this manner.
http://www.windytan.com/2013/01/the-gsm-buzz.html
https://maps.google.com/maps?ll=39.04082,-94.560871&t=h
I did that using her plots, but working backwards from the city hall to the freeway would only be tedious, not impossible.
Of course, I also find chip tape outs beautiful, much to my wife's dismay.
Several people in the restaurant were waiting for orders with their similar devices, which suggested to me this could be a pager system of some sort. Turning the receiver over, we see stickers with interesting information, including a UHF carrier frequency. For this kind of situations I often carry my RTL2832U-based television receiver dongle with me (the so-called rtl-sdr).
I knew I was forgetting something.
http://www.windytan.com/2013/09/the-burger-pager.html
I think this is what she was talking about? Note to self: buy one! :D
It's so cheap it's practically free (I mean come on, 3.2MHz BW for that price?). The included antenna is horrible but it suffices for small things like finding out something about the restaurant buzzers.
Oona is doing an extremely important service for Ham radio communities etc. She is bringing the knowledge of all of this to a wider audience on the internet.
But of course.
Could someone detail more information about the tools she used?
This is real Hacker News.
I'm not a big fan of the tl;dr movement, but I also don't like dauntingly long blog posts. Nails it every time. Hats off!