
Mystery signal from a helicopter - schappim
http://www.windytan.com/2014/02/mystery-signal-from-helicopter.html
======
graupel
We operate news helicopters at TV stations around the US and they all use a
similar system.

Basically the right channel of audio is typically the microphone from the
pilot or reporter and the left channel is the audio feed transmitting what is
basically modem data back with the GPS coordinates of the helicopter and some
other data.

This data is used at the antenna site to track the helicopter and point the
antenna in the correct direction to keep a line-of-site since the transmission
system from the helicopter to the receiver is line of site (microwave) based.

It's really cool to sit and watch the receive antenna track and move
responding to the movements of the helicopter miles and miles away.

The antenna is on the belly of the chopper here - [http://www.imt-
broadcast.com/super-pod?cat=Products](http://www.imt-broadcast.com/super-
pod?cat=Products)

The receiver is generally centrally located on a tower - [http://www.imt-
broadcast.com/silhouette?cat=Products](http://www.imt-
broadcast.com/silhouette?cat=Products) \- it's a parabolic dish inside a
radome like this.

~~~
unwind
I'm not a native speaker, but still have a pet peeve for that one. It's "line-
of-sight" ([http://en.wikipedia.org/wiki/Line-of-
sight](http://en.wikipedia.org/wiki/Line-of-sight)).

Light travels in a straight line over (human-scale) long distances, so you
need a straight line free from obstruction to see between two points. I'm sure
you know this and just made a typo, of course.

Thanks for the additional information about this interesting solution.

~~~
graupel
Yup, just a typo!

------
jgrahamc
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.

~~~
tezmc
You've probably already seen it, but in case you haven't: her talk at 30C3 was
excellent and is worth a watch.
[https://www.youtube.com/watch?v=R-2k6TMPMRo](https://www.youtube.com/watch?v=R-2k6TMPMRo)

~~~
lucb1e
Been there, was cool indeed! If you aren't planning to already, you should
come to the 31c3 :)

~~~
sitkack
It is a certain commitment to Germany over Christmas.

~~~
lucb1e
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 ;)

~~~
sitkack
That and Hamburg is a beautiful town.

------
habosa
Wow. People on HN do a lot of cool things but that really blew me away. It all
sounded so casual too.

This is real Hacker News.

~~~
atourgates
If I'd seen this recreated in an episode of CSI, I would have thought
"Bullshit."

~~~
cgate
Yup, I guess there is little overlap between the CS community and electronics
community.

~~~
TeMPOraL
Also, surprisingly, after being exposed to things like this over and over
again, people in CS community _still_ underestimate the capabilities of
technology.

------
nl
I love this:

 _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](http://www.windytan.com/2013/09/the-burger-pager.html)

~~~
wglb
_For this kind of situations I often carry my RTL2832U-based television
receiver dongle with me_

But of course.

~~~
dsuth
As you would, really.

------
zenocon
This is the kind of article that makes HN worth coming back for.

------
GauntletWizard
Nice bit of reverse-engineering, and an impressive hack from whoever built the
system.

~~~
jrockway
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.

~~~
jzwinck
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!)....

~~~
jahmed
Wow. I always thought SAP stood for Spanish Audio Program. TIL.

------
werner34
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 :(

~~~
NamTaf
You can basically reverse those terms for me. I'm a mech engineer who wished
he knew more/was better at the web-dev / big data stuff.

~~~
hiharryhere
Sounds like you guys should be friends.

~~~
lifeisstillgood
Sounds like if they ever met, big explosion !

------
salgernon
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.

    
    
      http://vlsiweb.stanford.edu/~jaeha/chip_gallery.html

~~~
hodgesmr
It's sold here:
[http://www.redbubble.com/people/windytan/works/9934517-the-s...](http://www.redbubble.com/people/windytan/works/9934517-the-
sound-of-the-dialup-explained)

------
xradionut
While I love the blog and the very clear explanations, none of this is new nor
amazing to the experienced RF engineer, enthusiast, or practitioner. What's
awesome is that the hardware and software are currently cheap enough that more
people can discover and enjoy the larger spectrum around them. Welcome!

Now go build some antennas! :)

------
amcnett
It'd be interesting to scrape videos for this kind of information in order to
map them en-masse. Great post!

------
throwwit
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.

~~~
sethhochberg
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.

------
sehugg
Another cool thing is that the author of Redis made a decoder for ADS-B to
decode aircraft transponder signals:
[https://github.com/antirez/dump1090](https://github.com/antirez/dump1090)

------
vhost-
The thing I love most about her work is it's witty, but to the point and I can
always understand it.

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!

~~~
DonGateley
What is the tl;dr movement?

~~~
coldtea
He means people complaining that a post is too long and so they won't read it.

------
quackerhacker
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.

~~~
anigbrowl
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.'

------
logicallee
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 :)

------
fellytone84
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?

~~~
maxerickson
I think so. It isn't a big deal to find the tennis courts in the beginning of
the video:

[https://maps.google.com/maps?ll=39.04082,-94.560871&t=h](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.

------
tomchurchill
The Kansas City Police helicopters are also equipped with 3 of our Augmented
Reality mapping Systems:

[http://www.churchillnavigation.com/media/videos/40-san-
juan-...](http://www.churchillnavigation.com/media/videos/40-san-juan-county-
sheriffs-ars-system)

------
c7b0rg
Suddenly, my telecom courses in CS now seem a lot more fun than they really
were. It's like magic.

------
mangeletti
Anyone else see the cop hit him @
[https://www.youtube.com/watch?v=TCKRe4jJ0Qk#t=1140](https://www.youtube.com/watch?v=TCKRe4jJ0Qk#t=1140)
(19min)?

------
atmosx
Exception profile and work. I never seen anything similar and never really
thought that this was possible. Really stunned :-)

------
niels
This is also commonly used on Model Planes flying "First Person View". See
[http://www.youtube.com/watch?v=A_AnqOFAs3Q](http://www.youtube.com/watch?v=A_AnqOFAs3Q)
for an example.

------
easy_rider
Can anyone recommend some cheap hardware to hookup my TG-UV2 [1] to my PC?

[1][http://www.eham.net/reviews/detail/8931](http://www.eham.net/reviews/detail/8931)

------
lucb1e
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.

------
rikacomet
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?

~~~
_nedR
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](http://www.bbc.co.uk/news/science-environment-20629671)

------
ErsatzVerkehr
I would love to try a "signals hacking" capture-the-flag.

------
sown
I need to learn HW.

Could someone detail more information about the tools she used?

------
hans
cool thing is, we can start watching them back ;/

and critique whether they're joy riding or actually working etc

------
sebastianconcpt
Jaw-dropping

------
nolite
wow.. this girl is superhuman...

------
inanov
hackers rule!

------
codr
this is rad.

------
cdelsolar
amazing!

------
mablae
github?

