Decoding radio telemetry heard on news helicopter video footage with GNU Radio | Hacker News Reader

Decoding radio telemetry heard on news helicopter video footage with GNU Radio

rtl-sdr.com

205 pointspenneyd36 comments

Highly recommend the “Advisory Circular Project”[1]. It takes ADS-B data grabbed from a network of 3000 pi+gnu radios [2], analyzes them for aircraft flying in circles(!), and tweets out the images[3].

This is better than FlightAware as you are getting raw unfiltered ADS-B/Mode S/MLAT location data broadcast from the aircraft and aren’t filtering out position only flights.

Here is an instance of the California Highway Patrol observation plane circling downtown Oakland last night for some reason: https://twitter.com/skycirclessf/status/1268408145224720384?...

[1] https://gitlab.com/jjwiseman/advisory-circular/

[2] https://www.adsbexchange.com/

[3] https://twitter.com/skycirclesdc/status/1268332759358947328?...

This is really cool. Pretty remarkable how a relatively simple heuristic captures the behavior so effectively.

Also, take a look at the timestamps for the most recent tweets from @skycirclesla.

Would be cool if the adsbexchange project added some audio fingerprinting and even skyward-facing cameras to start detecting and even identifying aircraft that don’t sqwawk/squit/etc.

Just because it takes a few clicks from the article to get there, Oona Raisanen (aka windytan) did this originally.

http://www.windytan.com/2014/02/mystery-signal-from-helicopt...

If this interests you at all highly recommend you check out her blog.

Oona has super interesting projects in the blog. Can highly recommend too!

Her 'sounds of dial-up' image is poster-worthy - https://oona.windytan.com/posters/dialup-final.png

Pure curiosity but do you know what software was used to generate the spectrogram in that poster?

The color scale used in it really looks like the old-school cathode ray oscilloscope displays.

edit: found it, windytan actually mentioned it in the blog page. It was done using 'baudline'. (http://baudline.com/)

She makes a lot of use of baudline. https://www.youtube.com/watch?v=YGdg_VC9LDI

Sometimes it's a pain in the ass to get it dialed in but once you do it's hard to beat.

One issue of the Finnish Skrolli magazine actually came with a poster with that picture. :)

She is one of my favorite hackers and role models. I always learn something new and fascinating when I read one her posts.

Thanks! I never found her blog with all my quacks and googles on SDR keywords.

>quacks

I've never heard this but I hope it catches on :)

Haha, it took me half a day to realize what it refers to.

Oh snap, she’s got an EP on Spotify! https://open.spotify.com/album/1Bl6FF8hHZcazhCIxzI46N?si=wrM...

Cool! She’s got more music and a bunch of cool experiments/demos on her YouTube channel: https://www.youtube.com/user/windnyan

I tried to do this years ago while working at TV station with a helicopter and despite owning (well, leasing) the chopper and owning the microwave equipment the vendor would not release a way to decode the lat/long data used to track the video antenna, which I wanted to pull into a google map to show the choppers position.

So instead I gave the pilot an early smartphone (this was 2006) set up to use cellular to send back lat/long data and pulled it in that way, resulting in this:

https://techcrunch.com/2008/05/16/become-a-virtual-newscopte...

Very cool! Is there a copy of that video linked in the article somewhere? It 404s

I found a screenshot! https://www.newscaststudio.com/wp-content/uploads/2008/05/ai...

Either you really did, 17min ago, or you just trolled us all with a “403: forbidden” for laughs.

The site has referer check. Enter the url manually (not click via hn), and the image loads fine.

I took a quick listen to the audio, and "Bell 202" immediately came to my mind. It crops up carrying Caller ID on landlines in North America, and railway end-of-train devices use it for sending their telemetry over narrowband FM. It's very well-suited for any situation where you want to send short, low-bandwidth bursts of data over an audio channel.

If you need to encode or decode Bell 202 or similar schemes such as V.23, the SpanDSP library [1] is very handy.

[1] https://github.com/jart/spandsp

This is great. I have one of those cheap RTL-SDR units, and it was well worth the $8 to pull in and decode ADS-B signals from overflying aircraft. There’s something exciting about obtaining data “over the air” in a way that completely circumvents the Internet.

And this is why I'm enjoying the heck out of playing with SDRs.

Do you have any suggestions on a good full duplex sdr to start with? The last one I remember wanting was maybe the lime something? ADS-B data is cool, but my main goal was/is to demonstrate use as a bug finder and maybe do some other spectrum fun with my pc accessories and tv, wlan, etc.

Depends on how cost sensitive you are. Currently the LimeSDR[1] is the best value (even at $300 and no case) because it is not only full duplex, it also supports MIMO operation. While the latter is intended to support things like 4G LTE it also gives one the ability to do direction finding as multiple receivers clocked by a phase locked LO allows you to do phase analysis of incoming signals.

The Ettus USRP B-series[2] is very well supported for about $1000.

The ADALM-PLUTO[3] at $150 is a bargain for a full duplex SDR but a range of 325 MHz to 3.8GHz leaves a lot of interesting spectrum out. That is less of a problem if you get a mixer and RF signal generator because you can up/down convert the HF/VHF/UHF bands up to 1 GHz as an IF and play with them there. There are some off the shelf solutions for this like the 'Ham it Up'[4] but you are at the mercy of their TXCO.

I have all of these solutions except for the USRP and find that when I reach for a radio to look at a signal I usually grab the LimeSDR.

[1] https://www.crowdsupply.com/lime-micro/limesdr

[2] https://www.ettus.com/product-categories/usrp-bus-series/

[3] https://www.digikey.com/products/en?keywords=PLUTO

[4] https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up-304/h...

Any recommendations for softwares to play around with?

I got a NooSDR (€30 ish on amazon). I agree so much that its 1090MHz(?) leaves so much to explore, but I didn't have much luck other than decoding TV/FM/DAB using CubicSDR, GQRX, and VLC.

I am more interested in using it with Python/GNU Radio so didn't bother installing those super cool web based tools yet. Since I'm just starting, I'd like to get a feel of using it with a general purpose "summary software" first. Essentially something that can lookup the frequency databases, etc. to tell me: what is it that I'm looking at; if its LSB/USB/FM, and these sorts of things. Overall, I quite enjoy CubicSDR for this, but I'd appreciate if you have suggestions or resources I could check out. Thanks for the info above!

I found gnuradio companion to be useful for just poking around. Assuming the radio has a gnuradio compatible driver then you can do a lot of basic things like tune it around various spectra and get a feel for its sensitivity and selectivity. You can try out lots of different things quickly with it.

Lately I've been looking at front end selectors and their impact on radio performance. I have been using pysignal to process snapshots of iq data from the radio in my test setup.

Thanks for the tip, this definitely narrows down problem space to poke around with.

Thank so much for taking the time to reply, very useful info.

I'm wondering where the raw video from the helicopter came from originally. My guess is that this isn't something you can do with an SDR and hobbyist equipment, but I would love to be proven wrong.

https://www.youtube.com/watch?v=2MprHxarmOI

The footage is direct from the news organisation. I'm guessing this is footage from their FLIR mounted camera, maybe captured streaming to their HQ. Is that what you mean?

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