6 ms·

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

205 points by penneyd 6y ago

stevehawk 6y ago
he could have just gone on flightaware and saved himself some time? for those interested in this also check out https://stratux.me https://stratux.me
- Brian_K_White 6y ago
  "You/they could have just..." always depends on what the goal was.
- Krasnol 6y ago
  Well...SSL_ERROR_BAD_CERT_DOMAIN.
- llacb47 6y ago
  no. flightaware censors data. Use http://tar1090.adsbexchange.com http://tar1090.adsbexchange.com
  - jcims 6y ago
    Also there are advantages to not having any dependency on Internet access to figure out where an aircraft is (or at least where it says it is haha)
    - avhon1 6y ago
      You could even be ambitious enough to use multiple RTL-SDRs to do triangulation to the aircraft and see if it is where it says it is. Alternatively, you could do passive radar with RTL-SDRs to perform the same verification and also to find aircraft that aren't identifying themselves with ADS-B.
      - jcims 6y ago
        Yeah mlat is tricky but i believe there are open source implementations. Your second point would be the fun one. Integrate a bunch of sensor data (passive radar, rf, audio, video, thermal) to locate/id sneaky aircraft.
jcims 6y ago
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-helicopter.html http://www.windytan.com/2014/02/mystery-signal-from-helicopt... If this interests you at all highly recommend you check out her blog.
- naavis 6y ago
  Oona has super interesting projects in the blog. Can highly recommend too!
  - jcims 6y ago
    Her 'sounds of dial-up' image is poster-worthy - https://oona.windytan.com/posters/dialup-final.png https://oona.windytan.com/posters/dialup-final.png
    - DoingIsLearning 6y ago
      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/ http://baudline.com/)
      - jcims 6y ago
        She makes a lot of use of baudline. https://www.youtube.com/watch?v=YGdg_VC9LDI 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.
    - naavis 6y ago
      One issue of the Finnish Skrolli magazine actually came with a poster with that picture. :)
  - fapjacks 6y ago
haram_masala 6y ago
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.
ChuckMcM 6y ago
And this is why I'm enjoying the heck out of playing with SDRs.
- arminiusreturns 6y ago
  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.
  - ChuckMcM 6y ago
    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 https://www.crowdsupply.com/lime-micro/limesdr [2] https://www.ettus.com/product-categories/usrp-bus-series/ https://www.ettus.com/product-categories/usrp-bus-series/ [3] https://www.digikey.com/products/en?keywords=PLUTO https://www.digikey.com/products/en?keywords=PLUTO [4] https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up-304/ham-it-up-plus.html https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up-304/h...
    - prashnts 6y ago
      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!
graupel 6y ago
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-newscopter-passenger-on-airfox-live/ https://techcrunch.com/2008/05/16/become-a-virtual-newscopte...
- skeletonjelly 6y ago
  Very cool! Is there a copy of that video linked in the article somewhere? It 404s
  - graupel 6y ago
    I found a screenshot! https://www.newscaststudio.com/wp-content/uploads/2008/05/airfox.jpg https://www.newscaststudio.com/wp-content/uploads/2008/05/ai...
    - dfee 6y ago
      Either you really did, 17min ago, or you just trolled us all with a “403: forbidden” for laughs.
      - voidon 6y ago
        The site has referer check. Enter the url manually (not click via hn), and the image loads fine.
flyinghamster 6y ago
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 https://github.com/jart/spandsp
paulgerhardt 6y ago
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?s=21 https://twitter.com/skycirclessf/status/1268408145224720384?... [1] https://gitlab.com/jjwiseman/advisory-circular/ https://gitlab.com/jjwiseman/advisory-circular/ [2] https://www.adsbexchange.com/ https://www.adsbexchange.com/ [3] https://twitter.com/skycirclesdc/status/1268332759358947328?s=21 https://twitter.com/skycirclesdc/status/1268332759358947328?...
- jcims 6y ago
  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.
ccostes 6y ago
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.
- skeletonjelly 6y ago
  https://www.youtube.com/watch?v=2MprHxarmOI 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?

205 points by penneyd 6y ago

he could have just gone on flightaware and saved himself some time? for those interested in this also check out https://stratux.me https://stratux.me

Brian_K_White 6y ago
"You/they could have just..." always depends on what the goal was.
Krasnol 6y ago
Well...SSL_ERROR_BAD_CERT_DOMAIN.
llacb47 6y ago
no. flightaware censors data. Use http://tar1090.adsbexchange.com http://tar1090.adsbexchange.com
- jcims 6y ago
  Also there are advantages to not having any dependency on Internet access to figure out where an aircraft is (or at least where it says it is haha)
  - avhon1 6y ago
    You could even be ambitious enough to use multiple RTL-SDRs to do triangulation to the aircraft and see if it is where it says it is. Alternatively, you could do passive radar with RTL-SDRs to perform the same verification and also to find aircraft that aren't identifying themselves with ADS-B.
    - jcims 6y ago
      Yeah mlat is tricky but i believe there are open source implementations. Your second point would be the fun one. Integrate a bunch of sensor data (passive radar, rf, audio, video, thermal) to locate/id sneaky aircraft.

jcims 6y ago

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-helicopter.html http://www.windytan.com/2014/02/mystery-signal-from-helicopt... If this interests you at all highly recommend you check out her blog.

naavis 6y ago
Oona has super interesting projects in the blog. Can highly recommend too!
- jcims 6y ago
  Her 'sounds of dial-up' image is poster-worthy - https://oona.windytan.com/posters/dialup-final.png https://oona.windytan.com/posters/dialup-final.png
  - DoingIsLearning 6y ago
    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/ http://baudline.com/)
    - jcims 6y ago
      She makes a lot of use of baudline. https://www.youtube.com/watch?v=YGdg_VC9LDI 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.
  - naavis 6y ago
    One issue of the Finnish Skrolli magazine actually came with a poster with that picture. :)
- fapjacks 6y ago

haram_masala 6y ago

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.

ChuckMcM 6y ago

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

arminiusreturns 6y ago
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.
- ChuckMcM 6y ago
  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 https://www.crowdsupply.com/lime-micro/limesdr [2] https://www.ettus.com/product-categories/usrp-bus-series/ https://www.ettus.com/product-categories/usrp-bus-series/ [3] https://www.digikey.com/products/en?keywords=PLUTO https://www.digikey.com/products/en?keywords=PLUTO [4] https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up-304/ham-it-up-plus.html https://www.nooelec.com/store/sdr/sdr-addons/ham-it-up-304/h...
  - prashnts 6y ago
    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!

graupel 6y ago

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-newscopter-passenger-on-airfox-live/ https://techcrunch.com/2008/05/16/become-a-virtual-newscopte...

skeletonjelly 6y ago
Very cool! Is there a copy of that video linked in the article somewhere? It 404s
- graupel 6y ago
  I found a screenshot! https://www.newscaststudio.com/wp-content/uploads/2008/05/airfox.jpg https://www.newscaststudio.com/wp-content/uploads/2008/05/ai...
  - dfee 6y ago
    Either you really did, 17min ago, or you just trolled us all with a “403: forbidden” for laughs.
    - voidon 6y ago
      The site has referer check. Enter the url manually (not click via hn), and the image loads fine.

flyinghamster 6y ago

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 https://github.com/jart/spandsp

paulgerhardt 6y ago

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?s=21 https://twitter.com/skycirclessf/status/1268408145224720384?... [1] https://gitlab.com/jjwiseman/advisory-circular/ https://gitlab.com/jjwiseman/advisory-circular/ [2] https://www.adsbexchange.com/ https://www.adsbexchange.com/ [3] https://twitter.com/skycirclesdc/status/1268332759358947328?s=21 https://twitter.com/skycirclesdc/status/1268332759358947328?...

jcims 6y ago
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.

ccostes 6y ago

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.

skeletonjelly 6y ago
https://www.youtube.com/watch?v=2MprHxarmOI 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?