6 ms·

Build a passive radar with software-defined radio

221 points by samizdis 4y ago

myself248 4y ago
Would it be possible to construct a network of passive radar receivers (assuming some time-sync between them, like the KiwiSDR's GPS receiver), and trilaterate the actual positions of planes? From there, the next step is to hide the ones that seem to line up with ADS-B data, and show only what's left, and that would be all the "black" flights...
- RF_Savage 4y ago
  Some ADS-B receivers do that with GPS sync. If a position has poor accuracy and is shown as "mlat" it' multilaterated based on when multiple receivers received the ADS-B packet. So while the plane is not transmitting it's location, the transmission can be used to identify and locating it. An actual passive radar network with multiple receive sites is reportedly a commerical product from multiple vendors, but it's not easy nor cheap.
inasio 4y ago
A scenario where all cellphones have this capability sounds a lot like the scene at the end of the Dark Knight.
- Trouble_007 4y ago
  Imaging with Your Wi-Fi Hotspot : https://physics.aps.org/articles/v10/50 https://physics.aps.org/articles/v10/50 Imaging Radar : https://en.m.wikipedia.org/wiki/Imaging_radar https://en.m.wikipedia.org/wiki/Imaging_radar 'WiFi radar/imaging' : <https://html.duckduckgo.com/html/?q='WiFi radar/imaging' https://html.duckduckgo.com/html/?q='WiFi radar/imaging'>
Thaxll 4y ago
Is it actually legal to build radars?
- H8crilA 4y ago
  It is legal to receive and process almost any electromagnetic radiation, yes. Transmission is licensed for nearly anything slightly below infrared, mostly because it would become a mess if everyone transmitted whatever they felt like. It is also restricted above UV, but for other reasons :)
  - heavenlyblue 4y ago
    It's not legal in the UK
    - ricktdotorg 4y ago
      as a UK person living in the US who recently passed the US (technician) Ham radio exam, it astonishes me how draconian the UK laws are about RF. it's even illegal to listen to UK air traffic control radio? what? how can they even be serious
      - bheadmaster 4y ago
        > it's even illegal to listen to UK air traffic control radio How exactly would they know that you're listening?
        isthisnametaken 4y ago
        Generally, they don't, and no-one cares. Airband scanners are freely available to buy online and in shops. It really manifests itself when you look online to see "listen to ATC" live streams and YouTube videos. There aren't any from the UK. https://www.liveatc.net/faq/ https://www.liveatc.net/faq/
- ilc 4y ago
  You can receive anything... sending is another issue. This is discussing passive radar, where you use another emitter, like a FM station or 20 to be transmitters, and your "radar" just sits and listens for the bounces off other objects.
aimor 4y ago
Where, online, are the SDR communities?
- RF_Savage 4y ago
  A random sampling: r/rtlsdr ##rtlsdr on libera.chat The SDR++ discord The RTL-SDR discord The Great Scott Gadgets discord The Signal Identification wiki's discord The Signals Everywhere discord and many other places and niches.
- ganoushoreilly 4y ago
  A lot of the discussions and chat I follow are on Various Discord servers and forums like https://www.rtl-sdr.com/ https://www.rtl-sdr.com/, also look into various defcon/bsides groups there's usually a handful there too. I joined the crowdsupply kraken funding and have been impressed with the hardware so far, but I only knew of them from their previous hardware. It's still a pretty niche topic relative to other things.
H8crilA 4y ago
This is cool but it's not quite a radar yet. He saw an increase in signal strenghth when a plane overflew his position and reflected some of the signal. Modern SAM systems are said to have the capability to track targets passively, for example by using reflected DVB-T transmissions. This is very important because combat aircraft have radar warning receivers, and it's best to not tell the enemy you're engaging him so that he can use countermeasures or perform evasive manoeuvres. Also SEAD/DEAD (suppression/destruction of enemy air defenses) is near impossible unless you can first locate the enemy air defense radars, which becomes a lot harder if you cannot simply home in on strong RF emitters.
- IrishJourno 4y ago
  Sorry if I didn't make this clearer in the article due to space constraints, but the TV surveillance antenna gives me a fair degree of directionality, enough to distinguish planes on different LGA and JFK approach/departures paths as they move through different parts of the sky, although once you get within 90 degrees of the reference signal all is lost. You also get a velocity and a range, albeit a bistatic one, similar to the first U.K. Chain Home radar stations.
  - H8crilA 4y ago
    Did you maybe write down more details somewhere else? Also, consider sending your article to the https://www.rtl-sdr.com/ https://www.rtl-sdr.com/ blog, it is really cool work!
    - IrishJourno 4y ago
      Thanks! I have notes scattered around, but they're not coherent (unlike the RTLs! <rimshot>) and I doubt I'll have time to publish them as once I've written an article I generally have to move on the next thing, which is the downside of being allowed to play with nice toys.
- CamperBob2 4y ago
  Some very nice results have been reported with a new multichannel coherent SDR: https://www.crowdsupply.com/krakenrf/krakensdr https://www.crowdsupply.com/krakenrf/krakensdr Haven't heard a lot of talk about this one yet, but the video at https://youtu.be/GZAbPsT3oRM?t=12 https://youtu.be/GZAbPsT3oRM?t=12 looks really promising.
anfractuosity 4y ago
Out of curiosity might it be possible to exploit signals generated by Over-the-horizon radar in a passive manner, for detection of planes etc? Or does reception of such signals have to be done near to where the transmitter is located.
- retrac 4y ago
  That's not too far off how radar was accidentally discovered, over and over. There is no one clear unambiguous first claim to radar, as far as I can tell. The general story is that plain ol' mediumwave/shortwave was bouncing off planes and ships as they passed, and operators couldn't figure out where the little signal spikes were coming from. Actual over-the-horizon radar systems have used transmitter and receivers at a significant distance from each other -- the Soviet Duga radar system in the 70s had its transmitter and receiver separated by ~50 kilometres or so. The receivers (and in active systems, also the transmitter) need to be in very precise time sync, and being physically close enough to run a direct cable makes that a lot easier. But theoretically, assuming the system is sensitive enough and time-synced enough and you have enough computational oomph available, an arbitrary number of receivers, at any distance, can be used to synthesize an arbitrarily large aperture. It's actually a similar matter to the synthetic aperture radio telescopes used in space astronomy, where telescopes with an effective aperture ~100 million kilometres wide have been created, using space-based radio telescopes linked with ground-based radio observatories. Such systems may not have the sensitivity of a 100 million kilometre wide telescope mirror (no matter to catch the photons since the "telescope" is mostly empty space) but it does have the equivalent angular resolution of such a 100 million km wide telescope mirror. It's mind-boggling when you consider the consequences of this as computation power improves. It will soon be possible to do this at such high speeds that it will allow frequencies into the far-infrared spectrum, not just microwave, for example.
  - Trouble_007 4y ago
    Soviet Duga Radar : https://en.m.wikipedia.org/wiki/Duga_radar https://en.m.wikipedia.org/wiki/Duga_radar Soviet Duga-2 Radar Tower : https://abandonedplacesmap.com/huge-secret-soviet-duga-2-radar-tower-in-the-woods-of-chernobyl/ https://abandonedplacesmap.com/huge-secret-soviet-duga-2-rad...
jbuzbee 4y ago
I worked on a downstream consumer of a passive radar system years ago and was amazed at its capabilities. We had it set up on a tennis court outside of Farnborough UK during a bi-annual air show and it was able to track all the activities of the various planes going through their routines. And I recall seeing commercial aircraft out in the English channel, 50 miles or so away. I don't know what became of the system, but there's an old marketing brochure online here: http://www.mobileradar.org/Documents/Silent_Sentry.pdf http://www.mobileradar.org/Documents/Silent_Sentry.pdf
- scoot 4y ago
- Trouble_007 4y ago
  Over-The-Horizon Radar (OTH) : https://en.m.wikipedia.org/wiki/Over-the-horizon_radar https://en.m.wikipedia.org/wiki/Over-the-horizon_radar
motohagiography 4y ago
Reminds me of stories of US stealth aircraft being detected by using reflected cellular signals. e.g. https://www.extremetech.com/extreme/49498-cell-phone-tech-could-id-stealth-planes https://www.extremetech.com/extreme/49498-cell-phone-tech-co... (2001) It seems like the same technique.
- Maursault 4y ago
  Reminds me of SNW 1x04[1] "You just turned a compass into a radar." - Captain Christopher Pike [1] https://www.youtube.com/watch?v=-NBxUqAHYTo&t=0m22s https://www.youtube.com/watch?v=-NBxUqAHYTo&t=0m22s

221 points by samizdis 4y ago

Would it be possible to construct a network of passive radar receivers (assuming some time-sync between them, like the KiwiSDR's GPS receiver), and trilaterate the actual positions of planes? From there, the next step is to hide the ones that seem to line up with ADS-B data, and show only what's left, and that would be all the "black" flights...

RF_Savage 4y ago
Some ADS-B receivers do that with GPS sync. If a position has poor accuracy and is shown as "mlat" it' multilaterated based on when multiple receivers received the ADS-B packet. So while the plane is not transmitting it's location, the transmission can be used to identify and locating it. An actual passive radar network with multiple receive sites is reportedly a commerical product from multiple vendors, but it's not easy nor cheap.

inasio 4y ago

A scenario where all cellphones have this capability sounds a lot like the scene at the end of the Dark Knight.

Trouble_007 4y ago
Imaging with Your Wi-Fi Hotspot : https://physics.aps.org/articles/v10/50 https://physics.aps.org/articles/v10/50 Imaging Radar : https://en.m.wikipedia.org/wiki/Imaging_radar https://en.m.wikipedia.org/wiki/Imaging_radar 'WiFi radar/imaging' : <https://html.duckduckgo.com/html/?q='WiFi radar/imaging' https://html.duckduckgo.com/html/?q='WiFi radar/imaging'>

Thaxll 4y ago

Is it actually legal to build radars?

H8crilA 4y ago
It is legal to receive and process almost any electromagnetic radiation, yes. Transmission is licensed for nearly anything slightly below infrared, mostly because it would become a mess if everyone transmitted whatever they felt like. It is also restricted above UV, but for other reasons :)
- heavenlyblue 4y ago
  It's not legal in the UK
  - ricktdotorg 4y ago
    as a UK person living in the US who recently passed the US (technician) Ham radio exam, it astonishes me how draconian the UK laws are about RF. it's even illegal to listen to UK air traffic control radio? what? how can they even be serious
    - bheadmaster 4y ago
      > it's even illegal to listen to UK air traffic control radio How exactly would they know that you're listening?
      - isthisnametaken 4y ago
        Generally, they don't, and no-one cares. Airband scanners are freely available to buy online and in shops. It really manifests itself when you look online to see "listen to ATC" live streams and YouTube videos. There aren't any from the UK. https://www.liveatc.net/faq/ https://www.liveatc.net/faq/
ilc 4y ago
You can receive anything... sending is another issue. This is discussing passive radar, where you use another emitter, like a FM station or 20 to be transmitters, and your "radar" just sits and listens for the bounces off other objects.

aimor 4y ago

Where, online, are the SDR communities?

RF_Savage 4y ago
A random sampling: r/rtlsdr ##rtlsdr on libera.chat The SDR++ discord The RTL-SDR discord The Great Scott Gadgets discord The Signal Identification wiki's discord The Signals Everywhere discord and many other places and niches.
ganoushoreilly 4y ago
A lot of the discussions and chat I follow are on Various Discord servers and forums like https://www.rtl-sdr.com/ https://www.rtl-sdr.com/, also look into various defcon/bsides groups there's usually a handful there too. I joined the crowdsupply kraken funding and have been impressed with the hardware so far, but I only knew of them from their previous hardware. It's still a pretty niche topic relative to other things.

H8crilA 4y ago

This is cool but it's not quite a radar yet. He saw an increase in signal strenghth when a plane overflew his position and reflected some of the signal. Modern SAM systems are said to have the capability to track targets passively, for example by using reflected DVB-T transmissions. This is very important because combat aircraft have radar warning receivers, and it's best to not tell the enemy you're engaging him so that he can use countermeasures or perform evasive manoeuvres. Also SEAD/DEAD (suppression/destruction of enemy air defenses) is near impossible unless you can first locate the enemy air defense radars, which becomes a lot harder if you cannot simply home in on strong RF emitters.

IrishJourno 4y ago
Sorry if I didn't make this clearer in the article due to space constraints, but the TV surveillance antenna gives me a fair degree of directionality, enough to distinguish planes on different LGA and JFK approach/departures paths as they move through different parts of the sky, although once you get within 90 degrees of the reference signal all is lost. You also get a velocity and a range, albeit a bistatic one, similar to the first U.K. Chain Home radar stations.
- H8crilA 4y ago
  Did you maybe write down more details somewhere else? Also, consider sending your article to the https://www.rtl-sdr.com/ https://www.rtl-sdr.com/ blog, it is really cool work!
  - IrishJourno 4y ago
    Thanks! I have notes scattered around, but they're not coherent (unlike the RTLs! <rimshot>) and I doubt I'll have time to publish them as once I've written an article I generally have to move on the next thing, which is the downside of being allowed to play with nice toys.
CamperBob2 4y ago
Some very nice results have been reported with a new multichannel coherent SDR: https://www.crowdsupply.com/krakenrf/krakensdr https://www.crowdsupply.com/krakenrf/krakensdr Haven't heard a lot of talk about this one yet, but the video at https://youtu.be/GZAbPsT3oRM?t=12 https://youtu.be/GZAbPsT3oRM?t=12 looks really promising.

anfractuosity 4y ago

Out of curiosity might it be possible to exploit signals generated by Over-the-horizon radar in a passive manner, for detection of planes etc? Or does reception of such signals have to be done near to where the transmitter is located.

retrac 4y ago
That's not too far off how radar was accidentally discovered, over and over. There is no one clear unambiguous first claim to radar, as far as I can tell. The general story is that plain ol' mediumwave/shortwave was bouncing off planes and ships as they passed, and operators couldn't figure out where the little signal spikes were coming from. Actual over-the-horizon radar systems have used transmitter and receivers at a significant distance from each other -- the Soviet Duga radar system in the 70s had its transmitter and receiver separated by ~50 kilometres or so. The receivers (and in active systems, also the transmitter) need to be in very precise time sync, and being physically close enough to run a direct cable makes that a lot easier. But theoretically, assuming the system is sensitive enough and time-synced enough and you have enough computational oomph available, an arbitrary number of receivers, at any distance, can be used to synthesize an arbitrarily large aperture. It's actually a similar matter to the synthetic aperture radio telescopes used in space astronomy, where telescopes with an effective aperture ~100 million kilometres wide have been created, using space-based radio telescopes linked with ground-based radio observatories. Such systems may not have the sensitivity of a 100 million kilometre wide telescope mirror (no matter to catch the photons since the "telescope" is mostly empty space) but it does have the equivalent angular resolution of such a 100 million km wide telescope mirror. It's mind-boggling when you consider the consequences of this as computation power improves. It will soon be possible to do this at such high speeds that it will allow frequencies into the far-infrared spectrum, not just microwave, for example.
- Trouble_007 4y ago
  Soviet Duga Radar : https://en.m.wikipedia.org/wiki/Duga_radar https://en.m.wikipedia.org/wiki/Duga_radar Soviet Duga-2 Radar Tower : https://abandonedplacesmap.com/huge-secret-soviet-duga-2-radar-tower-in-the-woods-of-chernobyl/ https://abandonedplacesmap.com/huge-secret-soviet-duga-2-rad...

jbuzbee 4y ago

I worked on a downstream consumer of a passive radar system years ago and was amazed at its capabilities. We had it set up on a tennis court outside of Farnborough UK during a bi-annual air show and it was able to track all the activities of the various planes going through their routines. And I recall seeing commercial aircraft out in the English channel, 50 miles or so away. I don't know what became of the system, but there's an old marketing brochure online here: http://www.mobileradar.org/Documents/Silent_Sentry.pdf http://www.mobileradar.org/Documents/Silent_Sentry.pdf

scoot 4y ago
Trouble_007 4y ago
Over-The-Horizon Radar (OTH) : https://en.m.wikipedia.org/wiki/Over-the-horizon_radar https://en.m.wikipedia.org/wiki/Over-the-horizon_radar

motohagiography 4y ago

Reminds me of stories of US stealth aircraft being detected by using reflected cellular signals. e.g. https://www.extremetech.com/extreme/49498-cell-phone-tech-could-id-stealth-planes https://www.extremetech.com/extreme/49498-cell-phone-tech-co... (2001) It seems like the same technique.

Maursault 4y ago
Reminds me of SNW 1x04[1] "You just turned a compass into a radar." - Captain Christopher Pike [1] https://www.youtube.com/watch?v=-NBxUqAHYTo&t=0m22s https://www.youtube.com/watch?v=-NBxUqAHYTo&t=0m22s