Someone presented a passive radar system using an RTLSDR receiving TV broadcasts reflected off of nearby planes at a 2017 GNURadio conference. If amateurs can do it, you can bet the military has already designed, built, tested, deployed, and retired a similar system.
This isn't exactly a new subject, the same concept powered the first radar guided missiles in the 1940s (enemy is illuminated by a ground or airborne radar, missile tracks the reflection).
I'm fairly certain I've already read an article in an IEEE magazine talking about this topic (passive radar via cell towers) a few years ago.
I interviewed at company and their project was applying the music algorithm to find covert radio transmitters.
They were direct sampling the RF signals and running them through a bunch of H100's to get the algorithm to operate near real time. (They were quite proud of their 20 or so H100's)
Maybe this post is about that? It really lacks any technical substance. A bunch of corpo-talk is your ask me.
They probably throw all the signals, phase information into a ML model. But likely think the model inputs are very proprietary information so they just say ~ML will solve it~.
KerberosSDR and later KrakenSDR are precisely this, and the guy behind it got a spanking after putting up a passive radar implementation that actually works ok publicly on GitHub sometime in the pre-AI era. Supposedly it was considered an ITAR issue, but the similar MLAT capability instead of phase coherent sensing like you get with a Kraken is basically deployed everywhere today (all of the ADS-B nodes that feel FlightAware, FlightRadar, etc.) It's certainly not novel and not in the way TFA wants to paint it.
He got spanked because the use in passive radar of illumination sources such as TV transmitters is specifically identified in the USML.
USML Category XI(a)(3)(xxvii):
> (xxvii) Bi-static/multi-static radar that exploits greater than 125 kHz bandwidth and is lower than 2 GHz center frequency to passively detect or track using radio frequency (RF) transmissions (e.g., commercial radio, television stations);
There are separate ITAR provisions for radio direction finding, but these come with plenty of exclusions for systems not designed for defence applications or signals intelligence etc, and otherwise not meeting certain performance requirements, such as those in 5A001.e.
I was the one that originally flagged the GitHub repo as potentially being sensitive. The primary thing with passive RF use with TV or radio stations is the bandwidth issue. I've been following this particular topic for years and thus was familiar with the ITAR reg dealing with it.
itar regs https://www.ecfr.gov/current/title-22/chapter-I/subchapter-M...
there's still / again a number of Czech companies in the sector ... the "passive Radar" came from a Czech cold war project (Tamara). Yes it had a spotlight moment when some F-117 were shot down in the Yugoslav war.
Yes, a lot of the ideas are not new.
Nevertheless, it is currently an active field of research. One of them is "Integrated Sensing and Communication" (ISAC [or ICAS/JC&S/...]).
One idea is to exploit the signal's structure - despite simply trying to correlate the received line-of-sight signal with its delayed copies.
Especially OFDM has a nice structure. You can estimate delays (-> distances) as frequencies along the subcarriers and Doppler shifts (-> velocities) as frequencies along consecutive OFDM symbols. Estimators like maximum likelihood, ESPRIT, MUSIC, and compressed sensing etc. are your friends here for high-resolution results.
Unfortunately OFDM has a problem with large Doppler shifts (velocities). Therefore, people are looking at other multiplexing schemes like OTFS or AFDM.
> For network operators, it raises a different question: could the infrastructure that already generates subscriber revenue also generate a second, sensing-based revenue stream?
Are there people who experience positive emotions in reaction to sentences like these? I just… even in my days when I thought social good came from states/organizations downward rather than from humans upward… even then, when I thought a God’s-eye view was achievable, that more and better measurable data were the way to get there, and that the main barrier to effective social regulation was poor legibility… I feel like even then this would ring craven and avaricious to me.
Oops, yep. Typing fast and thinking sloppily. I had in mind something closer to “exploitative” or “opportunistic.” Maybe it was my cravin’ for dinner speaking…
If you work for an organization whose mission aligns with violating people's privacy, you'd likely be thrilled to take this up the chain to your boss and suggest all sorts of creative uses for it.
I run some fairly large data structures and business software platforms for clients. I'm not impervious to the urge to creatively invent ways to mine their data in ways that would help a client's bottom line and win me a gold star, provided they're data in aggregate. But there have been things I've been asked to mine that I will outright rebel against doing and refuse to touch. This is partly a moral issue, but partly something else: If I appear to be the kind of person who would do that, I'll end up misused myself. If they're the type of client who would do it, I don't want them as a client.
If you disrespect humanity, or life, you disrespect yourself. Whatever comes at you as a result, you bring upon yourself.
This lesson has been demonstrated in every generation throughout history, and never seems to be learned.
The project here itself is a technical issue, but the potential monetization of it is disrespectful to humanity. Unfortunately, at any given time, there are enough sociopaths willing to profit from the worst possible uses of any new technology.
> For network operators, it raises a different question: could the infrastructure that already generates subscriber revenue also generate a second, sensing-based revenue stream?
That's kind of strange. What are you going to sense that the cellular network doesn't already know? Air traffic? Car traffic? Drones?
The most useful application for this is probably drone detection.
We might see this rolled out in China, which is setting up traffic control for the "low altitude economy".[1] This includes drones, now, and flying cars, soon. There's also interest in tracking balloons, traditional hot-air flying lanterns, and other small sky traffic obstructions. As usual, Shenzhen leads in this area.
Someone presented a passive radar system using an RTLSDR receiving TV broadcasts reflected off of nearby planes at a 2017 GNURadio conference. If amateurs can do it, you can bet the military has already designed, built, tested, deployed, and retired a similar system.
This isn't exactly a new subject, the same concept powered the first radar guided missiles in the 1940s (enemy is illuminated by a ground or airborne radar, missile tracks the reflection).
I'm fairly certain I've already read an article in an IEEE magazine talking about this topic (passive radar via cell towers) a few years ago.
I interviewed at company and their project was applying the music algorithm to find covert radio transmitters.
They were direct sampling the RF signals and running them through a bunch of H100's to get the algorithm to operate near real time. (They were quite proud of their 20 or so H100's)
Maybe this post is about that? It really lacks any technical substance. A bunch of corpo-talk is your ask me.
They probably throw all the signals, phase information into a ML model. But likely think the model inputs are very proprietary information so they just say ~ML will solve it~.
https://en.wikipedia.org/wiki/MUSIC_(algorithm)
KerberosSDR and later KrakenSDR are precisely this, and the guy behind it got a spanking after putting up a passive radar implementation that actually works ok publicly on GitHub sometime in the pre-AI era. Supposedly it was considered an ITAR issue, but the similar MLAT capability instead of phase coherent sensing like you get with a Kraken is basically deployed everywhere today (all of the ADS-B nodes that feel FlightAware, FlightRadar, etc.) It's certainly not novel and not in the way TFA wants to paint it.
Huh sounds like freedom of speech was abridged
ITAR is pretty much the opposite of freedom of speech
Well to be fair, ITAR is also about exporting physical weapons.
Phase coherence is ITAR? Or its use in passive radar is?
He got spanked because the use in passive radar of illumination sources such as TV transmitters is specifically identified in the USML.
USML Category XI(a)(3)(xxvii):
> (xxvii) Bi-static/multi-static radar that exploits greater than 125 kHz bandwidth and is lower than 2 GHz center frequency to passively detect or track using radio frequency (RF) transmissions (e.g., commercial radio, television stations);
There are separate ITAR provisions for radio direction finding, but these come with plenty of exclusions for systems not designed for defence applications or signals intelligence etc, and otherwise not meeting certain performance requirements, such as those in 5A001.e.
I was the one that originally flagged the GitHub repo as potentially being sensitive. The primary thing with passive RF use with TV or radio stations is the bandwidth issue. I've been following this particular topic for years and thus was familiar with the ITAR reg dealing with it. itar regs https://www.ecfr.gov/current/title-22/chapter-I/subchapter-M...
"New technology" circa summer 2001:
https://www.popsci.com/military-aviation-space/article/2001-...
https://www.heraldnet.com/2001/06/20/cell-towers-can-spot-st...
This is not new as the article claims: Passive radars using FM broadcast and 2G GSM were used in the 1990s Yugoslav war.
there's still / again a number of Czech companies in the sector ... the "passive Radar" came from a Czech cold war project (Tamara). Yes it had a spotlight moment when some F-117 were shot down in the Yugoslav war.
Only one was shot down.
And it was almost entirely due to poor opsec by the US, not unexpectedly fancy radars.
Yes, a lot of the ideas are not new. Nevertheless, it is currently an active field of research. One of them is "Integrated Sensing and Communication" (ISAC [or ICAS/JC&S/...]).
One idea is to exploit the signal's structure - despite simply trying to correlate the received line-of-sight signal with its delayed copies.
Especially OFDM has a nice structure. You can estimate delays (-> distances) as frequencies along the subcarriers and Doppler shifts (-> velocities) as frequencies along consecutive OFDM symbols. Estimators like maximum likelihood, ESPRIT, MUSIC, and compressed sensing etc. are your friends here for high-resolution results.
Unfortunately OFDM has a problem with large Doppler shifts (velocities). Therefore, people are looking at other multiplexing schemes like OTFS or AFDM.
There is an interesting dissertation from 2014 which shows how to use OFDM signals to do radar (distance and velocity estimation).
https://publikationen.bibliothek.kit.edu/1000038892/2987095
I'm not usually one to notice when I'm reading an article written by AI, but this one is really bad. Tone put me off from finishing it.
I stopped after the first paragraph for the same reason.
> starting to break down
If this article is going to pretend amateurs with SDRs have not been doing this for at least 10 years, then the whole writeup is bullshit.
"Starting to"? If it's this irrelevant in the beginning, then it's not going to get better.
> For network operators, it raises a different question: could the infrastructure that already generates subscriber revenue also generate a second, sensing-based revenue stream?
Are there people who experience positive emotions in reaction to sentences like these? I just… even in my days when I thought social good came from states/organizations downward rather than from humans upward… even then, when I thought a God’s-eye view was achievable, that more and better measurable data were the way to get there, and that the main barrier to effective social regulation was poor legibility… I feel like even then this would ring craven and avaricious to me.
Craven?
Oops, yep. Typing fast and thinking sloppily. I had in mind something closer to “exploitative” or “opportunistic.” Maybe it was my cravin’ for dinner speaking…
If you work for an organization whose mission aligns with violating people's privacy, you'd likely be thrilled to take this up the chain to your boss and suggest all sorts of creative uses for it.
I run some fairly large data structures and business software platforms for clients. I'm not impervious to the urge to creatively invent ways to mine their data in ways that would help a client's bottom line and win me a gold star, provided they're data in aggregate. But there have been things I've been asked to mine that I will outright rebel against doing and refuse to touch. This is partly a moral issue, but partly something else: If I appear to be the kind of person who would do that, I'll end up misused myself. If they're the type of client who would do it, I don't want them as a client.
If you disrespect humanity, or life, you disrespect yourself. Whatever comes at you as a result, you bring upon yourself.
This lesson has been demonstrated in every generation throughout history, and never seems to be learned.
The project here itself is a technical issue, but the potential monetization of it is disrespectful to humanity. Unfortunately, at any given time, there are enough sociopaths willing to profit from the worst possible uses of any new technology.
> For network operators, it raises a different question: could the infrastructure that already generates subscriber revenue also generate a second, sensing-based revenue stream?
That's kind of strange. What are you going to sense that the cellular network doesn't already know? Air traffic? Car traffic? Drones?
The most useful application for this is probably drone detection. We might see this rolled out in China, which is setting up traffic control for the "low altitude economy".[1] This includes drones, now, and flying cars, soon. There's also interest in tracking balloons, traditional hot-air flying lanterns, and other small sky traffic obstructions. As usual, Shenzhen leads in this area.
[1] https://eastasiaforum.org/2026/10/16/chinas-low-altitude-eco...
Flying cars already exist, they're called helicopters.