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.

▲ rpcope1 a day ago | parent | next [-]

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.

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skew-aberration a day ago | parent | next [-]

Phase coherence is ITAR? Or its use in passive radar is?

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bigfatkitten 21 hours ago | parent [-]

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.

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tj_astro 12 hours ago | parent [-]

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...

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skew-aberration 4 hours ago | parent [-]

So multistatic here is meaning multiple phase coherent receivers? MLAT is not considered multistatic passive radar?

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bigfatkitten 4 hours ago | parent [-]

MLAT is not radar at all for ITAR purposes.

MLAT ground stations just measure the time of arrival of the signal transmitted by the aircraft’s transponder. The difference in time of arrival at multiple ground stations allows the aircraft’s position to be calculated

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skew-aberration 3 hours ago | parent [-]

Very similar to passive radar. That's why I'm asking about what the legal distinction actually is. If I made my two MLAT stations phase coherent, would that make a difference?

	▲	bigfatkitten 2 hours ago \| parent [-]
		No, because it’s just a form of radio direction finding that wouldn’t be covered. Phase coherence has nothing to do with it.

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phendrenad2 a day ago | parent | prev [-]

Huh sounds like freedom of speech was abridged

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swiftcoder 20 hours ago | parent [-]

ITAR is pretty much the opposite of freedom of speech

	▲	knorker 12 hours ago \| parent [-]
		Well to be fair, ITAR is also about exporting physical weapons.

▲ kooi a day ago | parent | prev | next [-]

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)

▲ a day ago | parent | prev | next [-]

[deleted]

▲ schiffern 19 hours ago | parent | prev [-]

  >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.

"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...