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The really intriguing part is the "Custom ADC" here, seems like some kind of 1-bit ΣΔ oversampling ADC (704 MSPS?). Single differential transistor, and captured by FPGAs LVDS RX.

Neat way to reduce cost and pin-count? But I think the typical FPGA clock tree has poor jitter performance. Not using the internal PLL(s) might help with spurs but the clock buffers are unavoidable.

The documentation mentions it's likely further degraded by noise from switching regulators. Oh the joys of hunting RF noise sources.

Are you concerned about the issue that KrakenRF ran into with their passive radar demo project violating ITAR rules, or is that something that can easily be avoided by just not doing that specific kind of application?

Product looks cool, not sure what I’ll use it for but did just purchase it on crowdsupply :) How did you settle on that frequency range btw? It’s 4.9 - 6ghz, so it will visualize the higher freq WiFi, but I guess it will not work for the 2.4ghz WiFi, or Bluetooth which is also around that frequency? And I don’t know tooo much about RF, but would including support for that range also, have necessitated much more complex/expensive hardware/antennas ?

Really cool! Just ordered one. Do you guys have an active lab in SB?

What distance of drone detection would this theoretically have?

Super cool project I've been following for a while. Are you pivoting away from Earth-Moon-Earth radio astronomy? I first bookmarked this project when your site was hosted at https://open.space

Nice project, congrats!

Rx/TX isolation?

Typical image rejection (dB)?

Does it support hardware level timestamping to align tx and rx samples through soapy?

Super cool! I noticed you had a blurb about it being used for mesh networks? Could you please go into more details/provide links to resources to learn more about that?

if I put two of these far-ish apart, can I get better 3d/4d data?

That is super cool, man.

Do you have a demo for that 240 elements assembly?

Cool project! What is the max detection range?

can this sense mice?

Yep, been in the works for a while. Ericsson, Nokia Bell Labs and Qualcomm have been publishing press releases regarding ISAC and telecom providers also sees new potential market of S2aaS, especially if there is a push towards autonomous robots, vehicles that need the data for mapping & training data.

Future networks using millimeter-wave (mmWave) and sub-terahertz (THz) frequencies may collect or infer detailed information about people, devices, bystanders, passive objects, and environments in a sixth-generation (6G) deployment area. It may detect breathing and heart rate of biological bodies.

https://eprint.iacr.org/2026/1069

I have a feeling they are not planning to sell it to government agencies for $500. Our tax dollars will go a lot less far I expect.

Remember how for years starting in the late teens and fizzling out over covid university paper after university paper about "this is so cool look how we can see through walls by essentially using 5g and wifi as ambient light" and they steadily marched up the chain from simple room layouts to furniture layouts, occupant detection, occupant movement and then started being dressed up with the usual dogwhistle language about "emergency services" that people who are building tech to help infantry/police entry teams use to make it seem more noble and then after that it all just kinda stopped being publicized with any sort of regularity?

I'm not a conspiracy theorist but I'd say all the people working on that shit got hired.

Sorry not sorry for the run on sentence.

Fluke has made an acoustic imager for a while now. It is used for detecting leaks:

https://www.fluke.com/en-us/product/industrial-imaging/fluke...

Realtime sound visualization was actually a project I did 20 years ago as a freshman and that (probably?) inspired me to build this AR app in QuadRF.

On balance, I would say this RF version was 200x harder.

Not sure if you've heard of them, but they're starting to come to market with this exact thing aside from distance detection and more on the "which part is squeaking" side.

https://www.youtube.com/watch?v=l8-5lSVCR2w

I think you'll be very interested in this awesome project

https://ribbonfarm.com/2016/06/29/the-daredevil-camera/

The army has one of these for sniper triangulation, and Boeing made a civilian version for optimizing sound dampening on the 787. I don’t know if they kept doing that on subsequent planes but I would expect so given how enthusiastic they were about being able to apply the weight budget to greater effect.

You need really high clock rate sensing to differentiate the arrival time for sound from microphone arrays where they are all less than a nanosecond separated from each other.

respeaker and https://github.com/introlab/odas might be a good starting point without having to make hardware.

Making the hardware is fairly achievable without having to do fancy things. but if you want >8 channels you'll need to make some custom interface hardware.

There are products in this space, eg https://www.crysound.com/

Very cool stuff, can be used for drone detection at up to 200m. Accuracy is not super good, unless you make mic spacing a bit large.

Steve Mould did a cool video on this: https://m.youtube.com/watch?v=QtMTvsi-4Hw

I've seen http://soundryx.com/

Like in this Steve Mould video, "Acoustic cameras can SEE sound" [1]?

[1] https://www.youtube.com/watch?v=QtMTvsi-4Hw

I want that but for smell.

You should visit Orfield Labs in Minnesota.

There's a company in Austin that uses sound for drone localization, although I forget the name

ChatGPT tells me that it would take a very large array to detect distance with any accuracy

Whos paying the telcos for those 5G connections and also has the FCC been degraded so much that they would allow for undeclared radios in consumer products?

It always impresses me that technology ideas once exposed in the nefarious background of the Snowden revelations, has now become mainstream, almost passé among the technocratie, but then I remember that there is a very dominant event horizon where all technology is weaponized/de-weaponized according to the intentions of its users..

It's going to been pretty wild to see QuadRF being applied for things. I can only imagine there are weapons-technologists who will bolt this onto hunter/killer drones at some point. A lynchpin technology for the inevitable drone wars.

> I have heard claims of devices (mostly TVs) supposedly coming with secret 5G cell uplinks built

This is occasionally mentioned on HN, but I have not yet seen a specific instance of this. Please share if you know something about secret 5G cell modems used to spy on people.

It detects drones which send out RF signals at the same frequency band. Most drones used in Ukraine are tethered with thin optical wire exactly because one of the first anti-drone measures was to simply jam them at the frequencies the operators used.

There are some more advanced anti-drone measures at work: Like blasting them with directed high-energy microwaves to destroy the circuits.

> That might have some defense application considering what's going on in Eastern Europe right now.

This is a bog-standard phased-array RDF calibrated for WiFi freqs; that stuff is already in every single defense show.

Also, that's why there's jamming everywhere (to blind that kind of things) and why many UAVs are now tethered to optical fibers instead of being RF-controlled.

Very much so.

I had a friend who'd just gotten out of EE school as a non-traditional student who was working for a company that was making radars for tracking drones maybe five years before the 2022 Russian invasion.

That was an active system, similar in concept to the radars used in air defense system just scaled down and faster acting.

The one in this article is a passive system that sees the transmitter on the drone. The comm link is the obvious weak spot on the drone as it can be detected and jammed, it is fairly inevitable that lethal attack drones that work anonymously will be widespread as a result.

I don't see any professionals turning to this for EMC/EMI testing, they already have all the test equipment for that job.

I don't think it's any good for that. It's relatively narrowband and not the frequency you usually have issues with EMC on (5 to 6GHz - unless you are specially transmitting on this frequency you are unlikely to emit anything there).

Do you have specific SDR in mind? I thought the v2 dongle doesnt have the range of Wifi? SDR is something Ive just recently want to learn to help me understand electromagnetism

I'm not super familiar with this area, but couldn't it see harmonics?

It also appears to have a fairly narrow detection angle. This might work for spotting a drone when you already know roughly where it is, but that problem becomes infinitely harder when you have to scan the entire sky.

RF drone detection has been a challenging problem for quite a while. Lots of solid state radar/RF detection products have emerged in the space, but it is not a trivial problem. And that is for drones with active RF comms, anything flying autonomously is even harder to detect at a far enough range to actually do something about.

Is that a limitation of the antenna? I though QuadRF uses SDR so can see many frequencies, not just the wifi things like ESPARGOS [0]

From documentation, QuadRF: Operating frequency range of 4.9 - 6.0 GHz (C-Band).

0. https://espargos.net/

for lack of directonality?

Please elaborate. There are literary step-by-step videos on how to build these. E.g. https://www.youtube.com/watch?v=g3LT_b6K0Mc

Probably because the people working on them get job offers that come with clauses about not working on this stuff publicly.

Do share some more details please

The covered materials are very broad, though often limited to equipment built "for purposes of", like in this section.

Title 22 Chapter I Subchapter M Part 121 - The United States Munitions List - Category XI Paragraph b

Electronic systems, equipment or software, not elsewhere enumerated in this subchapter, specially designed for intelligence purposes that collect, survey, monitor, or exploit, or analyze and produce information from, the electromagnetic spectrum (regardless of transmission medium), or for counteracting such activities.

The explanation may be spelled ITAR.

We know the definitions of "see" and when we take it to be in the "visualize" sense, it tracks for me.

I'm guessing if you can "see" Wifi through a wall, you can also infer some things about what's behind the wall, because the signal will have certain obstruction patterns. It becomes an xray.

It's RF vision, it let's you visualize RF sources as a coloured blob overlay in real time.

check out https://QuadRF.com/docs/

Passive radar is fine for gigantic airliners with all regard for efficiency, none for radar cross section, and that fly above most obstacles. For drones you might be trying to scratch signal not only from below noise floor, but at the edges of quantization.

I don't think it was ever (past 30 years) particularly secret? The general concept is long (100+ years) established. However pulling it off used to be exorbitantly expensive.

It's actually sold on their Crowd Supply for $99 per 4-antenna RF tile, just as the said on their website.

See the 6-pack: https://www.crowdsupply.com/scale-rf/quadrf#products

Prices have gone a little insane in the last year though too to be fair to them.

$500 is a surprisingly good price for a 4x4 mimo SDR.

It looks like it has 4 tiles on it, no?

Antennae, and the front end that feeds into the SDR.

The lower the frequency, the bigger the antennae need to be (more or less) so a 2.4gig array would most likely be 2x the size of a 6ghz array.

Open source is the future. If everyone can work on it, we get better results for cheaper.

Open source doesn't mean the end of competition, since we are a competitive species.

I think the future economy is going to be some sort of UBI + large open source projects

set that alarm

https://news.ycombinator.com/item?id=48861717#48864989

Most major airports will already have a counter-UAS system, it's a huge industry.

One big issue with radar is that it has the same problem pilots and human observers do: it struggles to distinguish drones from anything else in the sky (birds, balloons, planes, etc.). This is an active and improving research space, but by and large with radar, when your pilots report a drone, you still don't know how to figure out if it's the typical mis-identification or something real.

If would likely need to track them well (not sure from this article/video if that's the case?) to be useful in that scenario...

Drawing a splodge in roughly the location (not sure if there's range info either? I doubt it if it's passive) overlaid on the video likely won't cut it...

Yes, primary radar has been useful for detecting airspace incursions since 1939. Nothing new here.

Phased array antennas (in use since the 1960s) and AESA (in use since the 1990s) are very mature tech that RF engineers are well aware of.

This gizmo is primarily interesting that it's pre-packaged at a price that hobbyists can afford.

Only the ones that use radio for control. The fiberoptic ones are "dark" to this setup.

There are more way advanced systems for cuas, where they infuse radar and visual and acoustic plus now AI to minimize the false positives, but practically speaking, they are not bullet proof and still fail. RID (remote ID) is a way to have a cooperative communication and was mandated in US, but there are ways too to spoof it and cloak it.

I want this. I have Wifi door lock too far away from base station. It was often stuck in a loop trying to connect to neighbours' Wifis. By try and error I managed to block those using metal foil, but it was hard work.