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Comment by mrtnmcc | Hacker News Reader

QuadRF creator here. Happy to answer questions!

We have a quick demo video as well: https://m.youtube.com/watch?v=QvniJk3uNyA

Along with a deeper dive video: https://m.youtube.com/watch?v=zdJ9Tbm8ALg

We didn't give Jeff great direction on camera alignment calibration or setting the radio gain but he seemed to mostly figure it out. We're improving the UI based on his suggestions (it's open source so you can customize it too)

The RF augmented reality is just one of many applications of this brand new 4x4 MIMO software-defined radio built from the ground up. The AR uses a web app to stream RF points that your phone/laptop browser then live-merges with your local camera in the browser. I've been obsessed with low latency and high frame rate to make it a truly AR experience. More technical details at https://QuadRF.com/

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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.

We've got the switching noise nailed down. Fortunately the LVDS jitter doesn't affect the sigma delta too badly because that impacts proportional to baseband frequency which is largely filtered out by the decimation filters beyond 40 MHz.. With a total of eight ADCs per QuadRF, you can see we are getting huge savings by being custom! While the per-ADC ENOB is 7-8 bits, another nice thing about phased arrays is that the quantization/ADC noise averages away between elements, so with 8 ADCs in QuadRF we pick up another 1.5 bit giving 8.5-9.5 ENOB, which is frankly better than most SDRs. For the bigger phased arrays that improves further quickly.

I like to think of myself as pretty well-versed when it comes to hardware and software and even some RF. But this conversation has me hitting search a lot, lol. It's fascinating reading experts talk about a domain I have less experience in.

Heh, welcome to RF; there are more rabbit holes to go down in domain specialty than I think there are grains of sand on a beach. I've gone down like... two. And I'm pretty overwhelmed.

I think that's why a lot of EEs and developers wind up getting an amateur radio license, or at least running a few fun RF projects.

Glad I’m not the only one. I’ve been tinkering with sensors, robotics, sdr and similar stuff for 20 years now, but this conversation was way over my head.

That’s so cool!

Reading these comments first, I assumed you were using a variant of Spartan 6 LVDS TDC trick which allows up to 200 Msps rates. (https://sps.ewi.tudelft.nl/pubs/Homulle15fpga.pdf)

But this is a really interesting use case as well, and something that could be used for a 16 channel logic analyzer with analog recording support like the Saleae Logic 16 Pro, but without expensive ADC from Analog Devices.

Yeah, jitter doesn't matter too much at low frequency IF. I/Q calibration is more likely to be the bottleneck. That and close-in spurs from the fractional PLLs.

I have very little experience with MIMO / phased-arrays, this application likely doesn't need ultra high SFDR.

Yes, I actually designed the I/Q calibration for many of Analog Device's transceivers (AD93x), and indeed it is a fun problem. If you're interested in what was done for QuadRF, you can read: https://QuadRF.com/cals/txqec.html (Warning: Math!)

Oh wow, the AD936x series was impressive for its I/Q calibration. Still is I guess, because there's been no compelling alternative even a decade later.

As I mostly deal with single channel applications, I get to use double superhet and avoid runtime calibration. Not an option here, Zero-IF has too much in the Pros column for multichannel.

Yes once you have runtime IQ compensation figured out in digital, its essentially free and easily puts your image rejection ratio into the -50 to -60dBc range. I don't have a write up on the RxQEC, but it's rather trivial: you periodically compute the 2x2 IQ correlation matrix, then take the sqrt (e.g., Cholesky) and multiply your incoming Rx samples by that inverse. You can extend that further for widerband by using FIR taps but here the baseband matching is good enough to go with "single tap"

For those confused about what this means, my understanding is this: when quantizing a wave you can use sampling rate to derive missing bits, so using even one bit can work if you do it fast enough, but jitter is a problem because it means the clock doesn't cleanly sync and it doesn't help non-quantization noise like those generated from switching supplies. Corrections welcome.

A good tutorial on sigma delta is https://www.analog.com/en/resources/technical-articles/sigma...

For a deeper dive, check out any of Richard Schreier's lectures.

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?

We don't support passive or active radar beyond basic near-field sensing. We also proactively submitted a detailed report to the State Department earlier this year showing we don't exceed any of the USML criteria for ITAR controls. Separately we have an ECCN determination under EAR. This does rule us out from exporting to a few places (Cuba, Iran, Russia, North Korea, Syria, and some regions of Ukraine). But we are able to ship to most countries.

> does rule out..... some regions of Ukraine

The occupied ones, presumably. But why is Ukraine broken up? Surely, you will be dealing with a government, and they'll know what to do/ where there current borders are.

Why would they be dealing with government and not some hobbyist on the wrong side of the border?

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 ?

Thanks for the support! C-band is really the sweet spot in terms of affordability and compact size (the scale of the antennas and array spacing increases proportional to the wavelength). Maybe at some point we'll develop something at 2.4, but more devices are moving into 5GHz these days.

Is there a decent rule of thumb about how this style of antenna scales with frequency?

I'd kinda like something like this that could do 2.4GHz, 850-950MHz and even down as low as 400MHz.

Would by uneducated guess that 2.4GHz antennas would be twice the size, 900MHz about 6 times the size, and 400MHz about 10 times the size?

My feel would be that 2.4 has the advantage of being much longer range and there are plenty of sources for 2.4 - if you wanted to look at back-scatter and not just sources of emission. The primary demo of this piece of equipment is looking at radiation sources, but as you guys show there are plenty of other possible applications. I feel like since 2.4Ghz stuff has been around for ages.. the stuff should be much cheaper? Just a guess though :) Would be curious to know what the reality looks like

And cool to see you guys are from Santa Barbara. Lots of relevant talent there :)

If you ever want to go into the KHz range, you could build a ship-scale platform to carry the antennas :D

This does look cool - but I suspect most of the stuff I'd use it with is 2.4 Ghz (i.e. ISM band) - IOT devices, wireless keyboard/mouse, wireless cameras, drones etc

Is a 2.4Ghz version mostly about the larger physical size? Or are there other technical limitations to overcome as well?

And cost wise - would it be 2x this version ($499) - or higher?

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

Yes open-space was a short-lived name: https://domainnamewire.com/2026/04/08/u-s-defense-contractor... (good story though) We finally settled on Scale RF for the company and Quad RF for the product (and Moon RF for the bigger phased arrays!). Yes that incident kind of made our brand a mess..

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?

Absolutely :) we're working on documenting an awesome Meshtastic demo. Should have a writeup next week to add to the Crowd Supply updates page. Also Roy on our team will be demoing it (along with the RF augmented reality) at Teardown 2026 in Portland if you're in that neck of the woods.

Is the RTL for the FPGA available to be tinkered with?

That is super cool, man.

Do you have a demo for that 240 elements assembly?

We should have a video about MoonRF once we finish the QuadRF mass production, look for it ~ early September! Will be legendary! You can read on how the multi-tile synchronization and calibration works here: https://QuadRF.com/docs/#phased-arrays

Nice project, congrats!

Rx/TX isolation?

Typical image rejection (dB)?

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

Tx/Rx isolation is about -35dB to -40dB depending on the Tx/Rx polarization selection. The QEC image rejection is about -50dBc in Rx, and about -40dBc in Tx (one-time cal, without background cal enabled). The Tx and Rx are perfectly synchronized. This allows you to easily do things like near-field 4x4 MIMO radar: https://www.youtube.com/watch?v=gVqESemU_AI

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

What distance of drone detection would this theoretically have?

I assume it depends mostly on what frequency and TX power the drone in question is using, as well as the RF environment you're operating in and the noise floor of the SDR

Cool project! What is the max detection range?

It really depends on the transmitter strength, but if you set the Rx gain high on the QuadRF, we get within 2dB of the thermal noise detection limit.. so about as good as is possible with a receiver this size. I believe a few km is easily doable with a consumer drone but we haven't focused on it.

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

of course? not working directly together maybe, but put them at right angles and you get depth without relying on signal amplitude analysis.

did I misunderstand the question?

Something like this: https://youtu.be/YZkLQsv3huo

that adds a time dimenstion- not a spacial one. I'm no expert- but I'd expect a quadrf to not even need a time dimension for that case (rf transmitters are very rarely buried among noise in a spacial dimension.). my terms might be wrong, but I doubt the concepts are.

can this sense mice?

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