It's an incredibly specific vanity domain called passiveradar.com. Who would want that unless they're a radar manufacturer or an expert in the field? In both cases, they would put their name on it, but there's no attribution whatsoever.
The site contains two short articles, mostly illustrated with photos lifted from elsewhere. For example, the schematic of how the radar works in the earlier article comes from:
https://www.researchgate.net/figure/A-schematic-diagram-show...
The article is also illustrated with what appear to be two vibecoded SVG animations that don't look quite right.
So, what's going on here? I suspect it's an attempt to farm domains for resale, or for LLM spam operations down the line?
An example would be a website creating awareness around a disease for which there is (or was at the time) only one or two treatments for, like ED, crohns, a specific type of cancer, etc. in fine print at the bottom will say “Pfizer” or “j&j” but no drugs are mentioned, just a call to “ask your doctor about possible treatments.”
Wasn't some Github repo ITAR'd, couple of years ago, due to having python code for some SDR doing this?
Edit: Found it. 3years ago https://www.reddit.com/r/RTLSDR/comments/yu9rei/krakenrf_pul...
GNSS interferometric reflectometry (GNSS-IR) uses navigation satellites as the transmitter for a bi-static radar. The measurement device is any GNSS receiver (even your phone).
The technique can estimate environmental parameters like sea level, soil moisture, snow depth, and vegetation water content from systematic changes in the the multi-path around the antenna.
There is an open source Python package for this technique: https://github.com/kristinemlarson/gnssrefl
An introductory paper "The Accidental Tide Gauge": https://www.kristinelarson.net/wp-content/uploads/2015/10/La...
A config that strikes me as obvious but doesn’t seem to be popular would be just bistatic where you fire your own transmitter far away from yourself?
There’s got to be a reason, but it seems like best of both worlds.
The survivability gains are also overhyped since 1. the enemy can just blow up the transmitters leaving you with a bunch of useless receivers and 2. most air defense doctrines already treat radars as something that should be distributed widely, so you can lose a few without the whole system collapsing.
The article goes into this only briefly, but modern radar systems don't just send out any random pulse but they very specifically tailor the waveform going out in order to do cool signal processing tricks like pulse compression. There is also the matter of frequency. The lower the frequency, the bigger the antenna you would need to get a proper direction reading out of it. Fire control radars typically operate in the X-band, around 10 GHz. Most civilian radio transmitters are around 100 MHz, so you'd need impractically large antennas and even then the bandwidth limitations would severely limit spatial resolution. One saving grace here is that stealth airplanes are typically most highly optimized against X-band radars from the direction they're going to bomb (forward), so you might have a better chance with a normal system, but then you still might not have a precise enough target to actually shoot at.
So while the multistatic system does offer some advantages, in practice it's just cheaper and (importantly for military use) requires less fiddly bits in the field to just use normal monostatic radars. Civilian use also doesn't benefit greatly from being multistatic. It's a bit like Tesla turbines or hyperloops: cool idea and it even "works" in a way, but the normal way of doing things is just way better when budgets and engineering realities come into play.
Source: I was a radar engineering officer in the Dutch navy about a decade back.
If each transmitter picks up the rebroadcasts if its own signals, then with some assumptions about the rebroadcast lag (or measurements of it added to the signal!), that's enough to know the range to each other transmitter, right? So maybe they do that and then just broadcast the ranges (tagged on to their main signal), then any remote receiver can work it all out from there.
Only in a flat environment without too much atmospheric distortions. As soon as you get multipath effects from eg waves bouncing off buildings and mountains then the computational complexity goes through the roof. Also I don't think you should underestimate how much the signal degrades in a "target path" vs the "direct path". The article mentions -60 dB and I think that is fairly optimistic. The transmitter power needs to be HUGE to make it work, so it would be much easier to have stationary transmitters. Normal radars manage to do this because they are highly directional, but multistatic radars need to look in all directions at once and need to up the power as a result.
We know of such grants and customers, we need motivated people to help us get the grant.
It is mostly a computational software problem that needs a cheap supercomputer, we believe we are experts at that [1].
We already have two test area's where we are not restricted by laws: the Ukraine battlefield (brimming wit jammers and radar) and a radio silence area LOFAR receiver next to a military low fly zone near a large nature reserve and sea.
We hope to find people through Hacker News who can help us get the funding. Maybe even apply at YC.
Please contact me through my HN profile.
See my other comment below on how passive radar could become a game changer (that got downvoted just because I mentioned it here).
Some nice graphics related to passive radar:
[1] Cheap Wafer Scale Integration Supercomputer https://www.youtube.com/watch?v=vbqKClBwFwI
[2] How The U.S. Will Track EVERY Vehicle from Space: SAR GMTI/AMTI https://www.youtube.com/watch?v=-GTpBMPjjFc
[3] The Insane Engineering of Starlink V3 https://www.youtube.com/watch?v=U6veU66z2TQ
There will be a few false positives from farmers coming to work the fields by our road, or people looking to hike in the nearby forests, etc. but it could be pretty fun nonetheless!
Those have always been good questions to ask, but especially these days.
https://www.silentiumdefence.com.au/our-solutions/space-doma...
but whether they have any connection or are just getting image jacked ... couldn't say.
If you have more than one receiver, the main issue is time sincronisation between the receivers.
Using the two transmitters will complicate things a lot
Halfway in the video he mentions the MIT (or Stanford) course of a professor who recently died. That course is online and has a lot of documentation (much better than this course.
Build Your Own Drone Tracking Radar: Part 1 https://www.youtube.com/watch?v=igrN_wd_g74&t=292s
You can contact me if you want more guidance. For passive radar you can just start with recorded data. I have access to huge amount of recordings on the Ukraine battlefield. Buying or building cheap antennas and radios is not needed for passive radar software development.
Radar was developed during the last two years of WOII, mainly in Boston at MIT and hundreds of companies each building a radar, most were deployed months later to win the war. Development after the war shifted to Silicon Valley, founding Silicon valley and the later chip and software startups decades later.
Carl also references Plato's Republic when visiting the actual cave where Plato lived.
Carl also references books classical mechanics but not the book the parent comment mentions but earlier ones like Al-Baghdadi, Cristian Huygens, Galileo, Newton.
Imagine a large number of crowdsourced software defined radio receivers with FPGA's and extremely accurate femto-second timing calibration connected to the internet spaced apart geographically and a distributed supercomputer to do all the realtime calculations. No single country or army would have this detector but everyone could use it for defense. Now imagine the resolution would be accurate enough for detecting planes, drones, birds, people, ground vehicles, ships, fish, insects, wind, tree leaves. We are close, we just need a cheap planetary deployment (like we had with SETI@home) and write better software. I imagine in 10 years we all have a detector, like we all have a smartphone or a router with a firewall. A passive radar in every building for spotting drones above our house and garden.