How Passive Radar Works

I will actually concur with one of the less upvoted comments here: the most fascinating thing about this article is the website. I've seen that pattern on HN a couple of times in the past couple of months.

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?

> By listening to how broadcasts like FM radio and digital TV bounce off objects, it's possible to determine their positions and velocities.

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...

There is a lot of talk of military uses here, but this technique is also used for environmental monitoring.

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...

I read a lot about passive radars trying to leech off of opportunistic waves, and lots about actual troops preferring to play hide-and-seem with anti-radiation weapons just to use active machines.

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.

I am searching for (part-time) business partners who want to pursue a grant (or find a customer) to develop and build a passive radar system.

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

This is fascinating! I'm very tempted to build a "early warning door bell". Being the only house on our road, it'd be fun to try and set up a few of these to detect when a car takes the exit from the bigger road ours connects to, and give a heads up that visitors are coming!

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!

A friend of mine did his PhD thesis on a passive radar that uses the GPS signal. I always found it such a brilliant idea, because the gps signal is everywhere and always available.

If one visualizes the electromagnetic field in the environment, including all objects in it and any changes, one would naturally come across many applications in sensing the associated changes in the field. One classic example is the eavesdropping case at Moscow US embassy in the former Soviet Union.

What's this website? Who put it up?

Those have always been good questions to ask, but especially these days.

I want this, but I do not have the experience with radio signals to build this myself without more guidance. Is there a DIY proof of concept I could lean on? How much more challenging will this be if you are in an area with overlapping FM signals from 2 transmitters sending the same signal?

Are there any clever tricks for the data processing involved here, given that the delay is a shift in the time domain and the Doppler effect is a shift in the frequency domain? Maybe involving fractional Fourier transforms, or wavelets?

I wonder if the many Starlink satellites can be used for this? True, the signals are low and are steered, but the nature of steering creates many side lobes that will be useable in this manner. It would be a complex computational task with satellites in motion as well as ground stations transmitting on offset frequencies. I suspect various research/military labs are playing with this?

a website for passive radars, cool xD