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How Passive Radar Works

passiveradar.com

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Re: How Passive Radar Works

#51

Post by Animats »

Here's a 10 year old study from Norway's navy.[1] It's a marginal technology for navies. It's more useful for defending urban areas from air strikes, because urban areas have lots of emitters, too many to attack.

There's a lot of current interest in what Iran is using for air defense. Search "Iran air defense passive radar". Some people speculate passive infrared. Some speculate passive radar. Nobody who's posting really knows, of course.

Ukraine uses many passive systems, including audio. Sort of like Shot Spotter, but for drones.

[1] https://apps.dtic.mil/sti/pdfs/ADA470685.pdf

Re: How Passive Radar Works

#52

Post by morphle »

amarant wrote: post #41

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. bu…

I agree, it will be a fun hobby. I predict we'll all have one on our house within the decade. We call them burglar alarms or porch pirate camera's

[1] Best Porch Pirate Moments of 2025 (All Clips) https://www.youtube.com/watch?v=avUWmpfoK10

[2] When Porch Pirates Get Caught In The Act https://www.youtube.com/watch?v=zR8Imw7EN78

Re: How Passive Radar Works

#54

Post by mitthrowaway2 »

vscode-rest wrote: post #10
smartscience wrote: post #7

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?

Lots of clever tricks, all ITAR controlled.

ITAR is only a US law.

Re: How Passive Radar Works

#55

Post by awesomeusername »

chromacity wrote: post #43
lokimedes wrote: post #37

Earlier quoted context omitted.

(Not so) funny enough - I just did the same thing for https://gunsight.com complete with Claude generated interactive simulations for ballistics. We are actually building radars, and are likely going to use the domain in the future, but with zero effort I transformed an otherwise parked domain into something with a minimal amount of utility. So I do recognize the pattern.

I understand why you're doing it, but as a person who has to wade through dozens of these "minimal amount of utility" sites on almost every search, you're not making things better for the rest of us (or for the people who do hands-on ballistic testing that the LLM is just repeating without attribution).

wading through sites is still a thing? web search is still a thing? ok

Re: How Passive Radar Works

#56

Post by [deleted] »

WJW wrote: post #29
amoshebb wrote: post #14

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.

Multistatic radars (of which bistatic are just the case with N=2) are like the nuclear fusion of radar systems: everybody agrees it would be neat to have them, but they're always 20-30 years in the future. In practice it is extremely difficult to maintain the precise timing synchronization required for radar systems. Especially when used in moving vehicles or in sparsely populated areas the expected error goes WAY up…

[deleted]

Re: How Passive Radar Works

#58

Post by autoexec »

awesomeusername wrote: post #55
chromacity wrote: post #43

Earlier quoted context omitted.

I understand why you're doing it, but as a person who has to wade through dozens of these "minimal amount of utility" sites on almost every search, you're not making things better for the rest of us (or for the people who do hands-on ballistic testing that the LLM is just repeating without attribution).

wading through sites is still a thing? web search is still a thing? ok

Web search is a thing that is increasingly filled with AI slop that drowns out actual content. "wading through sites" for me means "wading through sites returned in search results".

Re: How Passive Radar Works

#59

Post by goto1 »

chromacity wrote: post #35

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 a…

From the second article:

  There are two options for purchasing pre-made kits that use Blah2:  
  Retina.fm: An open-source project [...] (Full disclosure: I run this project)

Re: How Passive Radar Works

#60

Post by pseudohadamard »

kklisura wrote: post #23

> 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's a note on the .fm site saying once it's assembled it can't be exported from the US, and shipping is US-only although I'm not sure if that's due to ITAR or just because international shipping is a headache.
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