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How Passive Radar Works

passiveradar.com

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Re: How Passive Radar Works

#31

Post by stagger87 »

quantum_state wrote: post #4
sebasv_ wrote: post #2

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?

Would suggest to take a look at Jackson’s book on classical electrodynamics to get some intuition.

That's very evil to recommend a graduate electrodynamics book to learn more about passive radar. I would suggest taking a look at Platos Republic to get some intuition on why that is.

Re: How Passive Radar Works

#32

Post by WJW »

twic wrote: post #24
blittle wrote: post #15

Earlier quoted context omitted.

Probably more complicated to setup in a hostile environment because you'd need multiple transmitters, which also need to remain stationary, or at least you need to accurately know when they move.

Knowing where the transmitters are is vital. So wonder if you build in a positioning system to them. Each transmitter transmits a signal, but also rebroadcasts the signals it receives from the other transmitters on separate bands (these can be at lower power). If you can pick up a few transmitters, is that enough to build a model of where they are relative to each other, and then where they are relative to you? If ea…

> that's enough to know the range to each other transmitter, right?

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.

Re: How Passive Radar Works

#33

Post by morphle »

Aspos wrote: post #13
aurizon wrote: post #11

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?

Such radar would be a game changer.

Indeed, a global game changer for politics, defense, environment, climate, a step towards world governance.

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.

Re: How Passive Radar Works

#34

Post by alwa »

stagger87 wrote: post #31
quantum_state wrote: post #4

Earlier quoted context omitted.

Would suggest to take a look at Jackson’s book on classical electrodynamics to get some intuition.

That's very evil to recommend a graduate electrodynamics book to learn more about passive radar. I would suggest taking a look at Platos Republic to get some intuition on why that is.

If you want to make an apple pie from scratch, first you must invent the universe…

Re: How Passive Radar Works

#35

Post by chromacity »

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?

Re: How Passive Radar Works

#36

Post by TeMPOraL »

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…

Half-broken visualizations look suspiciously like ones I get from LLMs, so who knows, maybe it's some LLM setting up their first blog?

Re: How Passive Radar Works

#37

Post by lokimedes »

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…

(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.

Re: How Passive Radar Works

#38

Post by stagger87 »

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.

Uninformed FUD, not a single dsp "trick" related to passive radar is ITAR controlled. The equivalence the OP mentioned is literally described in every undergraduate dsp textbook.

Re: How Passive Radar Works

#39

Post by vscode-rest »

stagger87 wrote: post #38
vscode-rest wrote: post #10

Earlier quoted context omitted.

Lots of clever tricks, all ITAR controlled.

Uninformed FUD, not a single dsp "trick" related to passive radar is ITAR controlled. The equivalence the OP mentioned is literally described in every undergraduate dsp textbook.

k

Re: How Passive Radar Works

#40

Post by hammock »

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…

It’s reminiscent of what are known as “unbranded pharmaceutical websites,” which focus on educating patients about conditions and symptoms without promoting a specific brand-name drug, which means the regulatory bar is far lower and you don’t need to include any safety info etc.

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.”

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