21–30 of 66 posts
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.
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...
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...
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.
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.
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.
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.
Much more covert, and civilian infrastructure also less likely to be blown up.
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.
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.
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
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.
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.