6 ms·

Hmm, not your typical RADAR. This is basically using the RF emissions of the plane, and their detection at multiple RF detection stations with synchronized cloc

Hmm, not your typical RADAR. This is basically using the RF emissions of the plane, and their detection at multiple RF detection stations with synchronized clocks, to determine the difference in arrival time. The radio emissions all travel at the same speed through the air, the difference in arrival time can be used with some simple trig to figure out where the RF emitter is. There are a number of Time Difference of Arrival or TDOA systems out there. It is why I expect aircraft stop using their radios when they are about to engage their targets. That said, they are "easy" to jam in the sense that when you have two radio signals on the same frequency, they will interfere with direction finding. And there is a lot of noise in the RF spectrum out there, especially during thunderstorms.

catalogia 7y ago
>multiple RF detection stations with synchronized clocks, to determine the difference in arrival time. The radio emissions all travel at the same speed through the air, the difference in arrival time can be used with some simple trig to figure out where the RF emitter is. That's a fancy way to say 'triangulation'.
- fest 7y ago
  I believe it's technically trilateration, not triangulation.
  - coretx 7y ago
    Contemporary passive radar arrays are phase sensitive so it ain't that simple either.
- rmattes 7y ago
  It would be triangulation if the system was measuring the arrival angles of the incoming signals. If the system relying solely on arrival time differences, it's likely doing something based on trilateration.
jah 7y ago
Here's an interesting variation that uses RTL-SDR's: https://dopplerfish.com/passive-radar/ https://dopplerfish.com/passive-radar/
- brian_herman 7y ago
  Cool we can build our own radar!
JDulin 7y ago
More to the point, detecting a stealth aircraft is very different from shooting at a stealth aircraft. This radar would likely not have the location accuracy of where exactly the B-2 was to accurately engage it with a missile. Your accuracy would be limited by the rate of RF pings the B-2 is putting off, and then the margin-of-error of these RF waves and receiver. This is one difference between the B-2 and stealth fighters like the F-22 & F-35: The latter are not necessarily designed to be invisible, only impossible to reliably hit. Their shapes and radar-absorbent paint deflect, diffuse, or absorb the high-frequency bands used in the terminal guidance of missiles. So they are hard to target. But they can be picked up at range by long-distance, long-wavelength VHF and UHF radars. These frequencies, used in early-warning radars, have too low-optical resolution* however to be any good at aiming guns or missiles. The B-2's "flying wing" shape is able to not-interfere with these wavelengths though, and hence hides from them. In that sense, this is somewhat interesting, if neutered for the reasons you mention. *You can only localize the detection to a few sq hundred meters, even kms.
- jdironman 7y ago
  And also, searching the top speed of a B-2 at 628mph, if detected at 150 miles out only gives them 14 minutes. Which is both a lot, or a little. Depending on how prepared for action someone is.
  - ISL 7y ago
    Or a lot less than that, if the B-2 isn't using gravity munitions.
    - sfifs 7y ago
      Well since there are so few B2 and they are essentially irreplaceable, I imagine standard wartime doctrine for the adversary would be to ignore target protection as a concern and go straight for the plane even at the risk of losing several of yours by flying over territory you don't control. In reality, what would make a difference is coordinating communications and decision making.
- 7y ago
imglorp 7y ago
> they are "easy" to jam in the sense that when you have two radio signals on the same frequency, they will interfere with direction finding Nope, it's a more sophisticated algorithm they're using. Our company held all the patents for locating GSM cell phones calling 911 using UTDOA. The U is uplink, meaning the network of receivers listens when the phone talks. The patents entail each receiver taking a sample of the signal they heard in that time slot on that frequency. They upload the sample to a processor which tries to correlate all the samples with some DSP math, sliding them around in time to see if they match. If they do correlate, the offsets of each one is your delay for doing trilateration. So if you have multiple talkers at the same time, they can probably be subtracted out by the correlation step.
- BlindWanderer 7y ago
  ECM can be directional (phased array antenna). If an aircraft knew the approximate location of the receiving antennas it could theoretically jam them seperately.
greglindahl 7y ago
> That said, they are "easy" to jam in the sense that when you have two radio signals on the same frequency, Not at all. Check out the VLBI technique from radio astronomy, it's not hard to tell that there are two discrete signals. But that's not really the point: you can see stealth aircraft already with lower frequency radars, just not well enough to shoot them down. It's hard to imagine this passive technique being good enough to shoot them down, either. https://en.wikipedia.org/wiki/Stealth_technology#Low-frequency_radar https://en.wikipedia.org/wiki/Stealth_technology#Low-frequen...
- DarkmSparks 7y ago
  the low frequency radar thing relates to the active radar in the missile warhead. Not accurate enough for hit to kill missiles, but plenty for modern shaped charge warheads that only need to get within 250 meters or so of the target for a kill, and completely irrelevant for warheads supplemented with optical targeting that only need to be within 5 miles clear line of sight to confirm a lock.
DarkmSparks 7y ago
Passive radar uses background RF, usually TV transmitters. Which is why they are the first to go everytime America decides to punish a nation for trying to use something other than the dollar to trade oil or decides to crack down on opium smuggling. Not really enough though, which is how they lost all the F117s over Serbia in the 90s. One of which I have a framed picture of on the wall along side an original "sorry we didnt know it was invisible" flyer. Tech has come a long way since then.
- scurvy 7y ago
  > Not really enough though, which is how they lost all the F117s over Serbia in the 90s. One of which I have a framed picture of on the wall along side an original "sorry we didnt know it was invisible" flyer. < Only a single F117 was shot down over Serbia. https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk#Combat_loss https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk#Comba...
  - DarkmSparks 7y ago
    Perhaps choose a better source than wikipedia, like people who were there. https://images.app.goo.gl/vUd8z2gkWEtKWKcJ8 https://images.app.goo.gl/vUd8z2gkWEtKWKcJ8 even your source says they hit 2. They claim they downed 3. Americans denied they lost any for decades.
    - blago 7y ago
      A propaganda poster knowingly conflating the words stealth and invisible, a distinction its intended audience wouldn't be able to make, to mock the enemy? I think I'll stick with the Wikipedia source.
      - DarkmSparks 7y ago
        And even that says: Some American sources state that a second F-117A was damaged during the same campaign, allegedly on 30 April 1999;[61] the aircraft returned to base, but it supposedly never flew again.[62][63] Point is with AA missile is that getting them "on target" is almost as effective as a hit. target has to deploy its counter measures and return home, else next time they are destroyed.
throw0101a 7y ago
> ... their detection at multiple RF detection stations with synchronized clocks, to determine the difference in arrival time. I believe this is generally called multilateration (MLAT): * https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration * https://www.skybrary.aero/index.php/Multilateration https://www.skybrary.aero/index.php/Multilateration * https://www.sciencedirect.com/topics/engineering/multilateration https://www.sciencedirect.com/topics/engineering/multilatera... * https://www.navcanada.ca/EN/products-and-services/Pages/on-board-operational-initiatives-mlat.aspx https://www.navcanada.ca/EN/products-and-services/Pages/on-b...

catalogia 7y ago

>multiple RF detection stations with synchronized clocks, to determine the difference in arrival time. The radio emissions all travel at the same speed through the air, the difference in arrival time can be used with some simple trig to figure out where the RF emitter is. That's a fancy way to say 'triangulation'.

fest 7y ago
I believe it's technically trilateration, not triangulation.
- coretx 7y ago
  Contemporary passive radar arrays are phase sensitive so it ain't that simple either.
rmattes 7y ago
It would be triangulation if the system was measuring the arrival angles of the incoming signals. If the system relying solely on arrival time differences, it's likely doing something based on trilateration.

jah 7y ago

Here's an interesting variation that uses RTL-SDR's: https://dopplerfish.com/passive-radar/ https://dopplerfish.com/passive-radar/

brian_herman 7y ago
Cool we can build our own radar!

JDulin 7y ago

More to the point, detecting a stealth aircraft is very different from shooting at a stealth aircraft. This radar would likely not have the location accuracy of where exactly the B-2 was to accurately engage it with a missile. Your accuracy would be limited by the rate of RF pings the B-2 is putting off, and then the margin-of-error of these RF waves and receiver. This is one difference between the B-2 and stealth fighters like the F-22 & F-35: The latter are not necessarily designed to be invisible, only impossible to reliably hit. Their shapes and radar-absorbent paint deflect, diffuse, or absorb the high-frequency bands used in the terminal guidance of missiles. So they are hard to target. But they can be picked up at range by long-distance, long-wavelength VHF and UHF radars. These frequencies, used in early-warning radars, have too low-optical resolution* however to be any good at aiming guns or missiles. The B-2's "flying wing" shape is able to not-interfere with these wavelengths though, and hence hides from them. In that sense, this is somewhat interesting, if neutered for the reasons you mention. *You can only localize the detection to a few sq hundred meters, even kms.

jdironman 7y ago
And also, searching the top speed of a B-2 at 628mph, if detected at 150 miles out only gives them 14 minutes. Which is both a lot, or a little. Depending on how prepared for action someone is.
- ISL 7y ago
  Or a lot less than that, if the B-2 isn't using gravity munitions.
  - sfifs 7y ago
    Well since there are so few B2 and they are essentially irreplaceable, I imagine standard wartime doctrine for the adversary would be to ignore target protection as a concern and go straight for the plane even at the risk of losing several of yours by flying over territory you don't control. In reality, what would make a difference is coordinating communications and decision making.
7y ago

imglorp 7y ago

> they are "easy" to jam in the sense that when you have two radio signals on the same frequency, they will interfere with direction finding Nope, it's a more sophisticated algorithm they're using. Our company held all the patents for locating GSM cell phones calling 911 using UTDOA. The U is uplink, meaning the network of receivers listens when the phone talks. The patents entail each receiver taking a sample of the signal they heard in that time slot on that frequency. They upload the sample to a processor which tries to correlate all the samples with some DSP math, sliding them around in time to see if they match. If they do correlate, the offsets of each one is your delay for doing trilateration. So if you have multiple talkers at the same time, they can probably be subtracted out by the correlation step.

BlindWanderer 7y ago
ECM can be directional (phased array antenna). If an aircraft knew the approximate location of the receiving antennas it could theoretically jam them seperately.

greglindahl 7y ago

> That said, they are "easy" to jam in the sense that when you have two radio signals on the same frequency, Not at all. Check out the VLBI technique from radio astronomy, it's not hard to tell that there are two discrete signals. But that's not really the point: you can see stealth aircraft already with lower frequency radars, just not well enough to shoot them down. It's hard to imagine this passive technique being good enough to shoot them down, either. https://en.wikipedia.org/wiki/Stealth_technology#Low-frequency_radar https://en.wikipedia.org/wiki/Stealth_technology#Low-frequen...

DarkmSparks 7y ago
the low frequency radar thing relates to the active radar in the missile warhead. Not accurate enough for hit to kill missiles, but plenty for modern shaped charge warheads that only need to get within 250 meters or so of the target for a kill, and completely irrelevant for warheads supplemented with optical targeting that only need to be within 5 miles clear line of sight to confirm a lock.

DarkmSparks 7y ago

Passive radar uses background RF, usually TV transmitters. Which is why they are the first to go everytime America decides to punish a nation for trying to use something other than the dollar to trade oil or decides to crack down on opium smuggling. Not really enough though, which is how they lost all the F117s over Serbia in the 90s. One of which I have a framed picture of on the wall along side an original "sorry we didnt know it was invisible" flyer. Tech has come a long way since then.

scurvy 7y ago
> Not really enough though, which is how they lost all the F117s over Serbia in the 90s. One of which I have a framed picture of on the wall along side an original "sorry we didnt know it was invisible" flyer. < Only a single F117 was shot down over Serbia. https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk#Combat_loss https://en.wikipedia.org/wiki/Lockheed_F-117_Nighthawk#Comba...
- DarkmSparks 7y ago
  Perhaps choose a better source than wikipedia, like people who were there. https://images.app.goo.gl/vUd8z2gkWEtKWKcJ8 https://images.app.goo.gl/vUd8z2gkWEtKWKcJ8 even your source says they hit 2. They claim they downed 3. Americans denied they lost any for decades.
  - blago 7y ago
    A propaganda poster knowingly conflating the words stealth and invisible, a distinction its intended audience wouldn't be able to make, to mock the enemy? I think I'll stick with the Wikipedia source.
    - DarkmSparks 7y ago
      And even that says: Some American sources state that a second F-117A was damaged during the same campaign, allegedly on 30 April 1999;[61] the aircraft returned to base, but it supposedly never flew again.[62][63] Point is with AA missile is that getting them "on target" is almost as effective as a hit. target has to deploy its counter measures and return home, else next time they are destroyed.

throw0101a 7y ago

> ... their detection at multiple RF detection stations with synchronized clocks, to determine the difference in arrival time. I believe this is generally called multilateration (MLAT): * https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration * https://www.skybrary.aero/index.php/Multilateration https://www.skybrary.aero/index.php/Multilateration * https://www.sciencedirect.com/topics/engineering/multilateration https://www.sciencedirect.com/topics/engineering/multilatera... * https://www.navcanada.ca/EN/products-and-services/Pages/on-board-operational-initiatives-mlat.aspx https://www.navcanada.ca/EN/products-and-services/Pages/on-b...