Czech Passive Radar Detecting B-2 at 150 miles (2015) • Hacker News Board

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#41

Post by fest » Sat, Mar 14, 2020, 9:20 PM UTC

catalogia wrote: post #36

ChuckMcM wrote: post #26

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…

> 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'.

I believe it's technically trilateration, not triangulation.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#42

Post by nradov » Sat, Mar 14, 2020, 9:21 PM UTC

Many people fail to understand that there's a huge difference between detecting the presence of an aircraft and actually targeting it. Anti-aircraft weapons must be precisely targeted to have any chance of hitting. So a passive radar can be useful in limited circumstances for cueing other sensors but it can't accomplish much by itself.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#43

Post by londons_explore » Sat, Mar 14, 2020, 9:22 PM UTC

amluto wrote: post #20

nitrogen wrote: post #16

Earlier quoted context omitted.

Is there any risk of demodulator IF or other leakage from these receivers?

Given that it’s entirely reasonable to build a 3 GHz baseband receiver these days, you don’t need IF. The whole thing can probably be made to radiate almost indistinguishably from a cell phone or computer.

A cell phone moving at that kind of speed will stand out.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#44

Post by rmattes » Sat, Mar 14, 2020, 9:24 PM UTC

catalogia wrote: post #36

ChuckMcM wrote: post #26

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…

> 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'.

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.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#45

Post by nitrogen » Sat, Mar 14, 2020, 9:24 PM UTC

londons_explore wrote: post #43

amluto wrote: post #20

Earlier quoted context omitted.

Given that it’s entirely reasonable to build a 3 GHz baseband receiver these days, you don’t need IF. The whole thing can probably be made to radiate almost indistinguishably from a cell phone or computer.

A cell phone moving at that kind of speed will stand out.

Would a passive radar usually be moving?

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#46

Post by nabla9 » Sat, Mar 14, 2020, 9:25 PM UTC

mikeyouse wrote: post #2

They do claim it works on all stealth planes including the F-35, but the B-2 is now 30 years old and was designed in the mid 1980s. Detecting it from 150 miles is impressive, but when they're equipped with 250 mile standoff air-to-surface missiles, ultimately not very useful. I'd be curious how much better the stealth is in the world of supercomputers and CFD for modern planes as well.

B-2 is old but the stealth shaping is still much better than F-35 and there is much more internal structure inside the wings that absorb radar energy. The RAM paints used in B-2 are probably up to date with current technology as well.

B-2 is also inherently more stealthy to to Rayleigh scattering than F-35 is due to the size.

Stealth is not magic. Shaping is 90% of the stealth, rest is the materials and details.

Vera-type radars may be be able to detect stealth aircraft with low angular resolution but they can't be used for targeting.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#47

Post by JDulin » Sat, Mar 14, 2020, 9:27 PM UTC

ChuckMcM wrote: post #26

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…

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.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#48

Post by catalogia » Sat, Mar 14, 2020, 9:36 PM UTC

HumblyTossed wrote: post #13

mikeyouse wrote: post #2

They do claim it works on all stealth planes including the F-35, but the B-2 is now 30 years old and was designed in the mid 1980s. Detecting it from 150 miles is impressive, but when they're equipped with 250 mile standoff air-to-surface missiles, ultimately not very useful. I'd be curious how much better the stealth is in the world of supercomputers and CFD for modern planes as well.

> ...but the B-2 is now 30 years old and was designed in the mid 1980s. Given that the B-52 is 65 years old, built with 1955's technology, I would expect something more sophisticated to have a longer shelf life than 30 years.

That's not how it works. There are loads of planes much younger and more sophisticated than the B-52 which are no longer in service. To name just a few high profile examples: the SR-71, F-117, and Space Shuttle.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#49

Post by tolien » Sat, Mar 14, 2020, 9:39 PM UTC

networkimprov wrote: post #37

Retric wrote: post #21

Earlier quoted context omitted.

Drones represent a huge range of different things. Assuming you mean something that’s a replacement for military aircraft. In order to have a useful X,000miles range and useful payload you need to build fairly large drones which means a large target. If their cheap that directly translates into low speeds making them a very easy target for anti air guns, or low cost anti aircraft missiles. If you want a large fast dr…

A pilot severely limits the kinds of maneuver the craft can perform, where the craft can be deployed from, etc.

F-15s have pulled well over 10g without killing the pilot, however it damaged the airframe beyond repair. An aircraft that could routinely pull high-G manoeuvres would have to be reinforced to the detriment of its weight (and thus its size/range/load capacity) and cost.

The expected direction of drones is as loyal wingmen (i.e., to carry sensors, weapons and/or fuel) and to be low-cost (i.e., disposable). If your drone costs more than an F-35 you'll want to get it home again, whether there's a human inside or not.

Re: Czech Passive Radar Detecting B-2 at 150 miles (2015)

#50

Post by imglorp » Sat, Mar 14, 2020, 9:40 PM UTC

ChuckMcM wrote: post #26

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…

> 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.