qwsazxerfdcv
New Member
One criticism I have heard about stealth fighters is they betray there position when turning on there radar to detect and track enemy planes. Is this a problem?
Stealth fighters beaming out radar
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First off there are sophisticated electro-optical sensors (like the EO-DAS on the F-35, or the OLS on new Russian fighters), second-off AESA radars have Low Probability of Intercept operating modes (LPI) when they are much harder to detect.
Todjaeger
Potstirrer
Quick answer, no.
For an answer that is a bit longer... Whatever you were reading is of questionable accuracy.
There have been several generations of manned LO (Low Observable) aircraft, and that is the term which is generally used instead of 'stealth' simply because there is a great deal of baggage and misinformation/ignorance/lack of comprehension behind what LO is.
In the case of 'stealth' or LO aircraft activating their radar to detect/track enemy aircraft... The only aircraft which would be doing something like operationally at present is the F-22 Raptor. Earlier generations of LO aircraft had INT/ferret, strike, or attack mission roles, they were not designed or equipped to engage hostile aircraft. Now the radar aboard an F-22 is an APG-77 AESA (Active Electronically Scanned Array) which, due to the nature of have AESA can function, has a LPI (Low Probability of Intercept) mode. Due to the multiple T/R (Transmission/Receive) modules within the AESA, and the fact that the beams these modules are electronically steerable and able to vary the frequency. In short, the radar can be setup to scan an area of airspace ahead of the F-22, and the radar can do so in a mannery which is unlikely to trigger alerts from the RWR (Radar Warning Receiver) of hostile aircraft, and even if the RWR does give a warning, it is quite unlikely that it would be able to triangulate the position of the emitting F-22.
This also completely ignores the fact that if an aircraft like the F-22 were to engage in combat, it would most likely be with offboard sensor support from friendly aircraft like E-2 AWACS, or E-3 Sentries.
Once the F-35 enters service, that will be another LO fighter in service, but the APG-81 AESA which will be equipping the JSF models also has a LPI mode.
-Cheers
qwsazxerfdcv
New Member
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Thanks for the replies
I'm surprised, I would have thought if a fighter could detect a signal that traveled some distance, reflected of a plane, and traveled back it would be much easier for the illuminated plane to detect the signal since its so much stronger.
There is a lot of background noise from natural and manmade sources that create confusion. Older radar designs used a regular series of pulses on one frequency and at constant strength that could be easily sorted out from the background by both the user and the target. In LPI systems each pulse is a different frequency over a wide range with no specific pattern or strength. The LPI radar knows when each pulse was transmitted and on what frequency so it can sort them out. The target can still detect the pulses but it is much harder to determine if they are manmade or natural phenomena. :unknown
This results in radar detectors having a ‘false positive’ problem of generating to many alarms (and the user learning to ignore them) or ‘false negative’ where the alarm sounds too late, or not at all.
Scorpion82
New Member
That's indeed true and while radar technology has advanced, RWR technology did so as well. Todjaeger is however right that the information gathered by the RWR are not good enough to accurately target the aircraft, they can aid, but they would still require some support from other sensors. In other words LPI certainly works and as the name suggests it lowers the probability of detection, but it doesn't eliminate it.
The kinds of opponents with that kind of technology and coordination, outside of NATO are who exactly?
I am sure there is much that I do not know but I know that people have been working on this problem for many years. Most receivers are by nature narrow band and high gain. That gives you both good sensitivity and low noise to signal ratio. It also conserves the available spectrum so that many users can transmit and receive at the same time.
But the first radio transmitters were broad band what we would call today spread-spectrum. The first successful voice radio broadcast was from San Jose California to San Francisco in 1904. But that left only one channel for everyone to use.
The way I was led to believe a modern low probability of intercept radar would work was each pulse would be made up of hundreds of low power frequencies created at random separations and power levels and that the return signal processer would combine only the frequencies transmitted out of all those available, with some slack included to account for Doppler shift, and that the different frequency components and amplitude components would change randomly from pulse to pulse. Also to keep the overall peak power as low as possible, very long pulse widths would be used and then be compressed in the receiving process.
Pulse to pulse frequency hopping, as it was once called, does decrees to some extent radar intercept probability but a simple spinning wideband receiver will easily give you a bearing to the radar source on a circular scope. Many analog systems like this were once produced exactly for this reaso, if there is not too many other targets in the area at the same time.
I recommend to get the basics of the theory try
ABCs of Spread Spectrum - A Technology Introduction and Tutorial
as a start.
To my knowledge there is no open source premier to spread spectrum applications in open sources for non-communication applications. What little I know comes from tacking a few oblique hints, and a few off the record conversation, and adding it to my knowledge when I once worked in Electronic Warfare.
I once worked the other side of the problem, how to detect, identify, locate, record and perhaps fool not communications RF transmissions. You would be surprised what kind of information you come across when your job is to monitor a large part of the RF spectrum and we haven’t even mentioned, civilian signals and navigational aids.
qwsazxerfdcv & My2Cents, as a pleb myself, I see with rip's link that he alludes to and knows what he is talking about. If you delete communication and insert radar into most of the sentences, I think we will have a firm footing to how LPI radar can work
if you google "spread spectrim microwaves" this also gives a clue
if you google "spread spectrim microwaves" this also gives a clue
Another area that may interest you about the intercept problem of how to detect an artificial signal from the background noise can be found by reviewing various search technics from the various SETI programs. Though here we are looking at a completely different set of assumptions, many of the physical difficulties of finding a signal in and among the different kinds of noise, be it natural or artificial, are much the same.
Several years ago a Soviet radio astrometry group announced that they had detected a signal of extraterrestrial intelligence. It was an American spy satellite data link. The Soviet scientists were very smart guys, they were not dumb or they would not have been able to find the signal in the first place, but we are talking about hard signals to understand and identify. In tactical situations where the analytical resources at hand, are far less than you would find at an astronomical lavatory, you begin to see the difficulty.
On the other hand, the more you know about the signal that you are looking to intercept, the easier it is to detect and identify from among the noise. By excluding that which you know will not be part of the signal, you can improve the receiver’s signal at to noise ratio and thus improve that chances of intercept. Hence the reason why so very little information is available within the open sources.
Thanks for that, the mentioning of SETI reminded me of tech from some 20 yrs ago that went suddenly silent
the use of star/astral EMR used as passive reception and the interference of a platform interrupting the signals as it transverses, sort of like accoustic daylight in subs working on background emissions
It might be too hard to use in a moving platform, but I wonder if the computers are up to handling the data sets from enough to be functional in a fixed land based
the use of star/astral EMR used as passive reception and the interference of a platform interrupting the signals as it transverses, sort of like accoustic daylight in subs working on background emissions
It might be too hard to use in a moving platform, but I wonder if the computers are up to handling the data sets from enough to be functional in a fixed land based
Interesting that you should mention this. Some of these issues were some what address in other threads but I cannot recall their names. There are several systems under development that will supposedly be able to detect stealth air-craft passively. But the conversations were conducted ether by people who didn’t know very much about it or by people who used such complicated terminology that it very difficult for a non-expert to understand.
If you will indulge me I will try to explain the principals involved using common every day phenomena that we all have experience, by the use of analogies.
Most of the radars we are familiar with work much like a spotlight on a dark night. You control the direction, size, shape, intensity and color of the light beam you create and then you analyze the reflected energy of objects to both locate and identify objects within the beam. You also have the advantage that you are not distracted by other things you are not looking at.
In sunlight when the air is clear you have light coming from many different sources, in many colors, and intensities. And there are many other things in ambient light of which to distract you. The eye created by evolution over millions of years and backed up with the most powerful signal process ever known and greater than man can yet build, the human brain, evaluates all of this information and identifies objects and locations within the environment.
The real advantage of the spotlight is in its signal to noise ratio and not just in the added detection threshold. The intensity of the beam both creates enough reflected light to see and identify objects and also removes distractions, because the ambient light sources are generally below the threshold of the human eye to detect and are so automatically filtered out.
The night sky is full of starlight, air glow, and moonlight but most of it is below the eyes sensitivity threshold. likewise the sensitivity of our RF receivers and their noise levels, are not as good as you might assume.
But passively there are still phenomena that can be exploited to gain information from ambient conditions. Shadows often are larger and easier to detect that the objects that create them (bigger footprint) and can be detected from directions other than the objects themselves. (One type of over the horizon radar uses this effect exclusively) Yet it is often possible to deuce the identity of an object from its shadow and then trace the shadow back to its source.
Another type of detection that can be used is when an object blocks ambient light sources. Like when an air-plane flying at night blocks starlight as it moves across the sky though you cannot see the plain its self you know what it is and where.
To use these technics requires plentiful and consistent energy sources and the ability to detect and measure them, and then you must analyze the information.
RF ambient sources both natural and manmade are usually of insufficient strength and density to use for the detection of objects with the technology we have now . In some built up areas there is enough electronic noise to provide needed ambient background for passive detection and identification to work but in many place there is not and in time of war many manmade source would go off line.
However, in the ocean there are many natural and manmade sound sources amenable to the same technics which travel great distances and are always plentiful. Here the main problem is not in the sensitivity of the sensors, there are still some problems with resolving signal direction of the incoming sound paths I admit, but mostly the challenge is in the signal processing. They use supper computers just to make 3D maps of fixed geological formations, this problem is much harder but the solutions are coming. Also, like ultrasound you can inside objects not just see their shape.
I agree with you, it would take a lot of computer power to do anything in near real time, taking a month in a science lab to get a result wont do it.
It may take a next generation leap in computer power before it can be in anyway useable.
I would love to be a fly on the wall in one of the briefing on where passive imaging is heading
It may take a next generation leap in computer power before it can be in anyway useable.
I would love to be a fly on the wall in one of the briefing on where passive imaging is heading
SETI was looking for repeating signals. With LPI radar you are looking for non-repeating signals, or as close as the designer can come to that, it is like trying to prove a negative.
Finding the signal, unless it was bring beamed to a particular location, would not have been that difficult – it is encrypted, not invisible. Not being able to figure out that the source was moving relative to the stellar background and therefore must be in orbit shows a lack of understanding. But falling for it, failing to check and question, and reporting to the world at large, only the Press could pull that one off. :haha
A joke I assume? Or a typo? Don’t tell us -- it is more fun that way!
As to my mistake of the word lavatory, instead of laboratory, my dyslexia and spelling checker, strikes again.
SETI was looking for repeating signals. With LPI radar you are looking for non-repeating signals, or as close as the designer can come to that, it is like trying to prove a negative.
Finding the signal, unless it was bring beamed to a particular location, would not have been that difficult – it is encrypted, not invisible. Not being able to figure out that the source was moving relative to the stellar background and therefore must be in orbit shows a lack of understanding. But falling for it, failing to check and question, and reporting to the world at large, only the Press could pull that one off. :haha
A joke I assume? Or a typo? Don’t tell us -- it is more fun that way!
As to your observation
“SETI was looking for repeating signals. With LPI radar you are looking for non-repeating signals, or as close as the designer can come to that, it is like trying to prove a negative.”
Though it is true that repeating signals, is just one of the many assumptions put forth by SETI as a feature of a civilization which is trying to broadcast its presents to the rest of the galaxy, with the intention of then making its presents known. There is no reason to believe that signals which are not intended to be received by strangers would look like anything we currently know or be in a form we currently use or would understand as communications signals.
Because of that the SETI search algorithms are more exhaustive than just looking for that one feature. The point I was trying to make however is the problem in finding a signal within the noise envelop and now the ratio of the signal to noise is helped or hindered by what kind of signal you anticipate to be there to detect.
As to you comment,
“Finding the signal, unless it was bring beamed to a particular location, would not have been that difficult – it is encrypted, not invisible. Not being able to figure out that the source was moving relative to the stellar background and therefore must be in orbit shows a lack of understanding. But falling for it, failing to check and question, and reporting to the world at large, only the Press could pull that one off. “
It was difficult. The spy satellite’s RF data link was designed not only to be encrypted but to be invisible to detection for a reason. They did this, so as to not reveal the true function and the operating capacities of the satellite. There are a lot of satellites up there, most of which are not spy satellites, and of the ones that are spy satellites, they come in many different varieties which have different operating parameters. So many in fact that a nation will take different security precautions according to those operating parameters when trying to protect their secrets from those satellites, so the issue is an important one.
Many weapon tests and military training exercises are timed so as not to be within the timed observations of other nations’ satellite coverage. They do this so as to not reveal their full military capacities but to plan for this they first need know that it is a spy satellite, what kind it is, and what are satellite operational constraints.
As another factor to consider, is the spy satellite was not transmitting to a ground station but to higher orbiting relay satellite. This is true for a variety of reasons that I will let you do your own research to deduce. What the Soviet astronomers’ were able to detect was not a point source but back-scatter from a moving satellite transmitting to a different higher satellite moving against the background of celestial sources. Hence it was not as easy as you have assumed to identify the signal as a satellite source. As I said before the Soviet astronomers’ were not dumb, they just did not know what they were looking at.. It didn’t look human created to them but it was artificial hence their conclusion.
Even if they were detecting the backscatter, the apparent point to origin would have been moving against the background, which would not be observable from short duration boservations (less than a month) for a distant source (i.e. the Oort Cloud or farther). Therefore the source must be local, i.e. a satellite
I do not have the necessary background information to say what information the Soviet Astronomers’ had, the kind or type of equipment which they used or the analytical methods they employed to come to their conclusions. After their error was revealed, as you might expect, they did not want to increases their notoriety and made no attempt to justify their mistake.
So we will have to let their conclusions and why they made them remain undefended. Astronomical equipment is optimized for the detection and analyze of very week but constant astronomical sources and they are not designed to easily measure quickly changing ones so they might not of have the best equipment for this issue.
As to backscatter, backscatter is a defuse source and defuse sources are hard to locate because the scattering medium or mediums, whatever they may be, ionized gasses, micro meteorite trails, space junk, are themselves in constant flux.
As an aside, I have met all kinds of people in my life, but I have never met a dumb astronomer, be they professional or just a hardcore armature. They tend to run from smart to scary smart at least when it comes to things in astronomy.