Does IFF-ing a bandit give away your own stealthiness in any way?

[Ironious]

It's been 25 years since I was an AF maintainer but I suspect it works pretty much the same today. ATC radar has a separate radar set for SIF/IFF and it does continuously transmit interrogation pulses. Those are as easy to detect as the primary radar. Airborne is much more selective in when and where it emits but even if it aims a pencil beam at a specific target any receiver near that or in line with it will be able to detect that emission.  

[WobblyFlops]

In real life it's very clear to assume that aircraft definitely know if they are being interrogated and they can't transmit a valid reply. (Which won't necessarily mean that you were interrogated by a hostile aircraft to begin with, it can be a friendly with a broken IFF, or the crypto codes dumped, got inadvertantly zeroized or were improperly loaded.) However, how would a Russian interrogation show up for American fighter? I don't know. If you remember that the purpose of IFF is that it's yet another tool in the toolbox to detect friendly contact and to avoid blue on blue, this whole consideration loses most of its tactical relevancy. 

 

This should be a feature of the DCS Hornet for example controlled by the Mode 4 switch, but it isn't implemented at the moment. In the Hornet the IFF can be controlled in azimuth and range and you can use it independently of the radar scope from the Az/El page and you can even have it run automatically within a specified volume and it can even allow you to interrogate targets that are outside the range of your own sensors. So even if the indicators for this IFF exchange (M4 OK or IFF caution) get implemented eventually, you won't get any tactically relevant information out of it since someone can set up an auto IFF at to 80 miles, 140 degrees and they can interrogate any aircraft that are detected by them or they get from datalink. You can't really use this information to determine where they are looking and what they actually intend to engage. It's not going to tell you anything more than seeing a nails on the RWR.

 

 

[GGTharos]

5 hours ago, Ironious said:

Again, I can only speak to how ground radar operates in regards to this but both the primary and secondary (SIF/IFF) radar emit RF pulses in the direction the antennas are pointing as it spins around. Neither of these emissions target specific aircraft but rather are intended to return a reflected pulse (primary) and request a coded response (secondary) from any and all aircraft receiving the RF interrogation pulses. So, just because you receive the interrogation pulses does not mean you are specifically targeted for a reply.

 

This depends from aircraft to aircraft; some have the IFF antennae mounted on the dish (the eagle does for example) so they operate more or less the same way.   The Viper has them mounted in front of a canopy in a 4-antenna ESA, so they operate completely independent of the radar dish motion.

[darkman222]

It is starting to make sense. That the DCS F15 has some kind of "auto IFF" is not due to it being a low fidelity flaming cliffs aircraft instead it is really interrogating every radar contact with one radar sweep.

And in the F16 you'd have to manually give the command to interrogate because the radar and the IFF systems are independent. I am slowly starting to understand that IFF mystery.

[GGTharos]

I think the default on the real F-15 is not to auto-iff but you can command it to do so easily.  Also, this is software so really ... load your preference in with your tape/dtc and there you go

Edited August 27, 2021 by GGTharos

[Hammer1-1]

I always thought the IFF was just a transponder much like that of a squawk box in general aviation, but far more complex: you get a number assigned to you (for the day), and if your identifier doesnt match in the record then you come back IFF negative, or if you dont have a number to squawk you are an unknown...but its just a transponder xmit/receiver setup at the end of the day. I GET that theres more to it than that, such as encryption among others...

Edited August 27, 2021 by Hammer1-1

[GGTharos]

Yes, that's basically all there is to it from the DCS pilot perspective.  You send a signal and you either get a reply or not.  The reply can contain various information obviously.  Encryption and other factors are sort of irrelevant.

Edited August 27, 2021 by GGTharos

[Frederf]

35 minutes ago, Hammer1-1 said:

I always thought the IFF was just a transponder much like that of a squawk box in general aviation, but far more complex: you get a number assigned to you (for the day), and if your identifier doesnt match in the record then you come back IFF negative, or if you dont have a number to squawk you are an unknown...but its just a transponder xmit/receiver setup at the end of the day. I GET that theres more to it than that, such as encryption among others...

 

Not only "much like" but identical. Technically the civil system is "Mode A" (or C or S) and the military system is "Mode 3" but it's just a renaming. Squawk term originates from WWII IFF code name parrot. When F-16s fly in civil airspace and ATC says "squad 1234" they input 1234 into the mode 3 section of the IFF system.

 

Mode 1 and 2 are used concurrently. M1 is a short code 00 to 37 or 77 octal showing mission. Your F-105 Thunderchief in Vietnam would have a mode 1 according to its mission profile (bombing, CAS, etc.). M2 is same length as M3 and identifies your airplane by tail number. Sometimes the code can't even be set from the cockpit.

 

Mode 4 is just Mode 3 but with the ability to reject interrogations without the secret code and a time variable response to foil triangulation. Natural civil airplanes don't have this either.

[Hammer1-1]

I r so smrt

[Brass2-1]

“Combat Tree” in Vietnam (Click) was a great example of how IFF type RF signals CAN be used against the own ship broadcasting them. 

[GGTharos]

Today you need to deal with encryption, so Combat Tree probably doesn't apply as much.   Today we have 'cyberwarfare'.

[darkman222]

So this was the direction I was thinking. If the Mig 21 pilot had the chance to take notice of over-excessive IFF interrogations he probably would have been aware. As long as he knew about the existance of that system.

[GGTharos]

You're still not getting it.  The real EW environment is dense.   There's your guys emitting, their guys emitting, civilians emitting ... and what do you mean 'excessive interrogations'?

 

Your opponent only needs to do it one time with Combat Tree and he knows who you are.  What's the additional one interrogation going to tell you when you don't even know where it's coming from?

 

And again, if it's just that MiG and another aircraft and nothing else, what does he care about the IFF interrogation?  I mean what's the unknown going to do if not interrogate?  The fact that he's there is the problem, not the interrogation.

 

'But it tells me that he's interested in me!'

 

No, it tells you squat.  If he's a friendly or foe, you don't know.  And what if you don't pick up an interrogation?  Maybe he knows what everything in that direction is a bandit, maybe someone else told him.

Edited August 29, 2021 by GGTharos

[Hammer1-1]

I am about to post a video that has a LOT of help regarding this...its from F/A-18 PSF from way back in the day around Falcon 4.0.

I know its old, outdated and missing a bunch now, but its worth the watch.

 

Edited August 29, 2021 by Hammer1-1

[Ourorborus]

On 8/28/2021 at 3:27 AM, Ironious said:

It's been 25 years since I was an AF maintainer but I suspect it works pretty much the same today. ATC radar has a separate radar set for SIF/IFF and it does continuously transmit interrogation pulses. Those are as easy to detect as the primary radar. Airborne is much more selective in when and where it emits but even if it aims a pencil beam at a specific target any receiver near that or in line with it will be able to detect that emission.  

Actually most ATC RADARs are only SSR but outside of the military they only use Mode 3C and Mode S. Primary radars are not used too often anymore as the ATC environment is cooperative. SSR also has better range efficiency than Primary RADARs due to the bean only goin out not out and back.

 

Most Transponders, including Mode 1,2,4 and 5 tranponders fitted to miltary, have an interrogate light to show you are being interrogated.

 

 

[Cmptohocah]

On 8/28/2021 at 12:46 AM, Frederf said:

 

Mode 4 is just Mode 3 but with the ability to reject interrogations without the secret code and a time variable response to foil triangulation. Natural civil airplanes don't have this either.

I always wondered: how does the system match a blimp from the radar with a ping from the transponder to paint a friendly?

 

I mean it can't rely on the timing of the return, so how does it do it?

[GGTharos]

Location data may be encoded in the reply.  Alternatively or in parallel the time randomization may actually be pseudo-random possibly using the changing IFF key as a seed.  My meaning here is that the interrogator will know the delay of the successful reply.

Edited September 20, 2021 by GGTharos

[Frederf]

3 hours ago, Cmptohocah said:

I always wondered: how does the system match a blimp from the radar with a ping from the transponder to paint a friendly?

 

I mean it can't rely on the timing of the return, so how does it do it?

Civ ATC systems call the radar the primary and the transponder the secondary. The secondary surveillance radar is similar to a primary radar but it only works with transponders. Both primary and SSR get positional plots. Transponder can be resolved in both azimuth and range. At the moment of transponder reply the antenna is pointed in a direction = azimuth. Time round trip = range. Correlation is accomplished automatically or manually and works well on Mode A systems.

 

Mode C or S data is nice but not required.

[Cmptohocah]

11 hours ago, GGTharos said:

Location data may be encoded in the reply.  Alternatively or in parallel the time randomization may actually be pseudo-random possibly using the changing IFF key as a seed.  My meaning here is that the interrogator will know the delay of the successful reply.

 

I highly doubt, but again I am not an expert, that it can send position reports as this would mean that verifying which aircraft is friendly depends on the accurate position of both the transponder and the interrogator, which can be questionable.

Changing delay also doesn't really make sense as this would mean that all of the transponders/interrogators need to be synced and re-synced.

 

IMHO what makes sense to get the ranging info for the IFF system is the fact that all of the transponders that are friendly need to have same "delay/latency" so that the interrogator can time the response and then calculate distance in order to match it to the radar contact. I could be completely wrong about this also, so it would be great if someone can give more insight.

Basically the question I am trying to ask is: if we have two contacts on the radar that are on the same radial from us but at different ranges, how does IFF know which one is friendly and which one is foe?

Edited September 21, 2021 by Cmptohocah

[buur]

@Cmptohocah This is a very good question which also shows me that I haven't understand the whole radar topic.

Here is a good link for the general radar topic. https://www.radartutorial.eu/index.en.html
If I understand this video right (

)  than the different signals will disturb each other.

[okopanja]

On 8/29/2021 at 11:17 PM, GGTharos said:

No, it tells you squat.  If he's a friendly or foe, you don't know.  And what if you don't pick up an interrogation?  Maybe he knows what everything in that direction is a bandit, maybe someone else told him.

Perhaps the latest example on how things can go wrong with/without IFF even today :

 

https://www.bbc.com/news/world-europe-45556290

 

https://www.rt.com/news/438686-syria-russia-s200-il20/

 

Second one offers a bit more detailed flight plan, although some critical details are missing...

[GGTharos]

4 hours ago, Cmptohocah said:

I highly doubt, but again I am not an expert, that it can send position reports as this would mean that verifying which aircraft is friendly depends on the accurate position of both the transponder and the interrogator, which can be questionable.

 

Data encoding in the IFF signal is a thing, though I don't know which mode would include position.   It's been a while since I've read about it.

 

4 hours ago, Cmptohocah said:

Changing delay also doesn't really make sense as this would mean that all of the transponders/interrogators need to be synced and re-synced.

 

In fact they are.   The IFF key is loaded for everyone and clocks are synchronized.

 

4 hours ago, Cmptohocah said:

IMHO what makes sense to get the ranging info for the IFF system is the fact that all of the transponders that are friendly need to have same "delay/latency" so that the interrogator can time the response and then calculate distance in order to match it to the radar contact. I could be completely wrong about this also, so it would be great if someone can give more insight.

 

Again, the delay can be pseudo-random which means it is predictable, just not easily predictable.  Pretty much next to impossible without the key.

 

4 hours ago, Cmptohocah said:

Basically the question I am trying to ask is: if we have two contacts on the radar that are on the same radial from us but at different ranges, how does IFF know which one is friendly and which one is foe?

 

It doesn't.   You have to find other ways of splitting them  up, unless they're well separated in distance.

Edited September 21, 2021 by GGTharos

[Cmptohocah]

47 minutes ago, GGTharos said:

In fact they are.   The IFF key is loaded for everyone and clocks are synchronized.

I can't imagine this being the case. Imagine everything airborne in the area somehow getting their clocks synchronized. How would that even look like? How would the information be passed around? What if it doesn't reach someone? How can you even verify if it did?

[GGTharos]

34 minutes ago, Cmptohocah said:

I can't imagine this being the case. Imagine everything airborne in the area somehow getting their clocks synchronized. How would that even look like? How would the information be passed around? What if it doesn't reach someone? How can you even verify if it did?

 

It would look like this:  Clocks are reasonably precise onboard the aircraft.  They will be hacked on the ground and in the air they can be hacked still using GPS.   You don't have to imagine it, it's something that has been done for decades.  The methods, distribution of keys and other fun things have been figured out in terms of logistics as well a long time ago.

 

You don't have to imagine it, it's something that's simply done.

Edited September 21, 2021 by GGTharos

[Frederf]

Mode 3/A can do ranging. It's a call and response just like TACAN. Speed of light, time, distance.

 

An operator sitting at a scope in say 1970 would have a primary contact and a secondary contact. He chooses to correlate the two.

 

I don't know about M5 or newer but M4 and older has trivial clock requirements. M4 code changes once every 24h so systems only load two codes A and B today and tomorrow.

 

The F-16 AIFF system for example makes no attempt to correlate FCR and transponder returns. Both are displayed on the same display simultaneously but it is the pilot's judgment which interrogations belong to which radar targets.

 

The F-18 appears to have a more sophisticated system with manual and auto correlation.

Edited September 21, 2021 by Frederf