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Old 11-11-2019, 05:04 PM   #1
MobiSev
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Default Possibly a noob Fox 1 question

Since Fox 1's are guided by the host planes radar, how is it possible for a fox 1 to be fooled with chaff when the host does not lose lock? I've seen other posts saying that the Aim-7 is immune to chaff, and it does not make sense to me how the fox 1 itself should even react to chaff.
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Old 11-11-2019, 05:25 PM   #2
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im no expert
The AIM7 is indeed guided by the plane via "radio waves" ( i asume )
And when the enemy plane defend it self it will drop chaff that maybe will comfuse your radar and make the target lock break or jump arround.
enemy plane also uses Jamming so i guess its a combination of jamming, chaff and evasive manouver that will make the aim7 miss its target.

In some situations you might also loose a lock if enemy fly near the ground due to radar getting comfused ( or tracking become more difficult ). There are some nice videos of how radars work and how they "view the world" via its sensor on youtube
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Old 11-11-2019, 06:43 PM   #3
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Hi, I think he specified that the lock was maintained all the time.
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Old 11-11-2019, 07:30 PM   #4
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Most SARH still have a pulse Doppler seeker. Say the target is hard to see because it’s close to a notch so the missile seeker head mostly sees reflections off chaff, it can and will lose lock without the host aircraft losing lock. It’s a tiny seeker head, can be easily fooled compared to the giant microwave in a plane
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Old 11-11-2019, 09:16 PM   #5
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They track on reflected energy - think of SARH missiles as kind of like a cat chasing a laser spot.

Your aircraft shines essentially a radio spotlight on the enemy target, the radio-waves bounce of the target, the missile sees this and homes in on this reflection.

Chaff bundles are radio reflectors, by dumping some chaff the missile now sees several reflections - several 'laser spots' so to speak, so now the missile doesn't know which one to go after, hence how you can spoof them with countermeasures.

Obviously this is very very basic and this isn't deep at all and there is other stuff to it, but that's a basic insight into how chaff can confuse a Fox-1 (SARH) missile.

Your aircraft is less likely to be fooled and won't break lock because the RADAR on your aircraft is an active emitter (SARH missiles are essentially passive - they are 'receive' only), is way more powerful and has lots more going on to make sure it stays locked and doesn't get confuzzled by chaff bundles - I'm guessing (big guessing) that the illumination mode (which is also incidentally how a RWR knows you've fired and are actively engaging a target as opposed to just locking it in STT) which will be the mode used for fire-control of an SARH missile, either doesn't care/ or just isn't affected by chaff (I'm guessing there's a few different illumination modes), my other theory that the chaff slows down to the point where it falls within the velocity range of a Doppler RADAR's notch filter (Jabbers has a good video on how this works) and so gets filtered out like a ground return would, the target however carries on, so the RADAR retains locked, but the missile still can be spoofed, even if the target remains locked/illuminated by the launching aircraft.


Super basic explanation, but hopefully it helps.
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Old 11-11-2019, 10:18 PM   #6
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Quote:
Originally Posted by Lunatic98 View Post
They track on reflected energy - think of SARH missiles as kind of like a cat chasing a laser spot.

...

Chaff bundles are radio reflectors, by dumping some chaff the missile now sees several reflections - several 'laser spots' so to speak, so now the missile doesn't know which one to go after, hence how you can spoof them with countermeasures.

...
Excellent analogy. Thank you!
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Old 11-11-2019, 11:00 PM   #7
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The SARH missile without datalink will go after the largest radar reflection. If the SARH missile has a some logic to ignore chaff, then it will keep track of the target last known location, velocity and speed, and if the the sudden echo (chaff) that appears doesn't match to the track, then the missile will keep heading to the calculated direction for specific time (timer) IF the target would appear there as expected. If it doesn't appear there, then the missile can turn to the chaff as it is the last known target.
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Old 11-12-2019, 03:01 PM   #8
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In principle and especially as far as DCS is concerned, Lunatic98's explanation is spot on.

Keep in mind though that chaff in DCS is extremely oversimplified - they basically act as flares for radar-guided missiles. IRL, chaff stay in the air much longer and can cause radar interference (I don't know how true this is for modern radar systems, but it definitely used to be a thing). If used a lot over a certain area, chaff can create a zone of bad radar reliability and it obviously affects both sides.

Again, I don't know if this tactic is viable for the more modern stuff we have in DCS (APG-73 Phase II, APG-68(V)5, SPS-49 etc), but an air force could create a "chaff corridor" by dispensing chaff over enemy SAM-covered territory and thus create a window for strike aircraft to fly though. Perhaps it's not relevant/desirable today though, in the age of sophisticated Electronic Warfare.
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Old 11-13-2019, 03:05 PM   #9
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Quote:
Originally Posted by MobiSev View Post
Excellent analogy. Thank you!
You're welcome

There is a heck of a lot more to it as Harker said, but hopefully I've got the main principle correct.

Quote:
Originally Posted by Harker View Post
Again, I don't know if this tactic is viable for the more modern stuff we have in DCS (APG-73 Phase II, APG-68(V)5, SPS-49 etc), but an air force could create a "chaff corridor" by dispensing chaff over enemy SAM-covered territory and thus create a window for strike aircraft to fly though. Perhaps it's not relevant/desirable today though, in the age of sophisticated Electronic Warfare.
I guess it's down to RADAR mode is used and whatever counter-countermeasures processing we have now to filter out false returns. I'm guessing that Chaff would work best against monopulse RADARs and not pulse-Doppler systems or anything doing some fancy signal processing.
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Old 11-13-2019, 03:18 PM   #10
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There is the nice video of the F-16/18 where middle in the dog fight the released chaff gets their radars go crazy. So it effectively works against modern ones in fighters, why it is carried by everyone and even its release ain't trained as it causes so much trouble in peace time to all radars.
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