AIM-7's going ballistic with radar track

[Hummingbird]

I've noticed that the AIM-7M's often stop following a target that is perpendicular to them despite the F-14's radar still having the target locked.

 

Known bug or something new?

[GGTharos]

Sounds notchy to me.

[nighthawk2174]

Hard to say without seeing an ACMI.

[Hummingbird]

Sounds notchy to me.

 

For sure, but if the radar still tracks then why isn't the missile following? I mean I understand it if the missile was of the active type and went pitbull and was notched, but since it's semi active and the illuminating radar (AWG9) still has track, then why does the missile go ballistic?

[GGTharos]

Because the radar onboard the missile is notched.

 

Dint confuse yourself with active/semi active. The seeker is notched, there's no target to guide to.

[Hummingbird]

Because the radar onboard the missile is notched.

 

Dint confuse yourself with active/semi active. The seeker is notched, there's no target to guide to.

 

Didn't think it was possible when the AWG9 is still tracking the target perfectly.

[GGTharos]

The missile has a seeker onboard with a doppler filter. The only thing that has to do with the AWG-9 here is that it is emitting a signal which is picked up by the seeker.

[Noctrach]

The missile has a seeker onboard with a doppler filter. The only thing that has to do with the AWG-9 here is that it is emitting a signal which is picked up by the seeker.

 

 

True for DCS but shouldnt be happening for PD SARH as far as I'm aware, since the seeker can be slaved to a range-gated doppler return, which makes it nearly impossible to notch for longer periods of time. In DCS even a split-second notch will utterly spoof the missile, I've created another report on this last week. Even continuous wave guidance is already very sensitive to even small differences in doppler shift. The modeled doppler gate in DCS missiles seems unreasonably large.

 

Vulnerable to chaff or the guidance radar getting notched, sure, but the problem with DCS is that a missile getting notched even momentarily is utterly wasted, with zero chance of reacquiring.

Edited July 27, 2019 by Noctrach
fixed factual errors

[nighthawk2174]

Agreed, also a big issue for AH missiles like the AMRAAM, even the smallest of notches will completely kill the missile and it won't reacquire a target when it should be able to.

[QuiGon]

What if you fire the AIM-7 in CW mode? Can this still happen then?

[nighthawk2174]

The AIM-7M (emphasis on the M) IRL just cannot track CW it can only track PD, only the Aim-7F and earlier can track on CW.

[FortunateSon]

The AIM-7 doesn't have its own seeker head. It's guided all the way by the AWG-9. Hence, it shouldn't loose track as long as your STT lock remains valid.

[QuiGon]

The AIM-7M (emphasis on the M) IRL just cannot track CW it can only track PD, only the Aim-7F and earlier can track on CW.

uhm:

Yes, the later sparrows afaik were also capable of using CW as a kind of fall-back mode. And yes, in NORM CW will be used, you have to set it to SP PD to use pulse doppler.

 

That said, an rwr will still be able to see the AWG-9 doing "new" stuff indicating a missile launch so the effect in DCS will mostle be missile range.

 

The AIM-7 PD works differently than the AIM-54 which only requires momentary illumination and commands from the AWG-9, the AIM-7 is used in STT and requires constand PD updates and illumination.

:huh:

[Fri13]

The AIM-7 doesn't have its own seeker head. It's guided all the way by the AWG-9. Hence, it shouldn't loose track as long as your STT lock remains valid.

 

Does the AIM-7 seeker perform a filtering for target speed? Meaning, can you notch the missile seeker?

 

It doesn't matter what the guiding radar sees, if the missile seeker filters the target away. Meaning the target notches the missile and not the radar.

[FortunateSon]

Does the AIM-7 seeker perform a filtering for target speed? Meaning, can you notch the missile seeker?

 

It doesn't matter what the guiding radar sees, if the missile seeker filters the target away. Meaning the target notches the missile and not the radar.

 

Good question. I also should have been more precise in saying the AIM7 doesn't have an active radar seeker. It does have a passiv seeker however, question is whether that can filter as outlined above, I doubt it.

[GGTharos]

Uh, why doubt it? The rear receivers are there to sense the shooter's radar frequency and doppler filtering is part of this. That would be true in CW also. In fact, this MUST be available since the original sparrow developments in order to get the target closure component for the PN algo that is implemented within.

 

As for the 7M or later using CW as a fall-back mode, I really have my doubts. Certainly this would have to be selected at launch-time, and that capability was removed from all of the shooting platforms anyway - except for the version of the F-14 we have.

Edited July 29, 2019 by GGTharos

[QuiGon]

As for the 7M or later using CW as a fall-back mode, I really have my doubts. Certainly this would have to be selected at launch-time, and that capability was removed from all of the shooting platforms anyway - except for the version of the F-14 we have.

Isn't flood mode (which is also available on newer aircraft like the F/A-18C or the F-15C) making use of CW?

[Noctrach]

Isn't flood mode (which is also available on newer aircraft like the F/A-18C or the F-15C) making use of CW?

 

 

Nope, CW-Doppler and Pulse-Doppler are different variations on the same idea. The latter is the "natural evolution" of the former, getting rid of a lot of existing weaknesses. PD-STT is incredibly difficult to spoof due to the use of multiple doppler frequencies at the same time, combined with range-gating to filter out most false returns (background clutter, chaff).

 

 

The "downside" is that the processing stage is very resource-intensive and therefore only became feasible once digital systems started being widespread. The more frequencies you can use, the better your filtering, the smaller your notch gate, but the longer the processing takes.

It's logical that CW got phased out entirely with the advent of modern CPUs as there are no benefits to using it over PD.

[GGTharos]

No, FLOOD is a horn that floods some volume of space with HSTT waveform, not CW. The entire point behind the inverse-monopulse PD seeker is to get rid of CW which requires a separate illuminator. FLOOD passes the signal directly into the horn instead of the antenna (at least on the eagle), but it is the same signal.

[Noctrach]

That said it, compared to what I've read in literature the STT notch gate in DCS seems significantly larger than what they had even dating back to the early 80s... before we even take into account the effects of radar memory on the effectiveness of any notching.

 

 

I don't know if this is due to engine limitations or design choices but it does make a mockery of current SARH. (and ARH for that matter... AMRAAM is lightyears ahead of the Sparrow tech wise)

[nighthawk2174]

https://forums.eagle.ru/showpost.php?p=3902743&postcount=15

 

 

 

Also agreed Noctrach it seems that that the gates in DCS are rather quite large and not including track memory and coasting only makes it worse (if that's the proper name for it).

Edited July 29, 2019 by nighthawk2174