PD STT cannot be notched?

[KenobiOrder]

I dont have a track file presently because the tests I did got corrupted in typical fashion by the DCS track file system, but when I get the chance I will redo them and post them here. 

It would appear as though PD-STT cannot be notched. I had a friend fly a beam course using a F-15. He was able to maintain about plus or minus 7 knots of the 0 closure, but the radar never lost him, despite staying in the notch for very significant time, far longer than any track memory would be able to maintain. 

The appears to have been the case since the speed gate was added to PDSTT some time ago, which was obviously a good change but it seems to have introduced this problem. 

Tacview-20220824-193816-DCS-notch2.zip.acmi Tacview-20220824-192744-DCS-notch2.zip.acmi

[DSplayer]

Yes since the main lobe clutter filter is not used in PD-STT, it cannot be notched. An intended feature. You can still lose track if they enter the zero Doppler filter though.

[KenobiOrder]

2 hours ago, DSplayer said:

Yes since the main lobe clutter filter is not used in PD-STT, it cannot be notched. An intended feature. You can still lose track if they enter the zero Doppler filter though.

That's not how that works. Not having a main lobe clutter filter just means there is no null in the Doppler spectrum where the radar filters out anything appearing there. In tracking radars you have a velocity gate that tracks the targets Doppler, but there is still main lobe clutter that the target can fly into. It's possible that the awg9 would be able to track into the not via the target having significant strength relative to the main beam clutter, but that's practically impossible for a HPRF radar to do when the target is near co-range to the clutter since if the target and mlc are co range, the mlc will invariably be the larger target. 

This is why I did the tests with the target flying very low, because it would make sense to track through MLC if the difference is range between target and clutter is great enough that target signal exceeds clutter by enough to exceed the gain of any MLC filter or gain control threshold if there is no filter.

 

To put this in perspective, two F-15s with their obviously superior MPRF capable radars we're notched by two foxbats and broke their lock. They were flying very low, near co range to clutter. If an Eagle isn't immune, the AWG-9 sure as hell isnt.

 

Also the velocity gate HB added is not a special tomcat feature. It's basic to pretty much any tracking radar. 

 

[DSplayer]

21 minutes ago, KenobiOrder said:

That's not how that works. Not having a main lobe clutter filter just means there is no null in the Doppler spectrum where the radar filters out anything appearing there. In tracking radars you have a velocity gate that tracks the targets Doppler, but there is still main lobe clutter that the target can fly into. It's possible that the awg9 would be able to track into the not via the target having significant strength relative to the main beam clutter, but that's practically impossible for a HPRF radar to do when the target is near co-range to the clutter since if the target and mlc are co range, the mlc will invariably be the larger target. 

This is why I did the tests with the target flying very low, because it would make sense to track through MLC if the difference is range between target and clutter is great enough that target signal exceeds clutter by enough to exceed the gain of any MLC filter or gain control threshold if there is no filter.

 

To put this in perspective, two F-15s with their obviously superior MPRF capable radars we're notched by two foxbats and broke their lock. They were flying very low, near co range to clutter. If an Eagle isn't immune, the AWG-9 sure as hell isnt.

 

Also the velocity gate HB added is not a special tomcat feature. It's basic to pretty much any tracking radar. 

 

Quote

PD-STT MLC Filter Removed

We’ve removed the MLC Filter from the PD-STT submode. While digging deeper and researching further, we realised that the MLC is designed to be used in PD search modes, where doppler filters are used, and thus not used in PD-STT, as it uses the velocity tracker instead. 

The PD-search modes use doppler filters to determine target speed, so what doppler filter the echo matches is represented with a square brick on the display. In PD-STT the radar instead has a velocity tracker that looks for target returns within a rate gate centred around the target speed. This means that ultimately PD-STT locks should be more stable now and less prone to losing lock, as is now more congruent with the real radar and systems.

I'm just the messenger here.

[KlarSnow]

Just so we are clear here @DSplayerwhat they are saying there is the FILTER for MLC is removed, IE the piece of software that just nulls all returns that are in the MLC band. It says nothing about removing the actual clutter. What this allows is the target to get closer to, and/or compete with the clutter in the MLC instead of just auto dropping it because the radar is deleting/ignoring all returns there. the OP is correct this should not result in an unnotchable radar. Nowhere does HB say this, all they say is it makes it hold lock better and more reliably.

It should be HARDER to notch (which it is) but not impossible (Which I have not tested to see if it is or isnt).

There is a lot of confusion about this because MLC in respect to the AWG-9 means two things the Filter which is called MLC, and the Main Lobe Clutter itself, also referred to as MLC, which is always there in lookdown regardless of the filter being present or not.

[captain_dalan]

56 minutes ago, KlarSnow said:

... the OP is correct this should not result in an unnotchable radar. Nowhere does HB say this, all they say is it makes it hold lock better and more reliably.

It should be HARDER to notch (which it is) but not impossible (Which I have not tested to see if it is or isnt).

....

I am losing PD-STT locks from time to time, both in SP and in MP, though not that often and i've never actually explored or investigated the reasons behind those. Nor have i checked the tacviews. So it may be worth an investigation. 

EDIT: also worth noting, i usually try my best to engage in anti-notching maneuvers, so it may contribute to my experiences.....or not....

Edited September 2, 2022 by captain_dalan

[near_blind]

The Zero Doppler Filter still exists. If closure drops too low, the lock will drop 

[Naquaii]

Like KlarSnow says, it should be much harder than what it used to be in DCS before we changed it but it should still be possible. We'll continue to have a look at this and tweak it.

 

[Zaphael]

A PD-STT should be pretty damn hard to notch without combining some sort of ECM (chaffing). It is operating in both pulse ranging and Doppler shift across a very narrow beam and from a very powerful AWG-9 antenna.

 

[The_Tau]

14 hours ago, Zaphael said:

A PD-STT should be pretty damn hard to notch without combining some sort of ECM (chaffing). It is operating in both pulse ranging and Doppler shift across a very narrow beam and from a very powerful AWG-9 antenna.

 

Ah that would explain. I always wondered how PD STT get range on target.

[Zaphael]

34 minutes ago, The_Tau said:

Ah that would explain. I always wondered how PD STT get range on target.

Yeap. It's a pulse doppler radar and not just a Doppler radar.

https://en.m.wikipedia.org/wiki/Pulse-Doppler_radar

Notching target? MLC out.

Against less powerful radars, beaming the radar could reduce the returns and deny ranging information as well as velocity info. But AWG-9 was pretty powerful, and hence it could probably pick up a beaming target (or another aircraft 100 miles away).

Hence, you need to drop large qty of chaff rapidly to confuse and break the track of the radar while beaming (simultaneously presenting a lower RCS to the radar).

 

 

 

 

[KenobiOrder]

14 hours ago, Zaphael said:

A PD-STT should be pretty damn hard to notch without combining some sort of ECM (chaffing). It is operating in both pulse ranging and Doppler shift across a very narrow beam and from a very powerful AWG-9 antenna.

 

It should be hard to notch, but not impossible. If you look at the tacviews I posted, the target stays within 7 knots of the beam (or less) for extended periods. 

What do you mean its operating in both pulse ranging and doppler shift? It is operating at a high prf so range in ambigous. High PRF's tend to have maximum unambiguous ranges of 1nm or MUCH less even. True range to the target can be resolved by PRF switching, but you cannot filter out the ground clutter on the basis of range at high PRF, due to the fact that the clutter is present in every range bin. 

The main reason it should be hard to notch is due to the narrowness of the velocity gate.