Radar detect target inside Notch BUG

[GumidekCZ]

I want to report radar beeing able to detect targets inside of Doppler Filter speed gate (plus / minus 54 kts of my true speed).
KLJ-7 relative_radial_velocity_min = 27,777777777778 m/s
If closure rate with target is 545 kts na my true speed is 521 kts, everything in speed range +-54 knot of my true speed have to be filtered out, especialy against the ground. So with little math, notch will at this moment filter out anything inside of this speed range: 467 kts and 575 kts.
As you can se from track, I was able to find my target and fire a missile on it inside of Doppler filter speed range.

Shorty after launch the radar contact was lost, but still, above described error is bug worth of fixing.

JF-17_detection_in_notch_BUG.trkTacview-20211204-223118-DCS.zip.acmi

[AeriaGloria]

On 12/4/2021 at 2:00 PM, GumidekCZ said:

I want to report radar beeing able to detect targets inside of Doppler Filter speed gate (plus / minus 54 kts of my true speed).
KLJ-7 relative_radial_velocity_min = 27,777777777778 m/s
If closure rate with target is 545 kts na my true speed is 521 kts, everything in speed range +-54 knot of my true speed have to be filtered out, especialy against the ground. So with little math, notch will at this moment filter out anything inside of this speed range: 467 kts and 575 kts.
As you can se from track, I was able to find my target and fire a missile on it inside of Doppler filter speed range.

Shorty after launch the radar contact was lost, but still, above described error is bug worth of fixing.

JF-17_detection_in_notch_BUG.trk 635.3 kB · 11 downloads Tacview-20211204-223118-DCS.zip.acmi 124.19 kB · 8 downloads

Where did you get that doppler filter speed?

it is a value used very often in DCS, I know this value is used for the AI radar, but the radar in the module is coded with C++ and is not in LUA and can’t be viewed, it’s variable doppler gate is probably much more complicated then the single value In the LUA for the AI plane 

as you said you lost it right after launch. If that value is from the LUA it’s just for AI, and not taking into account doppler gate changes with look down look up, or distance based doppler filters or PRF

Edited January 2, 2022 by AeriaGloria

[AeriaGloria]

Looking at the sensor LUAs, here is some interesting things 

Radio velocity minimum for 

APG-68: 27.77 m/s

APG-71: 27.77 m/s

Apg-73: 27.77 m/s

N-011M Bars radar: 27.77 m/s

it is everywhere, honestly though I might put in a bug report about how the AI JF-17 KLJ-7 can only move its radar up 10 degrees! If the sensor LUAs were true for the player flyable modules, we wouldn’t be able to move the KLJ-7 30 degrees upward like we have since release 

[Mad_Shell]

The JF17 radar being able to magically see targets through the notch contrary to all the others planes in DCS has been here forever, and neither ED nor Deka have said a word about it...

[paco2002]

On 1/6/2022 at 7:03 PM, Mad_Shell said:

The JF17 radar being able to magically see targets through the notch contrary to all the others planes in DCS has been here forever, and neither ED nor Deka have said a word about it...

That's not true, don't say things that are not correct. Since more or less a year, notch gate is added to the JF. And it works as intended. If the JF-17 pilot changes the settings of the radar, it can maintain a couple of sweeps the target on the radar. 

[AeriaGloria]

I have been flying the JF-17 a lot lately after an almost year hiatus, and feel I lose targets quite often due to notch especially in high PRF. Yes one release there were issues but I see none now

[Mad_Shell]

On 1/11/2022 at 7:43 PM, paco2002 said:

That's not true, don't say things that are not correct. Since more or less a year, notch gate is added to the JF. And it works as intended. If the JF-17 pilot changes the settings of the radar, it can maintain a couple of sweeps the target on the radar. 

Please tell me why when I fly in a helicopter at 5 meters altitude and less than 20 knots the JF17 can reliably lock me while no other DCS module can do that? Sure I can break the lock, I have to fly like 5 knots...

 

Edited January 14, 2022 by Mad_Shell

[paco2002]

10 hours ago, Mad_Shell said:

Please tell me why when I fly in a helicopter at 5 meters altitude and less than 20 knots the JF17 can reliably lock me while no other DCS module can do that? Sure I can break the lock, I have to fly like 5 knots...

 

 

Because... You are moving with the helo. If you move, the radar detects you, you have 5 big things in the Mi8 turning and making sound on the Radar. That's the explanation

[Foogle]

On 1/14/2022 at 5:22 AM, Mad_Shell said:

Please tell me why when I fly in a helicopter at 5 meters altitude and less than 20 knots the JF17 can reliably lock me while no other DCS module can do that? Sure I can break the lock, I have to fly like 5 knots...

 

 

To iterate on Paco's comment, the Mi-8 has a blade tip speed of ~700ft/s, so you cannot hide in the notch because you are always on both sides the doppler filter; the radar is simultaneously reading you as advancing and retreating at ~414kts, in relation to the big spinning radar reflector you use to fly. 

 

Helicopters are always going to be in a bad place when it comes to radar detection. 

 

 

[AeriaGloria]

The Mi-8 also has the largest RCS of player aircraft in DCS at 12m squared. Depending distance, look up or down notch can change, I think if you upload a track Deka will surely take a look and try to fix anything that’s wrong, if it’s being detected at a relative radial velocity within the notch that exists at that particular range/look up or down/radar mode

 

 But it is important to note that DCS does not model the doppler return of helicopter rotors or any rotors/props. There is a fixed RCS for each helicopter and plays by same rules as airplane, just as susceptible to falling in the notch 

Edited January 17, 2022 by AeriaGloria

[Mad_Shell]

On 1/14/2022 at 11:51 PM, paco2002 said:

Because... You are moving with the helo. If you move, the radar detects you, you have 5 big things in the Mi8 turning and making sound on the Radar. That's the explanation

On 1/15/2022 at 4:54 PM, Foogle said:

To iterate on Paco's comment, the Mi-8 has a blade tip speed of ~700ft/s, so you cannot hide in the notch because you are always on both sides the doppler filter; the radar is simultaneously reading you as advancing and retreating at ~414kts, in relation to the big spinning radar reflector you use to fly. 

 

Helicopters are always going to be in a bad place when it comes to radar detection. 

 

 

The thing is, rotor RCS is not modelled in DCS, so that's not a factor here. If the JF17 can see a helicopter at very low relative radial speed, it will see a plane with very low radial speed all the same. The JF17 notch filter speed seems super low currently, which, to me, looks quite unrealistic given all the others modules in DCS have a higher notch speed, and there are IRL accounts of radars being very cluttered by false returns when the notch speed is too low (as modelled in the M2000C radar now). If someone can test what the exact JF17 notch filter speed is that would be great.

 

Edit: I will add that the myth of helicopters being so easily locked because of the radar return of the rotor is a gross oversimplification of the matter. The rotor return is very low (the area of the blades participating to the doppler shift is low, and the blades are mostly composite materials producing low returns), the generally low helicopter altitude means the high ground clutter renders the detection way harder (the detection distance can be divided by 10 or more according to some papers), and even if the radar detects the rotor return, that return is very confusing for the radar because you don't have a single doppler frequency, but a continuum of frequenies, both going away and toward the radar, and with high time variability. If the algorithms are not designed to specifically recognize that type of return, there is a high chance the radar won't be able to interpret the signal, or reject it as an anomaly.

Edited January 17, 2022 by Mad_Shell

[Blinky.ben]

On 1/14/2022 at 10:22 PM, Mad_Shell said:

me while no other DCS module can do that

Can you prove this? Cause there is a open bug at the moment where modules can lock onto helicopters hovering behind objects.

 

sure your not being biased here?

 

Edited January 18, 2022 by Blinky.ben

[Mad_Shell]

11 hours ago, Blinky.ben said:

Can you prove this? Cause there is a open bug at the moment where modules can lock onto helicopters hovering behind objects.

 

sure your not being biased here?

 

 

I talk from my experience in multiplayer. I'm regularly locked by the JF17 while I'm flying NOE at very low speeds, that never happens with any other jet...

Edited January 18, 2022 by Mad_Shell

[AeriaGloria]

While track might help, how fast were you going? 
 

There does seem to be something about the JF-17 radar causing emissions that are detected from unusually long distances, might be related, have they actually been able to shoot at you with fox 3? Did you talk to the pilot and see if they actually had you on scope with accurate data? I can try and test this, but I would like to know what speeds/aspects to look for. I assume this is in Gazelle so you are using RWR?