F-15C radar changes

[GGTharos]

9 hours ago, Cmptohocah said:

I agree it has nothing to do with the notch, it's just that he mentions it before the notch part and it reminded me that we have perfect binary radar acquisition in DCS. It would be great if we had some sort of radius inside which you can't really tell how many targets are there.

Simulating radar cells in software is not impossible but it is tricky, and in particular it adds complication of the 'ok well I can see only one target but why does the AI see everything', actual programming challenges aside.  You could probably represent the radar bins reasonably well using a sparse matrix.

9 hours ago, Cmptohocah said:

Another pair of Eagles, had the same issue in '99 against the Fulcrums as they initially taught there is only one there until they got separated enough and/or Eagles got close enough to be able to discriminate between the two.

It's not an eagle problem ... in fact the eagle had some of the best break-out capability out there.  AESA radars today make everything back then look like a joke though.

9 hours ago, Cmptohocah said:

Is medium pulse repetition frequency more resistant to notching? If so, I would be very happy to learn why.

On a practical level, it reduces the notch size.  There are tradeoffs (more false returns etc) which are only nebulously talked about.

[TaxDollarsAtWork]

I've got a feeling that neither side here knows what they're talking about when it comes to MPRF and radars
I'd recommend reading some radar theory

PRFs are independent of power
They merely determine how long a emitting bit most importantly a listening phase will be

Different PRFs are useful for gaining different pieces of information about different kinds of targets
As explained in more detail in this excerpt

"The use of different pulse repetition frequencies (PRFs) delivers significantly different behaviors to airborne radars. For instance, the main purpose for using low PRF is to obtain an unambiguous range measurement. However, the tradeoff when using a low PRF is that the measurement of the target's radial velocity is highly ambiguous and can result in missing some target detections. On the other hand, high PRF is used to reduce or eliminate ambiguities in the measurement of radial velocity. A high PRF, however, causes a highly ambiguous range measurement. The true range is resolved by transmitting multiple waveforms with different PRFs."

MPRF tries to take the best from both worlds to deal with issues of range and velocity ambiguity
And an ace up its sleeve is that last part in most MPRF radars of the 1980s and onwards

It's actually using multiple MPRFs, so a slightly low MPRF, MPRF, a slightly higher one and another one higher than that and comparing all that information as quickly as possible thanks to digital components running through duty cycles quicker than its contemporaries.


Why has ED refused to fix it?
God knows why, this company seems to hate money A LOT. It's a simple fix for a well loved plane.

Yet they rather let themselves get upstaged by a company that makes FSX mods...
They really shot themselves in the foot not doing a FF F-15C

I wonder what excuse they'd use, that they'd need to do have a 3rd party do it because of some Russia law
Gimmie a break

[USA_Recon]

On 8/20/2022 at 4:14 AM, TaxDollarsAtWork said:

Yet they rather let themselves get upstaged by a company that makes FSX mods...
They really shot themselves in the foot not doing a FF F-15C

I wonder what excuse they'd use, that they'd need to do have a 3rd party do it because of some Russia law
Gimmie a break

They are in a much better place today to do this right .

[Beamscanner]

I've recently come across detailed information for the early APG-63 within an older radar book. 

The 1st edition of the 'Introduction to Airborne Radar' has a chapter in it that the later editions do not have. This book is written by the company that built the APG-63. 

 

Chapter 29 "A Representative Multimode Radar" details the early variant of the APG-63. 

 

It states the following:

• HPRF
  • ~50% Duty Cycle (1 range bin)
  • Had 512 Doppler Bins
  • Receiver completely filtered out the doppler clutter region. It only processed the clutter free region.
    • This means that in HPRF, the radar should never have a negative impact from sidelobes.
• MPRF
  • 64 Range Bins and 16 Doppler Bins (1024 total bins)
    • Though only 9 - 11 Doppler bins were used (576 - 704 total bins used)
      • The extra doppler bins were created at no extra cost due to the FFT
      • (ie a 16 point FFT is easier to execute than a 11  point DFT)
  • Cycles through 9 PRFs
  • Uses a 13:1 Phase code for pulse compression
    • Allows for use of a longer pulse (high duty cycle = greater detection range)
    • While maintaining good range resolution
• Other details mentioned
  • The receiver has 2 channels. 
    • 1 Sum and 1 AUX
      • In STT, the AUX channel performs monopulse tracking (delta of Az and El)
      • In MPRF, and only in MPRF, it uses the guard antenna and performs sidelobe cancelation. 

[F-2]

3 hours ago, Beamscanner said:

I've recently come across detailed information for the early APG-63 within an older radar book. 

The 1st edition of the 'Introduction to Airborne Radar' has a chapter in it that the later editions do not have. This book is written by the company that built the APG-63. 

 

Chapter 29 "A Representative Multimode Radar" details the early variant of the APG-63. 

 

It states the following:

• HPRF
  • ~50% Duty Cycle (1 range bin)
  • Had 512 Doppler Bins
  • Receiver completely filtered out the doppler clutter region. It only processed the clutter free region.
    • This means that in HPRF, the radar should never have a negative impact from sidelobes.
• MPRF
  • 64 Range Bins and 16 Doppler Bins (1024 total bins)
    • Though only 9 - 11 Doppler bins were used (576 - 704 total bins used)
      • The extra doppler bins were created at no extra cost due to the FFT
      • (ie a 16 point FFT is easier to execute than a 11  point DFT)
  • Cycles through 9 PRFs
  • Uses a 13:1 Phase code for pulse compression
    • Allows for use of a longer pulse (high duty cycle = greater detection range)
    • While maintaining good range resolution
• Other details mentioned
  • The receiver has 2 channels. 
    • 1 Sum and 1 AUX
      • In STT, the AUX channel performs monopulse tracking (delta of Az and El)
      • In MPRF, and only in MPRF, it uses the guard antenna and performs sidelobe cancelation. 

I’ve got docs on the PSP processor. Maybe it’s time for a community apg-63 mod? Combined with the clickable fc3 could be the beginning of a FF F-15.

[henshao]

On 9/5/2022 at 3:35 PM, Beamscanner said:

HPRF

• ~50% Duty Cycle (1 range bin)

 

how can that be, was this velocity search mode

[Beamscanner]

9 hours ago, henshao said:

how can that be, was this velocity search mode

no.. 

 

Nearly all HPRF waveforms dont perform range 'detection'. Range is too ambiguous to be detected. It can however be 'resolved' after targets are detected.

 

A single "range bin" (otherwise described as having no range bins) is the norm for HPRF. 

 

Range is measured 'post detection' via freq modulated ranging (FMR) (except in VS)

 

 

In radar engineering, "detection" "post-detection" "resolving" all have very specific meanings.

Edited September 9, 2022 by Beamscanner

[henshao]

Ok I see now...HPRF in velocity search mode uses no FMR at all while normal HPRF uses "3 cycle (1 flat - for Doppler speed estimation, and with 2 linearly changed freq - for distance measurement)"

[F-2]

So it’s good now?

[GGTharos]

No, no changes are made.  If you're not picking up a flanker 95nm away in look-up/co-alt, this radar's range capability has not been corrected.

[Exorcet]

2 hours ago, F-2 said:

So it’s good now?

Yes, 80+ nmi detection range on fighters. Though besides the range, it's still a FC3 radar with all the weaknesses that come with it.

[GGTharos]

It was changed?

 

Edit:  Yes it was changed.  Shame on me for assuming.  Ok, I know what I must do then.  I shall be eating my hat.   Thanks for this change ED!  @BIGNEWY thanks for bringing it to the devs.

Edited October 29, 2022 by GGTharos

[henshao]

hy

1 hour ago, GGTharos said:

It was changed?

 

Edit:  Yes it was changed.  Shame on me for assuming. 

 

if they make a change and inexplicably don't put it in the changelog that's not on you bruv

from left to right we have an A-50, F-18, F-16, F-16CM, and Su-25

 

[Raven (Elysian Angel)]

On 6/23/2022 at 8:51 PM, henshao said:

however my F-15 wingman is reporting contacts at 150 miles and seemingly beyond

That's an AI quirk that's been around for quite a while. AI wingmen (including full-fidelity modules) can spot tanks parked 160nm behind them as well. It doesn't have anything to do with the F-15 specifically.

[Mike_Romeo]

[Beamscanner]

You can google an open source Canadian University Thesis that describes the APG-63 in vivid detail. (topic concerns its use on a CP-140 aircraft)

 

In it HPRF is mentioned as not having any signal loss due to sidelobes (ie low altitude performance loss).. As its receiver only collects energy from doppler clear regions. 

 

[F-2]

6 hours ago, Beamscanner said:

You can google an open source Canadian University Thesis that describes the APG-63 in vivid detail. (topic concerns its use on a CP-140 aircraft)

 

In it HPRF is mentioned as not having any signal loss due to sidelobes (ie low altitude performance loss).. As its receiver only collects energy from doppler clear regions. 

 

If we ever do get a FF F-15 we have some great references for developing the Radar.

[TaxDollarsAtWork]

While it's an improvement I still think it should be better

 

I'll have to find the test data from the 70s and test again

[henshao]

hopefully the radar pass over the f-18 and f-16 also affects all ED modules in terms of lookdown performance and track ranges

[Nahen]

21 hours ago, henshao said:

hopefully the radar pass over the f-18 and f-16 also affects all ED modules in terms of lookdown performance and track ranges

TRUE...

[falcon_120]

While it's an improvement I still think it should be better
 
I'll have to find the test data from the 70s and test again

I dont complain, it's a new life for the F15 as it's the only plane (except the F14/Phoenix combo) able to do very long range; 50/60nm, amraam shots, thus regaining their BVR 1st place again over the viper/hornet.

Obviously not having a link16 it's a big handicap that oblige you so much harder to work on the SA from other sources, but it's fun. But what is important is that between 60nm and 35 nm, and above angles 30, the eagle can dispute the sky and the F16/f18 cannot fight back unless they go low and put themselves in a defensive position.

Also apparently the F15 does not currently suffer from those absurd look-down penalties applied to the F16/f18 radars.

Enviado desde mi ELE-L29 mediante Tapatalk

[henshao]

On 11/12/2022 at 7:59 AM, Бойовий Сокіл said:

Just wait for the F-15E with the eye of sauron APG70.

the APG-63v1 should be "superior" to the APG-70

[falcon_120]

the APG-63v1 should be "superior" to the APG-70

is that so?

I guess it could make sense the optimization towards A2G instead of A2A, but curious to know the sources of that statement.

Enviado desde mi ELE-L29 mediante Tapatalk

[Nahen]

Subsequent versions of radars dedicated to the F-15C were specialized only for use against airborne targets. Which automatically puts them in a much better position than everyone else, where their work is "split" between A-A and A-G. The very issue of handling from the pilot's point of view is something definitely in favor of the AN/APG-63.

Of course, if we are talking about air to air use.

[F-2]

Over 40 of the last build F-15C where delivered with APG-70, couldn’t have been that deficient. As I understand it APG-63(v)1 was built due to difficulty getting spare parts for apg-70 due to short sighted supply issues dating back decades. Maybe their is a huge difference in performance but I’ve never seen it mentioned.