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Sparrow PD sv CW illumination pros and cons


MRaza

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Is there any advantage to using PD illumination, which requires PD-STT, for your AIM-7s other than a longer range?

 

In my opinion I'd rather use CW illumination with P-STT because in DCS, missiles are fired from rather close range and I would rather not waste a shot by getting notched while using PD-STT

 

Anyone agree or disagree?

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Based to texts that I just few days ago read, IIRC from F-14 pilots, against MiG-23's that Pulse mode is very vulnerable from ground clutter, requiring to be very careful that target didn't dive below horizon even when ground was tends of miles further than target against it. In this case they had 6° between flight level and horizon and were required to keep pushing lower if target was moving below them.

 

And then for Pulse Doppler mode it is enough that target turns 70° from you, not 90° but with very wide range of angles beaming and breaking lock by notching.

 

Just someone making a wide turn, diving down/up at 70° angle or higher and you will lose lock. Going at all against Earth and you lose them. Why you are in big trouble if you do not have a wingman that will seek a totally another angle to the target so that they can't avoid both of you as everytime either one would get a position. But if you can't get a shot soon, you will end up to close combat as it is inevitable unless enemy escapes.

 

And when it comes to that, IR seekers and guns....

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Is there any advantage to using PD illumination, which requires PD-STT, for your AIM-7s other than a longer range?

 

In my opinion I'd rather use CW illumination with P-STT because in DCS, missiles are fired from rather close range and I would rather not waste a shot by getting notched while using PD-STT

 

Anyone agree or disagree?

 

Depends on what Sparrow you are using, the AIM-7F is the last Sparrow to be able to home on a CW signal (it could also home on a PD signal which is why there is a switch to toggle between PD and CW guidance I think). After this one, the AIM-7M, AIM-7MH and AIM-7P could no longer do so, you have to use PD-STT for them to home in.

 

PD enables the missile seeker to acquire targets at a longer range amongst other things. Radar homing was more reliable in general using PD.

 

https://forums.eagle.ru/showthread.php?t=195679&page=3

 

EDIT : I think this is not modelled in game yet, I hope it will be.


Edited by Rex854Warrior
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Depends on what Sparrow you are using, the AIM-7F is the last Sparrow to be able to home on a CW signal (it could also home on a PD signal which is why there is a switch to toggle between PD and CW guidance I think). After this one, the AIM-7M, AIM-7MH and AIM-7P could no longer do so, you have to use PD-STT for them to home in.

 

PD enables the missile seeker to acquire targets at a longer range amongst other things. Radar homing was more reliable in general using PD.

 

https://forums.eagle.ru/showthread.php?t=195679&page=3

 

EDIT : I think this is not modelled in game yet, I hope it will be.

 

So AIM-7M, MH, and Ps could not be used in P-STT?

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So AIM-7M, MH, and Ps could not be used in P-STT?

 

From my understanding no. I was slightly dissapointed to see that the current AIM-7M on the F-14 tracks in P-STT. Only the AIM-7F, which will hopefully be added soon, should be able to home in either STT mode.


Edited by Rex854Warrior

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Ok so it's not that easy.

 

The difference between P and PD is simply the processing done by the host radar on the returns, which means that when you switch to P-STT or PD-STT you're still sending a pulsed signal which every Sparrow from the F Variant can home onto.

You also have a separate CW emitter in the cat if you desire to use it with the AIM-7F or if it is necessary for the particular variant of Sparrow you're using (any Sparrow before the F).

So this Sparrow switch in the back seat is only relevant when using Fs.

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Currently the difference is not modelled but like has been stated the main difference would be the lesser range when guiding in CW.

 

I've yet to see any information stating that the CW function was removed in the later missiles, my understanding was that it remained as a fallback, especially as the flood mode only works in CW.

 

I might be wrong though and if you have sources I'd be happy to take a look!

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Currently the difference is not modelled but like has been stated the main difference would be the lesser range when guiding in CW.

 

I've yet to see any information stating that the CW function was removed in the later missiles, my understanding was that it remained as a fallback, especially as the flood mode only works in CW.

 

I might be wrong though and if you have sources I'd be happy to take a look!

 

Ah ok, even with later missiles though, is CW illumination the standard form of guidance, with PD guidance only available if the SP PD switch is selected?

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Also, this seems to all be a bit of a catch 22 situation to me. I've always been told that an altitude advantage is important and I've always increased my altitude before firing a missile to get better range. But now it seems I should be doing the opposite in the f14...

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Ah ok, even with later missiles though, is CW illumination the standard form of guidance, with PD guidance only available if the SP PD switch is selected?

 

Nope, later variants of the sparrow can only guide on Pulsed signals. As GGTharos said in the AIM-7 post I sent, the AIM-7F was the only and the last sparrow to have both CW and PD homing, after that only PD.

I have a couple documents about late variants of the F-15 that say it uses a PD flood illuminator operating in HPRF, which confirms that CW was no longer required or standard. I'll try to get more documents specific to the AIM-7 but so far it's what I have.


Edited by Rex854Warrior

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If so the F-14 might be unable to use the later AIM-7s in flood mode as the F-14 flood is CW.

I'm just kinda wondering what conclusive sources you guys have saying that the later missiles for sure doesn't have CW?

 

In any case this might not be possible or even something that's necessary to model in our F-14 apart from the range differance.

 

The reason for the switch in the F-14 defaulting to CW is that it used to carry the models that couldn't guide in PD, that's why it has to be selected.

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Also, this seems to all be a bit of a catch 22 situation to me. I've always been told that an altitude advantage is important and I've always increased my altitude before firing a missile to get better range. But now it seems I should be doing the opposite in the f14...

 

Before the advent of Pulse Doppler Radars you could not lock on anything below you at all. So yes, altitude is an advantage if you have a Pulse Doppler radar...

 

...and...

 

...the conditions give you an advantage. Its not a cookie cutter case of always stay high or always stay low. That's why the plane have you on the pilot seat... to make those kind of decisions in real time.

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If so the F-14 might be unable to use the later AIM-7s in flood mode as the F-14 flood is CW.

I'm just kinda wondering what conclusive sources you guys have saying that the later missiles for sure doesn't have CW?

 

In any case this might not be possible or even something that's necessary to model in our F-14 apart from the range differance.

 

The reason for the switch in the F-14 defaulting to CW is that it used to carry the models that couldn't guide in PD, that's why it has to be selected.

 

I asked for GGTharos to send those documents to me if he could of course, so hopefully you'll have your answer soon. As for the documents I already have, since they're not enough on their own to prove the functionality was removed, I'll wait before sending them all to you.

If it was then indeed the CW flood on the F-14 was useless with the 7M. I guess this mode wasn't very important anyways and that the AWG-9 of the F-14B and A were no longer considered when making design choices for the AIM-7 after the 1980s. Maybe the AN/APG-71 had a PD flood illuminator ?

 

EDIT : I'm also wondering how do you enter flood mode in the DCS : F-14B ?

Also since you're here and I've become an opportunist 3 seconds ago, when is TWS AUTO coming ? :D


Edited by Rex854Warrior

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I asked for GGTharos to send those documents to me if he could of course, so hopefully you'll have your answer soon. As for the documents I already have, since they're not enough on their own to prove the functionality was removed, I'll wait before sending them all to you.

If it was then indeed the CW flood on the F-14 was useless with the 7M. I guess this mode wasn't very important anyways and that the AWG-9 of the F-14B and A were no longer considered when making design choices for the AIM-7 after the 1980s. Maybe the AN/APG-71 had a PD flood illuminator ?

 

EDIT : I'm also wondering how do you enter flood mode in the DCS : F-14B ?

Also since you're here and I've become an opportunist 3 seconds ago, when is TWS AUTO coming ? :D

 

The Flood mode is enabled automatically with AIM-7 selected when boresight is chosen (BRSIT), when in ACM without a sensor track or you loose target track with a AIM-7 launched with CW set.

The antenna will not emit though until the missile is launched if not already in the air.

 

In these cases the CW illumination is directed through the flood antenna, otherwise if you have a wcs track it will be directed through the normal antenna and directed at that track.

 

Unfortunately no news about the auto mode other than that it's being worked on! :-)

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If so the F-14 might be unable to use the later AIM-7s in flood mode as the F-14 flood is CW

 

My understanding is HPRF PD, at a sufficiently high duty cycle, is virtually the same as CW. Hence the term “Interrupted CW” (see reference below) I could be wrong but why couldn’t the PD signal be routed through the flood antenna?

 

From Radar Handbook 2nd Ed., Slonik:

The motivation for the use of PD in the seeker was to simplify the illuminator

in air-to-air systems. For early-generation airborne radars, which employed a

noncoherent pulse waveform, CW injection was the only practical solution. With

the advent of coherent PD radars, an alternative way to achieve virtually CW op-

eration without the penalty of the additional transmitter became available. This

was to select a high-PRF (pulse repetition frequency), high-duty-cycle (30 to 50

percent) waveform and to use only the central line of the PD spectrum, both in

the radar and in the seeker. This has sometimes been called interrupted CW

(ICW).3

A high PRF is defined as one which is unambiguous in doppler. Thus when the

receiver selects the central line, the spectrum is identical to the CW case. The

radar receiver must be protected during transmission (duplexing and/or gating).

In addition, the receiver may or may not use a range gate. If only the central-line

power of the PD spectrum is used (no range gate), the resulting loss must be ac-

cepted. Use of a range gate matched to the pulse avoids this loss. In either case,

the rest of the receiver and signal processing is the same as for a CW system.

 

I'm just kinda wondering what conclusive sources you guys have saying that the later missiles for sure doesn't have CW?

The 7F seeker was a conical scan type whereas the AIM-7M (M for monopulse:smilewink:) employed an inverse monopulse seeker which is not compatible with CW illumination.

 

From Radar Handbook 2nd Ed., Slonik:

The early systems all used conical scan for angle tracking because of its sim-

plicity. The limited available volume and discrete-component tube technology of

the period mandated a single-channel approach despite the performance limita-

tions of conical scan. The inverse receiver permitted the performance of

monopulse to be achieved with the single-channel simplicity of conical scan.

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I guess it all depends on nomenclature really, the natops manuals are notoriously ambigous in these regards.

 

While the CW illuminator in the F-14 has it's own path to the CW flood illuminator separate from the normal radar transmitter the manuals could very well call CWI just "CW".

 

We do know for sure that the F-14 could indeed use the later AIM-7s, the real question is whether the CW illuminator on the AN/AWG-9 was really a CWI illuminator or upgraded to it later on or not at all.

 

Unless we find evidence that proves that there were settings that could dud the later AIM-7s in the F-14 it's probably better to just leave the switch as is and when possible make the range lesser if set to NORM (CW) as we do not know for sure if this was modded later on or if the CW was indeed really CWI.

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Is there any advantage to using PD illumination, which requires PD-STT, for your AIM-7s other than a longer range?

 

In my opinion I'd rather use CW illumination with P-STT because in DCS, missiles are fired from rather close range and I would rather not waste a shot by getting notched while using PD-STT

 

Anyone agree or disagree?

 

So to answer your question, P-STT is better for guiding AIM-7s because the host radar can't get notched, the missile can be but that's much much harder to pull off for the defendant.

PD-STT allows you to lock at longer ranges and is usually more reliable but you can get notched so I'd suggest going PD-STT, then switching to P-STT a minute or so before firing just in case you loose him completely when going from a mode to another.

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So to answer your question, P-STT is better for guiding AIM-7s because the host radar can't get notched, the missile can be but that's much much harder to pull off for the defendant.

PD-STT allows you to lock at longer ranges and is usually more reliable but you can get notched so I'd suggest going PD-STT, then switching to P-STT a minute or so before firing just in case you loose him completely when going from a mode to another.

 

So would that suggest (when modelled) that we would be best arming up our Tomcat’s with AIM-7F’s so we have the option of either? What are the other performance differences between them? (Are we talking Vietnam era 2% PK vs Gulf War Era 18% PK? (Or something like that!))

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So would that suggest (when modelled) that we would be best arming up our Tomcat’s with AIM-7F’s so we have the option of either? What are the other performance differences between them? (Are we talking Vietnam era 2% PK vs Gulf War Era 18% PK? (Or something like that!))

 

Why would you want an AIM-7F ? Take the AIM-7M, which will probably be the latest version version we get on the cat, has better electronics, better ECCM,... then the F.

 

Also the low PK during the vietnam war was due to the host radars and missiles themselves being a lot worse.


Edited by Rex854Warrior

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Pulse mode is very vulnerable from ground clutter, requiring to be very careful that target didn't dive below horizon even when ground was tends of miles further than target against it. In this case they had 6° between flight level and horizon and were required to keep pushing lower if target was moving below them.

 

so essentially, unless you use it to search for/lock a target that has just notched you, its best to stay in a pulse doppler mode over pulse

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  • 3 months later...
so essentially, unless you use it to search for/lock a target that has just notched you, its best to stay in a pulse doppler mode over pulse

The other good reason to use pulse mode is to be able to lock on a target that has turned away from you and, while being outside your AIM-9s' reach, is inside the -100/+100 kt Doppler filter. It's instrumental if the bandit carries R-73s and has the helmet mounted sight.

 

The worst case is : you're in his 6 at around 6 or 7 miles, can't lock on him because of the -100/+100 kt filter, he makes a 90° turn and you still can't lock on him because of the perpendicular trajectories of your planes. Meanwhile, he locks an R-73 on you thanks to his HMS and you're dead meat.

 

If in this case he's already locked on thanks to your AWG-9's pulse mode, he can't turn enough to use the HMS and R-73: he'd suddenly find himself deep inside the no escape zone of your AIM-7s as well as in your AIM-9s' launch success zone.

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