AIM120 HPRF/MPRF signature in your RWR
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Would suggest there is not a lot useful in that thread… At least, for the case of 4.5th generation fighters with western avionics/EW.
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I’ve been trying to follow along here but I feel like I don’t understand what HPRF is. Why should it not register on RWR?
Are there any unclassified resources (docs or vids etc) that describe HPRF and MPRF at a technical level (frequency bands, wattage, etc)?
All I gather is it’s a mode tuned for high-aspect / closure-rate… and ostensibly higher pulse repetition frequency.
Is it just a quirk of the ALR-56 that it doesn’t pick it up… but what do we know about other planes, esp. Russian, Chinese, etc. I suppose there’s probably a matrix of what planes can detect which other planes/missiles. (eg. older block Migs or even Iranian F-14s etc may not even know what an amraam looks like, hprf or mprf.)
HPRF is a much weaker mode than mprf
Should it be seen by alr56 is totally unknown
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Well, imho, every xmit has its “burnthrough” range where it can be picked-up by listening eq. , in this case , the rwr. (which is a pretty good/sophisticated listening device, given the use case)
“burnthrough” = i didn’t mean jamming burnthrough here , but the range when rwr picks-up something, when db’s/mW are sufficient to detect even classify as “painting equipment” , you know, the brushWe can assume that all radars are heard at 1/4 further then their effective range (or more) , so we can “hear” them pretty much further then they can “see” us, give return.
While HPRF is maybe quiet, given low-power xmit, small radar, but it’s not oh so quiet as it close up our rwr ,… while I could believe that maybe it has some logic that controls xmit pwr , maintaining the return picture , contact… while keeping xmit power at the minimum required … SciFi … but not impossible…
Eg… As the sub/ship uses active sonar, eg… you want bigger range , you pump up the source kW … more kW = more nmi , better returns … and more dead whales/doplhins … eheh , and heard by everyone in vicinity , ~50nmi ??
So is it HPRF detectable., yes I believe so … at what range … ??? Probably before impact/miss in any case., when close enough. - its not the frequency/band/repetition pulse, but dB’s/mW of “known” noise which are listened for…
If H(arm)AS can pick-up 10-30kW at more then its range , why RWR couldn’t pick up 10W at 5-10nm … - that power is sufficient for radio/modem comms at even longer ranges
…just sayinCheers
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HPRF is a much weaker mode than mprf
Should it be seen by alr56 is totally unknown
Thanks … I suppose one other possibility is it “looks” too much like a mode of the APG-68 and RWR can’t disambiguate it from launching a/c
I suppose we also don’t really know, the real/various active-radar modes and ranges of the AA-12 then …
What tenets guide decisions, when faced with unknown/classified systems and capabilities … bias for balanced/fun gameplay? Would multiplayer BVR engagements be better or worse, with a slightly longer missile-warning? (I’m too newb to have much of an opinion.)
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Thanks … I suppose one other possibility is it “looks” too much like a mode of the APG-68 and RWR can’t disambiguate it from launching a/c.
As it sounds, it isn’t impossible… but again… scifi… guesswork.
Guiding Fox1 in STT and feeding mid-course correction datalink are technically completely different things… Fox1 STT uses ALL radar power to one bug , while mid-course corr for slammer can be done in RWS/TWS (almost search) modes, - so hence more LPI
We are talking about MPRF/HPRF modes of AMRAAM’s radar , which is not APG68 , so APG has already turned its role to amraam, amraam is active, APG is irrelevant now on.
What could be true ,…
MPRF are more “coarse pings” , larger target = better range = better interception path., but few secs of warning <m>before when it would happen in HPRF mode.
HPRF is high(er) resolution for smaller targets, mig21, helo. - at a bit reduced (radar) range … need 1-2sec longer guiding before active.So, mid-course correction , longer for HPRF - need closer to target , MPRF - you can snip target further , fire and forget
But both modes should trigger RWR when active , … problem is how much LPI is amraam’s radar… range of RWR pickup. - a good probability would be 15nm mprf / 10nm hprf … but…
Cheers</m>
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other way around, white fang - HPRF happens first, then MPRF. HPRF - Husky - works only for high closure rate (high aspect) contacts. I speculate this is due to the high pulse repetition frequency having too many ambiguous speeds for low doppler targets. MPRF - pitbull - activates some time after husky, closer to the target. The medium PRF works with high and low closure targets - speculating here - perhaps due to not having ambiguous speeds at this closer range and lower PRF.
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I haven’t done the math or even drawn this out on a napkin but my speculation would be … at extreme high closure-rate and intercept aspect-angle, the missile may just need a higher frequency of updates in case target begins to maneuver hard.
Thinking… AIM-120 is a 300lb bullet, coming out of its burn at around mach 4…
At colder aspect / slower closure (and also a bit slower missile airspeed) maybe it can afford to ping less frequently (and thus avoid detection, even as it gets closer)?
Again this is just pure, unbridled speculation … I know nothing, just fascinated by the science and engineering that goes into these systems.
I suppose my theory depends on what is the actual timing of the pulse-repetition rates we’re talking about … is MPRF one pulse every 10 seconds or 10 pulses every second. Probably something in between. If MPRF is less than 1 pulse/sec then my theory might make sense.
But … if that is the case, then there’s a condition where it would make sense to stay HPRF all the way into impact, if target is oblivious and continues to fly straight at you? I haven’t heard anyone suggest that it does that. But then again I’ve heard almost nothing, so who knows.
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MPRF one pulse every 10 seconds
Way, way higher. Like, three to thirty thousand a second.
If you are fascinated by this stuff, I’d recommend googling “medium PRF radar” and also possibly “fundamentals of electronic warfare” as good primers.
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Thanks … yes your theory of ambiguous range/velocity seems more apt.
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Ok, Bluewolf, but, yes and no.
Since you’re able to select slammer’s tgt type before launch, large, small, unkn.,
You’re already commanding preffered mode of operation in front, of course, its a subject to change if logic ai deternines best mode, hence “not forced”. - i want you to scan in these parameters but i cant, but is preferred…
So, only thing which logic respects is best target, of course there’s maybe iff in play.
You know while, nand, nor - fast logic., we’te using u/msec.
But i allways respect clear , sane, thinking, even i don’t see it at first.Cheers
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you’re able to select slammer’s tgt type before launch, large, small, unkn.,
You’re already commanding preffered mode of operation in front, of course, its a subject to change if logic ai deternines best mode, hence “not forced”. - i want you to scan in these parameters but i cant, but is preferred…the large, med, small, etc is for adjusting fuzing. The expanding-rod warhead does not rely on the missile physically hitting the target, then detonating. Instead it has a proximity fuze. It needs to know the size of the target to accurately calibrate the fuze, however. The consequence of having the wrong target size selected is that the missile may detonate too early. If you select “small” and fire at a bomber, the missile will likely detect the bomber and detonate far earlier than desirable. If you select “large” and fire at a small target, the missile may not detonate even when it is suitably close.
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hmmm… yes sure, but no, even from bms manual :
… even common sense suggests that UNKN = mprf/hprf combined … similar to APG scan , hi - in one way / med - in other way …
hprf have a smaller range but greater resolution , clutter, chaff … etcThe variables are: ∑AspectSelectorSize – HPRF requires target aspect to be within this many degrees of 180\. ∑HuskyMinClosure – HPRF will not activate unless range rate is higher than this threshold ∑HighAspectBomberHusky – Select LARGE target (AIM120 SMS page) to use this as HPRF range gate ∑HighAspectFighterHusky – Select MED or UNKN target (AIM120 SMS page) to use this as HPRF range gate ∑BomberPitbull – Select LARGE target (AIM120 SMS page) to use this as MPRF range gate ∑FighterPitbull – Select MED or UNKN target (AIM120 SMS page) to use this as MPRF range gate
fuzing is typical, proximity, impact , laser …
…ps, btw, interesting reads for amraam/sidewider RCS detection ranges by radar , unfortunately AESA, but there’s some talk about RWR also, down below
https://www.quora.com/At-what-distance-can-an-incoming-AIM-120-AMRAAM-be-detected-by-an-AESA-radar -
hprf have a smaller range but greater resolution , clutter, chaff … etc
HPRF has a greater range, not a smaller one. It has a smaller unambiguous range (due to higher PRF). Range resolution should be unaffected unless switching to MPRF also adjusts pulse width… of course, pulse width of the AIM-120 seeker is not public knowledge. If it were public knowledge, it would also be possible to calculate the notch speeds for the seeker.
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No my friend.
It is in nature phenomena that in case of same power source, higher frequencies travel faster but at shorter range.
Lower frequencies travel further., bigger amplitude, but they are slower.
Again in this case we’re talking about u/msec difference, but you cant win nature in any case.Interesting, hypersound propagation through water (sea) is more then hundred miles (whales) , like its frequecy range falls in sort of superconductivity, so totally opposite for typical behaviour of UHF/EHF, while U/VLF, like 50/60hz is normal behavior, long range, but nowhere at those ranges, maybe <100nmi in best case.
So, yes there is a case when hprf could have longer range then mprf, and that is at more power, juice., but if it is the same power source, hprf = faster returns, mprf = longer range, medium resolution.
Cheers
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higher frequencies travel faster but at shorter range.
Lower frequencies travel further., bigger amplitude, but they are slower.In this case, both Husky and Pitbull are both using the same frequency signal. They vary the pulse repetition frequency, not the emission wavelength. The pulse repetition frequency PRF is how frequently a pulse is emitted - thousands of times a second.
Say you have an analog radio transmitter and you hold down the push to talk. It emits, constantly, at a constant frequency. You can’t measure range with it. You can pulse the transmission though, by turning off and on the transmission - so now we have two different frequencies - one the transmitter frequency, and one the rate at which the transmitter is cycled on and off.
The longer the gap between individual pulses, the longer a range you can unambiguously measure. Using a couple interleaved PRFs together, you can calculate true range from several different ambiguous ranges.
the propagation rate of both HPRF and MPRF is the same as the emitted RF frequency isn’t changing. What is changing is how frequently a new pulse of RF is emitted.
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I have a vague remembrance from a past life that electromagnetic waves travel at the speed of light, whatever the frequency of said waves…
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key part there Jetsun: em travels at the speed of light, yes… and the speed of light, in a vacuum, does not depend on frequency.
The speed of light in air on the other hand, does vary slightly based on frequency, and a few other factors - its one of the most significant sources of error in GPS signals, actually.
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Had to refresh my memories here but the speed of EM waves depend on indice of refraction of the medium and not on its frequency, but I’m veeery rusty with all this stuff, so may be I’m missing something.
Anyway you made me curious about those High and Medium PRF and found this to help me try to start to get a clue
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Isn’t the index of refraction frequency dependent? I thought this is where dispersion comes from. In either case, it’s not something that is applicable to switching the PRF.
That’s a neat link. not a bad intro to the ideas of pulsed radar. Diagrams would help I think.
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In this case, both Husky and Pitbull are both using the same frequency signal. They vary the pulse repetition frequency, not the emission wavelength. The pulse repetition frequency PRF is how frequently a pulse is emitted - thousands of times a second.
Say you have an analog radio transmitter and you hold down the push to talk. It emits, constantly, at a constant frequency. You can’t measure range with it. You can pulse the transmission though, by turning off and on the transmission - so now we have two different frequencies - one the transmitter frequency, and one the rate at which the transmitter is cycled on and off.
The longer the gap between individual pulses, the longer a range you can unambiguously measure. Using a couple interleaved PRFs together, you can calculate true range from several different ambiguous ranges.
the propagation rate of both HPRF and MPRF is the same as the emitted RF frequency isn’t changing. What is changing is how frequently a new pulse of RF is emitted.
That’s where I mixed things up.
Yes, that’s true. I gave a it thought and got to same conclusion. So we’re actually talking about two (totally different) frequencies , the radar beam frequency and the “frequency” (cycle), since, of repetition pulse., which (in amraam) can be m/hprf. - no mention of LPRF, but “Bomber” setting would typically describe LPRF - big juicy return at long rangeI recall from (old sims) Janes F15/Fa18 … where you also could “play” with PRF values… BIG planes, bombers, are found at long ranges using LPRF (vs mprf/hprf) , HPRF best case is for target with high-closure rate , fighter on intercept course to you, similar to VS mode of APG.
Found it…. old story but , explained very well, everything is in there. … will take some time to grasp it in details… see you in 3-4 weeks :uham:
https://www.collectionscanada.gc.ca/obj/s4/f2/dsk2/ftp04/mq22118.pdfHPRF modes are used to detect high closing or receding velocity targets with good Doppler resolution. Since these targets normally appear in the clutter-free part of the spectrurn, target renirns cornpete only with receiver noise for detection. HPRF modes normally employ a high duty cycle, allowing maximum mean power on the target for a given peak power, and therefore maximum detection range for these types of targets. There are multiple range ambiguities, however, and HPRF modes inherently provide little range information. Coarse range resolution is possible with HPRF modes if fiequency modulation (FM) techniques are applied. FM techniques will be described in Subsection 3.6.4\. MPW modes lie between the two, and provide the best dl-aspect capability by cornbining desirable features of the LPRF and HPRF modes. At medium PRFs, the Doppler sidebands overlap, but to a lesser extent than during LPRF operation. There is norrnally no region free of sidelobe clutter (SLC) in the fkequency domain. The overlap of the central band and the immediate sidebands before sampling is shown in Figure 24\. Note that in this case, the mainlobe clutter is shown with a positive Doppler shift, reflecting an antenna pointing angle that is forward of the beam. Moving target detection is limited to detection in sidelobe clutter because the mainlobe clutter is simply too strong. Thus, for MW modes, the optimum antenna has very low sidelobes and a "clean" radome. MPRF modes produce ambiguities in both range and Doppler. These ambiguities are resolvable, however, when multiple PRFs are used. Good range and Doppler resolution are possible with MPRF modes, but MPRF modes nonnally require a higher signal processor Ioad than for HPRF modes.
Cheers @Blue, and Thank You.
ps… also @Jetsun . good find. … now when I got my “juices” flowing , I get to recall all of that… Its shit how you (ME) can forget in 20yrs that you actually knew those things … well, as you say … rusty:thumb:
ps2. … SO, maybe we can come to a conclusion that MPRF gives you range and HPRF gives you resolution ??? - there is surely a reason why those two modes comes exclusively in combined scan