Flood mode after lock is lost?

[red_coreSix]

Gotcha, but still the antenna beam is not shrinkable in any way isn't it?

[GGTharos]

Physically no, but the (useful) width of the beam is defined mathematically.

 

For example, 160nm mode (in the real jet) uses a 1.5deg bar spacing (or 1, I forget), while at 20nm or less it will use 3.4 or 3.5 deg spacing. At those distances you'll get enough of a return from the sides of the beam than at longer ranges (power falls off as you move away from the center).

[red_coreSix]

That makes sense, thanks.

[Svend_Dellepude]

Electro magnetic waves quickly becomes a complicated subject.

Sound waves are much easier. :)

[SinusoidDelta]

For illustration purposes:

[Nerd1000]

The APG-63 uses the HSTT mode for Sparrow guidance. FLOOD emits the exact same HSTT signal. That's straight out of the -34. AFAIK, FLOOD probably doesn't emit the m-link.

 

CW mode has been deleted from the -63 for decades now.

 

Sure it does. There's nothing stopping you from programming the RWR to say if STT and this much power -> missile launch.

 

Okay, didn't know that it was using the same emissions as HSTT for guidance. I suppose that makes sense- why have an entire extra mode if you don't need it?

 

On the topic of power being used to detect missile launches, it is certainly possible. I'd say that such a solution was nowhere near optimal because changes in signal strength could easily deceive the RWR. You'd probably get a launch warning whenever you're locked by a radar within a certain distance for example. In the same vein, an aircraft or SAM could launch on you without giving a warning by ensuring that the signal strength of their radar is never high enough to trip the RWR (Obviously this would reduce range, but that might be an acceptable tradeoff).

 

Still better than nothing if the only way to detect a launch is through changes in incoming power though.

[GGTharos]

On the topic of power being used to detect missile launches, it is certainly possible. I'd say that such a solution was nowhere near optimal because changes in signal strength could easily deceive the RWR.

 

I'm not saying it's a method of detecting missile launches. I'm saying:

 

You'd probably get a launch warning whenever you're locked by a radar within a certain distance for example.

 

And this is a choice by a given air force based on its doctrine. It's 'just' software.

 

In the same vein, an aircraft or SAM could launch on you without giving a warning by ensuring that the signal strength of their radar is never high enough to trip the RWR (Obviously this would reduce range, but that might be an acceptable tradeoff).

 

So how's that missile going to guide if it won't even trip your RWR? :)

 

Still better than nothing if the only way to detect a launch is through changes in incoming power though.

 

FLOOD will probably display a very quick power drop with increasing distance. You're shooting that energy out into a pretty huge cone.

[TAW_Blaze]

Physically no, but the (useful) width of the beam is defined mathematically.

 

For example, 160nm mode (in the real jet) uses a 1.5deg bar spacing (or 1, I forget), while at 20nm or less it will use 3.4 or 3.5 deg spacing. At those distances you'll get enough of a return from the sides of the beam than at longer ranges (power falls off as you move away from the center).

 

From experience I'll go ahead and guess this isn't modeled in DCS. Am I right?

[Nerd1000]

 

 

So how's that missile going to guide if it won't even trip your RWR? :)

 

 

for each pulse:

 

energy received by target aircraft is proportional to 1/D^2.

 

energy received by missile seeker is proportional to 1/D^4.

 

Therefore the amount of energy received by the missile increases more rapidly than the amount received by the target as distance decreases, at least if we talk in terms of % of energy received at any given arbitary range (if we talk in terms of absolute energy, i.e joules, that might not hold).

 

Depending on the specific situation, turning down the power of the radar and moving to closer range might allow the missile to track while the energy received by the target is still below that which would indicate a launch at maximum range. The graph I attached illustrates this better than my words- take a look at it, you should be able to see what I'm talking about.

[GGTharos]

Why does the receiving sensor care about anything other than the actual value of received energy?

The RWR antenna and the missile seeker's antenna aren't necessarily very different. The RWR antenna will always receive more energy than the missile's seeker, and we know for a fact that the RWR will pick up signals much further than the missile's seeker.

[Nerd1000]

Why does the receiving sensor care about anything other than the actual value of received energy?

The RWR antenna and the missile seeker's antenna aren't necessarily very different. The RWR antenna will always receive more energy than the missile's seeker, and we know for a fact that the RWR will pick up signals much further than the missile's seeker.

 

I know that. I'm working on the assumption that we want to use signal strength as the indicator for a lock-on or a launch. If we're doing that the RWR must have some kind of threshold signal strength for danger.

 

The missile needs a certain amount of incoming energy in order for its sensor to detect the target (in the graph I arbitrarily set this value to 0.1). Lets say the RWR wants to detect missile launches at maximum range. The RWR can detect signals at 0.1 strength as well, but we are interested in actual threats here. The RWR must have its threshold for a launch warning set to account for the stronger signal it will be receiving or it will create spurious warnings.

 

On the graph it turns out that when the missile is getting its arbitrary 0.1 signal strength, the RWR is getting around 0.31.

 

The second set of lines on my picture are what happens when we halve the strength of the radar signal. All ranges are reduced, but now at the distance where the missile is receiving 0.1 the RWR is only receiving a value of 0.22. If we had just set the RWR to say 'danger!' when signal strength reaches 0.31 then we would be in trouble.

 

This is of course all kind of irrelevant to the real deal because RWRs don't work like that, at least to my knowledge.

 

Now for a real-world anecdote from the formative days of radar that demonstrates the point:

 

During WW2, RAF coastal command bombers used ASV radar to search for U-Boats. When the Germans became aware of this they fitted their U-boats with a primitive RWR known as the 'Biscay Cross'. All it could do was detect signal strength. When it went over a certain threshold the U-boat would dive. Allied crews developed a method for overcoming this: As they approached the U-boat they turned the transmission power of their radar down. The signal strength at the U-Boat's end decreased, tricking the crew into thinking that the bomber was flying away, however for the bomber the decreasing range meant that the U-boat remained visible on their radar as they closed in.

Edited October 30, 2015 by Nerd1000

[GGTharos]

Some very modern radars reduce power, it's part of the LPI capability.

 

As for doing so when you launch a weapon ... I don't know that it gives you any advantages :)

 

But again, in the case of 'FLOOD at long range', I'd tend to agree. Except that FLOOD is an emergency mode. :)

[Beamscanner]

Sure it does. There's nothing stopping you from programming the RWR to say if STT and this much power -> missile launch.

 

That's not how RWRs are designed to work.. being locked up within X miles would constantly trigger a "missile launch".. and would never trigger a "missle launch" warning outside of Y miles. (not the case)

 

It IS true that Radar warning receivers have limited gains, bandwidth and sensitivity and thus require a signal to meet a certain threshold in order to process. But the amplitude in and of itself does not change the identification of the emitter... (EP techniques (LPI for instance) attempt to make use of these limiting factors, and many others)

 

There is a unique waveform associated with flood mode, nothing about that unique waveform changes when an AIM-7 is launched. As such, if a RWR is not designed to give launch warnings from that emission(only giving a hard lock indication) then it ALSO shouldn't when the missile has been fired in that mode. You cant determine if a missile is in the air or not, so its up to the programmers as to which indication is given. AFAIK it should give a missile launch warning(even if there isn't a missile in the air), because (again AFAIK) the waveform used is the exact same one used to illuminate a target during an AIM-7 missile launch.

 

This is a classic case of double standards.

 

Everything Nerd1000 has said is true.

Edited October 30, 2015 by Beamscanner

[GGTharos]

Which part is the double standard?

 

The part that in RL you can program the RWR to do anything you like (regardless of whether it makes sense or not), or the confusing talk about how RL may or may not apply to this simulator?

 

Behavior in the simulator is consistent with how the game models missile launch and detection of it by an RWR, rather than being consistent with reality.

 

Can you tell if the RWR picks up the m-link for the sparrow (is it even generated?) or, if an eagle locks you up in HSTT, should it just make the alarms go off?

 

All we have to go by is the -34, and it quite clearly states that the illumination for the Sparrow is HSTT, which can occur during a non-launch situation. FLOOD also emits HSTT. The only possible difference, again, by what material is available, would be that the radar might be generating an m-link. But that might not be true until later versions of sparrow.

[SDsc0rch]

let me see if i understand this correctly... to guide a sparrow requires HSTT and this "m-link"

 

((i readily admit i am ignorant of the whys and wherefores of this m-link - am i wrong to think "m-link" is short for "missile link"? ---- i'm assuming it gives some additional information that a sparrow needs))

 

continuing.. RWRs detect both the HSTT signal and the m-link signal, and in turn generate a launch warning in the target aircraft

 

 

 

but then at the same time, it seems like a sparrow CAN successfully guide to a successful intercept using flood mode only (HSTT but no m-link) ---- in an "emergency" -- ie.. loss of radar lock due to notch, hardware malfunction, etc

 

is this correct??

[Svend_Dellepude]

let me see if i understand this correctly... to guide a sparrow requires HSTT and this "m-link"

 

((i readily admit i am ignorant of the whys and wherefores of this m-link - am i wrong to think "m-link" is short for "missile link"? ---- i'm assuming it gives some additional information that a sparrow needs))

 

continuing.. RWRs detect both the HSTT signal and the m-link signal, and in turn generate a launch warning in the target aircraft

 

 

 

but then at the same time, it seems like a sparrow CAN successfully guide to a successful intercept using flood mode only (HSTT but no m-link) ---- in an "emergency" -- ie.. loss of radar lock due to notch, hardware malfunction, etc

 

is this correct??

 

Apparently yes, but it (Sparrow) might change the intercept path since it no longer recieves updates via M-link.

[blkspade]

Some very modern radars reduce power, it's part of the LPI capability.

 

Isn't the radar range selection of the F-15 -63 functionally a power output setting?

[GGTharos]

I haven't seen anything written to that effect in the -34. I have my doubts that this would be the case for the MSA series.

[Nerd1000]

let me see if i understand this correctly... to guide a sparrow requires HSTT and this "m-link"

 

((i readily admit i am ignorant of the whys and wherefores of this m-link - am i wrong to think "m-link" is short for "missile link"? ---- i'm assuming it gives some additional information that a sparrow needs))

 

continuing.. RWRs detect both the HSTT signal and the m-link signal, and in turn generate a launch warning in the target aircraft

 

 

 

but then at the same time, it seems like a sparrow CAN successfully guide to a successful intercept using flood mode only (HSTT but no m-link) ---- in an "emergency" -- ie.. loss of radar lock due to notch, hardware malfunction, etc

 

is this correct??

 

 

I'm fairly certain that the M-link is mid-course guidance for the sparrow- it has a much smaller antenna than the main radar, so it can't detect the reflections from the target at its max launch range. Instead the main radar radios course corrections to the sparrow until it is close enough for its seeker to see the target. The R-27 uses similar principles AFAIK.

 

Many but not all SARH missiles use this sort of feature, and there are a few ways of doing it: the RIM-8 Talos was a beam rider until it was close enough to go SARH. The HAWK by contrast doesn't use mid-course guidance at all- its called 'Homing All the Way Killer' for a reason.

[Nerd1000]

Flood mode does not have an M-link signal, as the APG-63 isn't tracking any target during this period and thus can not provide a intercept solution to the AIM-7.

 

the double standard is that people expect their RWR to give them lock on indications when being burned in flood mode, AND also getting a launch indication when that adversary has fired a missile in flood mode. Your RWR is only going to see one signal during the whole process, and as such cant tell if the enemy is just burning them or firing.

 

Nothing in the emission changes between initiating flood mode, and firing a missile in flood mode. Depending on what the RWR is designed to do, it will either only tell you that your locked up or that there is a missile in the air(even if there isn't).

 

As I said earlier, the illumination waveform that the AIM-7 seeker needs is a baseline standard. Meaning if you want to guide that missile you absolutely need this. However, you theoretically don't need the m-link. especially if your in close.

 

BTW, I highly doubt that the Mlink is being intercepted by these types of RWRs.. datalinks are not unique among each other. each DL signal is meant to emit one way (no powerful emission is needed so you can see a weak reflection). DL signals like these dont need to be on for long periods either, there are time slots over the period of the missile intercept when course corrections are needed, but unlike a illuminator it isn't emitting all the time.

 

And as you can see with the advent of Active Missiles+mid-course guidance half of the benefit is that you don't have to alert the enemy of the launch until the missile is right on top of them. This benefit wouldn't exist if the enemy could sense these datalinks.

 

I don't think there's anything in principle to prevent you from detecting the datalink to the missile, assuming that you have a sufficiently sensitive receiver (the missile manages, and its much smaller than your jet). It might be more accurate to say that in-game RWRs don't have this capability, as we don't know what newer designs (or even software updates to existing ones) are capable of.

[SDsc0rch]

so i guess we should really ask..

 

"should" we even get a launch signal??

 

 

(i feel like i'm stirring the pot LOL)

: )

[Beamscanner]

Probably not. The DCS F-15 manual mentions that some RWRs trigger a launch indication via the missile datalink. If GGTharos is correct, and the same HPRF waveform used to illuminate a target in STT is also used in flood mode then you wouldn't want to program your RWR to indicate a launch every time you get hard locked.

 

It's extremely unlikely that any link exists during flood mode, as there is no target tracking solution being generated by the radar. So no link, no launch warning.

 

One thing IS clear. You can NOT tell if a missile has been actually launched in FLOOD mode. Only that FLOOD mode has been turned on. So I guess what we see now in game (just a STT tone) is correct. Or at least makes the most sense.

 

 

Not a huge threat though. the missile fired can only be launched at 10 miles, has to fly a pure pursuit route to intercept you, and it requires the launching aircraft to fly straight towards you.

Edited November 13, 2015 by Beamscanner

[GGTharos]

From what I've heard, it would make sense to have the launch warning if the missile is launched in STT and the radar then transitions to FLOOD. I think the trains are obvious.

 

As for the missiles flying with FLOOD illumination, there's no reason for it to fly pure. The launch aircraft, yes, the missile, not so much IMHO.

[SDsc0rch]

stepping back for a minute and considering the big picture, lets not forget the AIM-9

 

flood mode is only useful within visual range - so is AIM-9

 

the sparrow is very visible - the sidewinder uses a smokeless motor

 

the AIM-7 requires illumination from launch till impact - the AIM-9 is fire and forget

 

so, in any situation where you have an AIM-7 and an AIM-9 onboard, the AIM-9 would be my go-to WVR choice

[Beamscanner]

As I said previously, the manual states that the RWR uses the presence of the mid-course guidance (from a SARH missile) to indicate a missile launch. Without this present, as with the FLOOD mode, it wouldn't know a missile was launched. The HPRF used for tracking is also used for illumination, thus it can't be used to tell if a missile was launched.

 

Im not denying that the midcourse link wouldn't disappear after a certain point, in your standard STT engagement. In game RWRs continue to warning you of the launch for a period of time after it disappears.

 

But a missile launch in FLOOD mode never generates this link in the first place. Thus, no launch warning.

 

 

The Missile has no range information and only sees the illumination off the target (providing it azimuth and elevation). The radar isn't tracking anything in flood mode. So the missile would have to be flying a pure pursuit path. (chasing this illumination)

 

 

@SDscorch

The key difference is better range with AIM-7

Edited November 13, 2015 by Beamscanner