How does the RWR determine range to a radar contact?

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kneecaps

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Unread post26 Aug 2004, 01:37

Presumably direction is determined by triangulation from different sensors...how is range to a contact determined?

Is detected signal strength for a known radar platform analysed to determine a range estimation?
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EriktheF16462

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Unread post26 Aug 2004, 12:42

You should not get any answers about this one. RWR is not something you should ask about etc.
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kneecaps

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Unread post26 Aug 2004, 18:23

I'm not after specifics for the Falcon! I'm not asking for system schematics :D

I just mean what technique is used in general, surely triangulation is not a secret!

Nor would the concept of estimating range based on signal strength!
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Loader

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Unread post26 Aug 2004, 18:35

Check this site:

http://www.tpub.com/content/fc/14099/index.htm

"Introduction to basic radar systems"

General Radar info, no airplane/system specfics.
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kneecaps

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Unread post26 Aug 2004, 18:45

thanks...I'll get on that :D

BTW a quick scout around revealed quite a bit of interesting info on the AN/ALR-56M RWR

http://www.iews.na.baesystems.com/busin ... 6m_001.pdf
http://www.fas.org/man/dod-101/sys/ac/e ... alr-56.htm
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EriktheF16462

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Unread post26 Aug 2004, 19:06

But those of us that work the jet won't talk about it. Let the net write what it wants.
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lamoey

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Unread post26 Aug 2004, 19:28

I have no idea how the RWR kit does it, but the easiest part is actually the distance. Nothing secret or magic about that.

Triangulation with 2 separate antennas can tell that there is a transmitter a certain distance away, but will not know the angle. It can be anywhere in a 360 degree 2 dimensional circle. Adding a third measurement makes it possible to reduce it to two possible locations. Adding a forth will in theory nail down the location. You do however not have any redundancies in the measurement, so the circular probability error will be very large, specially knowing how little angle difference each of the measurements offers (antenna separation). If you then take several measurements over time, and possibly after a turn then with a little processing capacity in the system the culprit can be nailed down quit accurately. Oh, and the same theory is used in the GPS system to calculate the position of the GPS antenna, except the observations are in opposite order, i.e. one receiving antenna, but 4 or more transmitters (satellites).

If the transmitting radar is of a type identified as an airborne source, then a 3 dimensional calculation must be done, but if it is a ground radar, then it is unlikely to be above you, so the calculation becomes much simpler as you can rule out that possibility.
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elp

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Unread post26 Aug 2004, 21:08

Pays to be extra careful. Some of the visitors to this site depend on the dots not being connected too much.

Anything I babble about is public consumption, and I stay away from getting too nutsy bolts on sensors, ECM, SEAD, tactics... other things like IFF and como stuff I am clueless anyway. There is endless public consumption info out there. Endless. There is also endless studys on the general science behind radar tech all over the net. Especially colleges that are famous for engineering.

The RWRs in the F-16 work like the RWRs in half a dozen other jets. The most important thing about RWRs today IMHO is accurate software updates. Sensors out in the wild pick up a new radar behavior, it is recorded, engineers evaluate it, run sims, and publish a new software update. RWR systems that aren't up to date and relevant to the threat you are going against, can cost lives.

Multi-platform cooperation for locating something falls under the broad brush of net-centric warfare. In strike warfare: The guy that delivers the killing blow who has super up to date info of a fresh target in his hand isn't in many cases, the guy who detected the target.
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Unread post27 Aug 2004, 02:00

kneecaps wrote:Presumably direction is determined by triangulation from different sensors...how is range to a contact determined?

Is detected signal strength for a known radar platform analysed to determine a range estimation?


The fact of the matter is that the RWR display does not indicate range to a threat. The distance from the center of the RWR display to a threat icon is a representation of threat lethality, not range. Lethality is usually a measure of the detected signal which, of course, is a function of range but there are obviously other factors.

None of what I mentioned here is classified, in this respect the -1 and the Falcon 4.0 manual read the same. 8)
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kneecaps

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Unread post27 Aug 2004, 13:10

habu2 wrote:The fact of the matter is that the RWR display does not indicate range to a threat. The distance from the center of the RWR display to a threat icon is a representation of threat lethality, not range. Lethality is usually a measure of the detected signal which, of course, is a function of range but there are obviously other factors.


Ah...makes more sense now :D
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lamoey

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Unread post27 Aug 2004, 16:44

Allthough range is not shown, it must be an integral part of determining the threat level. As soon as the type of threat is identified, the leathal range of that threat is most likely known, so then using that information together with the distance it can decide the threat level.
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JanHas

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Unread post27 Aug 2004, 17:49

Don't forget the HTS. Distance to the radar is needed in order to know when a (H)ARM is in range of the target.

Wouldn't it be likely that the range is normally determend as well. An SA-2 at 100 miles would look more dangerous on the RWR-scope than radarguided AAA at 1 mile, but in reality the AAA is much more dangerous at that moment so it would be logical to show the AAA as a bigger threat.

If you take a look at the HSD a ring is shown around the radarsite indicating the missile range. The place of that radar has to be determent. It's simply having enough sensors on your plane and a computer to calculate the delay in the radarsignal between the sensors to calculate range and the position relative to the plane.
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elp

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Unread post27 Aug 2004, 18:12

Some "secret" RWR displays:
  • "B" inside a diamond is a beer truck
  • "H" inside a diamond is a Hooters - Flashing means there are drink specials at that time.
  • "M" inside a diamond is a Heavy Metal Radio Station ( rare ) :twisted:
  • "S" inside a diamond is a strip bar ( but only real "high class" ones are in the software updates )
  • "911" flashing inside a diamond means Reno 911 is on right now.
  • "EM" flashing is an enemy mime ( I hate mimes ).
Some of the audibles that go with these are "need to know" ( kids shouldn't hear them) :lol:
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FlightTestJim

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Unread post27 Aug 2004, 19:37

Without crossing any sacred or secrecy lines, RWR (Radar Warning Receivers) and RTWS (Radar Threat Warning Systems) can be understood in fairly simple terms, though the actual hardware and software to make it all work in 'the real world' are quite sophisticated and complex.

Imagine if you were to walk through a huge, darkened hangar, and suddenly heard a noise off in the distance. Although you can't see the source, could you determine where the sound originated? Of course you could. But how?

The sound arrives at each of your your ears (aka your onboard sensors), at a slightly different arrival time, unless of course the sound (aka threat signal) is directly in front of you, or directly in back (or directly above or below too). So your brain (data processor) can determine where something is located, (it's bearing from you) merely by noticing, and comparing the different arrival times of the signal.

But imagine if you keep walking across the hangar floor, and the source of the sound hasn't moved. Within a few steps, you'll soon be able to get a very good approximation of where the sound is actually located in space, relative to you (range and bearing, and perhaps even elevation too).

Now suppose you recognized the sound, say perhaps a clock ticking (i.e. a known threat signal). Your brain (that most powerful of data processors again) would compare the signal strength with what it would expect to hear (from its known 'threat library') at different distances and closure rates (frequency, and doppler shift). This provides a very fine resolution of where the source of the sound is located spatially.

Even if the sound originated up in the overhead rafters, it wouldn't take very long to determine that too. And keep in mind, that you only have 2 audio sensors on board. Most modern military aircraft (and soon the commercial fleet) have more than just 2 sensors, and they scour many different RF spectrums for different threats (none of course being in the 'sound' frequency ranges). And as was pointed out earlier, as new threats are 'heard and recorded,' they are added to the threat library (software updates to the RWR/RTWS systems).

Side note: Way back when, I briefly met a very bright engineer at the Air Force Institute of Technology (AFIT), and he was working on a program called HAVE EAR (I think that was the official designation anyway). He designed a special pilot's flight helmet, with a unique audio speaker system so the pilot could determine where a radio call (or any other audio sound sent to his helmet's headsets), originated in relation to his own aircraft. So if his wingman was flying high and right, that's where his wingman's VHF conversation would seem to be in the pilots head. If it was ATC calling, it might sound like it was on the ground, well behind him. If a tanker boom operator was calling him in for a refuel, the call might seem to be right in front, even though he couldnt see the tanker yet. When the Sidewinder growled, it sounded like it came from the correct wingtip. I was able to wear the helmet, and it was very precise in it's location of sound, though he could manipulate it too. He was to my right side, talking into a mike, though he used the computer to generate the sound to my left side. So I could see him talking, but it sounded like he was on the wrong side of me the whole time.

The problem this engineer was trying to solve was task saturation and overload, where the modern fighter pilot has so very much information coming in to his eyes and ears, that its hard to sort it all out quickly and make good decisions. The theory was, that if the pilot heard the sounds from their approximate spatial location, he'd be able to sort, and prioritize them all a lot faster. The drawback was, that the aircraft needed many more antennae (VHF, UHF, et al), and signal processors, so it could actually determine where the radio signals actually originated (much like I described above). Adding more antennae, processors, wiring, weight, and complexity to an aircraft is never an easy sell, and I don't think the study went much beyond AFIT.
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lamoey

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Unread post27 Aug 2004, 20:17

FlightTestJim wrote:The drawback was, that the aircraft needed many more antennae (VHF, UHF, et al), and signal processors, so it could actually determine where the radio signals actually originated (much like I described above).

I don't know that much about Link16, but if it does send position information about other units in the area, including a tanker, then the location is known in advance, which would ease the calculation significantly, and also reduce/remove the need for aditional sensors or antennas. Please correct me if I'm wrong about Link16.
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