Disclaimer: The RWR in Arma/ACE is different than the one you would encounter in real-life or other sims. Everything included here applies to Arma and only Arma
RWR stands for Radar Warning Receiver, and in essence it senses what around you is emitting the radiation associated with radar, and delivers this information to you via display. It is not a radar, because of this it has certain limitations. Most notably being it can't tell you the exact position of a threat, just the general direction, and how strong the radar signal is which is used to estimate the distance. It also won't sense IR threats (heat seeking missiles and most MANPADs). The RWRs lack any sort of friendly identification system, though in the US RWR you can see what the threat type is, however the enemy may have gotten his hands on an F35 so be careful!
Direction of threat: Direction is indicated by 10 sets of colored circles, one large yellow, and one small green for each set. The RWR can track two two targets simultaneously, with the large yellow circles indicating direction to primary threat, and the small green indicating secondary threat (more on this later) From top-center to bottom they indicate: 10º, 30º, 50º, and 90º from center, with the bottom sets (the ones with outward pointing triangles) indicating the threat is behind you. If two circles are lit at the same time (as shown here) it means the target is somewhere between the two. For example if 30º and 50º are lit, the target is around 40º from you. When you have both a primary and secondary threat, it will flash back and forth between the two.
Distance to threat: Distance is indicated by a shrinking and growing strip of lights. Your aircraft is shown as a Yellow triangle on the bottom left. The closer the lights get to the triangle, the closer it is to you. The first light is ~2km, the middle is ~1km, and if the strip is full it's right on top of you. When you have both a primary and secondary threat, it will flash back and forth between the two.
Threat type: The threat type is indicated by 6 oblong yellow lights and accompanying letter. The primary threat type will have both the letter and the light turned on, while the secondary threat will have only the green letter turned on. Keep in mind, IR threats will not be displayed as the RWR only senses radars.
The threat types are:
П - Airborne Radar (Most fixed-wing except A10 and Su25. No rotary except Ka-50/52 and Apache)
3 - Long-Range Radar (not simulated)
X - Medium-Range Radar (not simulated)
H - Short-Range Radar
F - Early Warning Radar (not simulated)
C - AWACS (not simulated)
Missile Launch Warning: The red circle in the middle of the display will be a steady red when a threat is locked onto you and will start flashing to indicate the threat has fired a missile.
In this example I have two main threats and the RWR is flashing between these two displays. The primary threat is an aircraft very close to my front right, and the secondary threat is AA to my rear left at medium distance.
The US RWR is a lot more simple than the Russian one and so it's pretty obvious what you're looking at. The display indicates a top down view, with your aircraft at the center, and threats displayed around in the direction and relative distance. Each threat will have a two digit alphanumeric identifier, and either a box or a chevron. The identifier will tell you what the thread is, while the box indicates a ground threat and the chevron indicates an air threat.
In this example I have an Su27 to my 10 o'click close, a Tunguska to my 7 o'clock close, and a Shilka to my 4 o'clock close.
AH - Apache
AV - Harrier
KA - Ka-50/52
S6 - 2S6M1 Tunguska
23 - ZSU-23-4M Shilka
27 - Su-27s
30 - Su-30 FlankerC
34 - Su-34 Fullback
35 - F35
If I missed anything, let me know so I can add it
Edited by Macaco, 2014-04-11 @ 10:03.