Raven 3L, Cammando 2D, Atlas DC-D, Cicada 3M are the only mechs able to mount ECM
to review, ECM does:
a 1.5 ton 2 slot piece of equipment that can counter
Artemis,
BAP,
Tag bonuses (and the whole TAG system inside of 180m)
NARC - a system which takes more space, weighs more, requires real coordination and skill and has ammo.
other ECMs (terrible terrible idea that forces an arms race)
LRM locks (due to the mistakes of the past as well as the BS quartering of sensor range)
SRM locks (probably a good thing)
general targeting info
relegates AMS to almost pointlessness
has no exploding ammo
generates no heat
and cost less than a module by a factor of 15
here is a great explanation of what MWO plays like....."Double Blind"
You need to read the Double Blind rules. It is supposed to prevent Active Sensors from noticing opposing mechs until they are closer. 1/4 normal sensor range is a bit too much though, it should have been about 1/2.
For those who don't understand TT or the more advanced rules of TT Double Blind is a system where you do not get to see where your opponent is on the map. It requires three identical boards, one for each player and one that they both can see. A GM will make rolls to determine what is detected by various mechs and place those forces on the open board while players track their own "hidden" mechs on their private boards.
MWO is a "Double Blind" system. I can't see opponents on my map unless I can spot them with Sensors. I can still use the old Mark I eyeball however. It isn't a bad system. What is bad is that LRMs and SSRMs are reliant on Sensors when they SHOULDN'T be.
...It is supposed to. Read my explanation of Double Blind rules above. It should cut sensors in half and not allow mechs inside it to share their "r targeting". It is supposed to cut battlefield awareness. What should also be added though, is that BAP should allow you to notice areas of ECM on the map. So having a BAP mounted makes a reddish overlay roughly a circle show up within your sensor range(which BAP expands still). So while you wouldn't know exactly what is in the rough circle of "jamming" you could be pretty sure there was an ECM mech at the center. This sticks with TT rules as well as BAP will notice it is being jammed.
"In double-blind, ECM makes it harder to acquire sensor blips without LOS, but only so long as the spotting unit is within the jamming radius of the ECM suite. If the spotting unit has LOS, then ECM does nothing. If the spotting unit does not have LOS but is outside jamming range (180m), then ECM does nothing."
and after this went on in the MWO forums for 3 pages.............
Damn it... been playing Double Blind ECM wrong according to the actual wording of the rules. It strongly implies that it affects all sensor checks but has one sentence that changes the whole meaning to limit it to spotting mechs standing within the ECM bubble itself. I stand corrected and humbly eat crow. I even checked the Errata sheets to be certain.
ECM should not affect Sensor Ranges for mechs outside it's influence.