I think that the ECM should cause every mech in its radius to appear on enemy radars as grey triangles with no information. Missiles would still be able to lock on to these targets.
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This would be balanced because support mechs would really have to think before firing off their weapons because they wouldn't be able to tell the difference between friend or foe.
TAG and NARC should make these grey targets turn red as long as they are active.
I think that PGI should look into bringing something like the IFF Jammer from MW4 into MWO. This would cloak a single mech as ECM does now. However this jammer should not function under 180M.
Let me know what you think