As simply as possible:
Radar active: everything stays as it is.
Radar passive: You can´t detect mechs at any range.
No Data about enemy mechs is beeing send from You to your teammates.
Can be neutralized by NARC/TAG
But: You dont appear on enemy radar till 200m range.
Enemy BAP may detect You within 400m range.
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This option was enabled in Mechwarrior4 and worked fine :-)
Edited by Sephyr, 12 December 2015 - 02:56 PM.