I was first opened the subject on http://forum.mikrotik.com/t/rb2011uias-2hnd-weak-wireless-signal-problem/76887/6
What I have tried for now is;
Setting the region United States. But either with regulatory-domain or other settings, nothing worked .
I opened the device. Nothing seemed wrong. Antenna connectors seems little bit loose but I am not sure how it was supposed to be.
I pushed them gently to fix just in case. But they are not close fit like pcmci type wireless cards antenna connectors.
Device has ROS 6.12. And I checked and try almost everything include HT settings. BG mode only 20 Mhz , Fix TX 30 Dbm etc..