I'v got an RB 411AH with R42n-M inside.
Antenna - Omni 2.4GHz 9dB V
Antenna has been set on middle building of complex, and when I'm in other building ( my office in other building is in same level as antenna, maybe 1-2 meters lower, and distance is like 10-20m ) and my signal is very low, on Windows 7 wireless icon I got like 1-2 lines...
RouterBoard is powered with 25m long POE cable.
Some screenshots of settings: