I know it doesn't make any sense (at least, it doesn't to me), but I have the strangest situation over here:
I use a MacBook Pro (mid 2010) with a i7 2.66 GHz processor and 4GB of DDR3. The notebook is on my desk on my right side. I've connected a 23" ACD as external screen. When the screen is connected, the lid is closed.
AirPort Extreme (4th generation) which sends a signal (n-standard) to my Mac (and all other devices in our house).
For some reason, when the external ACD is connected I got a very bad signal. Signal strength even goes down to 1 sometimes. But when the ACD is disconnected and the lid is opened, the signal strength increases to normal proportions (40-80).
I can't figure out why the signal strength is influenced by connecting the ACD or not.