Did you know you can change the signal strength icon on your BB from bars to actual numbers with this keyboard short cut?
Try clicking ALT "NMLL" on your BB and watch the relatively uninformative bars change to real signal strength numbers. You should know a BB will stop synchronizing when the radio signal strength drops below about -106 to -108 dB. Anything below (well technically above) -85 dB is an indication of excellent radio reception.
More tricks can be found HERE