RSSI (Radio Signal Strength Indicator)

To monitor your signal strength in MAC OS while tweaking the wireless router; you can run this command in your terminal.

while x=1 ; do /System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport -I | grep CtlRSSI ; sleep 0.5 ; done

From the screenshot below, higher number corresponds to lower signal. "-" means loss. Thus, keep on tweaking!

You can stop this command from refreshing by hitting Control+C.