The signal strength is a combination of the actual 802.11x signal + Phone + Microwaves + other sources that might generate 2.4GHz “Noise” + Brain emissions of the user’s anxiety state (j/k), in other words it is visual representation of all the 2.4GHz in the atmosphere around the your Wireless hardware.
I.e. you might see High Signal Strength that Shows: Excellent (5 bars), but it is actually 30% signal + 70% noise.
Such a signal would be the reason for low bandwidth, and or frequent disconnection of the Wireless Network.
In contrast, a medium level Signal (3 Bars) that does not contains any noise would provide a match better connection.
Netstumbler is a free windows tool to see the signal to noise ratio.
If your router is not supported by Netstumbler, then try Kitz - DMT Tool