When I run:
iwconfig wlan0 | grep -i quality
on my Raspberry Pi, with a wifi card installed, it reports back to me with:
Link Quality=99/100 Signal level=48/100 Noise level=0/100
How can I get iwconfig or some other network tool to report the signal level back to me in dBm instead of an arbitrary fraction?
It's a matter of the Network Interface Card or of the relatives Drivers. To workaround you can use this simple formula I to do the conversion.
Of course is an approximation and results may vary from chipset to chipset but is how I solved.
You can alternatively find the correct Drivers if you know the wifi card is capable RSSI sampling. But that's usually not easy.