I've seen this question popping up around the Internet from time to time but thought I'd ask it here in case there is something more specific to the rt2x00 devices. The author of this page http//tim.cexx.org/?p=646
engineered a fairly simple version of the Wi-Spy spectrum analyzer by using a TI chip which is reportedly the same as that used by the Wi-Spy. All it uses is a raw signal strength register for each frequency across the 2.4GHz band.
I've been trying to figure out how to get something similar from my rt73, but as I'm a total noob when it comes to drivers and accessing such data. I don't even know whether it's possible on this hardware. Kismet seems to be able to show a display of all channels (1 through to 11) and will show data being received on channels other than the primary (eg if an AP is broadcasting on channel 6, it will show data on 5 and 7 etc) but it only shows this when it's a modulated 802.11 signal, and not interference from cordless phones, bluetooth devices, baby monitors, microwave ovens etc.
Is there a raw 'received signal strength' register that the drive can access to show the strength of any signal received on a given frequency?