Hi All,
In the spirit of d-i-y I thought I'd mention I was recently trying to help a mate setup his new VOIP router and we were getting crap range between that and his laptop, in spite of my little Trend 'Hotspot' detector (and Netstumbler) showing nothing else on the channel we selected.
Changing to *another* channel and getting better range suggested it was interference from *something* (but not a Wi-Fi device and nothing new there then).
Because of this issue (and liking real answers to such questions) I treated myself to a MetaGeek 'Wi-Spy' (Wi-Fi band PC based basic spectrum analyser) the other day and took it to my nephews when I was swapping an 11b dongle for a 11g PCI card.
I don't think this could be considered a 'Professional' tool but, it seems to do what it says on the tin .. ;-)
All the best ..
T i m