Edimax EW-7711USn (Ralink 3070 chipset) working fine on Powerbook G4 OS 10.4.11
I wanted to give a feedback report for anyone in my situation wanting to improve their wireless reception and searching for a USB adapter they can run on Tiger. I was pretty confused when researching it, so I thought it'd be worth giving my report.
I bought the Edimax EW-7711USn (from Amazon UK) which uses the Ralink 3070 chip (http://wikidevi.com/wiki/Edimax_EW-7711USn), but I presume this would go for any 3070 device.
I was told from Edimax UK that this is no longer supported on 10.4.
I saw on Ralink's website (http://www.ralinktech.com/en/04_support/support.php?sn=502) that only 10.5 and up are listed for the 3070 driver, though when you click on that link the next page says 10.3 and up. But I downloaded this driver and it had folders for 10.5-7 only.
But I also emailed Edimax Taiwan and they sent me an older unsupported driver (RTUSBD2870-3[1].0.0.0UI-3.0.0.0_2010_05_12) which is working fine for me so far. (I also have the file RTUSBD2870_7711.zip which I downloaded actually from the Edimax UK site ironically which when unzipped has the same driver.)
My installation procedure was to install the driver, restart, plug in USB device - which opens Ralink Wireless Utility automatically, open Network System Preferences, which told me it had found a new port 'Ethernet Adaptor (en4)', I followed the pop-up instructions (which I think was click show 'Ethernet Adaptor (en4)' and the just click "Apply now" to confirm I was using DHCP which I was). I also dragged it to the top as mentioned in other posts, though I think it worked without that. I also repaired permissions, but nothing showed up needing repair.
Then I was able to connect to a wifi hotspot in Ralink Wireless Utility. I couldn't get Macstumbler working with the Edimax so I can't give direct comparison between this device and the Airport. But the Airport wireless was offering me only one connection - the cafe I was sitting in, whereas the Ralink offered me 10 so that was a pretty good start.
Hope this is helpful for someone.
PowerBook, Mac OS X (10.4.11), 1.5 GHz 15" G4, serial: W84330J2QW3