In case of interest, I'm posting the below comment I just put in the Raspberry Pi forums. The R-Pi has polyfuses that limit the built-in USB ports to devices using less than about 140 mA of current. It turns out that you can use some USB WiFi adaptors directly without a powered hub, BUT only if you don't go too fast.
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Just compared two small USB-WiFi N adapters from ebay. Both devices connected easily from my WinXP laptop to my Linksys WRT160Nv2 router, reporting excellent signal and 72 Mbps link speed. It is interesting to see that both devices keep under the 100 mA limit while working the internet at my DSL speed. But going to a machine on the LAN, the speed goes up and the current draw goes up with it, above 150 mA which is more than the unmodified RPi USB port can reliably provide. So I'd expect either of these devices would be perfectly reliable for internet browsing used direct in the RPi without a supply, but UNreliable for heavy LAN use (eg. high-bitrate video streaming). ...Unless you have faster internet than I do, in which case, web use might hit overcurrent also.
By the way, the RTL8188CU device worked fine at the end of a six foot USB extension cable. The RT5370 device was not reliable on that cable, although it was fine with a 1-foot extender cable.
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http://www.ebay.com/itm/260976202890 (http://www.ebay.com/itm/260976202890)
Ralink RT5370 USB-WiFi N adapter (small external 2 dBi antenna)
standby: 66 mA
DSL provider speed test, transmitting: 75 mA (max) 12 Mbps
DSL provider speed test, receiving: 82 mA (max) 0.91 Mbps
iperf speed test to local WinXP box: 173 mA (max) 34.3 Mbps
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http://www.ebay.com/itm/330646461862 (http://www.ebay.com/itm/330646461862)
Ralink RTL8188CU USB-WiFi N adapter (internal antenna) <-EDIT: actually Realtek brand, not Ralink
standby: 84 mA
DSL provider speed test, transmitting: 96 mA (max) 11 Mbps
DSL provider speed test, receiving: 94 mA (max) 0.91 Mbps
iperf speed test to local WinXP box: 157 mA (max) 18.7 Mbps
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I compared the RT5370 with the included 4-inch long 2 dBi antenna and also a (claimed) 8 dBi TP-Link antenna about 11 inches long. I did not see much difference in the RSSI figures from inSSIDer. A directional antenna works better in open space than indoors with confused beam patterns from all the reflections.
Last item, the first RT5370 I got stopped working after a few days (the ebay guy sent a replacement; thanks!) so I took it apart to have a look, if you're interested:
https://picasaweb.google.com/lh/photo/_ ... directlink (https://picasaweb.google.com/lh/photo/_tEP1BttrZf09vMNXQJVxdMTjNZETYmyPJy0liipFm0?feat=directlink)
https://picasaweb.google.com/lh/photo/_ ... directlink (https://picasaweb.google.com/lh/photo/_6-kUL7Rrl3rVhggjDVSC9MTjNZETYmyPJy0liipFm0?feat=directlink)
Thanks a lot for sharing this rather useful info on some common USB 2.0 WiFi adapters. :)
[quote author="jbeale"]---
http://www.ebay.com/itm/330646461862 (http://www.ebay.com/itm/330646461862)
Ralink RTL8188CU USB-WiFi N adapter (internal antenna)
standby: 84 mA
DSL provider speed test, transmitting: 96 mA (max) 11 Mbps
DSL provider speed test, receiving: 94 mA (max) 0.91 Mbps
iperf speed test to local WinXP box: 157 mA (max) 18.7 Mbps
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Minor correction to prevent confusion:
RTL8188CUS (1T1R) (http://http://www.realtek.com/products/productsView.aspx?Langid=1&PNid=21&PFid=48&Level=5&Conn=4&ProdID=274), RTL8188SU (1T1R) (http://http://www.realtek.com/products/productsView.aspx?Langid=1&PNid=21&PFid=48&Level=5&Conn=4&ProdID=228), RTL8191SU (1T2R) (http://http://www.realtek.com/products/productsView.aspx?Langid=1&PNid=21&PFid=48&Level=5&Conn=4&ProdID=229), RTL8192CU (http://http://www.realtek.com/products/productsView.aspx?Langid=1&PNid=21&PFid=48&Level=5&Conn=4&ProdID=277) and RTL8192SU (2T2R) (http://http://www.realtek.com/products/productsView.aspx?Langid=1&PNid=21&PFid=48&Level=5&Conn=4&ProdID=231)
are Realtek (not Ralink) single-chip IEEE 802.11b/g/n USB controllers.
My favorite RTL8188SU based USB WiFi adapter is the LogiLink WL0085 (http://http://www.logilink.de/showproduct/WL0085.htm?seticlanguage=en) - it has a detachable
antenna (RP-SMA connector) and comes at < 10 EUR. So far it has worked flawlessly on all Linux
boxes/boardes I have used it with (various DVB-S/T Linux boxes, iMX233-OLinuXino (http://https://www.olimex.com/dev/imx233-olinuxino-maxi.html), CS-E9302 (http://https://www.olimex.com/dev/cs-e930x.html),
NSLU2 (http://http://en.wikipedia.org/wiki/NSLU2), GNUBLIN (http://http://en.gnublin.org/index.php/Main_Page) ...). and on Windows PCs. I have measured up to 175mA drawn by RTL8188SU
based adapters @ ~20Mbps (TX).
Interesting !
I always thought, those dongles were build to draw less than 150mA ...
I think I will have to make some tests to see how much my DLINK DWA140 draw when it has to connect a full power thought some walls ...
Just got one more, which I tested this evening in the same way. It draws more current both in standby and when active, although it is not any faster. It does see several more local APs via inSSIDer than the other two, smaller adapters, which may mean it is better at very-weak-signal work. In counting APs I do not count as separate a few groups of APs showing sequential MAC IDs, which I presume are the same physical device presenting different interfaces. One neighbor has a TRENDnet device listing eight different MAC addresses, which seems excessive (4 on ch.11, 4 on ch.8+4).
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http://www.amazon.com/gp/product/B002WBX9C6 (http://www.amazon.com/gp/product/B002WBX9C6)
TP-Link TL-WN722N USB-WiFi N adapter (external 4 dBi antenna)
standby: 123 mA
DSL provider speed test, transmitting: 140 mA (max) 0.91 Mbps
DSL provider speed test, receiving: 159 mA (max) 12.23 Mbps
iperf speed test to local WinXP box: 260 mA (max) 31.3 Mbps
ping to local WinXP: min/max/avg: 1/7/2 msec
24 different APs visible with provided 4 dBi antenna
29 different APs visible with TP-Link 8 dBi antenna
works OK with 6' USB cable
never goes higher than 65 Mbps indicated link speed, even at -24 dBm signal and about 5 feet from my AP
Just FYI, I got my 2nd R-Pi on Friday, and discovered a nice change. This issue is now less critical if you get one of the latest R-Pi boards (shipping as of last week) because of the change you see here:
https://picasaweb.google.com/1099282360 ... 0375008498 (https://picasaweb.google.com/109928236040342205185/Raspberry_Pi#5780498170375008498)
As you can see, USB fuses F1,F2 are now 0-ohm jumpers. Your total current draw including CPU & Ethernet is still limited by the 750 mA input fuse though. And heating of the board traces, if you bypass that fuse eg. by powering through the +5V on the GPIO pins.