I use an Alfa 2-watt (2000mw) antenna plus a USB AMPLIFIED extention cord to suction cup the Alfa to a window pointing at the modem. The two watts is to insure the upload signal is seen by the modem.
The ALFA 2000mw unit is a good one. Ultra easy. Plug it in let driver do its thing then use. Optional antennas that thread right into the connector atop the tiny amplifier. Its all so simple it is goof proof even by my 4th grade computer standards. Yeah yeah yeah sue me. I like stuff that works and cheap stuff that works and lasts is irresistable...
DATA ALLIANCE.COM in Nogales AZ is where I bought mine. It is so much more powerful than the competition it is embarrasing. Inexpensive, small and reliable. The 12 db whip antenna option is much more sensitive than the antenna that comes with the ALFA. just make sure you get the 2000mw version. It'll turn one bar into 5-bars.