"will have three sites(pc) to start with, about 250 yards/meters apart" is far beyond wifi specs.
But there is hope. In about post 17 of our forum sticky I posted how to use normal wifi routers as WAPs. You could use your EVDO ROUTER and use WAPS wired to your EVDO router. I decline to explain what a WAP is or why this fixes your system. You must be conversant with this technology to the point you get it with the words so far or I would be entering some tarpit.
i have a HUAWEI3G E220 usb modem, and i need to create a wireless network. It going to mounted in some sort of enclosure, inside, near the roof of warehouse. So i want this to be hastle free. Now the network will have three sites(pc) to start with, about 250 yards/meters apart.
Now i know that there is wirless routers out there that can do this, I just not sure of the range. Will i need an N router?(how close are they to finaliseing the stadard). Although alot of reviews rattle on about usb connectivity with regard to hard drives and the like, not many review cover this specifcally.
lastly i also intend bosting the week signal in the area with a GSM/HSDPA signal booster aerial, found here:- http://www.poyntingdirect.co.za/category.aspx?categoryID=22