I do not think it is an issue with bandwith, it is not a function of connection strength. If you take your antenna off, is the signal strength the same. I am thinking that ( if) at the same time your friends are getting good signal strength, your signal strength is poor with the antenna on. That issolates it to your pc or notebook. By the way is this a notebook or pc ? The antenna could be damaged. Try A NEW or high gain antenna, sold at most computer stores, make sure you get one with the right BNC connector. Could be that the whole card needs to be reinstalled ( high probability ). Could be a virus or trojan .... from my experience, college networks aer full of these.
so whenever i come home from college i just bring my computer in my room screw on my antenna and bang i have the internet...we have charter highspeed provider and Linksys for the wireless router.....i usually have a excellent signal strength when in my room..but now i only have maybe a bar and it losses the connection once and awhile....i dont under stand because when my friends come over with their laptops they have excellent strength full bars.....So far i have made sure that the router is in a good high place ;which it has always been in. made sure nothing like a wireless phone or anyother distraction that could ruin the signal....i made sure my wireless card was secured and the antenna was screwed in all the way...so i am kind of out of ideas....??????
