ive tired a few of them usb sticks and noramlly the software you get with them are poo....
i'd recommend using..
media portal @
http://www.team-mediaportal.com/
Windows media centre
this software wont guarantee a better signal but is interface is a lot easier to use. search youtube for mediaportal is actually a all in 1 htpc solution very powerful...
http://www.youtube.com/watch?v=9QnyQXjGkRw
if you still cant get signal but you have a internet connection
try
catchuptv.com
this site streams freeview channels its great i used it for over a year when i didnt have a Ariel in my room.....