Weak signal even if I'm only 5 meters away from my modem

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http://askubuntu.com – I'm having kind of a weak signal on Ubuntu, about 2 bars (I have a laptop), when i go on windows it really gets quicker (5 bars). What may cause this? My wifi worked as soon as I installed Ubuntu so i did not install a network driver. According to connection informations, I am using the ath9k drivers. I can provide more informations if needed. My wifi adaptor is a Atheros® WB225 (802.11b/g/n) and my bluetooth is set off. I also use a 2,4GHz wireless mouse which I have been told may cause interference? Anyway how can i fix this problem please? (HowTos)