strange problem wireless

Measured by what? If not Speedtest.net, please try that and see if it agrees.

Please attach a screen shot of the Networks page (don't collapse the Radar, Connection or Signal History) of the Xirrus Wi-Fi Inspector. If you need help with a screen shot see TSG Posting a Screenshot. FWIW to take screen shots with Windows Vista or latter I prefer to use the built-in Snipping Tool.