The "Cantenna" has been around a while and seems to work.
This page has directions and links to others.:
http://www.turnpoint.net/wireless/cantennahowto.html


Michael Eisenstadt wrote:
> I live near a public wifi hotspot which my older Linksys
> WUSB11 one eared antenna detects. I get up to 4 bars
> of signal strength in the Win XP Pro utility, but the
> connection randomly fails, sometimes when I click on
> a link and sometimes when I download something and
> sometimes not. Sometimes the connection is stable for
> hours, other times it fails every few seconds.
>
> I am writing to ask for your suggestions about
> possibly replacing the hardware and/or somehow
> tweaking the signal strength with some (homebuilt?)
> device.
>
> Thanks in advance for your help.
>
> Michael Eisenstadt
>
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>

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