Need long range wifi adapter

[larns23]

Where i work there is a restaurant next to the building that has a open cloud network which is free to use, but it's probably about 20 to 30 yards away and so the signal is weak.

Sometimes i can connect and it will work for about 30 mins then drop out for a while and maybe reconnect, but sometimes not at all.

I was wondering if someone can advise me on what i need to pick up the signal better.

I was looking at these Alfa models, http://www.alfa.com.tw/in/front/bin/...ategory=105463

Or is there something better that i can use?

thanks