Using Roamio on weaker wi-fi signal?

I am about to buy a Roamio to replace an excellent S3 that uses phone line for guide info. I have wi-fi from AT&T but at back of home where Tivo goes it is about 50 feet away. Signal shows usually 2 bars on a PC and works, so is the wi-fi in the new Tivo real good on weaker signals? Can an external antenna be added?