Hmmm, placing a reflector behind the antenna in the opposite direction of the emitter (transmitter) may work. Then again, your problem could be the opposite. Your signal dropping out before reaching the base station. Heck moving the pc 4 or 5 feet might help too.

Increase "gain" is the goal not a longer antenna that only induces more noise and in reality moves the antenna a little closer in some respects.

How to make a reflector you just pop on the existing equipment?

Some of those links Und3ertak3r posted tell you but your getting good reception most of the time already and those things are some high quality home made stuff. Stack some beer cans or a frying pan behind it.

Ok really, you've heard of the pringles can antenna, but there are some other really cheap parabolic projects out there with some more gain. Not only can you make them increase your "ears" but from a security point you can use them to reduce and eliminate broadcasts to specific areas, such as the starbucks across the street full of college skiddies :

Cheap as hell:

http://www.freeantennas.com/projects/template/

Thanks for the links Und3ertak3r