This cantenna design does away with the pigtail by using an n-type to reverse polarity male SMA adaptor. This adaptor connects your cantenna directly to a WiFi adaptor without need for a pigtail.
The microwave signal is processed in the adaptor so you can then use a long USB cable to connect from the WiFi adaptor to your computer without signal loss.
The cantenna is directional so you will need something like a tripod to direct and hold the cantenna in place. Expect about a 3dB improvement of the signal, which is roughly a doubling in power, and hopefully many more access points being revealed.
I won't go into detail about the construction of a cantenna but point you towards http://www.saunalahti.fi/elepal/antenna2.html for detailed measurements.
However, do look at the slide show to see the subtle difference that obviates the need for a pigtail.
High power WiFi USB adaptor with SMA connection for antenna ( I use an ALFA AWUS036H)
Can - over 76mm in diameter (Long and thin is better than short and fat)
N-type female chassis connector
N-type male to RPM SMA adaptor
Some thick unsheathed copper wire (about 1 to 1.5mm diameter mains wire is best)
Four small nuts and bolts to attach N-type female to can
Drill and bits (cone bit to make hole for n-type chassis connector)
You can see other self-reliant things I make and do at http://www.ecopunk.org.uk