This is a sample program I wrote to help you build your cantenna. It helped me built my aluminimum cantenna (normal size) If the applet doesn't load propably you don't have the Java Virtual Machine.
Aim at source and adjust to get the best signal. This should be much stronger than the whip antenna you had before. To improve the signal even more - much more - cut a 2 foot (0.6 m) wide by 1 foot (0.3 m) high sheet of concrete lathing screen with 1⁄4 inch (0.6 cm) or smaller holes and curve it slightly to form a parabolic dish, similar to a TV satellite dish. Instead of pointing the can at the signal source, point it at your screen which points at the signal so the back of the can points at the signal. It takes a bit of adjusting to get the curve of the screen and distance to the can exactly right. You can find formulas for calculating the exact focal point or use trial and error since you will see your signal gain double or even triple when you get the curve and distance just right. You can then make a wooden or aluminum frame to hold everything together in the right position. You can also use a real satellite dish and place the cantenna at the end of the arm at the position the TV antennas (the horn) usually go.