Step 7: What is a parabola and how do I make one?
The "B" lines are always perpendicular to the base line. The "A" lines change their angle in order to connect with the "B" lines. Use two yardsticks and a square. Plot points where the yardsticks cross over one another while the measurement shown on each yardstick is the same. The more points you plot, the more accurate your parabolic curve will be. If you are careful, you can plot only the left half of the curve and then flip it over to copy it onto the right half of the paper.
The end result is that any signal (TV, radio, sound, light) coming to the parabolic curve in parallel rays will be gathered in strength at the focal point and amplified because they are concentrated.