Step 7: What Is a Parabola and How Do I Make One?
The definition of a parabolic curve is "a line equidistant between a point and a straight line." Go to a large table top and make a large sheet of paper from small pieces of paper. Newsprint works if you are using a felt tip marker. Make it a color like red or green so it stands out from the printing on the newspaper. Draw a straight line across the bottom. At its center make a line perpendicular to the straight base line. At about 14 inches (35.5 cm) mark the focal point. The distance from the base line to the focal point is completely your choice, but it affects the size of the reflector you make. Mark a point midway between the base line and the focal point. This is the first point you have plotted on your parabolic curve.
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.