What must be done to prevent standing waves on a feed line connected to an antenna?

Standing waves are created when forward power traveling down a feed line is reflected back toward the transmitter. This reflection happens at the point of connection if there is a difference between the characteristic impedance of the feed line and the actual impedance of the antenna feed point. To entirely prevent these reflections and the resulting standing waves, the impedances must perfectly match. For example, connecting a 50-ohm antenna to a 50-ohm coaxial cable ensures that all transferred power is radiated and none is reflected. Many operators mistakenly believe that altering the length of the feed line fixes standing waves. While changing the feed line length can transform the impedance presented to the transmitter, it does not change the actual mismatch at the antenna, nor does it eliminate the standing waves present on the line itself.