Spread spectrum is a method in radio and other kinds of telecommunication. Its purpose is to overcome interference, noise and jamming of signals.
Sending electromagnetic signals through the air became possible in the later 19th century with wireless telegraphy. The fact that signals were affected by natural interference was soon discovered. By the early 1900s, wireless telegraphy could cross the Atlantic. Intercepting the enemy's radio communications and interfering with their transmission was important in World War II. Messages in code were intercepted and recorded for decryption and translation. Not only can radio signals be detected, but those listening can be detected, since radio receivers also emit a signal.
Above all, since radio direction-finding is widely used in civil and military aviation, ways are needed to reduce interference with these transmissions. The main method is spread spectrum. Spread spectrum systems transmit the message using a bandwidth that is wider than the bandwidth actually needed by the message signal. This spreading of the transmitted signal over a large bandwidth make the resulting wideband signal appear as a noise signal. This resists intentional and unintentional interference with the transmitted signal.