![]() ![]() Friedrich "Fritz" Mandl was a wealthy ammunitions manufacturer whose weapon systems later gave her inspiration for the patent. By the age of eighteen she had married her first of six husbands. Hedy was born in 1914 in Vienna and started training in the theater as a teenager in the 1920's. Both Hedy and George are most remembered for their main fields of activity, movies and music, but they each had a touch of the polymath inside of them, and their other passions allowed them to make a significant advance in the radio arts. Though attributed to multiple inventors, the first patent for frequency hopping was granted to actress Hedy Lamarr and composer George Antheil in 1942 for their "Secret Communications System" that was designed to protect Allied radio-guided torpedoes from being jammed by the Axis powers. Radio researchers found that another layer of communication security could be added by the use of frequency-hopping which was the first technique established in spread spectrum radio. The military and others can make use of codes and encryption to veil transmissions on single frequencies, but codes can be broken. Constant-frequency signals are easy to intercept. The second issue with using only one frequency in a communication is when the information being transmitted is of a sensitive nature. This category also included other non-malicious interference coming from transmissions on nearby frequencies. The first was interference caused by deliberate jamming on the desired frequency. But as radio has developed the inventors and researchers who expanded the state of the art found a couple of hitches that made it problematic for certain types of signals to remain parked on one frequency. That is all fine and dandy for typical uses of radio. ![]() ![]() The signal is kept on a single frequency so two people communicating can exchange information, or so a listener in the broadcast bands knows exactly where to go to find his favorite station. In the conventional transmission and receiving of signals, the frequency does not change over time, except for small fluctuations due to modulation. This gives the signal a much greater bandwidth than if its frequency had remained constant. In wireless communications spread spectrum radio is a transmission technique where the frequency of the signal is intentionally varied. ![]()
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