Telegraphy was originally published in German in 1908, but was translated into English in 1915 as the enemy started using frequency hopping on the front line. Zenneck was a German physicist and electrical engineer who had become interested in radio by attending Tesla's lectures on "wireless sciences". Wireless Telegraphy includes a section on frequency hopping, and, as it became a standard text for many years, it probably introduced the technology to a generation of engineers. A Polish engineer and inventor, Leonard Danilewicz, came up with the idea in 1929. Several other patents were taken out in the 1930s, including one by Willem Broertjes (, issued Aug. 2, 1932). During World War II, the US Army Signal Corps was inventing a communication system called SIGSALY, which incorporated spread spectrum in a single frequency context. But SIGSALY was a top-secret communications system, so its existence was not known until the 1980s. In 1942, actress Hedy Lamarr and composer George Antheil received for their "Secret Communications System", an early version of frequency hopping using a piano-roll to switch among 88 frequencies to make radio-guided torpedoes harder for enemies to detect or jam. The U.S. Navy rejected the idea, then seized it as "alien property" in 1942 (Lamarr was Austrian) but filed it away with no record of a working device being produced. Lamarr's and Antheil's idea was rediscovered in the 1950s during patent searches when private companies were independently developing direct-sequence Code Division Multiple Access, a non-frequency-hopping form of spread-spectrum, and has been cited numerous times since. In 1957, engineers at Sylvania Electronic Systems Division adopted the patented concept, combined with the recently invented transistor. In 1962, the US Navy finally utilized the technology during the Cuban Missile Crisis; Lamarr's and Antheil's patent had expired. A practical application of frequency hopping was developed by Ray Zinn, co-founder of Micrel Corporation. Zinn developed a method allowing radio devices to operate without the need to synchronize a receiver with a transmitter. Using frequency hopping and sweep modes, Zinn's method is primarily applied in low data rate wireless applications such as utility metering, machine and equipment monitoring and metering, and remote control. In 2006 Zinn received for his "Wireless device and method using frequency hopping and sweep modes." Variations Adaptive frequency-hopping spread spectrum (AFH) as used in Bluetooth improves resistance to radio frequency interference by avoiding crowded frequencies in the hopping sequence. This sort of adaptive