【正文】 避免的窄頻譜。實際同步數字系統(tǒng)窄波段上的時鐘頻率及其諧波傳播，導致在頻譜，在某些頻率可以超過法規(guī)限制電磁干擾（例如那些輻射的電磁能量在美國 FCC美國在日本和 IEC ， JEITA ）在歐洲。 它已經成為一種流行的技術，因為它僅需要簡 單的設備改造，以獲得監(jiān)管部門批準。由于這些設備的設計是重量輕，價格低廉，傳統(tǒng)的被動式，電子措施，以降低 EMI，如電容器或金屬屏蔽，是不是可行。 然而，擴頻時鐘，也可以為設計師創(chuàng)造的挑戰(zhàn)。】 請注意，這種方法不會減少總輻射能量，因此，系統(tǒng)不一定是不太可能會造成干擾。典型的測量接收機 EMC測試實驗室所使用的電磁頻譜分成約 120 千赫寬的頻帶。分發(fā)到一個更大的帶寬相同的能量，防止把任何一個窄帶超過法定限度的足夠的能量系統(tǒng)。這種情況的結果，在窄帶寬（ S），經歷了干擾少，敏感的電子設備，而寬帶的敏感性，甚至在其他頻率（如無線電接收機 調諧到一個不同的站）經營者，會遇到更多的干擾。然而，擴頻功能可以由用戶在某些情況下被禁用。這可能被視為一個漏洞 ，但一般只要忽視擴頻是默認啟用的。 The technology of frequencyhopping spread spectrum Frequencyhopping spread spectrum ( FHSS ) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels , using a pseudorandom sequence known to both transmitter and receiver . 。s first radiocontrolled submersible boat in 1898, when it became apparent the wireless signals controlling the boat needed to be secure from being disturbed, intercepted, or interfered with in any way. His patents covered two fundamentally different techniques for achieving immunity to interference, both of which functioned by altering the carrier frequency or other exclusive first had a transmitter that worked simultaneously at two or more separate frequencies and a receiver in which each of the individual transmitted frequencies had to be tuned in, in order for the control circuitry to respond. The second technique used a variablefrequency transmitter controlled by an encoding wheel that altered the transmitted frequency in a predetermined manner. These patents describe the basic principles of frequency hopping and frequencydivision multiplexing, and also the electronic ANDgate logic circuit. Frequency hopping is also mentioned in radio pioneer Jonathan Zenneck 39。s book was a leading text of the time, and it is likely that many later engineers were aware of German military made limited use of frequency hopping for munication between fixed mand points in World War I to prevent eavesdropping by British forces, who did not have the technology to follow the Polish engineer, Leonard Danilewicz , came up with the idea in 1929. Several other patents were taken out in the 1930s, including one by Willem Broertjes (Germany 1929, US Patent 1,869,695 , 1932). During World War II , the US Army Signal Corps was inventing a munication system called SIGSALY for munication between Roosevelt and Churchill, which incorporated spread spectrum, but due to its top secret nature, SIGSALY39。 signals could easily be jammed. The Antheil–Lamarr version of frequency hopping used a pianoroll to change among 88 frequencies, and was intended to make radioguided torpedoes harder for enemies to detect or to patent came to light during patent searches in the 1950s when ITT Corporation and other private firms began to develop Code Division Multiple Access (CDMA), a civilian form of spread spectrum, though the Lamarr patent had no direct impact on subsequent technology. It was in fact ongoing military research at MIT Lincoln Laboratory , Magnavox Government amp。s similarity to the FRS allocation, the system is a proprietary design, rather than an official US Federal Communications Commission (FCC) allocated service. Commercial use The 1976 publication of Spread Spectrum Systems by Robert Dixon, ISBN 0471216291 , was a significant milestone in the mercialization of this publications were either classified military reports or academic papers on narrow subtopics. Dixon39。s very small aperture ( VSAT ) satellite terminal syste m for newspaper newswire services, Del Norte Technology39。s OmniTRACS system for munications to trucks. In the Qualm and Equatorial systems, spread spectrum enabled small antennas that viewed more than one satellite to be used since the processing gain of spread spectrum eliminated interference. The Del Norte system used the high bandwidth of spread spectrum to improve location accuracy. In 1981, the Federal Communications Commission started exploring ways to permit more general civil uses of spread spectrum in a Notice of Inquiry docket. This docket was proposed to FCC and then directed by Michael Marcus of the FCC staff. The proposals in the docket were generally opposed by spectrum users and radio equipment manufacturers, although they were supported by the then HewlettPackard Corp. The laboratory group supporting the proposal would later bee part of Agilent . The May 1985 decision in this docket permitted unlicensed use of spread spectrum in 3 bands at powers up to 1 Watt. FCC said at the time that it would wele additional requests for spread spectrum in other resulting rules, now codified as 47 CFR permitted WiFi , Bluetooth , and many other pro